[Time-resolved photoluminescence of stimulated emission from ZnO nanoparticles]

The detailed room-temperature stimulated emission including its optical characteristics from nanosized ZnO particles prepared by homogenous precipitation method was investigated by time-resolved spectroscopy both from the frequency domain and time domain. As the excitation power was increased, sharp lasing peaks with the full width at half maximum less than 0.5 nm, similar to the FP lasing mode resonator mode, emerged rapidly from the emission spectra. Additionally, a narrow emission line intensity increased rapidly with increasing the excitation intensity, which was due to an exciton-exciton collision recombination, and the threshold excitation intensity was 7.2 GW x cm(-2). Upon higher excitation power, the lasing mechanism switched to electron-hole plasma (EHP). The EHP emission in the case of a higher excitation intensity appeared at a lower energy side of the E-E emission and replaced completely the E-E emission at the higher intensity. The EHP emission was red-shifted when further increasing the excitation intensity, compared to the E-E emissions. It was demonstrated that the red-shift of the EHP peak was attributed to the relevant band gap renormalization effect in the electron-hole plasma regime. At the same time, the emission lifetime was drastically reduced. Time-resolved spectrum of P band suggested a Gaussian-like decay time with only a few tens of picoseconds, compared to 2 ps, which is the limit of streak camera time resolution. The dynamic processes of lasing behavior and characteristics of the lasing emission in ZnO nanoparticles could be valuable and provide the information on crystal quality, exciton and lasing action in ZnO.