Influence of codoped Gd3+ ions on the spectroscopic site symmetry of Dy3+ ions in LaF3 single crystals†
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 (4F9/2 → 6H13/2 transition) pumped using a InGaN blue laser diode (LD) and a mid-infrared laser (6H13/2 → 6H15/2 transition) pumped using a 1280 nm LD.