The effects of varying the annealing period on the structure, morphology and optical properties of MgAl2O4:0.1% Mn2+ nanophosphors

In this study, magnesium aluminate nanopowders doped with manganese ions (MgAl2O4:0.1% Mn2+) were prepared by citrate sol-gel technique. The consequences on the structural, morphological and optical properties when varying the annealing period (AP) at a fixed annealing temperature of 800 degrees C and dopant concentration (0.1% Mn2+) were investigated. The AP was varied at the range of 1-6 h. X-ray powder diffraction (XRD) results showed that doping with 0.1% Mn2+ and varying the AP did not influence the crystal structure of the host (un-doped) material. The scanning electron microscope (SEM) images suggested that doping does not influence the morphology of the prepared nanopowders and varying the AP slightly influence the particle size. Transition electron microscopy (TEM) image suggested that the crystallite sizes were below 15 nm. The ultraviolet-visible (UV-Vis) diffuse reflection spectroscopy showed that the band gap of the MgAl2O4:0.1% Mn2+ can be tuned from 5.04 to 4.58 eV with varying AP. Photoluminescence (PL) results showed two emission peaks located at around 413 and 655 nm. They were attributed to the defect levels within the host material and to the (T-4(1) -> (6)A(1)) transitions of Mn2+, respectively. Increasing the AP significantly influences the luminescence of the prepared powders. The CIE coordinate results showed that the bluish emission colour can be changed to the violet region when AP was increased.