Analysis of varying Gd3+ concentrations on the structure and optical properties of ZnAl2O4:0.1% Eu3+; x% Gd3+ (0 ≤ x ≤ 1.2) synthesized via citrate sol–gel method

We report the preparation of 0.1% Eu 3+ ; x % Gd 3+ (0 ≤ x ≤ 1.2) ZnAl 2 O 4 phosphors using the citrate sol–gel method. X-ray diffraction (XRD) data revealed that all annealed samples consisted of the single phase of cubic ZnAl 2 O 4 structure. The scanning electron microscopic (SEM) images indicated pronounced effect of dual doping on the surface morphology of the phosphor. The estimated crystal sizes estimated by the XRD was confirmed by the high-resolution transmission electron microscopy (HR-TEM) to be approximately around 20 nm. The photoluminescence (PL) spectroscopy results revealed four distinct emission peaks located at 393, 400, 578 and 618 nm. The peaks at around 393 and 400 nm were attributed to the defect levels located at different positions on the host material (ZnAl 2 O 4 ). The emission peak at 578 and 618 nm were attributed to the 5 D 0 → 7 F 1 and 2 D 0 → 7 F 2 characteristic transition within the Eu 3+ ions. The International Commission on Illumination (CIE) colour coordinates revealed that the emission colour was not influenced by varying the concentration of Gd 3+ .