Luminescent properties and X-ray photoelectron spectroscopy study of ZnAl 2O 4:Ce 3+,Tb 3+ phosphor

Abstract

Cerium (Ce 3+)- and terbium (Tb 3+) co-doped zinc aluminate (ZnAl 2O 4) 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 ZnAl 2O 4 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 ZnAl 2O 4 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 ZnAl 2O 4:Ce 3+,Tb 3+ samples, with different concentrations of Ce 3+ and Tb 3+ ions, were excited at different wavelengths showed that green emission of Tb 3+ was sensitized by Ce 3+, i.e. there was energy transfer from Ce 3+ to Tb 3+ resulting in improvement of green emission from Tb 3+. This study therefore, sets out to discuss the sensitizing effect of Ce 3+ and the effect of annealing on the structure of ZnAl 2O 4:Ce 3+,Tb 3+.