Blends of benzoxazine monomers

This article describes synthesis, characterization and properties of blends of benzoxazine (Bz) monomers, i.e., m-alkylphenyl-3,4-dihydro-2H-benzoxazine (Bz-C), 6,6′-(propane-2,2-diyl)bis(3-phenyl-3,4-dihydro-2H-benzoxazine (Bz-A) and 3-phenyl-3,4-dihydro-2H-benzoxazine-p-carboxylic acid (Bz-pA). Binary blends of Bz-C with Bz-pA, and Bz-A with Bz-pA were prepared by first synthesizing Bz-C or Bz-A followed by the addition of all the ingredients of Bz-pA. In a similar manner, ternary blends of Bz-C, Bz-A and Bz-pA were prepared by first synthesizing Bz-C and subsequent addition of all the ingredients of Bz-A and Bz-pA in one pot. The Bz monomer blends were characterized by ¹H-NMR, FTIR spectroscopy, and differential scanning calorimetry. The temperature of onset of curing (T _o), due to ring-opening polymerization of Bz was found to decrease significantly by incorporation of carboxyl groups (Bz-pA) showing thereby the catalytic effect of acid functionality. Bz polymers showed good thermal stability and incorporation of Bz-pA in blends resulted in a highly cross-linked network. The interlaminar shear strength of glass fabric reinforced composites and the lap shear strength of metal–metal joints using these resin blends was also investigated.     

Luminescence characteristics of K2Ca2(SO4)3:Eu,Tb micro- and nanocrystalline phosphor

K₂Ca₂(SO₄)₃ microcrystalline pure, doped with Eu, Tb and co-doped with Eu, Tb was prepared by solid-state diffusion method. Nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by broadening of the XRD peaks using Scherrer's formula. The particle size of nanocrystalline powder material was approximately found to be around 20 nm. Thermoluminescence and photoluminescence were studied to see the effect of co-doping and particle size. Tb³⁺ co-doping decreases the intensity in the Eu²⁺ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The sensitivity of K₂Ca₂(SO₄)₃:Eu,Tb microcrystalline phosphor was around 15 times more than LiF-TLD 100 and 7 times more than CaSO₄:Dy. A high temperature peak (615 K) was observed in case of the nanoparticles, which was attributed to a particle size induced phase transition. This was confirmed by differential scanning calormetry measurements. The decrease in the sensitivity in case of nanoparticles is attributed to the particle size effect i.e. volume to surface ratio. Theoretical analysis of the glow curves was done by glow curve convolution deconvolution method to calculate trapping parameters of various peaks.     

Thermal behaviour of poly(allyl azide)

The paper describes the synthesis of low molecular mass poly(allyl chloride) (PAC) (M _n= 856-3834 g mol^-1) using Lewis acid (ALCL₃, FeCL₃, TiCL₄) and al powder. Branching in PAC was indicated on the basis of elemental analysis and ¹H-NMR spectroscopy. azidation of pac could be carried out at 100°C by using NaN₃ and DMSO as solvent. Curing of poly(allyl azide) (PAA) by cyclic dipolar addition reaction with EGDMA (ethylene glycol dimethacrylate, 5-45 phr) was investigated by differential scanning calorimetry and structure of cured polymer was confirmed by FTIR. A two-step mass loss was exhibited by uncured and cured PAA in nitrogen atmosphere. A mass loss of 20-28% (155-274°C) and 50-61% (330-550°C) was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Tb3+ co-doping and particle size on K2Ca2(SO4)3:EU phosphor

K₂Ca₂(SO₄)₃ doped with Eu, and co-doped with Tb were prepared by the solid state diffusion method. The nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by the broadening of the XRD peaks using Scherrer's formula. The particle size was found to be around 20?nm. Thermoluminescence (TL) was studied to see the effect of co-doping and particle size. Tb³⁺ co-doping decreases the intensity in the Eu²⁺ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The K₂Ca₂(SO₄)₃:Eu,Tb phosphor is found to be 0.33 times more sensitive than TLD-700H, but around 15 times more than LiF-TLD 100, and 7 times more than CaSO₄:Dy. The effective atomic number Z_eff is around 15, which is again comparable to CaSO₄:Dy.

However, very low sensitivity was observed in the case of nanoparticles. The decrease in the sensitivity is attributed to the particle size effect i.e., the volume-to-surface ratio. Study of photoluminescence (PL) of the material is also carried out.     

