M4LiBe4P7O24 and M4Li(Li3P)P7O24 (M = Cs, Rb): deep-ultraviolet nonlinear-optical phosphates with a tetrahedra-substituted paracelsian-like framework.

New paracelsian-like beryllophosphates M₄LiBe₄P₇O₂₄ and their tetrahedra-substituted phases M₄Li(Li₃P)P₇O₂₄ (MLiP₂O₆, M = Cs, Rb) were designed and synthesized. Interestingly, two types of phases undergo a structural transformation, resulting from the radius and valence charge number of tetrahedral cations. Four crystals demonstrate potential deep-UV NLO properties such as short absorption edges (<190 nm) and phase-matching SHG response. [ABSTRACT FROM AUTHOR]