Effect of defects on the band gap and photoluminescence emission of Bi and Li co-substituted barium strontium titanate ceramics

Since the discovery of an effective role for defects in improving the performance of ceramic materials in practical application, investigation of defects and their impact on the development of optical properties in condensed matter physics have received widespread attention. In this work we synthesized a lead free (Ba0.60Sr0.40)(1-x)(Bi, Li)xTiO3 (BST6:BLx%); (0%< 8%) ceramics using a conventional solid-state reaction method. X-ray diffraction patterns along with Rietveld refinement, Micro-Raman (MR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), UV-visible, Electron Spin Resonance (ESR) and photoluminescence (PL) measurements are utilized to characterize these ceramics. XRD, and Raman analysis have proven cubic phase symmetry with a contraction in bond length as the Bi and Li concentrations increased. XPS and ESR results confirm the presence of Ti3+ surface defects (TSD) and oxygen vacancies (VO) on the co-substituted samples sintered at high temperature. The optical results show a decrease in the bandgap energy from 3.14 eV to 2.76 eV and a wide-PL band emission on the green band, caused by recombination of the radiative free electrons and holes trapped around the surface oxygen vacancies. Defect levels created within the bandgap might act as recombination centres, and this can give the possibility of using BST6:BLx as a green light emission source in future practical applications.

Automated summary

The study synthesized a lead-free ceramic containing Bi and Li, finding that as the concentrations of Bi and Li increased, the ceramic exhibited cubic phase symmetry with a contraction in bond length. XPS and ESR results confirmed the presence of Ti3+ surface defects and oxygen vacancies on the surfaces of samples sintered at high temperature. Optical results showed a decrease in bandgap energy from 3.14 eV to 2.76 eV and a wide PL band emission on the green band, caused by recombination of radiative free electrons and holes trapped around the surface oxygen vacancies.