Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

One-dimension carbon self-doping g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanotubes: Synthesis and application in dye-sensitized solar cells

One-dimension carbon self-doping g-C₃N₄ nanotubes (CNT) with abundant communicating pores were synthesized via thermal polymerization of saturated or supersaturated urea inside the framework of a melamine sponge for the first time. A ～16% improvement in photoelectric conversion efficiency (η) is observed for the devices fabricated with a binary hybrid composite of the obtained CNT and TiO₂ compared to pure TiO₂ device. The result of EIS analysis reveals that the interfacial resistance of the TiO₂-dye|I₃^?/I^? electrolyte interface of TiO₂-CNT composite cell is much lower than that of pure TiO₂ cell. In addition, the TiO₂-CNT composite cell exhibits longer electron recombination time, shorter electron transport time, and higher charge collection efficiency than those of pure TiO₂ cell. Systematic investigations reveal that the CNT boosts the light harvesting ability of the photovoltaic devices by enhancing not only the visible light absorption but also the charge separation and transfer.

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Cobalt and Yttrium Modified TiO<Subscript>2</Subscript> Nanotubes Based Dye-Sensitized Solar Cells for Solar-Energy Conversion

The solar-energy conversion in eosin-sensitized solar cells based on cobalt and yttrium modified TiO2 nanotubes has been studied.It is established that the doping with metal ions shifts the absorption edge for Co and Y doped titanium dioxide samples to longer and shorter wavelengths, respectively. The efficiency of solar energy conversion depends on the wide bandgap of the semiconductor anode and reaches a maximum (4.4%) for yttrium-doped TiO₂ in comparison to that (4.1%) for pure titanium dioxide.     

Tunable luminescence properties and energy transfer of single-phase Ca<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>O: Dy<Superscript>3+</Superscript>, Eu<Superscript>2+</Superscript> multi-color phosphors for warm white light

The novel Ca_4?x(PO₄)₂O: xDy³⁺ and Ca_4?x?y(PO₄)₂O: xDy³⁺, yEu²⁺ multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca₄(PO₄)₂O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy³⁺-doped Ca₄(PO₄)₂O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy³⁺. Interestingly, Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy³⁺ to Eu²⁺ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu²⁺ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800–6700 K) and high CRI (R_a > 85) can be obtained by changing the Eu²⁺ co-doping contents in Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors. The optimized Ca_3.952(PO₄)₂O: 0.04Dy³⁺, 0.008Eu²⁺ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.     

Ultraviolet upconversion luminescence in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript>,Tm<Superscript>3+</Superscript> nanocrystals and its application in photocatalysis

Infrared-to-ultraviolet upconversion luminescence agent Y₂O₃:Yb³⁺,Tm³⁺ was prepared by a combustion method using citrate as a fuel/reductant. The prepared sample was characterized by X-ray diffraction, SEM, and fluorescence spectrophotometer. Two unusual ¹I₆ → ³H₆ (~297 nm) and ¹D₂ → ³H₆ (~363 nm) emissions from Tm³⁺ ions were observed at room temperature under 980-nm laser excitation. The change of upconversion emission intensity depending on the Yb³⁺ concentrations was discussed. The results showed that modest Yb³⁺ doping could make the upconversion emission of Tm³⁺ intense, and high Yb³⁺ concentrations might lead to fluorescence quenching. Moreover, the influence of ultraviolet upconversion luminescence on the photodegradation of methyl orange aqueous solution under solar light irradiation in the presence of TiO₂ catalyst doped with Y₂O₃:Yb³⁺,Tm³⁺ was also investigated. It was concluded from the experiment of this study that TiO₂/Y₂O₃:Yb³⁺,Tm³⁺ composite had higher photocatalytic activity than pure TiO₂ under solar light. This study would make TiO₂ utilize sunlight more efficiently and accelerate the practical application of photocatalytic technology in water treatment region.     

