Nonlinear optical (NLO) crystals are widely used to develop new laser source for their second-harmonic generation (SHG) properties. Searching new ultraviolet (UV) nonlinear optical crystals that can generate UV coherent sources has become the focus for active demand in laser and optical communication industry.

In a study published in J. Am. Chem. Soc., a research team led by Prof. YE Ning from Fujian Institute of Research on the Structure of Matter (FJIRSM) of Chinese Academy of Sciences (CAS) reported a new hydro-isocyanurate KLi(HC₃N₃O₃)·2H₂O (KLHCY) with outstanding UV NLO properties through solvent-drop grinding method.

Guided by anionic group theory, researchers firstly focused on alkali metal isocyanurates as candidates of new UV NLO crystals because large π-conjugated (HC₃N₃O₃)^2–group may provide excellent NLO properties and alkali metals can avoid absorption in the UV region.

Through the innovative combination of neutral reaction solvent-drop grinding method and powder second-harmonic generation (SHG) technique, they discovered a series of mixed alkali isocyanurates with large SHG responses, ABHC₃N₃O₃·xH₂O (AB=KLi, RbLi, RbNa, CsNa), based on the AOH-BOH-H₃C₃N₃O₃ (A/B=Li, Na, K, Rb, Cs) system.

Then the mixed alkali hydro-isocyanurate KLiHC₃N₃O₃·xH₂O was determined as KLi(HC₃N₃O₃)·2H₂O (KLHCY).

KLHCY is the promising UV NLO crystal with a large SHG coefficients (5.3×KDP), a high laser damage threshold (4.76GW/cm²) and a large birefringence (0.186), which reduces Type I phase-matching to 246 nm.

Centimeter-level KLHCY single crystals were easily grown by water solution method.

KLHCY with large SHG response can be synthesized and grown by solvent-drop grinding method and water solution method, respectively. (Image by Prof. YE’s group)