Maximum Absolute Sensitivity Research Articles

Rb2InCl5·H2O doped with Te4+ for fluorescence thermometry and coordinated water-related structural phase transformation.

Here, we synthesized Rb2InCl5·H2O with x Te4+ doping by the coprecipitation method, which converts the original nonluminance for pure Rb2InCl5·H2O into orange luminescence ascribed to Te4+ incorporation with an emission peak at 648 nm and a full width at half maximum of 142 nm (420.3 meV) at room temperature. The photoluminescence (PL) lifetime of Te4+-doped Rb2InCl5·H2O exhibits a strong temperature dependence, with a maximum absolute sensitivity (SA) of 12 × 10-3 K-1 at 260 K and a relative sensitivity (SR) of 3.5%K-1 at 300 K, demonstrating its capability for non-contact remote temperature measurement. Additionally, we capture the dynamic changes of coordinated water with temperature in Rb2InCl5·H2O through temperature-dependent Raman spectroscopy, analyze the resulting structural phase transformation associated with coordinated water, and investigate the reversibility of this phase transformation.

Optimizing the thermal stability of Tb3+-based phosphor through intervalence charge transfer compensation and charge transfer band edge red-shift

Thermal quenching (TQ) limits the large-scale practical application of most luminescent materials, so the investigation on thermal quenching phenomenon of phosphors has emerged as a prominent research area, garnering significant attention in academic circles. The thermal quenching performance is closely related to the charge transfer band (CTB) and intervalence charge transfer (IVCT) band. Herein, we study the correlation between CTB edge red-shift, IVCT band position and the thermal stability of Tb3+-based lithium tantalate phosphors, aiming to regulate the thermal quenching performance. The results show that totally anomalous thermal quenching (TATQ) was found to exist in LiTaO3:xTb3+ phosphors during the process of temperature rising, and the whole CTB edge absorption showed a red-shift and enhance with increasing temperature. Based on this characteristic phenomenon, under the excitation of CTB edge (270 nm), the phosphor exhibits obvious antithermal quenching. In addition, the existence of the Tb3+-Ta5+ IVCT band can be used as a compensation channel for Tb3+ 5D3 → 5D4 transition, which makes the phosphor produce stronger antithermal quenching performance. Accordingly, the co-regulation of the CTB edge red-shift and IVCT compensation effect was proposed. Modulation of Tb3+ concentration revealed that during thermal activation (λem = 547 nm), LiTaO3:0.005Tb3+ luminescence integral intensity (423 K) reaches 255.6% of the initial intensity, phosphor achieves the most excellent performance. The maximum absolute sensitivity (Sa) and relative sensitivity (Sr) for temperature sensing scheme based on the intensity ratio of excitation spectrum CTB and CTB-IVCT reaches 0.996%@523 K and 0.927%@523 K, respectively. The co-regulation strategy of thermal activation-induced CTB edge red-shift and IVCT compensation channel provides a promising research idea for developing Tb3+-based antithermal quenching luminescent materials.

Upconversion luminescence and thermosensitive properties of NaGd(PO3)4:Yb3+/Er3+

High-sensitivity optical temperature measurement has attracted extensive attention in both fundamental studies and practical applications. In this study, a series of upconversion (UC) luminescence phosphors composed of NaGd(PO3)4 (NGP) doped with 20 at% Yb3+ and various concentrations of Er3+ (0.5 at% as the optimal concentration) was synthesized by high-temperature solid-state method. And their crystal structure and the distribution of lanthanide dopants were analyzed using X-ray diffraction with Rietveld refinement verifies. Under 980 nm laser excitation, the obtained phosphors show the characteristic Er3+ upconversion green and red emission bands through two-photon processes. The fluorescence intensity ratio (FIR) based on the thermal coupled states demonstrates the thermal sensing ability in a wide temperature range of 200–573 K. The thermal sensitivity is relatively high with the maximum absolute thermal sensitivity Sa of 0.53 % K−1 (523 K) and the maximum relative thermal sensitivity Sr of 2.60 % K−1. The phosphor NGP:Yb/Er also exhibits high repeatability as the thermal sensors reach 97 %. These findings postulate the potential of NGP:Yb/Er as a promising candidate in optical thermal sensing applications.

