A ratiometric optical thermometer based on Bi3+ and Mn4+ co-doped La2MgGeO6 phosphor with high sensitivity and signal discriminability

In order to study the optical temperature sensing characteristics of phosphors with dual emission centers, a series of La2MgGeO6: Bi3+, Mn4+ phosphors were prepared by solid phase method at high temperature. Due to the different thermal responses of Bi3+ and Mn4+ ions, the fluorescence intensity ratio between the double emission centers is expected to be an effective method for temperature sensing. The structural phase and luminescence properties of the samples were characterized by X-ray powder diffraction, field emission scanning electron microscopy, ultraviolet spectrophotometer and fluorescence spectrometer. According to the structure of La2MgGeO6 host, it can be seen that Bi3+ ion can replace La3+ ion and Mn4+ ion can replace Ge4+ ion because the valence state of ions are the same and the ion radius is close. Through the excitation of ultraviolet light, La2MgGeO6: Bi3+, Mn4+ present two emission bands, which correspond to the Bi3+ ions 3P1 → 1S0 transition (emitting blue light) and Mn4+ ions 2Eg → 4A2g transition (emitting red light) respectively. Moreover, there is energy transfer from Bi3+ ions to Mn4+ ions. Based on the different temperature responses of Bi3+ blue emission and Mn4+ red emission, their fluorescence intensity ratio was used to discuss the temperature measurement characteristics. The absolute sensitivity and relative sensitivity of La2MgGeO6: Bi3+, Mn4+ phosphors reached the maximum value of 1.419% K−1 at 473 K and 3.027% K−1 at 383 K in the temperature range of 293–473 K. Therefore, La2MgGeO6: Bi3+, Mn4+ phosphors are excellent materials for optical temperature measurement.