Preparation and properties of luminous materials of CaSiO3: Pb, Mn by sol-gel method

The luminous materials of CaSiO₃: Pb, Mn were synthesized by sol-gel method and ultrasound technology. The properties of the phosphors were characterized by luminescence spectrum, differential thermal analysis and thermal gravimetry analysis (DTA-TG), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and transmission electron microscopy (TEM). The effects of factors such as the synthetic material compositions, ultrasound time and annealed temperature on phosphorescent brightness of sample were studied and the optimum synthetic conditions were determined. The results show that, compared with the sample made by the high temperature solid-state reaction, the luminescent intensity of the CaSiO₃: Pb, Mn sample increased by about 200% and the mean diameter of particles of the sample decreased by about 300 nm. __________ Translated from Chemical Research and Application, 2007, 19(2): 140–144 [译自: 化学研究与应用]     

Thermosensitive Water–Polymer Systems Studied by Luminescent Spectroscopy. Copolymers of N-vinylcaprolactam and N-vinylpyrrolidone

Thermosensitive aqueous solutions of N-vinylcaprolactam/N-vinylpyrrolidone (co)polymers were investigated by luminescent spectroscopy. Investigation of the luminescent intensity and the bound fraction of luminescence indicators interacting to the (co)polymers in water showed that the chemical structure of the water-soluble poly-N-vinylamides defines their functional and structural characteristics such as conformation, intramolecular mobility, compactization and complexation. It was established that the complexing ability of VCL-VP copolymers exceeds that of PVP even at a low content of VCL units. At 85 mol% of VCL the complexation and compactization of the macromolecules were found to be higher than that of pure PVCL. A hinge-like action of VP units incorporated in PVCL structure is suggested to be a reason of the extreme behavior observed for 85:15 VCL:VP composition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diffusion processes in silver-conducting solid electrolyte in terms of the Grafov-Ukshe model of adsorption relaxation of double layer

The results of impedance studies of an interface formed by solid electrolyte RbAg₄I₅ with iodine vapors and certain iodine complexes are compared with the results on the diffusion of minority charge carriers and color centers. The impedance results are analyzed based on the Grafov-Ukshe model for the adsorption relaxation of the double layer (ARDL) [1]. The obtained kinetic parameters agree within the experimental error with the diffusion coefficients found by independent methods. It is shown that the experimental data of impedance measurements agree with the results of calculations in terms of the Grafov-Ukshe ARDL model.     

Nature of intrinsic luminescence in the glasses of CaO–Ga2O3–GeO2 system

The intrinsic luminescence of glasses of the CaO–Ga₂O₃–GeO₂ system has been investigated. High chemical purity and optical quality glasses, both undoped and doped with transition and rare-earth ions with different compositions, were obtained by high-temperature synthesis. The influences of the basic glass composition, impurities (Cr³⁺, Mn²⁺, Eu²⁺, Nd³⁺, Ho³⁺, Er³⁺, and Ce³⁺) and different kinds of excitation, on the intrinsic luminescence of the CaO–Ga₂O₃–GeO₂ glasses were investigated. The nature and possible mechanisms of the intrinsic luminescence in glasses of this system are discussed. The proposed models of intrinsic luminescence are supported by electron spin resonance spectroscopy.     

Almost Chebyshev set with respect to bounded subsets

The uniqueness and existence of restricted Chebyshev center with respect to arbitrary subset are investigated. The concept of almost Chebyshev sets with respect to bounded subsets is introduced. It is proved that each closed subset in a reflexive locally uniformly convex (uniformly convex, respectively) Banach space is an almost Chebyshev subset with respect to compact convex subsets (bounded convex subsets and bounded subsets, respectively). Project supported by the National Natural Science Foundation of China, Natural Science Foundation of Zhejiang Province, and the State Major Key Project for Basic Researchers of China.     

Energy Levels in the Forbidden Band of the Bi4Ge3O12 Ceramics

Thermally stimulated luminescence in the Bi₄Ge₃O₁₂ ceramics and also in the ceramics of the parent components Bi₂O₃ and GeO₂ is investigated. The similarity of the curves of the thermally stimulated luminescence in bismuth germanate with the structure of eulytine Bi₄Ge₃O₁₂ and sillenite Bi₁₂GeO₂₀ is explained. The relation of the thermally stimulated luminescence band in Bi₄Ge₃O₁₂ (with a maximum at 143 K) to the disruptions in the germanium sublattice and of the thermally stimulated band (with a maximum at 187 K) to the recombination processes in the bismuth sublattice is shown. It has been established that the light sum in the Bi₄Ge₃O₁₂ ceramics is stored most effectively upon excitation by light in an energy region of 4.4 eV.     

Active center determinations on MgCl2‐supported fourth‐ and fifth‐generation Ziegler–Natta catalysts for propylene polymerization

Active center determinations on different Ziegler–Natta polypropylene catalysts, comprising MgCl₂, TiCl₄, and either a diether or a phthalate ester as internal donor, have been carried out by quenching propylene polymerization with tritiated ethanol, followed by radiochemical analysis of the resulting polymers. The purpose of this study was to determine the factors contributing to the high activities of the catalyst system MgCl₂/TiCl₄/diether—AlEt₃. Active center contents (C*) in the range 2–8% (of total Ti present) were measured and a strong correlation between catalyst activity and active center content was found, indicating that the high activity of the diether‐containing catalysts is due to an increased proportion of active centers rather than to a difference in propagation rate coefficients. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1635–1647, 2006     

Fast approximations for sums of distances, clustering and the Fermat–Weber problem

We describe two data structures that preprocess a set S of n points in (d constant) so that the sum of Euclidean distances of points in S to a query point q can be quickly approximated to within a factor of . This preprocessing technique has several applications in clustering and facility location. Using it, we derive an O(nlogn) time deterministic and O(n) time randomized -approximation algorithm for the so called Fermat–Weber problem in any fixed dimension.     

基于超级碳点的水致荧光“纳米炸弹”

介绍了一种发光性质依赖于水接触的新型纳米发光材料--基于超级碳点的发光"纳米炸弹"。在甲苯溶液中, 这种"纳米炸弹"光致发光很弱;当遇见水后, "纳米炸弹"分解为小的碳点, 光致发光显著增强。将"纳米炸弹"与纸复合可应用在喷水荧光打印和汗孔成像。目前, 大部分智能荧光材料存在光稳定性差, 潜在的生物毒性, 制备成本高, 或与传统喷墨打印不兼容等缺点。本文报道的碳基纳米材料没有(或很少有)这些缺点, 并可实际应用在光信息存储, 司法鉴定和医疗检测等领域。     

Influence of alkyl length on properties of piezofluorochromic aggregation induced emission compounds derived from 9,10-bis[(N-alkylphenothiazin-3-yl)vinyl]anthracene

Three 9,10-bis[(N-alkylphenothiazin-3-yl)vinyl]anthracene derivatives with different propyl, hexyl, and dodecyl side chains (AnPh₃, AnPh₆, and AnPh₁₂) were synthesized and confirmed by standard spectroscopic methods. All of the compounds exhibited obvious aggregation induced emission (AIE) and piezofluorochromic (PFC) properties. The PFC behaviors were investigated and showed that proportional alkyl-length dependent relationship existed not only in the ground states of the compounds, but also in the melted states compared with the fumed states of the compounds. The PFC mechanism was explored and ascribed to the crystalline–amorphous phase transformation. More importantly, these derivatives showed reversible significant PFC properties and reproducibility in various states including fumed, ground, annealed, and melted states, making them promising stimuli-responsive and smart luminescent materials for pressure-sensors, information-recording, and light-emitting device applications.