Toshihiro Kuzuya

Synthesis of Ag–In binary sulfide nanoparticles—structural tuning and their photoluminescence properties

In this report, we demonstrate the synthesis of binary sulfide Ag–In–S NPs using a Ag–In thiolate complex. Thermal decomposition of the thiolate complex provides Ag/AgInS2 heterostructured nanoparticles (NPs). A metathesis reaction between the thiolate complex and sulfur source leads to the formation of nearly monodispersed AgInS2 NPs with a chalcopyrite-like or orthorhombic structure. AgInS2 NPs with a chalcopyrite-like structure exhibited room temperature photoluminescence (PL). Spectral shift of the PL band depending on the excitation laser intensity and characteristic behavior of the PL decay time varying over a wide energy range within the PL band were observed. These results indicate that the PL of the AgInS2 NPs may be attributed to the donor–acceptor (D–A) pair recombination.

Phase control and its mechanism of CuInS2 nanoparticles.

CuInS(2) nanoparticles (NPs) usually take chalcopyrite-(CP) structure. Recently, CuInS(2) NPs with pseudo-wurtzite (WZ) structure, which is thermodynamically less favored, have been synthesized. However, the formation mechanism of this metastable-phase has not been understood yet. In this report, the key issue of phase selectivity of CuInS(2) (CIS) NPs has been investigated using various metal sources and ligands. Experimental results suggested that the crystalline structure and morphology of CIS NPs were decided by the stability of indium ligand complex; the active ligand reduces the precipitation rate of In(2)S(3), resulting in pre-generation of Cu(2)S seed NPs. Crystallographic analogy and superionic conductivity of Cu(2)S remind us that the formation of WZ CIS NPs is attributed to the pre-generation of Cu(2)S seed NPs and the following cation exchange reaction. In order to confirm this hypothesis, Cu(2-)(x)S seed NPs with various structures have been annealed in indium-ligand solution. This experiment revealed that the crystalline structure of CIS NP was determined by that of pre-generation Cu(2-)(x)S NPs. Our results provide the important information for the phase control and synthesis of ternary chalcogenide NPs with a novel crystalline structure.

Resonant enhancement of third-order nonlinear optical susceptibilities of Cd-free chalcopyrite nanocrystals within quantum confinement regime

Third-order nonlinear optical susceptibilities (χ(3)) have been investigated for chalcopyrite CuInS2 and AgInS2 nanocrystals within a strong confinement regime. The imaginary part of χ(3) (Imχ(3)) of 2.0- and 4.9-nm-sized CuInS2 nanocrystals and 2.6- and 4.3-nm-sized AgInS2 nanocrystals are negative and exhibit resonant enhancement around the absorption between the highest quantized levels of valence band and the lowest conduction band due to the state-filling effect. Figure of merit of |Imχ(3)| ranges 10−20–10−19 m3/V2, which is comparable to those of CdSSe nanocrystals.

Electrical conductivity of SmS polycrystals

The electrical conductivity of SmS polycrystals has been studied in the temperature range 300–870 K. It has been shown that, at 300 K ≤ T ≤ 700 K, the concentration of conduction electrons is determined by electron transfer from impurity donor levels, and at T > 700 K, by that from the samarium 4f levels.

Plasmonic enhancement of third-order nonlinear optical susceptibilities in self-doped Cu 2-x S nanoparticles

Heavily doped Cu2-xS nanoparticles with hole densities of ~1021 cm−3 were chemically synthesized and their localized surface plasmon resonance (LSPR) in the near-infrared region was investigated by nonlinear optical spectroscopy. We found that their third-order susceptibility χ(3) exhibits resonant enhancement around LSPR, similar to that in plasmonic noble metal nanoparticles. It was found that the maximum χ(3) value of Cu2-xS nanoparticles was comparable to that of Au nanoparticles with the same dimensions and concentrations. Our results indicate that Cu2-xS nanoparticles can be used as nonlinear optical materials operating in the near-infrared region, even though their near-field enhancement effect is slightly weaker than that of Au nanoparticles.

