Luminescent properties and X-ray photoelectron spectroscopy study of ZnAl2O4:Ce3+,Tb3+ phosphor

Cerium (Ce3+)- and terbium (Tb3+) co-doped zinc aluminate (ZnAl2O4) nanocrystals were successfully prepared by a combustion method using urea as fuel. The as-prepared samples were annealed in hydrogen atmosphere to improve their optical properties and crystallinity. The structure and morphology of the samples analyzed using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) showed that ZnAl2O4 crystallized in a well known cubic spinel structure. As deduced from X-ray photoelectron spectroscopy (XPS) data, there was partial inversion of cations in as-prepared (unannealed) samples implying that the ZnAl2O4 did not crystallize in a cubic normal spinel. Instead, the XPS data demonstrated possible structural readjustment from inverse to normal spinel after annealing. The excitation and emission data collected when ZnAl2O4:Ce3+,Tb3+ samples, with different concentrations of Ce3+ and Tb3+ ions, were excited at different wavelengths showed that green emission of Tb3+ was sensitized by Ce3+, i.e. there was energy transfer from Ce3+ to Tb3+ resulting in improvement of green emission from Tb3+. This study therefore, sets out to discuss the sensitizing effect of Ce3+ and the effect of annealing on the structure of ZnAl2O4:Ce3+,Tb3+.

► Highly crystalline ZnAl2O4:Ce3+,Tb3+ powder phosphors were prepared using solution combustion method at low temperature.
► Structural readjustment from normal to inverse spinel confirmed from XPS data.
► Energy transfer from Ce3+ to Tb3+ demonstrated.