利用第一性原理结合HSE06杂化泛函理论研究了ZrSSe、HfSSe及相关异质结的电子和介电特性。单层ZrSSe和HfSSe的电子结构计算结果表明，其为间接带隙半导体，带隙分别为1.196 0 eV和1.040 2 eV。观察发现，能带结构出现了明显的带嵌套（Band nesting）现象，说明ZrSSe和HfSSe在光照条件下能够产生强烈的光与物质相互作用。并且，材料由S原子与Se原子p轨道电子跃迁产生的介电特性在红外和可见光范围表现出优异的吸收性能。此外，对结构的局部平面平均态密度进行分析表明，基于ZrSSe和HfSSe可以形成三种不同界面特征的异质结，且与带边界相关的电荷密度分布在两种材料上。对ZrSSe/HfSSe异质结的光吸收谱计算发现，其吸收峰主要出现在红外和可见光范围内，其峰值吸收系数最高可达1.26×10⁶ cm^-1。对异质结的能量损失谱计算可知，ZrSSe/HfSSe异质结在可见光范围内具有较高的吸收率。研究揭示了两面神结构材料及其异质结的光物理性质，推动了这些材料在新型光电器件中的应用。

利用液相剥离法制备了WS₂纳米片，结合真空抽滤技术，控制上清液体积制备了不同厚度的WS₂薄膜。在此基础上，使用800 nm飞秒激光的Z扫描技术表征了WS₂纳米薄膜的三阶非线性吸收特性。研究发现，制备的不同厚度的WS₂都表现出可饱和吸收特性，可饱和吸收主要是由于单光子吸收所引起的泡利阻塞效应引起；随着厚度的增加，饱和强度基本不变，调制深度会有所提高，但是三阶非线性极化率虚部的绝对值和品质因子会降低。这主要是因为较厚的薄膜缺陷更多，更容易捕获光生载流子，从而三阶非线性吸收和厚度有一定的依赖关系。可饱和吸收可以用于调Q激光器以及锁模激光器，为WS₂薄膜在超快开关和超快激光的应用提供实验支持。

Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear optoelectronic devices, especially in terms of tuning nonlinear optical absorption. Taking advantage of an atomic defect formed easily by smaller size, molybdenum disulfide nanosheet is prepared successfully with a different size by gradient centrifugation. Interestingly, size-dependent sulfur vacancies are observed by high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy. The defect effect on nonlinear absorption is investigated by Z-scan measurement at the wavelength of 800 nm. The results suggest the transition from saturable absorption to reverse saturable absorption can be observed in both dispersions and films. First principle calculations suggest that sulfur vacancies act as the trap state to capture the excited electrons. Moreover, an energy-level model with the trap state is put forward to explain the role of the sulfur vacancy defect in nonlinear optical absorption. The results suggest that saturable absorption and reverse saturable absorption originate from the competition between the excited, defect state and ground state absorption. Our finding provides a way to tune the nonlinear optical performance of optoelectronic devices by defect engineering.