Optical-absorption edge in cadmium stannate selective coatings

Abstract

Cadmium stannate selective coatings have been prepared by a pyrolytic method in which two parts of 0.2M CdCl2⋅5H2O solution in ethyl alcohol and one part 0.2M solution of SnCl4⋅3H2O in acetic acid has been sprayed onto a heated substrate of glass and quartz. The films were transparent in the visible portion of the spectrum and exhibited interference colors. The absorption data is interpreted as being due to an allowed direct transition of energy gap of 2.8 eV and an indirect interband transition of energy gap of 2.2 eV. The absorption coefficient reaches values exceeding 105 cm−1 at the higher photon energies, which is expected for direct allowed transitions.