微/纳机电系统的发展、爆炸/冲击等极端压力环境下的压力探测对压力传感器提出新的要求：空间分辨率达到μm或nm量级、可探测的压力达到MPa或GPa量级、可应用于复杂的温度/压力环境、非接触式等等。然而，目前常用的压力传感器难以同时满足上述需求。量子点作为纳米尺度的光致发光材料，因其独特的能级结构和压力相关的发光特性，有望成为一种新型的纳米尺度压力传感材料。目前关于量子点在压力作用下的发光响应开展了初步研究，但是对于更复杂、更接近压力传感器实际应用工况的研究甚少，如温度变化、反复加-卸载等条件。同时，量子点尺寸、结构、材料对其受压发光特性的影响缺乏系统对比和分析。更重要的是，量子点发光特性随压力变化的微观机理研究也有待丰富。本论文通过设计搭建实验平台，针对不同尺寸、不同结构的CdTe、CuInS₂以及核-壳型CuInS₂/ZnS量子点，开展了不同温度、压力以及反复加-卸载等复杂实验条件下的发光特性研究，以量子点发光强度和光谱峰值能量两个主要荧光特征为指标揭示了不同量子点在不同实验条件下的发光响应规律。进一步，采用第一性原理计算研究了不同尺寸量子点的能隙在不同应变模式下的变化规律，从微观角度探究了光谱峰值能量随压力变化的机理。具体研究工作包括以下几方面：

1. 设计并搭建量子点在高温高压条件下的发光响应同步探测实验研究平台。平台包括荧光激发和探测单元、压力加载单元和温度控制单元。可实现针对量子点开展最高压力约为12 GPa、最高温度约为250 ℃的高温高压发光响应实验研究。该平台具有体积小、操作便捷等优势。另外，对实验平台中各单元参数的选择和注意事项等进行了系统测试和总结，这不仅便于本文实验工作的展开，也为进一步研发基于量子点的压力探测装置提供了参考。
2. 系统研究了几种典型量子点的发光响应，确定了量子点作为压力传感材料在接近实际应用工况条件下的响应规律和稳定性。针对不同尺寸和结构的CdTe、CuInS₂以及核-壳型CuInS₂/ZnS量子点，在不同压力范围、加-卸载次数、温度/压力条件下的发光响应开展了实验研究，主要内容包括： (ⅰ) 确定了不同量子点在压力载荷下的发光特性变化规律。实验结果表明，光谱峰值能量随着压力的增大而单调增加，其中CdTe和CuInS₂/ZnS量子点表现为二次函数关系，CuInS₂量子点表现出双线性函数关系，该函数关系可作为压力探测依据。然而，发光强度随压力的增大表现出先增强后衰减的非单调变化，最后甚至消失，这会影响量子点的压力探测范围。(ⅱ) 首次开展了量子点的反复加-卸载实验研究。结果显示，对于实验中的三种样品，仅有尺寸为1.5 nm的CuInS₂量子点的光谱峰值能量表现出加载历程依赖性，因而不便用于反复加-卸载循环的压力探测。其次，发光强度随着加-卸载循环次数的增加持续衰减，这将导致在多次加-卸载应用工况条件下，量子点所能探测的最大压力随着加-卸载次数的增多而降低。(ⅲ) 系统研究了温度对量子点发光-压力关系的影响。结果表明，光谱峰值能量随温度的升高持续减小，而发光强度随温度的升高表现为先增强后衰减的非单调变化。温度冷却后，由于高温诱导量子点微结构的不可逆变化，导致发光强度和光谱峰值能量均无法恢复。对于CdTe和CuInS₂/ZnS量子点，其光谱峰值能量-压力函数的系数在不同温度下表现出较好的一致性；而对于自发生长速率较高的CuInS_­2量子点，光谱峰值能量-压力函数的系数表现出较大的差异。这些研究成果可为量子点作为压力传感材料在接近实际工况下的应用提供参考和指导。
3. 系统研究了核/壳型量子点的发光响应特性，探明了含壳量子点作为压力传感材料的优势。针对无壳型CuInS₂和核-壳型CuInS₂/ZnS量子点实验研究了在不同温度、压力和反复加-卸载条件下的发光响应规律。结果表明，壳结构对核结构能起到有效的钝化和保护作用，使量子点的发光特性得到多方面的改善：发光强度得到有效增强，光谱峰值能量与压力的函数关系简单化，发光特性在高温/高压条件下更加稳定。因此，含壳量子点作为压力传感材料更有优势。
4. 开展第一性原理计算，阐明应变状态和尺寸对量子点能隙影响的微观机理。采用第一性原理计算，研究了不同尺寸CdTe量子点的能隙在静水压、冲击压和单轴压缩加载模式下对应变状态的依赖关系。结果表明，对于静水压和冲击压，能隙变化随应变的增大而增大，但静水压下能隙变化随应变的变化斜率更大；而对于单轴压缩，能隙变化随应变的增大主要表现为减小的趋势。对于尺寸依赖性，静水压基本不影响能隙变化-应变关系，但对于冲击压和单轴压缩，量子点尺寸越大，能隙变化越大。能隙变化随应变/尺寸的依赖性的直接原因取决于最低未占据分子轨道能量和最高占据分子轨道能量随应变的变形势之间的竞争关系及相对差异，基本原因是由于三种应变模式具有的不同应变三轴度导致成键态和反键态电子云随应变/尺寸的响应不同。

