Aliovalent-substituted synthesis for a non-centrosymmetric phosphate with enhanced nonlinear-optical response

Non-centrosymmetric structure is the most important prerequisite for a nonlinear-optical (NLO) material. Herein, a non-centrosymmetric phosphate LiRb₂Y₂(PO₄)₃ (1), which is transparent down to ultraviolet region, was synthesized by the high-temperature solid-state reactions and solution method. Its crystal structure features a three-dimensional framework composed of corner-sharing YO₆ octahedra and PO₄ tetrahedra. Although it is isostructural to the known langbeinite-type sulfate K₂Zn₂(SO₄)₃, 1 exhibits a sharply enhanced NLO effect (about 3 times that of K₂Zn₂(SO₄)₃). On the basis of structural analysis and theory calculations, the improved performance of compound 1 is mainly ascribed to the aliovalent replacement of ZnO₆ by YO₆ octahedra. Our studies indicated that it may be an effective method to develop non-centrosymmetric compounds by aliovalent substitution.