Eu-Mn energy transfer in white-light-emitting T-phase (Ba,Ca)2SiO4:Eu, Mn phosphor

White-light-emitting T-phase Eu²⁺/Mn²⁺-codoped (Ba, Ca)₂SiO₄ phosphors are achieved in terms of the energy transfer between Eu²⁺ and Mn²⁺ ions. All spectra consist of the relatively broad green and the red emission bands, which thus result in a warm-white color with a color temperature of ∼4000 K. With increasing Eu²⁺ ions at fixed Mn²⁺ concentrations, a strong correlation between the luminescence and the electron paramagnetic resonance spectra is observed. This demonstrates that Eu²⁺ doping causes a perturbation of Mn²⁺ sites and the violation of their selection rules that enhances Mn²⁺-related emissions.     

Surfactant-sensitized malachite green method for trace determination of orthophosphate in aqueous solution

A surfactant-sensitized spectrophotometric method for determination of trace orthophosphate has been developed using anion surfactant (Ultrawet 60 L) with molybdate and malachite green in low acidic medium (pH_T 1.0). The method detection limit (3 × standard deviation of blank, n = 10) was 8 nM and the calibration curve was linear over a range of 10-400 nM (r² = 0.997). The molar absorptivity was 1.26 × 10⁵ L mol⁻¹ cm⁻¹ at 600 nm with the background correction at 530 nm. The precision of method was 3.4% at 50 nM and 2.4% at 100 nM orthophosphate (n = 10). The hydrolysis of eight organic phosphorus and polyphosphate compounds was less than 2% of the total phosphorus present (5-10 μM). This method showed less arsenate interference than previous methods, with only 3% even in the presence of orthophosphate in the samples. No interference of silicate up to 40 μM was observed. Background anions (in an order of SO₄²⁻ > NO₃⁻ > Cl⁻) have greater effects than cations (Ca²⁺ > Mg²⁺ > Na⁺) on the reagent blank and the molar absorptivity of the color product.     

硅酸盐岩石微孔中流体混合物扩散系数的分子动力学模拟

用计算机模拟研究了受限于硅酸盐岩石微孔中等摩尔氩氪流体混合物的扩散系数.为验证程序的正确性,分别将宏量条件下氩和氪的分子动力学模拟值与文献实验值进行了比较.然后,对受限于硅酸岩平板壁面中氩氪流体混合物的扩散系数进行了模拟计算.根据计算结果提出了五个不同对比壁间距下氩氪混合流体扩散系数的经验模型,这些模型可应用于工业估算.     

Synthesis and Eu luminescence in new oxysilicates, ALa3Bi(SiO4)3O and ALa2Bi2(SiO4)3O [ACa, Sr and Ba] with apatite-related structure

New oxysilicates with the general formula ALa₃Bi(SiO₄)₃O and ALa₂Bi₂(SiO₄)₃O [ACa, Sr and Ba] are synthesized and characterized. Powder X-ray diffraction of these silicates show that they are isostructural with BiCa₄(VO₄)₃O which has an apatite-related structure. Eu³⁺ luminescence in the newly synthesized oxysilicates show broad emission lines due to disorder of cations. The relatively high intense magnetic dipole transition ⁵D₀→⁷F₁ points to a more symmetric environment. The photoluminescence results confirm that the compounds have apatite-related crystal structure.     

Preparation, structure, morphology, and dc and ac conductivity of the 88SiO2-6Li2O-6Nb2O5 (% mole) sol-gel derived glass-ceramics

The glass composition 88SiO₂-6Li₂O-6Nb₂O₅ (mole %) was successfully prepared by the sol-gel technique. The dried and translucent gel was heat-treated at temperatures between 500°C and 800°C. Lithium niobate crystallites, an important ferroelectric material, were detected in the gel derived glass-ceramics treated above 650°C. In the samples treated at 700 and 800°C the Li₂Si₂O₅ crystalline phase is present. The 800°C treated sample also presents the Li₃NbO₄ phase. The structure and morphology of the samples were studied by X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The SEM revealed that all the samples, heat-treated above 650°C, present crystallites embedded in the glass matrix. The particles detected in the 600°C treated sample are essentially amorphous, or with an incipient structure. The temperature dependence of the dc electrical conductivity (σ _dc ) shows two regions with different activation energies. The conductivity behaviour of the sample is mainly due to the mobile ion number. The ac conductivity (σ _ac ), measured at 1 kHz decreases with the rise of the treatment temperature due to the increase of the LiNbO₃ crystallites amount. The electrical behavior of the glass and glass-ceramics reflects the important role carried out by the treatment temperature in the gel-glass structure.     

Amperometric phenol biosensor based on sol-gel silicate/Nafion composite film

An amperometric biosensor based on tyrosinase immobilized in silicate/Nafion composite film has been developed for the determination of phenolic compounds. The Nafion polymer in the composite was used not only to overcome the brittleness of the pure sol-gel-derived silicate film but also to increase the long-term stability of the biosensor. Tyrosinase was immobilized by a thin film of silicate/Nafion composite on a glassy carbon electrode. Phenolic compounds were determined by the direct reduction of biocatalytically-liberated quinone species at −200 mV versus Ag/AgCl (3 M NaCl). The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH and operating potential were explored for optimum analytical performance of the enzyme electrode. The biosensor can reach 95% of steady-state current in about 15 s. The sensitivities of the biosensor for catechol and phenol were 200 and 46 mA/M, respectively. A detection limit of 0.35 mM catechol was obtained with a signal-to-noise ratio of 3. The enzyme electrode retained 74% of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.     

Li2EuSiO4, ein Europium(II)-dilithosilicat: Eu[(Li2Si)O4]

Li₂EuSiO₄, an Europium(II) Litho-Silicate: Eu[(Li₂Si)O₄] Single crystals of Li₂EuSiO₄ were first obtained by reaction of Eu₂SiO₄ with a melt of LiCl at 800 °C in a sealed tantalum tube. It crystallizes with the trigonal space group P3₁21, Z = 3, with a = 502.70(5), c = 1247.0(2) pm. The tetrahedra [LiO₄] and [SiO₄] are connected via common corners and thereby build up a three-dimensional network that leaves space for Eu²⁺ which is in an eightfold coordination. Li₂SrSiO₄ is isotypic with a = 502.59(4) and c = 1247.1(1) pm.