Optical Study on Electronic Structure of Rare-Earth Sesquioxides

Abstract

Reflectivity spectra of nine rare-earth sesquioxide (R₂O₃; R = La, Pr, Nd, Sm, Eu, Er, Tm, Yb and Lu) single crystals have been measured in the photon energy range from 0.5 to 50 eV at 300 K. The fundamental optical absorption has been clarified in connection with the electronic structure of R₂O₃. The absorption due to an intra-atomic optical transition of R 4f → R 5d6s was observed in the same energy region as the charge transfer excitation of {O} 2p → R 5d6s in the energy range of 6–15 eV. The absorption structure of the R 4f → R 5d6s transition and the R 5p → R 5d6s transition are explained by using the crystal field splitting of the 5d band and the multiplet structure of the 4f^n-1 final state in photoemission process. Fine structures due to the absorption of the R 4f → {O} 3s transition in the energy region of the {O} 2p → {O} 3s absorption were observed and also can be explained by the 4f^n-1 final state.