Spectroscopic study of Cr3+ ions in fluorochloro- and fluorobromozirconate glasses

Chromium doped fluorochloro- and fluorobromozirconate glasses have been prepared following and modifying standard methods. Electron probe microanalysis has been carried out to obtain the actual chlorine and bromine content of the samples. Optical absorption, steady-state excitation and emission, luminescence decay, and time-resolved spectroscopy measurements have been performed in order to study the Cr3+ neighborhood and its optical properties. The results have been interpreted in terms of the progressive substitution of the fluorine ions in the first coordination shell of Cr3+ by chlorine or bromine ions when their concentration increases in the glasses. From the analysis of the Fano antiresonances of the (4)A(2g)(F) --> E-2(g)(G), T-2(1g)(G) intraconfigurational transitions, up to five Cr3+ environments have been identified and 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 than 10% of fluorine ions substitution is enough to have all the Cr3+ ions hexacoordinated to chlorine or bromine ions. Values for the crystal field and Racah parameters, the Stokes shift, and the Huang-Rhys factor have been estimated from the absorption and luminescence data. The luminescence decay and time-resolved measurements of the T-4(2g)(F) level of Cr3+ have been explained by the presence of two opposite mechanisms: nonradiative transitions and energy transfer processes which predominate, respectively, in fluorozirconate and in the most substituted glasses. (C) 1998 American Institute of Physics.