Optical high temperature sensor based on enhanced green upconversion emissions in Er3+-Yb3+-Li+ codoped TiO2 powders.

The Er3+-Yb3+-Li+ codoped TiO2 powders have been prepared by sol-gel method. The strong enhancement of green and red upconversion emissions were obtained for Er3+-Yb3+ codoped TiO2 by additional Li+ codoping and investigated using 976 nm semiconductor laser diode excitation. The enhanced upconversion emissions by the addition of Li+ resulted from the formation of Li compound with lower crystal field symmetry. The fluorescence intensity ratio (FIR) of green upconversion emissions from the transitions of 2H(11/2) --> 4I(15/2) and 4S(3/2) --> 4I(15/2) of Er3+ in the Er3+-Yb3+-Li+ codoped TiO2 has been studied as a function of temperature in the range of 300-925 K, and the maximum sensitivity was determined to be 0.0025 K(-1). Er3+-Yb3+-Li+ codoped TiO2 material with the highest operating temperature up to 925 K, has higher temperature sensitivity and fluorescence efficiency being a promising candidate for applications in optical high temperature sensor.