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Luminescent materials usually suffer from thermal quenching at high temperature due to the aggravation of nonradiation relaxations. Herein, a giant enhancement of up conversion (UC) luminescence is observed in negative thermal expansion (NTE) Y 2 W 3 O 12 :Nd phosphor upon increasing the temperature from 310 to 790 K. In addition, the temperature-dependent UC emission is reversible. To penetrate into the mechanisms, the temperature-dependent luminescence intensity and lifetime are investigated for Nd doped negative and positive thermal expansion (PTE) phosphors. Based these investigation, we infer that the underlying mechanism of the giant enhancement for Y 2 W 3 O 12 :Nd phosphor are due to combined effects of phonon assisted absorptions and contraction of NTE crystals. Moreover, the observation of temperature-dependent near-infrared spectra (NIR) can support the mechanism from the other side. The present findings pave the way to overcome thermal quenching of Nd3+ ions and explore new thermal enhancement materials sensitized by Nd3+ ions. [ABSTRACT FROM AUTHOR]

In this work, SrLaAlO 4 :Er3+ (2 mol%),Yb3+ (4 mol%) upconversion phosphor was synthesized by using a combustion method. Later, CsPbBr 3-x I x (x = 0, 1.5 and 0.75) perovskite quantum dots (QDs) were synthesized by using hot injection method. According the analysis by X-ray diffraction, the SrLaAlO 4 :Er,Yb (SL:Er,Yb) phosphors and QDs had tetragonal and cubic phases, respectively. Moreover, the analysis by microscopy revealed that the SL:Er,Yb phosphors are composed of micro-grains with irregular morphology, while the CsPbBr 3-x I x QDs had a morphology of cubes. The surface of the SL:Er,Yb phosphors was decorated with CsPbBr 3-x I x QDs and obtained three composite powders: CsPbBr 3 +SL:Er,Yb, CsPbBr 1.5 I 1.5 +SL:Er,Yb and CsPbBr 2.25 I 0.75 +SL:Er,Yb. Those composites were firstly excited with UV light (380 nm) and produced emissions in the green and orange-red regions by downconversion. Interestingly, the emission intensity of the composite powders was 45–75 % higher than that for the individual CsPbBr 3-x I x QDs or SL:Er,Yb phosphors. Later, the same composite powders were excited with NIR light (980 nm), in consequence, intense green and yellow emissions were produced by upconversion. In particular, the CsPbBr 1.5 I 1.5 + SL:Er,Yb composite produced strong red emission by upconversion because the presence of the QDs on the SL:Er,Yb surface promoted the following cross relaxation process: 4I 11/2 (Er3+)+ 4F 7/2 (Er3+)→4F 9/2 (Er3+)+ 4F 9/2 (Er3+). In general, the quantum dots deposited on the SL:Er,Yb surface not only enhanced the red upconversion emission, but also provoked a color tuning when they are excited with NIR or UV light. Those last effects have not been reported in the literature previously. Thus, the results of this investigation demonstrate that combining perovskite quantum dots and the SL:Er,Yb forms a luminescent material able to tune its emission by upconversion or downconversion. This last property can be utilized for the design of new LED based lamps, which are employed for general illumination in houses and buildings. [ABSTRACT FROM AUTHOR]

(Ti 1-x Si x)O 2 :Er/Yb (0 ≤ x ≤ 0.3) phosphor was synthesized using spray pyrolysis, and the upconversion (UC) properties were optimized by varying the calcination temperature and Si content (x). By introducing Si into the TiO 2 matrix, the thermal stability of titania was effectively improved, allowing the anatase phase to be maintained even when the (Ti,Si)O 2 :Er/Yb phosphor was calcined at temperatures above 800 °C. From investigating the effect of crystal size on the UC emission of (Ti,Si)O 2 :Er/Yb, it was found the optimal crystal size of Antase to achieve the highest UC emission intensity is approximately 5.5 nm, beyond which the UC intensity decreases rapidly. With increasing Si content, the crystalltie size decreased linearly and more amorphous SiO 2 domains were formed in the anatase TiO 2 matrix, which could consume Er/Yb ions to form SiO 2 :Er/Yb with low UC emission. Resultently, the UC emission intensity was significantly affected by Si content. The optimal calcination temperature and Si content to obtain the highest UC luminescence were determined as 700 °C and 10 %, respectively. The optimized (Ti,Si)O 2 :Er/Yb showed approximately 2.7 times improved UC luminescence than TiO 2 :Er/Yb. [ABSTRACT FROM AUTHOR]

Upconversion luminescence presents obvious advantages in optical temperature sensing, nevertheless the application in complex scenarios is limited by luminescence thermal quenching. Herein, NaYS 2 :Yb3+,Nd3+ phosphors are synthesized by the solid-gas reaction method and used for temperature sensing. A series of emissions for Nd3+ from visible to near-infrared region are achieved based on energy transfer from Yb3+ to Nd3+ under 980 nm excitation. With elevating the temperature, significant thermal enhancement effect of nearly three orders of magnitude is detected in near-infrared emission of 4F 7/2 → 4I 9/2 , which is attributed to phonon-assisted energy transfer of Yb3+→Nd3+ and the corresponding thermal population effect. The thermal behaviors of thermally coupled energy levels for 4G 7/2 /2G 9/2 and 4F 7/2 /4F 5/2 in NaYS 2 :Yb3+,Nd3+ are evaluated by luminescence intensity ratio technique. Remarkably, the optical thermometer based on the enhanced emission of 4F 7/2 /4F 5/2 shows excellent temperature measurement performance, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing. These results not only provide a pathway to realize high performance temperature sensing, but also heighten the understanding of UC emission thermal enhancement. [ABSTRACT FROM AUTHOR]

Extremely intense blue upconversion luminescence (UCL) is got in Tm3+/Yb3+ co-doped BiTa 7 O 19 (BTO) phosphors, which are synthesized by solid phase sintering. The doping concentration of Tm3+ is fixed at 7 mol%, and the concentration of Yb3+ is adjusted. When the concentration of Yb3+ is 80 mol%, the strongest blue UCL can be obtained under 980 nm laser excitation. The blue UCL integral intensity under 808 + 980 nm laser co-excitation is 1.54 times of the sum of intensity under 808 and 980 nm single excitation, respectively. Blue UCL thermal enhancement behavior was found for all the samples under 808 or 785 nm laser excitation, and blue UCL thermal quenching happened under 660, 660 + 808, and 359 nm excitations. It is demonstrated that UCL thermal enhancement behavior is caused by oxygen defects. The possible electron transition pathways are proposed under excitation with different laser wavelengths. Using the luminescence intensity branching ratio (LIR) technique, the maximum relative temperature sensitivity range is calculated to be from 0.00610 to 0.00732 K−1 at 303 K. The experimental results show that BTO:Tm3+/Yb3+ has excellent blue UCL with thermal enhancement, which can have some applications in the field of UCL display and temperature sensing in high temperature environment. [ABSTRACT FROM AUTHOR]

The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO 3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO 3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO 3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO 3 :0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO 3 :0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source. [Display omitted] [ABSTRACT FROM AUTHOR]

To investigate a near-infrared-to-blue luminescence upconversion curing method for polymerizing resin cements under zirconia discs. Lava zirconia discs of different thicknesses (0.5–2.0 mm) were manufactured. First, the transmittances of the NIR and two blue lights (BLs) (LED and halogen lights) through these discs were measured. Second, NaYF 4 :Yb3+/Tm3+ upconversion phosphor (UP) powder was milled into 0.5-μm particle sizes. A light-curable resin cement VariolinkII base was chosen as the control (UP0), and an experimental cement (UP5) was prepared by adding 5 % UPs. These two cements were examined using multiphoton excitation microscopy for particle distribution. UP5 and UP0 were polymerized with or without zirconia shielding then subjected to a microhardness test. A multifold analysis was performed to examine the effects of zirconia thickness, curing protocols (pure BL or combined BL and NIR curing), and cement type. The transmittance of NIR was superior to that of BL through zirconia discs of all thicknesses. UP particles were homogeneously distributed in UP5 and emitted blue luminescence under 980-nm NIR excitation. UP5 showed higher microhardness values than UP0 under any curing protocol or zirconia shielding condition. The combination of 20-s BL and 40-s NIR curing yielded the highest microhardness in uncovered UP5. However, combining 40-s BL and 20-s NIR curing surpassed the other groups when the zirconia discs were thicker than 0.5 mm. NIR exhibits higher transmission through zirconia than BL. UP particles work as strengthen fillers and photosensitizers in cements. NIR upconversion curing could be a new strategy for polymerizing resin cements under thick zirconia restorations. • An NIR activated upconversion reaction was used to induce blue light (BL) emission. • The transmittance of NIR through zirconia discs is higher than conventional BL. • Phosphor particles work as photosensitizers and strengthen fillers in cements. • Combining BL and NIR effectively enhanced polymerization of cements under zirconia. [ABSTRACT FROM AUTHOR]

