Ultraviolet luminescence of epitaxial zinc oxide films subjected to one- and two-photon excitation

A study was made of ultraviolet luminescence emitted from epitaxial zinc oxide films as a result of radiative annihilation of A (n =1) excitons and simultaneous emission of several longitudinal optical phonons after one- and two-photon excitation. Stimulated emission was observed at the frequencies of phonon replicas when the excitation was of the two-photon kind. The results demonstrated the possibility of constructing a tunable near-ultraviolet laser from an epitaxial ZnO film subjected to two-photon pumping.