Upconversion enhancement and temperature sensing studies in Li+ ions incorporated GdPO4:Tm3+/Yb3+ phosphor

The GdPO4:Tm3+/Yb3+ phosphor codoped with various concentrations of Li + ions were synthesized for upconversion emission and optical thermometry studies. Excitation using 980 nm laser diode results in three upconversion (UC) emission bands with centre wavelengths of 478, 648 and 692 nm. These bands are originated from 1G4→3H6, 1G4→3F4, and 3F3→3H6 transitions of the Tm3+ ion, respectively. Li+ ions modified the local crystal symmetry around dopant ions, resulting enhanced UC emissions. The lifetime of the 1G4 level of Tm3+ ion was studied using a 980 nm laser excitation. The temperature sensing performances of GdPO4:Tm3+/Yb3+ and GdPO4:Tm3+/Yb3+/Li+ based on fluorescence intensity ratio (FIR) technique were evaluated in the temperature range 301–713 K under 980 nm excitation. Non-thermally coupled levels 3F3 (692 nm) and 1G4 (478, 648 nm) were utilized for FIR estimation. A maximum absolute sensitivity of 6.28 × 10−3 K−1 at 653 K and 18.71 × 10−3 K−1 at 713 K were observed for Li + undoped and codoped phosphors respectively. The result indicates that codoping of Li + ions improved the UC emission as well as optical thermometry. Moreover, CIE colour coordinates and anti-counterfeiting application were also exhibited.

Microwave assisted preparation of ternary scheelite CaMoO4: Er3+/Yb3+ nano-phosphors for up/down-conversion photoluminescence, temperature sensing and antibacterial properties

Due to their exceptional intrinsic optical characteristics, molybdate compounds have aroused significant attention in recent years for their effective up and downconversion luminescence. In the present study, a series of xEr3+/Yb3+ (x = 0.5 %, 1 %, 2 %, 4 % and Yb3+ =15 %) doped CaMoO4 nanophosphors synthesized through a microwave assisted approach and subsequently the comprehensive analysis of the functionalities such as optical properties, antibacterial traits and their integration with temperature sensing, have been explored. Furthermore, the structural refinement confirms the occurrence of tetragonal scheelite phase of the prepared materials. The morphology of the material was identified by FE-SEM and HR-TEM analysis which reveals particles are in spherical shape. Up-conversion luminescence intensities were found to be dependent on doping concentration, laser excitation power and external temperature upon 980 nm light excitation. The temperature sensing response of the optimized sample was examined based on intensity ratio of two emission bands that involves thermally connected energy levels of Er3+ ion. The maximum absolute sensitivity of 10.74 × 10−3 K−1 (at 500 K) was found, demonstrating its potential application in high temperature thermometry. The comprehensive analysis and the outcome of the present study suggests the potential prospect of the as-synthesized material in food preservation, medical equipment, water treatment, and as an optical coating agent for solid state luminous devices.

Using Principal Component Analysis for Temperature Readings from YF3:Pr3+ Luminescence

The method of measuring temperature using luminescence by analyzing the emission spectra of Pr3+-doped YF3 using principal component analysis is presented. The Pr3+-doped YF3 is synthesized using a solid-state technique, and its single-phase orthorhombic crystal structure is confirmed using X-ray diffraction. The emission spectra measured within the 93–473 K temperature range displays characteristic Pr3+ f-f electronic transitions. The red emission from the 3P0,1→3H6,3F2 electronic transition mostly dominates the spectra. However, at low temperatures, the intensity of the green emissions from the 3P0,1→3H5, deep-red 3P0,1→3F4, and the deep-red emissions from the 3P0,1→3F4 transitions are considerably lower compared to the intensity of the red emissions. Temperature variations directly impact the photoluminescent spectra, causing a notable increase in the green and deep-red emissions from the 3P1 excited state. We utilized the entire spectrum as an input for principal component analysis, considering each temperature as an independent group of data. The first principal component explained 99.3% of the variance in emission spectra caused by temperature and we further used it as a reliable temperature indicator for luminescence thermometry. The approach has a maximum absolute sensitivity of around 0.012 K−1. The average accuracy and precision values are 0.7 K and 0.5 K, respectively.

