Effect of nanoscaled SnO2 coating on ZnS:Mn phosphors under electron irradiation

The luminescence properties of SnO₂-coated ZnS:Mn phosphors are investigated. In the case of photoluminescence, emission intensities show little change when SnO₂ is coated on the surface of ZnS:Mn, while in the case of cathodoluminescence (CL), emission intensities vary depending on excitation energies. In order to determine the luminescence behaviors, surface analyses of the phosphors were performed. Auger electron spectroscopy showed that the width of the SnO₂ layer on the ZnS:Mn phosphor was saturated at approximately 120 nm. Also, X-ray photoelectron spectroscopy indicated that the SnO₂ layers are well formed and saturated when the molar ratios of Sn/Zn are larger than 0.005. These results suggest that the changes in the CL emissions can be attributed to a lowering of the junction barrier.     

Synthesis and characterization of the water-soluble silica-coated ZnS:Mn nanoparticles as fluorescent sensor for Cu ions

Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core–shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core–shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40 nm). Photoluminescence (PL) spectroscopy and UV–vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu²⁺ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu²⁺ concentrations as low as 7.3 × 10⁻⁹ mol L⁻¹, thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed.     

ZnS/SiO2协同包覆光阳极制备高效率Zn-Cu-In-Se量子点敏化太阳能电池

通过光阳极协同包覆的策略抑制Zn?Cu?In?Se(ZCISe)量子点敏化太阳能电池(QDSC)中光阳极/电解液界面上的电荷复合过程,提高电荷收集效率和电池光伏性能。采用溶液法在ZCISe量子点敏化的光阳极表面依次沉积包覆ZnS和SiO₂双钝化层,实现较单一ZnS包覆层更有效的界面电荷复合抑制作用,从而提高QDSC的性能。在包覆ZnS/SiO₂双钝化层后,所组装的ZCISe QDSC光电转换效率由传统单一ZnS包覆的12.17%提高到13.23%,这归因于双钝化层对光阳极/电解液界面电荷复合过程的有效抑制,电荷收集效率得到相应提升。     

Synthesis of Multifunctional Mn‐Doped CdTe/ZnS Core/Shell Quantum Dots

The synthesis of a novel water‐soluble Mn‐doped CdTe/ZnS core‐shell quantum dots using a proposed ultrasonic assistant method and 3‐mercaptopropionic acid (MPA) as stabilizer is descried. To obtain a high luminescent intensity, post‐preparative treatments, including the pH value, reaction temperature, reflux time and atmosphere, have been investigated. For an excellent fluorescence of Mn‐doped CdTe/ZnS, the optimal conditions were pH 11, reflux temperature 100°C and reflux time 3 h under N₂ atmosphere. While for phosphorescent Mn‐doped CdTe/ZnS QDs, the synthesis at pH 11, reflux temperature 100°C and reflux time 3 h under air atmosphere gave the best strong phosphorescence. The characterizations of Mn‐doped CdTe/ZnS QDs were also identified using AFM, IR, powder XRD and thermogravimetric analysis. The data indicated that the photochemical stability and the photoluminescence of CdTe QDs are greatly enhanced by the outer inorganic ZnS shell, and the doping Mn²⁺ ions in the as‐prepared quantum dots contribute to strong luminescence. The strong luminescence of Mn‐doped CdTe/ZnS QDs reflected that Mn ions act as recombination centers for the excited electron‐hole pairs, attributing to the transition from the triplet state (⁴T₁) to the ground state (⁶A₁) of the Mn²⁺ ions. All the experiments demonstrated that the surface states played important roles in the optical properties of Mn‐doped CdTe/ZnS core‐shell quantum dots.     

