Silver nanoclusters doped in X and mordenite zeolites as heterogeneous catalysts for the decomposition of carbamate pesticides in solution

Ag(I) nanoclusters doped in X and mordenite zeolites were prepared and analyzed using spectroscopy. Both experimental and theoretical studies of the prepared compounds show the presence of silver nanoclusters with various sizes and environments. The presence of Ag(I) nanoclusters doped in X and mordenite zeolites with high silver loadings enhanced the photodecomposition rate of carbofuran 215-and 184-fold, respectively, while the photodecomposition of carbaryl in the presence of these catalysts show room temperature rate constants that are 182-and 168-times faster than the photodecomposition of carbaryl in the absence of the silver-doped zeolite catalysts. The reaction rates were found to be dependent on the amount of silver loaded into the zeolite.     

Ga2O3-La2O3-Yb2O3-Er2O3(HO2O3)体系光谱性质的研究

根据稀土离子能级的特点,对Ga2O3-La2O3-Yb2O3-Er2O3(HO2O3)体系的光谱性质进行了探讨,发现它们有二类发光性质:Stokes发光和反Stokes发光,研究了发光强度和发射波长与掺杂离子的依赖关系,观察到由能量的共振转移引起的荧光浓度猝灭现象,并取得了最大发光强度时的掺杂离子浓度和一些规律性结果.     

Luminescence properties of silver(I)-exchanged zeolite Y and its use as a catalyst to photodecompose carbaryl in the presence of natural organic matter

Silver-doped Y-type zeolites with different silver loadings were prepared and analyzed spectroscopically at various temperatures. Several emission bands were observed for each AgY sample. Each emission band becomes dominant over the others by selecting a suitable excitation wavelength, indicating the presence of different silver clusters in zeolite Y. The study shows that the presence of AgY catalysts increases the photodecomposition rate of carbaryl by 4–42 times in comparison to the catalyst-free system, with the rate dependent on the amount of silver that was loaded on the Y-type zeolites. The presence of different concentrations of Suwannee River natural organic matter (NOM) affected the photodegradation reaction of carbaryl by allowing it to proceed via two different pseudo-first-order pathways. However, the presence of the silver-doped zeolite catalysts makes the photodecomposition of carbaryl proceed via first-order kinetics.     

Effect of Substituents on Luminescence of New Hydroxytetraphenylimidazole Derivatives

The effect of OMe and NO₂ substituents in the phenol ring of hydroxytetraphenylimidazole (HTPI) derivatives on their luminescence in solutions and in the solid phase has been studied. The presence of the nitro group leads to multiple luminescence. In addition to the band of the photoproduct of intramolecular proton transfer, which is single for unsubstituted HTPI, nitrosubstituted imidazoles additionally have emission bands at shorter and longer wavelengths. The ratio between the bands depends on the solvent, concentration, and excitation wavelength. In solutions and polymer media, it is possible to switch luminescence by changing the excitation wavelength, and under certain conditions, white light emission is observed.     

CaWO4:xEu3+,ySm3+,zLi+红色荧光粉的制备及光学性能

采用微波固相法制备了CaWO₄：xEu³⁺,ySm³⁺,zLi⁺红色荧光粉。测量样品的XRD图、激发谱、发射谱及发光衰减曲线,研究并分析了Eu³⁺、Sm³⁺、Li⁺的掺杂浓度,对样品微结构、光致发光特性、能量传递及能级寿命的影响。结果表明,Eu³⁺、Sm³⁺、Li⁺掺杂并未引起合成粉体改变晶相,仍为CaWO₄单一四方晶系结构。Eu³⁺、Sm³⁺共掺样品中,Sm³⁺掺杂为3%时,Sm³⁺对Eu³⁺的能量传递最有效。Li⁺掺杂起到了助熔剂和敏化剂的作用,使样品发光更强。在394 nm激发下,与CaWO₄：3%Eu³⁺样品比较,3%Eu³⁺、3%Sm³⁺共掺CaWO₄及3%Eu³⁺、3%Sm³⁺、1%Li⁺共掺CaWO₄样品的发光分别增强2倍及2.4倍。同一激发波长下,单掺Eu³⁺样品寿命最短,Sm³⁺、Eu³⁺共掺样品随Sm³⁺浓度增加,寿命先减小后增加,且掺杂了Li⁺的样品比不掺Li⁺的样品⁵D₀能级寿命有所增加。     

