Cs2VOF4(IO2F2): Rationally designing a noncentrosymmetric early-transition-metal fluoroiodate

Abstract

F-containing early-transition-metal (ETM) iodates are an interesting material class for the exploration of nonlinear optical (NLO) crystals. However, their rational structural design remains a great challenge due to the poor structural predictability of inorganic structures. In this report, we analyzed the structural features of F-containing ETM iodates and obtained some rules for guiding the synthesis of the different types of F-containing ETM iodates. With these rules, we have successfully synthesized a new ETM fluoroiodate, Cs₂VOF₄(IO₂F₂), which exhibits not only a large second harmonic generation (SHG) response (5 × KDP at 1064 nm and 0.7 × KTP at 2090 nm) but also a moderate birefringence (0.088@1064 nm) and a short UV cutoff edge (257 nm). This indicates that the rational structural design of F-containing ETM iodate NLO crystals is possible based on a good understanding of their structural chemistry.