Biexciton lasing of submicron-sized ZnO particle in a Fabry-Perot cavity.

We have observed the lasing of submicron-sized ZnO particle in a Fabry-Perot cavity at low temperatures. A thin alkali-halide crystal including a small amount of ZnO particles are sandwiched between two quartz plates arranged as a pair of opposite mirrors, that is, a Fabry-Perot cavity. Under low excitation due to a He–Cd laser, emissions of free and bound excitons and their phonon replicas are recognized markedly, while a biexciton emission band appears under high-dense excitation by a pulsed N₂ laser. Biexciton lasing is demonstrated as a narrowed emission by focusing the excitation light beam on an appropriate position being a ZnO particle in the cavity. When a cavity length satisfies the resonant condition, the lasing occurs in the spectral region of the biexciton emission band and with the very small divergence angle. The obtained threshold of excitation-power density is about 0.50 MW/cm². We discuss lasing in terms of stimulated emission caused by population inversion between biexciton and exciton states. [ABSTRACT FROM AUTHOR]