Level Assignment for Various Photoluminescence Bands of Tm^<3+> Ions in LiYF_4 Crystal

Photoluminescence and excitation spectra of Tm ions in LiYF_4 crystal have been investigated at 12 K. The luminescence is investigated under excitation with lights of 780, 680, 460, 360 and 266 nm wavelengths. The emission bands are observed to depend on the excitation wavelength, e.g. two emission bands at 1229 and 1201 nm are generated by the 460 nm excitation but not by 780, 680, 360 and 266 nm excitation. Comparing the emission spectra with the excitation spectra for the IR and visible emissions, we suggest the level assignment for the observed luminescence bands including the 288 and 286 nm UV emission bands