Optical properties of crystals of cuprous sulphides (chalcosite, djurleite, Cu1.9S, and digenite)

Thin crystals of chalcosite, djurleite, Cu1.9S, and digenite have been prepared and their absorption and reflection spectra measured with polarized light between 400 and 1200 nm using an integrating microspectrophotometer. The spectra were worked out in terms of the absorption coefficient and the refractive index. The variation of the absorption coefficient with photon energy has been expressed quantitatively in terms of two types of simple expressions, representing absorption by free carriers and direct and indirect band-to-band transitions. Chalcosite crystals were prepared by topochemical reaction from thin single crystals of CdS having the c-axis in plane. The other phases were obtained by controlled extraction of copper from chalcosite at room temperature, leaving the sulphur lattice intact.