Ba6In6Zn4Se19: a high performance infrared nonlinear optical crystal with [InSe3]3− trigonal planar functional motifs (This work is dedicated to Professor Wengdan Cheng on the occasion of his 70th birthday.)

An excellent nonlinear optical (NLO) material should satisfy many critical requirements simultaneously. How to balance all the requirements is a challenge, as they cause contradictory demands on structural attributes. Here, we use a high entropy strategy to integrate the advantages of ZnSe for a large NLO coefficient and a planar [InSe3]3− functional motif for phase matching. The resulting Ba6In6Zn4Se19 crystal shows excellent comprehensive NLO properties, i.e. a large effective NLO coefficient (2 × AgGaS2), a high laser induced damage threshold (LIDT, 15.5 × AgGaS2), a wide transmission range (0.52–22.5 μm), and an increased birefringence (Δn = 0.098) for phase matching. Theoretical calculations indicate that planar [InSe3]3− is an effective NLO functional motif for tuning birefringence and the “cocktail effect” realized via the high entropy strategy is important to improve the overall NLO performance. This study provides a promising way of developing new NLO materials with excellent comprehensive performance.