Highly-efficient double perovskite Mn4+-activated Gd2ZnTiO6 phosphors: A bifunctional optical sensing platform for luminescence thermometry and manometry

Remote temperature and pressure monitoring provides new and exciting chances to explore the variation of luminescence properties of compounds under extreme conditions. Herein, series of Mn4+-activated, double perovskite Gd2ZnTiO6 phosphors were prepared to develop novel, bifunctional sensors of temperature and pressure. Upon 345 nm excitation, bright red emission originating from Mn4+ is generated, and its intensity is affected by doping content, where the optimal intensity is achieved at 0.3 mol% of Mn4+ doping. The determined concentration quenching mechanism is mainly governed by a dipole-dipole interaction. The internal and external quantum efficiencies of the synthesized phosphors are as high as 95.6% and 83.2%, respectively. Besides, the crystal-field strength and nephelauxetic effect are theoretically discussed to identify their impacts on the emission characteristics of Mn4+. Furthermore, via analysing the temperature-dependent emission bandwidth and lifetime, the thermometric properties of the resultant phosphors are explored, and the maximum relative thermal sensitivities for the Gd2ZnTiO6:Mn4+ phosphor with optimal doping are 0.34% and 2.43% K-1 at 423 K, respectively. Additionally, the influence of pressure on the luminescence performance of the studied phosphors is investigated. When pressure increases, a significant red-shift of the emission band is observed, showing the pressure sensitivity is as high as 1.11 nm/GPa. Notably, during the compression and decompression processes, the prepared phosphors possess stable phase structure, which is confirmed by the pressure-dependent Raman spectra. These results suggest that the highly-efficient double perovskite Mn4+-activated Gd2ZnTiO6 phosphors are promising bifunctional luminescent platforms, for both luminescence thermometry and manometry applications.