Line narrowing effects and enhanced back scattering from ZnO colloids

The dependence of the fluorescence emission intensity from nano ZnO colloid as a function of incident laser power is investigated. Emission in the near UV region from ZnO particles in diethylene glycol medium is studied using frequency tripled radiations at 355 nm from Nd-YAG laser. The spectrum, which was broad at lower pump intensities, exhibits an increase in the intensity as well as line narrowing above a threshold. The emission occurs in all directions and varies with pumping area. Results indicate the phenomenon of random lasing action due to multiple scattering inside the highly disordered medium. Coherent back scattering experiments confirm multiple scattering and weak localization effects in these samples. These preliminary studies show that colloidal nano ZnO medium is a promising candidate for random lasers. C 2006 Springer Science + Business Media, Inc.