Sodium–rare earth carbonates with shorite structure and large second harmonic generation response

Two non-linear optical crystalline carbonates (Na3Y(CO3)3 and Na3Gd(CO3)3) were synthesized under subcritical hydrothermal conditions, and both of them crystallized in the non-centrosymmetric space group Ama2 (40). Their crystal structures, analogous to shorite, can be described as alternate stackings of [Na(CO3)2]∞ and [Na2RE(CO3)2]∞ (RE = Y, Gd) layers, which are parallel to the bc plane. Second harmonic generation (SHG) studies indicated that Na3Y(CO3)3 and Na3Gd(CO3)3 have large SHG responses of approximately 3.57 and 3.54 times that of KH2PO4 (KDP), respectively, and the SHG responses were phase-matchable in the visible region. Furthermore, they exhibited wide transparent regions from UV to near IR with short UV cut-off edges at about 220 nm, suggesting that these crystals are promising UV non-linear optical (NLO) materials.