Chen Weilong, Zhang Di, Zou Jie, Luo Jingdong
Department of Chemistry, City University of Hong Kong, Hong Kong SAR, 999077, China.
Shenzhen Research Institute, City University of Hong Kong, Shenzhen, 518057, China.
Small Methods. 2024 Nov;8(11):e2400162. doi: 10.1002/smtd.202400162. Epub 2024 Jun 7.
A full-scale analysis of the absorption edges by modified Tauc-Lorentz models is essential in determining the optical bandgap and Urbach energy of semiconductors, transparent conductors, ionic compounds, and dielectric materials. This technique has not yet been applied to analyzing organic nonlinear optical (NLO) materials. This problem is tackled by preparing high-quality films of guest-host NLO polymers with a wide thickness range from sub-micron to 200 microns, allowing accurate measurement of full-spectral absorption coefficients of NLO materials over four orders of magnitude by the UV-VIS-NIR spectroscopy. The Tauc model and a new Monolog-Lorentz model are used to study the optical absorption edge of guest-host NLO polymers containing various push-pull chromophores and the dependence of optical bandgap and Urbach edge on the structure and composition of materials is analyzed. The results reveal the critical transition of the Urbach exponential tail to a low energy tail that overlaps with vibrational overtones of materials at the telecom wavelengths. Determining the fundamental absorption region of organic NLO films in this study provides quantitative insight into the research to harness the resonance-enhanced nonlinear coefficients of materials by operating at the wavelengths near the band edge with the control of optical loss.
通过改进的陶赫-洛伦兹模型对吸收边进行全面分析，对于确定半导体、透明导体、离子化合物和介电材料的光学带隙和乌尔巴赫能量至关重要。该技术尚未应用于分析有机非线性光学（NLO）材料。通过制备厚度范围从亚微米到200微米的高质量客体-主体NLO聚合物薄膜来解决这一问题，这使得通过紫外-可见-近红外光谱能够准确测量NLO材料在四个数量级上的全光谱吸收系数。利用陶赫模型和一种新的单对数-洛伦兹模型研究了含有各种推-拉发色团的客体-主体NLO聚合物的光吸收边，并分析了光学带隙和乌尔巴赫边对材料结构和组成的依赖性。结果揭示了乌尔巴赫指数尾向低能尾的关键转变，该低能尾与电信波长下材料的振动泛音重叠。在本研究中确定有机NLO薄膜的基本吸收区域，为通过在带边附近的波长下操作并控制光损耗来利用材料的共振增强非线性系数的研究提供了定量的见解。
