UV Light Region Research Articles

Red Emitting Ca2SiO4:Eu2+ Phosphors for White Light Emitting Diodes

Development of highly efficient red phosphors available in the excitation by UV-and/or blue-LEDs is one of the most important issues to improve the performance of white-LEDs because the color rendering index of most commercial white-LEDs which consisted of blue-LEDs and YAG:Ce3+ is relatively low owing to a lack of red-light region. Silicon-based nitride phosphors such as CaAlSiN3:Eu2+ and Sr2Si5N8:Eu2+ possess excellent red-light emission when excited by blue-light region. However, preparation of such silicon-based nitride phosphors in pure form should be needed to sinter precursor powders under high pressure and temperature conditions. Alkaline earth orthosilicate phosphors activated with Eu2+ have been reported as high efficient phosphors. Such silicon-based oxide phosphors in pure form can be easily obtained by simple preparation techniques without any critical conditions mentioned above. Therefore, productivity and production cost for silicon-based oxide phosphors are advantageous for the commercial production of red phosphors. We have already reported red-emitting CaSrSiO4:Eu2+ phosphors excited by blue-light region.1) The wavelength at the maximum emission of CaSrSiO4:Eu2+ with Eu2+ of 10 mol.% was 615nm. In addition, we have recently discovered new red-emitting Ca2SiO4:Eu2+ phosphors with higher Eu2+ concentrations at 20-40 mol.% excited by blue-light region.2) Although Ca2SiO4:Eu2+ phosphors with Eu2+ of 0.1–5.0 mol.% exhibited a strong green emission excited under UV light region,3) Ca2SiO4:Eu2+ with Eu2+ of 20–40 mol.% exhibited red emission peaking at 640–655 nm when excited at 450 nm and the emission intensity was 1.05 times higher than that of commercial YAG:Ce3+ (P46). The new red-emitting Ca2SiO4:Eu2+phosphors should be one of the promising candidates for the next-generated red phosphors in the white LED applications. Reference: 1) S. Tezuka, Y. Sato, T. Komukai, Y. Takatsuka, H. Kato and M. Kakihana, Appl. Phys. Express 6 (2013) 072101, 2) Y. Sato, H. Kato, M. Kobayashi, T. Masaki, D. H. Yoon and M. Kakihana, Angew. Chem. Int. Ed. 53 (2014) 7756, 3) Y. Y. Luo, D. S. Jo, K. Senthil, S. Tezuka, M. Kakihana, K. Toda, T. Masaki, D. H. Yoon, J. Solid State Chem. 189(2012) 68. Figure: Fig. 1 Emission and excitation spectra of Ca1.2Eu0.8SiO4. Figure 1

TiO2/carboxylate-rich porous carbon: A highly efficient visible-light-driven photocatalyst based on the ligand-to-metal charge transfer (LMCT) process

A novel visible-light-driven photocatalyst based on TiO2/carboxylate-rich porous carbon composite (TiO2/CRPC) was successfully synthesized by low temperature carbonization process in air. Sodium gluconate plays a crucial role in the formation of TiO2/CRPC. Different functional groups of sodium gluconate play synergetic roles in the formation of TiO2/CRPC. XRD and Raman spectra studies indicated that there are two different TiO2 crystalline phases existing in TiO2/CRPC, which are anatase and brookite, and the CRPC is amorphous. Via FT-IR and XPS spectra investigations, it was demonstrated that carboxylate group, the ligand-to-metal charge transfer (LMCT) forming functional group, was solidified into the CRPC and form the LMCT complex on TiO2 surface through the fabrication of TiO2/CRPC. Compared with the pure TiO2, TiO2/CRPC exhibit enhanced absorption in the UV and visible light region around 260–600nm. The strong absorption in the visible light region gives TiO2/CRPC advantages over pure TiO2 for the degradation of organic pollutants. TiO2/CRPC can activate O2 in air under mild conditions and exhibit excellent visible-light-driven photocatalytic activities. However, TiO2/C composite obtained by using glucose instead of sodium gluconate exhibits poor photocatalytic activity, which demonstrated that carboxylate–TiO2 complexes are responsible for the prominent photocatalytic properties of TiO2/CRPC under visible light irradiation.

