Vinylsulfonylethyl derivatives of nucleic acid bases and their graft polymers on polyethyleneimine

Vinylsulfonylethyl (VSE) derivatives of the nucleic acid bases adenine, thymine, cytosine, and the nucleosides inosine and uridine have been prepared via a simple Michael reaction with divinyl sulfone. The VSE derivatives were grafted on a polyethyleneimine (PEI) backbone. PEI of different molecular weights (1400, 1800 and 50,000–100,000) were used and also two different molar ratios (1:1 and 1:2) of monomer to PEI were employed. From the ¹H-NMR and elemental analysis, it appeared that in almost all instances the grafting was quantitative. In one case, both 1-VSE-thymine and 9-VSE-adenine were grafted on the same PEI backbone. Interactions between some of these polymers were investigated by UV spectroscopy. The expected complementary base pairing was observed only in DMSO–ethylene glycol solvent system but not in DMSO. The adenine polymer showed a one-to-one interaction with the thymine polymer.     

Thermo and mechanoluminescence studies of BZT phosphor

Mechanoluminescence (ML) and thermoluminescence (TL) in barium zirconium titanate (BZT) is reported for the first time. The BZT powder sample, belonging to perovskite category is synthesized using solid state reaction technique. The sample is prepared at a temperature of 1200 °C. The obtained specimen is thoroughly characterized paying particular attention to their structure, composition, morphology and optical properties. The surface morphology and structural properties are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns confirm the formation of crystalline perovskite type cubic structure. Also, highly agglomerated, porous and regular shaped particles are seen by SEM. The optical properties of as prepared sample is presented and discussed in terms of ML and TL. The ML intensity is found to be maximum for the sample irradiated for 10 min. More than one maxima in TL glow curve reveals that the traps are distributed in separate groups at different depths and corresponding values are calculated using initial rise method.     

Mechanoluminescence and thermoluminescence of Mn doped ZnS nanocrystals

This paper reports the synthesis of ZnS:Mn nanocrystals by the chemical route in which mercaptoethanol was used as the capping agent. The particle size of such nanocrystals was measured using XRD and TEM patterns and was found to be in between 3and 5 nm. It was found that the peak position of TL glow curve and the TL intensity of ZnS:Mn nanoparticles increases as the particle size is decreased. The isothermal decay technique is used to determine the trap-depth. The stability of the charge carriers in the traps increase with the decrease in size of the nanoparticles. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap-depth with decreasing particle size. When a ZnS:Mn nanocrystal is deformed the peak intensity I_m increases linearly with the increasing height of the load. After I_m, initially the ML intensity decreases at a fast rate, and later on it decreases at a slow rate. The ML in ZnS:Mn nanocrystals can be understood on the basis of the piezoelectrically induced electron detrapping model.     

Mechanoluminescence and thermoluminescence of BaFCl:Sm 2+ and BaFBr:Sm 2+ crystals

The alkaline-earth fluorohalide crystals MFX, where M=Ca, Sr, Ba, Pb and X=Cl, Br, I, form an important class of materials crystallizing in the PbFCl-type tetragonal structure which is also called the matlockite structure. These compounds have long been of interest because of the various defect species which can be detected by spin resonance and associated techniques. The crystals were prepared by slow cooling of the melt of a stoichiometric mixture of BaF ₂ and the corresponding chloride or bromide under 0.2 bar of ultrapure argon (5N5), often slightly fluorinated. We have studied the mechanoluminescence (ML) of BaFBr:Sm ²⁺ and BaFCl:Sm ²⁺ crystals. It is seen that after the impact of a moving piston, initially the ML intensity increases with time, attains a maximum value and then it decreases with time up to a particular minimum value, and then it increases again, attaining a peak value and finally disappears. The first peak lies in the deformation region and the second peak lies in the post-deformation region. The ML intensity of the BaFCl:Sm ²⁺ crystal is much higher than the ML intensity of the BaFBr:Sm ²⁺ crystal. For different impact velocities, the ML intensity increases with velocity; and the total ML intensity attains a saturation value for higher impact velocities. The total ML intensity increases with the increase in the applied load. It is suggested that the moving dislocation produced during deformation of crystals captures holes from hole-trapped centers (like H centers), and the subsequent radiative recombination of the dislocation holes with electron gives rise to ML. Thermoluminescence (TL) of BaFBr:Sm ²⁺ and BaFCl:Sm ²⁺ crystals was studied after exposure to ultraviolet rays with the help of a TLD reader. The peak of TL for the BaFBr:Sm ²⁺ crystal is found at ～247°C and for BaFCl:Sm ²⁺ crystals at 283°C. The TL intensity initially increases with increase in the UV radiation and then it attains saturation for higher values of UV exposure. The absorption spectrum was recorded with the help of a UV–visible spectrophotometer (Shimadzu). The band found at 275 nm was attributed to H centers.     

