THE LOCAL-FIELD DISTRIBUTION OF GD3-METAL FLUORIDE GLASSES INVESTIGATED BY ELECTRON-PARAMAGNETIC-RESONANCE( IN TRANSITION)

The EPR spectra of Gd3+ in two transition metal fluoride glasses (PZG and PBI) have been extensively studied as functions of temperature, Gd 3+ concentration and microwave frequency (S, X, K and Q bands). The ma rked changes observed in the EPR spectra with temperature and concentr ation imply the existence of pairs of Gd3+ ions. The spectra of isolat ed Gd3+ ions were obtained at low temperature for samples with low Gd3 + doping concentration. Isolated Gd3+ ions are characterized by a fine -structure b(2)(0)-parameter distribution within the range 0.02-0.15 c m(-1). The simulations of these spectra are computed with a Czjzek fin estructure parameter distribution (this solution prohibits the existen ce of axial symmetry sites). It indicates a decrease of the number of geometrical constraints compared to those for Cr3+ and Fe3+ (octahedra l coordination in a fluoride medium), in agreement with the higher Gd3 + coordination numbers. Gd3+-ion sites are found to be more distorted in PZG than in PBI, suggesting that the glass network has an influence on the Gd3+ polyhedron distortion amplitude.