Enhanced sunlight-driven photocatalytic activity of graphene oxide/Bi2WO6 nanoplates by silicon modification

In order to improve the photocatalytic activity and reduce the cost of graphene oxide/Bi2WO6 (GO/BWO) nanohybrids for practical application, silicon-modified graphene oxide/Bi2WO6 (Si-GO/BWO) nanoplates were successfully prepared by a facile one-pot hydrothermal method. X-ray diffraction and BET study of the products reveal that the incorporation of Si atoms can greatly alter the microstructure of GO/BWO composite with enlarged specific surface area. The UV–vis diffuse reflectance spectra indicate that the obtained Si-GO/BWO nanoplates have enhanced absorption in both UV and visible light regions. The Si–GO/BWO nanocomposite shows increased photocatalytic activity on the degradation of high concentration RhB solution under visible light irradiation and simultaneously keeps a very high stability, due to the good textural properties. In addition, the incorporation of Si with a load of 19.3wt% could greatly reduce the cost of BWO based photocatalyst.

Broadband and high diffuse reflectivity of hollow mesoporous silica nanospheres and their UV light shielding ability for light-labile peroxides

We herein report the optical diffuse reflection properties of hollow mesoporous silica nanospheres (HMSNs). The HMSNs reflect more than 90% of the UV and visible light in the wide range of 240–800nm and more than 70% of the UV light shorter than 240nm, which are significantly higher than that of the bulk silica. The high reflectance of the HMSNs mainly arises from multiple scattering, which is caused by the disordered arrangement of nanospheres with thickness up to several hundred nanometers. Besides, the unique microstructure of HMSNs and the comparable size of HMSNs with UV light may also contribute to their high reflection according to the Mie scattering principles. Unlike semiconductor materials which shield UV light by absorbing UV light and generating reactive species, the HMSNs display extremely low absorption in the UV light region. The high UV light reflection properties as well as the specific hollow mesoporous structures of the HMSNs indicate their superior applications in UV light shielding devices.

CdTe and graphene co-sensitized TiO2 nanotube array photoanodes for protection of 304SS under visible light

CdTe/graphene/TiO2 films that served as photoanodes for cathodic protection application were prepared by an electrochemical deposition method. The deposition of graphene and CdTe nanoparticles (NPs) on the surface of the TiO2 nanotubes was confirmed by scanning electron microscope and transmission electron microscopy. The composites exhibited high light absorption in both the UV and visible light region. The results indicated that TiO2 nanotube photoelectrodes sensitized by 20-cycle graphene and 30-cycle CdTe NPs exhibited effective photocathodic protection properties for 304 stainless steel (304SS) under the visible-light illumination, with an photopotential of −750 mV versus saturated calomel electrode and a current density of 560 μA cm−2. Due to the efficient photogenerated charge separation, the three-component CdTe/graphene/TiO2 showed stronger photoresponse than pure TiO2 under visible-light illumination. In summary, the CdTe/graphene could improve the photocathodic protection properties of TiO2 films.

Preparation of polypyrrole sensitized TiO2 nanotube arrays hybrids for efficient photoelectrochemical water splitting

Stable polypyrrole-TiO2 nanotube arrays hybrids (PPy-TNTs) have been prepared by facile anodization and potentiostatic polymerization methods. The morphology and structure of PPy-TNTs are characterized by SEM, XRD, XPS. The amount of deposited PPy can be easily adjusted by electropolymerization time. UV–vis diffuse reflection spectra show that the polypyrrole can act as visible-light photosensitizer and the electrochemical impedance spectra suggest that the formed p-n junctions between PPy and TNTs can facilitate the charge separation and transfer. The photocurrent density of PPy-TNTs under simulated solar illumination (AM1.5, 100mW/cm2) is about 2.5 times compared with that of pristine TNTs. Incident photon to current conversion efficiency (IPCE) spectrum of PPy-TNTs increases in UV and visible light region. Moreover, The PPy-TNTs hybrids show much higher photoelectrochemical stability than the pure TNTs.

Impact of sulfur-, tantalum-, or co-doping on the electronic structure of anatase titanium dioxide: A systematic density functional theory investigation

In order to achieve the purpose of further improving the photocatalytic performance of sulfur (S)-doped anatatse titanium dioxide (TiO2) and providing an example to design an efficient photocatalyst, the electronic and optical properties of pure, S-doped, tantalum (Ta)-doped and S+Ta-codoped anatase TiO2 were systematically investigated by using the density functional theory within a GGA+U method. The results indicate that Ta codoping could improve the S incorporated into TiO2 lattice under reducing conditions. And the incorporation of Ta into S-doped TiO2 further increases the photocatalytic activity under visible-light irradiation compared with that of the S-doped TiO2: the distance from S-related impurity energy levels to the top of valence band is obviously decreased in S+Ta-codoped TiO2; and the calculated band gap of S+Ta-codoped TiO2 is smaller than that of S-doped TiO2; furthermore, through the synergistic effects between S and Ta, S+Ta-codoped TiO2 not only has the similar high absorption rate to S-doped TiO2 in the UV-light region, but also has higher absorption rate than S/Ta-doped TiO2 in the visible-light region.

