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Luminescence lifetime-based sensing is ideally suited to monitor biological systems due to its minimal invasiveness and remote working principle. Yet, its applicability is limited in conditions of low signal-to-noise ratio (SNR) induced by, e.g., short exposure times and presence of opaque tissues. Herein this limitation is overcome by applying a U-shaped convolutional neural network (U-NET) to improve luminescence lifetime estimation under conditions of extremely low SNR. Specifically, the prowess of the U-NET is showcased in the context of luminescence lifetime thermometry, achieving more precise thermal readouts using Ag 2 S nanothermometers. Compared to traditional analysis methods of decay curve fitting and integration, the U-NET can extract average lifetimes more precisely and consistently regardless of the SNR value. The improvement achieved in the sensing performance using the U-NET is demonstrated with two experiments characterized by extreme measurement conditions: thermal monitoring of free-falling droplets, and monitoring of thermal transients in suspended droplets through an opaque medium. These results broaden the applicability of luminescence lifetime-based sensing in fields including in vivo experimentation and microfluidics, while, hopefully, spurring further research on the implementation of machine learning (ML) in luminescence sensing., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Recently, the growing demand for temperature detection is pushing forward the flourishing development of noncontact optical thermometry. Herein, a new red phosphor Sr 2 InTa 1- x O 6 : x Mn 4+ (SIT: x Mn 4+ ) was first constructed and systematically investigated. Based on the fairly rapid decline of the lifetime from 0.403 to 0.008 ms by increasing the temperature from 25 to 450 K, a noncontact optical thermometer can be made from phosphor SIT:0.003Mn 4+ with S r = 1.396% K -1 at 375 K and S at 300 K. Because the luminescence is based on the outermost 3d orbits of Mn a = 0.0012 K -1 at 300 K. Because the luminescence is based on the outermost 3d orbits of Mn 4+ , the lifetime of SIT: x Mn 4+ is quite sensitive to the temperature, leading to a rapid decline of the lifetime with the increase in temperature. Moreover, multiple rounds of variable-temperature studies were performed to demonstrate the stability and reversibility of SIT:0.003Mn 4+ . This work suggests that Mn 4+ -phosphors are promising candidates for application as optical thermometric material.

Phosphors with rare earth (RE) ions are widely applied to optical temperature measurements. Moreover, the near-infrared (NIR) emission of phosphors has potential applications in the biological field. Herein, Gd 2 O 3 : x %Nd 3+ /Yb 3+ (0.2 ≤ x ≤ 0.8) samples are successfully synthesized by the sol-gel method, and their phase and morphology are characterized. The XRD data are refined by Rietveld. Under 980 nm continuous wave (CW) laser excitation, the upconversion (UC) and downshift (DS) emissions are studied. The temperature sensing performances of thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs) of Gd 2 O 3 : Nd 3+ /Yb 3+ phosphors are investigated through the fluorescence intensity ratio (FIR) technology. In the temperature range of 303-523 K, the maximum relative sensitivity of I 761 nm / I 550 nm reaches 6.54% K -1 , which is based on non-TCLs. At the same time, the maximum relative sensitivity of I 761 nm / I 1000 nm-1500 nm reaches 3.13%. In addition, the influence of the laser induced heating (LIH) effect is studied. Compared with square wave (SW) pumping, the relative sensitivity would decrease at CW excitation. Finally, the durability and temperature uncertainty are also discussed. The results prove that the Gd 2 O 3 :Nd 3+ /Yb 3+ samples present higher relative sensitivity and durability and lower temperature uncertainty in the biological window. Therefore, the phosphors can be used as optical thermometers in the biological field.

Proteins are involved in numerous cellular activities such as transport and catalysis. Misfolding during biosynthesis and malfunctioning as a molecular machine may lead to physiological disorders and metabolic problems. Protein folding and mechanical work may be viewed as thermodynamic energetically favorable processes in which stochastic nonequilibrium intermediate states may be present with conditions such as thermal fluctuations. In my opinion, measuring those thermal fluctuations may be a way to access the energy exchange between the protein and the physiological environment and to better understand how those nonequilibrium states may influence the misfolding/folding process and the efficiency of the molecular engine cycle. Here, I discuss luminescence thermometry as a possible way to measure those temperature fluctuations from a single-molecule experimental perspective with its current technical limitations and challenges., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Luminescence nanothermometry enables accurate, remote, and all-optically-based thermal sensing. Notwithstanding its fast development, there are serious obstacles hindering reproducibility and reliable quantitative assessment of nanothermometers, which impede the intentional design, optimization and use of these sensors. These issues include ambiguities or absence of established universal rules for quantitative evaluation, incorrect assumptions about the mechanisms behind the thermal response of the sensors as well as the dependence of the nanothermometers readout on external conditions and host materials themselves. In this perspective article, we discuss these problems and propose a series of standardization guidelines to be followed. This critical discourse constitutes the first required step towards the ubiquitous acceptance, by the scientific community, of luminescence thermometry as a reliable tool for remote temperature determination in numerous practical biomedical implementations.

In this paper, a microthermograph, temperature mapping with high spatial resolution, was established using luminescent molecules embedded ultrathin polymeric films (nanosheets), and demonstrated in a living small animal to map out and visualize temperature shift due to animal's muscular activity. Herein, we report super flexible and self-adhesive (no need of glue) nanothermosensor consisting of stacked two different polymeric nanosheets with thermosensitive (Eu-tris (dinaphthoylmethane)-bis-trioctylphosphine oxide: EuDT) and insensitive (Rhodamine 800) dyes being embedded. Such stacked nanosheets allow for the ratiometric thermometry, with which the undesired luminescence intensity shift due to focal drift or animal's z-axis displacement is eliminated and the desired intensity shift solely due to the temperature shift of the sample (living muscle) can be acquired. With the stacked luminescent nanosheets, we achieved the first-ever demonstration of video filming of chronologically changing temperature-shift distribution from the rest state to the active state of the muscles in the living animal. The polymer nanosheet engineering and in vivo microthermography presented in the paper are promising technologies to microscopically explore the heat production and heat transfer in living cells, tissues, and organisms with high spatial resolution beyond what existing thermometric technologies such as infrared thermography have ever achieved.

