Fluorescence intensity ratio optical thermometer YNbO4: Pr3+, Tb3+ based on intervalence charge transfer

Currently, due to the advantages of fast response, remote operations and good stability, non-contact optical temperature measurement technology based on fluorescence intensity ratio (FIR) has attracted intensive attention. Here, we successfully developed a novel Pr3+, Tb3+ co-doped YNbO4 phosphor which can be used as a non-contact optical thermometer. Under excitation at 295 nm, Pr3+, Tb3+ co-doped YNbO4 emits red light from Pr3+ (1D2 → 3H4) and green light from Tb3+ (5D4 → 7F5), simultaneously. Based on strong dependence of the emission intensity on temperature, the FIR of red and green emissions is designed as detection signal to accurately monitor temperature. The maximum absolute and relative sensitivities reached as high as 0.0125 K−1 at 508 K and 1.01% K−1 at 478 K, respectively. The luminous color of this phosphor is sensitive to the temperature, which provides the possibility for visualization of temperature measurement. There was little change in the luminescence intensity of Pr3+, Tb3+ co-doped phosphors after they went through five heating-cooling cycles. It is proved that the multi-phonon relaxation from 3P0 to 1D2 and intermediate charge transfer are responsible to the temperature-dependent luminescence of the phosphors. Optical thermometer based on the current phosphors show the advantages of high sensitivity, high precision and good repeatability. This indicates Pr3+, Tb3+ co-doped phosphors have potential application value in optical temperature sensing field.