Second Class Exciton Structure in Stannic Oxide

Abstract

A sharp line series has been found at the beginning of the fundamental optical absorption spectra of SnO 2 below 80°K for light polarized E ⊥ c . The series is identified as being a second class exciton structure, since it satisfies a hydrogen-like series relation beginning with n =2 quantum state and, in addition, is followed by a continuum spectrum with absorption coefficient varying as ( h ν- E gap ) 3/2 . The results of Zeeman effect measurements are consistent with group theoretical predictions based on a crystal field-split valence band of oxygen 2 p functions and a crystal field-split conduction band of Sn 5 s functions, both having their extrema at k =0. By a quantitative comparison with an anisotropic-exciton-mass formalism, the effective Rydberg constant, the band gap energy and the anisotropic exciton-reduced-masses are estimated as 0.0345 eV, 3.5969 eV (at 1.8°K) and µ x =0.33 m 0 , µ z =0.30 m 0 , respectively.