Highly sensitive dual-mode temperature measurement utilizing completely opposite thermal quenching luminescence

In recent years, phosphors have been used in the field of temperature sensing, which has aroused great interest because of its advantages of quick response, high sensitivity and high accuracy. However, exploring optical thermometers with ultra-high sensitivity remains a challenge. In this work, we have designed and synthesized Sm3+ and Mn4+ co-doped La3Mg2NbO9 phosphor for temperature sensing for the first time by utilizing the anomalous thermal quenching property of Sm3+ ions and the sensitive thermal quenching property of Mn4+ ions. Furthermore, the structure, elemental distribution, morphology and optical characteristics of La3Mg2NbO9:Sm3+,Mn4+ were studied in detail. Benefiting from the different responses of the Sm3+ and Mn4+ ions to temperature, the fluorescence intensity ratios of Sm3+ to Mn4+ in La3Mg2NbO9 samples show excellent optical thermometry performance in the range of 303–463 K. The maximum absolute sensitivity (Sa) and relative sensitivity (Sr) values of La3Mg2NbO9:Sm3+,Mn4+ sample reach as high as 0.117 K-1 (@463 K) and 4.48 % K−1 (@303 K), respectively. Furthermore, the maximum of Sa is 0.385 K−1 (@463 K) and the maximum of Sr is 4.54 % K−1 (@303 K) based on the fluorescence lifetime temperature measurement method. The temperature cyclotron curve of the sample proves that the sample has excellent stability and repeatability in temperature measurement. These results demonstrate that the designed La3Mg2NbO9:Sm3+,Mn4+ phosphor is promising for the field of non-contact optical temperature thermometry.

Up-Conversion Luminescence and Optical Temperature Sensing Properties of NaLuF4:Yb3+/Ho3+ Micron-Sized Crystals at Low Temperature.

Non-contact temperature sensors utilising the fluorescence intensity ratio and the unique up-conversion (UC) luminescence of rare-earth ions have numerous benefits; however, their operational temperature range has remained limited. In this study, NaLuF4:Yb3+/Ho3+ samples were prepared by the hydrothermal method. The samples exhibited exceptional UC luminescence properties at low temperatures. The intensity of the green emission (with peak wavelengths of 540 and 546 nm) gradually decreased with increasing temperature, and the green emissions showed a unique change at low temperatures. In addition, we studied the dependence of the UC luminescence intensity on the excitation power and the variation in the decay lifetime with temperature. The experiments revealed excellent luminous performance and significantly enhanced sensitivity at low temperatures; the maximum absolute sensitivity Sa and relative sensitivity Sr of the 540 and 546 nm thermally coupled energy levels were 1.02% and 0.55% K-1, respectively. The potential temperature sensing properties of Yb3+/Ho3+-co-doped NaLuF4 makes it suitable for temperature sensing applications at temperatures as low as 30 K. This study offers a novel approach for the advancement of temperature sensing technology at low temperatures.

Bimolybdate single crystals codoping with trivalent ytterbium and erbium ions for high-stable and high-sensitive optical thermometry

Replacing conventional powder polycrystalline materials with crystalline materials is an effective strategy to improve the sensing sensitivity, responsiveness, and anti-interference capabilities of the fluorescence intensity ratio (FIR) based optical temperature sensing techniques. In this work, Yb3+/Er3+ codoped bimolybdate single crystals, NaBi(MoO4)2 (NBM) with different Er3+ ion doping concentrations, were grown by the Czochralski method, in which is expected to be used for optical temperature sensing applications. The structure of the crystals was fully characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). Under 980 nm laser excitation, the crystals demonstrated notable green and slight red upconversion (UC) emissions, and the mechanism of UC luminescence was thoroughly investigated. The luminescence intensity was found to be contingent upon the doping concentration, which gradually decayed with increase of Er3+ ions. The optical temperature sensing performance of Yb3+/Er3+ codoped NBM single crystals was evaluated by the FIR technique based on the thermally coupled level of Er3+ ions (2H11/2/4S3/2). The experimental findings revealed that the 10 at% Yb3+, 10 at% Er3+: NBM crystal exhibited highest sensor sensitivity among the synthesized crystals, with a maximum absolute sensitivity of approximately 1.22 % K−1 at 510 K. Furthermore, the temperature sensing characteristics of the crystals appeared to be dependent on the doping concentration of Er3+ ions. In summary, the Yb3+/Er3+ codoped NBM single crystal showcased excellent sensor sensitivity and held considerable promise as materials for optical temperature sensing applications.