The Er3+/Yb3+ co‐doped tellurite glasses and glass‐ceramics (GCs) containing the Gd2Te6O15 phase were successfully fabricated via the conventional melting‐quenching technique followed by a crystallization regime. The Er3+/Yb3+ co‐doped tellurite glasses generated intense up‐conversion green (524 and 546 nm) and red (658 nm) emissions when stimulated by a 980 nm laser. The up‐conversion green emission intensity increased by 68 and 46 times with the increase of the Yb3+/Er3+ ratio, and the optimal Yb3+/Er3+ ratio was found to be 8:1. The surface crystallization process of the Gd2Te6O15 GCs was confirmed through analysis of crystallization kinetics and microscopic morphology. The up‐conversion luminescence and lifetime of Er3+ ions were enhanced by the precipitation of low‐phonon‐energy Gd2Te6O15 crystals. The GC sample crystallized at 480°C for 4 h showed the highest luminescence intensity. The optical thermometry properties of Er3+ ions at thermally coupled energy levels (2H11/2/4S3/2→4I15/2) were explored. The Gd2Te6O15 GCs co‐doped with 0.25 mol% Er2O3 and 2.0 mol% Yb2O3 exhibited an excellent temperature relative sensitivity (Sr) of 1.22% K−1 at 293 K and a great repeatability of 98.07%. These results suggest that the Er3+/Yb3+ co‐doped Gd2Te6O15 GCs show promise for optical thermometry. [ABSTRACT FROM AUTHOR]

Excitation wavelength controllable lanthanide upconversion allows for real-time manipulation of luminescent color in a composition-fixed material, which has been proven to be conducive to a variety of applications, such as optical anti-counterfeiting and information security. However, current available materials highly rely on the elaborate core–shell structure in order to ensure efficient excitation-dependent energy transfer routes. Herein, multicolor upconversion luminescence in response to both near-infrared I and near-infrared II (NIR-I and NIR-II) excitations is realized in a novel but simple NaYGeO4:Yb3+/Er3+ phosphor. The remarkably enhanced red emission ratio under 1532 nm excitation, compared with that under 980 nm excitation, could be attributed to the Yb3+-mediated cross-relaxation energy transfers. Moreover, multi-wavelength excitable temperature-dependent (295–823 K) upconversion luminescence realizes a ratiometric thermometry relying on the thermally coupled levels (TCLs) of Er3+. Detailed investigations demonstrate that changing excitation wavelength makes little difference for the performances of TCL-based ratiometric thermometry of NaYGeO4:Yb3+/Er3+. These findings gain more insights to manipulate cross-relaxations for excitation controllable upconversion in single activator doped materials and benefit the cognition of the effect of excitation wavelength on ratiometric luminescence thermometry. [ABSTRACT FROM AUTHOR]

The development of ultrasensitive thermometric phosphors has become an active area of research due to their appealing applications in the contactless temperature detection field. Herein, the scheelite-related compounds—CaGd 2 (WO 4) 4 : Nd3+, Yb3+ and CaGd 2 (MoO 4) 4 : Nd3+, Yb3+, which exhibit high sensing capacity—are successfully prepared and systematically characterized. The X-ray diffraction analysis reveals that CaGd 2 (WO 4) 4 : Nd3+, Yb3+ exhibits the monoclinic structure, whereas CaGd 2 (MoO 4) 4 : Nd3+, Yb3+ is in the tetragonal phase. The maximum phonon cut-off energy of CaGd 2 (WO 4) 4 : Nd3+, Yb3+ is 929 cm−1, slightly larger than that of CaGd 2 (MoO 4) 4 : Nd3+, Yb3+ (904 cm−1). Irradiated by 980 nm laser, PL spectra consist of the Nd3+: 4F j → 4I 9/2 (j = 7/2, 5/2, 3/2) and Yb3+: 2F 5/2 → 2F 7/2 emissions located in the near-infrared (NIR) range. Negative and positive thermal quenching behaviors are observed for the emissions of Nd3+ (754, 802, and 868 nm) and Yb3+ (1008 nm), respectively, attributed to the cooperative effects of the phonon-assisted energy transfer process of Yb3+ → Nd3+ and excited state absorption process of Nd3+. Moreover, the host material can affect the luminescence properties, thermal enhancement factor of the NIR anti-Stokes emission, and thermal sensing performance of the Nd3+-Yb3+ pair. Consequently, CaGd 2 (MoO 4) 4 : Nd3+, Yb3+ exhibits higher sensing sensitivity (S r-max = ∼6.00%K−1) than CaGd 2 (WO 4) 4 : Nd3+, Yb3+ (S r-max = ∼5.56%K−1). This study provides useful information for the construction of high-performance ratiometric thermometers based on the inverse thermal dependence of the NIR emissions of Nd3+ and Yb3+ ions. [ABSTRACT FROM AUTHOR]

Ratiometric thermometry is among the emerging applications in phosphor materials. Particularly, the technique of ultrafine-space thermometry has garnered significant attention in bio-imaging. Near-infrared (NIR) light, with its high tissue permeability, serves not only as an excitation source for up-conversion photoluminescence (UCPL) but also induces down-shifting photoluminescence (DSPL) at longer wavelengths. These luminescence mechanisms offer promising avenues for bio-available thermometry. In this study, we focused on highly bio-adaptable yttria-stabilized zirconia (YSZ), Zr0.85Y0.15O1.925, and prepared phosphor materials with yttrium partially substituted by ytterbium (Yb), erbium (Er), and thulium (Tm) using a hydrothermal reaction method. The synthesized YSZ:Yb–Er/Tm phosphors with different Yb3+ contents showed multi-line UCPL in the visible to NIR region due to Er3+ and Tm3+ ions under the laser irradiation at 980 nm; in particular, it showed strong UCPL at 800 nm originating from Tm3+. Furthermore, under the same excitation conditions, the phosphor exhibited not only UCPL but also DSPL due to 4I13/2 → 4I15/2 transition of Er3+ in the deeper NIR region of 1400–1700 nm. Interestingly, these DSPLs exhibit significant PL enhancement (anti-thermal quenching; anti-TQ) with increasing temperature. The thermometric properties based on the luminescence intensity ratio (LIR) of UCPL, which shows normal thermal quenching, and DSPL, which shows anti-thermal quenching, demonstrated excellent temperature sensitivity (Sr > 3% K−1 @ 283 K) and temperature resolution (δT < 0.1 K @ 283 K). This study suggests that the LIR thermometry technique using UCPL/DSPL, specifically anti-TQ/normal-TQ, can contribute to further advancements in luminescence-based temperature measurement. [ABSTRACT FROM AUTHOR]

Phosphors with multifunctional applications have attracted extensive research, especially in thermometer and anti‐counterfeiting fields. Herein, a series of Pr3+‐doped YNbO4 (YNO) phosphors with adjustable photoluminescence and red persistent luminescence (PersL) performances are developed. YNO host exhibits the blue self‐activated luminescence, and the different Pr3+ emission peaks possess various thermal stability properties due to the thermal quenching channel generated by the intervalence charge transfer state between Pr3+ and Nb5+ ions. Two kinds of fluorescence intensity ratio models with high absolute and relative sensitivities are realized to measure the temperature under dual‐wavelength excitation. Moreover, YNO:Pr3+ exhibits the red PersL with a duration of about 120 s upon ceasing the UV excitation light source. The fabricated YNO:Pr3+‐polydimethylsiloxane films display different luminescence patterns with the passage of time after turning off UV light, which can cleverly achieve dynamic conversion. These results demonstrate that YNO:Pr3+ phosphor has potential applications in dual‐wavelength excited thermometry and dynamic anti‐counterfeiting fields. [ABSTRACT FROM AUTHOR]

