EPR, thermo and photoluminescence properties of ZnO nanopowders

Nanocrystalline ZnO powders have been synthesized by a low temperature solution combustion method. The photoluminescence (PL) spectrum of as-formed and heat treated ZnO shows strong violet (402, 421, 437, 485 nm) and weak green (520 nm) emission peaks respectively. The PL intensities of defect related emission bands decrease with calcinations temperature indicating the decrease of Zn(i) and V(o)(+) caused by the chemisorptions of oxygen. The results are correlated with the electron paramagnetic resonance (EPR) studies. Thermoluminescence (TL) glow curves of gamma irradiated ZnO nanoparticles exhibit a single broad glow peak at similar to 343 degrees C. This can be attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centers. The trapping parameters of ZnO irradiated with various gamma-doses are calculated using peak shape method. It is observed that the glow peak intensity increases with increase of gamma dose without changing glow curve shape. These two characteristic properties such as TL intensity increases with gamma dose and simple glow curve structure is an indication that the synthesized ZnO nanoparticles might be used as good TL dosimeter for high temperature application. (C) 2011 Elsevier B.V. All rights reserved.

Structural, EPR, photo and thermoluminescence properties of ZnO:Fe nanoparticles

Zn(1-x)Fe(x)O(1+0.5x) (x = 0.5-5 mol%) nanoparticles were synthesized by a low temperature solution combustion route. The structural characterization of these nanoparticles by PXRD, SEM and TEM confirmed the phase purity of the samples and indicated a reduction in the particle size with increase in Fe content. A small increase in micro strain in the Fe doped nanocrystals is observed from W-H plots. EPR spectrum exhibits an intense resonance signal with effective g values at g approximate to 2.0 with a sextet hyperfine structure (hfs) besides a weak signal at g approximate to 4.13. The signal at g approximate to 2.0 with a sextet hyperfine structure might be due to manganese impurity where as the resonance signal at g approximate to 4.13 is due to iron. The optical band gap E-g was found to decrease with increase of Fe content. Raman spectra exhibit two non-polar optical phonon (E-2) modes at low and high frequencies at 100 and 435 cm(-1) in Fe doped samples. These modes broaden and disappear with increase of Fe do pant concentration. TL measurements of gamma-irradiated (1-5 kGy) samples show a main glow peak at 368 degrees C at a warming rate of 6.7 degrees Cs-1. The thermal activation parameters were estimated from Glow peak shape method. The average activation energy was found to be in the range 0.34-2.81 eV. (C) 2012 Elsevier B.V. All rights reserved.

Characterisation of microstructure and evaluation of optical and EPR properties of superhydrophobic copper dodecanoate films

Copper dodecanoate films prepared by emulsion method exhibit superhydrophobic property with water contact angle of 155 degrees and sliding angle of <2 degrees. The films have been characterised by using X-ray diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy techniques. Surface microstructure of copper dodecanoate consists of numerous microscale papillas of about 6-12 mu m in length with a diameter in the range of 360-700 nm. The superhydrophobicity of the films is due to their dual micronano surface morphology. The wetting behaviour of the film surface was studied by a simple water immersion test. The results show that copper dodecanoate film retained superhydrophobic property even after immersing in water for about 140 h. The optical absorption spectrum exhibits two broadbands centred at 388 and 630 nm that have been assigned to B-2(1g) -> E-2(g) and B-2(1g) -> B-2(2g) transitions of Cu2+ ions, respectively. The electron paramagnetic resonance spectrum exhibits two resonance signals with effective g values at g(parallel to)approximate to 2.308 and g(perpendicular to) approximate to 2.071, which suggests that the unpaired electron occupies d(x2-y2) orbital in the ground state. Copyright (C) 2011 John Wiley & Sons, Ltd.

Thermoluminescence and EPR studies of nanocrystalline Nd2O3:Ni2+ phosphor

Nanocrystalline Nd2O3:Ni2+ (2 mol%) phosphor has been prepared by a low temperature (similar to 400 degrees C) solution combustion method, in a very short time (<5 min). Powder X-ray diffraction results confirm the single hexagonal phase of nanopowders. Scanning electron micrographs show that nanophosphor has porous nature and the particles are agglomerated. Transmission electron microscopy confirms the nanosize (20-25 nm) of the crystallites. The electron paramagnetic resonance (EPR) spectrum exhibits a symmetric absorption at g approximate to 2.77 which suggests that the site symmetry around Ni2+ ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (chi) has been evaluated. Raman study show major peaks, which are assigned to F-g and combination of A(g) + E-g modes. Thermoluminescence (TL) studies reveal well resolved glow peaks at 169 degrees C along with shoulder peak at around 236 degrees C. The activation energy (E in eV), order of kinetics (b) and frequency factor (s) were estimated using glow peak shape method. It is observed that the glow peak intensity at 169 degrees C increases linearly with gamma-dose which suggest that Nd2O3:Ni2+ is suitable for radiation dosimetry applications. (C) 2012 Elsevier B.V. All rights reserved.

