Strategy for a Rational Design of Deep-Ultraviolet Nonlinear Optical Materials from Zeolites.

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play a crucial role in cutting-edge laser technology. In order to solve the serious layered growth tendency of the sole commercial DUV NLO crystal KBe2BO3F2 (KBBF), developing alternative systems of compounds with bulk crystal habits has become an urgent task for practical applications. Herein, a novel strategy was developed by applying non-centrosymmetric (NCS) cancrinite (CAN)-type zincophosphates {Na6(OH)2(H2O)2}Cs2[ZnPO4]6 with bulk-crystal habits as the prototype to design new DUV NLO crystals. Two new anhydrous alkali zincophosphates, namely, {(Li6 -xNaxO)A2}[(ZnPO4)6] (A = Cs, Rb; x = 2-3) crystallizing in the NCS hexagonal space group P63 (no. 173) with a CAN-type framework, were successfully synthesized via a modified fluoro-solvo-hydrothermal method by applying triethylamine (TEA) and concentrated NaF solution as a co-solvent. Interestingly, the rigidity of the NCS CAN-type framework acting as the host ensures the non-centrosymmetry of the resulting new compounds. Meanwhile, the replacement of water molecules by guest cationic species in the channels or cages can greatly improve the thermal stability of the resultant crystal and tune its NLO properties. The synergetic effect of the host framework and the guest species makes the two compounds transparent down to the DUV region (<200 nm) and exhibit SHG effects. Therefore, the proposed rational design strategy of applying the known zeotype NCS frameworks as prototypes together with the modified fluoro-solvo-hydrothermal method opens a great avenue for highly effectively exploring new DUV NLO materials.

Rational Design and Synthesis of a Deep-Ultraviolet Nonlinear Optical Fluorinated Orthophosphate: BaZn(PO4)F.

Rational design and tailored synthesis of noncentrosymmetric compounds with nonlinear optical (NLO) properties, especially in the deep-ultraviolet (deep-UV) region, remains a great challenge. Herein, we report on the development of a modified fluoro-solvo-hydrothermal method with two additive reagents (trimethylamine and NaF solution) as the solvents, using BaFe(PO4)(OH) ( P212121) as the prototype, for the rational design and tailored synthesis of the first deep-UV fluorinated orthophosphate, BaZn(PO4)F. It crystallizes in the polar space group Pna21 and exhibits transparency down to deep-UV region (<190 nm) with SHG effect at 0.26 × KH2(PO4). Its structure is built from strictly alternating ZnO4F trigonal bipyramids and PO4 tetrahedra, resulting in a four-connected ABW-type zeolite framework. First-principles calculations confirm the deep-UV absorption edge and reveal that ZnO4F plays an essential role in the NLO properties. The synergetic effect of Zn and F atoms leads to its more polar crystal structure, much deeper absorption edge, and better SHG effect than the prototype.