Encapsulated Co-ZnO nanospheres as degradation tool for organic pollutants: Synthesis, morphology, adsorption and photo luminescent investigations.

Zinc oxide (ZnO) nanostructures, both undoped and Co-doped, were synthesized through the solution combustion process. The diffraction patterns from powder XRD revealed that the materials were crystalline. The morphology of the spherically formed nanoparticles was visualized in SEM micrographs. FTIR spectra verified the existence of a defect-associated peak in Co-encapsulated ZnO (Zn0.98Co0.02O) NPs. Photoluminescence studies are undertaken. Malachite Green (MG) dye is used as a representative organic pollutant to study the adsorptive degradation of Co-doped ZnO nanomaterial. Moreover, the adsorption properties, including isotherm and kinetics, are investigated by analyzing the degradation of MG dye. Experimental parameters, such as the concentration of the MG dye, dosage and pH, were varied to ascertain favorable conditions for the degradation study. The results indicate that the MG dye is 70% degraded. After Co-doping, near-band edge emission in undoped ZnO changed into intense red defect emission and was directly correlated with changes in PL emission.

Adsorptive removal of Rhodamine B dye from aqueous solution by using graphene-based nickel nanocomposite.

In this work, reduced graphene oxide-nickel (RGO-Ni) nanocomposite is synthesized. X-ray diffraction (XRD), scanning electron microscopy (SEM) and SEM-EDS (Energy Dispersive X-Ray Spectroscopy) are used to study the crystalline nature, morphology and elemental composition of the RGO-Ni nanocomposite, respectively. As synthesized RGO-Ni nanocomposite is used to develop selective adsorptive removal of Rhodamine B (RhB) dye from the aqueous solution. The experiments have been performed to investigate RhB uptake via RGO-Ni nanocomposites which include, contact time (60 min), initial dye concentration (50 mg/100 ml), adsorbent dosage (0.5 mg) and pH 8 of dye solution. The equilibrium concentration is determined by using different models namely, Freundlich, Langmuir and Tempkin. Langmuir isotherm has been fitted well. Langmuir and Tempkin equations are determined to have good agreement with the correlation coefficient data. The kinetic study concluded that RhB dye adsorption follows with the pseudo-second-order kinetic model. Further, adsorption mechanism of RGO-Ni is proposed which involves three steps. The synthesized adsorbent is compared with the other adsorbents in the literature and indicates that RGO-Ni nanocomposite used in this study shown better results for a particular adsorption capacity than polymeric, natural and synthetic bioadsorbents. The regeneration and reusability experiments suggest RGO-Ni nanocomposite can be used for many numbers of times for purification/adsorption.

Nano-catalytic behavior of highly efficient and regenerable mussel-inspired Fe3O4@CFR@GO and Fe3O4@CFR@TiO2 magnetic nanospheres in the reduction of Evans blue dye.

Fe3O4@catechol formaldehyde resin coated @Graphene Oxide nanocomposite (Fe3O4@CFR@GO) and Fe3O4@catechol formaldehyde resin coated @TiO2 (Fe3O4@CFR@TiO2) nanocomposite were fabricated by hydrothermal method. Particularly, catechol bunches on the highest layer of nanospheres to play a mussel-inspired chemistry to assist combined with graphene oxide (GO) to wrap the Fe3O4@ coated nanosphere. The prepared catalyst was proven to be very efficient with less than a minute and vey less dosage (15-17 mg) in the adsorptive degradation of Evans blue dye. The adsorptive degradation of Evans blue dye with Fe3O4@CFR@GO and Fe3O4@CFR@TiO2 nanocomposites are studied by several variables like the dye concentration, dosage, pH, contact time and temperature. It shows maximum adsorption capacity of 0.1435 mg/g (Fe3O4@CFR@GO) and 9.345 mg/g (Fe3O4@CFR@TiO2) nanocomposites. The equilibrium concentration and the adsorption capacity were evaluated using three different isothermal models. The kinetic study determined that Evans blue dye adsorption was in good analogy with the pseudo-first-order kinetic model.

