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

Abstract

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.