A fundamental study on the effects of nano-silver incorporation on the structure and luminescence properties of color centers in γ′-alumina nanoparticles

Abstract

Xsilver/(1-X)γ’-alumina nanopowders (X = 0, 0.02, 0.04 and 0.06mol%) were synthesized and the structural, optical and luminescence properties were studied fundamentally. The Rietveld refinements of X-ray diffraction patterns were carried out on the basis of the tetragonal model with a space group of P4̅m2. The SEM images and the results obtained from average crystallite shape using the GFourier program indicated semi-spherical shape of alumina nanoparticles with diameter ranges from 16 to 50nm and average crystallite sizes of 2.12–2.54nm as well as rod-shaped silver nanostructures with diameter from 11 to 23nm, rod lengths between 20 and 100nm and average crystallite sizes of 13–30nm. Uv–vis absorption spectra of all samples showed two absorption bands at 6.02eV and 5.1eV related to the 1S→1P and 1S→21B electronic transitions in the color centers. The mechanisms involved in the luminescence of F-and F+-centers for the synthesized nanopowders were also studied. The effects of the local field of silver nanoparticle induced by localized surface plasmon resonance (LSPR) on the luminescence mechanisms of F-and F+-centers were investigated. The PL spectra of silver-doped samples showed two emission peaks at 3.13–3.20eV and 4.02eV related to 31B→1S of F-centers and 21B→1S of F+-centers transitions. Blue-shifts of about 0.13 and 0.15eV were occurred for the band emissions of F and F+-centers in nano state compared to the bulk state. With increasing of Ag concentration, the intensity and FWHM of the PL spectra for F and F+ emissions increased. PLE spectroscopy at the monitoring emission of 31B →1S transition was carried out to investigate the band excitation of F-centers.