| Summary: | The nonuniformity of the photoluminescence properties in a single grain scale of (Gd,Y)<sub>3</sub>Al<sub>2</sub>Ga<sub>3</sub>O<sub>12</sub>:Ce (GYAGG:Ce) ceramics was studied by scanning confocal microscopy and fluorescence lifetime imaging microscopy (FLIM). Oxide powders Gd<sub>1.5−x</sub>Ce<sub>x</sub>Y<sub>1.5</sub>Al<sub>2</sub>Ga<sub>3</sub>O<sub>12</sub> (x = 0.005, 0.015, 0.060) were fabricated by co-precipitation and thermally treated. Transparent ceramics samples were obtained in an oxygen atmosphere by pressureless sintering. With increasing Ce concentration in the composition, photoluminescence intensity at the grain boundaries decreases in comparison with the inner volume. Meanwhile, photoluminescence kinetics show the opposite behavior—slower at the grain boundaries and faster at the grain volume. These effects are found to be the most pronounced for the ceramic sample with a Ce content of 0.060 f.u. and are the consequence of an increase in the heterogeneity of the activator distribution at its high concentration in the ceramics. This observation set a limit in the Ce concentration in GYAGG:Ce garnet-type ceramics to reach the high-performing photo-luminescence features.
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