Zhao Yue, Liu Ling, Liu Shuangjie, Wang Yang, Li Yonghui, Zhang Xiao-Dong
Tianjin Key Laboratory of Brain Science and Neural Engineering, Academy of Medical Engineering and Translational Medicine, Tianjin University, Tianjin 300072, China.
Department of Physics, Shanxi Medical University, Taiyuan 030001, China.
ACS Omega. 2022 Mar 29;7(14):11956-11963. doi: 10.1021/acsomega.2c00071. eCollection 2022 Apr 12.
Near-infrared-II (NIR-II, 1000-1700 nm) fluorescence imaging is widely used for in vivo biological imaging. With the unique electronic structures and capability of band-gap engineering, two-dimensional (2D) materials can be potential candidates for NIR-II imaging. Herein, a theoretical investigation of the electronic structure and optical properties of iodine (I)-doped monolayer MoTe systems with different doping concentrations is carried out through simulations to explore their NIR optical properties. The results suggest that the emergence of impurity levels due to I doping effectively reduces the bandwidth of I-doped monolayer MoTe systems, and the bandwidth decreases with the increase in the I doping concentration. Although the I and Mo atoms possess clear covalent-bonding features according to the charge density difference, impurity levels induced by the strong hybridization between the I 5p and Mo 4d orbitals cross the Fermi level, making the doped systems exhibit metallic behavior. In addition, with the increase in the I doping concentration, the energy required for electron transition from valence bands to impurity levels gradually decreases, which can be linked to the enhancement of the optical absorption in the red-shifted NIR-II region. Meanwhile, with a higher I doping concentration, the emission spectra, which are the product of the absorption spectra and quasi-Fermi distributions for electrons and holes, can be enhanced in the NIR-II window.
近红外二区（NIR-II，1000 - 1700纳米）荧光成像被广泛应用于体内生物成像。凭借独特的电子结构和带隙工程能力，二维（2D）材料有望成为NIR-II成像的候选材料。在此，通过模拟对不同掺杂浓度的碘（I）掺杂单层碲化钼（MoTe）系统的电子结构和光学性质进行了理论研究，以探索其近红外光学性质。结果表明，I掺杂导致杂质能级的出现有效降低了I掺杂单层MoTe系统的带宽，且带宽随I掺杂浓度的增加而减小。尽管根据电荷密度差I和Mo原子具有明显的共价键特征，但I的5p轨道与Mo的4d轨道之间的强杂化诱导的杂质能级穿过费米能级，使得掺杂系统呈现金属行为。此外，随着I掺杂浓度的增加，电子从价带跃迁到杂质能级所需的能量逐渐降低，这与红移的NIR-II区域中光吸收的增强有关。同时，在较高的I掺杂浓度下，作为电子和空穴的吸收光谱与准费米分布乘积的发射光谱在NIR-II窗口中可以得到增强。