Heterovalent Zr4+/Nb5+‐Cosubstituted Negative Thermal Expansion Luminescent Materials with Anti‐Thermal Quenching Luminescence

AbstractRare earth luminescent materials based on negative thermal expansion (NTE) have achieved thermally enhanced photoluminescence, but these materials typically exhibit relatively weak luminescence intensity at room temperature. In this work, adopting the cationic heterovalent substitution strategy, a series of Sc2‐2xZrxNbxW3‐1.5xO12‐3x:Yb/Er (SZNWOx:Yb/Er) phosphors are prepared by solid‐state reaction. With the increase of x value, the substitution of Sc3+ by Zr4+/Nb5+ leads to a decrease in the local symmetry of Er3+. Compared with Sc2W3O12:Yb/Er (SWO:Yb/Er), this heterovalent substitution strategy significantly improves the luminescence intensity of SZNWOx:Yb/Er while retaining its anti‐thermal quenching luminescence and negative thermal expansion properties. By comparing and analyzing the temperature dependent temperature‐dependent steady‐state/transient spectra of SZNWO0.10:Yb/Er and SWO:Yb/Er phosphors, the anti‐thermal quenching mechanism is discussed from a new perspective. The luminescence intensity ratio (LIR) of the thermal coupled levels (TCL) of Er3+(2H11/2/4S3/2) is adopted for optical temperature sensing, achieving a maximum absolute sensitivity of 1.04% K−1 at 464 K and a maximum relative sensitivity of 1.08% K−1 at 298 K for the SZNWO0.10:Yb/Er phosphors. Finally, the potential applicability using the constructed flexible thin film to real‐world sensing scenarios is demonstrated, offering accurate and real‐time temperature monitoring at the local hotspot in the electronic component of the CPU chip.

Self-Powered and Self-Recovered Mechanoluminescent Electronic Skins for Detecting and Distinguishing Diverse External Stimuli.

The concept of simulating external mechanical stimuli to generate luminescence has been a long-standing aspiration in real-time dynamic visualization. However, creating self-power and self-restoring mechanoluminescent electronic skins for artificial sensors poses significant challenges. In this study, we introduce a cutting-edge triboelectric-mechanoluminescent electronic skin (TMES) that exhibits a remarkable response to multiple external stimuli. This advancement is achieved by integrating a mechanoluminescent intermediate layer within a triboelectric nanogenerator (TENG). When pressure is applied to TMES, the maximum detection voltage can reach hundreds of volts and the maximum correlation sensitivity is 11.76 V/N. Moreover, we incorporate luminescence materials into mechanoluminescence layer, and the maximum absolute sensitivity SR can reach 1.41%. The device can not only distinguish between external stimuli such as pressing and bending but also continuously track external mechanical stimuli. A 4 × 4 matrix and motion prediction of 8 different postures were established to further demonstrate the significant advantages of the developed device in spatial detection. The versatility and performance of the TMES hint at its vast potential in areas such as human-computer interaction and wearable electronics, paving the way for more intuitive and dynamic technological interfaces.

Dual-mode optical thermometer and spectral conversion for c-Si solar cells in Ag clusters and Yb3+ co-doped borate glasses

Borate glasses doped with Ag clusters and Yb3+ were prepared using the conventional melt-quenching method. Fluorescence spectra and decay curve measurements confirmed that energy transfer (ET) occurred from the Ag clusters to Yb3+. The fluorescent glasses can convert ultraviolet light to visible-infrared region which matches well with the spectral response of c-Si solar cells to improve the conversion efficiency. The lifetimes of Ag clusters decreased in Ag clusters mono-doped and Ag clusters/Yb3+ co-doped glasses as the temperature increased. Sensitivity values based on the fluorescence lifetime (FL) were calculated. Furthermore, a high optical sensitivity based on the fluorescence intensity ratio (FIR) technology and the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) were 4.79 % K−1 and 0.97 % K−1, respectively. Temperature cycling tests demonstrated the repeatability of the luminescence. These results indicate that this fluorescent glass can serve as an excellent temperature sensing material.