本论文的研究成果有助于理解复杂加载条件下不同量子点的发光响应以及微观机理，对基于量子点发光的压力传感材料的研究提供了新思路，并为新型纳米尺度压力传感器的设计和应用提供了参考和指导。

Pressure sensing for complex application scenarios, such as micro/nano electromechanical systems and the extreme conditions induced by explosion or shock compression, has placed new demands on pressure sensors: spatial resolution to the micron or nanometer scale, pressure range at the MPa or GPa level, responsible in complex temperature/pressure environments and non-contact detecting. However, the existing pressure sensors are basically difficult to meet the above requirements simultaneously. As nanoscale photoluminescence (PL) materials, quantum dots (QDs) are expected to become a new type of nanoscale pressure sensing materials due to their unique energy level structure and pressure-related PL properties. At present, preliminary progress has been obtained in the research on the response of PL properties of QDs under pressure, while experimental studies on more complex application conditions of pressure sensors are less involved, such as temperature, repeated loading-unloading, etc. Moreover, the effects of QD size, microstructure and material type on PL characteristics under pressure have not been systematically analyzed. More importantly, the microscopic mechanisms of the PL responses of QDs with pressure also need to be investigated. In the dissertation, an experimental platform was designed and built. Then, experiments of PL response were carried out on CdTe, CuInS₂ and core-shell CuInS₂/ZnS QDs with different sizes and structures under several complex conditions such as different temperatures, pressures and cycles of pressure loading and unloading. Two main fluorescence characteristics of the PL, namely, PL intensity and spectral peak energy (EPL ), were used as indicators to reveal the law of PL response for different QDs under different experimental conditions. Furthermore, the energy gaps of QDs of different sizes were studied under different strain patterns using first-principles calculations, and the mechanism of the response of EPL  with pressure was investigated from a microscopic perspective. The specific research work includes the following aspects.

