Effect of Annealing Temperature on the Structure, Morphology and Photoluminescence Properties of MgAl2O4:0.1% Eu3+ Nanophosphor Prepared by Sol-Gel Method

Un-doped and 0.1% Eu3+-doped magnesium aluminate (MgAl2O4) nanomaterials were synthesized using the sol-gel method. The effects of annealing temperature (AT) from 600-1300 degrees C on the crystal structure, morphology and photoluminescence properties were investigated. X-ray powder diffraction showed that below 650 degrees C the structure consists of poorly crystalline and amorphous phases. A cubic phase structure corresponding to MgAl2O4 was formed at AT above 700 degrees C. Generally, the crystallite sizes increased with an increase in AT. Energy-dispersive x-ray spectroscopy results confirmed the presence of the anticipated elementary composition. The scanning electron microscope and transmission electron microscope images suggested that the AT influenced the morphology, crystallite sizes and shape of the prepared phosphors. Photoluminescence (PL) results showed that the emissions peaks at 384 and 561nm originate from defects located at different levels within the host material. The emission peaks at 561 nm, 581 nm, 594 nm, 618 nm, 655 nm and 701nm were attributed to the ((D1F4)-D-5-F-7) ((D0F0)-D-5-F-7), ((D0F1)-D-5-F-7), ((D0F2)-D-5-F-7), ((D0F3)-D-5-F-7) and ((D0F4)-D-5-F-7) transitions of Eu3+ ion. Emission peaks from Eu3+ were observed to increase in intensity as the AT was increased. Luminescence enhancement was observed when increasing the AT to 650 degrees C, while further increase lead to luminescence quenching. The Commision Internationale de l'Eclairage (CIE) coordinates results showed that the emission colour shift can be tuned from bluish to reddish by varying the AT.