Towards deliberate design of persistent phosphors: a study of La-Ga admixing in LuAG:Ce crystals to engineer elemental homogeneity and carrier trap depths

This research investigated the crystal chemical principles related to the incorporation of incompatible atoms into a garnet host lattice. These considerations might be used to guide and drive the design of new garnet compounds with novel properties. The strongly incompatible La atoms at the Lu sites of the Lu3Al2Ga3O12:Ce host lattice served as a research model. This study showed the possibility of designing material properties by exploiting atom mismatches in a crystal lattice. Lu3Al2Ga3O12:Ce0.075% crystals with increasing concentrations of La3+ ions were grown from the melt using the micro-pulling down method. The concentration of La3+ ions above 0.300 at% imposed physical and chemical boundary conditions on the crystallization process. The radial distributions of the chemical elements were studied as a function of the concentration of La3+ ions. It was revealed that La3+ codoping significantly reduced the cross-sectional fluctuation of the Ga and Al atoms. Persistent green-yellow luminescence due to the inter-configurational 5d -> 4f transition of Ce3+ was observed after the blue-light excitation. The LuAGG:Ce0.075%,La0.015% phosphor showed long persistent luminescence for more than 14 h above 0.32 mcd m(-2), the detection limit of a human eye. The thermoluminescence glow curves revealed that the addition of La3+ ions increased the concentration of traps.