Luminescent nanometer-sized silicon particles are fabricated by laser ablation of a silicon target in helium gas. The formation of products is found to be governed by the dynamics of the laser-ablated silicon particles in the gas. The products deposited on silicon substrates exhibit light emission with a peak at 1.6 eV in the air, while 2.1 eV after annealing for 20 min at 800°C in oxygen gas. Applying the laser ablation technique, we demonstrate a novel technique for fabricating silicon particles embedded in a silicon dioxide film. The particles also exhibit visible light emission.

An AlGaN/GaInN heterostructure has been fabricated by metalorganic vapor phase epitaxy. We observed room-temperature (RT) violet stimulated emission from an optically pumped double heterostructure (DH) using GaInN as an active layer. The peak wavelength of the stimulated emission at RT from Al0.17Ga0.83N/Ga0.91In0.09N DH is 402.5 nm, and the threshold of excitation power density is about 0.13 MW/cm2.

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We have developed a method for synthesizing SiOx films with visible light emission, applying a laser ablation technique. The films were formed by depositing laser-ablated silicon particles in oxygen gas diluted with helium gas. Soft X-ray absorption spectroscopy revealed that the composition of the film is controlled by the total pressure of the gas. Films with particular composition exhibit intense red photoluminescence with a peak below 1.5 eV after annealing in argon gas at 1000°C. In addition to this, most of the films exhibit 2.2-eV photoluminescence after annealing at 500°C. On the basis of these results, the origin of the photoluminescence is discussed.

A new method for the determination of naturally occurring imino acids in plants was devised. This method comprises the formation of dinitrophenyl derivatives and their measurement by HPLC. The determination limits were 100 pmol for 4-hydroxypipecolic acid (HPA) and proline (Pro) and 10 pmol for pipecolic acid (Pip). The recoveries of HPA, Pro, and Pip from leaf homogenate of an Acacia species were 95.9 ± 2.8, 100.5 ± 1.7, and 101.1 ± 2.3%, respectively. HPA was found in leaves, seeds, and roots of five kinds of Acacia but not in leaves of other members of the legume family. The HPA content of Acacia dealbata link leaves was much higher in winter than in summer. From X-ray analysis, HPA was found to be hydrated by two water molecules that are situated in a vacant channel formed by the molecular arrangement of HPA. HPA had no remarkable physiological or pharmaceutical activities. Keywords: 4-Hydroxypipecolic acid; pipecolic acid; Acacia species; leguminous plants; determination

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