Complex Nature of the UV and Visible Fluorescence of Colloidal ZnO Nanoparticles

Time-resolved spectroscopy of colloidal ZnO nanoparticles has been carried out with a laser excitation at 248 nm. UV and visible fluorescence has been analyzed. Except for the known band gap 370-nm and impurity 510-nm emissions, we have found additional continua at ∼300, 430, and 545 nm. These continua were developed in solutions of different composition, with excess Zn²⁺ and OH^- ions, and in function of time. All but 510-nm fluorescence bands exhibit short nanosecond or subnanosecond decays. The green fluorescence at 510 nm originating from 4-nm particles in Zn²⁺-rich solutions is a much longer-lived, 1.0 μs. The band natures are discussed. Cluster size distribution and growth kinetics have been recovered from spectral measurements.