用于白光器件的高效石墨烯量子点发光材料研究

Making white-light light-emitting diodes (LEDs) and lasers have a common problem of no suitable luminescent material to provide a wide emission bandwidth for the coverage of the entire visible spectrum. Hence, phosphors (mixture of different rare earth materials) are commonly used to convert blue LEDs for white-light emission and the phenomena of highly nonlinear optical processes in optical fiber are usually used to obtain supercontinuum white lasing light. However, the need of rare earth materials to fabricate phosphors coating and the use of femtosecond lasers to generate supercontinuum emission obstruct the development of low-cost and compact white-light emitting devices. In this project, we propose to replace the optical media of white-light LEDs and lasers by high luminescent graphene quantum dots (GQDs) for the generation of white-light emission. This can be done by proper selection of the size distribution of the GQDs to achieve multiple wavelength emission. In addition, high luminous efficacy, high saturation power, and stable white-light emission can be obtained from the GQDs with appropriate control of the absorption and radiative transition processes via the influence of functional groups and the utilization of passivation to avoid photo-oxidation process. As a result, the use of GQDs can reduce the production cost and fabrication difficulties of white-light LEDs and lasers. Furthermore, we can avoid using phosphors so that excessive mining and refining of rare earths can be prevented to save our environment. We can also overcome the problem that most of the intellectual properties related to phosphors technologies (that had adopted for manufacturing of white-light devices) are owned by foreign companies. Hence, GQDs can be a new industry standard and platform to design and realize low-cost and compact diode-pumped white-light sources.

制备白光发光二极管及激光器件普遍面临一个问题就是没有合适的覆盖整个可见光区的宽光谱发光材料。因此，通常是采用稀土荧光粉将蓝光二极管的发光转化成白光或者是采用光纤中强光学非线性效应来获得超连续白色激光光源。然而，以上方法分别依赖稀土材料和昂贵的飞秒激光，这就严重阻碍了低成本、小型化、复合型白色发光器件的发展。本项目中我们采用高效石墨烯量子点(量子点)发光材料取代常规的白光二极管、激光器中的发光材料来产生白色发光。通过量子点尺寸调节及量子点功能化基团选择可以实现发光波长的调控。此外，量子点还具有高发光效率, 高饱和功率及稳定白光发射等特点。从而，量子点技术将极大的降低白光二极管及激光器的生产成本和复杂性。量子点二极管技术可以避免由稀土荧光粉造成的环境破坏和突破国外公司对稀土白色发光器件的技术垄断等问题。因此,石墨烯量子点将是一种实现低成本、紧凑型二极管泵浦白色光源系统的全新产业标准和设计平台。

适用于实现白光发光器件(如, 白光LEDs或激光)的新材料的研发为本项目的主要研究目标。然而，现在最为棘手的问题就是缺乏一种材料，其发射波段覆盖整个白光可见区域。除此之外，实现白光激光发射也同样也面临着成本高，封装复杂等问题。因此，适用于低成本集成白光LEDs或激光器件的新材料的研发对先进照明应用来讲至关重要。..本工作中，我们采用碳量子点作为光学增益介质，在室温条件下光激发下实现白光发射。其具有更为简单的合成工艺（相比石墨烯量子点），更低的原料成本，更为绿色环保等优点。然后，关键技术问题是，在蓝光激发下，是否可以选择合适的官能团使其实现宽带白光发射的同时保证较高的光转换效率。我们研究发现，有机硅烷官能团的选择，可以有效实现宽带白光发射；并在环氧树脂的参与下，实现光增益介质的固态腔体。最终，我们首次在较宽波段范围内的可调单模激光发射。另一方面，在460nm蓝光激发下，我们通过调控碳量子在环氧树脂中的溶解度避免颗粒之间的团聚，在长时间内（30天以上）保持高于60%白光转换稳定效率；其发光强度甚至可以与商用黄色荧光粉封装白光LEDs相媲美；通过调节环氧树脂薄膜厚度，实现色温在2500K到10000K之间的调节。综上所述，碳量子点有望成为替代现有商用封装LEDs用的黄色荧光粉，为新型绿色白光LEDs用荧光粉提供选择。最后，碳量子点通过有机硅烷修饰后有助于提高多光子吸收效率，基于此，在室温长波激发下首次实现了三光子上转换随机激光的发射。遗憾的是，较短的可操作寿命严重影响了碳量子点的商业应用进程。因此，我们拓展研究了稀土掺杂上转换纳米晶及钙钛矿半导体材料作为实现白光激光发射的光增益介质的可能。