ZnO纳米颗粒受激发射的时间分辨特性

Time-Resolved Photoluminescence of Stimulated Emission from ZnO Nanoparticles

在飞秒脉冲激光激发下,观察到了均匀沉积法获得的ZnO纳米颗粒的受激辐射现象,并从频域和时域两方面研究了ZnO纳米多晶的室温激射特性。氧化锌纳米颗粒中出现激子-激子散射导致的激射阈值为7.2 GW.cm-2,激射模式类似于F-P谐振腔模式,时域谱则表现为寿命曲线中出现快速衰减成分。与荧光的时间衰减曲线不同,P带时间衰减具有对称结构,高斯拟合结果只有几个ps,接近条纹相机的时间分辨率极限。研究ZnO纳米颗粒的受激发射与激光特性对揭示ZnO晶体的内部结构和激子激发态的性质、激光产生的机理等有重要意义。

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 recombina- tion, and the threshold excitation intensity was 7. 2 GW · 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 fur- ther 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.