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We have studied the origin of visible photoluminescence of Ge nanocrystals in SiO2 glassy matrix. Spectroscopic analyses of Ge nanocrystals indicate that the room-temperature photoluminescence comes from Ge nanocrystals of diameter of 4 nm or less. High-resolution electron microscopic studies imply that the structure of Ge nanocrystals of diameter ≤4 nm differs from the diamond structure. These data suggest that new nanostructure crystalline Ge having a character of direct optical transition exhibits the visible photoluminescence.

We have studied and compared the optical properties of both porous Si and the chemically synthesized planar and cubic Si skeleton clusters. Broad photoluminescence with large Stokes shifts were observed at the visible region in both samples. Spectroscopic analysis suggests that the surface of porous Si is similar to a condensation of Si clusters. Small Si clusters play a key role in the strong room-temperature photoluminescence in porous Si.

Electrodeposited Fe-Co films are commonly prepared in a boric-acid-based bath. In this research, we applied citric acid instead of boric acid for the plating of Fe-Co films because boron in the waste bath is restricted by environmental-protection regulations in Japan. We evaluated the effect of citric acid on the magnetic and structural properties of the films. The saturation magnetization of the Fe-Co films slightly increased while the Fe content in the Fe-Co films decreased with increasing citric acid concentration. The lowest coercivity value of 240 A/m was obtained at a citric acid concentration of 100 g/L. The plating bath with this citric acid concentration enabled us to obtain Fe-Co films with high saturation magnetizations and smooth surface morphologies.

The origin of visible photoluminescence of Ge microcrystals (pc-Ge) in SiOz glassy matrices was examined. The spectroscopic analyses and formation mechanism show that the origin of strong light emission with nanosecond decay time is attributed to the effective surface termination and the new nanostructure of pc-Ge with diameter less than 4 nm which forms from reduction reaction of germanium oxides at low annealing temperature.