Inch-sized K[NH2(CH2COO)2]: a High-Performance UV Nonlinear Optical Crystal Enabled by Novel Flexible π-Conjugated Building Units, [NH2(CH2COO)2]−

Abstract

High-performance ultraviolet (UV) nonlinear optical (NLO) crystals must exhibit three critical properties: a large second-harmonic generation (SHG) response, adequate birefringence, and a short UV cutoff edge. However, these key characteristics are often interdependent and challenging to achieve simultaneously within a single crystal. In this study, a novel non-centrosymmetric compound, K[NH₂(CH₂COO)₂] is introduced, synthesized from the innovative flexible π-conjugated group [NH₂(CH₂COO)₂]⁻. Benefiting from the excellent microscopic optical properties of the flexible π-conjugated [NH₂(CH₂COO)₂]⁻ groups, despite the suboptimal arrangement of groups within the compound, K[NH₂(CH₂COO)₂] still demonstrates a remarkable balance in its linear and nonlinear optical performance. This includes a strong SHG response of 3 times that of KDP, suitable birefringence of 0.088@1064 nm, and a short UV cutoff edge at 208 nm. Emphatically, high-quality, inch-sized single crystals (up to 60 × 46 × 30 mm³) are successfully grown using a water solution technique, paving the way for practical applications of this promising material.