| Summary: | Un-doped (Mg1.5Al2O4.5) and 0.88% Cd2+ doped MgxAl2O3+x nano-powders were synthesized via citrate sol-gel method. The Mgx concentration was varied in the range of 0.25 ≤ x ≤ 4.5. The X-ray diffraction (XRD) data revealed that Mg0.25Al2O3.25:0.88% Cd2+ consists of poorly crystalline and amorphous phases. For the MgxAl2O3+x:0.88% Cd2+ (0.5 ≤ x ≤ 4.5) series, the XRD revealed that the nano-powders consist of face centered cubic MgAl2O4 spinel crystal structure for x ≤ 2 and face centered cubic MgO crystal structure for x ≥ 2.5. The estimated crystal size ranged from 4 to 14 nm, which the estimated crystal size of the un-doped and the doped was confirmed by the transmission electron microscopy (TEM). The photoluminescence (PL) results showed that the un-doped and the 0.88% Cd2+ doped nano-powders generally emits a violet emission at 407 nm, which is attributed to the bandgap defects within the host material. The emission peaks at 495 and 656 nm are attributed to the F center and the abundance of oxygen vacancies within lattice due to a higher calcination temperature of 800 °C. The PL and XRD results showed the phase mutation from MgAl2O4 to MgO. The maximum PL intensity was observed from the Mg1.5Al2O4.5:0.88% Cd2+ sample. Increasing the Mgx content up-to 1.5 lead to luminescence intensity enhancement, while a further increase of Mgx content leads to concentration quenching. The International Commission on Illumination (CIE) color chromaticity showed that the color shifts from blue to greenish (blue-green vertex region) when ranging Mgx content. Keywords: Citrate sol-gel, Spinel, Cd2+-doped, Luminescence, CIE
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