Infrared emissions, visible up-conversion, thermoluminescence and defect centres in Er3Al5O12 phosphor obtained by solution combustion reaction

The Er₃Al₅O₁₂ phosphor powders were prepared using the solution combustion method. Formation and homogeneity of the Er₃Al₅O₁₂ phosphor powders have been verified by X-ray diffraction and energy-dispersive X-ray analysis respectively. The frequency up-conversion from Er₃Al₅O₁₂ phosphor powder corresponding to the ²H_9/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2 and the infrared emission (IR) due to the ⁴I_13/2 → ⁴I_15/2 transitions lying at ∼410, ∼524, ∼556, 645–680 nm and at ∼1.53 μm respectively upon excitation with a Ti-Sapphire pulsed/CW laser have been reported. The mechanism responsible for the frequency up-conversion and IR emission is discussed in detail. Defect centres induced by radiation were studied using the techniques of thermoluminescence and electron spin resonance. A single glow peak at 430°C is observed and the thermoluminescence results show the presence of a defect center which decays at high temperature. Electron spin resonance studies indicate a center characterized by a g-factor equal to 2.0056 and it is observed that this center is not related to the thermoluminescence peak. A negligibly small concentration of cation and anion vacancies appears to be present in the phosphor in accordance with the earlier theoretical predictions.     

An Efficient Synthesis of 1,5-Thiadiazepines and 1,5-Benzodiazepines by Microwave-Assisted Heterocyclization

A novel and efficient method for the synthesis of substituted thiazepines and diazepines has been developed. A simple one-pot reaction of chalcones 1a–f with 1-amino-2-mercapto-5-phenyl-1,3,4-triazole and o-phenylenediamine in the presence of a catalytic amount of sodium acetate under microwave irradiation gave 2-(3,8-diphenyl-7,8-dihydro[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepin-6-yl)phenoles 2a–f and 2-(2-phenyl-2,3-dihydro-1H-1,5-benzodiazepin-4-yl)phenoles 3a–f, respectively. The structure of all the synthesized compounds was elucidated on the basis of elemental analysis, IR, ¹H and ¹³C NMR, and mass spectral data.     

Radical Copolymerization of Acrylonitrile with Methyl Acrylate Complexed by Zinc Chloride

Abstract

The kinetics of the radical copolymerization of acrylonitrile with methyl acrylate complexed by zinc chloride (ZnCl₂) in dimethylformamide (DMF) was investigated at 60, 65, and 70°C. The kinetic data revealed that R_p was an inverse function of ZnCl₂ concentration and directly related to monomers concentration. The increase in the activation energy from 11.85 to 19.25 kJ·mol^?1 and the decrease in the value of the ratio of the propagation to termination rate constants (k_p ²/k_t ) from 0.08 to 0.06 L·mol^?1·s^?1 on the addition of ZnCl₂ indicated its retarding effect. The chain transfer constant of DMF for the system was 16.25 × 10^?4, accordingly the degree of polymerization decreased. The structure and composition of the copolymers determined by ¹H-NMR and elemental analysis was found to be alternating. The nonideal behavior of the glass transition temperatures determined by DSC also favors the alternation of monomer units in the copolymer. The reaction proceeds via a cross-propagation mechanism.     

Miscibility and Thermal Behavior of Pullulan/Polyacrylamide Blends

Blends of Pullulan (PU) and Polyacrylamide (PAM) having biomedical applications were prepared and characterized in order to evaluate the miscibility of natural component with the synthetic one. Blends with different composition ratios were prepared using water as common solvent. Viscosity, ultrasonic velocity and density were measured at 30 and 40°C. Furthermore, the blend films were prepared by a solution casting method and analyzed by DSC, FTIR and TGA methods. Results of ultrasonic and density methods revealed the semi-miscibility of the blend. Using viscosity data, interaction parameters (Chee's ‘μ’ and Sun's ‘α’) were computed. The values confirmed that the blend is miscible when the Pullulan content is less than 20% in the blend. Change in temperature had no effect on the miscibility nature of the blends. Intermolecular interactions of hydrogen bonding type were confirmed by DSC and FTIR methods. Thermal behavior of blends was investigated using TGA method.     