Fluoride-upconversion transparent ceramic materials doped with Er ions have attracted extensive interest due to their higher stability, lower phonon energy, and higher upconversion efficiency. xEr:Sr 5 (PO 4) 3 F (S-FAP) (x=0.5–5 at%) transparent ceramics have been synthesized by hot pressing sintering in this work, and the maximum optical transmittance of the sample reached 74.52 and 82.45% at 500 and 1000 nm, respectively. The XRD results of the powder and ceramic samples were consistent with the diffraction characteristics of the hexagonal S-FAP crystal structure. The SEM and TEM images of powder revealed that the morphology of the sample was composed of mostly rice grains with a diameter of around 20 nm. The XPS and EDS results confirmed the presence of Er3+ and the uniform distribution of Er elements. The thermally etched surface and cross section of ceramics revealed residual pores as the most important scattering source, and the SEM images of the ceramics show that Er doping can obviously promote the growth of the average grain size of S-FAP transparent ceramics. Furthermore, the upconversion luminescence characteristics and fluorescence lifespan of S-FAP transparent ceramics with varied Er doping concentrations were examined, as well as the upconversion luminescence process. The findings in this work indicate that Er:S-FAP transparent ceramics can be employed as a potential upconversion fluorescent material in display technology, biomedicine, temperature sensing, and other applications. • The xEr:S-FAP (x=0–0.05) transparent nanostructured ceramics with highly optical quality were prepared by hot-pressed sintering for the first time. • The microstructural characteristics, upconversion luminescence property, and mechanism of as-synthesized xEr:S-FAP transparent ceramics were investigated for the first time. • The wide visible light spectrum from red light to green light was achieved by changing the doping amount of Er3+ from 0.5 to 5 at%. [ABSTRACT FROM AUTHOR]

In this work, Yb3+ and Er3+-co-doped Sr 9 In(PO 4) 7 upconversion fluorescent materials with dual functionality were synthesized though simple high-temperature solid state method. Based on International Commission on Illumination (CIE) color coordinates, the calculation of color purity at different temperatures demonstrates the attainment of highly pure green luminescence (color purity >90 %) for the synthesized materials. The analysis of activation energy proves that synthesized materials are stable. Utilizing the fluorescence intensity ratio (FIR) of the thermally coupled energy levels (2H 11/2 , 4S 3/2) as a metric for optical sensing performance, absolute sensitivity and relative sensitivity are determined, and their maximum values are 0.44 % and 1.13 %, respectively. Inspired by the variation in CIE coordinates with temperature, thermally responsive two-dimensional barcode image was developed, demonstrating the practical application of Sr 9 In(PO 4) 7 :Yb/Er materials in the field of information security and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The upconversion fluorescence thermometry has been recognized as one of the most promising techniques for the temperature measurement and multi-mode fluorescence temperature sensing can improve the accuracy and widen the temperature range. Herein, a fluorescence thermometry was developed based on the MgAlON: Er3+ transparent ceramic. It was demonstrated that the enrichment of Er3+ in grain boundaries increased susceptibility to temperature variations of the cross-relaxation rate, which endowed the non-thermally coupled energy levels with temperature sensing properties and led to the multi-mode thermometric capability. A novel four-mode temperature sensor based on fluorescence intensity ratios (2H 11/2 /4S 3/2 and 4F 9/2 /4S 3/2) and fluorescent lifetimes (4F 9/2 and 4S 3/2) was realized in the temperature range of 180–500 K, which brought about the maximum absolute and relative sensitivities reached 0.0258 K−1 and 2.95% K−1, respectively. This work reveals that the MgAlON: Er3+ and the grain boundary functionalization of transparent ceramics could have potential applications for fluorescence thermometry. • A novel four-mode MgAlON: Er3+ fluorescent temperature sensor was prepared. • The maximum absolute and relative sensitivities of MgAlON: Er3+ reached 0.0258 K−1 and 2.95% K−1, respectively. • The grain boundary enrichment of Er3+ makes the cross-relaxation rate temperature-sensitive, forming a multi-mode fluorescence thermometry. [ABSTRACT FROM AUTHOR]

BiTa 7 O 19 (BTO) has two lattice structure, P–6C2 (188) ordered phase and P 6 3 / mcm (193) disordered phase. Ordered and disordered BTO:Er3+/Yb3+ upconversion phosphors (UCPs) were obtained by solid sintering with different temperatures. The lattice structure of all the samples was investigated by XRD, SEM and Raman spectroscopy, and upconversion luminescence (UCL) spectra were tested by spectrometers. The green integral UCL intensity of the disordered BTO:Er3+/Yb3+ UCP is 60.76 times than that of the ordered sample. By comparing Er3+/Yb3+ co-doped and Er3+ single-doped UCPs with different structures, it is found that the disordered structure enhances the energy transfer from Yb3+ to Er3+, which may be caused by the disordered structure reducing the distance between Yb3+ and Er3+. The absolute temperature sensitivity of the sample with the highest UCL intensity is 0.01005 K-1 at 352 K. All results suggest that the disordered structure of BTO host can greatly improve green UCL intensity and the disordered BTO:Er3+/Yb3+ UCPs are suitable for the application of optical temperature measurement. [ABSTRACT FROM AUTHOR]

Herein, Na 3 Y(VO 4) 2 :Nd3+,Yb3+,Ho3+/Er3+/Tm3+ are synthesized through the solid-state reaction method. By utilizing Yb3+-mediated energy transfer in Nd3+-sensitized various activators (Ho3+/Er3+/Tm3+) system, 808 nm excited multi-color upconversion luminescence is realized. Yb3+ plays an important role in energy transfer bridging, and the introduction of Yb3+ in Nd3+-sensitized system can significantly improve emission of activators by nearly two orders of magnitude. The main luminescence mechanism of Nd3+→Yb3+→Activators (Ho3+/Er3+/Tm3+) is proved via measuring the emission characteristics and luminescence decay curves. With efficient upconversion luminescence, the optical thermometry behaviors for Na 3 Y(VO 4) 2 :Nd3+,Yb3+,Ho3+/Er3+/Tm3+ are investigated. The maximum relative and absolute sensitivities are 1.08 % K−1 and 7.82 × 10−3 K−1 for Na 3 Y(VO 4) 2 :Nd3+,Yb3+,Er3+; 1.01 % K−1 and 4.22 × 10−3 K−1 for Na 3 Y(VO 4) 2 :Nd3+,Yb3+,Tm3+; and 1.08 % K−1 and 22 × 10−3 K−1 for Na 3 Y(VO 4) 2 :Nd3+,Yb3+,Ho3+, respectively. Based on the multi-color upconversion luminescence and high sensitivity thermometry performance, the Na 3 Y(VO 4) 2 :Nd3+,Yb3+,Ho3+/Er3+/Tm3+ phosphors have potential applications in fields of solid-state display and safety sign of high-temperature. [ABSTRACT FROM AUTHOR]

High-performance optical thermometer that can operate in the long-wavelength range of the second near infrared (1500 nm–1700 nm, NIR-IIb) biological window is in desperate need for bio-medical treatment. In this paper, a multipath temperature sensor Y 3 NbO 7 : Yb3+/Er3+ with pure cubic phase is synthesized by the high temperature solid state method. Under the excitation of 980 nm wavelength, efficient green upconversion emission attributed to thermally coupled Er3+: 2H 11/2 /4S 3/2 levels are found, through which an excellent temperature sensing properties are realized with the maximal absolute and relative sensitivity of approximately 0.54 % K −1 and 1.37 % K −1 as well as the minimal temperature resolution of about 0.024 K. More importantly, the sample exhibits remarkable temperature detection capacity in deep tissues, which is implemented by the thermally coupled Stark sublevels of Er3+: 4I 13/2 locating just in the NIR-IIb sub-window. Thanks to this appropriate response wavelength range, the maximal penetration depth of the NIR-IIb optical thermometer in the biological tissues can reach up to 8 mm. All the findings indicate that the present sample is a supernormal multipath thermometric probe with detectability in the deep biological tissues. [ABSTRACT FROM AUTHOR]

In this study, nitrogen-doped carbon dots (NCDs) modified ultrathin carbon nitride (g-C 3 N 4) nanosheets were synthesized by a simple secondary calcination method, which realizes efficient photocatalytic hydrogen production. The secondary calcination process can not only thermally exfoliate g-C 3 N 4 into ultrathin nanosheets, but also uniformly anchor NCDs (∼3 nm) on the surface of g-C 3 N 4. The photocatalytic results manifested that a very small amount of NCDs (0.5 wt%) loading on g-C 3 N 4 could achieve a high photocatalytic hydrogen production rate (5.21 mmol g−1 h−1). The reasons for the enhanced photocatalytic activity were analyzed. The ultrathin g-C 3 N 4 nanosheets facilitated the migration of photogenerated carriers. Moreover, NCDs/g-C 3 N 4 exhibited enhanced visible light absorption owing to the up-conversion fluorescence effect of NCDs and the narrow band gap caused by the decoration of NCDs. Furthermore, NCDs as electron acceptors can promote carrier separation. This combination strategy provides a basis for the synthesis of inexpensive, metal-free, and efficient carbon-based photocatalysts. Nitrogen-doped carbon dots (NCDs) modified ultrathin carbon nitride (g-C 3 N 4) nanosheets were synthesized. The enhanced photocatalytic mechanism of NCDs/g-C 3 N 4 composites was analyzed. [Display omitted] • NCDs/g-C 3 N 4 nanosheets were synthesized by a simple secondary calcination method. • The ultrathin g-C 3 N 4 nanosheets (∼8 nm) facilitated the migration of carriers. • The modification of NCDs promotes light absorption and carrier separation abilities. • The H 2 production rate of g-C 3 N 4 loaded with 0.5 wt% NCDs reached 5.21 mmol g−1 h−1. [ABSTRACT FROM AUTHOR]

