記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsomega.0c02855

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/ma13132987

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.apsusc.2020.146650

記述言語：英語   掲載種別：研究論文（学術雑誌）  

<jats:p>Herein, we report the effect of sonoluminescence and an initial dye concentration on the sonophotocatalysis of TiO2 for the degradation of eosin B, a textile dye. We first investigated the light illuminated during ultrasound irradiation (sonoluminescence) by photographic images, a radical indicator (luminol), and photoluminescence spectra of the detection range of 300–1050 nm. Next, we examined the synergistic effect of sonolysis on photocatalysis by comparing the dye degradation of sonophotocatalysis to that of individual contributions of sonolysis and photocatalysis. Since it was found that the synergist effect is highly engaged with a dye concentration and sonication power, we conducted the comparison test in different concentrations of eosin B (5 and 20 mg/L) and ultrasound powers (35.4, 106.1, and 176.8 W/cm2). When the concentration of dyes was low, negative synergistic effects were found at all ultrasound powers, whereas at the high concentration, positive synergistic effects were observed at high ultrasound power. This difference in synergistic effects was explained by the influence of ultrasound on dynamics of dye adsorption on the TiO2 surface.</jats:p>

DOI： 10.3390/catal10050500

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Luminescent films have many applications in industry such as display, lightings, and solar cells. To fabricate such films, composites of luminescent materials and organic resins are often considered. However, organic resins have a drawback of low long-term stability, especially under continuous exposure to UV light. In this manuscript, we investigate synthesis of ZnS:Mn2+ nanocrystals for highly luminescent materials composed of earth abundant elements, and fabrication of a luminescent silica film emibedding the ZnS:Mn2+ nanocrystals. We synthesized the ZnS:Mn2+ nanocrystals by a precipitation method and optimized their luminescent properties by Mn-doping concentrations. Perhydropolysilazane was chosen for a silica precursor since it allows easy fabrication of silica thin films by solution printing methods. Luminescent thin films were obtained by doctor-blade method using a colloidal solution of ZnS:Mn2+ nanoparticles dispersed in perhydropolysilazane solution. Curing of the printed layer was optimized and complete transformation to silica was realized without compensating luminescent properties of embedded ZnS:Mn2+ nanocrystals.

DOI： 10.1016/j.apsusc.2020.145441

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.0c02091

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Despite the many advantages which the conventional crystalline silicon solar cells (c-Si) have over other forms of renewable energy sources, they still have major drawbacks (energy loss) limiting their performance. One of the main reasons for energy loss is the ineffective utilization of short wavelength photons, especially within the UV region. The efficiency of the c-Si solar cell device can be improved by depositing the phosphor nanoparticle on top of the devise to capture and covert the UV photons from sunlight to visible or near infraded photons by a downcoversion process. Therefore, we have prepared and investigated luminescent and optical properties of downconverting nanophosphors composed of SiO2 co-doped with Ce and Tb. The dominant photoluminescence emission peak was observed at 544 nm and it was attributed to the D-5(4) -> F-7(5) transition of Tb3+. The phosphors synthesized were incorporated into poly poly-ethylene vinyl acetate (poly-EVA) films which were later overlaid on a commercial silicon solar cell to and its photocurrent efficiency were measured. The phosphor films recorded a significantly good transmittance (>= 76&#37;) and also displayed a UV absorption capacity compared to that of the plain poly-EVA film. Some of the films made from different concentrations of Ce and Tb, recorded an increase in the photocurrent efficiency when deposited on the solar cell, while other compositions recorded marginal decreases compared to that of the plain EVA film.

DOI： 10.1016/j.physb.2019.411711

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this report, well-dispersed ZnS nanoparticles were applied as inorganic additives for polyethersulfone (PES) membrane to improve anti-fouling performance. ZnS nanoparticles were synthesized by low temperature precipitation and phase inversion method was used to embed them into PES membrane for humic acid (HA) filtration. Intrinsic properties of the PES-ZnS composite membrane developed were investigated at different ZnS loadings. Compared to the control PES membrane, the PES-ZnS membrane improved hydrophilicity, porosity and thermal stability. Effect of ZnS on the flux recovery of the PES membrane fouled with HA was more pronounced than that as TiO2 was used as embedding materials. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jiec.2019.05.015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

ZnS nanoparticles with 90 nm diameter were synthesized by low-temperature method and immobilized onto the surface of polyvinylidene fluoride (PVDF) pellets prepared by phase inversion method. Results by FTIR and X-ray photoelectron spectroscopy revealed that the ZnS nanoparticles were immobilized tightly on the PVDF surface without their release and losing photocatalytic activity. The UV-absorption spectra showed that the PVDF matrix had no adverse effect on the optical properties of ZnS nanoparticles. Due to large size (5 mm) and excellent mechanical stability, the PVDF-ZnS pellets could be easily dispersed in the photocatalytic reactor treating methylene blue solution. The removal efficiency of the methylene blue with the PVDF-ZnS pellets was higher (more than 95&#37;) than that observed by the control PVDF pellets or ZnS nanoparticles tested. No change in the removal efficiency was observed as the PVDF-ZnS pellets were reused by performing photocatalytic tests at the same experimental conditions repeatedly.

