High-purity upconversion output color and excellent optical thermometry performance of lanthanide-doped Ba3Y4O9

Temperature detection based on the fluorescence intensity ratio (FIR) has been considered to be a promising technique for non-contact temperature measurement. Unfortunately, the FIR-based temperature sensor materials generally show low temperature sensitivity because of the narrow energy gap between the thermally coupled energy levels. In this work, lanthanide-doped Ba3Y4O9 (BYO) upconversion luminescent materials were synthesized in order to explore their potential application in optical thermometer. The crystal structure of the present samples was investigated by XRD and further refined by the Rietveld method, which indicate that the dopant ions successfully enter the host lattice by occupying Y3+ sites. Excited by 980 nm, BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ present high-purity green and blue output colors, respectively. Based on the analysis of emission intensity ratio and pump-power dependence, the upconversion emission mechanisms are systematically investigated. Subsequently, the temperature sensing performances of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ based on FIR technique are evaluated in the temperature range of 298-573 K under 980 nm excitation. Owing to the different temperature-dependent behaviors of different emission bands and larger energy gaps, the present materials display high sensitivity, good repeatability and excellent stability. The maximum absolute sensitivity of BYO:Ho3+/Yb3+ and BYO:Tm3+/Yb3+ reach as high as 79.62 x 10(-4) K-1 and 193.51 x 10(-4) K-1, respectively. Among them, the highest sensitivity of BYO:Tm3+/Yb3+ is far higher than those of other optical temperature sensors using the thermally coupled levels based on FIR technique. The results indicate that the present materials are promising for application as optical thermometer in non-contact temperature detection, and using FIR of F-5(1)/(5)G(6) and F-5(2,3)/K-3(8) multiplets (Ho3+), and( 3)F(2,3)/(1)G(4) (Tm3+) are feasible methods for accurate temperature detection.