Stokes and anti-Stokes blue light emissions of thermal-evaporated silica sub-micron wires

Based on the thermal evaporation of silicon monoxide at high temperature, an improved method has been developed for large-scale synthesis of ultralong amorphous silica sub-micron wires using polished p-Si wafers as substrates. The synthesis was done with and without thermite. The morphology and structure of the silica wires was investigated through field-emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy, and X-ray diffractometer. Almost uniform sub-micron wires with average diameters of 300 nm and length up to hundreds of micrometers were obtained in presence of thermite while sub-micron wires with many curved segments were obtained in absence of the thermite. Both forms of silica wires emitted blue lights at 478 nm (∼2.6 eV) under excitation at 351 nm (∼3.5 eV), while intense anti-Stokes blue emissions at 464 nm (∼2.7 eV) were observed under the 694 nm (∼1.8 eV) excitation due to the upconversion effect. This effect is associated with defect centers arising from high oxygen deficiency. The emissions from oxygen deficiency centers might be caused by multistep energy transfer from nonbridging oxygen hole centers to oxygen deficiency centers.