DOI： 10.1016/j.apsusc.2018.12.103

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In flame spray pyrolysis (FSP), the generation of uniform nanoparticles can be quite challenging due to difficulties in controlling droplet sizes during liquid spraying and uneven flame temperature. Here, we report a method to produce relatively uniform nanocrystals of a Tb3+ doped Y(2)O(3 )phosphor. In ethanol, metal nitrate precursors were simply mixed with organic surfactants to form a homogeneous solution which was then subjected to FSP. Depending on relative concentrations of the surfactant (oleic acid) to the metal precursors (yttrium and terbium nitrates), different sizes and morphologies of Y2O3:Tb3+ particles were obtained. By adjusting the surfactant concentration,Y2O3:Tb3+ crystals as small as 20 similar to 25 nm were acquired. X-ray diffraction and transmittance electron microscopy were used to prove that as-synthesized nanoparticles were highly crystalline due to the high temperature of FSP. X-ray photoelectron spectroscopy revealed that terbium dopants were well distributed throughout Y2O3 particles and a small portion of carbonate impurities were remained on the surface of particles, presumably originated from incomplete combustion of the organic surfactants. Photoluminescence (PL) spectra of Y2O3:Tb3+ nanocrystals exhibited a green light emission ensuring that the terbium doping was successfully occurred. However, when post-annealing was performed on the nanocrystals, their PL was dramatically enhanced indicating that quenching centers such as carbonate impurities and surface defects may have been removed by the annealing process. Owing to the continuous processability of FSP, this current method can be a practical way to produce nanoparticles in a large quantity. The obtained Y2O3:Tb3+ nanocrystals were used to fabricate a transparent film with poly-ethylene-co-vinyl acetate (poly-EVA) polymer, which was suitable for a spectral converting layer for a solar cell.

DOI： 10.1007/s11051-018-4347-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Near-infrared (NIR) quantum cutting phosphors serve as a potential material for fabricating photovoltaic spectral convertors. In many cases, quantum cutting phosphors are obtained via a wet chemical method coupled with a post-annealing treatment-a very costly process. In this report, we used continuous flame spray pyrolysis (FSP) for fabricating Y2O3:Tb3+-Yb3+ quantum-cutting phosphors without any post-treatment. Based on characterizations by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we found that as-synthesized Y2O3:Tb3+-Yb3+ phosphors exhibit hollow and shell-like micro-structures composed of highly crystalline and pure cubic-phase nanoparticles (< 50 nm). Photoluminescence studies of the phosphors revealed that NIR emissions appeared with the introduction of Yb to Y2O3:Tb3+. Phosphor size was successfully controlled by managing the concentration of the metal precursor solution for FSP. The Y2O3:Tb3+-Yb3+ phosphors were then embedded into transparent poly-ethylene-co-vinyl acetate (EVA) film to form a spectral convertor. The composite films of Y2O3:Tb3+-Yb3+ phosphors and poly-EVA were found to be highly transparent in the visible range (> 500 nm), making them suitable as spectral photovoltaic convertors.

DOI： 10.1007/s11164-018-3270-y

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To enhance the photoluminescence of lanthanide oxide, a cleat understanding of its defect chemistry is necessary. In particular, when yttrium oxide, a widely used phosphor,,,. undergoes doping, several of its atomic structures may be coupled with point defects that are difficult to understand through experimental results alone. Here, we report the Strong enhancement of the photoluminescence (PL) of Y2O3:Bi3+ via codoping with Li+ ions and suggest a plausible mechanism for that enhancement using both experimental and computational studies. The codoping of Li+ ions into the Y2O3:Bi3+ phosphor was found to cause significant changes in its structural and optical properties. Interestingly, unlike previous reports on codoping with several other phosphors, we found that Li+ ions preferentially occupy interstitial sites of the Y2O3:Bi3+ phosphor. Computational insights based on density functional theory calculations also indicate that Li+ is energetically more stable in the interstitial sites than in the substitutional sites. In addition, interstitially doped Li+ was found to favor the vicinity of Bi3+ by an energy difference of 0.40 eV in comparison to isolated sites. The calculated DOS showed the formation of a shallow level directly above the unoccupied 6p orbital of Bi3+ as the result of interstitial Li+ doping, which may be responsible for the enhanced PL. Although the crystallinity of the host materials increased with the addition of Li salts, the degree of increase was minimal when the Li+ content was low (<1 ma&#37;) where major PL enhancement was observed. Therefore, we reason that the enhanced PL mainly results from the shallow levels created by the interstitial Li+.

