Excitation selective thermal characteristics of Mg28Ge7.55−xGaxO32F15.04: Mn4+ and application in single/dual-mode optical thermometry

Abstract Currently, the transition metal ions Mn4+ are fascinating for its potential in diverse luminescence application fields. Herein, a series of Mg28Ge7.55−xGaxO32F15.04: Mn4+ phosphors available for optical thermometry have been obtained by introducing Ga3+ into Mg28Ge7.55O32F15.04: Mn4+. It is noteworthy that the phosphors show excitation selective thermal characteristics with temperature changing from 303 to 473 K, i.e., decreasing (270–340 nm/405–435 nm), essentially unchanged (356–378 nm), and increasing (445–500 nm), respectively. The emission intensity of anti-Stokes and Stokes peaks of Mg28Ge6.35Ga1.2O32F15.04: Mn4+ show inverse trends under the same excitation, which imply the application potential of the phosphor in single-mode optical thermometry. The relative sensitivity (Sr) of the single-mode thermometer reached 0.68% K−1. In addition, the Eu2+/Mn4+ dual-mode optical thermometer has also been realized by taking advantage of the significantly different thermal quenching characteristics of Mg28Ge6.35Ga1.2O32F15.04: Mn4+ and Ba2Mg(PO4)2: Eu2+ under the same 365 nm excitation. The maximum Sr value of Eu2+/Mn4+ dual-mode thermometer was 1.38% K−1. This work not only indicates Mg28Ge6.35Ga1.2O32F15.04: Mn4+ can be a promising candidate for optical thermometry, but also expands new horizons with the topological composite pathway toward rational designing and perfecting dual or even multi-mode thermometers.