Y2O3:Eu3+纳米晶的制备及其光学性能研究

以NaOH,Y(NO3)3.6H2O和Eu(NO3)3.6H2O为前驱体,通过添加络合剂PEG-2000,采用水热法,成功地合成了Y2O3∶Eu3+纳米棒和纳米管,并采用先进的测试手段对其结构和性能进行了表征与测试。探讨了Y2O3∶Eu3+纳米棒和纳米管的生长机制,同时研究了Y2O3:Eu3+纳米晶的光致发光性能。研究结果表明,水热温度、反应时间、NaOH的添加量和PEG-2000对产物形貌有着非常重要的影响,所制备的材料具有Eu3+的特征红光发射,并在Eu3+的掺杂量为5%(摩尔分数)时样品发光最好。     

Synthesis and photoluminescence of Y2O3:RE3+ (RE=Eu, Tb, Dy) porous nanotubes templated by carbon nanotubes

Y2O3:RE3+(RE=Eu, Tb, Dy) porous nanotubes were first synthesized using carbon nanotubes as template. The morphology of the coated precursors and porous Y2O3:Eu3+ nanotubes was determined by scanning electron Microscopy (SEM) and transmission electron microscopy (TEM). It was found that the coating of precursors on carbon nanotubes (CNTs) is continuous and the thickness is about 15 nm, after calcinated, the Y2O3:Eu3+ nanotubes are porous with the diameter size in the range of 50-80 nm and the length in micrometer scale. X-ray diffraction (XRD) patterns confirmed that the samples are cubic phase Y2O3 and the photoluminescence studies showed that the porous rare earth ions doped nanotubes possess characteristic emission of Eu3+, Tb3+, and Dy3+. This method may also provide a novel approach to produce other inorganic porous nanotubes used in catalyst and sensors.     

两步法制备单分散的Li掺杂Y2O3:Eu3+微球及其发光性能

Y2O3:Eu3+是最重要的红色荧光材料,通过两步法制备了具有单分散性的Li掺杂Y2O3:Eu3+微球并研究了其发光行为.首先采用共沉淀法制备出单分散Y2O3:Eu3+微球,而后在含有LiOH的乙醇悬浊液中利用超声-水热法获得Li掺杂Y2O3:Eu3+微球.通过SEM、XRD、PL光谱等分析,发现Li掺杂可明显降低Y2...     

Preparation and characterization of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu phosphors by combustion process

Europium-doped yttrium phosphors were successfully synthesized by combustion process using yttrium nitrate hexahydrate [Y(NO₃)₃·6H₂O], europium nitrate [Eu(NO₃)₃·6H₂O], and carbohydrazide [CO(N₂H₃)₂]. The process takes only a few minutes to obtain Y₂O₃:Eu phosphors. The resultant powders annealed at different temperature and were investigated by X-ray diffractometer (XRD), differential thermal analyzer/thermogravimeter (DTA/TG), Fourier transform infrared spectroscopy (FTIR), photoluminescence excitation and emission spectra (PL), and transmission electron microscopy (TEM). The results showed that the formation temperature of Y₂O₃ phase is significant low, compared to solid-state reaction route of constituent oxides. For luminescence property, the emission intensity of Y₂O₃:Eu phosphors synthesized by combustion process increases steadily with increasing europium amount from 1 mol% to 5 mol%.     

Hydrothermal synthesis and luminescence properties of core-shell-structured PS@SrCO<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> spherical particles

Nanocrystalline SrCO₃:Tb³⁺ phosphor layers were coated on monodisperse and spherical polystyrene particles by a typical hydrothermal synthesis without further annealing treatment, resulting in the formation of core-shell-structured polystyrene@SrCO₃:Tb³⁺ particles. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, as well as lifetimes were employed to characterize the resulting composite particles. Under ultraviolet excitation, the polystyrene@SrCO₃:Tb³⁺ phosphors show the characteristic ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission lines with green emission ⁵D₄–⁷F₅ (544 nm) as the most prominent group. The obtained core-shell phosphors are potentially applied in fluorescent lamps.     

