Absorption spectroscopy of Eu3+ ions in CsCdCl3 crystal: an evidence of nonequivalent sites

The polarized optical absorption study of Eu3+ ions in a CsCdCl3 crystal reveals an interesting behaviour in their electronic energy levels. In the crystal the trivalent Eu3+ ions replace the divalent Cd2+ ions; in order to maintain the charge neutrality the Eu3+ ions associate in pairs accompanying one vacancy. Our observation shows that the Eu3+ ions form two types of pair: (i) Eu3+–vacancy–Eu3+; and (ii) vacancy–Eu3+–Eu3+, and the Eu3+ ions feel two different trigonal (C3v) electrostatic crystal fields in these two types of pair. As a result they produce pair-type of absorption spectra for each energy level. The occurrence of two distinct lines corresponding to 7F0→5D0 transition elucidates the presence of two nonequivalent sites in the crystal.