Optical emission from disordered multi-branched ZnO nanorods formed by catalyst-free growth

We have demonstrated catalyst-free fabrication of multi-branched ZnO nanorods and their interesting optical properties. Under Xe lamp excitation (325 nm), it is found that the ethanol rinsing leads to an obviously enhanced ultraviolet emission at room temperature. Moreover, temperature-dependent emission spectra exhibit an anomalous temperature dependence of the ultraviolet emission intensity. This has been analyzed in terms of the competition between the radiative and nonradiative hopping processes using a model developed for disordered porous semiconductors. With femtosecond pulse excitation (640 nm), two-photon-induced photoluminescence is observed, which is confirmed by the quadratic dependence of the emission intensity on the excitation pulse energy.