Synthesis, characterization and optical properties of polymer-based ZnS nanocomposites.

Nanostructured polymer-semiconductor hybrid materials such as ZnS-poly(vinyl alcohol) (ZnS-PVA), ZnS-starch and ZnS-hydroxypropylmethyl cellulose (Zns-HPMC) are synthesized by a facile aqueous route. The obtained nanocomposites are characterized using various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV/vis spectroscopy and photoluminescence (PL). XRD studies confirm the zinc blende phase of the nanocomposites and indicate the high purity of the samples. SEM studies indicate small nanoparticles clinging to the surface of a bigger particle. The Energy Dispersive Analysis by X-rays (EDAX) spectrum reveals that the elemental composition of the nanocomposites consists primarily of Zn:S. FTIR studies indicate that the polymer matrix is closely associated with ZnS nanoparticles. The large number of hydroxyl groups in the polymer matrix facilitates the complexation of metal ions. The absorption spectra of the specimens show a blue shift in the absorption edge. The spectrum reveals an absorption edge at 320, 310 and 325 nm, respectively. PL of nanocomposites shows broad peaks in the violet-blue region (420-450 nm). The emission intensity changes with the nature of capping agent. The PL intensity of ZnS-HPMC nanocomposites is found to be highest among the studied nanocomposites. The results clearly indicate that hydroxyl-functionalized HPMC is much more effective at nucleating and stabilizing colloidal ZnS nanoparticles in aqueous suspensions compared with PVA and starch.

Influence of thiol capping on the photoluminescence properties of L-cysteine-, mercaptoethanol- and mercaptopropionic acid-capped ZnS nanoparticles.

Mercaptoethanol (ME), mercaptopropionic acid (MPA) and L-cysteine (L-Cys) having -SH functional groups were used as surface passivating agents for the wet chemical synthesis of ZnS nanoparticles. The effect of the thiol group on the optical and photoluminescence (PL) properties of ZnS nanoparticles was studied. L-Cysteine-capped ZnS nanoparticles showed the highest PL intensity among the studied capping agents, with a PL emission peak at 455 nm. The PL intensity was found to be dependent on the concentration of Zn(2+) and S(2-) precursors. The effect of buffer on the PL intensity of L-Cys-capped ZnS nanoparticles was also studied. UV/Vis spectra showed blue shifting of the absorption edge.

Synthesis, characterization and optical studies of highly luminescent ZnS nanoparticles associated with hypromellose matrix as a green and novel stabilizer.

ZnS nanoparticles stabilized by a carbohydrate-based matrix, hypromellose (hydroxypropyl methylcellulose) were prepared via a wet chemical method. The nanocomposite was characterized by X-ray diffraction, transmission electon microscopy and Fourier transform infrared spectroscopy. X-Ray diffraction patterns revealed a zinc blende structure. Thermogravimetric analysis suggested that polymer attached to the surface decomposes at 700 °C. Absorption measurements were carried out and calculation of the diameter polydispersity index (DPI) suggests the formation of monodisperse nanoparticles. The optical properties of the as-prepared samples were studied by UV/vis spectroscopy and steady-state photoluminescence (PL) spectroscopy. The PL studies indicate the applicability of these nanoparticles as biocompatible sensors or luminescence markers in future.

Effects of rare earth ions (Tb, Ce, Eu, Dy) on the thermoluminescence characteristics of sol-gel derived and γ-irradiated SiO2 nanoparticles.

Highly pure SiO2 and SiO2 :RE nanoparticles were synthesized by the sol-gel method. The morphological, structural and optical properties of the nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD results indicate that all the samples studied were free from impurities. SEM/TEM results indicate that the samples were well dispersed. Surface characterization of the nanocrystals by Fourier transform infrared spectroscopy has been carried out and the structure of surface-bound SiO2 based on spectral analysis is proposed. Thermoluminescence (TL) characteristics were investigated to study the influence of rare earth dopants (Tb, Ce, Eu, Dy) on SiO2 matrix subjected to 0.5 kG (1 h) γ-irradiation. Among these rare earth elements, Eu(3+) was found to be the most efficient dopant for SiO2 showing maximum thermoluminescence intensity. SiO2 :Eu0.5 seems to be a promising candidate for use as a TL dosimeter.

Investigation on the chemiluminescence reaction of the phenylhydrazine-luminol-peroxide system.

We studied the chemiluminescence (CL) oxidation of phenyl hydrazine-luminol with various organic and inorganic peroxides. Maximum CL intensity for this system was obtained for t-butylhydroperoxide. The enhancement in CL depended strongly on pH and was greatest at pH 12.5. The solvent drastically enhanced the CL intensity. DMSO was found to increase the CL intensity many-fold as compared to acetonitrile and water. The effect of temperature on CL intensity has also been studied. The CL spectra revealed a broad peak at 425 nm, which suggests excited 3-aminophthalate ion as the luminophor. A mechanism to explain the reactions is suggested.

Mechanoluminescence properties of gamma-ray-irradiated BaSO4:Eu phosphors.

