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The photoluminescence properties of ZnO nanoneedle arrays, grown on silicon substrate by electrodeposition, are studied over the temperatures from 10K to 300K. There exist three emission bands in ultraviolet, violet, and green regions, respectively. With increasing temperature, these bands show different temperature dependences: A normal redshift for the ultraviolet emission, S-shaped shift for the violet emission, and blueshift for the green one. The origins of these three bands and their temperature-dependent shifts are explained based on defect levels (zinc interstitial and oxygen vacancy levels) and carrier localization effect at the defect levels in addition to band-gap shrinkage.
Cao et al. (2006) studied this question.