Visible room-temperature photoluminescence of Ge-doped SiO2 glasses fabricated by a sol-gel process

Ge-doped SiO2 glasses are prepared by a sol-gel method using ethyl silicate (Si(OC2H5)4) and 3-trichologermanium propanoic acid (Cl3GeCH2CH2COOH) as starting materials. The Ge-doped SiO2 glasses show a strong room-temperature photoluminescence with peaks at 585 and 654 nm under the excitation of the 514.5 nm line of an Ar+ laser. The peak position of photoluminescence spectrum weakly depends on the Ge/Si ratio. The photoluminescence intensity increases sharply as the Ge/Si ratio is increased. The Ge-doped SiO2 gel glasses were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. It reveals that Ge atoms exist as amorphous GeO2 particles in the gel glasses. The size of the amorphous Ge oxide nanoparticles increases with an increase in the content of Ge in the starting materials, and thus optical absorption edge is shifted towards longer wavelengths. The 585 and 654 nm emissions may originate from the small “peroxy radical” and the nonbridging oxygens at the interface between the amorphous GeO2 core and outer SiO2 matrix, respectively.