Search

The tribo-mechanical properties of NiMoAl-Cr2AlC MAX phase composite coatings on stainless steel substrate have been investigated. NiMoAl with different amounts of Cr2AlC (10, 20, 50 and 100 wt.%) were prepared by turbo-mixing and deposited by High-Velocity Oxy-Fuel (HVOF) method on stainless steel substrate. The phase composition, microstructure, chemical composition, tribological and mechanical properties of the coatings were analyzed using x-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy-Dispersive x-ray analysis (EDAX), pin-on-disk wear testing rig and nanohardness tester, respectively. The worn surfaces were analyzed by metallurgical optical microscope, FESEM and three-dimensional surface profiler to understand the wear behavior in detail. The addition of the Cr2AlC MAX phase in NiMoAl enhances the mechanical properties and reduces the surface roughness and porosity. NiMoAl-20 wt.% Cr2AlC and Cr2AlC coatings containing equal amounts of oxygen and carbon in the tribofilm show the low coefficient of friction (COF) and wear rate. The addition of the Cr2AlC MAX phase in the NiMoAl matrix up to 20 wt.% reduces the wear rate by one order of magnitude and enhances the coating life by 7000 twist fatigue cycles.

Glasses with compositions xV(2)O(5) - (100 - x)0.8NaPO(3) - 0.2ZnO] (where 0.2

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.

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 Eu 2+ and Eu 3+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits a broad resonance signal at g = 4.195 which is attributed to Eu 2+ 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.

Rod like structures of hexagonal Y(OH) 3 :Ni 2+ and cubic Y 2 O 3 :Ni 2+ phosphors have been successfully synthesized by solvothermal method. X-ray diffraction studies of as-formed product shows hexagonal phase, whereas the product heat treated at 700 °C shows pure cubic phase. Scanning electron micrographs (SEM) of Y(OH) 3 :Ni 2+ show hexagonal rods while Y 2 O 3 :Ni 2+ rods were found to consist of many nanoparticles stacked together forming multi-particle-chains. EPR studies suggest that the site symmetry around Ni 2+ ions is predominantly octahedral. PL spectra show emission in blue, green and red regions due to the 3 T 1 ( 3 P)→ 3 A 2 ( 3 F), 1 T 2 ( 1 D)→ 3 A 2 ( 3 F) and 1 T 2 ( 1 D)→ 3 T 2 ( 3 F) transitions of Ni 2+ ions, respectively. TL studies were carried out for Y(OH) 3 :Ni 2+ and Y 2 O 3 :Ni 2+ phosphor upon γ-dose for 1–6 kGy. A single well resolved glow peaks at 195 and 230 °C were recorded for Y(OH) 3 :Ni 2+ and Y 2 O 3 :Ni 2+ , respectively. The glow peak intensity increases linearly up to 4 kGy and 5 kGy for Y(OH) 3 :Ni 2+ and Y 2 O 3 :Ni 2+ , respectively. The kinetic parameters such as activation energy ( E ), frequency factor ( s ) and order of kinetics ( b ) were estimated by different methods. The phosphor follows simple glow peak structure, linear response with gamma dose, low fading and simple trap distribution, suggesting that it is quite suitable for radiation dosimetry.

MgSrAl10O17:Cr3+ powder phosphor has been synthesized by a solution combustion method at furnace temperature of 500 °C in a short time (

Manganese-doped LaMgAl11O19 powder has been prepared by an easy combustion method. Powder x-ray diffraction and scanning electron microscopy have been used to characterize the as-prepared phosphor. The electron paramagnetic resonance (EPR) spectrum of LaMgAl11O19:Mn2+ phosphor exhibits six-line hyperfine structure centered at g ≈ 1.973. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) for the resonance signal at g ≈ 1.973 have been calculated as a function of temperature. The photoluminescence spectrum exhibits green emission at 516 nm, which is attributed to 4T1 → 6A1 transition of Mn2+ ions. From EPR and luminescence studies, it is observed that Mn2+ ions occupy Mg2+ sites and Mn2+ ions are located at tetrahedral sites in the prepared phosphors.

Thermally stable superhydrophobic coatings have been prepared using Polyvinylidene fluoride (PVDF)Multiwalled carbon nanotubes (MWCNTs) by spray coating method. The effects of MWCNT (0 – 66 wt%) and temperature (300 to 623 K) on wettability have been studied. A transformation from hydrophobic to superhydrophoic state was achieved with increase of CNT content. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies reveal that with increase in CNT content, -phase of PVDF decreases suggesting that MWCNT has strong effect on the phase separation of PVDF. Field emission scanning electron microscopy (FESEM) studies show that the coatings have rough surface with porous structure. With increase in CNT content the protrusion like structures decreased reaching micro/nano scales. The coatings were thermally stable upto 573 K exhibiting superhydrophobicity and thereafter transformed to superhydrophilic state at 623 K. Energy dispersive X-ray spectroscopy (EDXS) analysis show the absence of fluorine after annealing at 623 K suggesting decomposition of PVDF. X-ray photoelectron spectroscopy (XPS) of C1s and F1s core levels in as-deposited PVDFMWCNT coating show the presence of CF2 related species. Concentration of fluorine drastically decreases after heat treatment of the coating at 350 C. The main advantage of the present method is feasibility for application over large area and the coatings are stable upto 573 K.

