Synthesis, second-harmonic generations (SHG), and photoluminescence (PL) properties of Ca4Bi6-xLnxO13 (Ln=La and Eu) solid solutions

Abstract

Noncentrosymmetric (NCS) Ca4Bi6-xLnxO13 (Ln=La and Eu; x=0, 0.06, and 0.12) solid solutions have been synthesized through conventional solid state reactions by using CaCO3, Bi2O3, and Ln2O3. Crystal structures of the reported materials have been determined by powder X-ray diffraction using Rietveld method. Ca4Bi6-xLnxO13 solid solutions crystallizing in the polar NCS space group, C2mm (No. 38), are composed of uni-dimensional bands with BiO3 and BiO5 polyhedra. Second-harmonic generation (SHG) measurements, using 1064nm radiation, indicate that Ca4Bi6-xLnxO13 solid solutions are type-I phase-matchable and reveal moderate SHG efficiencies ranging from 30 to 80 times that of α-SiO2. Detailed structure-SHG property relationship analyses suggest that the net moment arising from the alignment of the asymmetric polyhedra of the lone pair cation, Bi3+ in Ca4Bi6-xLnxO13 solid solutions is critical for the observed SHG phenomena. Photoluminescence (PL) properties measurements on Ca4Bi6-xEuxO13 solid solutions reveal the characteristic narrow emission lines attributable to 5D0→7Fj (j=4, …, 0) transitions and confirm the unsymmetrical coordination environment of the doped-Eu3+ cation sites. Further PL measurements at different temperatures suggest that while Ca4Bi6-xEuxO13 exhibit the nonradiative emissions at high temperatures, the solid solutions show the radiative emissions with strong intensities at low temperatures.