Luminescence and energy migration in the garnet Gd3Li3Te2O12 doped with several rare earths and uranium

Energy transfer phenomena have been observed by activating the garnet host-lattice Gd3Li3Te2O12 with Eu3+, Dy3+, Tm3+, and U6+. Eu3+ acts as an effective trap for Gd3+ excitons. Even at very low europium concentrations emission from Eu3+ ions can be observed showing both energy migration among the Gd3+ ions and efficient transfer to Eu3+. Also Dy3+ is an effective activator for Gd3+ excitons, transfer being possible both from the Gd3+ 6I and 6P levels. Tm3+ is not very effective in picking up energy from the Gd3+ sublattice. The weak transfer occurs mainly from the Gd3+ 6I levels which are in close resonance with the Tm3+(3P) levels. U6+, occupying Te6+ sites in the host-lattice, is a very effective trap for Gd3+ excitons. Even very low (≤10 ppm) uranium concentrations are sufficient to pick up almost all excitation energy from the Gd3+ sublattice. The spectral data indicate a high energy transfer probability from Gd3+ to U6+ ions, based to a large extent on an exchange interaction.