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Graphical abstract Highlights • Yb/Er/Eu: Gd 2 Ti 2 O 7 powders are prepared by a simple sol-gel method • Red emission is due to the high CR possibility of 4F 7/2 + 4I 11/2 → 4F 9/2 + 4F 9/2. • Trace amount of Er3+ are used to reduce deleterious CR between Er3+ and Eu3+. • Excitation-dependent multi-color emissions are achieved. • These systems are suitable for anti-counterfeiting application. Abstract Lanthanide ions with abundant energy levels are widely adopted to actualize controllable colorful emissions. Herein, green to red emissions are obtained in Yb/Er: Gd 2 Ti 2 O 7 phosphor by controlling the Er3+ doping content. With further introducing Eu3+ ions, excitation-dependent multi-color emissions are achieved. The related mechanisms are investigated systematically. Our results reveal these systems with bright up- and down- conversion emissions have potential application for anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The ultrasmall Yb/Er: CaF 2 NCs are chosen as an example to certify the upconversion emission intensity can be greatly enhanced through combining various approaches together, including doping Na + ions to promote the growth the particle size and tailor the crystal-field environment of the emitters, control shell thickness to lower the non-radiative decay and tune Yb 3+ concentration in the shell to enhance the absorption of the excitation energy. In comparison with Na + -free 20Yb/2Er: CaF 2 NCs (~ 2 nm), the upconversion luminescence of 20Yb/2Er: CaF 2 @10Yb: CaF 2 NCs (~ 9 nm) containing ~ 0.5 mmol Na + ions in the core and 10% Yb 3+ in the shell with 5 nm thickness intensifies for about 95 times. [ABSTRACT FROM AUTHOR]

Negative thermal quenching effect (TQE) refers to a phenomenon that the luminescence intensity increases as the temperature increases, which is reported in a few rare-earth doped upconversion (UC) nanocrystals (NCs). However, it is still difficult to enhance the negative TQE for those NCs without changing the particle size. Herein, through comparing the temperature dependent UC emission intensity variations between the Yb/Er co-doped CaF 2 and BaF 2 NCs as well as the CaF 2 :Yb/Er and BaF 2 :Yb/Er based core/shell NCs with different shell layers, we verify that the negative TQE can be improved by employing the matrix with lower phonon energy owing to the reduced possibility of the multi-phonon assisted non-radiative relaxation. This novel method for the improvement the negative TQE may found potential applications in anti-counterfeiting and temperature sensing fields. • Yb/Er co-doped CaF 2 and BaF 2 NCs with similar particle size is prepared. • CaF 2 :Yb/Er and BaF 2 :Yb/Er based core/shell NCs with different shells are prepared. • Negative thermal quenching effect are observed in these NCs with similar particle sizes. • Negative thermal quenching effect is evidently modulated by tuning phonon energy. [ABSTRACT FROM AUTHOR]

The strong 1830 nm emission is realized in Yb/Tm:NaYF 4 @Yb:NaYF 4 core/shell nanocrystals for the first time. The optimal Tm 3+ concentration, shell thickness and composition respectively are 2 mol%, 6.5 nm and inert NaYF 4 . In comparison with Yb/Tm:NaYF 4 nanocrystals, the luminescence intensity of Yb/Tm:NaYF 4 @NaYF 4 core/shell nanocrystals enhances about 160 times. [ABSTRACT FROM AUTHOR]

Abstract: Solvothermal reactions of Cd(OAc)2·2H2O with 3,3′-azodibenzoic acid (H2L) in N,N′-dimethylformamide (DMF) or DMF/MeOH at 100°C or 120°C gave rise to three cadmium(II) coordination polymers {[CdL(DMF)2]·0.5DMF} n (1), [CdL(DMF)(MeOH)] n (2) and {[Cd3L3(DMF)4]·0.5DMF} n (3). Complexes 1–3 were characterized by elemental analysis, IR, powder X-ray diffraction and single-crystal X-ray diffraction. In 1–3, dinuclear [Cd2L4(DMF)4] (1) or [Cd2L4(DMF)2(MeOH)2] (2) unit and trinuclear [Cd3L6(DMF)4] (3) unit acts as a four-connecting node to link its equivalent ones via sharing L ligands to form 2D layers, which are further connected through the C−H⋯π (1) or hydrogen-bonding interactions (2–3) to afford 3D networks with the 41263 topology. The network of 1 allows other one to be penetrated for the formation of twofold interpenetrating pcu net. The formation of 1–3 provided an interesting insight into solvent and temperature effects on the construction of coordination polymers under solvothermal conditions. In addition, the photoluminescent properties of 1–3 in solid state at ambient temperature were also investigated. [Copyright &y& Elsevier]