利用SnO2:Sb干凝胶部分升华产物处理ZnS:Mn荧光粉

以SnCl2•2H2O、SbCl3为原料, 通过溶胶-凝胶法制备SnO2:Sb干凝胶. 利用干凝胶氧化过程中的部分升华产物对新制的ZnS:Mn荧光粉进行了表面处理. 在固定氧气流量和氧化时间的条件下, 考察了SnO2:Sb干凝胶与ZnS:Mn荧光粉的质量比和氧化温度对处理后荧光粉电阻率的影响. 当干凝胶粉与荧光粉的质量比为3.0, 氧化温度为500 ℃处理后荧光粉的电阻率明显下降. 对处理后的荧光粉进行了室温光致荧光(PL)光谱、X射线衍射(XRD)以及透射电镜(TEM)分析. 结果表明对荧光粉进行表面处理没有改变荧光粉的光致发光性质和晶体结构.     

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4:Eu phosphors via sol-gel process

Europium-doped nanocrystalline GdVO₄ phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO₂@Gd_0.95Eu_0.05VO₄ core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd_0.95Eu_0.05VO₄ layers begin to crystallize on the SiO₂ spheres after annealing at 600 ^°C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd_0.95Eu_0.05VO₄ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by ⁵D₀-⁷F₂ transition of Eu³⁺ (618 nm, red). The PL and CL intensities of Eu³⁺ increase with increasing the annealing temperature and the number of coating cycles. The optimum concentration for Eu³⁺ was determined to be 5 mol% of Gd³⁺ in GdVO₄ host.     

Water-soluble silica-overcoated CdS:Mn/ZnS semiconductor quantum dots

Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts.     

Synthesis and protective properties of titanium nitride coatings on willemite

The instability of brightness and light output of a photoluminescent phosphor based on Mn²⁺-activated willemite (Zn₂SiO₄:Mn) were examined as influenced by the ultrafine titanium nitride layers synthesized based on a molecular layering technique. Using the technique of radical-recombination luminescence excited in a stream of hydrogen atoms, the spectral characteristics of the initial and of modified phosphors were determined.     

Fabrication and luminescent properties of the core-shell structured YNbO4:Eu/Tb@SiO2 spherical particles

The core-shell structured YNbO₄:Eu³⁺/Tb³⁺@SiO₂ particles were realized by coating the YNbO₄:Eu³⁺/Tb³⁺ phosphors onto the surface of spherical silica via a sol-gel process. The obtained materials were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra. The results indicate that 600 °C annealed samples consist of amorphous silica core and crystalline YNbO₄:Re shell, having perfect spherical morphology with uniform size distribution. Upon excitation by UV or electron beam, these phosphors show the characteristic ⁵D₀-⁷F_1-4 emission lines of Eu³⁺ and the characteristic ⁵D₄-⁷F_3-6 emission lines of Tb³⁺. The PL intensities of Eu³⁺ can be tuned by altering the annealing temperature and the coating number of YNbO₄:Eu³⁺ layers.     

Structural and IR Spectroscopic Analysis of Sol-Gel Processed CuFeMnO4 Spinel and CuFeMnO4/Silica Films for Solar Absorbers

Black colored CuFeMnO₄ spinel powders and films were prepared using sol-gel process from Mn-acetate and Fe- and Cu-chloride precursors. Films were deposited by dip-coating technique and heat-treated at 500°C. For CuFeMnO₄/silica films 3-aminopropyl-triethoxysilane (3-APTES) or tetraethoxysilane (TEOS) were used in molar proportion (Mn : Cu : Fe) : silica = 1 : 1. Films and powders were prepared by heating at 500°C. IR spectroscopic measurements were employed to follow the hydrolysis-condensation reactions in (Mn : Cu : Fe)/3-APTES sols hydrolysed with water, and (Mn : Cu : Fe)/TEOS sols hydrolysed with (NH₃)_aq (Stöber processing). The resulting coatings were examined with transmission electron microscopy (TEM) combined with electron dif-fraction analyses, Rutherford back scattering (RBS) and proton induced X-ray emission (PIXE) techniques. Results revealed that (Mn : Cu : Fe)/3-APTES films had a composite structure consisting of the upper Cu_1.4Mn_1.6O₄ spinel and the lower amorphous SiO₂ layer. RBS measurements confirmed the composite structure, showing also that the composition of the film was Mn : Cu : Fe = 1 : 0.96 : 0.29, i.e. close to the precursors ratio Mn : Cu : Fe = 3 : 3 : 1. (Mn : Cu : Fe)/TEOS films prepared from sols which were catalysed with (NH₃)_aq consisted of amorphous monodispersed spherical SiO₂ particles with a size of about 400–420 nm. Solar absorbance (a _s) and thermal emittance (e _T) values of CuFeMnO₄ (500°C) and (Mn : Cu : Fe)/TEOS films (500°C) showed that CuFeMnO₄ films could be used as potential selective coatings for solar absorbers in solar collector systems.     