The high spatial resolution and contactless optical readout capabilities of luminescence thermometry offer significant advantages in numerous fields, including biomedicine, space exploration and optoelectronics. In addition, robust, reproducible, and accurate temperature measurements are essential in these areas. The ultra‐wide band gap semiconductor material Ga2O3 is a suitable host for optical sensing in harsh environments due to its high stability. In this work, the thermometric operation of Ga2O3:Cr‐based microcavities are evaluated. They are designed as follows: Ga2O3:Cr microwires are encapsulated in multilayers fabricated by atomic layer deposition (ALD), which act as both Bragg reflectors and protective layers for the thermometric sensor. Prior to the ALD encapsulation step, focused ion beam carved trenches at the microwire ends are necessary to accommodate the multilayer coating. The structural and optical properties of the devices are assessed experimentally, analytically and by simulations. The developed microthermometers can be easily calibrated using a cubic polynomial for the temperature‐dependent resonant peak position shift. A better than 0.5 °C temperature resolution and accuracy for temperatures above −80 °C is demonstrated. Additionally, the devices show robustness against excitation laser densities of at least 34 W mm−2, can operate at temperatures up to 600 °C and remain functional in liquids. [ABSTRACT FROM AUTHOR]

Real-time monitoring of temperature changes in substation equipment is crucial for preventing failures and ensuring a stable power supply. Currently, temperature monitoring of substation equipment primarily relies on manual infrared thermometry, which has limitations such as strong operational dependence, susceptibility to interference, and difficulty in detecting internal faults. The luminous intensity ratio (LIR) is a stable optical parameter unaffected by factors such as spectral loss and environmental influences, making it suitable for temperature detection. The multi-emission characteristics of rare-earth-doped upconversion (UC) materials are highly compatible with LIR technology, demonstrating their potential in high-precision temperature monitoring. Here we introduces a non-contact temperature monitoring method for substation equipment based on NaErF4@ NaYF4 core-shell UC materials and LIR technique. Experiments show that the method has high accuracy and sensitivity within temperature range of 25 °C to 225 °C, with a sensitivity as high as 35 x 10-3 °C-1, effectively monitoring temperature changes both inside and outside the equipment. This provides a new technical solution for temperature monitoring of substation equipment. [ABSTRACT FROM AUTHOR]

Yb3+/Er3+-doped Bi2(MoO4)3−z(WO4)z phosphors were synthesized via a hydrothermal method combined with subsequent calcination. Under the excitation of a light source of 980 nm, Bi2(MoO4)3:Yb3+/Er3+ phosphors exhibited strong upconversion green light and weak red light emissions. By doping WO42− in Bi2(MoO4)3:Yb3+/Er3+ phosphors, the upconversion luminescence intensity of the phosphors significantly enhanced, which is 42 times higher than that of the undoped WO42− phosphor. With an increase in WO42− doping content, the final color coordinates of Bi2(MoO4)3−z(WO4)z:Yb3+/Er3+ phosphors were (0.2352, 0.7274), which is closer to the standard green CIE coordinates. The maximum CP of WO42−-doped phosphors is as high as 116.68%, which is 74.44% higher than that of the undoped WO42− phosphor. Based on the thermally coupled energy levels (TCLs) of Er3+ (2H11/2/4S3/2 → 4I15/2) in Bi2(MoO4)2.7(WO4)0.3:14%Yb3+,3%Er3+ phosphor, the SR value reached a maximum of 0.0081 K−1 at 323 K and the SA value reached a maximum of 0.0099 K−1 at 398 K. The obtained Bi2(MoO4)3−z(WO4)z:Yb3+/Er3+ phosphors are suitable for upconversion luminescent materials for green displays and have potential advantages in optical temperature measurement. [ABSTRACT FROM AUTHOR]

Temperature‐responsive dynamics of excited‐state population in terbium (Tb) ions may open the door for the advancement of high‐performance photothermal feedback windows. However, obtaining robust luminescence and superior transparency in Tb‐doped ceramics continues to pose a formidable challenge, leaving them far away from photonic application. Here, to fill this important gap, the demonstration of Tb doped transparent ceramics for luminescent thermometric windows is reported. Y2Zr2O7:Tb (YZO:Tb) ceramics are used as an illustrative example. After a sequence of thermal treatments, the defect centers F/F+ and defect clusters [TbY4+−O2−−TbY4+$Tb_{\mathrm{Y}}^{{{4}^ + }} - {{O}^{2 - }} - Tb_{\mathrm{Y}}^{{{4}^ + }}$] and [TbY4+−e•$Tb_{\mathrm{Y}}^{{{4}^ + }} - {{e}^ \bullet }$] in these YZO:Tb transparent ceramics are eliminated, resulting in a notable enhancement of their in‐line transmittance from 71% to 76%, making it close to the theoretical limit. Moreover, the corresponding photoluminescence increased significantly, reaching a factor of 296 times. Furthermore, a temperature feedback window is designed using the excitation intensity ratio (EIR) or single‐band luminescence intensity ratio (SBLIR) mode, which presents high sensitivity (1.04%) and high repeatability (98%). This work not only provides a paradigm in the application of the Tb doped transparent ceramics for temperature sensing windows, but also suggests a pathway to build efficient thermometers based on excited state population deployment in window systems. [ABSTRACT FROM AUTHOR]

The SC‐YAG:Tb@YAG:Pr‐SCF composite epitaxial structure consisting of a 1 mm thick single crystal substrate of YAG:Tb garnet and a thin (9 µm) single crystalline film of YAG:Pr garnet is fabricated, and its luminescent properties are examined toward luminescence thermometry. The possibility to efficiently excite, individually or simultaneously, the Tb3+ and Pr3+ dopants by their intense allowed 4f→5d transitions is executed to reach relative thermal sensitivity higher than 1% K−1 over the range of temperatures as wide as 100–625 K and above 0.5% K−1 over 13–650 K. The obtained results demonstrate that using intra‐ and inter‐configurational emission transitions of Pr3+ and other lanthanides makes it possible to design wide‐range luminescence thermometers with high sensitivity spanning the entire operating limits. [ABSTRACT FROM AUTHOR]

In this work, we report on the synthesis and investigation of new hybrid multifunctional iron oxide nanoparticles (IONPs) coated by coumarin-bound copolymer, which combine magneto- or photothermal heating with luminescent thermometry. A series of amphiphilic block copolymers, including Coum-C11-PPhOx27-PMOx59 and Coum-C11-PButOx8-PMOx42 bearing luminescent and photodimerizable coumarin moiety, as well as coumarin-free PPhOx27-PMOx57, were evaluated for their utility as luminescent thermometers and for encapsulating spherical 26 nm IONPs. The obtained IONP@Coum-C11-PPhOx27-PMOx59 nano-objects are perfectly dispersible in water and able to provide macroscopic heating remotely triggered by an alternating current magnetic field (AMF) with a specific absorption rate (SAR) value of 240 W.g−1 or laser irradiation with a photothermal conversion efficiency of η = 68%. On the other hand, they exhibit temperature-dependent emission of coumarin offering the function of luminescent thermometer, which operates in the visible region between 20 °C and 60 °C in water displaying a maximal relative thermal sensitivity (Sr) of 1.53%·°C−1 at 60 °C. [ABSTRACT FROM AUTHOR]

