Absorption and Fluorescence Spectra of Tm³⁺ in YVO₄ and YPO₄

The optical absorption spectra of trivalent thulium in single crystals of YVO 4 and YPO 4 were measured in the range from 5000 to 29000 cm −1 including the Zeeman effect at 85, 4.2, and 2K. Furthermore the fluorescence spectrum in YVO 4 between 19000 and 25000 cm −1 was investigated. Some special features of the spectra can be explained by the assumption that in several cases the crystal field eigenfunctions consist essentially of one free ion Ψγ J M . From the splitting of Tm 3+ in YVO 4 values for the crystal field parameters were determined.