沉淀法合成纳米晶上转换发光材料Y_2O_2S:Yb,Er

采用沉淀法在不同温度下合成了纳米上转换发光材料Y2O2S∶Yb,Er,运用XRD、TEM和上转换发光光谱对其进行表征。结果表明,使用该法在700℃即能合成纳米上转换发光材料Y2O2S∶Yb,Er,随着合成温度的升高,产物的粒径从60到120nm逐渐增大。上转换发光光谱显示该材料主要有2个发射带,其中红光发射的中心波长位于668nm,绿光发射的中心波长位于525和550nm。此外,对材料的上转换发光过程进行了探讨。     

In situ synthesis and photoluminescence of Eu3+ doped Y(OH)3@β-NaYF4 core-shell nanotubes

Eu(3+) doped Y(OH)(3)@β-NaYF(4) core-shell nanotubes were prepared by an in situ synthesis method. The photoluminescence properties were studied under different excitation wavelengths. When the excitation wavelength is 363, 380, and 397 nm, the spectral configurations are similar, and are different from that under 414 nm excitation. The peak location of (7)F(0)→(5)D(3) shifted with excitation wavelength, indicating that the nanocrystals have multiple luminescence centers or emitting states.     

Upconversion Luminescence through Cooperative and Energy-Transfer Mechanisms in Yb3+-Metal-Organic Frameworks

Lanthanide-doped metal–organic frameworks (Ln-MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide-based upconversion luminescence in these materials. Here, 1,3,5-benzenetricarboxylic acid (BTC) and trivalent Yb³⁺ ions were used to generate crystalline Yb-BTC MOF 1D-microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb-BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb³⁺-based upconversion and energy transfer. Yb-BTC MOFs doped with Er³⁺, Ho³⁺, Tb³⁺, and Eu³⁺ ions exhibit both the cooperative luminescence from Yb³⁺ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb³⁺ is observed in the MOFs doped with Tm³⁺, Pr³⁺, Sm³⁺, and Dy³⁺. The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln-MOFs exhibiting upconversion.     

The Photodecomposition of 1,l-Dichloro-2,2-bis(5′-chloro-2′-methoxyphenyl)ethylene (MPE), an Analogue of DDE

The solution-phase photodecomposition of l, l-dichloro-2,2-bis(5′-chloro-2′-methoxy-phenyl)ethylene (MPE) has been studied at an excitation wavelength of 313 nm in the presence of O₂ as well as in vacuum-degassed solutions. Only two non-volatile compounds are produced: 2,5-dichloro-3-(5′-chloro-2′-methoxyphenyl)benzofuran (BFD) and a minor product which was not identified. The BFD represents approximately 90% of the total non-volatiles. The volatile products were identified as CH₃Cl, CH₄ and HC1, with CH₃C1 being approximately 99.9 % of the total volatiles. Photolyses were carried out in C₆H₁₂ and CCI₄ solvents, the same products being observed in both solvents. Variation of MPE concentration has little or no effect on the relative quantum yield of decomposition. The photodecomposition of MPE does not follow the same pathway as the photodecomposition of DDE.     

White luminescence of Tm-Dy ions co-doped aluminoborosilicate glasses under UV light excitation

Tm³⁺ and Dy³⁺ ions co-doped aluminoborosilicate glasses were prepared in this study. The luminescence properties of the glasses were analyzed. A combination of blue, green, yellow, and red emission bands was shown for these glasses, and white light emission could be observed under UV light excitation. White light luminescence color could be changed by varying the excitation wavelength. Concentration quenching effect was investigated in this paper. Furthermore, the dependence of luminescence properties on glass compositions was studied. Results showed that the luminescence intensity changed with different network modifier oxides, while the white color luminescence was not affected significantly.     

