Photoluminescence studies of porous ZnO nanorods

Porous ZnO nanorods were prepared by thermal annealing at 700 °C in argon atmosphere. Temperature-dependent photoluminescence (PL) was carried out to investigate the optical properties of the porous ZnO nanorods. The average diameter and density of the pores formed on the surface of the porous ZnO nanorods are 25nm and 1:2 × 10¹⁰ cm_-2, respectively. Six peaks at 3.380, 3.366, 3.338, 3.267, 3.227, and 3.198 eV, corresponding to free exciton (FX), neutral donor bound exciton (D⁰X), first-order longitudinal optical phonon replica of free exciton (FX-1LO), FX- 2LO, FX-3LO, and FX-4LO emissions, are obtained at low temperature (10 K). The FX emission peak energy of the porous ZnO nanorods exhibits an anomalous behavior as the temperature is increased to 100 K. The activation energy of the porous ZnO nanorods is found to be about 8.6 meV, and the values of fitting parameters to Varshni's empirical equation are α = 6 × 10^-4 eV/K and β = 680 K.