Mj. Lochhead et al., LUMINESCENCE SPECTROSCOPY OF EUROPIUM(III) NITRATE, CHLORIDE, AND PERCHLORATE IN MIXED ETHANOL-WATER SOLUTIONS, Inorganic chemistry, 33(9), 1994, pp. 2000-2003
A detailed study of the luminescence properties of europium(III) nitra
te, chloride, and perchlorate in mixed ethanol-water solutions has bee
n performed. Eu3+ ion concentrations were varied from 0.05 to 0.5 M, a
nd solutions ranging from aqueous to those with an ethanol/water molar
ratio of 57 were investigated. Luminescence spectra and lifetimes hav
e 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. E
uropium nitrate complexes in the ethanol-water solutions containing on
e, two, and three inner-sphere nitrate ions have been observed. Lifeti
mes 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 perchlo
rate ions do not enter the inner coordination sphere. The results of t
his study have particular application to the optical characterization
of the sol-gel process using Eu3+ as a luminescent probe.