Optical Study on Electronic Structure of Rare-Earth Sesquioxides

Abstract

Reflectivity spectra of nine rare-earth sesquioxide ( R 2 O 3 ; 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 R 2 O 3 . The absorption due to an intra-atomic optical transition of R 4 f → R 5 d 6 s was observed in the same energy region as the charge transfer excitation of O 2 p → R 5 d 6 s in the energy range of 6–15 eV. The absorption structure of the R 4 f → R 5 d 6 s transition and the R 5 p → R 5 d 6 s transition are explained by using the crystal field splitting of the 5 d band and the multiplet structure of the 4 f n -1 final state in photoemission process. Fine structures due to the absorption of the R 4 f → O 3 s transition in the energy region of the O 2 p → O 3 s absorption were observed and also can be explained by the 4 f n -1 final state.