Abstract: The photodimerization of methyl 2-naphthoate (1), ethyl 2-naphthoate (2) and butyl 2-naphthoate (3) in cucurbituril (CB) aqueous solution was investigated. The product distribution and fluorescence spectral changes suggest that CB[8] can encapsulate two molecules of alkyl 2-naphthoate (1 or 2) and thereby facilitate a cubane-like photodimer formation. Subtle changes in either cavity size of CB[n] or alkyl substitutes can significantly modulate the interaction of CB[n] with 2-naphthoate derivatives affording remarkable alterations in their photochemical reactivity. [Copyright &y& Elsevier]

Biosensors working in the second near-infrared (NIR-II) spectral region have recently gained great attention owning to their deep tissue bioimaging and high spatiotemporal resolution. However, there is still a challenge to develop efficient nanothermometers based on NIR-II luminescence. Herein, we present a pioneering advancement in the field of nanothermometry by synthesizing a novel nanothermometer, a composite of fluoride nanocrystals and quantum dots. This NaYF 4 :1Nd-Ag 2 S QDs@SiO 2 nanocomposite demonstrates exceptional functionality, being excited by a single light irradiation at 808 nm for NIR-II luminescence imaging. Notably, the composite emits at two distinct wavelengths-1064 nm and 1125 nm, attributable to Nd3+ and Ag 2 S QDs, respectively. This unique emission profile enables deeper tissue penetration, mitigating overheating risks compared to conventional excitation sources at 980 nm. Furthermore, the nanomaterials exhibit remarkable temperature-sensing capabilities, with maximum sensitivities of 0.81%K−1 (S R) at 333 K. These superior sensitivities outperform many existing temperature sensors relying on thermally coupled Stark sublevels. The SiO 2 matrix not only encapsulates and protects the fluoride nanocrystals and quantum dots but also shields them from aqueous environments, ensuring outstanding luminescence stability. Our findings highlight the potential of this nanothermometer as a highly efficient temperature sensor with promising applications in cutting-edge bioapplications. This development introduces a new frontier in temperature sensing and bioimaging, showcasing its potential for transformative contributions to the field. [Display omitted] • Successful synthesis of a novel nanothermometer based on a composite comprising fluoride nanocrystals and quantum dots. • The emission intensity of Nd3+ and Ag 2 S QDs serves as a temperature sensing mechanism (0.81%K−1 (S R) at 333 K). • A versatile platform allows the integration of two different luminescent nanomaterials to meet customized requirements. • The SiO 2 matrix shields NCs and Ag 2 S QDs from water environments, ensuring excellent luminescence stability. [ABSTRACT FROM AUTHOR]

X-ray excited optical luminescence (XEOL) imaging shows great potential applications in security inspection and computed tomography. Lanthanide doped fluoride nanoscintillators (NSs) do not only exhibit advantages of simple synthetic procedures, tunable emissions and high environmental stability, but also show many new properties through constructing core/shell architectures. However, the strong hysteresis scintillation luminescence greatly restrict their practical applications. Herein, we verify that this hysteresis can be fully restricted by employing core/shell structure to inhibit the generation of Frenkel defects and incorporating Gd3+ ions to introduce extra energy migration process. As a result, upon continuous X-ray irradiation, the XEOL intensity of the LiYF 4 : 15Tb/25Gd@LiYF 4 core/shell NSs almost keeps unchanged. Our results provide important information for designing new NSs with greatly reduced hysteresis scintillation luminescence, which show promising applications in the field of stable X-ray imaging. [Display omitted] • Hysteresis scintillation is greatly restricted in the LiYF 4 : 15Tb/25Gd@LiYF 4 NSs. • Upon continuous X-ray irradiation, its XEOL intensity is only increased ∼1.6%. • The core/shell structure can inhibit the generation of Frenkel defects. • Incorporating Gd3+ ions can introduce extra energy migration process. [ABSTRACT FROM AUTHOR]

