Boltzmann thermometer with broadband emission in Mn4+-Doped β-Ga2O3 crystals

Abstract

The luminescence properties of Mn4+-doped β-Ga2O3 are strongly affected by the surrounding crystal field within the [MnO6] octahedral site, which is substitute for GaⅡ site, as determined through the first-principles calculations. The crystal field strength parameters Dq, B, and C are computed, and the Tanabe-Sugano diagram is redrawn for C/B = 6.7. The temperature dependence of the optical spectra is thoroughly examined, revealing the thermal quenching mechanisms involving the thermal activation energy of 2Eg and 4T2g, which are 378 ± 26 cm−1 and 3527 ± 25 cm−1, respectively. In order to further investigate the temperature sensing characteristics, the absolute (Sa) and relative (Sr) sensitivities are obtained. At 303 K, the Sr is determined to be 0.72 %K−1, while Sa is estimated to be in the range of 10−2 (below 0.05 K-1) for the Mn4+ doped β-Ga2O3 thermometers. The thermal resolution δT is demonstrated to be below 0.1 K, surpassing that of traditional Nd3+ and Er3+-doped thermometers. Moreover, a linear relationship between the energy separation ΔE of the thermally coupled 2Eg-4T2g energy levels and the crystal field strength Dq is observed in numerous materials. With this consideration, the nature of the thermometer, along with its Sa and Sr, can be roughly predicted and designed for various operational conditions.