Thermoluminescence and photoluminescence study on 150 MeV proton beam irradiated K2Ca2(SO4)3:Eu phosphor

This paper investigates the thermoluminescent response of K₂Ca₂(SO₄)₃:Eu prepared by solid state diffusion method, to 150 MeV proton beams. The structural confirmation of the sample was done using the XRD technique revealing the polycrystalline nature and the formation of the compound. Samples in the form of pellets were irradiated by 150 MeV proton clinical beams with dose range of 0.1 Gy–300 Gy. Thermoluminescence glow curves of the irradiated samples were recorded and studied. It has been found that the phosphor shows a characteristic single peak at around 420 K. The TL response is linear in the range up to 200 Gy and then becomes supralinear for higher doses. Photoluminescence spectra of the sample have also been studied and reported. When the material was excited at 320 nm, single emission bands were observed at 436 nm, which can be assigned to the transitions between the lowest band of the 4f⁶5d configuration and the ground state ⁸S_7/2 of the 4f⁷ configuration of Eu²⁺ ion, confirming the incorporation of the impurity in the prepared sample. The excitation spectra of these samples at emission wavelength of 436 nm show a major band at 320 nm. The linear TL response of K₂Ca₂(SO₄)₃:Eu and low fading with good reusability, makes it a potential candidate to be used as a dosimeter for detecting the doses of proton beams for specific applications.     

Studies on luminescence properties and energy transfer in Ce/Dy co-doped CaS nano-phosphors

Luminescence properties of CaS:Ce co-doped with dysprosium has been studied. Ce/Dy co-doped CaS nanophosphors (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50, CaS:Ce_0.75Dy_0.25) were synthesized using the solid state diffusion method. The phase purity of the samples was confirmed using XRD data. The particle size was calculated using Debye–Scherrer formula and was found to be varying between 50 and 60 nm for all the three samples (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50 and CaS:Ce_0.75Dy_0.25). TEM image analysis of CaS:Ce_0.50Dy_0.50 shows nearly spherical particles with diameter varying between 50 and60 nm. One way energy transfer from Dy³⁺ to Ce³⁺ in CaS host has been investigated using photoluminescence studies. Thermoluminescence of these nanophosphors has been studied for 0.5 Gy–21 kGy dose of gamma rays and the dose linearity of CaS:Ce_0.50Dy_0.50 has been compared with CaSO₄:Dy (standard TL dosimeter). Linear behavior over a large dose range between 0.5 Gy and 21 kGy was found for CaS:Ce_0.50Dy_0.50 as compared to CaSO₄:Dy (nanocrystalline and microcrystalline) but it is found to be less sensitive than microcrystalline CaSO₄:Dy. To identify the peaks of Ce³⁺ and Dy³⁺ in CaS, the TL spectra of CaS, CaS:Ce, CaS:Dy and CaS:Ce_0.50Dy_0.50 were recorded. The addition of dopants does not add new peaks in CaS but aid to enhance the TL emission. The peaks in CaS may be associated to intrinsic traps in the host lattice.     

Luminescence studies and effect of etching on cerium-doped CaS nanoparticles

Cerium-doped calcium sulphide nanoparticles were synthesized using the solid state diffusion method. The formed nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption spectroscopy and photoluminescence (PL) spectroscopy. The XRD pattern confirmed a cubic CaS phase with an average grain size of 53 nm of the formed samples. The TEM image showed non-agglomerated particles with an average size of 60 nm, which is in close agreement with the XRD result. The PL-emission spectrum showed peaks at 506 and 565 nm due to the transition from the excited state to the ground state of Ce³⁺. The effect of etching has been studied on the luminescent properties of CaS:Ce phosphors. With an increase in the etching time there is decrease in the size of the particles, as a result of which the PL spectrum showed a slight blue shift. The UV-visible absorption spectrum also showed a blue shift with an increase in etching time, which is in agreement with the nanosize effect.     

Luminescence study of γ-ray and C5+ ion beam-irradiated LiCaBO3:Cu phosphor

Cu-doped LiCaBO₃ phosphors were prepared by modified solid-state synthesis and the formation of compound was confirmed by X-ray diffraction study. LiCaBO₃:Cu⁺ (Cu?=?0.02, 0.05, 0.1 and 0.2?mol%) were studied for photoluminescence (PL) study and prominent PL emission spectra were obtained for Cu⁺ with transition ³d₉⁴s₁?→?³d₁₀. The phosphors were further studied by thermoluminescence (TL) property for exposure to γ-ray irradiation of 1.2?rad with ¹³⁷Cs source. TL of LiCaBO₃:Cu was also studied for C⁵⁺ (3.75?×?10¹²?ion?cm^?2) beam irradiation for 1?min exposure time. Trapping parameters (activation energy and frequency factor) for single deconvoluted peaks were obtained by Chen's peak shape method.     

Swift heavy ion induced structural modification and photo-luminescence in CaS:Bi nanophosphors

CaS:Bi nanocrystalline powder of average grain size 35 nm was prepared by wet chemical co-precipitation method and irradiated with 100 MeV oxygen ions at fluences between 1×10¹² and 1×10¹³ ion/cm². The irradiation induced damage and modifications were studied using X-ray Diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. With the increase in ion fluences, the crystallinity of CaS was destroyed upto 25.9 % for the reflection (200) and 21.1 % for the reflection (220) and the peaks broadens at a much faster rate due to grain breaking process. Structural parameters such as grain size, strain and dislocation density have shown a significant change after ion irradiation. The effects of different dopant concentrations on PL emission intensity after irradiation were also investigated. A blue shift of the photoluminescence peak with increasing ion fluence was noticed and was also ascribed to a decrease in the CaS grain size.