Upconversion luminescence in langatate ceramics doped with Tm3+ and Yb3+

Ultraviolet (365 nm, 1D2→3H6), blue (480 nm, 1G4→3H6), red (650-660 nm, 1G4→3F4+3F2,3→3H6), and infrared (800 nm, 3H4→3H6) upconversion luminescence, were obtained for the first time in La3Ga5.5Ta0.5O14:Tm:Yb ceramic sample, synthesized by solid-state reaction, pumped at 973 nm. Yb3+→Tm3+ energy transfer processes accounting for population of the emitting levels of Tm3+ are discussed. Also, the back-transfer process Tm3+→Yb3+ was observed. The decay curves of the metastable levels 1D2, 1G4, 3H4, and 3F4 of Tm3+ and 2F5/2 of Yb3+ were analyzed. The cross-relaxation microparameters of Tm3+ were found. The efficiency of the Yb3+→Tm3+ transfer was estimated.