Electron traps in Gd<Subscript>3</Subscript>Ga<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>12</Subscript>:Ce garnets doped with rare-earth ions

The curves of thermally stimulated luminescence of Gd₃Ga₃Al₂O₁₂:Ce³⁺ ceramics (a nominally pure sample and samples doped with rare-earth ions) are measured in the temperature range of 80–550 K. The depth and the frequency factor of electron traps established by Eu and Yb impurities are determined. An energy-level diagram of rare-earth ions in the bandgap of Gd₃Ga₃Al₂O₁₂ is presented.     

Electrocatalytic applications of platinum-decorated TiO<Subscript>2</Subscript> nanotubes prepared by a fully wet-chemical synthesis

Pt-decorated \(\hbox {TiO}_{2}\) nanotubes Pt@TiO₂ are prepared only by applying a set of facile wet-chemical redox reactions to ion track-etched polycarbonate templates. First, a homogeneous layer of Pt nanoparticles is deposited onto the complex template surface by reducing potassium tetrachloroplatinate with absorbed dimethylaminoborane. Second, the template is coated with a conformal \(\hbox {TiO}_{2}\) layer, using a chemical bath deposition reaction based on titanium(III) chloride. After the removal of the template, the rutile-type \(\hbox {TiO}_{2}\) nanotubes remain decorated with Pt nanoparticles and nanoparticle-clusters on their outside. During the process, neither vacuum techniques nor external current sources or addition of heat are employed. The crystallinity, composition, and morphology of the composite nanotubes are analysed by X-ray diffraction, scanning and transmission electron microscopy as well as by energy-dispersive X-ray spectroscopy. Finally, the obtained materials are examplarily applied in the electrooxidation of ethanol and formic acid, and their performances have been evaluated. Compared to conventional carbon black-supported Pt nanoparticles, the Pt@TiO₂ nanotubes show higher reaction rates. Mass activities of 2.36 \(\hbox {A}\hbox { mg}_{\rm Pt}^{-1}\hbox { cm}^{-2}\) are reached in ethanol oxidation and 7.56 \(\hbox {A}\hbox { mg}_{\rm Pt}^{-1}\hbox { cm}^{-2}\) in the formic acid oxidation. The present structures are able to exploit the synergy of Pt and \(\hbox {TiO}_{2}\) with a bifunctional mechanism to result in powerful but easy-to-fabricate catalyst structures. They represent an easily producible type of composite nanostructures which can be applied in various fields such as in catalytics and sensor technology.     

Methylammonium cation deficient surface for enhanced binding stability at TiO<Subscript>2</Subscript>/CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> interface

Heterojunction interfaces in perovskite solar cells play an important role in enhancing their photoelectric properties and stability.Till date,the precise lattice arrangement at TiO2/CH3NH3PbI3 heterojunction interfaces has not been investigated clearly.Here,we examined a TiO2/CH3NH3PbI3 interface and found that a heavy atomic layer exists in such interfaces,which is attributed to the vacancies of methylammonium (MA) cation groups.Further,first-principles calculation results suggested that an MA cation-deficient surface structure is beneficial for a strong heterogeneous binding between TiO2 and CH3NH3PbI3 to enhance the interface stability.Our research is helpful for further understanding the detailed interface atom arrangements and provides references for interfacial modification in perovskite solar cells.     

