THE VIBRONIC SPECTROSCOPY OF PR3+ IN YOCL AND LAOCL

Vibronic transitions in the emission and excitation spectra of Pr3+ in REOCl (RE = Y, La) are reported. The influence of the Pr3+ concentration on the vibronic spectra of Pr3+ is investigated for La1-xPrxOCl (x less-than-or-equal-to 0.1). Concentration enhancement of the vibronic transitions is observed in the excitation spectra only. This phenomenon is ascribed to the superexchange interaction between Pr3+ ions over distances of about 8 angstrom. Evidence that the vibronic transition probability A(VIB) for the H-3(4)(1,2) <-- --> P-3(0) transition of Pr3+ in LaOCl is the same in emission and excitation is presented. The values of A(VIB) for this transition are larger in YOCl:Pr3+ than in LaOCl:Pr3+, and scale with the transition probabilities for the zero-phonon lines. This suggests that the DELTA-process contribution to the vibronic coupling strength dominates. The observed vibronic spectra of Pr3+ in REOCl give increased support for this suggestion.