Artificial neural network modeling of photocatalytic removal of a disperse dye using synthesized of ZnO nanoparticles on montmorillonite

In this study, the photocatalytic ability of ZnO/Montmorilonite (ZnO/MMT) nanocomposite under UV-A, UV-B and UV-C radiation was investigated. ZnO nanoparticles were synthesized on the surface of MMT and used as photocatalyst in decolorization of Disperse Red 54 (DR54) solution. Synthesized nanocomposite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) techniques and nitrogen adsorption/desorption isotherms curves. The average width of synthesized ZnO particles is in the range of 30–45nm. Effect of UV light regions, initial dye concentration, initial dosage of nanocomposite, and reusability of catalyst was studied on decolorization efficiency. The highest decolorization efficiency was achieved under UV-C radiation. A three-layered feed forward back propagation artificial neural network model was developed to predict the photocatalysis of DR54 under UV-C radiation. According to ANN model the ZnO/MMT dosage with a relative importance of 49.21% is the most influential parameter in the photocatalytic decolorization process.

Low-cost and flexible ultra-thin silicon solar cell implemented with energy-down-shift via Cd0.5Zn0.5S/ZnS core/shell quantum dots

Flexible ultra-thin silicon solar cells with power-conversion-efficiency of 12.4 % implemented with an energy-down-shift layer show stable, flexible and twistable characteristics.

Syntheses, crystal structures, weak interaction, magnetic and luminescent properties of two new organic–inorganic molecular solids with substituted chlorobenzyl triphenylphosphinium and tetra(isothiocyanate)cobalt(II) anion

Two new organic–inorganic molecular solids of tetra(isothiocyanate)cobalt(II) dianion and meta-substituted benzyl triphenylphosphinium, [2ClBzTPP]2[Co(NCS)4] (1) and [4ClBzTPP]2[Co(NCS)4] (2) ([2ClBzTPP]+=1-(2′-chlorobenzyltriphenylphosphonium) and [4ClBzTPP]+=1-(4′-chlorobenzyltriphenylphosphonium), were prepared and characterized by elemental analysis, FT-IR, UV–vis spectra, ESI-MS and single crystal X-ray diffraction method. Both 1 and 2 crystallize in monoclinic, and the Co(II) ion of the [Co(NCS)4]2− anion shows a distorted tetrahedral coordination geometry. The CH⋯Cl, CH⋯S hydrogen bonds were found in 1 while CH⋯S, CH⋯Co, p⋯π, CH⋯π interactions were found in 2 consolidating the stacking of the crystal. Magnetic susceptibility measurement in the temperature range 2–300K shows that 1 and 2 exhibit a weak antiferromagnetic coupling behavior. Upon excitation at 268nm, two molecular solids show the luminescent emission peak in the UV-light region in the solid state at room temperature.

Visible-light induced photocatalytic activity of electrospun-TiO2 in arsenic(III) oxidation.

In practical implementation of TiO2 semiconductors, utilization of their outstanding properties is mainly hindered by poor material quality and high operational costs. In this contribution, the electrospinning method was employed to fabricate N-doped mixed-crystalline TiO2 with exposed high-energy facets. The Ti oxide transformation process was thoroughly studied. During the mixed crystal structure formation process, the high-energy facets could be preserved due to the lower calcination temperature and the protective role of polyvinylpyrrolidone (PVP) in the electrospinning process. In addition, after calcination, the N doping, generated by the decomposition of PVP, extended the absorption spectrum of TiO2 to the visible region. These TiO2 fibers exhibited superior photooxidation of arsenite (III) to arsenate (V)in both the UV and visible light regions, mainly attributed to the exposure of high-energy facets, robust separation of photoexcited charge carriers between the anatase/rutile phases, and narrow band gap induced by the in situ N doping. Combining both robustness and scalability, the TiO2 fibers produced via this electrospinning process have the potential for a broad range of applications.

