Heqing Yang

Photoluminescence of Ge nanoparticles embedded in SiO2 glasses fabricated by a sol–gel method

Ge nanoparticles with different sizes in silica glasses were prepared by a sol–gel method using Cl3–Ge–C2H4–COOH as a Ge source. The size of the Ge nanoparticles decreases with a reduction in the content of Ge in the starting materials, and thus the optical absorption edge shifts to a higher energy. Silica gel glasses doped with Ge nanoparticles showed a strong room-temperature photoluminescence with peaks at 568, 607, 672, 722, and 775 nm. The peak position of photoluminescence spectrum scarcely depends on the Ge/Si ratio. However, the photoluminescence intensity increases sharply as the Ge/Si ratio is reduced. The photoluminescence arises from the Ge clusters of diameter of <1–2 nm with a molecular character instead of nanocrystalline Ge with the diamond structure.

Femtosecond nonlinear optical properties of carbon nanoparticles

The nonlinear optical properties and ultrafast electron-relaxation dynamics of carbon nanoparticles were investigated by using the femtosecond optical Kerr effect and pump-probe techniques. The blueshift of the absorption edge with the decrease of the size of the nanoparticles reveals the opening of the gap. The magnitude of χ(3) for carbon nanoparticles is calculated to be 8.3×10−13u2009esu, which arises from the contribution of delocalized feature of the π electrons. The decay of photobleaching includes a fast and a slow component, which are assigned to the relaxation of the free carriers and trapped carriers, respectively. It is found that the lifetimes of two components of bleaching decrease as temperature of heat treatment is increased.

Sol-gel preparation of Ge nanocrystals embedded in SiO2 glasses

Abstract Ge nanocrystals embedded in SiO 2 glasses were prepared by an easy sol–gel method. The gels synthesized through hydrolysis of Si(OC 2 H 5 ) 4 and 3-trichloro-germaniumpropanoic acid (Cl 3 –Ge–C 2 H 4 –COOH) were heated at 600°C for 10xa0h in air atmosphere to form GeO 2 –SiO 2 glasses. The gel-glasses were further heated at 500–700°C in H 2 gas atmosphere, in which Ge 4+ were reduced to precipitate cubic Ge nanocrystals. The size of Ge crystals is estimated to be from 1 to 13xa0nm according to the XRD and TEM. The optical absorption edge shifts to higher energy with decrease in the content of Ge in the starting materials, and in the heating temperature and time in H 2 gas atmosphere. This phenomenon is interpreted in terms of a quantum confinement effect of electrons and holes in the Ge nanocrystals.