We explore the interrelationships between the green 510 nm emission, the free-carrier concentration, and the paramagnetic oxygen-vacancy density in commercial ZnO phosphors by combining photoluminescence, optical-absorption, and electron-paramagnetic-resonance spectroscopies. We find that the green emission intensity is strongly influenced by free-carrier depletion at the particle surface, particularly for small particles and/or low doping. Our data suggest that the singly ionized oxygen vacancy is responsible for the green emission in ZnO; this emission results from the recombination of a photogenerated hole with the singly ionized charge state of this defect.

The ultraviolet photoluminescence of ZnO/ZnGa 2 O 4 composite layer grown by the thermal oxidation of ZnS with gallium was investigated by the time-resolved pho-toluminescence as a function of measuring temperature and excitation power. With increase of excitation power, the D 0 X emission is easily saturated than the DAP emission from ZnO/ZnGa 2 O 4 composite layer, and which is dramatically enhanced as compared with that from pure ZnO layer grown without gallium. The radiative re-combination process with ultra-long lifetime controlled the carrier recombination of ZnO/ZnGa 2 O 4 composite layer. C

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