Fundamental Optical Absorption in Magnesium Oxide

Abstract

The optical absorption and reflectivity of single crystals of MgO and the optical absorption of thin films of MgO, both supported by a LiF substrate and unsupported, have been measured in the energy range from 6 ev to 13.5 ev. Absorption peaks due to impurities were observed at 6.0 ev, 6.3 ev, and 6.9 ev. The room-temperature fundamental absorption and reflectivity spectra are interpreted in terms of an exciton peak at 7.6 ev with a probable second peak at 8.8 ev. Some evidence is present for additional exciton structure on the low-energy side of the first peak. The width of the forbidden energy band in MgO is estimated to be about 8.7 ev. The effects of temperature and internal strains on the absorption spectra are discussed.