Perovskite lanthanum aluminate nanoparticles applications in antimicrobial activity, adsorptive removal of Direct Blue 53 dye and fluoride.

In the present study, efficient adsorptive removal of fluoride and Direct Blue 53 (DB-53) dye solution on perovskite lanthanum aluminate (PLA) has been investigated. To characterize the prepared PLA with analytical techniques like FTIR, SEM, EDS, PXRD, PHZPC and BET. The influence of adsorbent dose (0.05-0.6) gL-1, pH (2-12), contact time (0-60 min) and initial adsorbate concentration (0-50 mg L-1) were studied on adsorption process. Mathematical modeling of kinetics and isotherms were computed using equations. The pseudo-second-order kinetic and Halsey isotherm equilibrium model are best fitted with experimentally computed data with R2 > 0.96. The value of free mean energy EDR per adsorbate molecule was 1.77 kJmol-1 (fluoride) and 1.86 kJmol-1 (DB-53) with an adsorption capacity 25.103 and 38.03 respectively, hence nature of adsorption suggested as physisorption process. The maximum Langmuir adsorption capacity of PLA was investigated to be 40.8 mgg-1 (fluoride) and 71.4 mgg-1 (DB-53). Present study PLA deficits efficient adsorbent for fluoride and DB-53 dye for ground and industrial wastewater. Further, the effect of in-vitro antimicrobial studies was carried out against six test microorganisms. PLA showed, a maximum antibacterial effect at MIC 63 µg mL-1 for Gram-negative bacteria: Pseudomonas aeruginosa (NCIM 5029) due to the interaction between the positively charged nanoparticle and negatively charged cell wall.

Synthesis and characterization of Zinc oxide nanoparticles utilizing seed source of Ricinus communis and study of its antioxidant, antifungal and anticancer activity.

ZnO nanoparticles have been synthesized using solution combustion technique and its antioxidant, antifungal, anticancer activity was studied. Ricinus communis plant seed extract used as fuel in synthesis by the solution combustion technique. Powder X-ray diffraction (PXRD) demonstrates the arrangement of a crystalline hexagonal stage (ICDD card number 89-1397) with space aggregate P63mc (186) and cell parameters a = b = 3.253, c = 5.213 Å. The normal crystallite measure is 20 nm which is ascertained by Debye - Scherer's formula. The Purity of the sample and metal to oxygen bond development was affirmed by utilizing Fourier transformation infrared (FTIR) spectroscopy and the particle size and shape was confirmed by HRTEM. Antifungal action of ZnO NPs was studied against Aspergillus and Penicillium by well dispersion strategy. The antifungal activity shows that ZnO NPs constitute as an effective fungicidal agent against both Aspergillus (4 ±â€¯0.5 mm) and Penicillium (3 mm ±â€¯0.4 mm) at 30 µg/mL fixation. ZnO nanoparticles were subjected to antioxidant activity. The objective of the study was to analyze the anticancer property of ZnO NPs on MDA-MB 231 cancer cells. To check the efficacy of the synthesized drug ZnO NPs MTT assay was performed, that determines % viability and/or cytotoxicity. IC50 of ZnO NPs in case of MDA-MB-231 breast cancer was 7.103 µg/mL. Anticancer outcome demonstrates that ZnO NPs is active against in MDA-MB-231 cells.

Comparison of anticancer activity of biocompatible ZnO nanoparticles prepared by solution combustion synthesis using aqueous leaf extracts of Abutilon indicum, Melia azedarach and Indigofera tinctoria as biofuels.