The Sm3+-doped Y 2 MgTiO 6 phosphor was successfully synthesized by high-temperature solid-phase method. X-ray diffraction, photoelectron spectroscopy and scanning electron microscopy characterized the phase, electronic structure and morphology. Meanwhile, the luminescence properties were analyzed, and the results showed that the Y 2 MgTiO 6 :Sm3+ phosphors emit vibrant orange light when excited at 407 nm, with emission peaks at 565 nm, 603 nm, and 649 nm. The luminescence efficiency of the sample reaches 79.71% of the initial intensity at 423 K. The temperature sensing properties of Y 2 MgTiO 6 :Sm3+ phosphors were investigated between different wavelength bands based on the fluorescence intensity ratio (FIR) technique, where FIR (I 565 /I 649) had the maximum relative sensitivity of 0.26% K−1 at 298K. The quantum yield of the sample was 59.88%, with calculated Correlated Color Temperature of 1646 K. The research results suggest that Y 2 MgTiO 6 :Sm3+ phosphors have potential applications in optical temperature sensing and w-LEDs devices. [ABSTRACT FROM AUTHOR]

Rare-earth (RE) doped aluminum nitride (AlN) holds great promise for integrated optoelectronic devices. Here, the Ho and Yb co-doped AlN (AlN:Ho3+/Yb3+) submicron towers were prepared by a direct nitridation route. XRD, Raman, XPS and EDS studies showed successful doping of Ho and Yb ions into AlN. SEM images show that the submicron towers have an interesting layered structure by layer-by-layer stacking of hexagonal AlN nanosheets. Under excitation at 980 nm, AlN:Ho3+/Yb3+ submicron towers exhibit up-conversion (UC) luminescence at 540, 550, 659, and 762 nm, which are due to Ho3+/Yb3+ system from 5F 4 , 5S 2 →5I 8 , 5F 5 →5I 8 , and 5F 4 , 5S 2 →5I 7 respectively. Based on the intensity ratio and decay lifetime of UC luminescence, the optical temperature sensing characteristics are investigated from 298 K to 548 K. The maximum relative sensitivities associated with the intensity ratio of I 540, 550 and I 659 and decay lifetime of 659 nm are as high as 2.73% K−1 and 0.43% K−1, respectively. This work broadens the optoelectronic properties of RE doped AlN. [ABSTRACT FROM AUTHOR]

Germanate tellurite glasses doped with Eu3+ and Tb3+ were synthesized by the conventional melt-quenching method. There is no indication of the energy transfer between dopant ions in this host, but the co-dopants exhibit excellent color purity of 100% for Eu3+ and 80% for Tb3+. The co-doped glass exhibits yellow luminescence. The quantum yield of the Eu3+ emission is equal to 23% under 395 nm excitation. The thermal quenching of Eu3+ and Tb3+ luminescence occurs at different temperature ranges, which enables the thermal sensing properties of the material. The relative fluorescence intensity ratio (FIR) sensitivity of 0.16% K−1 was recorded in the wide range of temperatures spanning from −193 °C up to 0 °C. The temperature dependence of the decay times was also studied. The lifetime-based temperature sensitivity was determined to be 0.95% K−1 at 250 °C for Tb3+5D3 level emission and 0.3% K−1 at 225 °C for Eu3+5D1 level emission. [ABSTRACT FROM AUTHOR]

Multifunctional materials with optical temperature sensing and anti-counterfeiting properties have vast application prospects in our daily life, but the development of them still faces huge challenges. Herein, a novel SrY 2 O 4 :Bi3+,Er3+ phosphor with multicolor luminescence was synthesized triumphantly. Stimulated by different ultraviolet (UV) lights, the sample exhibits blue or green emissions, while emits yellow up-conversion luminescence under 980 nm laser irradiation. Interestingly, abnormal thermal quenching and thermal stimulation enhanced persistent luminescence are realized in SrY 2 O 4 :Bi3+,Er3+. Benefiting from the distinct responses of Bi3+ and Er3+ luminescence to temperature, thermochromism is verified when excited by UV or 980 nm light. Furthermore, the color shift from yellow-green to dark yellow is seen as the 980 nm laser power density reduces or the distance between laser source and the sample increases. Based on the luxuriant luminescence properties, multimode optical temperature sensing and dynamic anti-counterfeiting are constructed. All findings indicate that the multicolor emissive SrY 2 O 4 :Bi3+,Er3+ material offers a fresh outline for the exploitation of multiple optical thermometry and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

A fast and simple method for the synthesis of solid solutions based on erbium-doped yttrium oxide (Y1–xErx)2O3 was developed. The crystal structures of the samples were determined by x-ray diffraction methods. The compounds exhibited greenish-yellow upconversion emission upon IR laser excitation (980 nm). An increase in the erbium concentration in (Y1–xErx)2O3 caused a color change and a growth in the intensity of the upconversion luminescence. The maximum upconversion luminescence intensity was observed for the oxide with x = 0.05. A two-photon excitation mechanism was determined based on the dependence of the emission line intensities associated with 2H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions on the pumping power. The absolute and relative sensitivities were calculated from the temperature dependences of the ratio of emission lines corresponding to transitions from thermally coupled excited 2H11/2 and 4S3/2 levels and showed the promise of the oxides as materials for noncontact temperature sensing. [ABSTRACT FROM AUTHOR]

Visible and near-infrared (NIR) upconversion luminescence (UCL) emissions originating from the BaY2F8: Yb3+, Tm3+ systems were investigated under a laser excitation at 980 nm. The BaY2F8:20 mol% Yb3+, x mol% Tm3+ and BaY2F8: y mol% Yb3+, 0.5 mol% Tm3+ phosphors showed prominent UCL at 800 and 810 nm. The optimized doping concentrations of Yb3+ and Tm3+ in the BaY2F8 host matrix were evaluated, their spectroscopic properties were determined, and studies on their temperature-dependent behaviour were carried out. The temperature-sensing properties were studied by generating the fluorescence intensity ratio (FIR) of the UCL peaks originating from the thermally-coupled energy levels of the Tm3+ ions. The Stark sublevels of 1G4 level of Tm3+ ions were utilized to estimate the temperature-sensing abilities of the phosphor. [ABSTRACT FROM AUTHOR]