Series of Er3+/Yb3+-codoped Gd 2 Mo 3 O 12 (GMO:Er3+/2 x Yb3+) microparticles with dual-mode luminescence were fabricated with the assistance of sol-gel method. The phase structure, morphological information, upconversion (UC) and down-shifting luminescence properties of the final products were systematically investigated. At 980 nm light irradiation, strong UC emissions rise in all the products and their intensities depend on the dopant concentration, where the optimum status occurs at x = 0.25 and the two-photon capture procedure results in the UC emission mechanism. Besides, excited at 378 nm, the down-shifting photoluminescence is also gained in resulting samples. By means of the fluorescence intensity ratio technique, the thermometric properties of the studied samples were investigated through analyzing the diverse thermal quenching features of the green emissions from thermally coupled levels of Er3+. When the UC emission is selected, the maximum absolute and relative sensitivities of the GMO:Er3+/2 x Yb3+ microparticles are 0.0076 and 1.15% K−1, respectively, whereas they shift to 0.0036 and 0.89% K−1, respectively, when the down-shifting photoluminescence is adopted. Note that, the sensor sensitivities of developed microparticles are related to the luminescence mode, while they do not depend on Yb3+ content. These results suggest that the GMO:Er3+/2 x Yb3+ microparticles are promising thermosensitive luminescent materials for optical thermometry and their thermometric features can be tuned through changing luminescence mode. [ABSTRACT FROM AUTHOR]

Thermal quenching that the upconversion (UC) luminescence intensities decrease with increasing temperature limits the application of UC luminescence materials in the field of optical temperature sensing. Herein, we report that Tm3+/Yb3+ doped Gd 2 O 3 phosphors achieve thermal enhancement of UC luminescence with the multiphonon assisted process. Significantly, a possible mechanism of Yb3+ ions in thermal enhancement and multiphonon assisted UC luminescence process is proposed. Based on the luminescence intensity ratio technique of non-thermally coupled energy levels, research shows that thermal enhancement can effectively improve the optical temperature sensing absolute sensitivity. Owing to the near-infrared excitation and strong near-infrared emission, the UC luminescence of the Gd 2 O 3 : Tm3+/Yb3+ phosphors can penetrate 12 mm pork tissue and achieve UC thermal enhancement in 287-314 K after penetrating 6 mm pork tissue, which shows its potential in vivo application. The results not only provide a pathway to realize the thermal enhancement of UC luminescence and the improvement of the temperature sensing sensitivity, but also promote the understanding and utilization of the UC luminescence thermal enhancement. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the upconversion(UC) and downshifting(DS) luminescence and thermal sensing performances of the CaIn 2 O 4: RE3+/Tm3+/Yb3+(RE=Er, Ho) phosphors are investigated in detail. The bright UC emission bands from 450 to 900 nm and the DS luminescence bands from 1000 to 1700 nm are obtained under 980 nm excitation. The typical near infrared(NIR) emisson band(∼1550 nm) of Er3+ ions and the NIR emission band(∼1200 nm) of Ho3+ ions are gained. The temperature sensing features of CaIn 2 O 4: RE3+/Tm3+/Yb3+ (RE=Er, Ho) phosphors are investigated with the luminescence intensity ratio (LIR) technique. The results indicate that the maximum relative sensitivity (S Rmax) of CaIn 2 O 4: Er3+/Tm3+/Yb3+ sample reaches 1.576% K-1 at 313 K, and the S Rmax of CaIn 2 O 4: Ho3+/Tm3+/Yb3+ sample reaches 0.797% K-1 at 353 K in UC range. In addition, the higher temperature measuring sensitivities have been obtained in NIR-II region with the DS luminescence of CaIn 2 O 4: RE3+/Tm3+/Yb3+ phosphors. The above results indicate that the CaIn 2 O 4: RE3+/Tm3+/Yb3+ phosphors show bright emission bands in visible and NIR-II, and higher sensitivity for temperature measurement. The CaIn 2 O 4: RE3+/Tm3+/Yb3+ phosphors present great application in optical temperature measurement. [ABSTRACT FROM AUTHOR]

Most thermometers suffer from thermal quenching resulting in low signal to noise ratio at elevated temperature. To overcome thermal quenching, we fabricated a negative thermal expansion (NTE) thermometer based on Sc 2 Mo 3 O 12 :Nd3+/Yb3+/Er3+ phosphor. Under 808 nm excitation, the upconversion (UC) emissions of Er3+ ions show the thermal enhancement and its 524 nm emission increases 10-fold as the temperature increased from 310 to 670 K. Furthermore, the temperature sensing behaviors are investigated. It is found fluorescence intensity ratio (FIR) of 524–559 nm is linear with temperature over a wide range of 310–790 K. The maximum relative sensitivity is 0.84% K−1 at 310 K. These results indicate such phosphor not only achieves a high sensitivity, but also exhibits excellent performances at high temperature due to its thermal enhancement. [ABSTRACT FROM AUTHOR]

Lanthanide-doped upconversion (UC) nanoparticles (NPs) have attracted great attention in many emerging applications. Although multilayer structures have been employed to strengthen UC intensity, balancing the energy transfer (ET) efficiency from sensitizer to activator as well as the back energy transfer (BET) efficiency remains a critical issue. Herein, the ET processes in the BaYF 5 -based core/shell/shell NPs are comprehensively manipulated, resulting in greatly enhanced UC intensity. By using the sub20 nm BaYF 5 :2Yb2Er@BaYbF 5 @BaYF 5 nanostructure, the efficiencies of incident light absorption and ET from the sensitizer in the interlayer to the activator in the core are improved, while the BET is limited. The UC intensity of this nanostructure was approximately 3.7 times that of normal BaYF 5 :20Yb2Er@BaYF 5 NPs. The isolation of Yb and Er can remarkably restrict the negative thermal quenching (NTQ) effect, resulting in improved temperature sensing performance. Moreover, the BaYF 5 :2Yb2Er@BaYbF 5 @BaYF 5 NPs can be used for selective sensing of rhodamine B. Our results highlight the comprehensive manipulation of ET processes in a core/shell/shell nanostructure to significantly improve the UC intensity. [ABSTRACT FROM AUTHOR]

Rare-earth-doped NaYF 4 nanoparticles are considered crucial upconversion luminescent materials with many applications, including anti-counterfeiting printing, biological imaging, and optical information storage. This work presents progress in obtaining hydrophilic pigments based on NaYF 4 :Er,Yb@SiO 2 nanoparticles, and their utilization in water-based ink printing for anti-counterfeiting applications. Coating NaYF 4 :Yb/Er microparticles with SiO 2 shells can provide several benefits for printing purposes, such as improved stability, dispersion, and ease of printing. The hydrophilic core-shell structured β-NaYF 4 :Er, Yb@SiO 2 microparticles were successfully prepared using the hydrothermal synthesis and sol-gel Stober method. The obtained microparticles were characterized by Scanning Electron Microscopy, X-ray diffraction, and Energy-dispersive X-ray spectroscopy. Such characterizations confirm that the Er3+ and Yb3+ ions are incorporated in NaYF 4 cores, the NaYF 4 :Er, Yb cores are in hundreds of nanometer sizes, and the NaYF 4 :Er, Yb microparticles are coated by a silica layer of 50 nm thick. Both NaYF 4 :Er, Yb and NaYF 4 :Er, Yb@SiO 2 behave as up-conversion luminescent microparticles for both green and red emissions. The CIE chromaticity coordinates indicate that both the nanoparticles have their greenish color under excitation at 980 nm. Although decorating the NaYF 4 :Er, Yb nanoparticles with the SiO 2 shell decreases luminescent intensity (by a factor of 2), this step is still necessary to achieve hydrophilic surfaces for preparing water-based printing inks. Using the synthesized NaYF 4 :Er, Yb@SiO 2 as a pigment, a new water-based ink formula was created based on Polyamide as a polymer matrix. The obtained ink is printable on paper and on transparent and flexible Polyethylene substrate. The printed patterns with a height of 2 cm and a width of 2.5 cm were observed clearly under the irradiation of a 980 nm LED. Their durability in terms of sharpness and color was also assessed after six months. [ABSTRACT FROM AUTHOR]

