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°C on the crystal structure, morphology and photoluminescence properties were investigated. X-ray powder diffraction showed that below 650°C the structure consists of poorly crystalline and amorphous phases. A cubic phase structure corresponding to MgAl₂O₄ was formed at AT above 700°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 561 nm 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 701 nm were attributed to the (⁵D₁ → ⁷F₄) (⁵D₀ → ⁷F₀), (⁵D₀ → ⁷F₁), (⁵D₀ → ⁷F₂), (⁵D₀ → ⁷F₃) and (⁵D₀ → ⁷F₄) 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°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.