SPECTROSCOPIC STUDY OF CR3+ IONS IN FLUOROCHLOROZIRCONATE AND FLUOROBROMOZIRCONATE GLASSES

Chromium doped fluorochloro- and fluorobromozirconate glasses have bee n prepared following and modifying standard methods. Electron probe mi croanalysis has been carried out to obtain the actual chlorine and bro mine content of the samples. Optical absorption, steady-state excitati on and emission, luminescence decay, and time-resolved spectroscopy me asurements have been performed in order to study the Cr3+ neighborhood and its optical properties. The results have been interpreted in term s of the progressive substitution of the fluorine ions in the first co ordination shell of Cr3+ by chlorine or bromine ions when their concen tration increases in the glasses. From the analysis of the Fano antire sonances of the (4)A(2g)(F) --> E-2(g)(G), T-2(1g)(G) intraconfigurati onal transitions, up to five Cr3+ environments have been identified an d assigned to: 6 F-, 5 F- and 1 Cl- or 1 Br-, 3 F- and 3 Cl- or 3 Br-, 1 F- and 5 Cl- or 5 Br- and 6 Cl- or 6 Br-. It is deduced that less t han 10% of fluorine ions substitution is enough to have all the Cr3+ i ons hexacoordinated to chlorine or bromine ions. Values for the crysta l field and Racah parameters, the Stokes shift, and the Huang-Rhys fac tor have been estimated from the absorption and luminescence data. The luminescence decay and time-resolved measurements of the T-4(2g)(F) l evel of Cr3+ have been explained by the presence of two opposite mecha nisms: nonradiative transitions and energy transfer processes which pr edominate, respectively, in fluorozirconate and in the most substitute d glasses. (C) 1998 American Institute of Physics.