Lanthanide doped fluoride nanoparticles (NPs) exhibit tunable X-ray excited persistent luminescence (XEPL), which show promising applications in optical imaging, cancer therapy and information storage. Although a few progresses have been achieved in enhancing the XEPL of lanthanide activators, there is no report about the influence of crystallinity on the XEPL intensity. In this work, we verify that the XEPL intensity can be improved by optimizing the NP crystallinity. Our results reveal that better crystallinity benefit the lower non-radiative relaxation possibility but also the restriction of the formation of Frenkel defects. This work provides important information for the development of lanthanide doped fluoride nanoparticles with superior XEPL performances. • The influence of crystallinity on the XEPL intensity was studied for the first time. • Better crystallinity inhibits the formation of Frenkel defects. • It exists optimal crystallinity for stronger XEPL. [ABSTRACT FROM AUTHOR]

A series of Er 3+ doped and Er 3+ /Yb 3+ codoped SrTiO 3 nanocubes with varying dopant concentrations have been successfully synthesized by a facile hydrothermal method. The doping effects on phase purity, morphology and microstructure of samples were identified by power X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that SrTiO 3 nanocubes have a typical perovskite structure with the edge length ranging 20–50 nm. The Er 3+ and Yb 3+ ions were successfully doped into the crystal lattice of SrTiO 3 , but did not alter crystal structure of SrTiO 3 . The photon up-conversion (UC) photoluminescence (PL) measurements indicated that the intense green light emission of Er 3+ ions around 525 nm, 550 nm and red light emission centered at 670 nm in UC processes populated by 980 nm laser excitation have been achieved in SrTiO 3 nanocubes. Moreover, the PL intensity of Er 3+ -doped SrTiO 3 nanocubes was greatly enhanced while introducing the Yb 3+ to the crystal structure, especially the red emission. The mechanisms for these emissions probably due to the excited state absorption (ESA) and energy transfer (ET) process. Er 3+ /Yb 3+ -codoped single-crystal perovskite SrTiO 3 nanocubes could be interesting objects for applications in mechanical−electrical luminescence such as electric field modulation luminescence and mechanoluminescence. [ABSTRACT FROM AUTHOR]

The development of multifunctional nanocrystals has attracted growing interest lately in the biological and medical sciences. Herein, the dual-mode luminescence properties and optical thermometric performances of Tm3+, Yb3+: Gd 2 Zr 2 O 7 nanocrystals synthesized by a facile hydrothermal method are investigated systematically. Upon 980 nm excitation, the upconversion (UC) luminescence spectra of the obtained samples consist of blue (485 nm), red (655 and 681 nm), and near-infrared (785 nm) emission bands of Tm3+ ions. Diversely, the X-ray excited luminescence (XEL) spectra contain a strong ultraviolet (UV) emission from Gd3+ ions (314 nm), a weak defect-related emission band (400–600 nm), and several tiny emissions from Tm3+ ions. To realize the optical thermometry in the biological window, the luminescence intensity ratio (LIR) between 3F 2,3 → 3H 6 (681 nm) and 1G 4 →3F 4 (655 nm) transitions is employed for temperature sensing, giving high absolute and relative sensing sensitivities (S a-max = ∼1064 × 10−4 K−1, S r-max = ∼2.32%K−1). Therefore, the present Tm3+, Yb3+: Gd 2 Zr 2 O 7 nanocrystals could be useful in optical thermometry, photodynamic therapy, and X-ray imaging. • Dual-mode luminescence and thermometric properties of Tm3+/Yb3+: Gd 2 Zr 2 O 7 are studied. • UCL spectra consist of blue, red and NIR emissions of Tm3+ upon 980 nm excitation. • UV emission from Gd3+ is predominant under X-ray excitation. • LIR of 681 nm–655 nm shows high sensing sensitivity with S r-max of 2.32% K−1. • Tm3+/Yb3+: Gd 2 Zr 2 O 7 could be used for optical thermometry and photodynamic therapy. [ABSTRACT FROM AUTHOR]

