Vacuum ultraviolet 4ƒ^95d → 4ƒ^10 interconfigurational transitions of Ho^3+ ions in LiLuF_4 single crystals

The laser-induced fluorescence spectrum (LIF) of LiLuF4:Ho3+ single crystals pumped by a molecular F2 pulsed-discharge laser at 157.6 nm is obtained in the vacuum ultraviolet (VUV) and UV regions of the spectrum. The observed transitions originate from the levels and the edge of the 4f95d electronic configuration, and they are assigned to the 4f95d→4f10 interconfigurational transitions. The LIF spectra for the dipole-allowed transitions can be explained provided that phonon trapping of the lattice vibrations is taking place within the Stark components of the 4f95d electronic configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. We observed five main transitions between the ground level 5I8 of the 4f10 electronic configuration and the Stark components of the levels of the 4f95d electronic configuration in the spectral range between 125 and 150 nm, and we observed four main spin-forbidden transitions in the spectral range from 153 to 170 nm.