The temperature-dependent (\(T = 4.5 \, \hbox {-} \, 500 \, \hbox {K}\)) optical constants of monolayer \({\text {MoS}}_2\), \({\text {MoSe}}_2\), \({\text {WS}}_2\), and \({\text {WSe}}_2\) were investigated through spectroscopic ellipsometry over the spectral range of 0.73–6.42 eV. At room temperature, the spectra of refractive index exhibited several anomalous dispersion features below 800 nm and approached a constant value of 3.5–4.0 in the near-infrared frequency range. With a decrease in temperature, the refractive indices decreased monotonically in the near-infrared region due to the temperature-dependent optical band gap. The thermo-optic coefficients at room temperature had values from \(6.1 \times 10^{-5}\) to \(2.6 \times 10^{-4} \, \hbox {K}^{-1}\) for monolayer transition metal dichalcogenides at a wavelength of 1200 nm below the optical band gap. The optical band gap increased with a decrease in temperature due to the suppression of electron–phonon interactions. On the basis of first-principles calculations, the observed optical excitations at 4.5 K were appropriately assigned. These results provide basic information for the technological development of monolayer transition metal dichalcogenides-based photonic devices at various temperatures.

单层分子\({\text {MoS}}_2\) 、 \({ \text {MoSe}}_2\) 、 \({\text {WS}}_2\)和\({\text {WSe}}_2\)通过光谱椭圆光度法在 0.73–6.42 eV 的光谱范围内进行研究。在室温下，折射率光谱在800 nm以下表现出多种反常色散特征，并在近红外频率范围内接近3.5-4.0的恒定值。随着温度的降低，由于光学带隙与温度相关，折射率在近红外区域单调降低。室温下的热光系数的值从\(6.1 \times 10^{-5}\)到\(2.6 \times 10^{-4} \, \hbox {K}^{-1}\)对于单层过渡金属二硫属化物，波长为 1200 nm，低于光学带隙。由于电子-声子相互作用的抑制，光学带隙随着温度的降低而增加。根据第一性原理计算，对 4.5 K 处观测到的光学激发进行了适当分配。这些结果为不同温度下单层过渡金属二硫属化物基光子器件的技术发展提供了基础信息。