Institute of Micro/Nano Photonic Materials and Applications, School of Physics and Electronics, Henan University, Kaifeng 475004, China.
Phys Chem Chem Phys. 2018 Oct 31;20(42):27105-27114. doi: 10.1039/c8cp04940h.
Surface oxygen-containing defects of graphene nanosheets (G NSs) are important for the nonlinear optical (NLO) properties in optoelectric devices. G NSs with different surface oxygen-containing defects are successfully tuned by a chemical reduction process, and are characterized by several experimental measurements of morphology and structure and by spectroscopy. Their NLO properties are measured with the Z-scan technique and the NLO transmission method using a 30 picosecond single-pulse laser source at 532 nm wavelength. Their NLO susceptibility is enhanced 11.8 times (from 0.38 × 10-12 esu to 4.5 × 10-12 esu) with the decrease in the density of surface oxygen-containing groups, while it is reduced 7.2 times (2.7 × 10-12 esu) with a further decrease in oxygen. Accordingly, the nonlinear absorption coefficient of graphene is increased from 0.51 cm GW-1 to 5.90 cm GW-1, and then decreased to 3.41 cm GW-1, indicating that the NLO response of graphene NSs should be weakened whether the component of surface oxygen-containing groups is too large or too small. The local field effect arising from surface oxygen-containing groups and isolated sp2 clusters is the dominant mechanism for the NLO improvement, while the connection of small sp2 clusters depresses the optical nonlinearity. An evolution from two-photon absorption to saturable absorption with the decrease of surface oxygen concentration is obtained. The intensity-related NLO absorption and refraction in NSs are also discussed. Tuning the surface oxygen-containing defects of graphene is a useful way to enhance the optical nonlinearity for potential applications in devices.
石墨烯纳米片（GNSs）的表面含氧缺陷对于光电设备中的非线性光学（NLO）性质非常重要。通过化学还原过程成功地调节了具有不同表面含氧缺陷的 GNSs，并通过形貌和结构的几个实验测量以及光谱学进行了表征。使用 30 皮秒单脉冲激光源在 532nm 波长下，通过 Z 扫描技术和 NLO 透射法测量了它们的 NLO 性质。随着表面含氧基团密度的降低，其 NLO 敏感性增强了 11.8 倍（从 0.38×10-12 esu 增加到 4.5×10-12 esu），而随着氧的进一步减少，其敏感性降低了 7.2 倍（2.7×10-12 esu）。因此，石墨烯的非线性吸收系数从 0.51cmGW-1增加到 5.90cmGW-1，然后降低到 3.41cmGW-1，表明无论表面含氧基团的组成过大还是过小，石墨烯 NSs 的 NLO 响应都应减弱。表面含氧基团和孤立 sp2 团簇引起的局域场效应是 NLO 改善的主要机制，而小 sp2 团簇的连接则抑制了光学非线性。随着表面氧浓度的降低，从双光子吸收到饱和吸收的转变得到了证实。还讨论了 NSs 中与强度相关的 NLO 吸收和折射。调节石墨烯的表面含氧缺陷是增强光学非线性的一种有效方法，可应用于器件中。
