单层与双层WSe2纳米片层的光致发光

采用气相沉积法制备了WSe₂二维纳米材料，对其低温光致发光谱进行了研究。结果表明：随着WSe₂层数的增加，其光致发光强度单调下降；当WSe₂层数从单层增加为双层时，其发光强度急剧下降，表明其能带结构已从直接带隙转变为间接带隙。进一步研究了双层WSe₂的变温光致发光谱，发现随着温度的升高，双层WSe₂发光峰中A峰峰位的变化基本符合半导体带隙的温度变化规律，而I峰峰位红移与温度基本成线性关系，表明双层WSe₂同时存在间接和直接跃迁，且直接跃迁和间接跃迁特性不同。

Photoluminescence Properties of WSe2 Monolayer and Bilayer Nanosheets

We systematically studied the low-temperature (12 K) photoluminescence (PL) spectroscopies of WSe₂ nanosheets prepared by vapor deposition technique. It is found that PL intensity monotonically decreases with the increasing of WSe₂ nanosheet layers. In particular, the PL intensity dramatically decreased when the thickness of WSe₂ films changed from monolayer to bilayer, which indicated that there is a direct-to-indirect transition in the band gap of WSe₂ nanosheets. Then we focused on the variable temperature photoluminescence of the bilayer structure. When the temperature increases from 12 K to 300 K, the temperature-dependent evolution of the direct transition energy (peak A) is approximately consistent with the common formula obeyed by bulk semiconductors, while the indirect transition energy (peak I) can only be described by a linear relationship with temperature. This indicates that peak A and peak I have different transition characteristics and these two transition characteristics coexist in bilayer WSe₂ simultaneously.