Recently, there has been an upsurge in the use of naturally available fuels for solution combustion synthesis (SCS) of nanoparticles. Although many reports suggest that these biofuels pose less harm to the environment, their strategic advantages and reliability for making NPs has not been discussed. In the present work, we try to address this issue using plant extracts as biofuels for the SCS of zinc oxide nanoparticles as a model system. In the present work, combustion synthesis of ZnO NPs using lactose and aqueous leaf extracts of Abutilon indicum, Melia azedarach, Indigofera tinctoria as biofuels has been carried out. A comparative analysis of the obtained powders has been conducted to understand the strategic advantages of using plant extracts over a chemical as combustion fuel for the synthesis of zinc oxide nanoparticles. The X-ray diffractograms of the samples revealed the presence of Wurtzite hexagonal structure with varying crystallite sizes. Morphological studies indicated that samples prepared using biofuels had smaller diameter than those prepared using lactose as fuel. Surface characteristics of the samples were measured by X-ray photoelectron spectroscopy. Qualitative phytochemical screening of aqueous leaf extracts revealed the presence of many phytochemicals in them, which might be responsible for combustion. Gas chromatography mass spectrum was carried out to detect the phytochemicals present in the aqueous extracts of the leaves. Further, anticancer evaluation carried out against DU-145 and Calu-6 cancer cells indicated higher anticancer activity of zinc oxide nanoparticles prepared using biofuels. The results of blood haemolysis revealed the biocompatibility of zinc oxide nanoparticles at lower concentrations. In conclusion, we propose that multiple other studies would be required in order to vindicate the potential advantages of using naturally available fuels in SCS.

Charge compensation assisted enhancement of photoluminescence in combustion derived Li+ co-doped cubic ZrO2:Eu3+ nanophosphors.

Red light emitting cubic Zr0.99Eu0.01O2:Li+ (0-9 mol%) nanoparticles are synthesized by a low temperature, self-propagating solution combustion method using oxalyl di-hydrazide (ODH) as fuel. In this study, we report systematic investigation of the effect of lithium ion (Li+) concentration on the structural properties and the photoluminescence of zirconia. With increasing lithium concentration, the crystallinity of the samples increases and the lattice strain decreases. The higher crystallinity is likely due to charge compensation achieved by replacing one Zr4+ ion by a Eu3+ and a Li+ ion. Scanning electron micrographs (SEM) reveal a mesoporous structure characteristic of combustion derived nanomaterials. Photoluminescence (PL) spectra show that the intensity of the red emission (606 nm) is highly dependent on Li+ ion concentration. Furthermore there is a promising enhancement in the associated lifetime. Upon Li+ doping, the PL intensity of the samples is found to increase by two fold compared to the undoped sample. Variation of PL intensity with Li+ concentration is attributed to the differences in probability of non-radiative recombination (relaxing). Intensity parameters (Ω2, Ω) and radiative properties such as transition rates (A), branching ratios (ß), stimulated emission cross-section (σe), gain bandwidth (σe × Δλeff) and optical gain (σe × τ) are calculated using the Judd-Ofelt theory. The calculated values suggest that in optimally co-doped samples, in addition to improved crystallinity and charge compensation, the lowering of Eu3+ site symmetry and the increase in the covalency of Eu-O bonding due to interstitial Li are responsible for the observed enhancement in PL intensity.

A single phase, red emissive Mg2SiO4:Sm3+ nanophosphor prepared via rapid propellant combustion route.

Mg2SiO4:Sm3+ (1-11 mol%) nanoparticles were prepared by a rapid low temperature solution combustion route. The powder X-ray diffraction (PXRD) patterns exhibit orthorhombic structure with α-phase. The average crystallite size estimated using Scherer's method, W-H plot and strain-size plots were found to be in the range 25-50 nm and the same was confirmed by Transmission Electron Microscopy (TEM). Scanning electron microscopy (SEM) pictures show porous structure and crystallites were agglomerated. The effect of Sm3+ cations on luminescence of Mg2SiO4 was well studied. Interestingly the samples could be effectively excited with 315 nm and emitted light in the red region, which was suitable for the demands of high efficiency WLEDs. The emission spectra consists of four main peaks which can be assigned to the intra 4-f orbital transitions of Sm3+ ions 4G5/2→6H5/2 (576 nm), 4G5/2→6H7/2 (611 nm), 4G5/2→6H9/2 (656 nm) and 4G5/2→6H11/2 (713 nm). The optimal luminescence intensity was obtained for 5 mol% Sm3+ ions. The CIE (Commission International de I'Eclairage) chromaticity co-ordinates were calculated from emission spectra, the values (0.588, 0.386) were close to the NTSC (National Television Standard Committee) standard value of red emission. Coordinated color temperature (CCT) was found to be 1756 K. Therefore optimized Mg2SiO4:Sm3+ (5 mol%) phosphor was quite useful for solid state lighting.

