Effective Density of Phonon States for NdCl3from Vibronic Spectra and Applications to Ion-Lattice Interactions

An effective density of phonon states of Nd${\mathrm{Cl}}_3$ has been extracted from the vibronic spectra accompanying several electronic transitions of ${\mathrm{Pr}}^{3+}$ and ${\mathrm{Nd}}^{3+}$. The derived $g^{*}\left(\omega \right)$ has a very similar structure for all parent electronic transitions. Anomalies in the vibronic spectra occur for certain optical phonons, and are ascribed to interactions of pairs of ${\mathrm{Nd}}^{3+}$ ions via the phonon field. Use is made of the derived $g^{*}\left(\omega \right)$ in explaining various features of phonon-induced relaxation.