LUMINESCENCE SPECTROSCOPY OF EUROPIUM(III) NITRATE, CHLORIDE, AND PERCHLORATE IN MIXED ETHANOL-WATER SOLUTIONS

A detailed study of the luminescence properties of europium(III) nitrate, chloride, and perchlorate in mixed ethanol-water solutions has been performed. Eu3+ ion concentrations were varied from 0.05 to 0.5 M, and solutions ranging from aqueous to those with an ethanol/water molar ratio of 57 were investigated. Luminescence spectra and lifetimes have been used to identify inner-sphere interactions between Eu3+ and the counterion of the salt in solution. The frequency of the 5D0 --> F-7(0) transition was used to identify different inner-sphere complexes. Europium nitrate complexes in the ethanol-water solutions containing one, two, and three inner-sphere nitrate ions have been observed. Lifetimes of the europium nitrate solutions ranged from 110 to 380 mus, with the longer lifetimes corresponding to solutions with a higher ethanol/water ratio and a larger number of inner-sphere nitrate ions. In the europium chloride solutions, an increased inner-sphere interaction of the chloride ion was observed as the ethanol/water ratio was increased. Lifetimes of these solutions ranged from 110 to 190 mus. Studies of europium perchlorate ethanol-water solutions indicate that the perchlorate ions do not enter the inner coordination sphere. The results of this study have particular application to the optical characterization of the sol-gel process using Eu3+ as a luminescent probe.