Associated Aspects on Structure, Morphology and Photoluminescence of MgAl ₂ O ₄ :x% Gd ³⁺ Nanophosphor Prepared via Citrate Sol–Gel Method

MgAl ₂ O ₄ :x% Gd ³⁺ (0 ≤ x ≤ 3) nano-powders were prepared via the citrate sol–gel method. The x-ray diffraction confirmed that the prepared samples consist of the cubic crystalline structures. There was no secondary phases due to Gd ³⁺ doping. The estimated average grain sizes were found to be in the order of 8 nm. Energy dispersive spectroscopy showed the presence of the anticipated elements (Mg, Al, O, and Gd). The scanning electron microscope results revealed that the morphology of the samples is influenced by the Gd ³⁺ concentration. Transmission electron microscopy analysis revealed that the prepared samples are in the nano-scale range. Selected area electron diffraction patterns indicated highly crystalline structure and the intensities of the bright spots varied with Gd ³⁺ concentration. Photoluminescence studies showed two distinct emission peaks at 385 and 392 nm, which are certainly attributed to the defects levels located at different positions on the host material (MgAl ₂ O ₄ ). The emission peaks located at 315 and 628 nm were respectively attributed to the ⁶ P _7/2 → ⁸ S _7/2 and ⁶ G _7/2 → ⁶ P _3/2 transitions in the Gd ³⁺ ion. The luminescence intensity of the 388 nm decreased with an increase in the Gd ³⁺ concentration. Commission Internationale de l’Eclairage (CIE) coordinates showed that the violet emission color from host cannot be tuned by varying Gd ³⁺ concentration.