High sensitivity temperature sensing material In2Li3P3O12: Bi3+, Eu3+ based on effective energy transfer from Bi3+ to Eu3+

In recent years, fluorescent temperature sensing materials have been widely studied because they can realize remote non-destructive temperature measurement. High temperature sensitivity and excellent temperature resolution are the eternal pursuit of fluorescence temperature sensing. Here, we report the preparation, structure, luminescent properties and temperature sensing performance of phosphor In2Li3P3O12: Bi3+, Eu3+. Eu3+ singly doped samples can emit red light under 270 nm excitation. There is effective energy transfer from Bi3+ to Eu3+ in the Bi3+ and Eu3+ co-doped samples. Doping Bi3+ on the basis of doping Eu3+ can significantly enhance the luminescence intensity of Eu3+ ions. Ultraviolet light from Bi3+ and red light from Eu3+ are chosen to design a fluorescence intensity ratio thermometer for more accurate temperature detection. The temperature sensing technology has a maximum absolute and relative sensitivity is up to 0.0087 K−1 at 298 K−1 and 2.71 % K−1 at 325 K, respectively. This has a higher sensitivity than many phosphors available on the market. This indicates that it is a kind of fluorescence temperature sensing material with great potential.

Investigation of the sensitization effect of Yb3+ in Yb, Er co-doped Sr5(PO4)3F transparent ceramics: From single-band red upconversion to temperature sensing behavior

Lanthanide-ion-doped red upconversion (UC) fluorescent materials with excellent signal-to-noise ratio, stability, and red-green luminous intensity ratio have proven of tremendous research importance for biomedical, three-dimensional (3D) displays, sensors, and other sectors. In this study, xYb, 1Er: Sr5(PO4)3F (S-FAP) (x=0–5 at%) transparent ceramics with outstanding optical quality were fabricated by hot pressing the co-precipitation powder with high sintering activity. The energy dispersive X-ray (EDX) results showed that the trivalent lanthanide ions were evenly doped into the S-FAP ceramic lattice. Increased Yb3+ doping considerably restricted the growth of ceramic grain size, which should be attributable to a decrease in sintering activity under high Yb doping conditions. The co-doping of Yb3+ successfully resulted in a significant improvement in up/down conversion efficiency via effective energy transfer mechanisms and the optimization of the electron population at the energy level of red-green emission. Furthermore, single-band red upconversion luminescence with the greatest red-green upconversion luminescence integral intensity ratio of 125.74 was discovered under 980 nm laser pumping at room temperature. The energy transition process involved in the phenomenon of the up-conversion luminescence intensity shift of red-green emission has been thoroughly examined. Finally, the noncontact optical thermometric ability based on fluorescence intensity ratio (FIR) technology showed that the maximum absolute sensitivity (Sa) of the 5Yb1Er sample in the temperature range of 320–556 K is 1.1×10−3 K−1, implying the possible use of Yb/Er-doped S-FAP transparent ceramics in the field of optical thermometers.

Judd-Ofelt analysis of Sm3+ doped Ca2LiMg2V3O12 phosphors: Unveiling luminescent and thermometric properties for multifunctional applications

