Spectral studies on erbium doped potassium lithium tantalate niobate single crystal grown by the step-cooling technique

An erbium doped K_0.603Li_0.397Ta _0.428Nb_0.572O₃ single crystal was grown by the step-cooling technique. The crystal has a tetragonal tungsten bronze-type structure at room temperature with a Curie temperature of 303°C. There are Er ions characteristic absorption bands around 449, 485, 521, 550, and 652 nm in the visible absorption spectrum. Upconversion fluorescence spectra and power dependence centered at 527 nm, 548 nm, and 660 nm under 975 nm excitation were measured at room temperature. Decay lifetimes of the 548 nm and 660 nm emission bands are 281 μs and 420 μs, respectively. The lifetime of the 548 nm emission corresponding to the transition of ⁴S_3/2 → ⁴I_15/2 is ten times the lifetime of the same transition of Er³⁺ in LiNbO₃ crystal and twice in KYb(WO ₄)₂ crystal. The crystal might become a promising upconversion laser material. The upconversion mechanism of Er³⁺ in the sample was discussed based on decay curves and pump power dependence analyses in this work.