Rarehyphen;earth sesquisulfide crystals have been grown by the Czochralski method. The crystals as grown are opaquenhyphen;type semiconductors. Diffusion of sulfur into semiconducting crystals at 1200deg;C produces transparent insulators having the same crystal structure, lattice parameters, bandgap, and optical spectrum as the semiconductors. Electrical conductivity can be controlled over 12 orders of magnitude by heating crystals in an atmosphere of sulfur. Assignments of Nd3plus;Jlevels observed in the spectrum of insulatorhyphen;type Nd2S3are made with the aid of a calculation of freehyphen;ion wavefunctions and energy levels. A crystalhyphen;field calculation based onOhsymmetry describes the details of the observed spectrum. Even at 4deg;K observed4fthinsp;rarr;thinsp;4ftransitions in Nd2S3are broader than in other Nd3plus;salts and are shifted about 300 cmminus;1to the red of the Nd2O3spectrum.
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