6 research outputs found
Photoluminescence time decay of surface oxygen-deficient centers in pure and Ge-doped silica
Luminescence activity of surface and interior Ge-oxygen deficient centers in silica
We report a comparative study on the optical activity of surface and interior Geâoxygen deïŹcient centers in pressed porous and
solâgel Ge-doped silica, respectively. The experimental approach is based on the temperature dependence of the two photoluminescence
bands at 4.2 (singletâsinglet emission,
S1!
S0) and 3.1 eV (tripletâsinglet emission,
T1!
S0), excited within the absorption
band at about 5 eV. Our data show that the phonon assisted intersystem crossing process, linking the two excited electronic states, more eïŹective for surface than for interior centers in the temperature range 5â300 K. For both centers, a distribution of the activation
energies of the process is found. Based on the results of quantum chemical calculations of the electronic structure of (HO)2Ge:
molecule it is suggested that the electronic de-excitation pathway involves two excited triplet states (S1! T2! T1!
S0) and shows
structural dependence on the OâGeâO angle.
2005 Elsevier B.V. All rights reserved