A rapid and universal bacteria-counting approach using CdSe/ZnS/SiO2 composite nanoparticles as fluorescence probe

In this paper, a rapid, simple, and sensitive method was described for detection of the total bacterial count using SiO₂-coated CdSe/ZnS quantum dots (QDs) as a fluorescence marker that covalently coupled with bacteria using glutaraldehyde as the crosslinker. Highly luminescent CdSe/ZnS were prepared by applying cadmium oxide and zinc stearate as precursors instead of pyrophoric organometallic precursors. A reverse-microemulsion technique was used to synthesize CdSe/ZnS/SiO₂ composite nanoparticles with a SiO₂ surface coating. Our results showed that CdSe/ZnS/SiO₂ composite nanoparticles prepared with this method possessed highly luminescent, biologically functional, and monodispersive characteristics, and could successfully be covalently conjugated with the bacteria. As a demonstration, it was found that the method had higher sensitivity and could count bacteria in 3 × 10² CFU/mL, lower than the conventional plate counting and organic dye-based method. A linear relationship of the fluorescence peak intensity (Y) and the total bacterial count (X) was established in the range of 3 × 10²–10⁷ CFU/mL using the equation Y = 374.82X − 938.27 (R = 0.99574). The results of the determination for the total count of bacteria in seven real samples were identical with the conventional plate count method, and the standard deviation was satisfactory.     

Improved water resistance of SrAl2O4: Eu2+, Dy3+ phosphor directly achieved in a water-containing medium

In this paper, a heterogeneous precipitation method utilizing urea hydrolysis was adopted to coat a SiO₂ layer on the surface of SrAl₂O₄:Eu²⁺, Dy³⁺ long persistence phosphors. To avoid phosphor hydrolysis in a water-containing coating medium, the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) were concerned and carried out. The crystal phases, surface morphologies, hydrolysis stability and water resistance on afterglow properties of coated phosphors were investigated. Scanning electron microscopy, energy dispersive spectrum analysis, transmission electron microscope and Fourier transform infrared spectrum results confirmed that a continuous, uniform and compact SiO₂ coating layer was successfully obtained on the phosphors surface. A theoretical coating amount of 5% or higher was found to be good for hydrolysis stability. Photoluminescence results revealed the coated phosphors showed much better water resistance on afterglow properties than the uncoated phosphor. We also discussed and proposed the hydrolysis restriction mechanism of SrAl₂O₄:Eu²⁺, Dy³⁺ in the water-containing coating medium.     

Synthesis and characterization of high-quality ZnS, ZnS:Mn2+, and ZnS:Mn2+/ZnS (core/shell) luminescent nanocrystals

High-quality ZnS, ZnS:Mn2+, and ZnS:Mn2+/ZnS (core/shell) nanocrystals (NCs) were synthesized via a high-boiling solvent process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The monodisperse ZnS NCs (size = 8 nm), which self-assembled into several micrometer-sized domains, were achieved by adopting poly(ethylene glycol) (PEG) in the reaction process (without using a size-selection process). The obtained ZnS:Mn2+ and ZnS:Mn2+/ZnS core/shell NCs are highly crystalline and quasimonodisperse with an average particle size of 6.1 and 8.4 nm, respectively. All of the as-formed NCs can be well dispersed in hexane to form stable and clear colloidal solutions, which show strong visible emission (blue for ZnS and red-orange for ZnS:Mn2+ and ZnS:Mn2+/ZnS) under UV excitation. The growth of a ZnS shell on ZnS:Mn2+ NCs, that is, the formation of ZnS:Mn2+/ZnS core/shell NCs, resulted in a 30% enhancement in the PL intensity with respect to that of bare ZnS:Mn2+ NCs due to the elimination of the surface defects.     

