Influence of Na+, Ca2+ and R3+ (R = Y, Lu, Gd) co-doping on the spectroscopic properties of Pr3+:BaF2 single crystal

Abstract

A series of high quality x%Pr³⁺:BaF₂ (x = 0.6, 1, 2); (1%Pr³⁺, 2%Na⁺):BaF₂; (1%Pr³⁺, y%Ca²⁺):BaF₂ (y = 3, 5) and (0.6%Pr³⁺, 10%R³⁺):BaF₂ (R = Y, Lu, Gd) crystals were grown by temperature gradient technique (TGT). The Raman spectra, absorption spectra, fluorescence spectra, and fluorescence decay lifetime were measured. XRD patterns indicate that the as-synthesized samples are pure BaF₂ phase. The absorption cross-section of Pr³⁺ ions in the BaF₂ matrix can be greatly improved by co-doping R³⁺ ions, while improvement by Na⁺ and Ca²⁺ ions is marginal. The fluorescence characteristic of Pr³⁺ ions can be effectively regulated by co-doping Na⁺, Ca²⁺, R³⁺ (R = Y, Lu, Gd) ions of different valence states. When R³⁺ ions are introduced, the fluorescence spectra show the strongest orange emission and the CIE chromaticity coordinates of Pr³⁺ ions are also in the orange region. When single-doped Pr³⁺ ions and Na⁺ or Ca²⁺ ions are introduced, the fluorescence lifetime of the ³P₀ level is double exponential decay, and the short lifetime is the main proportion. However, the fluorescence centers tend to homogeneous and stable by R³⁺ ions co-doping and the fluorescence lifetime exhibits single-exponential decay, which is fitted to 49.7 μs, 47.8 μs and 49.6 μs of (0.6%Pr³⁺, 10%R³⁺):BaF₂ (R = Y, Lu, Gd), respectively. All the results show that (Pr³⁺, Gd³⁺):BaF₂ and (Pr³⁺, Na⁺):BaF₂ are excellent laser gain media for high-efficiency orange and red laser operation.