This study investigated the luminescent and thermometric properties of pure and Sm³⁺-doped Ca₂LiMg₂V₃O₁₂ (CLMV) garnet-type vanadates synthesized by the solid-state reaction method. The synthesized materials, with varying Sm³⁺ concentrations (0.01–0.09 mol%), were comprehensively characterized using powder X-ray diffraction (PXRD) analysis to confirm their phase purity. Diffuse reflectance spectroscopy (DRS) measurements were employed to determine the band gap energy of both pure CLMV and CLMV:0.07Sm³⁺ samples. Photoluminescence (PL) excitation and emission spectra were recorded for the pure and Sm³⁺-doped CLMV phosphors using an excitation wavelength of 345 nm and monitoring the emission at 618 nm. These spectra revealed detailed information about the energy levels involved in light emission processes. An efficient energy transfer from the (VO₄)³⁻ groups to the Sm³⁺ ions was observed, exceeding 48%. This energy transfer process is crucial for achieving high-intensity luminescence in Sm³⁺-doped materials. Judd–Ofelt (J-O) theory was applied from the emission spectra and calculate the Judd–Ofelt intensity parameters, which govern the radiative properties of the Sm³⁺ ions. Based on the J-O analysis, the branching ratio (β) was estimated to be greater than 75%. This value, exceeding the threshold of 50% for display devices, signifies the suitability of the phosphor for solid-state lighting applications due to its efficient light emission. The thermal quenching behavior of both the Sm³⁺ ions and the (VO₄)³⁻ groups was further investigated to explore the optical thermometric characteristics of the Sm³⁺-doped CLMV phosphors. Notably, a maximum absolute sensitivity (Sa) of 0.35 K⁻1 and a relative sensitivity (Sr) of 2.55% K⁻1 were achieved, demonstrating the materials potential for non-contact optical temperature sensing applications. Lifetime decay analysis revealed double exponential decay behavior, indicating the presence of multiple luminescence centers within the phosphor. The average lifetime in the millisecond range further supports the suitability of these materials for practical applications. Finally, the CIE color coordinates, correlated color temperature (CCT), and color rendering index (CRI) values were also reported, providing insights into the colorimetric properties of the Sm³⁺-doped CLMV phosphors. These aspects are crucial for optimizing the materials for solid-state lighting applications.

Tunable multicolor-emission in Eu3+ and Tb3+ codoped Cs2NaInCl6:Sb3+ double perovskite nanocrystals and its dual-model anti-counterfeiting and temperature-sensing applications

Lead-free metal halide double perovskites with non-toxicity and stable self-trapped excitons (STEs) have received considerable attention in the field of photoelectric applications. However, it is difficult to achieve independent control of its photoluminescence performance to meet the requirements of multi-band emission. Herein, a doping strategy was employed to introduce lanthanide ions (Ln3+) into Cs2NaInCl6:Sb3+ nanocrystals (NCs), enabling the multicolor emission modulation ranging from blue to red and even white light. Benefiting from the efficient energy transfer from Sb-related self-trapped excitons to Ln3+ ions, green and red emissions originate from the 5D0→7FJ (J = 1, 2, 3, 4) transition of Eu3+ ions and 5D4-7FJ (J = 6, 5, 4, 3) transition of Tb3+ ions, respectively. According to the tunable polychromatic photoluminescence characteristics of doped NCs, the dual-mode fluorescent anti-counterfeiting applications were exhibited. Furthermore, the distinct temperature sensitivities exhibited by blue (453 nm) and red (617 nm) emission in Cs2NaInCl6:Sb3+/Eu3+ NCs provide the opportunity for the optical thermometry, which demonstrates the maximum absolute and relative sensitivity are 0.0018 and 0.43 % K−1, respectively. These results indicate that the synthesized codoped NCs have the potential applications in multifunctional fields, such as optical thermometer, fluorescence anti-counterfeiting, and multicolor-LEDs.

Thermosensitive chameleon films based on polystyrene doped with complexes of europium(III) and terbium(III)

New complexes of Eu(III) and Tb(III) tris(β-diketonates) with Lewis bases were synthesized. The spin-coating technique was used to produce composite films consisting of polystyrene (PS) polymer doped with mixtures of Eu(III) and Tb(III) complexes with different ratio of luminophores. An increase in the content of the Tb(III) complexes in the 5 %Eu x%Tb films intensifies emission of both the Tb3+ and Eu3+ ions due to occurring intermolecular energy transfer and leads to a significant increase in photostability of the material (the loss of luminescence intensity ratio did not exceed 0.5 %/hour). These photostable films were characterized as potential luminescent temperature sensors. The temperature sensitivity of their luminescence intensity and lifetime was investigated in the range of 298–383 K. The maximum absolute sensitivity of the films reaches 6.00 µs/K and exceeds that of all known lanthanide-containing thermal sensors designed for measuring physiological temperatures. In combination with changeable luminescence colors of the films, such a sensitivity makes these materials promising colorimetric thermal sensors for in situ temperature measurements.

