一维石墨烯纳米条带上转换基础研究

The charge carriers of graphene behave like massless Dirac Fermion, and its astonished electronic properties make the transfer of charges and energy easier than most other materials,and have a potential to be anti-stokes emission.The band gap of perfect graphene sheet approaches zero, while the fluorescence properties of translation are much related to its energy level.Since the band gap of graphen quantum dots(GQDs) derives from quantum confinement,the research on upconversion of graphene are focused on carbon quantum dots(CQDs).If the excitation light is noncoherent sunlight,the upconversion emission intensity of CQDs is very low and almost zero.However, can CQDs equalto GQDs? and can the GQDs represent graphene? Our research presents two routes to upconversion of graphene, 1)quasi-free standing graphene nanoribbons(GNRs) and 2) epitaxial GNRs. By tuning width of GNRs,aspect ratio , dopant, coupling between the adjacent layers and chirality of edges, we try to build up a relationship between the upconversion and both the boundary chirality and inner topological defects.To this end, we should have a deep understanding of the intrensic upconversion of graphene excited by noncoherent light and pulsed laser respectively. Finally, a high quantum productivity and intense emission of photon can be reached.

石墨烯中的载流子为无质量的Dirac 费米子，在电子转移和能量转移上具有独特的性质，从而使得光子激发的反斯托克斯能量输出成为可能。然而完美的石墨烯是零带隙的，而荧光性质一般认为与带隙有关。由于量子限域效应和边界效应，石墨烯量子点的带隙可调控，因此目前有关石墨烯上转换的研究，多集中在碳量子点上。碳量子点的上转换发光很弱，在非相干光源激发下，其上转换发光几乎可以忽略。然而，碳量子点是否等同于石墨烯量子点？石墨烯量子点是否代表石墨烯真正的发光性质？ 本研究分别通过非相干光源和相干脉冲激光光源激发，对近自由和外延石墨烯纳米条带进行调控，探索其宽度、长宽比、掺杂、层间耦合作用以及手性对一维石墨烯上转换的影响，认识一维石墨烯在不同光源激发下的上转换机理。最终验证和实现一维石墨烯上转换的可操控性，制备出稳定的上转换新材料。

碳材料的荧光转换，尤其是对太阳光的转换具有重要的应用价值。制备高效转换的石墨烯量子点或条带是目标；进而能够实现宏量制备和充分掌握转换机制；因而精准可控实现石墨烯量子点（非碳量子点）制备，一维石墨烯纳米条带制备并实现手性控制，及石墨烯条带的掺杂及复合等时先决条件。掌握石墨烯条带非相干光源激发、连续激光激发及脉冲激光激发的荧光转换机制是进一步优化转换的基础。. 采用富勒烯球改性法，可以有效实现高质量石墨烯量子点的有效制备，且发现石墨烯量子点在特定条件下，荧光发光强度呈爆发式增强；探索了多种模板法，获得了石墨烯及类石墨烯一维纳米条带的有效生长方法，不仅可以控制条带的高度、宽度和疏密度，甚至总结出了有效控制条带手性的方法；由于纯粹的石墨烯纳米条带的非相干光源上转换效率很低，因而制备了多种量子点和纳米线来进行复合；我们发现一定尺寸的6H碳化硅颗粒具有很强的荧光发射性能，且单色性很好，具备了激光的某些特征；当在颗粒周围包裹站立的石墨烯条带后，太阳光激发衬底激光，实现非相干光源激发石墨烯条的高量子产率发光。此外，无定型硅量子点的合成依赖于氢气环境，低密度硅液体的稳定存在，证实硅液体具有多型性，且对石墨烯具有很强的荧光增强效果。980nm连续激光和1064 nm皮秒激光的荧光实验表明，石墨烯条带的上转换分别符合反斯托克斯机制和Plasmon机制。.