Lanthanide doped nanocrystalline fluoride optical materials have been explored for diverse applications in the solar energy harvesting, industry, medical, forensic and biological fields because of high photoluminescence quantum yield and low phonon energy. In this manuscript, Er3+/Yb3+:BaYF 5 nanocrystals were synthesized by hydrothermal process. These nanocrystals were investigated through X-ray diffraction (XRD), SEM/TEM, Raman, quantum yield, photoluminescence upconversion (UC) and downconversion (DC) studies. XRD patterns exhibited the cubic phase and no phase deviation with the addition of Er3+ and Yb3+ ions. The TEM images illustrate the cubic-like morphologies of the obtained nanocrystals. Raman spectrum unveils the characteristic vibrational bands with an intense band at 498 cm−1, which is considered the phonon energy of the BaYF 5 matrix. Under 488 nm excitation, the near infrared (NIR) emission of Er3+ increases up to 5 mol% and then decreases for a 10 mol% doped sample. Photoluminescence DC quantum yield of Er3+/Yb3+:BaYF 5 sample is measured by using integrating sphere in the visible region under 488 nm (Xe flash lamp) excitation, is 4.25%. Under 900 nm laser excitation, intense NIR emissions at 978 and 1550 nm corresponding to Yb3+ (2F 5/2 → 2F 7/2) and Er3+ (4I 13/2 → 4I 15/2) ions, respectively, were observed. With the increase of Yb3+ concentration, the NIR emissions of both Er3+ and Yb3+ increase to 5 mol% and then decrease to 10 mol%. The strength of green UC emission of Er3+ decreases with increase of Er3+ concentration, whereas it enhances with the rise of Yb3+ concentration under 980 nm laser excitation. Two-photon UC process is confirmed as the slopes of the green, and red intensities are 2 and 2. These nanocrystals exhibit intense UC and DC emissions under 980 nm and 480 nm, respectively, which can be suitable for improving the efficiency of solar cells. [ABSTRACT FROM AUTHOR]

The Pechini sol-gel reaction technique has been used to produce Tm3+, Yb3+ co-doped YVO 4 and Li+/K+/Zn2+ codoped YVO 4 : Tm3+,Yb3+ phosphors. Post-heat treatment (at 800 °C) was given to all the samples to strengthen the material's structural and optical characteristics. Prepared phosphors exhibit blue and near-infrared (NIR) light. The crystalline structure and morphology of the prepared phosphors were studied by using powder X-ray diffraction (PXRD), Fourier transform Infrared spectroscopy (FTIR) and scanning electron microscope (SEM). All prepared phosphors crystallise in the tetragonal crystal structure having space group I 4 1 / amd. Prepared phosphors, when pumped with the laser at 980 nm, give strong upconversion emission in blue and NIR regions that correspond to Tm3+ transitions 1G 4 →3H 6 and 3H 4 →3H 6 , respectively. Li+/K+/Zn2+ co-doping enhances the luminescence intensity significantly. Among Li+/K+/Zn2+ ions, Zn2+ co-doping increases the upconversion emission intensity mostly compared to others, the blue emission intensity get increased by ∼7 times and the NIR by ∼6 times. The main cause of enhancement in the emission intensity may be primarily due to the charge imbalance and asymmetry in the crystal field. Further, optical temperature sensing was also investigated by using the fluorescence intensity ratio (FIR) of the transitions (3F 2,3 →3H 6) and (3H 4 →3H 6). Co-doping of Li+/K+/Zn2+ ions also affects the temperature sensitivity. The relative sensitivity and absolute sensitivity of the samples were also calculated. This study indicates that this phosphor is a suitable candidate as a blue phosphor for display devices, WLEDs and optical temperature-sensing probes. [ABSTRACT FROM AUTHOR]

In this study, the SiO 2 – CaO (SC) and SiO 2 – CaO – P 2 O 5 (SCP) glass powders doped with 0.3 mol% of Tm3+ and 4 mol% of Yb3+ ions were prepared by the sol–gel method. The samples were immersed for four weeks in a simulated physiological environment (Dulbecco's phosphate-buffered saline, DPBS) to investigate the bioactivity of the glasses. Their structure, morphology, and spectroscopic properties were investigated in the function of immersion time. X-ray diffractograms and infrared spectra showed that after incubation in DPBS, the hydroxyapatite starts to build up after 1–3 days. The energy dispersive X-ray spectroscopy analysis indicated the dynamics of ion exchange resulting from the biomineralization process in the glasses. Moreover, the upconversion emission spectra of Tm3+ were measured for all samples under 980 nm excitation wavelength in resonance with the 2F 7/2 → 2F 5/2 absorption of Yb3+. It was observed that the upconversion luminescence continuously decreased and the decay times shorten slightly after the immersion in the buffer. In vitro cytotoxicity assays revealed that the SC glass was biocompatible for all tested cell lines (human chondrocytes, osteoblasts, and fibrosarcoma). However, the SCP powder showed an inhibitory effect on human chondrocyte and fibrosarcoma cells in small concentrations and fibrosarcoma cells in high concentrations. [ABSTRACT FROM AUTHOR]

Luminescence thermometry is strongly desired in many fields due to the capability of remote temperature measurement with fast response and high spatial resolution. For developing excellent luminescence thermometer, we systematically investigated the upconversion (UC) emissions from Er3+-Yb3+-Cr3+ tri-doped garnet-structured phosphors under the excitation of 980 nm laser. The influence of Ga3+/Al3+ dopant ratio in Y 3 Al 5- x Ga x O 12 on the UC luminescence was studied in detail by the X-ray diffraction patterns, Raman spectra, FT-IR spectra and Judd-Ofelt theory. Research revealed that the increase of Ga3+ doping content could reduce the symmetry of rare earth (RE) ions site and simultaneously weaken the nonradiative relaxations, favoring the RE luminescence and the subsequent energy transfer (ET) from RE to Cr3+. More importantly, because of the thermally strengthened ET from Er3+ ions, about 27-fold enhancement in Cr3+ UC luminescence was successfully achieved within Er3+-Yb3+-Cr3+ tri-doped Y 3 Ga 5 O 12 as temperature ascended from 303 to 873 K, which consequently leaded to the emission color switching in response to temperature change. These advances in the as-prepared garnet phosphors provide potential opportunity for vision-guided temperature sensing with high sensitivity (∼ 4.38% K−1) and low measurement uncertainty (∼ 0.29 K). [ABSTRACT FROM AUTHOR]

Wollastonite (CaSiO 3) is a well-known rock-forming mineral and an important constituent in ceramics and cement industries due to its outstanding mechanical, chemical, and thermal stabilities. Despite technological importance, functional properties such as photon upconversion in CaSiO 3 wollastonite ceramics have not been studied. In this contribution, Yb- and Er-doped CaSiO 3 (Yb/Er–CaSiO 3) wollastonite ceramics were synthesized via microwave hydrothermal technique followed up by heat-treatment in an air environment. X-ray diffraction and transmission electron microscopy studies confirmed the β-wollastonite (2M) phase in the synthesized samples heat-treated at 1050 °C. X-ray photoelectron spectroscopy analysis has shown that the binding energy of Ca 2p orbitals decreases after doping, indicating a change in the crystal environment of Ca in the CaSiO 3 and hence a successful incorporation of Yb3+ and Er3+ ions in the lattice. The 980 nm excitation resulted in ultraviolet, violet and strong green and red upconversion emissions as well as downshifting infrared emissions due to the energy transfer between Yb3+ and Er3+ ions. An absolute upconversion quantum yield in the 400–800 nm range is 0.04%. The most intense phonon band was observed at 969 cm−1 in the Yb/Er–CaSiO 3 system. This study demonstrates that the β-wollastonite can be developed as a new kind of efficient upconversion phosphor material. [ABSTRACT FROM AUTHOR]

Composite nanoparticles consisting upconversion nanoparticles (β-NaYF 4 :Yb/Er) and nitrogen doped TiO 2 nanoparticles were constructed via a chemical assembly method. Efficient energy transfer was enabled since the upconverted energy matched up with the band gap of N-TiO 2. This enables the resulting composite nanoparticles to possess excellent Rhodamine B (RhB) degradation activity under near infrared (NIR) light irradiation. Composite β-NaYF 4 : Yb/Er-N-TiO 2 nanoparticles were synthesized via a chemical assembly method. They exhibited excellent Rhodamine B degradation activity under NIR light irradiation due to their high upconversion efficiency and high energy transfer efficiency. [Display omitted] • β-NaYF 4 :Yb/Er exhibits high UC efficiency after optimizing the synthetic process. • Nitrogen doping narrows the band gap of TiO 2. • β-NaYF 4 :Yb/Er is assembled with N-doped TiO 2 via an esterification reaction. • Energy transfer between β-NaYF 4 :Yb/Er and N-doped TiO 2 is permitted. • Composite β-NaYF 4 :Yb/Er and TiO 2 nanoparticles show high photocatalytic activity. [ABSTRACT FROM AUTHOR]