Here, this study reports single-band red upconversion emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor by doping Mn2+. The optimum concentration of Mn2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ phosphor was 0.20. The intensity of red and green emissions is increased by 27.4 and 19.3 times, respectively. Compared with the samples without Mn2+ ions, the red-green integral strength ratio of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ sample was significantly increased by 28.4 times, reaching 110.9. The UCL mechanism was explored by analyzing the down-conversion luminescence spectra, absorption spectra, UCL spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Mn2+ co-doped β-Ba2ScAlO5. The enhancement of upconversion red light is achieved through energy transfer between defect bands and Er3+ ions, as well as energy transfer between Mn2+ ions and Er3+ ions. In addition, the Mn2+ doped β-Ba2ScAlO5: Yb3+/Er3+ red UCL phosphors have great potential for ambient temperature sensing in the 298–523 K temperature range. The maximum sensitivity of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ phosphor as a temperature sensor at 523 K is 0.0247 K−1. [ABSTRACT FROM AUTHOR]

We report the synthesis and single-crystal X-ray diffraction, magnetic, and luminescence measurements of a novel family of luminescent cage-like tetranuclear silsesquioxanes (PhSiO15)8(LnO15)4(O)(C5H8O2)6(EtOH)2(CH3CN)2-2CH3CN (where Ln = Tb, 1; Tb/Eu, 2; and Gd, 3), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds 1 and 2 exhibit characteristic Tb[sup 3+] and Tb[sup 3+]/Eu[sup 3+]-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound 3 is used to assess the energies of the triplet states of the acac ligand. For compound 1, theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the [sup 5]D4 Stark components, while the mixed Tb[sup 3+]/Eu[sup 3+] analog 2, with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb[sup 3+]-to-Eu[sup 3+] energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the [sup 5]D4^[sup 7]F5 (Tb[sup 3+]) and [sup 5]D0^[sup 7]F2 (Eu[sup 3+]) transitions in the range 11-373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound 2, operating in the range 11-373 K with a maximum relative sensitivity of 2.0% K[sup -1] at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications. [ABSTRACT FROM AUTHOR]

Lanthanide ion-doped up-conversion (UC) luminescent materials are highly coveted for their utility in diverse applications such as anti-counterfeiting, fluorescence labeling, and temperature sensing. Here, we attempt to adopt SrY2S4 as a novel host lattice for UC luminescence and high-sensitive optical thermometry under near-infrared irradiation. The results show that the single Er3+-doped SrY2S4 samples present their main emissions in green and red regions under 1550 and 980 nm excitations, which correspond to the H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The green to red intensity ratio increases with the Er3+ concentration under both 980 and 1550 nm excitations. The mechanisms of UC luminescence and energy transfer are further systematically investigated by UC spectra and fluorescence decay dynamics. Furthermore, the non-contact temperature sensing performance of the SrY2S4:10%Er3+ sample is explored via employing fluorescence intensity ratio (FIR) technology. At an excitation of 980 nm, the maximum absolute sensitivity (SA) reaches 7.5 × 10−3 K−1 at 480 K. By utilizing a much safer excitation laser of 1550 nm, the maximum SA achieves 8.4 × 10−3 K−1 at 450 K, with a high and stable SA of more than 7.9 × 10−3 K−1 over a broad temperature range of 360–570 K. The relative sensitivity is 1.06% and 1.01% K−1 under 980 and 1550 nm excitations, respectively. These results indicate that the ternary sulfide SrY2S4 can be adopted as a novel host to achieve promising UC luminescence and thermal sensing performance. [ABSTRACT FROM AUTHOR]

In response to the sensitivity limitation of ratiometric luminescence thermometers, herein we propose a novel temperature readout, which exploits two pairs of thermalized energy levels in trivalent lanthanide ion-activated phosphors, to provide significantly enhanced sensitivity. This method is called the luminescence intensity ratio squared (LIR2) method. It is a combination of the dual-excitation single emission band ratiometric (SBR) and conventional (Boltzmann) luminescence intensity ratio (LIR) techniques. The relative sensitivity of LIR2 is the sum of the sensitivities of each method, and its thermal dependence is predicted theoretically. We explain the LIR2 method in detail and identify the perspective of lanthanide-activated probes. The performance of the proposed approach was evaluated using YVO4:Eu3+ and YNbO4:Eu3+ powders and compared with those of the SBR and LIR techniques. The LIR2 method displayed significantly better thermometric performance than SBR and LIR over a wide temperature range (300–850 K). [ABSTRACT FROM AUTHOR]

Tm3+/Yb3+-codoped ZrScW2PO12 microparticles were prepared in order to solve the problems of the severe thermal quenching and unsatisfactory thermometric properties of most luminescent materials. The synthesized materials exhibit a rarely observed negative thermal expansion (NTE) effect, which was verified by in situ X-ray diffraction experiments, performed under high temperature conditions. Upon excitation with a 980 nm laser, bright blue upconversion (UC) emissions originating from Tm3+ were observed. Moreover, owing to the promoted energy transfer, cross-relaxation and non-radiative decay processes at high temperatures triggered by the NTE effect, the observed UC emissions arising from 1G4 and 3F2,3 levels show non-monotonic responses to temperature. By analysing the temperature-dependent luminescence intensity ratio of these UC emissions originating from the non-thermally coupled levels of Tm3+ (1G4 and 3F2,3), the thermometric properties of the prepared microparticles were investigated in detail. Interestingly, the maximum absolute and relative sensitivities of the synthesized compounds are 0.09 and 1.45% K−1, respectively, which are independent of Yb3+ content, but they can be manipulated by employing different sensing modes. Our results manifest that the exploitation of the NTE effect is an efficient way to control the UC luminescence features of rare earth ions and to realize high performance optical thermometry. [ABSTRACT FROM AUTHOR]

We report on the synthesis, photoluminescence optimization and thermometric properties of Sr3Al2O5Cl2:Eu2+ and SrAl2O4:Eu2+ phosphor powders. The photoluminescence of Sr2.9Al2O5Cl2:0.1Eu2+ phosphors exhibits a blue-shift with an increasing annealing temperature owing to a decrease in the crystal field strength of the host caused by evaporation of Cl from the material. The quenching of the blue band in favour of the red band observed in the luminescence spectra of Sr2.9Al2O5Cl2:0.1Eu2+ with an increased annealing temperature was explained using the mechanism of the Landau-Zener transitions. The quantum yield and the lifetime of the phosphors depend on the annealing temperature. Phosphor samples annealed at 850 °C, 1000 °C, 1200 °C and 1500 °C were found to be potential luminescence thermometers using the luminescence spectral method. For Sr3Al2O5Cl2:Eu2+ annealed at 1000 °C, the temperature-dependent dual-band intensity ratio demonstrated a high-temperature sensitivity of ∼1.47%/°C in the temperature range of 23 °C to 40 °C which is superior to other reported phosphors with a microsecond decay time, suggesting that the material has potential for sensitive thermometry applications at ambient temperatures. [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]