Synthesis, characterization and photoluminescence properties of Bi³âº co-doped CaSiO3:Eu³âº nanophosphor.

Ceramic luminescent powders with the composition Ca(0.96-x)Eu0.04Bi(x)SiO3 (x=0.01-0.05) were prepared by solution combustion method. The nanopowders are characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) techniques. PXRD patterns of calcined (950°C for 3h) Ca(0.96-x)Eu0.04Bi(x)SiO3 powders exhibit monoclinic phase with mean crystallite sizes ranging from 28 to 48 nm. SEM micrographs show the products are foamy, agglomerated and fluffy in nature due to the large amount of gases liberated during combustion reaction. TEM micrograph shows the crystalline characteristics of the nanoparticles. Upon 280 nm excitation, the photoluminescence of the Ca(0.96-x)Eu0.04Bi(x)SiO3 particles show red emission at 611 nm corresponding to 5D0→7F2 transition. It is observed that PL intensity increases with Bi(3+) concentration. Our work demonstrates very interesting energy transfer from Bi(3+) to Eu(3+) in CaSiO3 host.

Synthesis, luminescence properties and EPR investigation of hydrothermally derived uniform ZnO hexagonal rods.

One-dimensional (1D) zinc oxide (ZnO) hexagonal rods have been successfully synthesized by surfactant free hydrothermal process at different temperatures. It can be found that the reaction temperature play a crucial role in the formation of ZnO uniform hexagonal rods. The possible formation processes of 1-D ZnO hexagonal rods were investigated. The zinc hydroxide acts as the morphology-formative intermediate for the formation of ZnO nanorods. Upon excitation at 325 nm, the sample prepared at 180°C show several emission bands at 400 nm (∼3.10 eV), 420 nm (∼2.95 eV), 482 nm (∼2.57 eV) and 524 nm (∼2.36 eV) corresponding to different kind of defects. TL studies were carried out by pre-irradiating samples with γ-rays ranging from 1 to 7 kGy at room temperature. A well resolved glow peak at ∼354°C was recorded which can be ascribed to deep traps. Furthermore, the defects associated with surface states in ZnO nano-structures are characterized by electron paramagnetic resonance.

Zn2TiO4:Eu(3+) nanophosphor: self explosive route and its near UV excited photoluminescence properties for WLEDs.

A simple and low-cost solution combustion method was used to prepare Eu(3+) (1-11mol%) doped Zn2TiO4 nanophosphors at 500°C using zinc nitrates as precursors and oxalyl di-hydrazide (ODH) as fuel. The final product was calcined at 1100°C for 3h and then characterized by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible absorption (UV-Vis). The PXRD patterns of the sample calcined at 1100°C show pure cubic phase. The crystallite size was estimated using Scherrer's method and found to be in the range 20-25nm and the same was confirmed by TEM studies. Effects of Eu(3+) (1-11mol%) cations on the luminescence properties of Zn2TiO4 nanoparticles were studied. The samples exhibit intense red emission upon 395nm near ultra violet (NUV) excitation. The characteristic emission peaks recorded at ∼578, 592, 613 and 654nm may be attributed to the 4f-4f intra shell transitions ((5)D0→(7)Fj=0,1,2,3) of Eu(3+) cations. The CIE chromaticity co-ordinates and CCT were calculated from emission spectra and the values (x, y) were very close to NTSC standard values for red emission and CCT was close to Plankian locus. Therefore, the present phosphor may be highly useful for display applications.

Role of flux on morphology and luminescence properties of Sm(3+) doped Y2SiO5 nanopowders for WLEDs.