Here, La 2 MgGeO 6 : Bi3+, Er3+ samples were synthesized by the high-temperature solid-phase method, and the up/down-conversion luminescence properties were investigated with the excitation of near-infrared light (980 nm and 1550 nm) and ultraviolet light (322–378 nm). Under the excitation of ultraviolet light, the sample can exhibit the characteristic broadband blue emission (Bi3+ ions) and green emission (Er3+ ions). When excited with near-infrared light, the sample has only typical green and orange up-conversion emission bands. The green and orange luminescence could be achieved by adjusting the excitation wavelength. In addition, the sample can present multicolor luminescence with the change of pump power and temperature. At the same time, the temperature measurement performance of the phosphor was explored by using the fluorescence intensity ratio technique based on the Er3+ ion thermal coupling energy level (2H 11/2 /4S 3/2) and non-thermal coupling energy level (2H 11/2 /4F 9/2). The maximum temperature sensitivity reached 1.23 %K−1 and 0.99 %K−1, respectively. Therefore, La 2 MgGeO 6 : Bi3+, Er3+ samples could be candidates for multicolor anti-counterfeiting and temperature sensors material. • La 2 MgGeO 6 : Bi3+, Er3+ phosphors are used as a dual-mode temperature sensor to discuss the TCEL and NTCEL. • The phosphor can not only be used in optical temperature measurement, but also can achieve anti-counterfeit encryption. • Polychromatic luminescence can be realized by changing excitation wavelength, temperature and other conditions. • Using FIR technology to explore the temperature sensing performance, the phosphor is highly sensitive to temperature. [ABSTRACT FROM AUTHOR]

Trivalent lanthanide ions are widely used for the realization of scintillation, while the narrow transition lines do not benefit the overall integral intensity. In this work, Mn2+ doped LiLuF 4 NPs are employed to realize strong broad emission for the first time. Upon X-ray irradiation, the strong broad emission from 500 to 700 nm corresponding to the Mn2+: 4T 1 →6A 1 transition is observed. Through incorporating Ce3+ and Gd3+ ions, the X-ray excited optical luminescence (XEOL) intensity is greatly improved owing to the introduce of energy transfer pathways of Gd3+→Mn2+ and Ce3+→Gd3+→Mn2+. After coating a LiLuF 4 shell, both the XEOL intensity and X-ray irradiation stability are improved. Our results may promote the exploration of new kinds of scintillators with broad band emissions. • Mn: LiLuF 4 NPs are employed to realize strong broad emission for the first time. • Gd3+ ions are used to improve the XEOL intensity via Gd3+.→Mn2+ energy transfer. • Ce3+ ions are used to improve the XEOL intensity via Ce3+.→Gd3+→Mn2+ energy transfer. • A LiLuF 4 shell is used to improve both the XEOL intensity and X-ray irradiation stability. [ABSTRACT FROM AUTHOR]

A novel NIR emitting scintillator with 825 nm was developed by doping Sm2+ in Cs 4 Eu(Br,I) 6 crystal. The single crystals of Cs 4 Eu(Br,I) 6 :Sm were successfully grown by the Bridgman method. The crystal structure and valence state was approved by XRD and XPS methods. The luminescence properties and energy transfer were systematically investigated. The energy transfer mechanism is variable for different Sm2+ concentration. The PL decay profiles show that the Sm2+-related emission has fast decay of nanosecond. The proportion of fast decay can be tunable by adjusting Sm2+ doped concentration. The Sm2+ doped europium -host material will have a potential application for unclear detection as near-infrared (NIR) scintillators. • The novel NIR emitting Cs 4 Eu(Br,I) 6 :Sm scintillation crystals were successfully grown by the Bridgman method and the luminescence properties is tunable. • The proportion of nonradiative energy transfer from Eu2+ to Sm2+ was improved and the PLQY of Sm2+-related is up to 42.1%. • The fast decay time component of Sm2+ (50 ns) is up to 31.8% for Cs 4 Eu(Br,I) 6 : 3 mol%Sm crystal. • The proposed Sm2+ doped europium -host material principle is an effective method to develop near-infrared (NIR) scintillators for nuclear radiation detection. [ABSTRACT FROM AUTHOR]

