Photophysical studies of uranyl complexes—VI. Luminescence spectra of bis(imidazolium) tetrachlorodioxouranate(VI) and bis(2-methylimidazolium) tetrachlorodioxouranate(VI)

Abstract

The photoluminescence spectra of the title compounds have been studied under conditions of high resolution at cryogenic temperatures. The luminescence obtained from the 2-methyl imidazolium salt was found to be well behaved, in that all emission originated from intrinsic uranyl centers and all luminescence decay curves consisted of single exponentials. In contrast, the emission associated with the imidazolium salt was found to originate both from intrinsic uranyl groups and from luminescence traps. The analysis of the luminescence decay curves obtained at cryogenic temperatures revealed that the lifetimes characteristic of the trap emission were significantly shorter than those associated with the intrinsic luminescence. The magnetic dipole allowed origins were found to be split by the rhombic crystal field in each system, but this splitting was observed to be 11 cm −1 or less. All other features present in either spectrum were assigned as vibronic in nature and they represent coupling of the various O-U-O or U-Cl vibrational modes with the pure electronic origins.