LiFePO<Subscript>4</Subscript>/TiO<Subscript>2</Subscript>/Pt composite film used as effective and robust counter electrode for dye sensitized solar cells

A series of composite films based on LiFePO₄/TiO₂/Pt were synthesized and used as counter electrodes for dye sensitized solar cells (DSSCs). The composites are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET). These analysis results demonstrate that the crystal structure of LiFePO₄ in composite is not changed, and the prepared LiFePO₄/TiO₂/Pt composite films hold a rough surface and porous structure which provide more catalytic activity sites for I₃ ^? reduction and more space for I^?/I₃ ^? diffusion. The DSSC based on LiFePO₄/TiO₂/Pt composite CEs shows a high power conversion efficiency of 6.23% at a low Pt dosage of 2%, comparable to the conventional magnetron sputtering Pt CE (6.31%). The electrochemical analysis reveals that the presented composite CEs have good electrocatalytic activity and low charge transfer resistance. Furthermore, the DSSCs based on LiFePO₄/TiO₂/Pt composite CE exhibit high stability under the continuous tests condition and electrolyte soaking. The results suggest that this LiFePO₄-based composite film could be a perspective electrode for practical application of DSSCs and it maybe provide a potential for further research about photo-charging lithium-ion batteries.     

Spectral parameters of Nd3+ ion in Nd<Superscript>3+</Superscript>:LaCa<Subscript>4</Subscript>O(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystal

The spectral parameters of Nd³⁺ ions in Nd:LaCa₄O(BO₃)₃ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters Ω_λ are Ω₂ =1.98 × 10^–20 cm², Ω₄ =2.39 × 10^–20 cm², Ω₆ =1.38 × 10^–20 cm², the radioactive lifetime is 655 μs, the quantum efficiency is 10%, and the fluorescence branch ratios were calculated: β₁ = 0.51, β₂ = 0.42, β₃ = 0.066, β₄ = 0.003. Electronic Publication     

Sn<Superscript>4+</Superscript> and La<Superscript>3+</Superscript> co doped TiO<Subscript>2</Subscript> nanoparticles and their optical,photocatalytic and antibacterial properties under visible light

Sn⁴⁺ and La³⁺ co-doped TiO₂ photocatalytic material with nanoparticle structure have been successfully prepared using SnCl₂·2H₂O and La(NO₃)₃·6H₂O as precursors. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy and UV–visible spectroscopy have been used to for the characterization of the morphology, crystal structure, particle size and optical properties of the samples. The photocatalytic properties of sample with various amount of La doped TiO₂ have been studied by photo degradation of methyl orange (MO) in water under visible light. XRD patterns showed both rutile and anatase phases for 5 mol% of Sn and 5–10 mol% of La. But anatase phase with a little rutile phase was formed for 5 mol%Sn and 10 mol%La. The prepared Sn and La co doped TiO₂ photo-catalyst showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of MO solution under visible irradiation. Antibacterial behavior towards E. coli was then studied under visible irradiation. The synthesized T-5%Sn-10%La powder exhibited superior antibacterial activity under visible irradiation compared to the pure TiO₂.     

Rapid synthesis and enhancement in down conversion emission properties of BaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>,RE<Superscript>3+</Superscript> (RE<Superscript>3+</Superscript>=Y,Pr) nanophosphors

BaAl₂O₄:Eu²⁺,RE³⁺ (RE³⁺=Y, Pr) down conversion nanophosphors were prepared at 600 °C by a rapid gel combustion technique in presence of air using boron as flux and urea as a fuel. A comparative study of the prepared materials was carried out with and without the addition of boric acid. The boric acid was playing the important role of flux and reducer simultaneously. The peaks available in the XPS spectra of BaAl₂O₄:Eu²⁺ at 1126.5 and 1154.8 eV was ascribed to Eu²⁺(3d _5/2) and Eu²⁺(3d _3/2) respectively which confirmed the presence of Eu²⁺ ion in the prepared lattice. Morphology of phosphors was characterized by tunneling electron microscopy. XRD patterns revealed a dominant phase characteristics of hexagonal BaAl₂O₄ compound and the presence of dopants having unrecognizable effects on basic crystal structure of BaAl₂O₄. The addition of boric acid showed a remarkable change in luminescence properties and crystal size of nanophosphors. The emission spectra of phosphors had a broad band with maximum at 490–495 nm due to electron transition from 4f ⁶5d ¹ → 4f ⁷ of Eu²⁺ ion. The codoping of the rare earth (RE³⁺=Y, Pr) ions help in the enhancement of their luminescent properties. The prepared phosphors had brilliant optoelectronic properties that can be properly used for solid state display device applications.     

