Ultraviolet nonlinear optical crystals A3SrBi(P2O7)2(A = K, Rb) with large second harmonic generation responses

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Abstract
Ultraviolet nonlinear optical (UV NLO) crystals are the key and basic materials for solid-state lasers. Phosphates as UV NLO crystals are limited in practical applications due to their weak second-harmonic generation (SHG) response. In this work, two non-centrosymmetric pyro-phosphates of K3SrBi(P2O7)2 and Rb3SrBi(P2O7)2 have been synthesized by a high-temperature solution method. Systematic property measurements show that they both have short UV cut-off edges (∼240 nm) and large SHG responses (4 × KDP for K3SrBi(P2O7)2 and 2.1 × KDP for Rb3SrBi(P2O7)2). Thus, they are both promising UV NLO candidates. In particular, K3SrBi(P2O7)2 shows the strongest SHG response in the family of A3BBi(P2O7)2 (A = K, Rb, B = Sr; A = Rb, Cs, B = Ba, Pb), which is about twice higher than that of isomorphic Rb3SrBi(P2O7)2. The study of the structure–property relationship shows that the synergistic effect of P2O7 dimers and BiO6 polyhedra is the main contribution to their excellent NLO properties. And better orientations of P2O7 dimers and larger distortion of BiO6 units play important roles in enhancing the SHG response of K3SrBi(P2O7)2.
Funding Information
  • Natural Science Foundation of Tianjin City (20JCJQJC00060, 19JCZDJC38200)
  • National Natural Science Foundation of China (22071179, 51802217, 51972230, 61835014, 51890865)
  • Tianjin Science and Technology Program (19ZYPTJC00070)
  • National Key Research and Development Program of China (2016YFB0402103)