PHOTOCONDUCTIVITY OF THE UNDOPED GAMMA-CE2S3 AND DOPED GAMMA-[NA]CE-2-S-3 RARE-EARTH SESQUISULFIDES

This paper reports the spectral responses of the steady-state and modu lated photoconductivity in undoped gamma-Ce2S3 single crystals and pre ssed powder pellets and the modulated photoconductivity in doped gamma -[Na]Ce2S3 (Na/Ce = 0%, 5%, 12%, and 20%) pressed powder pellets. Thei r analysis clearly indicates the presence of several levels between th e valence and conduction bands. Taking into account the temperature de pendence of the spectral responses and the electron lifetimes that cou ld be estimated, a band structure model is proposed for gamma-Ce2S3 se squisulfide, discriminating between defect levels and cerium 4f levels . The influence of the substitution/insertion of sodium on the electro nic structure is also discussed.