Synthesis of novel Dy3+ activated Ba2CaZn2Si6O17 phosphors for white light‐emitting diodes

Dysprosium ion (Dy³⁺) activated Ba₂CaZn₂Si₆O₁₇ phosphors were synthesized using high temperature solid‐state reaction method. Powder X‐ray diffraction (PXRD) analysis confirmed the phase formation of the as‐prepared phosphors. Scanning electron microscopy (SEM) analysis disclosed an agglomeration of particles with an irregular morphology. Under 350 nm excitation, the emission spectrum of Dy³⁺ ions showed bands at 481 nm (blue), 577 nm (yellow) and 674 nm (red). The influence of the Dy³⁺ concentration on its emission intensity was investigated. The optimum concentration of Dy³⁺ ions in the Ba₂CaZn₂Si₆O₁₇:Dy³⁺ phosphors were found to be x = 0.06. The critical energy transfer distance was calculated. The fluorescence lifetime was also determined for Ba₂CaZn₂Si₆O₁₇:0.06Dy³⁺. The Commission International deI’Eclairage (CIE) chromaticity coordinates of the phosphor were calculated to be x = 0.304, y = 0.382. The activation energy for the thermal quenching was calculated to be 0.168 eV. These results indicated that the Ba₂CaZn₂Si₆O₁₇:Dy³⁺ phosphor might be a potential candidate for near ultraviolet (NUV)‐based white light‐emitting diodes.     

Luminescent studies of binuclear ternary europium(III) pyridineoxide tetrazolate complexes containing bis‐phosphine oxide as auxiliary co‐ligands

A new class of antenna chromophores so called ‘tetrazolates’ have not been explored much for lanthanide luminescencent complexes. However, we have already published several articles considering pyridineoxide tetrazolates as sensitizer with lanthanide ions. Although this class of antenna attracted much less attention because of its poor photoluminescence quantum yields (tris‐pyridineoxide tetrazolate europium complex = 13% in solution) we tried and successfully achieved to improve the photoluminescence quantum yields for this particular antenna molecule by replacing coordinated water from the inner coordination sphere of europium ion by introducing phosphine oxides as additional chromophore. In the present article the two bis‐phosphine oxides attach two molecules of tris‐pyridineoxide tetrazolate europium(III) complex which leads to the improvement of the overall molar absorption coefficients as well as photo‐physical properties of the complexes. We found more than two‐fold increase (31% in solution) in photoluminescence quantum yield with one of the coordinated phosphine oxides comparing with that of tris‐pyridineoxide tetrazolate europium(III) complex.     

Preliminary results on the photoluminescence and optically stimulated luminescence in Cu‐doped and Ag‐doped ZnB2X4 (B = Li,Na, K: X = Cl,Br) compounds

Photoluminescence, and optically stimulated luminescence in ZnB₂X₄ (B; Li,Na,K: X; Cl,Br) compounds doped with Cu⁺ or Ag⁺ were studied. Double humped emission bands attributable to the activators were observed in all the samples. The observed photoluminescence of Cu⁺ and Ag⁺ could be identified with 3d⁹4s¹?3d¹⁰ and 4d⁹5s¹?5d¹⁰ transitions respectively. The longer wavelength band (400–500 nm range) could be attributed to the Cu⁺ or Ag⁺ ion replacing alkali ion at the octahedral alkali site whereas short wavelength band (340–400 nm range) is attributed to a Cu or Ag ion at tetrahedral zinc site. The short wavelength band was found to be intense compared with long wavelength and gave an indication that most of the Cu or Ag ions prefered a tetrahedral Zn site compared with the octahedral alkali site. All the samples exhibit optically stimulated luminescence (OSL). The sensitivity was found to be lattice dependent. The lowest sensitivity of about 1% compared with Al₂O₃:C was observed in lithium lattices whereas highest the sensitivity of about 290% was observed in the case of Cu‐doped ZnNa₂Br₄.     