High effective electrocatalytic oxidation of cyclohexanol on stable Fe-Mn/Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> membrane electrode

A new composite electrode material with iron-manganic oxide coating (Fe-Mn/Mn₂O₃) was prepared, and its catalytic performance for oxidizing cyclohexanol was investigated in this work. The new electrode material, based on iron substrate covered with electrolytic manganese, was obtained by further coating the manganese surface with 50 % manganese nitrate solution and then conducting program thermal decomposition treatment. X-ray diffraction (XRD) was used to determine the surface crystal phase compositions, which were Mn and Mn₂O₃. The catalytic results showed an excellent electrocatalytic performance on the oxidation of cyclohexanol, and the main products were cyclohexanone and hexanedioic acid. According to our experiment results and the literature reports, the existence of mixed valent Mn^III and Mn^IV played a key role in the electrocatalytic oxidation process. A probable process was proposed: the Mn^IV seized the hydrogen from cyclohexanol, the resulting cyclohexaneoxy radical was oxidized into cyclohexanone, and then the absorbed cyclohexanone was further oxidized into hexanedioic acid.     

Preparation and electrochemical study of a new magnesium intercalation material Mg1.03Mn0.97SiO4

Orthorhombic magnesium manganese silicate (Mg_1.03Mn_0.97SiO₄) was prepared and evaluated as a new cathode material for rechargeable magnesium batteries. Although the electrochemical activity of the Mg_1.03Mn_0.97SiO₄ synthesized by high-temperature solid-state reaction is low, the magnesium storage capacity of nanosized Mg_1.03Mn_0.97SiO₄ prepared by modified sol–gel route and in situ carbon coating reaches 244 mAh g⁻¹. The capacity increase mechanism during charge/discharge cycling was also preliminary studied.     

Synthesis and electromagnetic properties of polyaniline-coated silica/maghemite nanoparticles

Polyaniline coated silica/maghemite nanoparticles (PANI/SiO₂/γ-Fe₂O₃ composites) were synthesized by the combination of a sol-gel process and an in-situ polymerization method, in which ferrous and ferric salts as well as tetraethyl orthosilica (TEOS) acted as the precursor for γ-Fe₂O₃ and silica, respectively. As a result, the SiO₂/γ-Fe₂O₃ particle showed a core-shell structure, with γ-Fe₂O₃ as the magnetic core and silica as the shell of the particle. The shell thickness can be controlled by changing the TEOS concentration. The PANI/SiO₂/γ-Fe₂O₃ composites revealed a multilayer core-shell structure, where PANI is the outer shell of the composite. The doping level and the conductivity of PANI/SiO₂/γ-Fe₂O₃ composites decreased with increasing the TEOS content due to the presence of the less coated PANI on the SiO₂/γ-Fe₂O₃ core at higher TEOS content. For a SQUID analysis at room temperature, all γ-Fe₂O₃ containing composites showed a typical superparamagnetic behavior. The saturation magnetization of SiO₂/γ-Fe₂O₃ nanoparticles decreased with increasing the TEOS content due to the increase in silica shell thickness, while the saturation magnetization of PANI/SiO₂/γ-Fe₂O₃ composites also decreased with increasing the TEOS content, which is attributed to the lower conductivity of PANI in the composites at higher TEOS content.     

