Green upconversion luminescence in Er³⁺:BaTiO₃ films

Green upconversion emissions at 548 and 528 nm have been obtained from sol-gel derived nanocrystalline Er³⁺:BaTiO₃ films under 980 nm excitation. The green emissions are attributed to the ground-state (4/_15/2) -directed transitions from ²H_11/2 (528 nm) and ⁴S_3/2 (548 nm) of Er³⁺ ions. Analysis of the temporal evolution of the emission at 548 nm shows that both excited state absorption of individual ion and energy transfer between the two neighboring ions contribute to the upconversion emissions in Er³⁺ (3 mol %):BaTiO₃ film. The lifetime of the dominant emission at 548 nm is about 90 μs.