Luminescent materials that display quick spectral responses to thermal stimuli have attracted pervasive attention in sensing technologies. Herein, a programmable luminescence color switching in lanthanide‐doped LiYO2 under thermal stimuli, based on deliberate control of the monoclinic (β) to tetragonal (α) phase transition in the crystal lattice, is reported. Specifically, a lanthanide‐doping (Ln3+) approach to fine‐tune the phase‐transition temperature in a wide range from 294 to 359 K is developed. Accordingly, an array of Ln3+‐doped LiYO2 crystals that exhibit progressive phase transition, and thus sequential color switching at gradually increasing temperatures, is constructed. The tunable optical response to thermal stimuli is harnessed for colorimetric temperature indication and quantitative detection, demonstrating superior sensitivity and temperature resolution (Sr = 26.1% K−1, δT = 0.008 K). The advances in controlling the phase‐transition behavior of luminescent materials also offer exciting opportunities for high‐performance personalized health monitoring. [ABSTRACT FROM AUTHOR]

Luminescence thermometry has recently been gaining popularity in science and technology fields. However, most reported works have used the fluorescence intensity ratio (FIR) to obtain the temperature based on thermally coupled energy levels (TCLs), which have hindered the sensitivity of the technique and limited its applications. Here, NaYF4:Yb/Tm@NaYF4:Yb/Ho microcrystals were prepared using a hydrothermal method. Based on the non-thermally coupled energy levels (NTCLs) of the double luminescent ionic centers Tm3+ and Ho3+, the materials exhibited temperature-dependent luminescence in the range of 304 K to 574 K. The maximum sensitivities were found to be Sa = 0.135 K−1 at 574 K and Sr = 1.101% K−1 at 484 K based on red (Tm3+) and green (Ho3+) emission bands. This study has provided a promising new strategy to break the TCL restriction and has shown the material to have potential applications in luminescence thermometry. [ABSTRACT FROM AUTHOR]

We report the synthesis and single-crystal X-ray diffraction, magnetic, and luminescence measurements of a novel family of luminescent cage-like tetranuclear silsesquioxanes (PhSiO1.5)8(LnO1.5)4(O)(C5H8O2)6(EtOH)2(CH3CN)2⋅2CH3CN (where Ln = Tb, 1; Tb/Eu, 2; and Gd, 3), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds 1 and 2 exhibit characteristic Tb3+ and Tb3+/Eu3+-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound 3 is used to assess the energies of the triplet states of the acac ligand. For compound 1, theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the 5D4 Stark components, while the mixed Tb3+/Eu3+ analog 2, with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb3+-to-Eu3+ energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the 5D4→7F5 (Tb3+) and 5D0→7F2 (Eu3+) transitions in the range 11–373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound 2, operating in the range 11–373 K with a maximum relative sensitivity of 2.0% K−1 at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications.

Eu3+ doped-Oxyfluorophosphate glasses with a general composition 75 NaPO 3 - (25-x) CaO – x CaF 2 (with x ranging from 0 to 25 mol%) were prepared and their spectroscopic changes induced by the addition of fluorine and when applying a thermal treatment in order to grow crystals in the glasses were investigated. The addition of CaF 2 at the expense of CaO reduces Ω 2 and Ω 4 parameters indicating that the Eu3+ ions are located in less covalent and well separated sites in oxyfluorophosphate glasses. An increase in the CaF 2 content at the expense of CaO also leads to an increase in the absolute thermometric sensitivity from (4.2 × 10−4) K−1 to (17.6 × 10−4) K−1 at 523 K while decreasing the relative thermometric sensitivity from 3.0% to 1.4%. The heat treatment leads to the precipitation of crystals, the composition of crystal phase depends on the glass composition. For the glasses with x = 0 and 10, the thermal treatment increases Ω 6 while reducing Ω 4 , as a result of an enhanced stiffness and reduced covalency of dopant's environment due to the precipitation of various crystals. As Ω 2 remains unchanged, the Eu3+ are suspected to remain mainly in the amorphous part of the glass-ceramics in agreement with the lack of sharp peaks in the emission spectrum. For the glasses with x = 20 and 25, Ω 2 increases indicating a change in the site symmetry of Eu3+ resulting from the dopant entering the CaF 2 crystalline phase. Due to the changes in the Eu3+ sites in the heat treated glasses, the heat treatment of the glass increases the absolute thermal sensitivity, but reduces the relative thermal sensitivity. The oxyfluorophosphate glass-ceramic with x = 25 exhibits high absolute thermometric sensitivity compared to oxyfluorophosphate glass, but also comparatively low relative sensitivity of 0.5% K−1. [ABSTRACT FROM AUTHOR]

Ratiometric luminescence thermometry is a promising method for non-contact and non-invasive thermometry. Maintaining consistently high temperature sensitivity over a wide temperature range is still a challenge for many ratiometric luminescence thermometers. Here, we have developed a novel transparent germanate glass-ceramic containing NaY 3 F 10 :Yb3+/Tm3+/Er3+ nanocrystals. The crystalline content of which remained highly stable during a tunable heat treatment process. Compared with glass, the upconversion luminescence of the glass-ceramic, which originated from the thermally and non-thermally coupled energy levels of Tm3+ and Er3+, was significantly enhanced. Using the temperature-dependent fluorescence intensity ratios of selected upconversion emissions, a ratiometric thermometry scheme with high temperature sensitivity was constructed. The relative sensitivity maintained at a high level (1.30–2.61 %K−1) over the experimental temperature range (323–573 K). The best resolution and repeatability were ±0.13 K and 99.6%, respectively. This transparent glass-ceramic is an excellent candidate for ratiometric thermometry, which is expected to be applied to fibre-optic thermometers. [ABSTRACT FROM AUTHOR]

This study synthesized LaF3–LaOF:Yb3+/Ho3+via a solid-state reaction method and analyzed its optical properties and temperature sensitivity. Specifically, the crystalline structure of each sample—composed of LaOF (tetragonal) and LaF3 (hexagonal)—were analyzed under X-ray diffraction. In addition, their photoluminescence (PL) properties were analyzed, with peaks observed at 543, 654, and 755 nm. The highest PL intensity was observed at 543 nm for a molar ratio of La:Yb:Ho = 1:0.05:0.001. Furthermore, the temperature characteristics of each sample were analyzed to determine the absolute and relative sensitivities as 0.0232 K−1 and 0.357 %K−1, respectively. [ABSTRACT FROM AUTHOR]

