Influence of codoped Gd3+ ions on the spectroscopic site symmetry of Dy3+ ions in LaF3 single crystals

Abstract

In this paper, a series of Dy³⁺/Gd³⁺ codoped LaF₃ (LDG) single crystals were grown by the Bridgman–Stockbarger method. The influence of non-optically-active Gd³⁺ ions on the luminescence of Dy³⁺ ions in LaF₃ crystals has been explored. Dy³⁺/Gd³⁺ ions substitute for the La lattice in LaF₃, and the local site symmetry of each subset of Dy³⁺ will be distorted from C₂ to lower symmetry C₁. Based on the measured low temperature excitation and emission spectra, it can be proved that Dy³⁺ ions occupy the same kind of spectroscopic site in Dy³⁺/Gd³⁺ codoped LaF₃ crystals, and codoped Gd³⁺ ions do not change the spectroscopic site symmetry of Dy³⁺. When Gd³⁺ ions were codoped into the Dy³⁺:LaF₃ crystal, Dy–Gd clusters were formed around single Dy³⁺ ions to isolate Dy³⁺ ions from each other and weakened the concentration quenching effect of Dy³⁺ ions. When 2 at% Dy³⁺ and 1 at% Gd³⁺ ions were doped into the LaF₃ crystal, the strongest yellow luminescence was obtained under excitation at 349 nm and 453.75 nm, respectively. While doped with 2 at% Dy³⁺ and 2 at% Gd³⁺ ions, the LDG crystal exhibited the strongest mid-infrared fluorescence emission intensity. This concludes that the LDG crystals are suitable for achieving a yellow laser (⁴F_9/2 → ⁶H_13/2 transition) pumped using a InGaN blue laser diode (LD) and a mid-infrared laser (⁶H_13/2 → ⁶H_15/2 transition) pumped using a 1280 nm LD.