Preparation and photoluminescence of sol-gel-derived Ge-nanocrystals-doped SiO2 glasses

Ge nanocrystal-embedded SiO2 glasses were successfully prepared by a sol-gel process. The glasses synthesized through hydrolysis of Si(OC2H5)4 and GeCl4 were heated in the presence of hydrogen at 400 to 700 degree(s)C, in which Ge4+ ions were reduced to precipitate nanosized Ge crystals. Glasses doped with Ge nanocrystals of a diameter of approximately 5 nm showed the optical absorption edge at approximately 2.5 eV and a strong room temperature photoluminescence with peaks at 2.35, 2.15 eV and weak at 1.85 eV. Large Ge crystals precipitated by heating above 800 degree(s)C showed no photoluminescence.