The optical spectroscopic properties of Mn5+ doped into ten host lattices have been studied. The influence of both chemical variation [phosphates(V), arsenates(V), and vanadates(V)] and structural variation (spodiosites, apatites, and Li3PO4-type salts) on the luminescence properties is studied in detail. By varying the host lattice, the position of the sharp luminescence band can be varied from 8300 to 8960 cm−1. Excited state splittings, luminescence lifetimes, and sideband intensities are correlated with the geometrical distortion of the MnO3−4 tetrahedron. In all the host lattices, the luminescence originates from the 1E excited state at all temperatures. It is essentially unquenched at room temperature in apatite and Li3PO4-type lattices, whereas in spodiosites up to 90% of the luminescence may be quenched at room temperature.

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The absorption, excitation, and luminescence spectra of MgAI,O, : Co2+ are studied. The spectra are measured at temperatures from 4.2 to 300 K. From the low temperature absorption spectra the Racah parameters and energy level assignments are derived. Three emission bands are found, one in the visible and two in the infrared region. The visible one is assigned to the "T,("P) --f "A, transition. In the infrared the 4T,(4P) + "T, and 4T,(4P) + "T,("F) transitions are observed. It is shown that the luminescence originates from different Co2+ sites situated in a weak ligand field. The luminescence decay curves are measured in a wide range of temperatures (from 4.2 to 300K) and found to be non-exponential. The temperature dependence of luminescence and the mechanism of non-radiative deactivation of the "T, ("P) level is briefly discussed.

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