The study involves preparation of samarium doped Y2SiO5 (YSO) nano powders by solution combustion method using urea as a fuel for the first time. Effect of different fluxes on the crystallization behavior, morphology and photoluminescence (PL) properties of YSO:Sm(3+) (1-9 mol%) were investigated. The final product was characterized by Powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM) and UV-Vis spectroscopy. The average crystallite size estimated by Debye-Scherer's and Williamson-Hall plots were found to be in the range of 10-50 nm. Samples calcined at 1100°C show pure monoclinic X1 phase; whereas, samples calcined at 1200 and 1300°C show pure X2 phase of YSO. Photoluminescence (PL) studies of Sm(3+) (1-9 mol%) doped YSO for near ultra violet (NUV) excitation (407 nm) was studied in order to investigate the possibility of its use in white light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm(3+), such as (4)G5/2→(6)H5/2 (∼560 nm), (4)G5/2→(6)H7/2 (600-613 nm), (4)G5/2→(6)H9/2 (∼650 nm), (4)G5/2→(6)H11/2 (715 nm) and (4)G5/2→(6)H13/2 (763 nm) respectively. The emission intensity of the phosphor was found to be enhancing after addition of fluxes. Further, the emission at 600-613 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for near ultra violet excitation.

GdAlO3:Eu(3+):Bi(3+) nanophosphor: synthesis and enhancement of red emission for WLEDs.

GdAlO3, GdAlO3:Eu(3+) and GdAlO3:Eu(3+):Bi(3+) nanophosphors were synthesised by solution combustion technique. Pure orthorhombic phase was obtained from powder X-ray diffraction (PXRD) studies. Scanning electron microscopy (SEM) micrographs showed the porous, agglomerated and irregular shaped particles. The particle size obtained by transmission electron microscopy (TEM) measurement was in good agreement with the values obtained by Debye Scherrer's and W-H plots. The selected area electron diffraction (SAED) pattern show single crystalline nature of the sample. Photoluminescence (PL) measurements were carried out for GdAlO3:Eu(3+) and GdAlO3:Eu(3+):Bi(3+) phosphors excited at a wavelength of 274nm. The characteristic emission peaks of Eu(3+) ions were recorded at 590, 614, 655 and 695nm corresponding to (5)D0→(7)FJ (J=1, 2, 3, 4) transitions respectively. However, with addition of Bi(3+) ions in GdAlO3:Eu(3+), PL intensity drastically enhanced. Orange red color was tuned to deep red color with the addition of Bi(3+) ions in GdAlO3:Eu(3+) phosphor. Therefore, the phosphor was highly useful as red component in WLEDs. A single well resoled glow peak at 225°C was recorded in GdAlO3 and GdAlO3:Eu(3+). Further, with addition of Bi(3+) ions, an additional peak at 300°C was recorded. TL glow curves of different UV-exposed GdAlO3:Eu(3+):Bi(3+) show two TL peaks at 207 and 300°C respectively. The 207°C peak show simple glow peak structure and its intensity increases linearly up to 25min and after that it decrease.

Luminescence studies and EPR investigation of solution combustion derived Eu doped ZnO.

ZnO:Eu (0.1 mol%) nanopowders have been synthesized by auto ignition based low temperature solution combustion method. Powder X-ray diffraction (PXRD) patterns confirm the nanosized particles which exhibit hexagonal wurtzite structure. The crystallite size estimated from Scherrer's formula was found to be in the range 35-39 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal particles are agglomerated with quasi-hexagonal morphology. A blue shift of absorption edge with increase in band gap is observed for Eu doped ZnO samples. Upon 254 nm excitation, ZnO:Eu nanopowders show peaks in regions blue (420-484 nm), green (528 nm) and red (600 nm) which corresponds to both Eu2+ and Eu3+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits a broad resonance signal at g=4.195 which is attributed to Eu2+ ions. Further, EPR and thermoluminescence (TL) studies reveal presence of native defects in this phosphor. Using TL glow peaks the trap parameters have been evaluated and discussed.

Role of Cu2+ ions substitution in magnetic and conductivity behavior of nano-CoFe2O4.

