Photoinduced conversion of optically active defects in germanium-doped silica

Optical absorption, photoluminescence (PL), and electron paramagnetic resonance (EPR) data on unirradiated and UV-irradiated Ge-doped silica are reported. The analysis of the UV-induced effects shows the following facts: (i) both components of the 5-eV absorption band are partially bleached, as well as the PL excited within this absorption band; (ii) more consistent UV-induced changes arise at higher energies where bands at 5.8 and 6.4 eV grow during the treatment; (iii) Ge-E' and Si-E' EPR centers are UV generated, confirming their involvement in the photoconversion process but ruling out previous attribution of the 6.4 eV to Ge-E' centers; and (iv) the absorption band at 6.4 eV shows previously unobserved emission properties, probably due to excitation transfer processes.