1. The experimental platform for testing PL response of QDs under high pressure and temperature was setup. The platform consists of three units: fluorescence excitation and detection, pressure loading and temperature control. With the platform, experiments on PL responses of QDs can be carried out with pressure up to 12 GPa and temperature up to 250 ℃. Compared with the traditional platform for PL response detection, the three parts are designed to be independent with each other and convenient for operation. Further, the equipment parameters and precautions of each part are systematically tested and summarized, which not only facilitates the experiments in the dissertation, but also provides a reference for related researchers to build a QD-based pressure sensing platform.
2. PL responses of serveral typical QDs under conditions close to actual applications were investigated. Experiments on CdTe, CuInS₂ and core-shell CuInS₂/ZnS QDs of different sizes and structures were carred out to investigate their PL responses at different pressure, temperature and loading-unloading conditions. The main results including: (ⅰ) The PL response of different QDs under pressure show that the EPL  increases monotonically with increasing pressure. For CdTe and CuInS₂/ZnS QDs, the relationship between EPL  and pressure exhibits a quadratic function, while a bilinear function is found suitable for CuInS₂ QDs. The relationship between EPL  and pressure can be used as the basis for QD-based pressure sensing materials. However, the PL intensity shows a non-monotonic variation. It enhances first and then decays with the increasing pressure, and finally disappears, which can affect the pressure detection range of QDs as pressure sensing materials. (ⅱ) The repetitive pressure loading-unloading experimental research of QDs was carried out for the first time. The results show that for the three types of QDs, only the CuInS₂ QDs with size of 1.5 nm exhibit loading history dependence and thus are inconvenient to be used for pressure detection in repeated loading-unloading cycles. Additionally, the PL of QDs decays continuously with the increase of the number of loading-unloading cycles, which leads to the decrease of the maximum pressure detectable by QDs. (ⅲ) The effect of temperature on the pressure related PL characteristics was systematically studied. The results show that the EPL  decreases continuously with the increase of temperature, while the PL intensity enhances first and then decays with temperature. After the temperature cools down, both the EPL  and PL intensity cannot be recovered due to the irreversible changes of microstructure of QDs induced by high temperature. In addition, for CdTe and CuInS₂/ZnS QDs, the coefficients of the EPL -pressure functions show good consistency at different temperatures. However, for the CuInS₂ QDs with high spontaneous growth rate, the coefficients of EPL -pressure functions show large differences with temperature. The results could provide reference and guidance for developing QD-based pressure sensing materials under actual application conditions.
3. The merits of shell-coated QDs as pressure sensing materials are confirmed by systematical study of the PL responses of bare CuInS₂ and core-shell CuInS₂/ZnS QDs under different temperature, pressure and loading-unloading conditions. The results show that the shell structure can play an effective role in passivating and protecting the core structure of QDs, and it leads to the improvement of PL properties of QDs in various aspects. The PL intensity is effectively enhanced. The functional relationship between the EPL  and pressure is simplified. The PL properties are more stable than the bare QDs under high pressure or high temperature conditions. Therefore, shell-covered QDs are more advantageous as pressure sensing materials.
4. First-principles calculations were carried out to clarify the microscopic mechanism of the effect of strain state and size on the energy gap of QDs. Using the first-principles method, the dependences of the energy gap of CdTe QDs with different sizes on the strain state under hydrostatic compression (HC), shock compression (SC) and uniaxial compression (UC) modes were investigated. The results show that for HC and SC, the change of energy gap increases with strain, but the slope of the change of energy gap with strain is larger under HC. While for UC, the change of energy gap mainly shows a decreasing trend with strain. For size dependence, HC hardly affects the energy gap change-strain relationship, while for SC and UC, the larger the QD size, the larger the energy gap change. The direct reason of the strain/size dependence of the energy gap depends on the competition relationship and relative difference between the deformation potentials of the lowest unoccupied molecular orbital energy (LUMO) and the highest occupied molecular orbital energy (HOMO) with strain, while the basic reason is the different strain/size response of the bonding and anti-bonding electron clouds due to the different strain triaxiality of the three types of strain modes.

Results in the dissertation help to understand the PL response and microscopic mechanism of different QDs under complex loading conditions. It provides new ideas for the study of pressure sensing materials based on the PL of QDs. Moreover, the results also provide valuable reference and guidance for the design and application of novel nanoscale pressure sensors.