Ahmed Safayet, Cheng Ping Kwong, Qiao Junpeng, Gao Wei, Saleque Ahmed Mortuza, Al Subri Ivan Md Nahian, Wang Ting, Alam Tawsif Ibne, Hani Sumaiya Umme, Guo Zong Liang, Yu Siu Fung, Tsang Yuen Hong
Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Shenzhen Research Institute, The Hong Kong Polytechnic University, 518057 Shenzhen, Guangdong, People's Republic of China.
ACS Nano. 2022 Aug 23;16(8):12390-12402. doi: 10.1021/acsnano.2c03566. Epub 2022 Jul 25.
The nonlinear optical (NLO) properties of two-dimensional (2D) materials are fascinating for fundamental physics and optoelectronic device development. However, relatively few investigations have been conducted to establish the combined NLO activities of a 2D material. Herein, a study of numerous NLO properties of 2D gallium sulfide (GaS), including second-harmonic generation (SHG), two-photon excited fluorescence (TPEF), and NLO absorption are presented. The layer-dependent SHG response of 2D GaS identifies the noncentrosymmetric nature of the odd layers, and the second-order susceptibility (χ) value of 47.98 pm/V (three-layers of GaS) indicates the superior efficiency of the SHG signal. In addition, structural deformation induces the symmetry breaking and facilitates the SHG in the bulk samples, whereas a possible efficient symmetry breaking in the liquid-phase exfoliated samples results in an enhancement of the SHG signal, providing prospective fields of investigation for researchers. The generation of TPEF from 800 to 860 nm depicts the two-photon absorption characteristics of 2D GaS material. Moreover, the saturable absorption characteristics of 2D GaS are realized from the largest nonlinear absorption coefficient (β) of -9.3 × 10, -91.0 × 10, and -6.05 × 10 cm/GW and giant modulation depths () of 24.4%, 35.3%, and 29.1% at three different wavelengths of 800, 1066, and 1560 nm, respectively. Hence, such NLO activities indicate that 2D GaS material can facilitate in the technical advancements of future nonlinear optoelectronic devices.
二维（2D）材料的非线性光学（NLO）特性对于基础物理学和光电器件的发展具有重要意义。然而，针对二维材料的综合NLO活性开展的研究相对较少。在此，我们针对二维硫化镓（GaS）的多种NLO特性展开了研究，包括二次谐波产生（SHG）、双光子激发荧光（TPEF）以及NLO吸收。二维GaS的层依赖SHG响应确定了奇数层的非中心对称性质，47.98 pm/V（三层GaS）的二阶极化率（χ）值表明了SHG信号的高效性。此外，结构变形会导致对称性破缺并促进块状样品中的SHG，而液相剥离样品中可能存在的有效对称性破缺会导致SHG信号增强，为研究人员提供了新的研究方向。800至860 nm范围内TPEF的产生描绘了二维GaS材料的双光子吸收特性。此外，二维GaS的饱和吸收特性可通过在800、1066和1560 nm三个不同波长下分别为-9.3×10、-91.0×10和-6.05×10 cm/GW的最大非线性吸收系数（β）以及24.4%、35.3%和29.1%的巨大调制深度（）得以实现。因此，这种NLO活性表明二维GaS材料能够推动未来非线性光电器件的技术进步。
