KNa2Y2B2O6F3: a beryllium free deep-UV nonlinear optical crystal with well-balanced properties.

A novel rare earth fluoroborate deep-UV crystal, KNa2Y2B2O6F3, was identified through the functional-motif assembly strategy. This compound exhibits a wide bandgap of 5.6 eV with an UV cutoff below 200 nm, a moderate birefringence of 0.041 at 532 nm, and a strong SHG response comparable to that of KDP.