Optical Spectrum of Single-Crystal Nd2S3

Abstract

Rare‐earth sesquisulfide crystals have been grown by the Czochralski method. The crystals as grown are opaque n‐type semiconductors. Diffusion of sulfur into semiconducting crystals at 1200°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 Nd³⁺ $J$ levels observed in the spectrum of insulator‐type Nd₂S₃ are made with the aid of a calculation of free‐ion wavefunctions and energy levels. A crystal‐field calculation based on $O_h$ symmetry describes the details of the observed spectrum. Even at 4°K observed $\text{4f\hspace{0.17em}→\hspace{0.17em}4f}$ transitions in Nd₂S₃ are broader than in other Nd³⁺ salts and are shifted about 300 cm⁻¹ to the red of the Nd₂O₃ spectrum.