A Non‐π‐Conjugated Molecular Crystal with Balanced Second‐Harmonic Generation, Bandgap, and Birefringence

Abstract

AbstractTraditional nonlinear optical (NLO) crystals are exclusively limited to ionic crystals with π‐conjugated groups and it is a great challenge to achieve a subtle balance between second‐harmonic generation, bandgap, and birefringence for them, especially in the deep‐UV spectrum region (Eg > 6.20 eV). Herein, a non‐π‐conjugated molecular crystal, NH3BH3, which realizes such balance with a large second‐harmonic generation response (2.0 × KH2PO4 at 1064 nm, and 0.45 × β‐BaB2O4 at 532 nm), deep‐UV transparency (Eg > 6.53 eV), and moderate birefringence (Δn = 0.056@550 nm) is reported. As a result, NH3BH3 exhibits a large quality factor of 0.32, which is evidently larger than those of non‐π‐conjugated sulfate and phosphate ionic crystals. Using an unpolished NH3BH3 crystal, effective second‐harmonic generation outputs are observed at different wavelengths. These attributes indicate that NH3BH3 is a promising candidate for deep‐UV NLO applications. This work opens up a new door for developing high‐performance deep‐UV NLO crystals.