Previous works have been already reported on multiphonon-assisted non-resonant energy transfer in Ce3+-Er3+-doped tellurite glasses. However, it is not clear the mechanism of the radiative emission of Er3+ centered at 1530 nm. In this paper, we reported a better understanding of the mechanism of interactions between those two rare-earth ions via a systematic study. For that, we will explore the energy transitions between Ce4+/Ce3+ and Er3+ ions in a tungsten-tellurite glass to both emission (in the near infrared) and upconversion (in the visible) spectrum. Here, Ce4+ and Ce3+ were obtained in an Er3+-doped tellurite glasses via the addition of different concentrations of CeO 2 as part of the composition of the samples. Emission spectrum, under a 980 nm excitation, giving rise to a series of interactions between Ce3+↔Er3+ resulting in: (i) a subtle increase of the Er3+ emission intensity in the near-infrared region for 0.1 mol% of CeO 2 , and then a decrease in the emission for higher CeO 2 concentration in both cases without any significant increase in the bandwidth, and (ii) a decrease of the visible upconversion emission intensity with the addition of CeO 2. Such interactions are achieved via a coupling yielding and energy transfer from both rare-earth ions. [ABSTRACT FROM AUTHOR]

Germanate-based oxyfluoride transparent glass-ceramic functionalized by Tm3+:Ca 2 YbF 7 nanocrystals was newly developed. The tremendously enhanced upconversion emission of 3F 2,3 energy levels by in situ crystallization was extremely beneficial for constructing optical thermometry involving the indirect thermally coupled energy levels (1G 4 and 3F 2,3) of Tm3+ ions. Utilizing the fluorescence intensity ratio technique, the thermometry potentials of PG and GC8 were systematically evaluated based on the emissions from 3F 2,3 and 1G 4 energy levels. The relative and absolute sensitivities, thermometry resolutions, and repeatabilities were superior to many reported materials. This work provides an avenue for precipitating ternary fluoride nanocrystals containing rare earths in germanate-based oxyfluoride glass, and proposes a promising way to achieve high performance optical thermometry based on the emissions from widely spaced energy levels. [ABSTRACT FROM AUTHOR]

Morphology and size controls are critical for the research of luminescent nanomaterials. In this work, La 2 O 3 :18%Yb3+/2%Er3+ nanoparticles were synthesized by a urea-assisted coprecipitation process, where the morphology and size of nanoparticles could be precisely controlled by adjusting the doping concentration, urea dosage and reaction time. With increasing Yb3+ doping concentration and reaction time, morphological evolution processes from nanosheets to nanospheres to nanofibers were observed. The experimental results revealed that the nanospheres could only be synthesized when 18%Yb3+ and 2%Er3+ were doped into the La 2 O 3 host, where the size of the nanospheres could be precisely controlled by adjusting the urea dosage. The effects of the particle morphology and size on the upconversion luminescence of La 2 O 3 :18%Yb3+/2%Er3+ nanoparticles were investigated. In addition, the chemical stability of La 2 O 3 :18%Yb3+/2%Er3+ nanospheres in air was investigated by recording XRD and upconversion luminescence spectra after exposure to air for different periods. The experimental conclusions were useful for further probing the effects of the particle morphology and size on the upconversion emission of Er3+. The upconverted luminescence and chemical stability of morphologically controllable La 2 O 3 :Yb3+/Er3+ nanoparticles. [Display omitted] • La 2 O 3 :Yb3+/Er3+ UC nanoparticles were synthesized via the co-precipitation method. • The morphology was controlled by adjusting doping concentration and reaction parameters. • The UC luminescence of La 2 O 3 :Yb3+/Er3+ was associated with the particle morphology and size. [ABSTRACT FROM AUTHOR]

In this study, Y 2 O 3 : Al3+/Er3+ crystals materials (AYE) were synthesized through laser annealing. The structure and spectral characteristics of Al3+ ions doping in Y 2 O 3 : Er3+ crystals are discussed in detail. With the incorporation of Al3+ ions, the AYE structure experiences a phase transformation characterized by a sequence of monophasic and biphasic states: monophasis-biphase-biphase-monophasis-biphase. When the concentration of Al3+ ions is 0–50 %, AYE has fluorescence characteristics under 980 nm excitation, and its I 563 nm / I 799 nm shows non-thermal coupling phenomenon at low temperature and thermal coupling phenomenon at high temperature, with a maximum relative sensitivity of 1.643 %K−1. When the concentration of Al3+ ion is 60 %-98 %, AYE shows a strong thermal radiation phenomenon under the excitation of a 980 nm laser. Its initial laser power density is as low as 0.71 W/mm2. This is about three times lower than the initial power density of thermal radiation generated by the same level of material. In summary, Y 2 O 3 : Al3+/Er3+ crystals materials have a broad application prospect in the field of temperature sensing and thermal radiation materials. • The structural changes of Y 2 O 3 : Er3+/Al3+ materials were studied when the concentration of Al3+ ions changed from 0-98%. • When the concentration of Al3+ ion is 0~50%, the material exhibits fluorescence characteristics. • The transition from thermal coupling to non-thermal coupling is discovered and explained. • The concentration of Al3+ ions is 60 %-98 %, and the material exhibits excellent thermal radiation characteristics. • The initial power density of thermal radiation is 0.71 W/mm2. The initial thermal radiation temperature is 1270 K. [ABSTRACT FROM AUTHOR]

A simple and rapid grinding method for preparing Er3+-doped and Er3+/Yb3+co-doped Cs 3 Bi 2 Cl 9 upconversion phosphors was developed. We avoid to employ strong acids as reaction solvents, aligning with the principles of green chemistry. By controlling the thermal treatment temperature and adding BiCl 3 , a reversible phase transformation process between Cs 3 Bi 2 Cl 9 and Cs 3 BiCl 6 perovskite phosphors was achieved. The Er3+/Yb3+ co-doped Cs 3 Bi 2 Cl 9 phosphors emit green light under 980 nm excitation, whereas Cs 3 BiCl 6 phosphors emit red light. Their temperature sensing performance was tested through variable-temperature processes. Compared to Er3+-doped Cs 3 Bi 2 Cl 9 phosphors, the co-doped Er3+/Yb3+ phosphors have a higher relative sensitivity of 1.60 % K−1. Compared to previously reported materials, Cs 3 Bi 2 Cl 9 phosphors show enhanced sensitivity in temperature sensing. The study demonstrates that lead-free halide perovskites' unique color-tunability not only underscores the innovativeness of this synthetic strategy but also provides a significant technological foundation for temperature sensing applications. Given their environmental friendliness and facile preparation process, these phosphors possess notable advantages for industrial production and hold promise as potential candidates for next-generation high-performance phosphor materials. • A grinding method for preparing Cs 3 Bi 2 Cl 9 phosphors using a green chemistry approach. • Reversible phase transitions between Cs 3 Bi 2 Cl 9 and Cs 3 BiCl 6 can be controllinged by thermal treatment and BiCl 3 addition. • Er3+/Yb3+ co-doped Cs 3 Bi 2 Cl 9 emit green light under 980 nm excitation, while phase-transformed Cs 3 BiCl 6 emit red. • Cs 3 Bi 2 Cl 9 phosphors co-doped with Er3+/Yb3+ show improved sensitivity compared to Er3+single doping. [ABSTRACT FROM AUTHOR]

The low-voltage operation of blue organic light-emitting diodes (OLEDs) is critical for reducing power consumption and improving device lifetime. This review briefly summarizes the history and origin of low-voltage electroluminescence and its realization in recent reports. In particular, upconversion OLEDs, which use the charge transfer state as an intermediate state to facilitate blue emission via triplet–triplet annihilation, present a promising solution. Thus, continued efforts aimed at reducing the driving voltage, including the exploration of new materials and device structures, are expected to significantly contribute to expanding the applications of blue OLEDs. • Turn-on voltages of blue OLEDs are reviewed. • Minimizing charge injection barriers is vital to reduce turn-on voltage. • Extremely low turn-on is realized in upconversion OLED via charge transfer state. [ABSTRACT FROM AUTHOR]

The main goal of the work was to develop phosphorescent coating for investigations of surface temperature distribution resulted from short duration and high energy thermal events such as small rocket engine testing. For that purpose, we developed thermal history paint with upconverting Gd 2 O 3 : Er3+, Yb3+, Mg2+ nanopowder. The developed paint was heated by Joule effect with precise control over temperature and heating time. Photoluminescence signal of cooled samples was excited with 980 nm laser and collected in automatic manner with use of an optical fibre probe connected to photospectrometer. The results show that irreversible changes of paint emission are temperature and heating time specific for calcination temperatures from 700 °C to 1150 °C. Calibration curves were prepared for heating times of 10, 60 and 180 seconds. Finally, 2D surface temperature samples were determined with use of upconverting thermal history paint and compared to IR camera and pyrometric measurements. The results indicate that uncertainty of temperature measurement below 10 °C was achieved for temperatures above 1000 °C. It has been demonstrated that developed thermal history paint allows for measurements of 2D surface temperature distribution with high spatial resolution and good agreement to standard measurements techniques like thermal camera and pyrometer. [Display omitted] • Changes of fluorescence after short heating time is achieved by use of nanosensors. • Strong upconversion emission of nanoparticles persist after paint layer deposition. • Irreversible changes of paint emission are temperature and heating time specific. [ABSTRACT FROM AUTHOR]