DOI： 10.1021/acs.inorgchem.7b01353

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Impurity doping and synthesizing polymorphic particles are the common strategies to improve activity of TiO2 photocatalyst by lowering the band gap and enhancing electron-hole separation rate. However, these two approaches have side effects. Doping of impurities make space charge region (SCR) thinner near the surface, which requires smaller sized particles than undoped TiO2 for the optimal performance. Polymorphic TiO2 particles, in which rutile and anatase phases coexist in a particle, are usually large due to energetic unstability of the rutile phase in a fine particle. For this contradiction that one needs small size while the other needs large size, two effects are not easy to be combined. In this study, we suggest a dual-doping strategy to solve the contradictory problem of SCR reduction by donor doping and inevitable size growth in polymorphic particles. We successfully dope W, a band gap narrower, into fine size of polymorphic particles by Sn-codoping, a promoter of the anatase-to-rutile transformation (ART), and demonstrate greatly improved photocatalytic activity. The accelerated ART by Sn-doping could keep the size of polymorph junctioned TiO2 small (similar to 10 nm) as lower temperature annealing become able to induce the ART. The concept of dual doping with a band gap narrower and an ART promoter provides a way to synthesize highly active photocatalysts by overcoming the drawback from shortened SCR length. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apcatb.2017.04.020

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Properties of the quantum-cutting phosphors are dependent on various factors such as dopant concentration, crystallinity, homogeneity, particle size and surface morphology. Effective control of the above parameters can enhance the quantum-cutting ability of the phosphor material. Nano-sized particles of Y2O3:Tb3+,Yb3+ were prepared with a solution-based co-precipitation method and subsequent calcination. Effective control of the reaction parameters and doping concentration helped to produce uniform nanostructures with high quantum-cutting efficiency up to 181.1 &#37;. The energy transfer mechanism between Tb3+ and Yb3+ was studied by considering their spectroscopic properties and time-resolved spectroscopy. The high efficiency and small particle size of the quantum-cutting phosphor Y2O3:Tb3+,Yb3+ make it a suitable candidate for its application in solar cells.

DOI： 10.1007/s11164-016-2427-9

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Understanding the roles of point defects in optical transitions is a key to the desirable engineering of photochemical materials. In this study, the origins of the significantly varying optical and photochemical properties of Nb-doped anatase TiO2 were systematically investigated, using density functional theory (DFT) calculations and experimental verifications. We found from DFT calculations that the desirable band gap reduction of anatase TiO2 by similar to 0.1 eV reported in many of experimental reports and the resultant improvements of photocatalytic and photovoltaic efficiencies of Nb5+-doped anatase TiO2 are due to the formation of complex (Nb-T1-V-Ti)(3)- as the compensator of Nb-Ti(+). Our experiments demonstrated that the O-2-rich annealing, which is expected to increase the concentration of desirable (Nb-TI-V-Ti)(3-) complex, narrows band gap of TiO2 and strongly enhances the photocatalytic activity of Nb-doped TiO2 particle. On the contrary, pure TiO2 showed rather worse photocatalytic performances when annealed in O-2 rich atmosphere, which is due to the formation of deep level by O-interstitial defect (O-1). Theoretically obtained charge effective masses could further explain the different photocatalytic activities of undoped and Nb-doped TiO2. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apcatb.2017.01.039

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Monodispersed ZnS nano-spheres were synthesized by a simple precipitation. By adjusting the concentration of Zn and S sources, the particle size and morphology were easily controlled. Careful examination of the obtained particles suggested porous structures composed of building blocks of small crystallites, ca. 4-13.4 nm in diameter. A higher [S]/[Zn]-precursor ratio resulted in a bigger crystallite size but a smaller particle size, and vice versa, for the lower precursor ratio. However, an extreme [S]/[Zn] ratio of 20 provided no spherical aggregation, but a formation of amorphous aggregates. We consider the rate to nucleation and the diffusion-controlled aggregation of crystallites to be important parameters in determining particle sizes and size distributions. Size homogeneity of the obtained ZnS nano-spheres, especially with a [S]/[Zn]-precursor ratio of 5, afforded a photonic crystal array that can potentially benefit the photocatalytic activity. When the photocatalytic activities of the ZnS nano-spheres obtained via different conditions were compared, it was found that spherical aggregation and high surface areas have a positive effect on catalytic activity. Although using a [S]/[Zn] ratio of 20 provided the highest surface area, the amorphous aggregation and overly excessive use of S caused a detrimental influence on the catalytic activity.

