| 研究実績の概要 |
Properties of lanthanides-doped nanocrystals were studied since the optical gain was derived from the doped nanocrystals. The size dependent study shows that nanocrystals of large size would have high quantum efficiency. Quenching effect derived from adsorbed ligands on the surface of nanocrystals is the main reason for the size dependent phenomenon. Ligands with short methylene chain showed weak quenching effect. By considering about the procedure of synthesis and emission properties, we synthesized citrate-capped KY3F10 nanocrystals with the size of about 20 nm by a hydrothermal method. The synthesizing procedure was carefully selected to prepare such nanocrystals.
The parameters that control the fabrication process of self-written waveguides were studied. Bisphenol A ethoxylate diacrylates (BPAEDA), P3B, IRT were used as monomer, photoinitiator, and photosensitizer, respectively. The concentrations of chemicals decide the rate of photopolymerization process. Power of the induced laser influences the speed of writing waveguides. High power is helpful to write, but difficult to maintain the shape of waveguides. Wavelength of laser decides the length of waveguides. The mixture of monomer, photoinitiator, and photosensitizer has a broad absorption band in visible and near-infrared regions. If the wavelength of induced laser is in the absorption bands, it is difficult to fabricate long waveguides. The self-writing technique is derived from the nonlinear effect of monomers. Technique of doping chalcogenide nanoparticles into polymers was developed to enhance nonlinearity.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
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理由
The study of emission properties of lanthanide-doped nanocrystals has been partially finished. The size dependent discussion shows the optimal particle size range might be selected around 20-30 nm. The ligands adhered on the surface of nanocrystals should have short methylene chain. Thus, citrate was selected. By a hydrothermal method, citrate capped nanocrystals with 20 nm were synthesized. Polymers doped with these nanocrystals have high transparency and well emission properties. For the applications in the C band, Er3+,Yb3+ and Ce3+ were used as activator and sensitizers. Other lanthanide ions were planned to be tested, e.g. Tb3+, Ho3+, Dy3+, and Pr3+. At present, however, investigation of Dy3+ and Pr3+ has not been completed yet. Measurement of quantum efficiency is undergoing to quantitatively investigate the sensitizing effect of other lanthanide ions and to practically select the crystal hosts.
Investigation of the technique of laser-induced self-written waveguides is well progressing as planned. Parameters, such as wavelength and power of induced laser were well understood. Waveguides with the length of about 1 cm can be well reproduced. Complex structures, for example spatial “X”-type are under fabricating. The self-written technique is derived from a nonlinear effect. To enhance nonlinearity of polymers, chalcogenide nanoparticles were attempted to dope into polymers, which has a high nonlinearity. Chalcogenide nanoparticles were successfully doped into PMMA. But chalcogenide nanoparticles doped BPAEDA was difficult to polymerize. Further effort should be made.
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| 今後の研究の推進方策 |
Measurement of quantum efficiency of Er3+-doped nanocrystals will be completed. According to quantum efficiency, optimal concentration of dopants and hosts are finally decided. The percentage of nanocrystals in polymers will be carefully determined to maintain a high transparency. Laser-induced self-written waveguide containing nanocrystals will be fabricated. Optical gain and amplified spontaneous emission of the waveguide in the C band will be studied. Due to the upconversion emissions of Er3+, optical gain in visible region will also be studied.
Laser-induce self-written waveguides with complex spatial structure should be fabricated. The angles of incident light from two single mode fibers will be precisely controlled. Cross-waveguides on the same planar with the “X” and “Y” type will be prepared. Optical gain and loss of these complex waveguides containing nanocrystals will be measured. Vertical position of the two incident fibers will be adjusted precisely to fabricate spatial “X” type structure. The optical coupling between the two waveguides will be studied.
Based on the spatial “X” type, the optical logical gate will be studied. Signal propagates in one waveguide, and pump light propagates in the other. The doped nanocrystals have high optical gain in the C band. When pump light pass through the cross point of the two waveguides, the signal light will be amplified. If the pump light is pulsed, the output of signal should be pulsed. Thus, optical logical gate can be achieved in the complex waveguide structure containing nanocrystals.
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