Herein, a series of Er3+ self-sensitized NaYS 2 phosphors are synthesized by the solid-gas reaction method for a novel upconversion luminescence thermometer. Er3+ possesses abundant excited state energy levels in the near-infrared region, enabling efficient upconversion luminescence by absorbing different near-infrared wavelength light. Compared to 980 nm excitation, the emission intensity is enhanced by nearly an order of magnitude under 1532 nm excitation, which can be attributed to the larger absorption cross-section of 4I 13/2 and stronger absorption efficiency for Er3+. Based on the luminescence intensity ratio technique, the optical thermometry behaviors of NaYS 2 :Er3+ under different wavelength excitation are evaluated by employing the thermally coupled energy levels of 2H 11/2 /4S 3/2. It can be deduced that the excitation wavelength has no significant effect on the temperature sensing parameters. Compared to other typical upconversion luminescence thermometers, NaYS 2 :Er3+ thermometer exhibits not only excellent sensitivity performance but also high upconversion luminescence efficiency, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing. • Upconversion properties and mechanisms of Er3+ self-sensitized NaYS 2 under 980/1532 nm excitation were analyzed. • LIR technique based on 2H 11/2 /4S 3/2 of NaYS 2 :Er3+ was used for temperature sensing. • Wide-range and highly-sensitive optical temperature sensing was realized. • No significant effect of excitation wavelength on thermometry parameters of Er3+ was inferred by analyzing the performance. [ABSTRACT FROM AUTHOR]

Multicolor luminescence and optical thermometry hold charming potential applications in many fields, which are likely to be achieved in one rationally designed unit. Herein, a triple-wavelength (980 nm, 1550 nm and 808 nm) responsive upconversion microcrystal, using Er3+ ions as sensitizers, is proposed, which can generate tunable emission color from red to yellow and then to green. The modulated population route and energy transfer process of Er3+ are perceived to be the reason for tunable luminescence color upon excitation-wavelength. In addition, based on thermally coupled energy levels (TCLs), i.e., 2H 11/2 /4S 3/2 and non-thermally coupled energy levels (NTCLs), i.e., 2H 11/2 /4F 9/2 of Er3+ ions, the temperature-dependent upconversion properties were investigated. The maximum relative sensing sensitivity (S r) of NaYF 4 :0.5%Tm/20%Er was found to be 1.373 % K−1 at 313 K, outperforming the majority of the same type thermometers. The results indicate that the NaYF 4 :0.5%Tm/20%Er microcrystals serve as a promising candidate for multicolor anticounterfeiting and optical thermometry applications. • Multicolor emission can be obtained from 0.5%Tm20%Er sample. • Based on triple-wavelength responsive, novel information encryption strategies are proposed. • 0.5%Tm20%Er microcrystals possess the maximum relative sensitivity of 1.373%K−1 at 313K under 980 nm excitation. [ABSTRACT FROM AUTHOR]

• The optoelectronic properties of hexagonal ZnO were notably improved through post-synthesis ultrasonication. • Ultrasonic treatment resulted in a substantial increase in photocurrent. • Ultrasonicated zinc oxide (S-ZnO) demonstrated a significant reduction in charge carrier recombination. • Ultrasonication induced shifts in the band-edge potential of S-ZnO, contributing to the material's improved properties. • Construction of a Z-scheme heterojunction with graphitic carbon nitride extended the photocatalytic activity of S-ZnO to solar light. In this study, we enhanced ZnO photocatalytic activity by synthesizing nanostructures with high aspect ratio of exposed polar facets. Post-synthesis ultrasonication induced morphological reconfiguration, improving optoelectronic properties, charge carrier separation, photocurrent, and shifted the valence band edge potential to higher positive values, providing a heightened overpotential for hydroxyl radical formation. The resulting overpotential for hydroxyl radical formation significantly boosted phenol degradation under UV light. To extend photoresponse, we employed ultrasonication to create a direct Z-scheme heterostructure with gCN, preventing particle aggregation. The S-ZnO/gCN photocatalyst, exhibiting a highly ordered structure, demonstrated superior photocatalytic activity under solar light for phenol degradation. Experimental results showed that increased dissolved oxygen accelerated hydroquinone and catechol formation, enhancing phenol degradation. Experimental results were supported by theoretical calculations. This innovative approach not only improves ZnO photocatalytic activity but also broadens its application to solar light-driven reactions. [Display omitted] [ABSTRACT FROM AUTHOR]

Temperature-dependent behavior of phosphors has recently attracted significant research attention. This is due to the widespread applications of phosphors. Unfortunately, the thermal quenching effect in many phosphors greatly limits their performance at high temperatures. Herein, negative thermal quenching phosphor β-Ba 3 LuAl 2 O 7.5 : 0.3Yb3+, 0.03Er3+ is synthesized using the high-temperature solid-state method. X-ray Rietveld refinement and EPR results indicate the defect state of oxygen vacancy. Temperature-dependent upconversion luminescence spectra demonstrate that the green and red emission intensities increase with temperature to reach maximums at 398 K and 348 K respectively. Diffuse reflectance spectrum and downshifting luminescence spectrum prove that the defect state is near the 4F 7/2 state of Er3+ ions. The defect state traps electrons at room temperature and releases them to populate the 4F 7/2 state of Er3+ ion at elevated temperatures to cause the observed thermal enhancement of upconversion luminescence. This material's negative thermal quenching effect makes it a suitable candidate for applications in displays and anti-counterfeiting. • Negative thermal quenching phosphor β-Ba 3 LuAl 2 O 7.5 : 0.3Yb3+, 0.03Er3+ is obtained by the high-temperature solid-state method. • The green and red emission intensities increase evidently at high temperatures. • The defect traps and releases electrons to the 4F 7/2 state of Er3+ explaining the abnormal thermal enhancement. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparing porous bioactive scaffolds successfully with codoped up-conversion crystals. • Reporting for the first time green light emission at 2.23 cd/m² intensity under 980 nm from biophotonic scaffolds. • Demonstrating nitric oxide release from biophotonic scaffolds under 980 nm, for smart drug delivery systems. • Confirming scaffold emissions under 980 nm after 2 weeks in simulated body fluid for long-term application. For the first time, the preparation of 3D biophotonic scaffolds is reported. Scaffolds are prepared using the porogen burn-off technique and are capable of converting NIR to green emission, used to release nitric oxide from S-Nitroso-N-Acetylpenicillamine. NIR to green conversion is obtained by mixing CaWO 4 crystals (codoped with Yb3+ and Er3+) with bioactive borosilicate glass prior to the sintering process. The scaffold fabrication process has a detrimental impact on the upconversion properties of the crystals embedded in the porous scaffold due to the formation of internal/surface crystalline defects and surface chemical bonds in the crystals. Nonetheless, we demonstrate that the brightness of the green emission, under 980 nm pumping, is sufficient to release nitric oxide from the scaffold covered with S-Nitroso-N-Acetylpenicillamine. Addition of upconverter crystals, in the bioactive scaffold, has no impact on porosity, mechanical properties, reactivity in simulated body fluid nor cytocompatibility. The progressive dissolution of the scaffold, associated with the precipitation of a reactive layer (HA), has no noticeable influence on the green emission under 980 nm pumping, showing that the development of such biophotonic scaffolds opens the path to light actuated drug release in a spatial–temporal manner, in vivo. Degradation of the up-converter particles does not lead to differences in cells viability. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced polymer-based composites prepared by photocuring technology offer notable advantages. However, the traditional UV curing technology faces challenges in balancing curing efficiency, penetration depth, and mechanical properties when producing high-thickness fiber-reinforced composites. This study introduced a new method for crafting thick glass fiber reinforced composites via upconversion particle-assisted near-infrared photopolymerization (UCAP). Near-infrared (NIR) radiation had superior penetration in glass fiber composites system, effectively curing of specimens exceeding 20 mm in thickness. Through micro-CT and atomic force microscopy, it was verified that UCAP specimens had fewer interfacial defects and a wider interphase, making contribution to enhanced interlaminar and interfacial shear strength. Additionally, uniform curing effectively alleviated stress concentration under external forces, resulting in a 78.5 % increase in flexural strength and a 32.1 % increase in impact toughness for UCAP specimens compared to UV-cured ones. This approach facilitated rapid outdoor curing of large-sized glass fiber composites with sustained structural stability, showcasing the potential application of UCAP in high-performance glass fiber composites rapid prototyping. • Photo curing of high-thickness glass fiber composite using high penetration NIR. • NIR cured composites exhibit enhanced interfacial performance and reduced internal defects compared to UV curing ones. • NIR cured specimens exhibit uniform stress distribution compared to UV curing specimens. • Composites cured by NIR demonstrate higher flexural strength compared to those cured using UV. [ABSTRACT FROM AUTHOR]

