Exciton-Assisted UV Stimulated Emission with Incoherent Feedback in Polydisperse Crystalline ZnO Powder

A comparative analysis of the features UV-stimulated emission (SE) various disordered active materials based on ZnO crystallites for a random laser (RL) was carried out. The superlinear increase in intensity UV photoluminescence (PL) band polydisperse nano-micro-crystalline (PNMC) powder at wavelength λ = 387 nm and some narrowing its halfwidth range 20 ÷ 15 with increasing pump indicates lasing incoherent feedback (FB). properties similar PL bands under same conditions thin film containing hexagonal microdisks, as well samples monodisperse nanopowder nanoparticle sizes 100 nm, indicate stimulated radiation coherent feedback. It is shown that, among studied materials, PNMC widely dispersed ranges size from 50 to several microns, which turn, consists nanograins dimensions ~25 most suitable creating room temperature. dominant factor SE transitions exciton–exciton scattering conditions. possible mechanisms this continuous spectrum are discussed. average optical gain coefficient αg RL system estimated αg~150 cm−1.