Optical properties of single crystals of heavy lanthanide chlorides

Abstract

Studies of heavy lanthanide chlorides may provide important information on the degree of Ln 3+–ligand bond covalency. Monocrystals of LnCl 3·6H 2O, where Ln = Dy, Ho and Er, were grown and spectroscopic investigations were performed at room temperature and at low temperatures down to 4.2 K in order to understand the nature of the Ln 3+–L bonds. The intensities of the electronic lines and the Judd–Ofelt parameters were calculated and compared with those obtained for chlorides of light lanthanides (i.e. Ce(III), Pr(III) and Nd(III)). Room temperature Raman and IR studies of the compounds under investigation were also performed. The relationship between hypersensitivity and covalency is discussed. The change of vibronic coupling strength along the lanthanide ion series does not modify monotonically. The ion-pair interactions are especially visible for the 5I 8 → 5F 2 and 5I 8 → 5F 3 transitions in the HoCl 3·6H 2O low temperature spectra.