Mesocrystalline TiO<Subscript>2</Subscript> nanosheet arrays with exposed {001} facets: Synthesis via topotactic transformation and applications in dye-sensitized solar cells

A facile,fluorine-free approach for synthesizing vertically aligned arrays of mesocrystalline anatase TiO2 nanosheets with highly exposed {001} facets was developed through topotactic transformation.Unique mesocrystalline {001}-faceted TiO2 nanosheet arrays vertically aligned on conductive fluorine-doped tin oxide glass were realized through topotactic conversion from single-crystalline precursor nanosheet arrays based on lattice matching between the precursor and the anatase crystals.The morphology and microstructure of the {001}-faceted TiO2 nanosheets could be readily modulated by changing the reactant concentration and annealing temperature.Owing to enhanced dye adsorption,reduced charge recombination,and enhanced light scattering arising from the exposed {001} facets,in addition to the advantageous features of low-dimensional structure arrays (e.g.,fast electron transport and efficient charge collection),the obtained TiO2 nanosheet arrays exhibited superior performance when they were used as anodes for dye-sensitized solar cells (DSSCs).Particularly,{001}-faceted TiO2 nanosheet arrays ～15 μm long annealed at 500 ℃ showed a power conversion efficiency of 7.51％.Furthermore,a remarkable efficiency of 8.85％ was achieved for a DSSC based on double-layered TiO2 nanosheet arrays ～35 μm long,which were prepared by conversion from the precursor nanoarrays produced via secondary hydrothermal growth.     

Green synthesis of white-light-emitting ZnSe:Eu<Superscript>2+</Superscript>, Mn<Superscript>2+</Superscript> quantum dots in an aqueous solution

High-quality ZnSe:Eu, Mn quantum dots (QDs) with white light emitting were synthesized via a green preparation method in an aqueous solution using thioglycolic acid as a stabilizing agent. The composition of the QDs could be flexibly controlled by varying the amount of Eu or Mn cation. The effects of reflux time and Eu²⁺ ion dopant concentration on the luminescence properties were systematically investigated. The obtained QDs were characterized by photoluminescence spectrometry, X-ray powder diffraction, and high-resolution transmission electron microscopy. The proposed method formed cubic ZnSe:Mn²⁺, Eu²⁺ QDs with the maximum emission peak at 460 and 580 nm. In the optimal condition, the quantum yields of ZnSe:Mn²⁺, Eu²⁺ QDs could reach 27.68%. The CIE color coordinates were (0.328, 0.334), which agreed with those of pure white light (0.33, 0.33). The results verified that the ZnSe:Mn²⁺, Eu²⁺ QDs exhibited potential in light-emitting diode applications.     

Luminescence properties of monodispersed spherical BaWO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> microphosphors for white light-emitting diodes

Monodispersed spheres (1–4 μm in diameter) of BaWO₄:Eu³⁺ (hereafter BWO:Eu) red-phosphor exhibiting intense emission at 615 nm were synthesized via a mild hydrothermal method. X-ray diffraction, scanning electron microscope, photoluminescence excitation and emission spectra, and decay curve were used to characterize the properties of BWO:Eu phosphors. An intense red emission was obtained by exciting either into the ⁵L₆ state with 394 nm or the ⁵D₂ state with 465 nm, that correspond to two popular emission lines from near-UV and blue LED chips, respectively. The values of Ω _2,4 experimental intensity parameters (13.8 × 10⁻²⁰ and 8.2 × 10⁻²⁰ cm²) are determined. The high-emission quantum efficiency of the BWO:Eu phosphor suggests this material could be promising red phosphors for generating white light in phosphor-converted white light-emitting diodes.