Facile Growth of an Ultraviolet Hydroisocyanurate Crystal with Strong Nonlinearity and a Wide Phase-Matching Region from π-Conjugated (HC₃N₃O₃)²– Groups

Mixed-alkali-metal hydroisocyanurate nonlinear-optical crystal RbLi(HC 3 N 3 O 3 )·2H 2 O was grown by a facile aqueous solution method. It exhibits a short phase-matching wavelength (λ PM = 239 nm) and a strong second-harmonic-generation response ( d eff = 2.1KDP) benefitting from the well-aligned planar π-conjugated (HC 3 N 3 O 3 ) 2– anions, as confirmed by the first-principles calculations. Moreover, solar blind ultraviolet radiation can be reached using the title crystal via a fourth-harmonic-generation technique of a Nd-based laser, i.e., 1064 nm/4 = 266 nm.