Using a high-temperature solid-phase method, a series of La 2 MgGeO 6 : Bi3+, Eu3+ samples with different doping amounts of Bi3+ and Eu3+ were obtained. The crystal structure, morphology, luminescence characteristics, temperature-varying luminescence spectrum, fluorescence attenuation curve, and energy transfer mechanism of the samples were explored. In La 2 MgGeO 6 : Bi3+, Eu3+ phosphors, Bi3+ and Eu3+ ions occupy the La3+ ion position. Under ultraviolet (UV) excitation, the emission spectra of LMGO: Bi3+ and the excitation spectra of LMGO: Eu3+ have significant spectral overlap, indicating that there is energy transfer between Bi3+ and Eu3+. By adjusting the doping amounts of Eu3+, adjustable luminescence can be obtained in the co-doped samples. According to the varying temperature-dependence trends of Bi3+ and Eu3+ ions, fluorescence intensity ratio technology was used to explore the temperature-sensing characteristics of Bi3+ and Eu3+ ions. The maximum absolute sensitivity and relative sensitivity were 0.074%·K−1 and 2.389%·K−1, respectively. In addition, by monitoring the lifetime decay time of Bi3+ with temperature, the maximum temperature sensitivity of the La 2 MgGeO 6 : Bi3+ samples was 4.09%·K−1. The above results indicate that La 2 MgGeO 6 : Bi3+, Eu3+ samples can be used as potential luminescent materials for temperature detection. • La 2 MgGeO 6 : Bi3+, Eu3+ is explored to be a very promising optical thermometric materials. • The LMGO: Bi3+, Eu3+ shows high signal discriminability in the blue and red regions. • The LMGO: Bi3+, Eu3+ phosphors can circumvent the drawbacks of TCL-based phosphors. • The fluorescence intensity ratio and decay life of the material are highly sensitive to temperature. • The thermal-quenching mechanism of Bi3+ and Eu3+ were discussed. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphors converted to light-emitting diodes (pc-LED) sources have extensive application prospects in medical imaging, foodstuff analysis and plant growth fields. However, there are some shortcomings in NIR phosphors, such as narrow emission band and poor thermal stability. Here a new wide band NIR luminescent phosphor Cr3+-doped Sr 3 Sc 4 O 9 (SSO) is introduced. The emission spectrum ranges from 600 nm to 1000 nm, with a peak value of 761 nm and the value of full width at half maximum (FWHM) is 120 nm. The internal quantum efficiency (IQE) of sample is about 87% according to the fitting result. The most appropriate doping concentration is x = 0.02 and the best excitation wavelength is 468 nm, which matches the commercial blue chip. At the same time, the phosphor shows good thermal stability in variable temperature spectrum test, and can maintain 70.4% emission intensity at 373 K relative to room temperature. To better understand its practical applications, packaged pc-LED is designed to show good NIR light penetration in spectral penetration tests. This study provides an excellent choice of NIR phosphors. • Sr 3 Sc 4 O 9 :Cr3+ phosphors are promising near-infrared (NIR) emission materials. • The phosphors retain 70.4% of initial emission intensity at 373 K. • The IQE of sample is about 87%. • The pc-LED device can be applied in NIR penetration analysis. [ABSTRACT FROM AUTHOR]

Near-infrared II (NIR-II, 1000–1700 nm) fluorescent probes have received extensive attention in the field of biomedicine due to their deep tissue penetration, high spatial resolution and superior signal-to-noise ratio. In this work, the Ce3+ ions with high concentration were doped into both the core and shell layer of the NaErF 4 @NaYF 4 NCs. Compared to the NaErF 4 @NaYF 4 NCs, the NIR-II emission intensities of the NaErF 4 :20Ce@NaYF 4 :20Ce core@shell NCs increases about 5.1 times under 808 nm excitation. We verify that doping part of Ce3+ ions in the shell could not only preserve the high concentration of Er3+ ions in the core, but also facilitate the nonradiative relaxations of 4I 11/2 → 4I 13/2 followed by the enhanced NIR-II emission intensity. The emission light could be clearly observed even at the depth of 6 mm, which show promising application in deep tissue imaging. • Uniform NaErF 4 :Ce@NaYF 4 :Ce active-core@active-shell NCs was prepared. • The NIR-II luminescence intensity was significantly improved by Ce3+ ions doping. • The emission light was clearly observed at the depth of 6 mm. [ABSTRACT FROM AUTHOR]

