玻璃基铅盐量子点的载流子弛豫动力学及其受激辐射研究

Due to the strong quantum confinement effect, lead chalcogenide (e.g., lead sulfide-PbS, lead selenide-PbSe) quantum dots (QDs) in glass matrix (abbreviated as PbS:Glass and PbSe:Glass) represent potential applications in these fields including broad-bandwidth near infrared light sources and QD lasers. The fundamental optical properties and regular recombination mechanisms have been extensively investigated in these glass-based lead salt QDs. Few reports, however, can be accessible about the fast relaxation process related to stimulated emission in this kind of material systems, and furthermore, the issue still remains to be addressed about the limitation of current "bulk" models based on the ideal semiconductor two-level system describing the temperature dependence of the basical optical parameters, such as the lowest excitonic emission energy (i.e. E_(1Se-1Sh), also called Eg) and its full width at half maximum (FWHM), and so on. In this project, the steady-state and transient optical spectroscopy under different experimental conditions (e.g., the change of temperature, the change of excitation densities and/or excitation wavelength under continuous wave (cw) excitation or pulsed mode) will be employed to systematically investigate the key parameters and the complicated relaxation mechanisms in the glass-based lead salt QD material systems. Approaches to enhance the filling factor of lead chalcogenide QDs in glass matrix and to optimize the size distribution of QDs in glass matrix will be optically discussed. By analyzing the influence of the dark-state-related exciton-phonon coupling effect during the carrier relaxation process on the distribution of every exciton states in the excitonic fine structure, the optical "dark" model that is perfectly suitable for the three- or multi-level QD system will be established and represented, in contrast to the traditional semi-empirical expressions that were derived from the ideal bulk semiconductors. Based on these, the carrier fast relaxation process, in particular the fast relaxation dynamics related to stimulated emission in these material systems will be studied, in order to investigate the necessary experimental condition for generating this peculiar process and the related influence factors. Subsequently the originations of stimulated emission and the accompanied "intrinsic" spontaneous emission as well as the regular spontaneous emission will be physically clarified (e.g., either from bright state, or from dark state, or even from free exciton state). These results could provide a brief guideline to pave the way towards the fabrication of QD light sources or lasers based on lead chalcogenide in glass matrix.

量子局域效应显著的玻璃基铅盐（如硫化铅、硒化铅等）量子点在光通讯、量子点光源等领域存在应用前景，其光学性质和常规复合机制已被广泛研究，但与受激辐射相关的快速弛豫过程鲜见报道、且现有'体'模型在描述其关键参数（如第一激子发光峰及其半峰宽）温度相关性时存在一定局限性。本项目拟利用变条件稳态/超快光谱测试手段（如吸收谱、光致发光谱等）对上述量子点体系进行研究，从光学上探讨提高玻璃基铅盐量子点填充因子、优化量子点尺寸分布的有效途径，分析载流子弛豫过程中与激子暗态相关的声子耦合作用对激子布居的影响，建立适用于三/多能级量子点系统的光学'暗态'模型，进而聚焦材料体系的快速弛豫过程、特别是与受激辐射相关的快速弛豫动力学过程，研究产生这一特殊过程的关键实验条件和影响因素，从机制上揭示受激辐射及其伴随的'本征'自发辐射、以及常规自发辐射的物理起源（如亮态、暗态、自由态），为研制玻璃基铅盐量子点激光提供基础。

铅盐量子点（如硫化铅、硒化铅等）具有强的量子局域效应，发光效率显著且其激子带隙红外波段连续可调，是近红外波段连续宽光源和窄带宽光源研制方面的理想材料。相较于广泛研究的胶体基质而言，玻璃基质机械强度高、性质稳定、特别是可以进行光纤拉丝，使得玻璃基铅盐量子点在光纤光源领域具有实际应用前景。目前，有关该材料体系的基本光学性质和常规复合机制已被广泛研究，但与受激辐射相关的快速弛豫过程鲜见报道、且现有‘体’模型在描述其关键参数（如第一激子发光峰及其半峰宽）温度相关性时存在一定局限性，因此，项目主要是利用变条件稳态/超快光谱测试手段（如吸收谱、光致发光谱等）对硫化铅和硒化铅量子点的玻璃基材料体系进行研究，从光学上探讨提高玻璃基铅盐量子点填充因子、优化量子点尺寸分布的有效途径，分析载流子弛豫过程中与激子暗态相关的声子耦合作用对激子布居的影响，建立适用于三/多能级量子点系统的光学‘暗态’模型，进而聚焦材料体系的快速弛豫过程、特别是与受激辐射相关的快速弛豫动力学过程，研究产生这一特殊过程的关键实验条件和影响因素，从机制上揭示受激辐射及其伴随的‘本征’自发辐射、以及常规自发辐射的物理起源（如亮态、暗态、自由态）。.项目研究过程中，通过自己建立的变条件（如温度、稳态光泵浦、变脉冲条件的瞬态光泵浦等）高集成光谱系统，我们获得了玻璃基铅盐量子点的最佳制备条件、实现了基于量子点尺寸分布有序的特殊光纤结构，获得了半峰宽近2um的宽带宽光谱输出、以及特殊泵浦条件下铅盐量子点的超快（25~40ps）受激辐射过程；结合理论分析，我们发现铅盐量子点激子带隙温变关系并不满足经典的Bose-Einstein分布、而是满足Boltzmann的新型量子模型；通过对玻璃基质组分的优化，实验上首次观测到铅盐量子点基态激子的劈裂机制及其弛豫/复合动力学；这些结果将推动基于光泵浦的窄/宽带宽量子点光源材料研制。

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