Electronic structure and luminescence studies of Bi doped MgO nanophosphors

Abstract

Mg1-xO:Bi-x (x = 0.01-0.5 mol%) nanophosphors have been prepared using the solution combustion method and subsequent annealing at 1173 K in air. Rietveld refinement on X-ray diffraction (XRD) data confirmed the rock-salt phase formation in pure and Bi3+ doped MgO (space group; Fm3m). Lower Bi3+ ion concentrations in Mg1-xO:Bi-x (x = 0.01 and 0.05 mol%) lead to tensile strain and increased lattice parameters of MgO. Higher doping concentrations of Bi3+ ions (x = 0.1-0.5 mol%) lead to a decrease in the lattice strain, unit cell parameters, and Mg-O bond length. Transmission electron microscopy (TEM) images along with selected area electron diffraction (SAED) patterns confirmed the crystalline nature of Mg1-xO:Bix samples with an average particle size of similar to 37.5 nm. X-ray absorption spectroscopy (XAS) results at the Mg K-edge and Bi L-edge confirmed the Mg2+ ions and Bi3+ ions in Mg1-xO:Bi-x samples throughout the Bi doping range. O-K edge XAS conveys the hybridization of the frontier orbitals of O and Bi atoms. UV-visible absorption spectroscopy measurements convey the defect-induced absorption peak shifting in Mg1-xO:Bi-x compounds. Dopant and host defect-assisted PL emission is observed, with prominent emission in the blue region owing to the transition between P-3(1) to S-1(0) and P-3(0) to S-1(0) of Bi3+. The quenching effect on PL properties has been observed beyond 0.05 mol% doping of Bi3+ ions. The presence of various defect states and their stability with re-trapping and charge transfer behaviour have been analyzed by thermoluminescence studies of gamma-irradiated samples, which enable the Mg1-xO:Bi-x samples for potential applications in display device dosimetry.