Sol-gel method for synthesizing visible photoluminescent nanosized Ge-crystal-doped silica glasses

Ge-nanocrystal-embedded SiO2 glasses were 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 400–700 °C, in which Ge4+ ions were reduced to precipitate nanosized Ge crystals. Glasses doped with Ge nanocrystals of diameter of ∼5 nm showed a strong room-temperature photoluminescence with peaks at 2.32, 2.17, and 2.0 eV. Large Ge crystals precipitated by heating at 800 °C showed no photoluminescence.