Polar polymorphism: alpha- and beta-KCsWP(2)O(9)nonlinear optical materials with a strong second harmonic generation response

摘要

To design ultraviolet (UV) nonlinear optical (NLO) materials, we focused on the combination of second-order Jahn-Teller (SOJT) cations and PO4. After systematic investigation, we discovered two polar polymorphs of KCsWP2O9, which were synthesized through a conventional high temperature method in an open system. These compounds exhibit a large second harmonic generation (SHG) response (up to 16.8 x KH2PO4, KDP) at 1064 nm. Meanwhile, high temperature phase beta-KCsWP(2)O(9)possesses a short UV cutoff edge (<270 nm) despite the presence of a d(0)element W. First-principles electronic structure analyses suggest that the strong SHG response of alpha- and beta-KCsWP(2)O(9)is attributed to non-bonding O-2p orbitals (in the VB) and strong orbital interactions of W-5d orbitals and O-2p orbitals in WO6(in the CB). This work may offer new guidance for the subsequent synthesis of d(0)transition metal containing NLO crystals with a large SHG response.