Luminescence quenching at high dopant concentration and temperature typically limits the brightness of luminescence materials, which remains a major obstacle in diverse technological applications, especially in the field of luminescence thermometry. In this work, a unique class of non‐concentration quenching double‐tungstate phosphors is reported that feature the near‐unity quantum yield of Tb3+ and Eu3+ emissions induced by the structural confinement effect. Mechanistic studies affirm that the activator ions can be isolated in NaYW2O8 crystal to confine the absorbed photon energy, leading to a relatively high quenching concentration of various lanthanide activators. By facilitating interionic cross‐relaxation at heavy dopant concentration, a remarkable thermal enhancement of Tb3+ emissions over 20‐fold upon the excitation of excited‐state absorption is recorded. In contrast, thermally quenched emissions are detected under the excitation of ground‐state absorption. This excitation wavelength‐dependent thermal behavior of Tb3+ emissions is harnessed for single‐band ratiometric thermometry, registering superior thermal sensitivity and resolution (Sr = 4.01% K−1, δT = 0.1 K). The advances in combating concentration and thermal quenching of luminescence materials provide exciting opportunities for flexible thermometry in real‐world sensing scenarios. [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]

This study synthesized LaF3–LaOF:Yb3+/Ho3+via a solid-state reaction method and analyzed its optical properties and temperature sensitivity. Specifically, the crystalline structure of each sample—composed of LaOF (tetragonal) and LaF3 (hexagonal)—were analyzed under X-ray diffraction. In addition, their photoluminescence (PL) properties were analyzed, with peaks observed at 543, 654, and 755 nm. The highest PL intensity was observed at 543 nm for a molar ratio of La:Yb:Ho = 1:0.05:0.001. Furthermore, the temperature characteristics of each sample were analyzed to determine the absolute and relative sensitivities as 0.0232 K−1 and 0.357 %K−1, respectively. [ABSTRACT FROM AUTHOR]

The impact of composition control and energy transfer on luminescence thermometry was investigated in a TbIII/EuIII dual-emitting molecular cluster-aggregate, known as {Ln20}. The study of lifetime dynamics sheds new light on how one can take advantage of rational planning to enhance thermometric performance and gaining insights into intriguing optical properties. [ABSTRACT FROM AUTHOR]

Color tunable phosphors of Mn4+ and Tb3+ co-doped double-perovskite SrGdLiTeO6 (SGLT) were synthesized in this work. The crystal parameters and photoluminescence performances were investigated in detail. By taking advantage of the different thermal quenching strengths between Mn4+ and Tb3+ ions, the emission color of SGLT:0.7%Mn4+/1%Tb3+ changed from red to green, which could be used for high-temperature temperature warning indication. Moreover, according to the luminescence intensity ratio (LIR) technique, wide temperature-range optical thermometry was developed and further, the maximum relative sensitivity (SR1) value of the SGLT:0.7%Mn4+/5%Tb3+ phosphor was determined to be 1.49% K−1 at 560 K. On the other hand, the sensing properties were also analyzed based on the temperature-dependent lifetime method. The most interesting thing is that the maximum SR2 value reached 1.88% K−1 at 573 K. This work proved that the Mn4+ and Tb3+ co-doped double-perovskite SrGdLiTeO6 could be potentially used in temperature warning indication and high sensitivity luminescence thermometry. [ABSTRACT FROM AUTHOR]

In this work, spherical Na(La,RE)(MoO 4 ) 2 (RE = Eu/Yb-Er) double molybdates were prepared using the rare earth hydroxide (La,RE)(OH)SO4 as a self-sacrificing template. The composition, structure, morphology, up/down conversion luminescence and fluorescence lifetime (FL) of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fluorescence spectrophotometer, and Fourier transform infrared (FT-IR) spectrophotometer. The results indicate that highly pure spherical Na(La,RE)(MoO 4 ) 2 (RE = Eu/Yb-Er) samples can be obtained from the proposed route. The room temperature and temperature-dependent up/down conversion luminescence properties of the resulting Na(La,RE)(MoO 4 ) 2 (RE = Eu/Yb-Er) phosphors were analyzed in detail. The temperature-sensing performances for the two phosphors in both fluorescence intensity ratio (FIR) and FL modes were evaluated. Classical down and up-conversion photoluminescence (PL) from Eu 3 + and Er 3 + were observed. The down conversion phosphors were proved to be capable of sensing temperature via FL mode, and the maximum absolute sensitivity (SA) and maximum relative sensitivity (SR) were found to be 5 9 × 1 0 − 4 K − 1 (298 K) and 5 2 × 1 0 − 4 K − 1 (523 K), respectively. The up conversion phosphors Na(La,Yb,Er)(MoO 4 ) 2 were well capable of sensing temperature via FIR mode through thermally coupled 2H 1 1 / 2 , 4S 3 / 2 levels (I 5 2 0 /I 5 5 1) , and the maximum absolute sensitivity (SA) and maximum relative sensitivity (SR) were found to be 3 5 × 1 0 − 4 K − 1 (523 K) and 1 1 5 × 1 0 − 4 K − 1 (348 K), respectively. Spherical Na(La,RE)(MoO4)2 phosphor can be prepared using (La,RE)(OH)SO4 as the template by sacrificial-template hydrothermal reaction. The Na(La,Eu)(MoO4)2 phosphor is capable of sensing temperature via FL mode, and the maximum SA and maximum SR were found to be 59 × 10–4 K–1 (298 K) and 52 × 10–4 K–1 (523 K), respectively. While the Na(La,Yb,Er)(MoO4)2 phosphor is capable of sensing temperature via FIR mode, and the maximum SA and maximum SR were found to be 335 × 10–4 K–1 (523 K) and 115 × 10–4 K–1 (348 K). [ABSTRACT FROM AUTHOR]

Development of novel ultraviolet (UV) upconversion materials has been emerging as a hot research topic for application in tunable UV lasers, photocatalysis, sterilization, tagging, and most recently luminescence thermometry. We readily synthesized a series of Ho3+/Gd3+ co-doped LiYO2 upconversion phosphors by a traditional high-temperature reaction. Under excitation from a blue ∼445 nm laser, LiYO2:Ho3+,Gd3+ polycrystalline powders yield intense sharp ultraviolet B (UVB) upconversion luminescence from Gd3+ 6Pj (j = 7/2, 5/2, 3/2) excited states. By means of steady and dynamic photoluminescence spectra, we systematically investigated the involved two-photon absorption upconversion as well as the accompanying energy transfer processes between Ho3+ and Gd3+ ions in the LiYO2 host lattice. Interestingly, the distinguishable UVB luminescence constituents from Gd3+ 6Pj excited states exhibit sensitive temperature dependence in a 353–673 K range. Shedding light on thermal equilibria between Gd3+ 6Pj UV-emitting levels, their luminescence intensity ratios follow Boltzmann statistics for the application of new luminescence thermometry. For the scheme of 6P7/2–6P3/2 thermally coupled levels, it works over a temperature range of 373–673 K with a maximum relative sensitivity (Sr) of about 1.07% K−1 at 373 K, and its 6P7/2–6P5/2 counterpart works over 353–533 K with a maximum Sr of about 0.83% K−1 at 353 K. Overall, our study provides a new pathway to develop UV upconversion materials, and promotes the application of Gd3+-related UV luminescence constituents in sensitive temperature sensing over a wide temperature range. [ABSTRACT FROM AUTHOR]

