Optical absorption of Cu₂O in the near infrared and the role of metallic inclusions

Abstract

We have measured the optical absorption characteristics of copper oxide single crystals in the range from 1.1 to 2.0 eV. The crystals were annealed at various oxygen pressures at high temperatures and quenched to room temperature. A major, broad, previously unknown absorption peak was found at 1.6 eV which we relate to the formation of copper inclusions in the oxide. Although experimental data on thin copper films agree with our assumptions, we cannot reconcile our results with scattering theory of small metal spheres embedded in a dielectric. Agreement between scattering theory and optical absorption may be achieved for nonspherical particles for which as yet no other experimental evidence exists.