Improved Whispering-Gallery Mode Lasing of ZnO Microtubes Assisted by the Localized Surface Plasmon Resonance of Au Nanoparticles

Improving near-band edge ultraviolet (UV) emission while suppressing defect-related visible emission is of great importance in short wavelength optoelectronic applications of ZnO, especially for UV lasing. In this paper, Au nanoparticles were designed and decorated on ZnO microtubes so as to exhibit suitable extinction spectra matching with the defect emission of ZnO. The UV emission was clearly enhanced along with decrease in the visible emission as the Au nanoparticles were decorated on the ZnO microtube surface. The enhanced stimulated emission from the Au-decorated whispering-gallery microcavity was further investigated systematically through a series of experiments of optimization of the sputtering time to control the Au nanoparticle size and the corresponding optical behaviors. A 10-fold enhancement of the whispering-gallery mode lasing was obtained when the Au sputtering time was set as 7 seconds. The enhancement was explained on the basis of a mechanism of electron transfer process assisted by the localized surface plasmon resonance (LSPR) effect.