Fluorescence properties of Eu3+ and Eu2+ in Al2O3-SiO2 glass

Absorption, fluorescence and optical excitation spectra of the Eu2+ and Eu2+ ions in Al2O3-SiO2 glass prepared by the sol-gel method are investigated. When the Eu3+-doped glass is healed in H-2, the Eu3+ ions are almost reduced to the Eu2+ ions. By reheating of the Eu2+-doped glass in air, the fluorescence intensity for the Eu2+ ions decreases, and the fluorescence intensity for Eu3+ ions increases with increasing the heating time and is saturated to 1.5 times of the intensity before heating in H-2. This significant increase in the Eu3+ fluorescence is related to the energy transfer from Eu2+ ions to Eu3+, in which the energy corresponding to the 4f(6)5d(E-g) --> S-8(7/2) transition of the Eu2+ ion causes to excite the Eu2+ ion to the D-5(2) state. When the Eu2+-doped glass is irradiated with a Hg lamp for 2 h, the fluorescence intensity for the Eu3+ ions returns no more than 10% of the intensity before healing in H-2. This behavior is thought to be related to the capturing of the excited electrons in the trapping centers near the Eu2+ ions. (C) 1998 Elsevier Science B.V. All rights reserved.