基于高荧光效率窄带隙IV-VI族PbSe量子点掺杂钠铝硼硅酸盐玻璃的近红外波长可调纳晶量子点光纤激射

Nanocrystal quantum dots (QDs), synthesized by the nanochemical method, attract much attention in recent years due to their unique optical and electronic properties, exhibiting desirable prospects for optoelectronic devices in the future. Compared with nanofilms grown by MBE(Molecular Beam Epitaxy), mono-disperse QDs possess advantages on simple synthesized techniques, small yet tunable sizes, and controllable doping concentrations in optical media. Among studies on QDs, one of spotlights has been on II-VI QDs (e.g., CdSe, CdSe/ZnS, CdS etc.) which emit wavelengths in visible region. For IV-VI PbSe, PbS, emitting in near infrared (IR) region, the current studies are focused on observations of the fluorescence absorption/emission of the QDs, for example, studying on size-dependent optical properties of the PbS QDs by combining the QD absorbance spectra with detailed elemental analysis of the QD dispersions, demonstrating coherent and directional emission at 1.55 μm from a PbSe QD electroluminescent device on silicon, and measuring absorption/photoluminescence (PL) spectra of PbSe QDs. However, there has been no report on stimulated emission of PbSe QDs observed in laboratories. In this project, we present for the first time a PbSe QD doped fiber laser based on the nanocrystal doped silicate glass with high PL efficiency and narrow bandgap. Depending on the doped concentration and the QD size, the near IR PL emission of the PbSe QD doped glass will be investigated in details based on the theory about the emitting transition of QD confined levels, the quantum-size effect and the surface polarization effect of QDs. Doping PbSe QDs in glass and making the glass into fibers by using a twice heat treatment and the fiber technique, we will study characteristics of IR absorption-PL spectra of the QD fibers. Applying the fiber-laser technique to configure an all-fiber ring resonator consisted of the QD fiber, WDM (Wavelength Division Multiplexer), and FBG (Fiber Bragg Grating), we will research the population inversion of PbSe QDs in the resonator, the excited emission, and performance of the outputting laser, to realize in laboratory the PbSe QD doped IR laser with low threshold, steady, and working at room temperature. This project developes a novel type of nanocrystal QD doped IR lasers, forming and keeping an advantage in the laser region, and creating new applications of IR lasers in broad regions, e.g., fiber telecommunications, scientific researches, materials engineering, and biomedicines.

提出并实现基于高荧光效率窄带隙IV-VI族PbSe量子点掺杂钠铝硼硅酸盐玻璃的近红外波长可调纳晶量子点光纤激射。 基于量子点约束能级的辐射跃迁理论，利用量子点尺寸效应和介质表面极化效应，通过制备高荧光效率窄带隙PbSe量子点掺杂钠铝硼硅酸盐玻璃，探索其近红外荧光辐射与量子点尺度、数密度之间的关系，发展掺杂玻璃基底中量子点的红外辐射理论。采用二次熔融热处理及光纤拉制技术，制备量子点光纤，研究量子点光纤的吸收－辐射光传输特性。由量子点光纤、波分复用器、光纤光栅等构成全光纤光栅谐振腔，研究谐振腔中PbSe量子点的能级粒子数反转、受激辐射及其输出特性，实验实现1550nm波长、宽频连续可调、低阈值、持续、稳定并可在室温下工作的掺杂硅酸盐玻璃基底PbSe量子点激射。 本项目是掺杂硅酸盐玻璃基底PbSe纳晶量子点激射的首次尝试，可填补激光在近红外特需波长上的空白，形成并保持我国在该领域的领先优势。

首先，采用玻璃熔融法，通过大量实验，优化了在钠铝硼硅酸盐玻璃基底中形成PbSe量子点的热熔融二次退火的基础玻璃配方、方法和热处理条件，得到了具有强荧光辐射、量子点分布均匀、数密度适中、量子点中心粒径~5nm、中心辐射波长位于近红外1.55 m的掺杂硅酸盐量子点玻璃。测量和确定了量子点玻璃的吸收-辐射特性、斯托克斯频移、吸收截面和辐射截面等。其次，结合二次退火和熔融拉丝法，成功拉制出了具有不同直径、不同长度、含不同量子点数密度的量子点光纤，测量了量子点光纤的吸收-辐射谱以及传光特性，确定了具有最大荧光辐射强度的量子点光纤长度、量子点数密度等。然后，实验测量和确定了量子点光纤能产生激射的量子点数密度阈值、泵浦激励阈值、最佳光纤长度以及激射饱和等系列参量，搭建了环形腔全光纤激射实验装置，实现了在1.55 m近红外波段、低阈值、持续、稳定并在室温下工作的量子点光纤激射。进一步，采用计算机建模和数值计算，对实验观测到的现象进行了数值模拟计算，揭示了形成激射的粒子数反转、能级跃迁、量子点吸收谱带蓝移、二次吸收-辐射等在量子点光纤激射中独特现象的本质，解释了量子点光增益及激射形成的机理，使得人们能深刻理解并有可能将其发展成新型的激光器件——量子点光纤激光器。. 通过上述工作，我们顺利完成了本课题的研究任务和目标，获得了系列研究成果。这些成果发展了玻璃基底中量子点的红外辐射-吸收理论，摸索出了量子点光纤的拉制技术和工艺，提出了量子点光纤激射的关键技术参量，实验首次实现了近红外量子点光纤激射，形成了自己独特的发展方向和技术路线。