CRYSTAL-GROWTH AND OPTICAL-PROPERTIES OF RARE-EARTH SESQUISELENIDES AND SESQUISULFIDES - NEW MAGNETOOPTIC MATERIALS

Single crystals of stoichiometric rare earth selenides and sulphides w ere grown by various techniques, the transparent rare earth selenide c rystals being grown for the first time. Optical properties of the grow n crystals were investigated. Transmission and reflection spectra show that rare earth selenides are wide gap (E(g)=2 eV) semiconductors wit h a wide range of transparency 0.6-33 mu m and high refractive index ( n=3). Strong Faraday rotation was found for selenides. Cerium selenide has the highest value of rotation, approaching a record value for par amagnets. Analysis of the dependence of the band gaps of sulphides and selenides on the atomic number of the lanthanide led to the conclusio n that the 4f levels of cerium in sesquichalcogenides are located insi de the band gap.