Observation of Electron−Hole Carrier Emission in the Eu3+-Doped Silica Xerogel

The luminescence properties of Eu 3+ encapsulated in sol−gel-derived optically transparent silica gels were investigated by time-resolved laser spectroscopy. At the xerogel stage, the emission spectra originated mainly from Eu 2+ at 410 nm, and only a small contribution from Eu 3+ at 580 nm and electron−hole (e - −h + ) carrier at 530 nm were observed. It is proposed that in the presence of Eu 3+ the carriers, e - −h +, were generated during the polycondensation reaction of silica and trapped at the defect sites of sol−gel matrix. The formation of e - −h + carrier was illustrated to be responsible for the surface-assisted reduction of europium ions, where the ejected electrons from the oxygen-associated hole centers react with Eu 3+ encapsulated in silica gel to produce Eu 2+ ions.