Vibronic intensities in the optical absorption spectra of Pr3+ in Cs2NaPrxY1−xCl6: concentration and temperature dependence

The 3H4→3P0 transition in the absorption spectra of Pr3+ in the hexachloroelpasolites Cs2NaPrxY1−xCl6 (x = 0.1 to x = 1) have been measured from 300 to 10 K. The electronic spectra are dominated by electric-dipole allowed vibronic origins enabled by Herzberg-Teller coupling. The two odd parity vibrations of the [PrCl6]3− ion (ν3 and ν4) appear strongly in the vibronic sidebands and are accompanied by weaker lattice vibrations. The small change in the oscillator strength of the vibronic transitions is readily accounted for by the change in lattice parameter with x. There is no evidence for cooperative effects.