Greben Michael, Vorontsov Dmytro, Dědic Roman, Khoroshyy Petro, Ludvíková Lucie, Valenta Jan
Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czechia.
Institute of Organic Chemistry and Biochemistry of the CAS, Flemingovo nam. 2, 166 10 Prague 6, Czechia.
Nanoscale. 2025 Jan 16;17(3):1602-1615. doi: 10.1039/d4nr03842h.
This study employs a combination of spectroscopic techniques, including absorption, photoluminescence (PL), time-resolved PL kinetics, and transient absorption measurements, to elucidate the dynamics of excited states of oleic acid (OA)-capped colloidal PbS quantum dots (QDs) in toluene with a mean size of approximately 3 nm. PL decay profiles were properly treated employing either fitting or fitting-free models to extract average decay lifetimes and lifetime distributions. Our findings highlight the profound impact of factors such as particle concentration, size, surface treatment, and the surrounding environment on the optical properties of PbS QDs. We observed a notable blue shift in both absorption and emission spectra, along with shorter decay lifetimes, when the concentration of the particles was reduced. This effect was attributed to the dynamics of concentration-selective ligand desorption on the surface of PbS QDs. An observed distinct peak in the spectral dispersion of average lifetimes was linked to an external origin, which was proved by the addition of varying OA volumes, evidently affecting these features. This study also explores how the PL emission of PbS QD suspensions varies with experimental parameters, such as excitation pulse duration and laser power. A gradual reduction in average lifetimes was demonstrated under the modulation of pulse duration from 15 μs to 150 ns, illustrating a transition from continuous-wave (cw) excitation to quasi-pulsed excitation. This transition was shown to be accompanied by a noticeable shift in the lifetime distributions towards shorter durations, as a consequence of various onset components in the QD ensemble. Comparing with truly pulsed excitation, we experimentally confirmed that the amplitude-average lifetime under cw excitation matches the intensity-average lifetime under pulsed excitation. Lastly, we noted linear and nonlinear behaviors in the PL amplitude as a function of excitation power, with the average lifetime remaining nearly constant under pulsed excitation conditions.
本研究采用了多种光谱技术的组合，包括吸收光谱、光致发光（PL）、时间分辨PL动力学和瞬态吸收测量，以阐明平均尺寸约为3 nm的油酸（OA）包覆的胶体硫化铅（PbS）量子点（QD）在甲苯中的激发态动力学。使用拟合或无拟合模型对PL衰减曲线进行适当处理，以提取平均衰减寿命和寿命分布。我们的研究结果突出了颗粒浓度、尺寸、表面处理和周围环境等因素对PbS量子点光学性质的深远影响。当颗粒浓度降低时，我们观察到吸收光谱和发射光谱均出现明显的蓝移，同时衰减寿命缩短。这种效应归因于PbS量子点表面浓度选择性配体解吸的动力学。在平均寿命的光谱色散中观察到的一个明显峰值与外部来源有关，通过添加不同体积的OA证明了这一点，显然这会影响这些特征。本研究还探讨了PbS量子点悬浮液的PL发射如何随实验参数变化，如激发脉冲持续时间和激光功率。在脉冲持续时间从15 μs调制到150 ns的情况下，平均寿命逐渐降低，这说明了从连续波（cw）激发到准脉冲激发的转变。由于量子点集合中的各种起始成分，这种转变伴随着寿命分布明显向更短持续时间的偏移。与真正的脉冲激发相比，我们通过实验证实了cw激发下的幅度平均寿命与脉冲激发下的强度平均寿命相匹配。最后，我们注意到PL幅度随激发功率的线性和非线性行为，在脉冲激发条件下平均寿命几乎保持不变。