Thermoluminescence, photoluminescence and EPR studies on Mn2+ activated yttrium aluminate (YAlO3) perovskite

Thermoluminescence (TL) measurements were carried out on undoped and Mn2+ doped (0.1 mol%) yttrium aluminate (YAlO3) nanopowders using gamma irradiation in the dose range 1-5 kGy. These phosphors have been prepared at furnace temperatures as low as 400 degrees C by using the combustion route. Powder X-ray diffraction confirms the orthorhombic phase. SEM micrographs show that the powders are spherical in shape, porous with fused state and the size of the particles appeared to be in the range 50-150 nm. Electron Paramagnetic Resonance (EPR) studies reveal that Mn ions occupy the yttrium site and the valency of manganese remains as Mn2+. The photoluminescence spectrum shows a typical orange-to-red emission at 595 nm and suggests that Mn2+ ions are in strong crystalline environment. It is observed that TL intensity increases with gamma dose in both undoped and Mn doped samples. Four shouldered TL peaks at 126, 240, 288 and 350 degrees C along with relatively resolved glow peak at 180 degrees C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115 degrees C along with two well defined peaks at similar to 215 and 275 degrees C. It is observed that TL glow peaks were shifted in Mn doped samples. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped, and Mn doped samples were determined at different gamma doses using the Chens glow peak shape method and the results are discussed in detail. (C) 2012 Elsevier B.V. All rights reserved.

Structural, EPR, optical and Raman studies of Nd2O3:Cu2+ nanophosphors

Nanocrystalline Nd2O3:Cu2+ (2 mol %) phosphors have been prepared by a low temperature solution combustion technique. Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd2O3 (900 degrees C, 3 h) and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of as-formed and Cu2+ doped Nd2O3 phosphors show that the particles are irregular in shape and porous in nature. TEM results also confirm the nature and size of the particles. The EPR spectrum exhibits two resonance signals with effective g values at g(parallel to) approximate to 2.12 and g(perpendicular to) approximate to 2.04. The g values indicate that the site symmetry of Cu2+ ions is octahedral symmetry with elongated tetragonal distortion. Raman studies show major peaks, which are assigned, to F-g and combination of A(g) + E-g modes. It is observed that the Raman peaks and intensity have been reduced in Cu2+ doped samples. UV-Visible absorption spectra exhibit a strong and broad absorption band at similar to 240 nm. Further, the absorption peak shifts to similar to 14 nm in Cu2+ doped samples. The optical band gap is estimated to be 5.28 eV for Cu doped Nd2O3 nanoparticles which are higher than the bulk Nd2O3 (4.7 eV). This can be attributed to the quantum confinement effect of the nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis, luminescence and EPR studies on CaSiO 3: Pb, Mn-nano phosphors synthesized by the solution combustion method

Nano-ceramic phosphor CaSiO 3 doped with Pb and Mn was synthesized by the low temperature solution combustion method. The materials were characterized by Powder X-Ray Diffraction (XRD), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The Electron Paramagnetic Resonance (EPR) spectrum of the investigated sample exhibits a broad resonance signal centered at g=1.994. The number of spins participating in resonance (N) and its paramagnetic susceptibility (�) have been evaluated. Photoluminescence of doped CaSiO 3 was investigated when excited by UV radiation of 256 nm. The phosphor exhibits an emission peak at 353 nm in the UV range due to Pb 2+. Further, a broad emission peak in the visible range 550-625 nm can be attributed to 4T 1� 6A 1 transition of Mn 2+ ions. The investigation reveals that doping perovskite nano-ceramics with transition metal ions leads to excellent phosphor materials for potential applications. © 2012 Elsevier Ltd and Techna Group S.r.l.

