Quantitative evidence for the existence of Wannier-Stark levels

Measurements of the conductivity characteristics of CuxS-ZnS:Mn,Cu film heterojunctions provide quantitative evidence for the existence of Wannier-Stark levels. Corresponding peaks in the electroluminescence characteristics are also ascribed to the electron-phonon resonance states by Wannier (1960). It is suggested that temperature effects may be relatively unimportant.