Synthesis and characterization of CaAlxOy:Eu2+ phosphors prepared using solution-combustion method

Europium-doped calcium aluminate (CaAlxOy:Eu2+) phosphors were obtained at low temperatures (500 °C) by the solution - combustion of corresponding metal nitrate-urea solution mixtures. The particle size and morphology and the structural and luminescent properties of the as-synthesized phosphors were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Auger spectroscopy, transmission electron spectroscopy (TEM) and photoluminescence (PL). It was found that the Ca:Al molar ratios showed greatly influence not only on the particle size and morphology, but also on their PL spectra and structure. With the Ca: Al molar ratios increasing from 6:100 to 26:100, the structure of as-synthesized phosphor changed from CaAl12O19 to monoclinic CaAl2O4 and the dominant emitting light from red to blue, implying that the oxidation state of doped europium ions changed from trivalent to divalent due to the structure variation of host lattice. A blue phosphor with almost pure phase can be easily prepared by solution combustion method with suitable Ca:Al molar ratio.