The effects of varying the Eu³⁺ concentration on the structural and optical properties of Mg_1.5Al₂O_4.5:x% Eu³⁺ (0 ≤ x ≤ 2) nanophosphors prepared by sol–gel method

Mg_1.5Al₂O_4.5:x% Eu³⁺ (0 ≤ x ≤ 2) nanopowders were successfully synthesized via sol–gel method. The X-ray diffraction (XRD) spectrum revealed that the Mg_1.5Al₂O_4.5:x% Eu³⁺ matches the single phase of face-centred cubic MgAl₂O₄. The estimated average crystallite sizes calculated using the XRD spectra were found to be in the order of 4 nm. The estimated crystal size was confirmed by the high-resolution transmission electron microscopy. The energy dispersive X-ray spectroscopy confirmed the presence of all expected elementary composition (Mg, Al, O and Eu). The field emission gun scanning electron microscope showed that varying the Eu³⁺ concentration influence the morphology of the prepared nanophosphor. The photoluminescence results showed that the host emits the violet colour at around 382 nm, which was attributed to the defects within the band gap (E_g) of host material. The Eu³⁺-doped samples showed the emission at around 560, 580, 593, 618, 655 and 704 nm which are, respectively, attributed to the ⁵D₁ → ⁷F₃, ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃ and ⁵D₀ → ⁷F₄ characteristic transitions in Eu³⁺. The International Commission on Illumination colour chromaticity showed that the Eu³⁺ doping influences the emission colour.