Transition from Eu³⁺ to Eu²⁺ in SiO₂ matrix prepared by sol-gel

Activated silica matrix fluorescent materials doped with Al³⁺ and Eu²⁺ are prepared by sol-gel method. The effects of different atmospheres and annealing temperatures on luminescent properties are characterized by analysis techniques including X-ray diffraction, infrared spectroscopy and fluorescence spectra. When being excited at 281 nm wavelength, the fluorescent materials show a strong broad blue emission band, with the emission center at 430 nm and the FWHM of 56 nm. The results indicate that the blue emission is derived from 4f₆ 5d to 4f₇ transition of the Eu²⁺ ions. Al³⁺ ion plays a key role in the process of deoxidization from Eu³⁺ to Eu²⁺. Al³⁺ and B³⁺ can enhance the blue-emission intensity. Also it is found that the highest luminescent intensity of the samples occurs in the sample Eu-03 annealed at 1150 °C in N₂ atmosphere.