Anomalously small 4f-5doscillator strengths and 4f-4felectronic Raman scattering cross sections forCe3+in crystals ofLuPO4

The oscillator strengths for the 4$f^1$→5$d^1$ transitions of ${\mathrm{Ce}}^{3+}$ in ${\mathrm{LuPO}}_4$ were measured from absorption spectra and compared to calculated values. The measured oscillator strengths were found to be between 2.5 and 20 times smaller than the corresponding theoretical values. In addition, absolute cross sections for electronic Raman scattering between the levels of the 4$f^1$ configuration of ${\mathrm{Ce}}^{3+}$ in ${\mathrm{LuPO}}_4$ were measured and found to be significantly smaller than those expected from theory. Both of these discrepancies may be explained by a reduction in the radial integral, 〈4f‖r‖5d〉, for ${\mathrm{Ce}}^{3+}$ in the solid state. Absorption data obtained from the literature for the 4$f^1$→5$d^1$ transitions of ${\mathrm{Ce}}^{3+}$ in a number of host crystals were used to establish a correlation between the cerium-ion–ligand distance and the reduction in the 〈4f‖r‖5d〉 integral. Effects on electronic Raman scattering cross sections for rare-earth ions in crystals are discussed.