The exciton photoluminescence of zinc oxide is studied in the temperature range 5–300 K. The formation of the exciton emission band profile in the spectra of undoped crystals, high-purity powder, and thin ALD films 4–450 nm in thickness at 300 K and at excitation by a He–Cd laser is analyzed. The effects of the photodesorption and photoadsorption of atmospheric oxygen on the exciton emission spectrum of a ZnO powder in sequential vacuum–air cycles have been studied at room temperature during continuous excitation by a He–Cd laser.