In this paper, CaGa 2 S 4 :3%Nd,5%Yb; CaGa 2 S 4 :5%Yb; CaGa 2 S 4 :3%Nd compounds were synthesized, and their photoluminescence (PL) spectra, PL excitation (PLE) spectra and PL decay properties were studied at room temperature under one-photon and multi-photon excitation in a wide range of excitation intensities. The synthesis of the CaGa 2 S 4 compound was carried out by a solid-phase reaction of a stoichiometric mixture of CaS and Ga 2 S 3 powders in a quartz ampoule. Yb and Nd doping was carried out during the synthesis process using YbF 3 and NdF 3. PLE spectra were studied in the wavelength range from 250 to 850 nm, and PL spectra in the range of 400–1500 nm. It has been shown that after introducing Yb3+ ions into thiogallate crystals with Nd3+ ions, a new band near 488 nm is formed and the PL intensity increases by 1–2 orders of magnitude. The anti-Stokes PL spectra of CaGa 2 S 4 : Nd, Yb crystals in the visible region of the spectrum (400–700 nm) were studied when excited by continuous wave laser radiation with a wavelength of 975 nm. The kinetics of PL decay of all types of compounds at different wavelengths of single- and multi-photon excitation were determined. Depending on the PLE conditions, wavelength and intensity of the exciting radiation, monoexponential and non-monoexponential decay kinetics were observed with decay times in the range of 20–90 μs. Possible mechanisms of PLE and PL of CaGa 2 S 4 crystals doped with neodymium and ytterbium ions are discussed. • The photoluminescence (PL) efficiency of CaGa 2 S 4 :3%Nd doped with Yb3+ upon Stokes excitation increases by 1–2 orders of magnitude. • The increase in PL efficiency is explained by the formation of charge transfer states of the Yb3+ ion with the matrix. • The charge transfer of the Yb3+ ion to the matrix is manifested in the PL excitation spectrum and its decay kinetics. • During anti-Stokes excitation, the population of the upper excited state occurs with the participation of two-photon absorption of Yb3+ ions, and emission is with the predominant participation of Yb2+ ions. [ABSTRACT FROM AUTHOR]

In this paper, a detailed study of the Er/Yb/W tri-doped BaBi 2-x-y Nb 2-z Er x Yb y W z O 9 (BBN) system and a comparison of undoped, Er-doped, Er/Yb co-doped and Er/Yb/W tri-doped BBN systems are presented. All the BBN ceramics are prepared using the solid-state approach. The XRD spectra demonstrated that each BBN composition has an orthorhombic geometry. The UCL spectra are traced at 980 nm and exhibit two distinctive green bands and one red band at 535 nm, 556 nm, and 673 nm, respectively. The UCL intensity improves with W6+ concentration and reaches a maximum at (z = 0.02); after this concentration, the quenching effect occurs. The pump power variation on UCL spectra confirmed the involvement of two photons. The time-resolved fluorescence analysis was done for green and red emissions, and it was observed that the time decay increased for higher dopant concentrations, suggesting a non-radiative transition at higher dopant concentrations. The FIR technique measured the absolute sensitivity and had a value of 0.91 % K−1 at 573 K. These improvements suggest that the prepared material may help develop advanced electronic equipment for multifunctional applications. • A detailed study of undoped, Er-doped, Er/Yb co-doped, and Er/Yb/W tri-doped BBN is presented. • The UCL spectra exhibit two distinctive green bands and one red band at 535 nm, 556 nm, and 673 nm, respectively. • The time decay analysis for green and red emission bands increased for higher dopant concentrations. • The FIR technique measured the absolute sensitivity and had a value of 0.91 % K−1 at 573 K. [ABSTRACT FROM AUTHOR]

NaYF 4 :Yb3+/Er3+Tm3+@TiO 2 -CQDs showed excellent upconversion luminescence performance and the efficiency of photovoltaic cells was enhanced by 3.10% under 1 sun intensity irradiation and 1.24% under infrared light (＞760 nm) irradiation. [Display omitted] • NaYF 4 :Yb3+/Er3+/Tm3+@TiO 2 -CQDs was developed as dual-upconversion luminescent material for photovoltaic cells. • Core@shell structure profit to enhance the upconversion luminescence intensity. • CQDs played a synergistic role in dual-upconversion with NaYF 4 :Yb3+/Er3+/Tm3+. • NaYF 4 :Yb3+/Er3+/Tm3+@TiO 2 -CQDs improved the utilization of infrared light. Rare-earth doped upconversion luminescence (UCL) is of great significance in improving the utilization of infrared (IR) light from solar radiation, especially in the efficiency enhancement of photovoltaic (PV) cells. However, the low level of luminescence efficiency remains a great challenge. Here, we designed NaYF 4 :Yb3+/Er3+/Tm3+@TiO 2 -CQDs upconversion luminescent materials. The construction of the core–shell structure and the loading of carbon quantum dots (CQDs) resulted in a 9-fold enhancement of upconversion luminescence and a 3.02% enhancement of the efficiency of the photovoltaic cell. These data indicate that the construction of the core–shell structure can effectively inhibit the surface quenching of the luminescent particles, and that the energy transfer between the carbon quantum dots and the rare earth ions has a synergistic effect on the efficiency enhancement of the photovoltaic cell. Meanwhile, the TiO 2 shell layer also enables the prepared materials to have better properties of self-cleaning and degradation of organic pollutants, which will further improve the visible light utilization of PV cells. NaYF 4 :Yb3+/Er3+/Tm3+@TiO 2 -CQDs provides new ideas for the practical application of PV cell efficiency enhancement and the design of new materials. [ABSTRACT FROM AUTHOR]

Accurate on-site detection of nitrite in complex matrices remains a significant challenge. Herin, we construct a self-ratio optical bimodal portable kit via co-assembling NaErF 4 :0.5%Tm@NaYF 4 @NaYbF 4 :0.5%Tm@NaYF 4 (Er:Tm@Yb:Tm) and nitrogen-doped carbon platinum nanomaterials (Pt/CN) in sodium alginate (SA) hydrogel. Pt/CN nanomaterials are synthesized by high-temperature sintering using a zinc-based zeolite imidazolium framework as a sacrificial template. The Pt/CN nanozyme possesses excellent oxidase-like activity to produce the oxidation state 3,3′,5,5′-tetramethylbenzidine (oxTMB). Nitrite mediates diazotization of oxTMB to trigger the change of absorption signals, accompanying the ratio fluorescence response of the Er:Tm@Yb:Tm. Crucially, Er:Tm@Yb:Tm and Pt/CN are embedded in SA hydrogel to fabricate a portable kit with efficient and sensitive performance. An image processing algorithm is used to analyze the nitrite-induced signal change of the portable hydrogel kit, resulting in detection limits of 0.63 μM. This method has great potential for point-of-care applications due to its reliability, long-term stability, accuracy, sensitivity, and portability. [ABSTRACT FROM AUTHOR]

Photoremovable protecting groups (PPGs) have become significant optical molecular tools in modern biomedicine. The unique property of photorelease allows noninvasively manipulating physiological processes with high spatial-temporal resolution. Red/near-infrared (NIR) light activatable is crucial for biomedical applications. Apart from red/NIR light absorbing PPGs, the short-wavelength light absorbing PPGs could also achieve photolysis upon red/NIR light excitation by simply introducing appropriate photosensitizers, displaying significant superiorities in chemical synthesis and photobleaching resistance. Besides, the main molecular scaffolds of PPGs are remained unchanged, avoiding unpredictable photolysis performance degradation. In this review, the mechanisms, design principles and biomedical applications of the sensitized photolysis will be well discussed and summarized, hoping to provide guidelines and references for developing relevant photorelease systems and their biomedical applications. [Display omitted] • Sensitized photolysis achieves red/NIR excitation of short-wavelength light absorbing PPGs • Superiorities in synthesis, photobleaching resistance and preventing photolysis performance degradation are highlighted. • Mechanisms, design principles and biomedical applications are summarized. • Challenges and developing trends of the sensitized photolysis strategy are discussed. [ABSTRACT FROM AUTHOR]

Constructing heterojunction photocatalysts that can make additional utilization of near-infrared (NIR) light has been a global scientific problem and has gained widespread research interest. Upconversion nanoparticles (UCNPs) collaborate with semiconductors to construct UCNPs-based photocatalysts that are used to improve solar energy utilization. In this work, the as-prepared UCNPs-based photocatalysts consisting of NaGdF 4 :Yb3+/Er3+ (NGFYE) and bismuth oxyiodide (BOI) are synthesized by chemical epitaxial growth method and in-situ calcination process. The crystalline phase, morphology, optical and electrochemical properties of NGFYE@BOI samples are investigated in detail. Besides, Bi 4 O 5 I 2 /Bi 5 O 7 I Z-type heterojunction is confirmed by EPR test. Moreover, the photocatalytic elimination of tetracycline hydrochloride (TCH) and its photocatalytic mechanism by NGFYE@BOI samples are explored. This work may provide a promising idea for the efficient and controlled synthesis of UCNPs-based photocatalysts, which will contribute to the future utilization of solar energy. [Display omitted] • The weight fractions of Bi4O5I2 and Bi5O7I in BOI-380 sample are 90.787% and 9.213%, respectively. • The shortened fluorescence lifetime and absorption-emission spectral overlap reveal the existence of FRET process. • EPR measurement is confirmed that the formation of Z-scheme heterojunction between Bi4O5I2 and Bi5O7I. • The degradation rates of TCH by NGFYE@Bi 4 O 5 I 2 /Bi 5 O 7 I are 85.79% (λ ≥ 400 nm, 1 h) and 28.47% (λ ≥ 800 nm, 3 h), respectively. [ABSTRACT FROM AUTHOR]

