Mechanism for Size Dependence of Light Emission From ZnO Nanocrystallites

Broadband light emission of different sized ZnO nanoparticles (17 nm to 300 nm) has been measured under picosecond laser excitation. Each spectrum consists of three Gaussian components including one emerging inside band-gap. Such inside band-gap band shows a clear dependence of the weighted intensity on the sizes of nanoparticles. Originated from our simplified one-dimensional (1D) model it has been qualitatively deduced that such size dependence match with the surface-state modified band structure. Additionally, a critical grain size as 110 nm for surface states recombination of ZnO nanoparticles has been found experimentally.