Nanocomposite blend gel polymer electrolyte for proton battery application

A proton-conducting nanocomposite gel polymer electrolyte (GPE) system, [35{(25 poly(methylmethacrylate) (PMMA) + 75 poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP))?+?xSiO₂}?+?65{1 M NH₄SCN in ethylene carbonate (EC) + propylene carbonate (PC)}], where x?=?0, 1, 2, 4, 6, 8, 10, and 12, has been reported. The free standing films of the gel electrolyte are obtained by solution cast technique. Films exhibit an amorphous and porous structure as observed from X-ray diffractometry (XRD) and scanning electron microscopy (SEM) studies. Fourier transform infrared spectrophotometry (FTIR) studies indicate ion–filler–polymer interactions in the nanocomposite blend GPE. The room temperature ionic conductivity of the gel electrolyte has been measured with different silica concentrations. The maximum ionic conductivity at room temperature has been observed as 4.3?×?10^?3?S?cm^?1 with 2 wt.% of SiO₂ dispersion. The temperature dependence of ionic conductivity shows a typical Vogel-Tamman-Fulcher (VTF) behavior. The electrochemical potential window of the nanocomposite GPE film has been observed between ?1.6 V and 1.6 V. The optimized composition of the gel electrolyte has been used to fabricate a proton battery with Zn/ZnSO₄·7H₂O anode and PbO₂/V₂O₅ cathode. The open circuit voltage (OCV) of the battery has been obtained as 1.55 V. The highest energy density of the cell has been obtained as 6.11 Wh?kg^?1 for low current drain. The battery shows rechargeability up to 3 cycles and thereafter, its discharge capacity fades away substantially.     

Distereoselective one-pot synthesis of pyrimidopyrimidines using sulfated tin oxide as a reusable catalyst： An extension of Biginelli-type reaction

The Biginelli-type compounds 4,5,8a-triarylhexahydropyrimido[4,5-d]pyrimidine-2,7（1H,3H）-diones were synthesized by a one-pot three-component reaction using sulfated tin oxide as a reusable catalyst. This method has the advantages of high yields, short reaction time, simple starting materials and reusability of catalyst for several times.     

Solvent-Free Green Synthesis of Azines and Their Conversion to 2,5-Disubstituted-1,3,4-thiadiazoles

A solvent-free, clean, and efficient method has been developed for the synthesis of 2,5-disubstituted-1,3,4-thiadiazoles via azines. This approach exploits the synthetic potential of clean reactions and offers many advantages such as excellent product yields, easy isolation of products, and ecofriendly benign reaction conditions. The newly synthesized compounds were analyzed by infrared, ¹H NMR, ¹³C NMR, and elemental analysis.     

Dielectric and ac impedance studies of nanostructured CaCu3Ti3.90Ce0.10O12 electro-ceramic synthesized by citrate-gel route

Effect of doping at Ti⁴⁺ site by Ce³⁺ has been examined in CaCu₃Ti_3.90Ce_0.10O₁₂ synthesized by citrate-gel route. DTA/TG analysis of dry powder gives pre-information about formation of final product around 850 °C. X ray diffraction analysis confirmed the formation of CaCu₃Ti_3.90Ce_0.10O₁₂ phase of the ceramic sintered at 950 °C for 12 h. Microstructure has been studied using scanning electron microscopy and confirmed the average grain size found in nano range 200–400 nm in system CaCu₃Ti_3.90Ce_0.10O₁₂.The nature of relaxation behavior of ceramic was also rationalized by using the impedance and modulus spectroscopy. The bulk conductivity indicates an Arrhenius-type thermally activated process. The ac conductivity spectrum obeyed the Jonscher power law. The complex impedance diagrams of the ceramic exhibited a significant contribution from the grains, grain boundaries and electrode. The activation energies calculated from the grain-boundary relaxation time constant was found to be 0.49 eV which confirmed the Maxwell–Wagner type of relaxation present in the ceramic.     

Boc-protected 1-(3-oxocycloalkyl)ureas via a one-step Curtius rearrangement: mechanism and scope

1-(3-Oxocyclobutyl) carboxylic acid (4a) was converted into N-Boc-protected 1-(3-oxocyclobutyl) urea (5a), a key intermediate for the preparation of agonists of metabotropic glutamate receptor 5, in one-step when treated with diphenyl phosphoryl azide and triethylamine in tert-butanol. The mechanism of the reaction involves a nucleophilic addition of the in situ generated tert-butyl carbamate to the isocyanate intermediate. This reaction is applicable to other 1-(3-oxocycloalkyl) carboxylic acids but not to linear γ-keto carboxylic acids.