Optical properties of ZnO submicron particles grown by using vapor phase transport

Metal-catalyst-free ZnO submicron particles were prepared by using vapor phase transport (VPT). Sol-gel spin-coated ZnO seed layers were employed instead of metal catalysts. Temperature dependent photoluminescence (PL) was carried out to investigate the optical properties of the ZnO submicron particles. The diameter of the hexahedral- and the spherical-shaped ZnO submicron particles was scattered in the range of 100 to 500 nm. Five peaks, at 3.379, 3.364, 3.333, 3.245, and 3.151 eV, corresponding to free exciton (FX), neutral donor bound exciton (D°X), and first-order longitudinal optical phonon replicas of free excitons (FX-1LO), FX-2LO, and FX-3LO emissions, are obtained at low temperature (10 K). The intensities of these peaks decreased and their position red-shifted with increasing temperature. The thermal activation energy for the exciton with increasing temperature in the ZnO submicron particles was found to be about 53.8 meV, and the values of the fitting parameters for Varshni's empirical equation were α = 7.4 × 10^-4 eV/K, β = 680 K, and E_g(0) = 3.380 eV.