量子点功能化石墨烯光学非线性的调控与增强研究

Graphene to be used as a potential material for the next generation of photonic devices has attracted extensive attention. However, its nonlinear optical response is still relatively weak comparing with the practical requirement. This property makes designing subwavelength all-optical devices extremely difficult and thus largely limits the integration density of photonic devices. Presently, it is reported that the optical nonlinear response can be enhanced by functionalizing graphene. However, the important charge transfer process and the mechanism of the effect on optical nonlinearity are not clear, which leads to the failure to achieve the objective enhancement of optical nonlinearity through functional structure with specific charge transfer process. In this project, in the II-VI semiconductor quantum dots functionalized graphene system, the charge transfer process including charge transfer direction, electron transition and relaxation and charge transfer bridge and the mechanism affecting the optical nonlinearity are systematically studied by means of regulating potential difference, energy difference and link difference between the quantum dots and the graphene through changing the quantum dot size, energy state structure and electronic states and surface modification. The dependency relations among the structure, charge transfer process and the optical nonlinearity are revealed, so as to realize the regulation of charge transfer with functional structure, and then realize the regulation and enhancement of the optical nonlinearity. The results of this project will lay a foundation for the practical application of the functional graphene in the field of photonic devices.

石墨烯作为潜在的下一代光子器件材料备受瞩目。然而，其光学非线性响应还相对较弱，造成亚波长全光器件的设计极为困难，限制了光子器件的高密度集成。目前报道发现，功能化石墨烯能够增强光学非线性响应，但其中对光学非线性起重要作用的电荷转移过程及其作用机理尚不清楚，导致无法通过具有特定电荷转移过程的功能化结构实现光学非线性的目标增强。本项目拟在II-VI族半导体量子点功能化石墨烯体系中，采用量子点尺寸、能态结构和电子态及表面修饰基团调控量子点与石墨烯之间的电势差、能级差和链接桥梁的方法，深入系统研究电荷转移过程（电荷转移方向、电子跃迁与弛豫、电荷转移桥梁）对光学非线性的作用机理，揭示出功能化结构-电荷转移过程-光学非线性之间的依存关系，在此基础上实现通过结构对电荷转移过程的调控，进而实现光学非线性的增强与调控，为功能化石墨烯纳米材料在光子器件上的实际应用提供科学参考。

石墨烯因具有光学损伤阈值高和光子能量损耗低的特点，在激光技术、信息存储、现代通讯等领域中的光子器件上具有广泛的应用前景。但石墨烯的非线性光学性能需要进一步提高，而其中电荷转移的影响尚不清楚。本项目提出了一种利用具有较好非线性光学性质的量子点与石墨烯复合的方法，深入探讨电荷转移对非线性光学响应的影响及机制，以实现材料光学性能（特别是三阶非线性）的调控与增强。本项目主要采用湿化学方法，制备了金属(Au、Ag、Cu)、金属氧化物 (ZrO、SnO2、α-FeOOH)、硫化物 (CdS、Au@CdS、Au@ZnS、CuS、Mn-CdS、Bi2S3、Sb2S3、α-MnS、γ-MnS、Ni-ZnS)、硒化物 (CdSe、Cu2Se、MoSe2、ZnSe)、卤化物钙钛矿(CH3NH3PbBr3)等一系列纳米粒子与石墨烯的复合材料，以及辅助研究用的量子点与多壁碳纳米管(MWCNT)、黑鳞烯(BP)、金属有机框架(MOF)等复合材料，通过材料结构、物性表征手段与Z-扫描技术等方法，研究了材料在可见-近红外波长下的三阶非线性光学特性，揭示了电荷转移的作用机理，得到了一系列具有优秀三阶非线性性能的量子点功能化石墨烯复合材料。在波长532nm和1064nm、脉宽30ps、重复频率10Hz的近乎皮秒单脉冲条件下，项目团队得到了量子点功能化石墨烯比石墨烯增强6-60倍的三阶非线性极化率(~1.2X10^-10esu)以及3-6倍的饱和吸收调制深度（~34.5%）。本项目获得的电荷转移非线性作用机理、增强的非线性极化率和饱和吸收调制深度，为进一步研究开发基于石墨烯复合材料的光子器件，尤其为接下来研究中红外波段的激光锁模，奠定了相关科学工作基础。