Circularly polarized luminescence of helically assembled pyrene π‐stacks on RNA and DNA duplexes

In this report, we describe the circularly polarized luminescence (CPL) of the RNA duplexes having one to four 2′‐O‐pyrene modified uridines ( Upy ) and the DNA duplexes having two, four, and six pyrene modified non‐nucleosidic linkers ( Py ). Both the pyrene π‐stack arrays formed on the RNA and DNA double helical structures exhibited pyrene excimer fluorescence. In the pyrene‐modified RNA systems, the RNA duplex having four Upy s gives CPL emission with g_lum value of <0.01 at 480 nm. The structure of pyrene stacks on the RNA duplex may be rigidly regulated with increase in the Upy domains, which resulted in the CPL emission. In the DNA systems, the pyrene‐modified duplexes containing two and four Pys exhibited CPL emission with g_lum values of <0.001 at 505 nm. The pyrene π‐stack arrays presented here show CPL emission. However, the g_lum values are relatively small when compared with our previous system consisting of the pyrene‐zipper arrays on RNA.     

Quantification of the presence and activity of specific microorganisms in nature

Traditional techniques for assessment of microbial numbers and activity generally lack the specificity required for risk assessment following environmental release of genetically engineered microbial inocula. Immunological and molecular-based techniques, such as DNA probing and genetic tagging, were initially used to determine the presence or absence of microorganisms in environmental samples. Increasingly they are being developed for quantification of populations of specific organisms, either indigenous or introduced, in the environment. In addition, they are being used to quantify the activity of particular organisms or groups of organisms, greatly extending the range of techniques available to the microbial ecologist. This article reviews the use of traditional techniques for the quantification of microbial population size and activity and the application of molecular techniques, including DNA probing, genetic marking, use of fluorescent probes, and quantitative PCR, in combination with advanced cell detection techniques such as confocal laser scanning microscopy and flow cytometry.     

Combustion synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+, Tb3+ phosphor.

Eu(2+), Dy(3+) and Tb(3+) co-doped strontium aluminate phosphor with high brightness and long afterglow was synthesized by a combustion method, using urea as a reducer. The properties of SrAl(2)O(4):Eu(2+),Dy(3+),Tb(3+) phosphor with a series of initiating combustion temperatures, urea concentrations and boric acid molar fractions were investigated. The sample at initiating combustion temperature of 600 degrees C exhibited an intense emission peak at 513 nm, in which the phosphor existed as a single-phase monoclinic structure. The experimental results showed that the optimum ratio of urea is 2.0 times higher than theoretical quantities and that the suitable molar fraction of H(3)BO(3) is 0.08. The average particle size of the phosphor was 50-80 nm and its luminescence properties were studied systematically. Compared with SrAl(2)O(4):Eu(2+),Dy(3+) phosphor, the initial luminescence brightness improved from 2.50 candela (cd)/m(2) to 3.55 cd/m(2) and the long afterglow time was prolonged from 1290 s to 2743 s.     

CO2激光照射对青椒、茄子种子及幼苗生长点超弱发光影响的研究

本文利用ＣＯ２激光照射青椒、茄子干种子后,观察刺激剂量、半致死剂量对种子及幼苗生长点超弱发光的影响,从而探索超弱发光是否可作为激光照射后衡量种子活力综合反应的一项指标。其结果表明：１．青椒、茄子干种子超弱发光的动态变化随着照射间隔期的延长,其不同剂量之间超弱发光强度的差异也相应变小,照射时间最长的半致死剂量组２５″、３５″,其超弱发光由最高降为最低;激光刺激剂量组３″、１３″的超弱发光强度始终高于ＣＫ。２．青椒、茄子种子发芽过程中超弱发光表现为激光刺激剂量组均极显著高于ＣＫ;半致死剂量２５″、３５″均极显著低于ＣＫ。３．激光组的活体生长点和提取液的超弱发光均极显著高于ＣＫ;活体生长点的超弱发光低于提取液的超弱发光。     

The effect of different solvents on the ATP/ADP content and growth properties of HeLa cells

Testing of the effects of xenobiotics in cultured cells often requires the use of organic solvents to effect suspension of the test agents in cell culture media. However, the toxic effects of the solvents themselves may introduce artifacts, which obscure interpretation of the experimental results. In this article, the toxicity of different solvents commonly used for solvation of a variety of xenobiotic agents was studied. We show that ethanol, acetone, isooctane, methanol, and hexane were considerably less toxic than the more commonly used solvent, DMSO, when ATP content and growth rates of HeLa cells exposed to these solvents was measured. © 1998 John Wiley & Sons, Inc. J Biochem Toxicol 13: 11–15, 1999