The BiVO 4 :Ho3+-Yb3+ upconverting phosphors have been synthesized by using the chemical co-precipitation method and optimized with 0.7 % Ho3+ + 6 % Yb3+ combination through frequency upconversion emission study. The synthesized phosphors have been characterized through XRD (X-Ray diffraction), FESEM (Field emission scanning electron microscopy), HR-TEM (High resolution- Transmission electron microscopy), UV–vis diffuse reflectance spectroscopy (DRS), Raman, and FT-IR (Fourier transform infrared spectroscopy). The XPS (X-ray photoelectron spectroscopy) analysis has been performed to study the elemental composition, chemical, and electronic states of the atoms present in the optimized sample. The specific surface area of the pure and optimized phosphors has been determined through BET (Brunauer-Emmett-Teller) analysis. From the XRD analysis, it is clear that on doping, the crystal structure of BiVO 4 changes from monoclinic to tetragonal structure. The values of rate constants for the photocatalytic performance of the upconverting codoped and pure BiVO 4 phosphors under the illumination with an artificial solar lamp for degradation of MB dye are found to be 0.00498 min−1 and 0.00269 min−1, respectively. To verify these results, the same experiment has also been performed under the visible LED (Light-emitting diode) light illumination. This enhancement of ∼ 85 % in the rate constant of the photocatalytic performance ensured the utilization of the NIR portion of the light by the codoped BiVO 4 phosphors through the frequency upconversion process. The material's recycling photocatalysis experiment for three cycles has been performed to check its reusability. The upconversion emission and XRD analysis of the materials after photocatalysis have been performed. From this study, it is confirmed that the stability of the sample is better even after three cycles of photocatalytic dye degradation experiment. • Ho3+-Yb3+ co-doped BiVO 4 phosphors were successfully synthesized with the chemical co-precipitation method. • The upconversion emission studies were done by using a 980 nm CW laser source, and the dopant concentration was optimized. • The structural, morphological, optical properties, functional group, and compositional analyses have been done. • The photocatalytic dye degradation studies under artificial solar light and visible LED light were performed. • The better photocatalytic activity of codoped BiVO 4 ensured the utilization of NIR portion of light for photocatalysis. [ABSTRACT FROM AUTHOR]

Optical temperature sensing has attracted significant attention owing to its unique characteristics of rapid response, non-contact detection, high resolution and high sensitivity. In this study, a series of Gd 3 BWO 9 : Yb3+, Ho3+ upconversion phosphors were synthesized by solid-state synthesis, and the optimal sample was Gd 3 BWO 9 : 0.32 Yb3+, 0.003Ho3+. The upconversion emission spectrum was measured under the excitation of 980 nm laser, and the emission peaks in the bands of 528–560 nm and 630–680 nm corresponded to the green emission (5F 4 /5S 2 →5I 8) and red emission (5F 5 /→5I 8) of Ho3+. The S R and S A of Gd 3 BWO 9 :0.32 Yb3+, 0.003Ho3+ in the range of 300 K–625 K were calculated. At 300 K, both the relative sensitivity S R and the absolute sensitivity S A reached their maximum values, which are S R(max) = 0.73 % K−1 and S A(max) = 0.0508 K-1, respectively. The Gd 3 BWO 9 : 0.32 Yb3+, 0.003Ho3+ phosphor has a very high absolute sensitivity, and hold great application potential in optical temperature sensing. • The upconversion of Ln 3 BWO 9 : Yb3+, Ho3+ phosphors is investigated. • The Ln 3 BWO 9 : Yb3+, Ho3+ phosphor can be used in optical thermometry with a wide temperature range from 300 K to 625 K. • Ln 3 BWO 9 : Yb3+, Ho3 phosphor shows a high S A value of 5.08 % K−1 at 300 K. [ABSTRACT FROM AUTHOR]

Host material plays an important role in obtaining efficient photon upconversion and downshifting luminescence. Generally, fluoride and oxyfluoride glasses-based materials are used for high-efficiency photon upconversion. However, the poor thermal stability of fluoride glasses and the toxicity of fluorine ions limit their applications. In this report, Yb/Ho-doped CaSiO 3 wollastonite phosphors have been demonstrated as efficient red-emitting upconversion phosphors. The phosphors have been synthesized by microwave hydrothermal process followed by heat treatment at 1050 ​°C in the air environment. 2M phase of the β-wollastonite has been confirmed by X-ray diffraction and Raman spectroscopy while the existence of the Yb and Ho dopants in the CaSiO 3 lattice has been confirmed by X-ray photoelectron spectroscopy. The synthesized samples showed strong red upconversion emission centered at 662 ​nm and near-infrared downshifting emissions at 2016 ​nm upon 980 ​nm excitation. The emissions were found to depend significantly on the Ho concentration. Temporal evolution of the main emission bands was investigated to show that the energy transfer upconversion from Yb to Ho ions was responsible for the efficient upconversion and downshifting phenomenon. [Display omitted] • CaSiO 3 , wollastonite, mineral can be an excellent host for lanthanide upconversion. • Intense red upconversion emission observed in Yb/Ho-CaSiO 3 upon 980 ​nm excitation. • Upconversion quantum yield of 0.02% obtained in 20Yb/1.0Ho-CaSiO 3 in 500–780 ​nm range. [ABSTRACT FROM AUTHOR]

The development of laser technology has created intense demand for optical confinement materials with high performance. Herein the authors have been investigated Yb3+-singly doped and Yb3+/Nd3+-codoped SiO 2 -based oxyfluoride glasses in terms of their optical absorption, and their near-infrared (NIR) and up-conversion (UC) emissions including emission decay profiles. Under 808 nm laser diode (LD) excitation, four NIR emission bands were observed i.e., (Nd3+: 4F 3/2 → 4I 9/2 , Yb3+: 2F 5/2 → 2F 7/2 , Nd3+: 4F 3/2 → 4I 11/2 , and Nd3+: 4F 3/2 → 4I 13/2) in co-doped glasses. NIR emission cross-sections [ (σ emi) stimulated, (σ M emi) from Mc-cumber theory] were calculated for 2F 5/2 → 2F 7/2 (∼1030 nm) transition of Yb3+ ion. σ emi was found to be highest (26.27 × 10−21 cm2) for the Yb3+: 2F 5/2 → 2F 7/2 transition in N2 glass. UC emission spectra recorded at 980 nm LD show bands centered at 500, 536, 595 & 610, and 664 nm, attributed to 4G 9/2 → 4I 9/2 , 4G 7/2 → 4I 9/2 &4G 7/2 → 4I 11/2, 4G 5/2 → 4I 9/2 , and 4G 9/2 → 4I 13/2 transitions, respectively. Decay profiles were analyzed for Yb3+: 2F 5/2 → 2F 7/2 (∼1030 nm) and Nd3+: 4F 3/2 → 4I 11/2 (∼1057 nm) transitions at 808 nm LD. Energy transfer (ET) process from Nd3+ to Yb3+ in present glasses were detailed. [ABSTRACT FROM AUTHOR]

This paper presents the upconversion emission and magnetic properties of NaGdF 4 :Yb, Er nanoparticles separately doped with Fe and Mg in the 10–40% concentration. The XRD analysis validates the structural properties of NaGdF 4 :Yb, Er nanoparticles with different concentrations of the dopants. The XPS spectra of Fe-doped NaGdF 4 :Yb, Er and Mg-doped NaGdF 4 :Yb, Er nanoparticles reveal the presence of the dopants and their valency. The 30%Mg doping resulted in an intense red upconversion emission at 650 nm compared to the Fe-doped NaGdF 4 :Yb, Er due to the high lifetime of 254 μs for the 4F 9/2 → 4I 15/2 (660 nm) energy level transitions of Er3+ ion. The Mg-doped nanoparticles showed a 2.7 red-to-green emission intensity ratio, 5.7 for Fe doping at the same 30% concentration and above this doping level, upconversion emission quenching resulted. The room temperature VSM study demonstrated paramagnetic property in the Mg-doped NaGdF 4 :Yb, Er nanoparticles characterized by negligible coercivity and retentivity with low saturation magnetization. Similar behaviour is also observed for the Fe-doped nanoparticles up to 20% concentration, and it became weak ferromagnetic at a high 30 and 40% dopant. In addition, the present work demonstrated the optical trapping of individual magnetic nanoparticles of 30%Fe-doped NaGdF 4 :Yb, Er by using a single beam optical tweezer technique under the tightly focused 980 nm diode laser interaction and the estimated trap stiffnesses is 1.85 pN μm−1 W−1. The multifunctional upconversion red emission, magnetic and optical trapping properties obtained in NaGdF 4 :Yb,Er,30%Fe nanoparticles can be used as a single particle probe in the theragnostic application. [ABSTRACT FROM AUTHOR]