Un-doped and 1.5% Pb2 þ doped zinc aluminate (ZnAl2O4) was successfully prepared at a relatively low
temperature ( $ 80 °C) using the sol–gel process. The Zn/citric acid (CA) mole fraction was varied from
0.083 to 1.3. The X-ray diffraction (XRD) data revealed that most of the annealed samples consist of the
cubic ZnAl2O4 structure with ZnO impurities. The surface morphology of the phosphors was influenced
by the Zn/CA mole fractions. The increase in the CA content lead to the morphological evolution and
transformation from small particles to rods-like-needles. The nanopowder samples exhibited violet
luminescence that varied from 400 to 410 nm, which suggested that the CA content affected the bandgap
energy of the host. The results suggest that the emission originated either from the host, Pb2 þ or ZnO
impurities. Emission at 400 nm is attributed to the oxygen vacancies (V0*) in the host and emission peak
at 410 nm is attributed to the intrinsic defects emission of ZnO, while the emission at 552 nm is
attributed to the second order emission of the excitation wavelength. The emission intensity was
influenced by the Zn/CA mole fractions. The CIE colour coordinates of all samples are close to each other
in the blue region. Two distinct peaks were observed at around 160 and 385 °C in thermo luminescence
(TL) glow curve, which indicates that there are two set of traps.