For the first time ever, the luminescence spectra of Cr 3+ centers in two chlorite crystals are presented. Chromium ions occupy the strong crystal-field site M4 in the brucite sheet and the intermediate crystal-field site in the inner octahedral sheet for purple and green chlorite, respectively. We discuss the influence of an effective positive charge on the Cr 3+ ion and an effective negative charge of ligands on the differences in the values of the Dq and B parameters. It is concluded that the presence of Fe 2+ ions and other point defects, as well as concentration quenching, causes the very short luminescence lifetimes of chromium ions.
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Czaja et al. (2013) studied this question.
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