Dual-mode optical thermometry based on Bi3+/Sm3+ co-activated BaGd2O4 phosphor with tunable sensitivity

A series of the BaGd2O4:Bi3+, Sm3+ phosphors with dual emission centers were prepared by high-temperature solid-phase method. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, fluorescence spectroscopy, lifetime decay curve, and variable temperature emission spectroscopy were used to systematically study the structure, luminescence performance, and temperature characteristics of the samples. At ultraviolet stimulation, BaGd2O4:Bi3+, Sm3+ phosphors exhibit broad band blue emission, corresponding to the transition of Bi3+ from 3P1 level to 1S0 level, and sharp red characteristic emission, corresponding to the Sm3+ ions’ energy level transition from 4G5/2 to 6Hm/2(m = 5,7,9). In addition, the Bi3+ and Sm3+ ions’ emission positions in BaGd2O4 host are ideally separated. Based on the property, FIR can be employed to test the difference of temperature in response to performances between Bi3+ blue light emission and Sm3+ red light emission. For the Bi3+/Sm3+ co-doped system, it is found that their relative sensitivity gradually decreases with the increase of the Sm3+ ion concentration, the value of maximum can reach 1.105%K−1, which makes it possible to synthesize temperature sensing materials with adjustable sensitivity. The relative sensitivity can also be calculated by experiments related to the decay lifetime, and the value of maximum obtained was 1.662%K−1. Thus, BaGd2O4:Bi3+, Sm3+ systems are superior non-contact optical pyrometer materials with ultrahigh temperature sensitivity and superhigh signal discriminability.