Sol-Gel Synthesis of Ge Nanocrystals-Doped Glass and Its Photoluminescence

Ge nanocrystal-embedded SiO₂ glasses were prepared by a sol-gel process. The glasses synthesized through the hydrolysis of Si(OC₂H₅)₄ and GeCl₄ were heated in H₂ gas atmosphere at 500 to 800°C, in which Ge⁴⁺ ions were reduced to precipitate nanosized Ge crystals with the size smaller than 10 nm diameter. Glasses doped with Ge nanocrystals of diameter of ≈5 nm showed the optical absorption edge at ≈2.8 eV and a broad photoluminescence exhibiting the peak at around 2.2 eV. Large Ge crystals precipitated by heating above 800°C showed no photoluminescence.