Radiative energy transfer in ZnAl2O4:0.1% Ce3+, x% Eu3+ nanophosphor synthesized by sol–gel process

Zinc aluminate (ZnAl2O4) hosts and 0.1% Ce3+, x% Eu3+ co-activated ZnAl2O4 phosphor were successfully prepared at a relatively low temperature (~80 °C) using the sol–gel method. The co-activator (Eu3+) concentration was varied in the range of 0≤x≤2 mol%, while the 0.1% Ce3+ was kept constant. The X-ray diffraction (XRD) data revealed that all annealed samples consisted of the pure cubic ZnAl2O4 structure. The estimated crystallite size was in the range of 18–21 nm in diameter. The results showed that the full width at half maximum (FWHM) increased with the increase in Eu3+ mol%, which suggested a decrease in particle size. The nanopowder microstructure revealed that the material consisted of non-uniform sizes and the loss of lattice fringes as the Eu3+ concentration was increased suggested the increase in strain or disorder. The photoluminescence (PL) results showed that the host, activated and co-activated nanophosphor emitted at different wavelengths. The peak shifts suggested that the luminescence might originate either from the defects in the host, Ce3+ or Eu3+ ions. The incorporation of the co-activator (Eu3+) at higher concentration resulted in radiative energy transfer from Ce3+→Eu3+. The CIE colour coordinates showed a shift from the blue to orange region as the Eu3+ concentration was increased.