为探究二维层状过渡金属硫化物的激子效应, 尤其是上转换过程, 以层状 WS2 样品为例开展了研究。利用 532 nm 连续激光和显微拉曼技术, 探究了 WS2 晶体中 X0、X- 激子态物理起源和基本物理性质。利用 633 nm 连续激光, 实现了 WS2 晶体的单光子上转换荧光增强, 证实了其背后的双共振物理机制, 即入射光与 X- 激子态共振, 在光学 声子 A1g、E12g 的辅助下跃迁至高能级 X0 激子态, 最后自发辐射上转换荧光。此外, 进一步对双共振上转换荧光的影响因素进行了分析, 包括曝光时间、温度和激发功率。拟合结果表明适当增加曝光时间、减小环境温度和增加激发功率, WS2 的上转换荧光效率会得到提升。

In order to explore the exciton effect of two-dimensional layered transition metal sulfide, especially the up-conversion fluorescence process, the layered WS2 sample was taken as an example to study. Using 532 nm continuous laser and micro-Raman technology, the physical origin and basic properties of X0 and X- exciton of WS2 crystal were investigated. The continuous laser of 633 nm was used to realize single photon up-conversion fluorescence enhancement, which confirmed the physical mechanism of double resonance, that is, the incident light resonates with the X- exciton state, then exciton transitions to the high-energy X0 exciton state with the aid of optical phonons A1g and E12g, and finally produces spontaneous up-conversion fluorescence. In addition, the influencing factors of X0 were further analyzed including exposure time, temperature and excitation power. The fitting results showed that the up-conversion fluorescence efficiency could be improved by appropriately increasing the exposure time, decreasing the ambient temperature and increasing the excitation power.