Synthesis, structure and magnetic behavior of a new three-dimensional Manganese phosphite-oxalate: [C2N2H10][Mn2(OH2)2(HPO3)2(C2O4)]

A novel manganese phosphite-oxalate, [C₂N₂H₁₀][Mn₂^II(OH₂)₂(HPO₃)₂(C₂O₄)] has been hydothermally synthesized and its structure determined by single-crystal X-ray diffraction. The structure consists of neutral manganese phosphite layers, [Mn(HPO₃)]_∞, formed by MnO₆ octahedra and HPO₃ units, cross-linked by the oxalate moieties. The organic cations occupy the middle of the 8-membered one-dimensional channels. Magnetic studies indicate weak antiferromagnetic interactions between the Mn²⁺ ions.     

3-Aminopropyltriethoxysilane-functionalized manganese doped ZnS quantum dots for room-temperature phosphorescence sensing ultratrace 2,4,6-trinitrotoluene in aqueous solution

New strategies for silica coating of inorganic nanoparticles became a research hotspot for enhancing the mechanical stability of colloidal particles and protecting colloidal particles against oxidation and agglomeration, and so on. In this paper, 3-aminopropyltriethoxysilane (APTES)-functionalized Mn doped (AF MnD) ZnS QDs was prepared to be firsyly through the use of silane coupling agents to form an active layer of silica, then sol-gel reaction of TEOS co-deposited with APTES on the surface of resultant active layer of silica. The emitted long lifetime room-temperature phosphorescence (RTP) of the resultant nanomaterials allows an appropriate delay time so that any fluorescent emission and scattering light can be easily avoided. The APTES anchored on the layer of silica can bind 2,4,6-trinitrotoluene (TNT) species to form TNT anion through acid-base pairing interaction, the TNT anion species may increase the charge-transfer pathways from the nanocrystals to nitroaromatic analytes, therefore further enhance the quenching efficiency of RTP. Moreover, APTES as capped reagents can enlarge the spectral sensitivity and enhance RTP response of nanocrystals to the electron-deficient nitroaromatic and nitrophenol species. Meanwhile, AF MnD ZnS QDs also exhibited a highly selective response toward TNT analyte through significant color change and quenching of ⁴T₁ to ⁶A₁ transition emission. This AF MnD ZnS QDs based sensor showed a very good linearity in the range of 0.05-1.8 μM with detection limit down to 50 nM (quenching percentage of phosphorescence intensity of 8%) and RSD of 3.5% (n = 5). The reported QDs-based chemosensors here open up a promising prospect for the sensitive and convenient sensing of TNT explosive.     

MnOx Nanoparticles Supported on a New Mesostructured Silicate with Textural Porosity

A two‐step synthesis of a novel mesostructured silicate, KIL‐2, and its manganese‐containing analogue, Mn/KIL‐2, has been developed. KIL‐2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m². The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL‐2 contains octahedrally coordinated Mn³⁺ (80 %) and tetrahedrally coordinated Mn²⁺ (20 %) ions. Mn³⁺ ions are present in the extra‐framework MnO_x nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn²⁺ ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non‐toxic nature and cost‐effective synthesis, Mn/KIL‐2 thus exhibits properties that are needed for an environment‐friendly catalyst.     

Luminescence Properties of Mn2+-Doped Sol-Gel Glasses

Mn²⁺-doped 1Al₂O₃-99SiO₂ glasses have been prepared by a sol-gel method and their photoluminescence (PL) properties have been studied for the first time. The effect of ZrO₂ and TiO₂ on the luminescence properties has also been studied. In addition, the PL of Mn: 1Al₂O₃-99SiO₂ is compared with Mn:SiO₂. The emission spectra of all the samples containing Al₂O₃ show a band around 620 nm, and the sample without Al₂O₃ shows two bands around 620 and 650 nm. These emission bands are all assigned to the ⁴T₁ ⁶A₁ transition of octahedrally coordinated Mn²⁺ · ZrO₂ and TiO₂ have fluorescence quenching effect. The relative fluorescence intensity of Mn²⁺-doped sol-gel 1Al₂O₃-99SiO₂ is much stronger than that of Mn²⁺-doped sol-gel SiO₂. The difference of the emission wavelength between host materials is explained in terms of the ligand field effect.