Hg-Based Infrared Nonlinear Optical Material KHg4Ga5Se12 Exhibits Good Phase-Matchability and Exceptional Second Harmonic Generation Response

• Published in: Chemistry of materials 2017-09, Vol.29 (18), p.7993-8002
• Main Authors: Zhou, Molin, Yang, Yi, Guo, Yangwu, Lin, Zheshuai, Yao, Jiyong, Wu, Yicheng, Chen, Chuangtian
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.7b03143

High-performance infrared (IR) nonlinear optical (NLO) materials with large NLO response and suitable birefringence are urgently needed for various applications. A Hg-based IR NLO material KHg4Ga5Se12 with such desirable properties has been newly discovered. In the structure, obviously distorted HgSe4 and GaSe4 tetrahedra are connected to each other by vertex-sharing to form a three-dimensional framework with the counterion K+ residing in the cavities. Remarkably, all the NLO-active building units in the title compound are arranged in a completely parallel manner. Such a topological structure and the large susceptibility of the Hg–Se bonds enable the material to achieve good phase-matchability with a tremendous powder second harmonic generation (SHG) response at 2.09 μm that is about 20-times that of the benchmark material AgGaS2 (one of the largest responses among all the phase-matchable IR NLO chalcogenides reported to date). The optical band gap of KHg4Ga5Se12 was determined as 1.61 eV. Moreover, on the basis of the electronic band structure, the real-space atom-cutting analysis, the SHG-weighted electronic densities, and the local dipole moments calculations, the origin of the superior linear and nonlinear optical properties of the title compound is ascribed to the (Hg/Ga)­Se4 group. The calculated values for the maximum coefficient d 33 and birefringence (Δn) at 2.09 μm are −65.257 pm/V and 0.072, respectively. Such values agree well with experimental observations. Our study demonstrates that Hg-based metal chalcogenides are a class of IR NLO material with competitive features (good phase-matchability, very large SHG efficiency, wide transparency) desirable for practical applications.