Thorium doped and thorium-carbon co doped metastable β-Bi2O3

Abstract

β- Bi2O3 was stabilized by doping it with 10 mol % of thorium following solution combustion synthesis and co precipitation method. The samples have been characterized extensively. Formation of tetragonal β- Bi2O3 was confirmed for these samples from powder X-ray diffraction and Raman spectroscopy measurements. The presence of oxygen vacancies in these samples was inferred from the band near 615 cm−1 in the Raman spectra as well as emission in the blue region in photoluminescence spectra. While flaky morphology was noticed for β-Bi2O3 sample from combustion synthesis, sample from co precipitation method showed porous morphology. The inclusion of thorium was verified from energy dispersive spectral analysis. The optical band gap of 10 mol % thorium doped β-Bi2O3 sample prepared by combustion synthesis was 2.24 eV which was lower than undoped α-Bi2O3 (2.67 eV). Further reduction in the band gap was observed for 10 mol % thorium doped β-Bi2O3 sample from co precipitation method (2.03 eV). Such a drastic reduction was attributed to the additional doping of carbon (7.87%) in the sample as verified from X-ray photoelectron spectroscopic analysis. Samples from combustion synthesis and co precipitation methods exhibited BET surface area of 209 and 117 m2/g, respectively. Although samples from both these synthetic methods showed the presence of defects, β-Bi2O3 from co precipitation method showed better efficiency than the sample from combustion method due to band gap narrowing.