Cross relaxation-enhanced NIR-Ⅱ fluorescence in negative thermal expansion phosphor Sc2(MoO4)3 for thermal sensing

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.