Comparison of sol-gel and solid state prepared Eu2+ doped calcium aluminates

The Eu2+ doped calcium aluminates (CaAl2O4:Eu2+) was prepared by the sol-gel method. The structure and luminescence properties of the title compound were studied and compared to the corresponding properties of the materials prepared by a conventional solid state reaction. The use of the sol-gel method in preparation lowered the reaction threshold temperature by c.a. 200 oC. An unusual hexagonal form of CaAl2O4:Eu2+, which cannot be prepared by the solid state reaction, was obtained by a sol-gel method. The 4 UV excited luminescence and afterglow bands of the hexagonal CaAl2O4:Eu2+ were observed at a slightly longer wavelength than that of the normal monoclinic phase due to small differences in the crystal field effect on the splitting of the excited 4f65d1 configuration of the Eu2+ ion. The afterglow lifetime of the hexagonal phase was slightly longer than that of the monoclinic one due to deeper traps. (author)