Structural and optical properties of La and Gd substituted Bi4 − xMxV2O11 − δ (0.1 ≤ x ≤ 0.3)
Bi4 − xMxV2O11 − δ (M = La, Gd; 0.1 ≤ x ≤ 0.3) is synthesised by a solid state reaction method to study the effect of La3+ and Gd3+ substitution for Bi on the structural and optical properties. The as-prepared samples are characterised by X-ray diffraction, Fourier transform infrared analysis, UV–visible spectroscopy, scanning electron microscopy and energy-dispersive spectroscopy. The refinement results confirmed that even substituted samples exhibit monoclinic structure with space group C2/m. The parameters like band gap energy; Urbach energy has been calculated from the UV–visible spectra. It has been observed that even substitution at the bismuth site by isovalent cations decreases the energy band gap. The lowest observed band gap is 1.86 eV for Bi3.9La0.1V2O11 − δ. The grain size and defects were observed to increase with increasing substitution along with the amount of secondary phase.