Synergy effect in the photocatalytic degradation of textile dyeing waste water by using microwave combustion synthesized nickel oxide supported activated carbon

Nickel oxide nanoparticles supported activated carbon (NSAC) photocatalyst was successfully prepared using a cost-effective microwave irradiation method. The earned UV light-sensitive NSAC composites were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, High-resolution scanning electron microscope with energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller surface area analyzer. Optical properties of NSAC composites were investigated using UV–Vis diffuse reflectance spectroscopy and photoluminescence spectroscopy, which exposed prolonged light absorption in UV light region and hold better charge separation capability, respectively, as compared to pure NiO. The photocatalytic activity was tested by the degradation of textile dye waste water (TDW) under UV light irradiation. Chemical oxygen demand of TDW was calibrated before and after the photocatalysis experiment under UV light to evaluate the mineralization of wastewater. The results demonstrated that NSAC composites showed imposing photocatalytic enrichment over pure NiO. The coordinated blending of the oxygen vacant sites, structural defects of NiO along with electron transmission capacity, and presence of surface oxygen on AC has led to the lasting light absorption, delayed charge recombination, and sustenance, which favor the enrichment of the photocatalytic activity of NSAC.

Effects of structure, morphology, and up-conversion on Nd-doped BiVO4 system with high photocatalytic activity

Nd-doped BiVO4 photocatalysts with high photocatalytic activities have been synthesized by the microwave hydrothermal method. The effects of Nd doping on structural transformation, morphology, chemical valence, optical properties, and photocatalytic activities of Nd-doped BiVO4 photocatalysts were investigated systematically. It is found that Nd doping and pH of the reaction precursor can induce the stabilization of tetragonal zircon BiVO4, and Nd3+ ions have been incorporated into the BiVO4 lattice. The structure and morphology of BiVO4 play a significant role in the photocatalytic activity. The UV–vis diffuse reflectance spectra of Nd-doped BiVO4 present four absorption peaks at 532, 590, 690 and 750nm due to the excitation of Nd3+ species. The strong up-conversion fluorescence spectra of Nd-doped BiVO4 suggest the existence of up-conversion process, and the value of k/BET could reflect the effect of up-conversion lively and directly in Nd-doped BiVO4 system. The contribution of high photodegradation activities to Nd-doped BiVO4 catalysts under simulated sun-light is mainly from UV-light region. The mechanism of up-conversion upon sun-light excitation is proposed in favor of the improved photocatalytic activities of Nd-doped BiVO4.

Synergy effect in the photocatalytic degradation of textile dyeing waste water by using microwave combustion synthesized zinc oxide supported activated carbon

AbstractNickel oxide nanoparticles supported activated carbon (NSAC) photocatalyst was successfully prepared using a cost-effective microwave irradiation method. The earned UV light-sensitive NSAC composites were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, High-resolution scanning electron microscope with energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller surface area analyzer. Optical properties of NSAC composites were investigated using UV–Vis diffuse reflectance spectroscopy and photoluminescence spectroscopy, which exposed prolonged light absorption in UV light region and hold better charge separation capability, respectively, as compared to pure NiO. The photocatalytic activity was tested by the degradation of textile dye waste water (TDW) under UV light irradiation. Chemical oxygen demand of TDW was calibrated before and after the photocatalysis experiment under UV light to evaluate the mineralization of wastewate...

Enhanced visible light photocatalytic activity for the hybrid MoS2/anatase TiO2(0 0 1) nanocomposite: A first-principles study

First-principles calculations based on density functional theory were carried out to investigate the electronic and optical properties of the hybrid MoS2/anatase TiO2(001) nanocomposite. The influence of MoS2 hybridization on energy gap, interfacial charge transfer, and visible light response of the MoS2/TiO2(001) complex was analyzed. The hybridization of MoS2 showed an obvious red shift in the optical absorption edge and an enhanced absorption in the visible and UV light region. The efficient photosensitization of MoS2 and the stable interface between MoS2 and TiO2(001) slab could facilitate the electrons transferred from MoS2 to TiO2(001) slab, resulting in the enhanced visible light response.

One-dimensional mesoporous Fe2O3@TiO2 core–shell nanocomposites: Rational design, synthesis and application as high-performance photocatalyst in visible and UV light region

An ideal photocatalyst for degradation of organic pollutants should combine the features of efficient visible light response, fast electron transport, high electron–hole separation efficiency, and large specific surface area. However, these requirements usually cannot be achieved simultaneously in the present state-of-the-art research. In this work, we develop a rational synthesis strategy for the preparation of one-dimensional (1D) mesoporous Fe2O3@TiO2 core–shell composites. In this strategy, FeOOH nanorods are firstly coated by TiO2 shell, followed by a calcination process. The as-prepared composites are thoroughly investigated with X-ray powder diffraction, scanning electron microscope, energy dispersive spectroscopy, transmission electron microscope, N2 adsorption–desorption isotherms, UV–visible diffuse-reflectance spectra, and photoluminescence spectra. Endowed with the advantages of its composition and specific structural features, the presented sample possesses the combined advantages mentioned above, thus delivering evidently enhanced photocatalytic activity for the degradation of methyl orange under UV light irradiation and Rhodamine B under visible light irradiation. And the possible mechanism of the enhanced photocatalytic performance is proposed.

