? were measured. It was pointed out that k exc. = 415 nm is most suitable for measuring the Ho 3? emission beside the Er 3? . The emission of trivalent holmium and erbium ions was measured independently using time-resolved measurements and tentative assignment of luminescence lines to C 3v and C 4v symmetry sites was proposed. Besides for natural fluorite crystal, the transitions between Stark energy levels of lanthanide ions were presented.

Minerals are the source of rare earth elements (REE), and knowledge of the amount of REE in different minerals is necessary for a mineralogist. We propose steady -state luminescence measurement as a quick and non -destructive method for detecting several lanthanide ions present together in the same sample. By using excitation and emission spectra of each 4f ion, rare earth ions could be easily identified.

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.