Cobalt copper ferrite nanopowders with composition Co1-xCuxFe2O4 (0.0≤x≤0.5) was synthesized by solution combustion method. The powder X-ray diffraction studies reveal the formation of single ferrite phase with particle size of ∼11-35 nm. Due to increase in electron density with in a material, X-ray density increase with increase of Cu2+ ions concentration. As Cu2+ ions concentration increases, saturation magnetization decreases from 38.5 to 26.7 emu g(-1). Further, the squareness ratio was found to be ∼0.31-0.46 which was well below the typical value 1, which indicates the existence of single domain isolated ferrimagnetic samples. The dielectric and electrical modulus was studied over a frequency range of 1 Hz to 1 MHz at room temperature using the complex impedance spectroscopy technique. Impedance plots showed only one semi-circle which corresponds to the contributions of grain boundaries. The lower values of dielectric loss at higher frequency region may be quite useful for high frequency applications such as microwave devices.

Synthesis and luminescence properties of Sm3+ doped CaTiO3 nanophosphor for application in white LED under NUV excitation.

CaTiO3:Sm(3+) (1-11 mol%) nanophosphors were successfully synthesized by a low temperature solution combustion method [LCS]. The structural and morphological properties of the phosphors were studied by using Powder X-ray diffractometer (PXRD), Fourier transform infrared (FTIR), X-ray photo electron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). TEM studies indicate that the size of the phosphor is ∼20-35 nm. Photoluminescence (PL) properties of Sm(3+) (1-11 mol%) doped CaTiO3 for NUV excitation (407 nm) was studied in order to investigate the possibility of its use in White light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm(3+), such as (4)G5/2→(6)H5/2 (561 nm), (4)G5/2→(6)H7/2 (601-611 nm), (4)G5/2→(6)H9/2 (648 nm) and (4)G5/2→(6)H11/2 (703 nm) respectively. Further, the emission at 601-611 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for the application for near ultra violet (NUV) excitation. Thermoluminescence (TL) of the samples irradiated with gamma source in the dose range 100-500 Gy was recorded at a heating rate of 5°Cs(-1). Two well resolved glow peaks at 164°C and 214°C along with shouldered peak at 186°C were recorded. TL intensity increases up to 300 Gy and thereafter, it decreases with further increase of dose. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics were estimated and results were discussed in detail.

Gd(1.96-x)Y(x)Eu0.04O3 (x = 0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors: propellant combustion synthesis, structural and luminescence studies.

Gd(1.96-x)Y(x)Eu0.04O3 (x = 0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors were synthesized by propellant combustion method at low temperature (400°C). The powder X-ray diffraction patterns of as formed Gd1.96Eu0.04O3 showed monoclinic phase, however with the addition of yttria it transforms from monoclinic to pure cubic phase. The porous nature increases with increase of yttria content. The particle size was estimated from Scherrer's and W-H plots which was found to be in the range 30-40 nm. These results were in well agreement with transmission electron microscopy studies. The optical band gap energies estimated were found to be in the range 5.32-5.49 eV. PL emission was recorded under 305 nm excitation show an intense emission peak at 611 nm along with other emission peaks at 582, 641 nm. These emission peaks were attributed to the transition of (5)D0→(7)FJ (J = 0, 1, 2, 3) of Eu(3+) ions. It was observed that PL intensity increases with increase of Y content up to x = 0.98 and thereafter intensity decreases. CIE color co-ordinates indicates that at x = 1.47 an intense red bright color can be achieved, which could find a promising application in flat panel displays. The cubic and monoclinic phases show different thermoluminescence glow peak values measured under identical conditions. The response of the cubic phase to the applied dose showed good linearity, negligible fading, and simple glow curve structure than monoclinic phase indicating that suitability of this phosphor in dosimetric applications.

Synthesis, characterization and spectroscopic investigation of Cr3+ doped wollastonite nanophosphor.