Specific features of the structure of semiconducting sms polycrystals in the homogeneity region

The structure and thermal properties of polycrystalline samples of samarium monosulfide have been investigated in the homogeneity region (Sm1 + xS at 0 < x < 0.17). The X-ray structural parameters and porosity of the samples have been measured, and their correlation with the thermodynamic parameters of the first-order phase transition occurring in polycrystalline samarium monosulfide at temperatures in the range from 240 to 260 K in Sm1 + xS has been established. It has been assumed that the measured nanopores correspond to voids between misoriented coherent X-ray scattering regions. It has been shown that the maximum of the absorbed heat energy is achieved in the case where the volume of the pore becomes comparable to the volume of the nucleus of a new phase of samarium sulfide, which is calculated from thermodynamic relationships.

Structural transformation and photoluminescence modification of AgInS2 nanoparticles induced by ZnS shell formation

AgInS2 nanoparticles were capped by ZnS via a widely used procedure to fabricate core/shell nanoparticles with highly efficient luminescence. The nanoparticle structures were investigated by ultrahigh-resolution analytical electron microscopy. We found that Zn–Ag–In–S nanoparticles were created by ZnS capping at ~480 K, which suggests that the luminescence enhancement reported for such core/shell nanoparticles is not caused by the passivation of surface defects by ZnS shells but by Zn doping. Quasi-core/shell nanoparticles could be obtained by ZnS capping without heating. However, their luminescence efficiency remained unchanged, indicating that surface passivation was ineffective when ZnS shells were formed at room temperature.

Carbon dioxide absorption and release properties of pyrolysis products of dolomite calcined in vacuum atmosphere.

The decomposition of dolomite into CaO and MgO was performed at 1073 K in vacuum and at 1273 K in an Ar atmosphere. The dolomite calcined in vacuum was found to have a higher specific surface area and a higher micropore volume when compared to the dolomite calcined in the Ar atmosphere. These pyrolysis products of dolomite were reacted with CO2 at 673 K for 21.6 ks. On the absorption of CO2, the formation of CaCO3 was observed. The degree of absorption of the dolomite calcined in vacuum was determined to be above 50%, which was higher than the degree of absorption of the dolomite calcined in the Ar atmosphere. The CO2 absorption and release procedures were repeated three times for the dolomite calcined in vacuum. The specific surface area and micropore volume of calcined dolomite decreased with successive repetitions of the CO2 absorption and release cycles leading to a decrease in the degree of absorption of CO2.

CO2 Absorption/Release Properties of Lithium Silicate (Li2SiO3) Powders Prepared by the Sol-Gel Process

The sol-gel synthesized powder was a single phase Li2SiO3. This synthesized powder was reacted with CO2 at temperatures ranging from the ambient temperature to 511 K, and the products can reverted reversibly to Li2SiO3 above 511 K. The degree of absorption was defined as the value obtained by dividing the fractional mass gain of Li2SiO3 after absorption by the fractional mass gain corresponding to a 100% reaction. Consequently, the degrees of absorption of the sol-gel synthesized powders were determined to be 9.6%, 13.9%, 16.1% and 20.4% under the absorption condition at 313 K, 333 K, 353 K and 373 K for an exposure time of 115.2 ks, respectively. The specific surface area of synthesized powder was measured as 40 m2/g, higher than that of Li2SiO3 synthesized by solid state reaction of 30 m2/g. After CO2 absorption, the specific surface area of synthesized Li2SiO3 was increased with the increase of absorption degree because of the volume expansion. Compared with Li2SiO3 synthesized by solid state reaction, Li2SiO3 powder synthesized by sol-gel process possessed bigger specific surface areas and higher micro pore volumes. Through the measurement of FE-SEM and BET, the average diameter of micro pores was decreased after CO2 absorption, because of the generation of Li2CO3. The absorption behavior could be best explained by an intraparticle diffusion mechanism, that is, the diffusion of CO2 gas through the reaction product with an apparent activation energy of 28 kJ∙mol-1 was a rate-determining step of the absorption reaction.

Solution-phase synthesis and photoluminescence characterization of quaternary Cu[sub 2]ZnSnS[sub 4] nanocrystals

Cu2ZnSnS4 (CZTS) nanocrystals were synthesized via solution phase route and their lattice defects were investigated by photoluminescence measurements. Ionization energies of the defect levels were estimated to be 10 and 72 meV from thermal quenching behavior of the photoluminescence spectra. These values are quite different from those experimentally estimated for vapor-grown CZTS films and crystals and theoretically calculated for bulk CZTS. The results indicate that the defects are characteristic of CZTS nanocrystals synthesized in the solution phase.