New Na5Y(MoO4)4: Yb3+, Er3+ phosphors: Up-conversion luminescence and temperature sensing characteristics

Currently, the development of new up-converting fluorescent materials for manufacturing optical temperature sensing device with high accuracy and precision has always been significant pursuits of many researchers. In this work, we have synthesized new Na5Y(MoO4)4: Yb3+/Er3+ phosphors via solid-state reaction route, and the influences of dopant concentration on UCL performance were discussed. The results revealed that the introduction of Yb3+ enhanced the luminescence intensity, and the optimal concentration combination was 0.20Yb3+/0.04Er3+. Doping Yb3+ and Er3+ did not affect the phase structure of the phosphor. Several emission peaks at 529, 552 and 668 nm of Er3+ were found to be temperature-dependent within the scope of 298–573 K. Through the utilization of fluorescence intensity ratio technique (FIR, I529/I552 and I529/I668), dual-mode temperature measurement was realized. The maximum relative sensitivity (Sr-max) of 1.77 % K−1 (@298 K) utilizing thermally coupled energy levels (TCELs) and the maximum absolute sensitivity (Sa-max) of 12.0 % K−1 (@573 K) based on the non-TCELs were achieved. Furthermore, Yb3+/Er3+ co-doped Na5Y(MoO4)4 phosphors exhibited excellent photothermal repeatability and temperature resolution. The results indicated that the novel Na5Y(MoO4)4 phosphor provided the possibility for the development of temperature sensing materials with high sensitivity.

LiYF4:Er3+ for near-infrared luminescent cryothermometry

We explore the possibility of using the luminescence of LiYF4:Er3+ to measure cryogenic temperatures. Temperature dependences (2.5 K → 190 K) of the luminescence intensity ratios and linewidths are studied in the regions of infrared transitions 4I13/2 → 4I15/2 (∼1.5 μm) and 4I11/2 → 4I15/2 (∼0.98 μm) using high-resolution Fourier spectroscopy. Pairs of spectral lines 6550–6510 cm−1, 10176–10161 cm−1, and 6482–6478 cm−1 can be used for ratiometric Boltzmann thermometry with maximum absolute sensitivity at temperatures of 28.8, 10.8, and 2.9 K, respectively, and corresponding relative sensitivities of 6.9, 18.5, and 70% K−1 at these temperatures. The temperature dependence of the linewidth of 6510 cm−1 line is favorable for measuring higher temperatures.

High-performance of optical thermometry based on the non-thermally coupled levels in YVO4: Yb3+/Er3+/Tm3+ nanocrystals

Hydrothermally fabricated nanocrystals YVO4: Yb3+/Er3+/Tm3+ were investigated for up-conversion (UC) luminescence and optical temperature sensing performance. Upon 980 nm excitation, the luminescence intensity firstly increases and then decreases with raising Yb3+ doping content and reaches the maximum at 15 mol%. Considering the strong UC emission, the temperature sensing behavior was investigated based on the fluorescence intensity ratio (FIR) technique in temperature range of 293–573 K. The study was focused on the non-thermally coupled levels (NTCLs) including transitions 3F2,3 → 3H6 and 1G4→3H6 of Tm3+, transitions from the 4S3/2, stark sublevel 4S3/2(2), and 4F9/2 to the ground state 4I15/2 of Er3+ owing to their various temperature-dependent behaviors. Through using the stark sublevel 4S3/2(2) of Er3+, the maximum absolute sensitivity (SA) of 0.0563 K-1, relative sensitivity (SR) of 2.334 %K−1 and the minimum temperature resolution of 0.0058 K was achieved with good repeatability. The experimental results indicate that the as-obtained YVO4: 15%Yb3+/1%Er3+/1%Tm3+ nanocrystals can be potential candidates for nano-dimensional optical thermometry applications.