Structural characterization, EPR and thermoluminescence properties of Cd-1 (-) xNixSiO3 nanocrystalline phosphors

Cd-1 - xNixSiO3 (x = 1-7 mol%) nanophosphors have been prepared for the first time by the combustion method using oxylyldihydrizide as a fuel. Powder X-ray diffraction results confirm the formation of monoclinic phase. Scanning electron micrographs show that Ni2+ influences the porosity of samples. The optical energy gap is widened with increase of Ni2+ ion dopant. The electron paramagnetic resonance spectrum of Ni2+ ions in CdSiO3 exhibits a symmetric absorption at g = 2.343 and the site symmetry around Ni2+ ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (chi) has been evaluated. The thermoluminescence intensity is found to increase up to similar to 20 min ultra-violet exposure and thereafter, decrease with further increase of ultra-violet dose. The kinetic parameters such as activation energy (E), frequency factor (s)and order of kinetics was estimated using glow peak shape method and the results are discussed. (c) 2012 Elsevier Ltd. All rights reserved.

Structural, EPR, optical and magnetic properties of alpha-Fe2O3 nanoparticles

alpha-Fe2O3 nanoparticles were synthesized by a low temperature solution combustion method. The structural, magnetic and luminescence properties were studied. Powder X-ray diffraction (PXRD) pattern of alpha-Fe2O3 exhibits pure rhombohedral structure. SEM micrographs reveal the dumbbell shaped particles. The EPR spectrum shows an intense resonance signal at g approximate to 5.61 corresponding to isolated Fe3+ ions situated in axially distorted sites, whereas the g approximate to 2.30 is due to Fe3+ ions coupled by exchange interaction. Raman studies show A(1g) (225 cm(-1)) and E-g (293 and 409 cm(-1)) phonon modes. The absorption at 300 nm results from the ligand to metal charge transfer transitions whereas the 540 nm peak is mainly due to the (6)A(1) + (6)A(1) —> T-4(1)(4G) + T-4(1)(4G) excitation of an Fe3+-Fe3+ pair. A prominent TL glow peak was observed at 140 C at heating rate of 5 degrees C s(-1). The trapping parameters namely activation energy (E), frequency factor (s) and order of kinetics (b) were evaluated and discussed. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis, characterization, EPR, photo and thermoluminescence properties of YAlO3:Ni2+ nanophosphors

YAlO3:Ni2+ (0.1 mol%) doped nanophosphor was synthesised by a low temperature solution combustion method. Powder X-ray diffraction (PXRD) confirms the orthorhombic phase of yttrium aluminate (YAlO3) along with traces of Y3Al5O12. Scanning Electron microscopy (SEM) shows that the powder particles appears to be spherical in shape with large agglomeration. The average crystallite sizes appeared to be in the range 45-90 nm and the same was confirmed by transmission electron microscopy (TEM) and Williamson-Hall (W-H) plots. Electron Paramagnetic Resonance (EPR) and photoluminescence (PL) studies reveal that Ni2+ ions are in octahedral coordination. Thermoluminescence (TL) glow curve consists of two peaks with the main peak at similar to 224 degrees C and a shouldered peak at 285 degrees C was recorded in the range 0.2-15 kGy gamma-irradiated samples. The TL intensity was found to be increasing linearly for 224 degrees C and 285 degrees C peaks up to 1 kGy and thereafter it shows sub-linear (up to 8 kGy) and saturation behavior. The trap parameters namely activation energy (E), order of kinetics (b), frequency factor (s) at different gamma-doses were determined using Chens glow peak shape and Luschiks methods then the results are discussed in detail. Simple glow peak structure, the 224 degrees C peak in YAlO3:Ni2+ nanophosphor can be used in personal dosimetry. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis, characterization, EPR and thermoluminescence properties of CaTiO3 nanophosphor

Calcium titanate (CaTiO3) nanophosphors were synthesized by three different routes namely solution combustion (SC), modified solid-state reaction (MSS) and solid-state (SS) methods. Rietveld refinement studies revealed the presence of an orthorhombic structure with traces of CaCO3. The crystallite sizes were found to be in the 43-45 nm range. TEM studies also confirm the nano size with well crystalline nature. EPR spectrum for SS method exhibits a broad resonance signal at g = 2.027 is attributed to TiO6](9-) center, whereas in MSS sample the resonance signals are attributed to surface electron and hole trapping sites. The TL behavior has been investigated for the first time using gamma-irradiation. TL glow peak at 169 degrees C were recorded in CaTiO3 prepared by SC, MSS and SS methods. The trapping parameters such as activation energy (E) and order of kinetics (b) were estimated using peak shape method and results are discussed in detail. (C) 2013 Elsevier Ltd. All rights reserved.

Luminescence studies and EPR investigation of 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 thermo-luminescence (TL) studies reveal presence of native defects in this phosphor. Using TL glow peaks the trap parameters have been evaluated and discussed. (C) 2014 Elsevier B.V. All rights reserved.