Spectroscopy and calculations for ${4f}^N\to {4f}^{N-1}5d$ transitions of lanthanide ions in ${\mathrm{LiYF}}_4$

Excitation spectra of transitions between the ${4f}^N$ and ${4f}^{N-1}5d$ configurations of ${\mathrm{Ce}}^{3+},$ ${\mathrm{Pr}}^{3+},$ and ${\mathrm{Nd}}^{3+}$ in ${\mathrm{LiYF}}_4$ have been measured using UV and VUV synchrotron radiation. Both zero-phonon lines and vibronic bands are observed. The energy levels and transitions intensities are reproduced by a theoretical model that extends established models for the ${4f}^N$ configuration by including crystal-field and spin-orbit interactions for the $5d$ electron and the Coulomb interaction between the $4f$ and $5d$ electrons.