Characterization of germanium site distribution in zeolite ITQ-7 by photoluminescence

Zeolite ITQ-7 containing germanium emits luminescence upon excitation at the wavelength of the absorption maxima; control experiments with amorphous GeO2 and all-silica zeolites indicate that the emission is attributable to Ge atoms occupying framework positions; the emission decays on the nanosecond time scale and it fits to variable proportions of three exponential kinetics, this being compatible with the presence of three families of Ge atoms in the solid.     

Infrared (1.2-1.6 microm) luminescence in Cr4+:Yb3Al5O12 single crystal with 940 nm diode pumping

Infrared (1.2-1.6 microm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (lambda=940 nm). The Cr4+ emission band was observed with its peak at 1.34 microm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda=1.03 microm). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the 3B2(3T2)-3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 microm) output.     

Highly uniform and monodisperse beta-NaYF(4):Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprism crystals: hydrothermal synthesis and luminescent properties

beta-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb3+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu3+ (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to 5D0-3 --> 7FJ (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively. When doped with 5% Tb3+ ions, the strong DC fluorescence corresponding to 5D4 --> 7FJ (J = 6, 5, 4, 3) transitions with 5D4 --> 7F5 (green emission at 544 nm) being the most prominent group that has been observed. In addition, under 980 nm laser excitation, the Yb3+/Er3+- and Yb3+/Tm3+-codoped beta-NaYF4 samples exhibit bright green and whitish blue up-conversion (UC) luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.     

The Photochemistry of Carbamates,I

Abstract

The photodecomposition of 4-dimethylamino-3,5-xylyl-N-methyl carbamate (Zectran) in aerated and degassed solution has been carried out. Three major photoproducts were detected and characterized to be: 4-dirnethylamino-3,5-dimethyl Rhenol, 4-hydroxy-2,6-dimethyl-N-methyl benzamide and 4-monomethylamino-3,5-xylyl-N-methyl carbamate. The phenol and benzamide products suggest that one of the pathways of photodecomposition of Zectran is via a photo-Fries rearrangement. The ortho-benzamide (5-dimethylamino-4,6-dimethyl-2-hydroxy-N-methyl benzamide) which could also be expected to occur in a photo-Fries reaction, was not observed. The excitation wavelength was > 296.7 nm, i.e. radiation available in the solar spectrum. Thus the products observed in this study may be expected to occur in the environment as a result of the action of sunlight on Zectran.     

Optical investigations of alkali metal thiomanganates(II) containing isolated complexes as well as chain and planar compounds

Tetracoordinated Mn(II) complexes providing different molecular structures were investigated using various spectroscopical procedures. Na(6)MnS(4) contains separate pseudotetrahedral Mn-S complex units, K(2)MnS(2) has chains of edge-shared tetrahedra, and Cs(2)Mn(3)S(4) crystallizes in corresponding layers. Also doped materials, i.e., Cs(2)(Mn(x)Zn(1-x))(3)S(4) with 0.0 < x < 1.0, are considered. Absorption spectra recorded from samples incorporated in polyethylene pellets and excitation spectra taken from pure materials at 15-20 K temperature are assigned on the basis of energy level calculations obtained from the angular overlap model. All compounds exhibit intensive emission in the red, some of them also in the yellow region, which both are investigated in the temperature range from 12.5 to 250 K, in some cases varying the excitation power and excitation wavelength. Decay measurements supply lifetimes and activation energies evaluated from Arrhenius plots. The results support an assignment of both types of emissions to MnS(4) complex entities for all compounds, the red emission from the lowest excited level (Kasha luminescence) and the yellow emission, observed for some of the compounds with increasing intensity at lower temperature, from higher electronic levels.     

