Wide bandgaps and strong SHG responses of hetero-oxyfluorides by dual-fluorination-directed bandgap engineering.

A wide bandgap is an essential requirement for a nonlinear optical (NLO) material. However, it is very challenging to simultaneously engineer a wide bandgap and a strong second-harmonic generation (SHG) response, particularly in NLO materials containing second-order Jahn-Teller (SOJT) distorted units. Herein, we employ a bandgap engineering strategy that involves the dual fluorination of two different types of SOJT distorted units to realize remarkably wide bandgaps in the first examples of 5d-transition metal (TM) fluoroiodates.