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy3+,Tm3+ single-doped or co-doped K3Y(PO4)2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy3+,Tm3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm3+ and Dy3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm3+ to Dy3+, the emission of Dy3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy3+,Tm3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10−3 K−1, which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K3Y(PO4)2:Tm3+,Dy3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields. [ABSTRACT FROM AUTHOR]

Pressure and temperature are fundamental physical parameters, so their monitoring is crucial for various industrial and scientific purposes. For this reason, we developed a new optical sensor material that allows monitoring of both the physical parameters. The synthesized material exhibits upconversion (UC) emission of Er3+ in the red and green spectral regions under NIR (975 nm) laser irradiation. These UC emissions are strongly temperature-dependent, allowing multimode temperature sensing, either based on the luminescence intensity ratio between thermal-coupled energy levels (TCLs) or non-thermal-coupled energy levels (NTCLs) of Er3+ ions. Meanwhile, the luminescence lifetime of the 4S3/2 state of Er3+ ions was used as the third temperature-dependent spectroscopic parameter, enabling multi-parameter thermal sensing. Moreover, the observed enhancement of laser-induced heating of the sample under vacuum conditions allows for the conversion of the luminescent thermometer into a remote vacuum sensor. The pressure variations in the system are correlated with changes in the band intensity ratio (525/550 nm) of Er3+ TCLs, which are further applied for optical, contactless vacuum sensing. This is because of the light-to-heat conversion effect, which is greatly enhanced under vacuum conditions and manifests as a change in the intensity ratio of Er3+ bands (525/550 nm). The obtained results indicate that an Y2Mo4O15:Er3+/Yb3+ (YMO) phosphor has great application potential for the development of multi-functional and non-invasive optical sensors of pressure and temperature. [ABSTRACT FROM AUTHOR]

Luminescence thermometry has emerged as a very versatile optical technique for remote temperature measurements, exhibiting a wide range of applicability spanning from cryogenic temperatures to 2000 K. This technology has found extensive utilization across many disciplines. In the last thirty years, there has been significant growth in the field of luminous thermometry. This growth has been accompanied by the development of temperature read-out procedures, the creation of luminescent materials for very sensitive temperature probes, and advancements in theoretical understanding. This review article primarily centers on luminescent nanoparticles employed in the field of luminescence thermometry. In this paper, we provide a comprehensive survey of the recent literature pertaining to the utilization of lanthanide and transition metal nanophosphors, semiconductor quantum dots, polymer nanoparticles, carbon dots, and nanodiamonds for luminescence thermometry. In addition, we engage in a discussion regarding the benefits and limitations of nanoparticles in comparison with conventional, microsized probes for their application in luminescent thermometry. [ABSTRACT FROM AUTHOR]

Optical thermometers are advantageous for temperature measurement in electromagnetic fields and aggressive environments; however, their composition mostly relies on materials doped with expensive and resource-limited rare earth ions. In this article, we describe the application of calcium aluminate doped with transition metal ions (Mn2+ and Cr3+) in optical thermometry, employing optical fibres for signal transmission. Upon excitation with 450 nm laser diode radiation, changes in the luminescence of Mn2+ ions in the 500–550 nm band are followed along with changes in the Cr3+ band at 750–800 nm. The application has been tested in the temperature range from 20 °C to 800 °C. The temperature dependence of Cr3+ luminescence encompasses the high-temperature range, whereas the luminescence band of Mn2+ ions gives an increase in the total intensity and provides a more consistent change in the range from 400 °C to 550 °C. [ABSTRACT FROM AUTHOR]

In this work, we report on the synthesis and investigation of new hybrid multifunctional iron oxide nanoparticles (IONPs) coated by coumarin-bound copolymer, which combine magneto- or photothermal heating with luminescent thermometry. A series of amphiphilic block copolymers, including Coum-C11-PPhOx27-PMOx59 and Coum-C11-PButOx8-PMOx42 bearing luminescent and photodimerizable coumarin moiety, as well as coumarin-free PPhOx27-PMOx57, were evaluated for their utility as luminescent thermometers and for encapsulating spherical 26 nm IONPs. The obtained IONP@Coum-C11-PPhOx27-PMOx59 nano-objects are perfectly dispersible in water and able to provide macroscopic heating remotely triggered by an alternating current magnetic field (AMF) with a specific absorption rate (SAR) value of 240 W.g−1 or laser irradiation with a photothermal conversion efficiency of η = 68%. On the other hand, they exhibit temperature-dependent emission of coumarin offering the function of luminescent thermometer, which operates in the visible region between 20 °C and 60 °C in water displaying a maximal relative thermal sensitivity (Sr) of 1.53%·°C−1 at 60 °C.

Germanate tellurite glasses doped with Eu3+ and Tb3+ were synthesized by the conventional melt-quenching method. There is no indication of the energy transfer between dopant ions in this host, but the co-dopants exhibit excellent color purity of 100% for Eu3+ and 80% for Tb3+. The co-doped glass exhibits yellow luminescence. The quantum yield of the Eu3+ emission is equal to 23% under 395 nm excitation. The thermal quenching of Eu3+ and Tb3+ luminescence occurs at different temperature ranges, which enables the thermal sensing properties of the material. The relative fluorescence intensity ratio (FIR) sensitivity of 0.16% K−1 was recorded in the wide range of temperatures spanning from −193 °C up to 0 °C. The temperature dependence of the decay times was also studied. The lifetime-based temperature sensitivity was determined to be 0.95% K−1 at 250 °C for Tb3+5D3 level emission and 0.3% K−1 at 225 °C for Eu3+5D1 level emission.

Following astonishing growth in the last decade, the field of luminescence thermometry has reached the stage of becoming a mature technology. To achieve that goal, further developments should resolve inherent problems and methodological faults to facilitate its widespread use. This perspective presents recent findings in luminescence thermometry, with the aim of providing a guide for the reader to the paths in which this field is currently directed. Besides the well-known temperature read-out techniques, which are outlined and compared in terms of performance, some recently introduced read-out methods have been discussed in more detail. These include intensity ratio measurements that exploit emissions from excited lanthanide levels with large energy differences, dual-excited and time-resolved single-band ratiometric methods, and phase-angle temperature readouts. The necessity for the extension of theoretical models and a careful re-examination of those currently in use are emphasized. Regarding materials, the focus of this perspective is on dual-activated probes for the luminescence intensity ratio (LIR) and transition-metal-ion-activated phosphors for both lifetime and LIR thermometry. Several particularly important applications of luminescence thermometry are presented. These include temperature measurement in catalysis, in situ temperature mapping for microfluidics, thermal history measurement, thermometry at extremely high temperatures, fast temperature transient measurement, low-pressure measurement via upconversion nanoparticle emission intensity ratios, evaluation of the photothermal chirality of noble metal clusters, and luminescence thermometry using mobile devices. Routes for the development of primary luminescence thermometry are discussed in view of the recent redefinition of the kelvin. [ABSTRACT FROM AUTHOR]