Unique synthesis, structure determination, and optical properties of seven new layered rare earth tellurite nitrates, RE(TeO3)(NO3) (RE = La, Nd, Eu, Gd, Dy, Er, and Y)

Abstract

Seven new rare earth tellurite nitrates, RE(TeO3)(NO3) (RE ¼ La, Nd, Eu, Gd, Dy, Er, and Y), have been synthesized in closed autoclaves in the absence of solvent using TeO2 and corresponding rare earth metal nitrate hydrates. Although all the reported rare earth tellurite nitrates are stoichiometrically equivalent, the crystal structures are different. While RE1(TeO3) (NO3) (RE1 ¼ La and Nd) crystallizing in the monoclinic space group, P21/n (No. 14) exhibit layered backbones composed of RE1O9, TeO3, and NO3 groups, RE2(TeO3)(NO3) (RE2 ¼ Eu, Gd, Dy, Er, and Y), crystallizing in the orthorhombic space group, Cmca (No. 64) reveal layered frameworks consisting of RE2O8, TeO4, and NO3 units. The frameworks include infinite chains of (TeO3)n. Band gaps derived from the UVevis diffuse reflectance spectral data for the title compounds range from 3.6 to 4.4 eV depending on the extent of 4d, 5d, and/or 4f orbitals of rare earth metal cations as well as the distortions arising from unsymmetrical tellurites. Other characterizations including infrared spectroscopy, thermal analyses, dipole moment calculations, and photoluminescence measurements are also discussed.