Interrelationships between the green 510nm emission, the free-carrier concentration, and the paramagnetic O-vacancy density were studied, in commercial phosphors, by using photoluminescence, optical absorption, and electron paramagnetic resonance techniques. It was found that the green emission intensity was strongly affected by free-carrier depletion at the particle surface; especially in the case of small particles and/or low dopant contents. The data suggested that the singly-ionized O vacancy was responsible for the green emission of ZnO. This emission resulted from the recombination of a photo-generated hole with the singly ionized charge state of this defect.

K.Vanheusden, W.L.Warren, C.H.Seager, D.R.Tallant, J.A.Voigt, B.E.Gnade: Journal of Applied Physics, 1996, 79[10], 7983-90