In the clinical diagnosis and treatment of diseases, there is an urgent need to find suitable materials for real-time temperature monitoring of biological tissues. The paper provides a detailed study of the effects of Nd 3+ doping concentration on the negative thermal expansion performance and NIR fluorescence properties of Sc 2 (MoO 4 ) 3 . The results obtained from Rietveld refinement of in-situ XRD data indicates that high concentration of Nd 3+ doping significantly influences the negative thermal expansion performance of the material, as well as alters the temperature-dependent changes in NIR fluorescence intensity and lifetime. In addition, a NIR fluorescence lifetime temperature probe doped with Nd 3+ /Yb 3+ /Er 3+ has been constructed. When the temperature increased from 303 K to 403 K, the fluorescence intensity of the probe at 1538 nm increased by a factor of 127.5. Furthermore, as the temperature rose from 323 K to 403 K, the fluorescence lifetime of the probe at 1538 nm extended from 41.93 μs to 204 μs. By utilizing the lifetime of Er 3+ for temperature sensing, a relative sensitivity of 6.03%K −1 was achieved at 323 K, indicating significant potential application value of this probe in the field of biological temperature measurement.
In the field of disease diagnosis and treatment, achieving highly sensitive temperature sensing via non-contact methods based on fluorescence continues to present a significant challenge. This study investigated the influence of the cross-relaxation (CR) process of Tm 3+ ions at varying concentrations and the negative thermal expansion (NTE) property of the matrix on the luminescent properties of Sc 2 (MoO 4 ) 3 :Yb 3+ /Tm 3+ materials under diverse temperature conditions, and further evaluated their potential application value in the field of temperature sensing. At room temperature, the analysis of the concentration dependence of the emission spectra reveals that the intensities of the emission peaks originating from higher energy levels ( 1 G 4 , 3 H 4 , and 3 H 5 ) and the lowest excited state ( 3 F 4 ) exhibit significant variation with the doping concentration. As the doping concentration increases, the temperature enhancement factor for the fluorescence intensity of high-energy level transition ( 1 G 4 → 3 H 6 ) progressively decreases from 21.6 to 1.2. In contrast, the temperature enhancement factor for the lowest excited state transition ( 3 F 4 → 3 H 6 ) markedly increases from 471 to 2964. At a concentration of 8%, the temperature extension factor of the fluorescence lifetime at 1627 nm ( 3 F 4 → 3 H 6 ) can reach 7.2, whereas at a concentration of 0.5%, this factor is 2.7. These suggests that the CR process between Tm 3+ ions exerts markedly distinct influences on the luminescence intensities and lifetime in Sc 2 (MoO 4 ) 3 :Yb 3+ /Tm 3+ materials. In addition, this study employs the fluorescence intensity ratio of I 1629 nm / I 1197 nm for temperature sensing, thereby achieving high sensitivity in temperature measurement.
Rare earth (RE 3+ )-doped phosphors generally suffer from thermal quenching, in which their photoluminescence (PL) intensities decrease at high temperatures. Herein, we report a class of unique two-dimensional negative-thermal-expansion phosphor of Sc 2 (MoO 4 ) 3 :Yb/Er. By virtue of the reduced distances between sensitizers and emitters as well as confined energy migration with increasing the temperature, a 45-fold enhancement of green upconversion (UC) luminescence and a 450-fold enhancement of near-infrared downshifting (DS) luminescence of Er 3+ are achieved upon raising the temperature from 298 to 773 K. The thermally boosted UC and DS luminescence mechanism is systematically investigated through in situ temperature-dependent Raman spectroscopy, synchrotron X-ray diffraction and PL dynamics. Moreover, the luminescence lifetime of 4 I 13/2 of Er 3+ in Sc 2 (MoO 4 ) 3 :Yb/Er displays a strong temperature dependence, enabling luminescence thermometry with the highest relative sensitivity of 12.3%/K at 298 K and low temperature uncertainty of 0.11 K at 623 K. These findings may gain a vital insight into the design of negative-thermal-expansion RE 3+ -doped phosphors for versatile applications.
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