Structural inhomogeneity of Ge-doped amorphous SiO2 probed by photoluminescence lifetime measurements under synchrotron radiation

We report a study of the photoluminescence (PL) time decay of the B-type center, characterized by an optical absorption band peaked at similar to 5.2 eV and two related PL bands peaked at similar to 3.2 eV and similar to 4.3 eV, in sol-gel Ge-doped a- SiO2 under excitation by synchrotron radiation. Measurements were carried out by excitation in UV and in vacuum-UV (VUV), and were performed in the temperature range from 8 K up to 300 K in order to isolate the effects of the intersystem-crossing process, proposed to link the two emission bands of the center. Repeating the time decay measurement at several emission energies falling inside the 4.3 eV band, we have observed a variation of the PL decay lifetime with spectral position. The estimated lifetime decreases by more than 25% on increasing emission energy both at high and at low T. The results are interpreted as a fingerprint of the inhomogeneity of the centers and suggest that this method is a direct tool to probe the environment effects on the optical properties of point defects. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.