Abstract: A new coordination polymer, namely [Zn(Hnbdc)2(bpe)]n (1) (H2nbdc=3-nitrobenzene-1,2-dicarboxylic acid and bpe=1,2-bi(4-pyridyl)ethylene), has been hydrothermally synthesized and characterized preliminarily by elemental analysis, infrared spectroscopy, thermal analysis, and X-ray diffractions. Single crystal X-ray diffraction showed that compound 1 possesses a ladder-like topology structure featuring carboxyl-bridged dinuclear Zn(II) spaced by parallel bpe coligand pairs and has the capacity of undergoing a 100% photochemical [2+2] cycloaddition reaction to transform into compound [Zn(Hnbdc)2(rctt-tpcb)]n (2) in a single-crystal to single-crystal form. In addition, the fluorescent property of 1 was also investigated. [Copyright &y& Elsevier]

A series of Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ (x = 0, 0.5, 1, 1.5, 2) phosphors were synthesized on the basis of high temperature solid-state reaction strategy. Its phase composition, optical spectral properties, fluorescence lifetime and temperature sensitivity were investigated in detail. Under excitation at 342 nm, the emission spectra of Ca 2 MgSi 2 O 7 : Ce3+, Eu2+ exhibit a purple emission band (Ce3+ ions) and a green emission band (Eu2+ ions). The emission band of Ce3+ overlaps with the excitation band of Eu2+, indicating that there may be energy transfer (ET) between the two ions. The decreasing fluorescence lifetime of Ce3+ with increasing Eu2+ concentration further proves the existent of ET process in Ca 2 MgSi 2 O 7 : Ce3+, Eu2+ phosphor. In addition, Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ solid solution was designed and synthesized by Sr2+ substituting Ca2+. As Sr2+ gradually replaced Ca2+, the blue-shift of Ce3+ and Eu2+emission band were caused by the change of crystal field. With the increase of temperature, the fluorescence intensity of Ce3+ and Eu2+ emission bands decreased slowly and rapidly, respectively. Hence, in the Ce3+/Eu2+ co-activated Ca 2- x Sr x MgSi 2 O 7 phosphor, Ce3+ ions and Eu2+ ions can be used as fluorescence intensity ratio (FIR) signals. The maximum relative sensitivity can reach 2.43% K−1 (at 293 K) under 342 nm excitation. The above results indicate that Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ phosphors are potential candidates for optical thermometer materials. • The Ca 2- x Sr x MgSi 2 O 7 : Ce3+, Eu2+ (x = 0, 0.5, 1, 1.5, 2) phosphors are promising optical thermometric materials. • The emission peaks of Ce3+ and Eu2+ blue-shift due to the change of crystal field caused by Sr2+ replacing Ca2+. • FIR based on dual luminescence center can overcome the disadvantage of fluorescence intensity ratio based on TCL. • The thermal-quenching mechanism of Ce3+ and Eu2+ were discussed. [ABSTRACT FROM AUTHOR]

Abstract: A novel Cd(II)/4-pya coordination polymer {[Cd(μ-Cl)(4-pya)(H2O)]2 ·4H2O}∞ (1) (4-pya= trans-4-pyridylacrylate) was synthesized and structurally characterized. Single-crystal X-ray diffraction revealed that 1 consists of a 2D (4,4) network constructed from the 4-pya bridging ligand and the dimeric [Cd(μ-Cl)]2 cores, in which each six-coordinated Cd(II) ion adopts an octahedral coordination geometry. Each 2D layer is further stacked along the a axis through hydrogen bonding interactions to afford a 3D hydrogen-bound network. An infinite water chain is generated via hydrogen bonds into each resulting 1D channel. The luminescent properties of 1 in the solid state were investigated. [Copyright &y& Elsevier]