Photocatalytic degradation of textile-dyeing wastewater by using a microwave combustion-synthesized zirconium oxide supported activated carbon

Zirconium oxide nanoparticles supported activated carbon (ZrSAC) was successfully synthesized using a simple microwave irradiation method. The derived UV light sensitive ZrSAC composites were characterized using powder X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), high resolution scanning electron microscope (HRSEM) with energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and Brunauer Emmett Teller (BET) surface area analyzer. Optical properties of ZrSAC composites were studied using UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy (PL), which exposed prolonged light absorption in UV light region and hold better charge separation capability, respectively as compared to pure ZrO2. The photocatalytic activity was tested by the degradation of textile dye waste water (TDW) under UV light irradiation. Chemical oxygen demand (COD) of TDW was measured before and after the photocatalysis experiment under UV light to evaluate the mineralization of wastewater. The results demonstrated that ZrSAC composites showed a splendid photocatalytic enrichment over pure ZrO2. The coordinated blending of the oxygen vacant sites, structural defects of ZrO2 along with electron transmission capacity and presence of surface oxygen on AC has led to the lasting light absorption, delayed charge recombination, and sustenance, which favor the enrichment of the photocatalytic activity of ZrSAC.

Photoluminescence Properties of Novel Host‐Sensitized Y6WO12:Dy3+ Phosphors

Novel host‐sensitized Y6WO12:xDy3+ (0.01 ≤ x ≤ 0.20) phosphors were synthesized via solid‐state reaction process. X‐ray diffraction analysis confirmed the phase formation of Y6WO12:Dy3+ materials. The photoluminescence excitation and emission spectra, concentration effect, thermal‐quenching, and decay properties were investigated. The phosphor could be excited by the UV light region from 300 to 400 nm, and it exhibited blue (478 nm) and yellow (568 nm) emission corresponding to 4F9/2–6H15/2 transitions and 4F9/2–6H13/2 transitions, respectively. The WO6 groups in the host lattices can absorb UV light efficiently, and then transferred the energy to the activator Dy3+ ions, resulting in near white light emission. The optimum dopant concentration of Dy3+ ions in Y6WO12:xDy3+ was around 5 mol% and the critical transfer distance of Dy3+ was calculated as 12 Å. The fluorescence lifetime was also determined in Y6WO12:0.05Dy3+. The temperature dependence of photoluminescence properties was investigated from 300 to 480 K and the prepared Y6WO12:Dy3+ phosphors showed poor thermal‐quenching properties.

Improved photocatalytic decolorization of methyl orang over Pd‐doped Bi2O3

In this article, Pd‐doped Bi2O3 photocatalysts with different molar ratios of Pd/Bi (1/100, 2/100, 3/100, 4/100, and 5/100) have been prepared by a facile sol–gel method. The photocatalysts prepared were characterized by Brunauer‐Emmett‐Teller method (BET), X‐ray diffraction (XRD), UV/Vis diffuse reflectance, scanning electron microscopy (SEM), X‐ray photoelectron spectroscopic (XPS) techniques, and surface photovoltage (SPV), respectively. The results indicate that Pd‐doped enhances the photo‐induced charge separation efficiency and leads to different electronic properties when Pd‐doped Bi2O3 photocatalysts are illuminated by different wavelengths of light: one is an electron acceptor in the UV light region, while the other is an electron donor in the visible light region. The photocatalytic activity of Pd‐doped Bi2O3 photocatalysts for decolorization of methyl orange aqueous solution was evaluated, the result shows that 4% Pd possesses the best photocatalytic activity under UV light irradiation and 3% Pd possesses the best photocatalytic activity under simulated sun light irradiation, and the possible reason is suggested. Doping with Pd is an effective way to promote the photocatalytic performance of Bi2O3. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 1229–1234, 2014

Microwave-Assisted Hydrothermal Synthesis and Photocatalytic Properties of Cr and La-Codoped SrTiO<sub>3</sub> Photocatalyst

Cr and La-codoped SrTiO3nanoparticles were successfully prepared by a microwave-assisted hydrothermal synthesis. The products were characterized by XRD, TEM, BET specific surface area, and UV-Vis absorption spectra. The photocatalytic activity was determined by deNOxability under irradiation of a 450 W high-pressure mercury lamp. The products could absorb the visible light and showed high photocatalytic ability for the decomposition of NOxgas. All samples showed the photocatalytic activities superior to that of commercial titania (Degussa P25) in both UV and visible light regions.