Strong visible up-conversion emission in Tb3+, Tm3+ and Tb3+-Tm3+ co-doped tellurite glasses sensitized by Yb3+

Up-conversion luminescence characteristics under 975 nm excitation have been investigated with Tb3+/Tm3+/Yb3+ triply doped tellurite glasses. Here, green (547 nm: (5)D(4)-->(7)F(4)) and red (660 nm: (5)D(4)-->(7)F(2)) up-conversion (UC) luminescence originating from Tb3+ is observed strongly, because of the quadratic dependences of emission intensities on the excitation power. Especially, the UC luminescence was intensified violently with the energy transfer from the Tm3+ ions involves in the Tb3+ excitation. To the Tb3+/Tm3+/Yb3+ triply doped glass system, a novel up-conversion mechanism is proposed as follows: the energy of (3)G(4) level (Tm3+) was transferred to (5)D(4) (Tb(3+)) and the 477-nm UC luminescence of Tm3+ was nearly quenched.     

Preparation, characterization and investigation of catalytic activity of Li-doped LaFeO3 nanoparticles

Nanometer oxides Li-doped LaFeO₃ with a high photocatalytic activity were synthesized by the acetic acid based sol-gel route. X-ray diffraction, transmission electron microscopy, differential thermal analysis, atomic absorption spectrum, infrared absorption spectrum analyzer and UN-Vis spectrophotometer technologies were used to characterize the products. The photocatalytic activities of the samples were studied with measurement of effect of photodecomposition of Methyl blue solution and organism in arcylon effluents. The results show that LaFeO₃ doped lithium has better photocatalytic activity than pure LaFeO₃ particles, and the optimum amount doped lithium is x = 0.03.     

Hexafluoroacetone photochemistry: Internal conversion versus intersystem crossing

The hexafluoroacetone photodecomposition quantum yield is calculated as a function of pressure at 24° and 313 nm using the established mechanism of excited state processes and rate parameters determined by previous luminescence and photodecomposition studies. Agreement with experiment can be obtained if internal conversion increases relative to intersystem crossing as the excitation energy is increased.     

CaWO_4∶xEu~(3+),ySm~(3+),zLi~+红色荧光粉的制备及光学性能

采用微波固相法制备了CaWO_4∶xEu~(3+),ySm~(3+),zLi~+红色荧光粉。测量样品的XRD图、激发谱、发射谱及发光衰减曲线,研究并分析了Eu~(3+)、Sm~(3+)、Li~+的掺杂浓度,对样品微结构、光致发光特性、能量传递及能级寿命的影响。结果表明,Eu~(3+)、Sm~(3+)、Li~+掺杂并未引起合成粉体改变晶相,仍为CaWO_4单一四方晶系结构。Eu~(3+)、Sm~(3+)共掺样品中,Sm~(3+)掺杂为3%时,Sm~(3+)对Eu~(3+)的能量传递最有效。Li~+掺杂起到了助熔剂和敏化剂的作用,使样品发光更强。在394 nm激发下,与CaWO_4∶3%Eu~(3+)样品比较,3%Eu~(3+)、3%Sm~(3+)共掺CaWO_4及3%Eu~(3+)、3%Sm~(3+)、1%Li~+共掺CaWO_4样品的发光分别增强2倍及2.4倍。同一激发波长下,单掺Eu~(3+)样品寿命最短,Sm~(3+)、Eu~(3+)共掺样品随Sm~(3+)浓度增加,寿命先减小后增加,且掺杂了Li~+的样品比不掺Li~+的样品~5D_0能级寿命有所增加。     

EuBO3的低温水热合成及光谱可调性质研究

采用低温水热法合成了稀土硼酸盐EuBO3的纯相样品.利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)和荧光光谱仪(PL)对样品的结构、形貌、价态及发光性质进行了研究.结果表明,该样品属六方晶系,在不同的矿化剂和碱度下呈现不同的自组装形貌.当以NaOH或NH3.H2O为矿化剂时,该样品分别沿着(100)和(002)晶面生长.因为Eu离子以混合价态形式存在,样品表现出光谱可调性,当激发波长为270～360 nm时,样品荧光由红色转为橙色,经粉紫光变为蓝光.