Electronic spectra of PrCl63-

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Abstract
The electronic absorption spectrum, electronic Raman spectrum of Cs2NaPrCl6, luminescence spectrum of Cs2NaPrCl6 and Cs2NaYCl6: PrCl6 3-, and the excitation spectrum of Cs2NaYCl6: PrCl6 3- have been studied between room and liquid helium temperatures. Twenty-four transitions from the (3 H 4)Γ1 electronic ground state to excited crystal field components have been observed and assigned from the absorption spectrum. Under excitation in the blue two luminescent states are identified at room temperature and these are assigned to (3 P 0)Γ1 and (3 P 1)Γ4. Twenty-six (of the expected 29) luminescence transitions from (3 P 0)Γ1 have been observed and detailed assignments are given. The moeity mode and lattice mode vibronic structure have been interpreted in detail, with specific reference throughout to the effects of the O h 5 → C 4h 5 phase transition in Cs2NaPrCl6. These lead to (i) a splitting and magnetic dipole intensity enhancement of some zero phonon lines, (ii) different lattice vibration structure and (iii) the appearance of further fine structure for moeity mode vibronic origins in Cs2NaPrCl6. In two transitions of Cs2NaYCl6: PrCl6 3- Fermi resonance leads to appreciable vibronic coupling between electronic levels and these effects are predictably absent in Cs2NaPrCl6. An investigation has been made of the electronic origin intensity due to Pr3+ at defect sites in both materials. The failure of crystal field theory to predict the energy level scheme, and the MD intensities of some transitions is discussed. A comparison has been made with the luminescence and excitation spectra of Cs2NaYBr6: PrBr6 3-. The fourth and sixth degree crystalline field parameters are each about 10 per cent smaller in the latter anion than in PrCl6 3-.