Infrared (IR) nonlinear optical (NLO) crystal, as the core device of all solid-state laser, plays a critical role in generating new mid-/far-IR (3–20 μm) lights based on frequency conversion technologies. Hence, exploring new IR nonlinear optical materials is an urgent need for advanced photoelectric technologies. However, the discovery of new materials with strong second-order NLO response, wide band gap and broad IR transparent region that covering the 3–5 and 8–14 μm IR atmospheric windows is challenging. Chalcophosphate, combining the structural advantages of chalcogenide & phosphate, and showing a high probability (~30 %, much higher than the one of ~15 % in the inorganic compounds) to generate noncentrosymmetric crystal structures, was demonstrated as a promising system for searching new IR NLO crystals with excellent optical properties, and a great many NLO-active chalcophosphates were reasonably designed and fabricated.

Recently, to advance the targeted design of high-performance IR NLO crystals, the research group at Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Science reviewed the abundant structural and chemical diversities of chalcophosphates, with a particular emphasis on the connection modes of distinguished [PxQy] units; and the efficient progress on the structural design that achieved in the thiophosphate-, selenophosphate-, and mixed anionic-based chalcophosphate IR NLO candidates in recent years. Finally, the upcoming opportunities and challenges in the captivating fields were discussed.

The paper was published in Coordination Chemistry Reviews with the title“Chalcophosphates: A plentiful source of infrared nonlinear optical materials”. This work was financially supported by the Strategic Priority Research Program of the Chinese Academy of sciences (XDB0880000), the Natural Science Foundation of the Xinjiang Uygur Autonomous Region (2024D01E30), and the National Natural Science Foundation of China (22475234, 22335007, 22193044 and 22361132544).

 The structural chemistry and design strategy of chalcophosphate IR NLO materials.