Abstract
Abstract Polarized absorption spectra of Pr+3 in LaCl3 and LaBr3 as well as in PrCl3 and PrBr3 were observed. In crystals with 1 mol. % doping generally only the pure electronic transitions are seen. In more concentrated crystals, satellites lying close to the electronic transitions appear, which are interpreted as being due to vibronic transitions. The theory of vibronic transitions for the dilute salt is developed and it predicts a spectrum very similar to that of the pure salt. This is in agreement with experiment. Approximations valid when the optical phonon branch energies are relatively independent of k lead to factor group selection rules. These selection rules are found to be consistent with the observed spectra with a few exceptions which are readily explained. Tentative identifications of crystalline vibrational modes are made from a consideration of: 1 polarized vibronic spectra and selection rules; 2 frequency shift in the comparison of LaCl3 and LaBr3 spectra; 3 far infrared data of B uchanan , M urphy and C aspers .(1) The difference between longitudinal and transverse frequencies of an optical phonon branch is discussed.
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