Pnictides: An emerging class of infrared nonlinear optical material candidates

New infrared nonlinear optical (IR NLO) crystals with strong NLO efficiency, high laser damage threshold, excellent phase-matching ability and good IR transmittance, are urgently desirable because the commercial IR NLO materials (e.g., AgGaS2, AgGaSe2, and ZnGeP2) with inevitable defects are limited for high power laser applications. Pnictides are highly promising IR NLO candidate materials due to their probably large second-order NLO coefficient. After years of silence, the exploration on pnictide NLO crystals has emerged bring out numbers of excellent IR NLO pnictides. This review summarizes the achievements on IR NLO pnictides by focusing on their crystal structures and several key NLO indexes, and then get deep insight into their structure-property correlations. Furthermore, the existing issues and prospective development of NLO pnictides are also proposed and discussed.