Second-harmonic generation (SHG) and photoluminescence properties of noncentrosymmetric (NCS) layered perovskite solid solutions, CsBi_1−xEu_xNb₂O₇ (x = 0, 0.1, and 0.2)

Solid solutions of noncentrosymmetric (NCS) Dion–Jacobson phases, CsBi_1−xEu_xNb₂O₇ (x = 0, 0.1, and 0.2), have been synthesized through standard solid-state reactions. Powder X-ray diffraction analysis suggests that the solid solutions crystallize in the NCS polar orthorhombic space group, P2₁am (no. 26). CsBi_1−xEu_xNb₂O₇ reveal layered perovskite structures that are composed of corner-shared distorted NbO₆ octahedra and the stereoactive A-cation, Bi³⁺. Powder second-harmonic generation (SHG) measurements of the reported materials show that CsBiNb₂O₇, CsBi_0.9Eu_0.1Nb₂O₇, and CsBi_0.8Eu_0.2Nb₂O₇ possess SHG efficiencies 50, 30, and 25 times that of α-SiO₂, respectively. The decrease in the SHG for Eu³⁺-doped compounds is attributable to the deficiency of the net moment generated from the polyhedra of the polarizable lone pair cation, Bi³⁺. The stronger electric dipole transition bands compared to those of the magnetic dipole transitions in the photoluminescence emission spectra of CsBi_1−xEu_xNb₂O₇ confirm the asymmetric coordination environment of Bi³⁺/Eu³⁺ sites in the framework.