DOI： 10.1002/cjoc.201600725

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Precipitation and re-precipitation of metal ions has been carried out from original and supernatant solution producing Bi3+ - Eu3+ doped Y2O3:Eu3+ and Eu3+/Tb3+ doped Y2O3, respectively. Shorter reaction time is unable to consume all metal ions present in the solution which can be utilized through re precipitation process. The doping of Bi3+ - Eu3+ in Y2O3 helps to absorb maximum UV light. The activation of Y2O3 matrix by Bi3+ and Eu3+ ions, together and separately, were studied considering the excitation energy transfer to the luminescence centers. The successful replacement of Y3+ by RE3+ ions can help for fine tuning of emission wavelength. Re-precipitation of supernatant solution by adding terbium precursor can successively produce uniform sized Tb3+ doped Y2O3:Eu3+. The re-precipitation of the supernatant solution ensures maximum consumption of metal ions for higher product yield and possible fine tuning of emission wavelengths. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.materresbull.2016.06.016

記述言語：英語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The binary TiO2-ZrO2 particles were better alternative to TiO2 particles as photocatalyst to reduce humic acid fouling in photocatalytic membrane reactor. The structure of the TiO2-ZrO2 particles was strongly dependent upon the content of zirconium as an additive. A composition of 50&#37; TiO2 with 50&#37; ZrO2 was optimal in terms of physicochemical properties. The effect of TiO2-ZrO2 particles on the reduction of humic acid fouling was further improved by the presence of divalent cations such as calcium. Nevertheless, the stability of polymeric membranes in longer-term operation using a hybrid photocatalytic membrane reactor for water treatment applications may remain a challenge. (C) 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jiec.2014.04.012

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Bi3+ as a dopant in wide-band-gap yttria (Y2O 3) has been used as a green light emission center or a sensitizer of co-doped rare earth elements. Because the photoluminescence (PL) properties of Y2O3:Bi3+ vary remarkably according to heat treatment, the roles of point defects have been an open question. By using first-principles calculations and thermodynamic modeling, we have thoroughly investigated the formation of point defects in Y2O 3:Bi3+ at varying oxygen partial pressures and temperatures, as well as their roles in PL. The photoabsorption energies of the Bi3+ dopant were predicted to be 3.1 eV and 3.4 eV for doping at the S6 and the C2 sites, respectively, values that are in good agreement with the experimental values. It was predicted that an oxygen interstitial (Oi) and an oxygen vacancy (VO) are the dominant defects of Y2O3:Bi3+ at ambient pressure and an annealing temperature of 1300 K (3.19 × 1016 cm-3 for 1&#37; Bi doping), and the concentrations of these defects in doped Y2O3 are approximately two orders of magnitude higher than those in undoped Y2O3. The defect in Y 2O3:Bi3+ was predicted to reduce the intensity of PL from Bi3+ at both S6 and C2 sites. We verify our computational predictions from our experiments that the stronger PL of both 410 and 500 nm wavelengths was measured for the samples annealed at higher oxygen partial pressure. This journal is © the Partner Organisations 2014.

DOI： 10.1039/c4tc00438h

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Bi3+ as a dopant in wide-band-gap yttria (Y2O3) has been used as a green light emission center or a sensitizer of co-doped rare earth elements. Because the photoluminescence (PL) properties of Y2O3:Bi3+ vary remarkably according to heat treatment, the roles of point defects have been an open question. By using first-principles calculations and thermodynamic modeling, we have thoroughly investigated the formation of point defects in Y2O3:Bi3+ at varying oxygen partial pressures and temperatures, as well as their rotes in PL. The photoabsorption energies of the Bi3+ dopant were predicted to be 3.1 eV and 3.4 eV for doping at the S-6 and the C-2 sites, respectively, values that are in good agreement with the experimental values. It was predicted that an oxygen interstitial (01) and an oxygen vacancy (V-O) are the dominant defects of Y2O3:Bi3+ at ambient pressure and an annealing temperature of 1300 K (3.19 x 10(16) cm(-3) for 1&#37; Bi doping), and the concentrations of these defects in doped Y2O3 are approximately two orders of magnitude higher than those in undoped Y2O3. The defect V-O(2+) in Y2O3:Bi3+ was predicted to reduce the intensity of PL from Bi3+ at both S-6 and C-2 sites. We verify our computational predictions from our experiments that the stronger PL of both 410 and 500 nm wavelengths was measured for the samples annealed at higher oxygen partial pressure.

DOI： 10.1039/c4tc00438h

記述言語：英語