BaSO(4) activated with various concentrations of Eu were prepared by solid-state reaction technique. Thermoluminescence (TL) and mechanoluminescence (ML) of γ-ray-irradiated BaSO(4):Eu(2)O(3) phosphors were recorded. In the TL glow curve of the phosphor a single peak at 170°C was observed. The TL of the phosphors were also recorded after deforming the phosphors by dropping a piston of mass 0.4 kg onto them with different impact velocities. TL intensity (after deformation) decreased with increasing the impact velocity. In the ML intensity vs time curve two peaks were observed. ML intensity increased with increasing impact velocity of the piston and the time corresponding to peak ML intensity shifted to a shorter time value. ML intensity decreased drastically when it was recorded after annealing the sample at 170°C. The BaSO(4) phosphors activated with 0.1 mol% of Eu(2)O(3) showed optimum TL and ML. The photoluminescence emission spectrum of the sample showed that Eu enters as Eu(2+) ion in host lattice.

Deformation luminescence produced during application and release of pressure on to gamma-irradiated CaF2:RE crystals.

Calcium fluoride CaF2 is an interesting host lattice for rare earth (RE) activators. CaF2 crystals doped with different concentrations of Dy, Ce, Er and Gd have been grown by the Bridgman technique and their deformation luminescence (DL) induced by room temperature gamma irradiation has been recorded. When a uniaxial pressure is applied on to gamma-irradiated CaF2:RE crystals, initially the DL intensity increases with time, attains a maximum value and then it decreases with time. Although the DL intensity produced during the release of pressure is less, its rise and decay behaviours are similar to that obtained during the application of pressure. The DL intensity depends on dopant, concentration of dopant, irradiation doses and mass of the load or applied pressure. It is suggested that the moving dislocation produced during deformation of crystals capture holes from hole trapped centres (like perturbed Vk centre) and the subsequent radiative recombination of the dislocation holes with electrons give rise to DL.

Correlation between thermoluminescence and mechanoluminescence of gamma-irradiated Dy activated potassium and magnesium mixed sulphate.

Thermoluminescene (TL) and mechanoluminescence (ML) properties of gamma-irradiated Dy activated potassium and magnesium mixed sulphate have been studied. (K2Mg2:Dy) (SO4)3 samples having different concentrations of Dy were prepared by solid-state diffusion method. Two distinct peaks, the first approximately 130 degrees C and the second approximately 273 degrees C, are observed in the TL glow curve. It is also observed that TL intensities of both peaks decrease when TL glow curves were recorded after deforming the irradiated samples. Only one peak is observed in the ML intensity vs. time curve and the ML intensity decreases markedly with the post-irradiation annealing (to remove 130 degrees C TL peak) of the sample. Both ML and TL intensities have been observed optimum for 1 mol% of Dy in the mixed sulphate system. It is suggested that the recombination of electrons with the free radicals (anion radicals produced by gamma irradiation) released from the traps during the thermal or mechanical excitation is responsible for luminescence in this system.

Indoor radon concentration in the rural dwellings of Chhattisgarh state (India).

Inhalation of radon and its daughter products is the major contributor to the total exposure of the population to natural radiation. An indoor radon survey has been carried out in the state of Chhattisgarh (80.26 degrees N to 84.41 degrees N and 17.8 degrees E to 24.1 degrees E), India under the national coordinated radon project of the Department of Atomic Energy. In the frame of this project indoor radon concentration has been measured in 105 dwellings situated in different villages of Chhattisgarh state. Houses were selected for measurements to cover the most common type of houses generally existing in the rural areas. Measurements have been done on quarterly integrating cycle for one full year in each dwelling using radon cup dosemeter employing LR-115, type-II (pelliculable), solid-state nuclear track detectors. The gamma radiation level was also checked in each dwelling using a gamma survey meter. It was found that the annual average indoor radon concentration in these dwellings varies from 9.91 to 87.84 Bq m(-3) with overall mean value of 26.48 Bq m(-3). Gamma level in these rural dwellings varies from 14.84 to 26.56 microR h(-1) with mean value of 18.68 microR h(-1). We observed that the radon concentration is relatively higher in the houses where the floor is bare but relatively lower in those houses where the floor is tiled or cemented.

Mechano and thermoluminescence of gamma-irradiated CaSO4:Dy phosphor.

In order to have a better idea of the interaction of the defect centres produced by y-irradiation with dislocation in the processes of deformation destruction, mechanoluminescence (ML) and thermoluminescence (TL) of gamma-irradiated CaSO4:Dy, these phosphors have been investigated. CaSO4:Dy phosphors were prepared by dissolving CaSO4.2H2O in sulphuric acid and evaporating the excess acid around 300 degrees C. ML was excited impulsively by dropping a load on to the sample. Two peaks have been observed in the ML intensity against time curve. The total light output, i.e. integrated ML intensity, increases with concentration of dopant, strain rate and with irradiation doses. The TL glow curves of CaSO4:Dy phosphors at different concentrations of dopant and irradiation doses were also recorded. Studies of the influence of post-irradiation annealing on the ML of CaSO4:Dy show that with the removal of the TL dosemetric peak (approximately 210 degrees C) the ML intensity decreases markedly. A spectroscopic study of ML and TL has also been carried out to elucidate the mechanism of ML. Correlation between ML and TL has also been found.