Taro Uematsu

Nanoparticles of I–III–VI semiconductors are promising candidates for novel non-toxic fluorescent materials. However, removal of defect levels responsible for their broad-band emission has not been successful to date. The present study demonstrates, for the first time, the coating of core AgInS2 nanoparticles—one of the I–III–VI group semiconductors with a bandgap in the visible region—with III–VI group semiconductors. The AgInS2/InSx and AgInS2/GaSx (x = 0.8–1.5) core/shell structures generate

Luminescent AgInS2−AgGaS2 solid solution nanoparticles were synthesized by thermal decomposition of a single-source precursor, AgInyGa1−y(S2CN(C2H5)2)4 in oleylamine. Transmission electron microscopy showed formation of nanoparticles of good crystallinity with their size ranging from 4 to 5 nm. X-ray powder diffraction spectra showed peaks which were attributable to the chalcopyrite structure, and their peaks were continuously shifted to higher angle as the Ga to In ratio increased. Photolumines

Among cadmium-free quantum dots (QDs), ternary or quaternary chalcogenide semiconductor QDs composed of groups 11, 13, and 16 elements have extensively been studied. Herein, monodispersed quaternary nanoparticles of silver indium gallium sulfide (AgInxGa1–xS2) are synthesized by a new route that specifically produces the target product without solid byproducts. The difference in the reactivity between groups 11 and 13 metals with chalcogen is a common issue in synthesizing the groups 11, 13, and

Recent advances in in situ transmission electron microscopy (TEM) techniques have provided unprecedented knowledge of chemical reactions from a microscopic viewpoint. To introduce volatile liquids, in which chemical reactions take place, use of sophisticated tailor-made fluid cells is a usual method. Herein, a very simple method is presented, which takes advantage of nonvolatile ionic liquids without any fluid cell. This method is successfully employed to investigate the essential steps in the g

Cadmium-free quantum dots (QDs) consisting of silver-indium-gallium-sulfide (AIGS) quaternary semiconductors were successfully synthesized using a metal-dithiocarbamate complex with sufficiently high reactivity to produce metal sulfides. The introduction of a gallium diethyldithiocarbamate precursor decreased the reaction temperature to produce active intermediates, which were subsequently converted into AIGS QDs at 150 °C with silver and indium acetates. Because of the low reaction temperature,

Ternary and quaternary semiconductor quantum dots (QDs) are candidates for cadmium-free alternatives. Among these, semiconductors containing elements from groups 11, 13, and 16 (<i>i.e.</i>, I-III-VI₂) are attracting increasing attention since they are direct semiconductors whose bandgap energies in the bulk state are tunable between visible and near infrared. The quaternary system of alloys consisting of silver indium sulfide (AgInS₂; bandgap energy: <i>E</i> _g

Photoetching of CdTe nanocrystals was applied to thiol-capped CdTe quantum dots (QDs) to control their fluorescence wavelength. CdTe QDs with a high quantum yield (49%) were synthesized in aqueous solution, and they were successfully photoetched in strong alkaline (pH = 13.5) conditions. When monochromatic light was used, size-selective photoetching could be conducted; the photoetching proceeded until the band gap energy of the CdTe QDs increased to the energy corresponding to the wavelength of

Redox-dependent emission quenching of low toxic ZnS-AgInS(2) semiconductor nanocrystals was studied and the obtained behavior was found to be applicable to fabrication of fluorescent biosensors in combination with redox enzymes.

Metal–organic framework (MOF) based light harvesting has been attracting considerable attention as an artificial antenna for photochemical and photophysical applications. Herein, we report the photoluminescence enhancement of semiconductor quantum dots (QDs) via efficient energy transfer from a light-harvesting framework (IRMOF-3) surrounding each QD as a surface modifier. IRMOF-3 crystals were directly grown on the surface of QDs without any intermediate layer such as polymers. The observed pho

Quenching of emissions from cadmium telluride (CdTe) nanoparticles was distinctly observed by the addition of various electrochemically active organic molecules. The quenching ability of organic molecules is greatly influenced not only by their valency and redox potential but also by a type of capping ligand and the particle size of the CdTe nanoparticles. These effects are systematically studied through the fluorescence intensity and its lifetime changes based on photoinduced electron transfer

Investigating metal-ion transport in ionic liquid media is important to realize batteries and electrodeposition, which utilize intriguing properties of the media. An in situ electrochemical scanning electron microscopy together with X-ray fluorescence spectrometry is developed by a simple modification of an instrument as a tool for the investigation. Diffusion of silver ions (Ag+) in an ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonylamide (BMI-TFSA) is monitored as the time var

A spectrally narrow band edge emission is generated in the green region from cadmium-free quantum dots comprised of silver indium gallium sulfide coated by gallium sulfide shells. The thickness of the gallium sulfide shell is increased by using gallium tris(diethyldithiocarbamate) as a supplementary precursor showing a strong adhesion with the quantum dot cores. Photoluminescence intensity and spectral shape of the core/shell quantum dots with the thicker shells are unchanged after 90 days. An i

The electron transfer between the fluorescent ZnS–AgInS2 solid-solution (ZAIS) nanoparticles (NPs) and redox species is investigated in an aqueous solution in terms of chemosensors and photocatalysts. In a case where the ZAIS NPs and quenchers are oppositely charged, very efficient photoluminescence (PL) quenching (KS ≈ 106 M–1) is observed because of the specific adsorption of quenchers on particles. The quenching magnitude increases with the potential gap between the photoexcited NPs and quenc

A simple method for evaluating the conditions of ligands used to stabilize photoluminescent cadmium chalcogenide nanoparticles is reported. Photoluminescence quenching in the presence of electron acceptors was observed for nanoparticles modified with alkylamines and alkanethiols having different chain lengths, which are commonly used as capping ligands for semiconductor nanoparticles. The magnitude of quenching significantly varied with the ligand type and with time after nanoparticle purificati