Recent progress in the design of IR nonlinear optical materials by partial chemical substitution: Structural evolution and performance optimization

Infrared nonlinear optical (IR-NLO) crystals as a crucial part in all-solid-state lasers to generate coherent tunable laser beam in the IR range, an important spectral interval for molecular spectroscopy, medical treatment, atmospheric sensing, and scientific researches. Currently, commercially available IR-NLO materials are very rare, limited to chalcopyrite semiconductors (e.g., AgGaS2, AgGaSe2 and ZnGeP2). Unfortunately, all of them present certain limitations, which significantly restrict their applications in high-power laser devices. For this reason, it is extremely urgent to discover new type of IR-NLO compounds with better overall performance. Yet, one of the biggest challenges is how to create the non-centrosymmetric (NCS) crystal structures, which is the prerequisite for the generation of IR-NLO candidates. To accomplish this objective, various approaches have been introduced to design new NCS compounds and many most advanced IR-NLO candidates have been discovered during the past decades. Among them, molecular engineering strategies, especially partial chemical substitution based on the known NCS or centrosymmetric (CS) maternal structures, have been confirmed as a simple yet highly effective method to design and synthesize new high-performance IR-NLO materials. This strategy can not only achieve CS-to-NCS or NCS-to-NCS structural transformation, but also effectively improve the IR-NLO performance of target materials through simple element or basic building unit substitution. In this review, 33 selected examples (including 11 types of CS-to-NCS compounds and 22 types of NCS-to-NCS compounds) ranging from zero-dimensional (0D) isolated clusters to three-dimensional (3D) complex frameworks designed through the partial chemical substitution strategy are discussed and summarized systematically. Finally, some useful conclusions and the future development opportuni-ties and challenges of IR-NLO materials based on the rational partial chemical substitution are briefly discussed.(c) 2023 Elsevier B.V. All rights reserved.