Unraveling the valence states of manganese ions and the effects of composition variation and post-processing in YGG1--LuGG :Mn garnet optical sensor

Transition metal manganese ions possess multiple valence states, and the change of local coordination environments would seriously influence their energy-level schemes and luminescence properties. Herein, YGG1-x-LuGGx:Mn garnet phosphors were proposed, the valence states of manganese ions and the effects of composition variation and post-processing were investigated systematically. Based on the temperature-dependent photoluminescence (PL) spectral analysis and XPS survey, the existing manganese ions are verified as Mn3+ and Mn4+. And both co-doping of Zr4+ ions and reduction processing can enhance and weaken the emissions of Mn3+ and Mn4+, respectively. Besides, introducing lutetium ions causes a PL blueshift of the two kinds of manganese ions and raises the resistance to thermally induced fluorescence quenching of Mn3+. Moreover, as for LuGG:Mn, the reduction treatment gives rise to a new garnet phase with a larger lattice parameter than that of the LuGG phase because of the existence of the LuGa antisite-defects. Finally, the combination of Mn3+ and Mn4+ ions demonstrates outstanding temperature sensing performance, further verifying the application potential of YGG1-x-LuGGx:Mn phosphors in optical thermometry.