Contribution of Excitons to the Edge Luminescence in Zinc Oxide

The photoluminescence of "pure" Zn0 at 77°K has been investigated. Multiple-emission maxima, both "intrinsic" and "extrinsic," have been observed in the near ultraviolet. Narrow emission bands (half-widths ≤3 Å) near 3690 Å are ascribed to the annihilation of bound (impurity) excitons. A broad asymmetrical band (half-width $\approx 22$ Å) near 3747 Å is shown to be closely characterized by theory of the annihilation of free (intrinsic) excitons with the simultaneous emission of longitudinal optical phonons. Multiphonon emission bands, separated by approximately the energy of the longitudinal optical phonon, are observed at longer wavelengths. An emission band near 3677 Å is suggested to originate from the "direct" annihilation of free (intrinsic) excitons.