J. Sytsma et al., 2-PHOTON EXCITATION OF THE 4F1 -] 5D1 TRANSITIONS OF CE3+ IN LUPO4 AND YPO4, Physical review. B, Condensed matter, 47(22), 1993, pp. 14786-14794
Two-photon excitation (TPE) spectra of the 4f1 --> 5d1 transitions of
Ce3+ in LuPO4 and YPO4 have been investigated. For Ce3+ in LuPO4, tran
sitions to four out of the five 5d1 levels are observed as zero-phonon
lines. The symmetry properties of the levels were obtained from the p
olarization dependence of the TPE signals, Measurements on Ce3+ in YPO
4 support the given assignments. Although a crystal-field fit yields a
satisfactory rms energy deviation, an unrealistic value of the spin-o
rbit coupling parameter, zeta5d1, is obtained. The vibronic coupling a
ppears to be smaller than for the single-photon absorption spectra, an
d the vibronic bands show a rich structure. There are striking differe
nces between the energies and the relative intensities of the vibronic
lines and the associated zero-phonon lines. The vibronic coupling is
also found to be strongly dependent on the Ce3+ concentration.