Electron paramagnetic resonance determination of the local field distribution acting on Cr3+and Fe3+in transition metal fluoride glasses (TMFG)

Cr 3+ and Fe 3+ ions are used as paramagnetic probes of the local order in diamagnetic transition metal fluoride glasses (TMFG). EPR observations are made at S, X, K and Q band frequencies at different temperatures. It follows from the frequency dependence of the spectra that Cr 3+ and Fe 3+ ions are characterized by a continuous fine-structure parameter distribution in the range 0.06-0.55 cm -1 for Cr 3+ and 0.04-0.33 cm -1 for Fe 3+ . The simulations of these spectra are computed with a fine-structure parameter distribution P(h 2 0 , lambda ) whose expression is determined by analogy with the distribution of electric field gradient P(V zz , eta ) developed by Czjzek considering amorphous solids with random ionic coordination. An excellent agreement between observed and calculated spectra is obtained whatever the frequency band.