多种晶体结构的碳纳米晶体的制备、发光性质及其相变过程的研究

Carbon nanocrystals have attracted great interest recently. The source materials for synthesizing carbon nanocrystals are diverse and fruitful. The synthesized carbon nanocrystals may have different crystal structures and different morphologies. Their luminescence ranges from the near-infrared to the near-UV region (300-1000 nm). They have wide potential applications in quantum information processing and single-photon generation and detection, phototransistors, light emitting diodes and lasers, solar cells, photocatalysis, and biological labels and therapy. However, currently, the luminescence mechanisms of the various carbon nanocrystals remain unclear and debated. In particular, every proposed mechanism can only explain one specific luminescence phenomenon observed in a specific experiment. In this proposal, we plan to give a comparative study of the luminescence properties of various carbon nanocrystals with different crystal structures (graphite, diamond, or C8); we shall study the phase transitions of the various types of carbon nanocrystals under irradiation of lasers or electrons, and study the variations of the luminescence properties as the phase transition occurs. We shall synthesize highly-monodisperse carbon nanocrystals with different crystal structures by using the hydrothermal or microwave-irradiation method. We shall change the surface structures of the carbon nanocrystals and dope them. By using various microstructural characterizations and optical spectroscopies as well as theoretical analyses, we hope to deeply understand the intrinsic and defect energy levels, the electronic transition channels, and the light absorption and emission processes in the carbon nanocrystals. In addition, we hope to identify the specific luminescent defects and edge states in the carbon nanocrystals.

碳纳米晶体发光是目前国际上的研究热点。碳纳米晶体的制备原材料来源丰富，制备出的材料具有不同的晶体结构和多样化的形貌，发光光谱跨越近紫外到近红外波段（300-1000 nm）；它们的应用前景极为广阔，从量子信息处理和单光子产生/探测、光晶体管、发光二极管和激光、太阳能电池、光催化到生物荧光标记和医疗等。然而人们对碳纳米晶体的发光机制仍缺乏了解，已提出的发光机制往往只能解释特定的实验现象。本申请中我们拟对各种晶体结构（石墨、金刚石、C8等）的碳纳米晶体的发光性质进行比较研究，并研究在激光束和电子束照射下的晶体结构相变及其对发光性质的影响；通过水热法和微波法等制备单分散性高的各种碳纳米晶体，并对其进行表面改性和掺杂，利用各种微结构和光谱表征手段进行研究，并结合理论分析，以获得对于碳纳米晶体的内禀和缺陷能级结构、电子跃迁通道以及光吸收和发射动力学等的完整认识，并识别出各种具体发光缺陷和边缘态。

碳等绿色环保的纳米晶体是当前国际上的研究热点。碳纳米晶体的原材料丰富，制备出的材料具有多种晶体结构，其发光在近紫外到近红外波段可调，应用前景广阔：从固体发光和显示、激光、光伏器件、光催化到生物荧光标签和药物传递等。我们对具有金刚石和C8等晶体结构的碳纳米晶体以及其它相关纳米晶体的结晶生长、相变和发光特性等进行了深入研究，取得一批既具有科学意义又具有潜在应用价值的研究成果。.我们研究了金刚石和C8碳以及碳化硅等量子点的结晶过程和相变、发光机制以及电致发光器件和传感应用等，取得一些原创性强的研究成果。生长出直径仅为几纳米的金刚石和C8结构碳纳米晶体，研究了结晶温度对碳纳米晶体表面结构和发光的影响，以及溶液pH值变化所导致的碳纳米晶体的结构相变。利用多种实验表征并结合第一性原理计算发现金刚石和C8碳纳米晶体表面存在多种与碳和氧相关的发光基团。研究表明，与碳和氧相关的表面发光缺陷普遍存在于含氧元素的量子点中。对碳化硅纳米晶体和团簇的发光性质进行了研究，发现其具有多种颜色的发光，部分发光峰也来自于与碳和氧相关的表面缺陷。研究并制备出基于C8碳纳米晶体的可通过电压调控的具有蓝、红双色发光的电致发光器件，研究并制得基于碳化硅量子点的具有准白光发射的电致发光器件。对这些器件内部的载流子输运和复合发光机制进行了研究，发现量子隧道效应和类似于pn结的载流子注入机制分别主导了这些量子点器件在不同电压下的载流子输运。提出了由于界面势垒削弱而导致的载流子复合发光空间发生转移的机制。另外，还研究了若干种量子点的发光特性及其中的激子和声子效应。研究了碳量子点和氧化锌量子点的光子再吸收过程，并在此基础上建立了定量描述量子点光再吸收过程的理论模型，可以用其研究各种胶体量子点体系的发光性质。