Infrared-to-visible up-conversion emissions and thermometric applications of Er3+-doped Al2O3

Er3+-doped Al2O3 has been prepared by a sol–gel method, using aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of erbium nitrate [Er(NO3)3·5H2O]. The phase structure of θ-(Al,Er)2O3 phase was obtained for the 0.1 mol. % Er3+-doped Al2O3 at the sintering temperature of 1273 K. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+, were detected by a 978-nm semiconductor laser diode excitation. The temperature dependence of green up-conversion emissions was studied over a wide temperature range of 295–725 K, and reasonable agreement between the calculated temperatures obtained by the fluorescence intensity ratio theory and the measured temperature was obtained, which proved that Er3+-doped Al2O3 has a good potential for the development of high-temperature sensors. It has some advantages compared to glasses due to its higher thermal and mechanical resistance and allows measurements in a large temperature range.