Influence of excitation power and doping concentration on the upconversion emission and optical temperature sensing behavior of Er³⁺: BaGd₂(MoO₄)₄ phosphors

Abstract

Generally, the effects of excitation power and dopant concentration on the optical temperature sensing behaviors of rare earth (RE) doped materials based on the fluorescence intensity ratio (FIR) technique are disregarded. In this paper, Er3+: BaGd2(MoO4)4 phosphors with different concentrations were fabricated by the high temperature solid-state reaction method. The results show that the variation of FIR (2H11/2/4S3/2) with excitation power is not only related to the laser-induced heating effect, but also the diverse power-dependences of 2H11/2 and 4S3/2 levels. Consequently, the temperature calibration curves change at different excitation power densities. When the calibration curve obtained at a low power density is applied to estimate the temperature of the object excited at a high power density, a large overestimate of the temperature rise induced by the optical heating effect can be caused. Besides, the temperature sensing sensitivity depends on the Er3+ doping concentration, which increases first with concentration to a maximum and then reduces. The maximal absolute sensitivity is ~110.5 × 10−4 K−1 in 5mol% Er3+: BaGd2(MoO4)4 phosphor, which is among the highest values of RE ions doped phosphors based on thermally coupled levels recorded before.