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Laser-selective-excitation and optical-absorption techniques have been used to establish comprehensive sets of energy levels of the F and hydrogenic varieties of the tetragonal symmetry (C4, ) centers in CaF& and SrF&, of three multihydrogenic centers observed in both CaF2 and SrF2 and of the M, X, and M' Nd + cluster centers present in CaF2. Polarization of the various spectral lines of the C4, symmetry centers was used to determine the symmetry labels of all energy levels of these centers up to the F3/2 multiplet, for which crystal-field fits are reported. A noteworthy feature of the Nd + centers is their strong upconversion fluorescence giving a visual perception of "white" emission under selective laser excitation to energy levels of the G, /2 G7/2 multiplets near 17350 cm ' in the yellow. Excitation with a single frequency in this region enables observation of fluorescence from many multiplets up to the D3/2 multiplet near 28 200 cm '. Fluorescence lifetimes for emission from the F3/p multiplet are reported for several centers. The Nd'+ cluster centers show small splittings in their sharper transitions, which is attributed to Nd +-Nd'+ coupling effects.

Raman spectra of single crystals of the layered compounds SbI, and AsI, at 15K are reported. Polarization measurements allow the eight principal peaks to be classified according to symmetry species. Results of a group theoretical analysis based on both molecular and ionic descriptions of the crystal structure are discussed, and assignments of the observed spectra are proposed. Some ramifications of the more ionic nature of SbI, on its spectrum are briefly described.

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