Photoconductivity of the undoped γ-Ce2S3 and doped γ-[Na]Ce2S3 rare earth sesquisulfides

This paper reports the spectral responses of the steady-state and modulated photoconductivity in undoped γ-Ce2S3 single crystals and pressed powder pellets and the modulated photoconductivity in doped γ-[Na]Ce2S3 (NaCe = 0%, 5%, 12%, and 20%) pressed powder pellets. Their analysis clearly indicates the presence of several levels between the valence and conduction bands. Taking into account the temperature dependence of the spectral responses and the electron lifetimes that could be estimated, a band structure model is proposed for γ-Ce2S3 sesquisulfide, discriminating between defect levels and cerium 4f levels. The influence of the substitution/insertion of sodium on the electronic structure is also discussed.