This work explores the preparation of nanocrystalline Cr(3+) (1-5 mol%) doped CaSiO3 phosphors by solution combustion process and study of its photoluminescence (PL) behavior. The nanopowders are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy. PXRD results confirm monoclinic phase upon calcination at 950°C for 3h. SEM micrographs indicates that the powder is highly porous and agglomerated. The TEM images show the powder to consist of spherical shaped particles of size ∼30-60 nm. Upon 323 nm excitation, the emission profile of CaSiO3:Cr(3+) exhibits a narrow red emission peak at 641nm due to (2)E→(4)A2 transition and broad band at 722 nm due to (4)T2g→(4)A2g. It is observed that PL intensity increases with increase in Cr(3+) concentration and highest PL intensity is observed for 3 mol% doped sample. The PL intensity decreases with further increase in Cr(3+) doping. This decrease in PL intensity beyond 3 mol% is ascribed to concentration quenching. Racah parameters are calculated to describe the effects of electron-electron repulsion within the crystal lattice. The parameters show 21% reduction in the Racah parameter of free ion and the complex, indicating the moderate nephelauxetic effect in the lattice.

Study on low temperature solution combustion synthesized Sr(2)SiO(4):Dy(3+) nano phosphor for white LED.

A series of Dy(3+) (1-5mol.%) activated Sr2SiO4 nanophosphors were prepared by low temperature solution combustion method using oxalyl dihydrazide (ODH) as a fuel. The obtained phosphor was well characterized by powder X-ray diffraction, scanning electron microscopy, and UV-visible spectroscopy. The average crystallite sizes were estimated by Debye-Scherrer formula and Williamson-Hall plots and found to be in the range 20-32nm. Energy band gap was found to be widened with increase of Dy(3+) ion dopant. Photoluminescence spectra consist of three main groups of peaks in 460-500nm (blue), 555-610nm (yellow) and 677nm (red) respectively. These peaks were assigned to transition of (4)F9/2→(6)H15/2,13/2,11/2. The critical distance between Dy(3+) ions and quenching site was found to be ∼16.71Ǻ. The chromaticity co-ordinates of all the prepared phosphors were located in white light; as a result Dy(3+) activated Sr2SiO4 is a promising single phased phosphor for white light emitting diodes. Thermoluminescence (TL) of Dy(3+) doped Sr2SiO4 nanophosphors were investigated using γ-irradiation in the dose range 1-6kGy at a warming rate of 2.5°Cs(-1). The phosphors show a well resolved single glow peak at ∼145°C. The kinetic parameters were estimated by different methods and the results discussed. The TL intensity increases linearly with γ-dose at room temperature. The effect of fading with storage time was found to be ∼66% which is highly useful in radiation dosimetry.

Effect of different fuels on structural, photo and thermo luminescence properties of solution combustion prepared Y(2)SiO(5) nanopowders.

Y(2)SiO(5) nanopowders are prepared by solution combustion method using DFH, sugar and urea as fuels. The final product was well characterized by powder X-ray diffraction, Scanning Electron Microscopy and UV-Vis spectroscopy. The average crystallite size was estimated using Debye-Scherer's formula and Williamson-Hall plots and are found to be in the range 34-40nm for DFH, 45-50nm for urea and 35-42nm for sugar respectively. X1-X2 type YSO phase was obtained for all the samples calcined from 1200 to 1400°C. The optical energy band gaps (Eg) of the samples were estimated from Tauc relation and varies from 5.58 to 5.60eV. SEM micrographs of sugar and urea used Y(2)SiO(5) show agglomerated particles with porous morphology. However, for the sample prepared using DFH fuel observed to be almost spherical in shape. Thermoluminescence (TL) properties of γ-irradiated (1-5kGy) and UV irradiated (1-30min) Y(2)SiO(5) nanopowder at a heating rate of 2.5°Cs(-1) was studied. The samples prepared by using urea and sugar fuels show a broad TL glow peak at 189°C. However, DFH used Y(2)SiO(5) show a well resolved peak at 196°C with shouldered peak at 189°C. Among the fuels, DFH used Y(2)SiO(5) show simple glow peak structure which perhaps useful in radiation dosimetry. This may be due to fuel and particle size effect. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics are estimated by Chens glow peak shape method.