Synthesis of some graft polymers of uracil

Poly-6-(acryloyloxymethyl)uracil was prepared by radical-catalyzed polymerization of monomeric 6-(acryloyloxymethyl)uracil. The reaction of 6-chloromethyluracil with the potassium salt of polyacrylic acids of molecular weights 5000 and 90,000 gave polymers with both carboxylate groups and 50–70% pendant uraciles. Some inferences concerning the arrangement of uracil groups are drawn from the nuclear magnetic resonance (NMR) spectra of the latter polymers. No interaction between poly(A) and the synthetic polymers could be observed.     

Mechanoluminescence by impulsive deformation of γ-irradiated Er-doped CaF2 crystals

An impulsive technique has been used for mechanoluminescence (ML) measurements in γ-irradiated Er doped CaF₂ crystals. When the ML is excited impulsively by the impact of moving piston on to γ-irradiated CaF₂:Er crystals, two peaks are observed in ML intensity with time and it is seen that the peak intensities of first and second peaks (I_m1 and I_m2) increase with increasing impact velocity. However the time corresponding to first and second peaks (t_m1 and t_m2) shifts towards shorter time values with increasing impact velocity. It is also seen that the total ML intensity I_Total initially increases with the impact velocity and then it attains a saturation value for higher values of the impact velocity. We have presented a theoretical explanation for the observed results.     

Growth and synthesis of Sr<Subscript>3</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>8</Subscript>:Dy<Superscript>3+</Superscript> nanorod arrays by a solid state reaction method

Sr₃MgSi₂O₈:Dy³⁺ Nano-rods were synthesized by using solid state reaction method. The structural properties, morphology and band structure properties of the phosphor was studied. The structural properties were examined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Bonding behaviour of the phosphor was also determined by recording the FTIR spectra of the phosphor. Band structure i.e. band gap of the phosphor was determined by recording the absorption spectrum. The absorption spectrum was recorded for the sample and the band gap was determined by using Tauc plot. Band gap of the phosphor was found around 5.4 eV.     

Characterization and luminescence properties of Gd2O3 phosphor

Gd₂O₃ phosphor was synthesized by combustion synthesis using gadolinium nitrate hexahydrate as precursor and urea as fuel. Structural and surface morphology were studied by X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Chemical composition analysis of the phosphor was performed by Fourier-transform infrared spectroscopy, and tts optical properties were characterized by use of photoluminescence (PL) and thermoluminescence (TL) techniques. In PL spectra, feeble emission at 490 nm (blue) and intense emission at approximately 545 nm (green) are observed after excitation at 300 nm. TL measurement was performed on the Gd₂O₃ phosphor by irradiating it with γ-rays (1 kGy). A well resolved glow peak at 226.4 °C was observed. Kinetic data were estimated from the TL glow curve by use of Chen’s peak-shape method; the results are discussed in detail. The average particle size of the Gd₂O₃ phosphor was 41 nm; a monoclinic phase was formed at a firing temperature of 500 °C. This was in agreement with SEM and TEM results.