A simple and inexpensive combustion method was used to prepare Fe3+ doped YAlO3 perovskite within few minutes at low temperature (400 ± 10 °C). This might be useful in lowering the cost of the material. The final products were well characterized by various spectroscopic techniques such as PXRD, SEM, TEM, FTIR and UV–Visible. The average crystallite size was estimated from the broadening of the PXRD peaks and found to be in the range 45–90 nm, the results were in good agreement with the W–H plots and TEM. The crystallites show dumbbell shape, agglomerated particles with different size. The TL glow curves of 1–5 kGy γ-irradiated YAlO3:Fe3+ (0.1 mol%) nanopowder warmed at a heating rate of 3 °C s−1 records a single glow peak at ∼260 °C. The kinetic parameters namely activation energy (E), order of kinetics (b) and frequency factor (s) were determined at different gamma doses using the Chens glow peak shape method and the results were discussed in detail. The photoluminescence spectra for Fe3+ (0.1–0.9 mol%) doped YAlO3 records the lower energy band at 720 nm (4T1 (4G) → 6A1 (6S)) and the intermediate band located at 620 nm (4T2 (4G) → 6A1 (6S)) with the excitation of 378 nm. The higher energy band located at 514 nm was associated to 4E + 4A1 (4G) → 6A1 (6S) transition. The resonance signals at g values 7.6, 4.97, 4.10, 2.94, 2.33 and 1.98 were observed in EPR spectra of Fe3+ (0.1–0.9 mol%) doped YAlO3 recorded at room temperature. The g values indicate that the iron ions were in trivalent state and distorted octahedral site symmetry was observed.

Thermoluminescence properties of YAlO3:Dy3+ nanophosphor prepared by a low temperature solution combustion (SC) method using oxalyl dihydrazide as a fuel were studied and the results were compared to bulk phosphor prepared by solid state (SS) synthesis. Powder X-ray diffraction patterns confirm the orthorhombic phase of SC and SS methods. Rietveld refinement was used to estimate the cell parameters of undoped and Dy3+ doped YAlO3. Scanning electron micrographs reveal dumbbell shape particles. Electron paramagnetic resonance spectra of YAlO3:Dy3+ nanophosphors were studied at 293 K, 77 K and 10 K. Thermoluminescence responses of SC and SS prepared phosphor were studied using gamma irradiation in the dose range 0.1-6 kGy at a warming rate of 1 degrees C s (1) at room temperature (RT). The optimized concentrations of Dy3+ ions in YAlO3 was found to be 3 mol%. The trapping parameters (i. e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen's method. The low fading and linear response in the wide range (0.1-1 kGy) suggests the possibility of usage of SC prepared phosphor in dosimeter applications. (C) 2013 Elsevier B. V. All rights reserved.

Despite being a particularly good emitter, use of divalent Eu has been seriously limited. This is because severe reducing environments or special hosts are needed during synthesis of divalent Eu containing phosphors. In this work we stabilize Eu in its 2+ state (in CaAl2O4) using an open-air solution combustion reaction. The impact of fuel (F) to oxidizer (O) molar ratios (F/O = 0.5-2.0) on luminescence properties is explored. Chromaticity of Eu:CaAl2O4 depends sensitively on the F/O ratio. In general, higher F/O inhibits Eu3+ and promotes Eu2+ formation, which in turn improves the quality of the blue phosphor. EPR spectra show inhomogeneous broadening effects with the increase in F/O ratio, which suggests that disorder creation is promoted when F/O is increase. This is also confirmed by an increase in emission line width in PL spectra, when F/O is increased. (C) 2013 Elsevier B.V. All rights reserved.

The mechanical, thermal, and optical properties, along with the microstructure and electron paramagnetic resonance (EPR) spectra, have been studied for MgAl 2 O 4 :Cr 3+ spinel glass and glass–ceramics. The activation energy of the crystallization has been estimated from the differential scanning calorimetry (DSC) study using different models and is found to vary within 255–270 kJ/mol for the un-doped precursor glass. The microstructure of the glass–ceramics has been characterized using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The TEM images demonstrate the presence of cubic crystals in the glass–ceramics of uniform size 10–15 nm. X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy reveal the presence of MgAl 2 O 4 spinel as the only crystalline phase, formed in the heat-treated glass–ceramics. The EPR spectrum of Cr 3+ doped glass sample exhibits a broad resonance signal with effective g = 1.97 whereas in glass–ceramic sample an additional weak resonance signal is observed at g = 3.83. The excitation spectrum exhibits two bands in the visible region. The emission spectrum exhibits an intense red emission at 690 nm which is characteristic of Cr 3+ ions caused by the spin-forbidden 2 E g → 4 A 2g transition. All the mechanical properties are found to have improved in the glass–ceramics when compared to glasses. A good combination of micro-hardness (∼6.0 GPa), high fracture toughness (∼5.0 MPa m 1/2 ), 3 point flexural strength (∼100 MPa) and elastic modulus (∼55 GPa) has been obtained for the glass–ceramic samples.

Glass of the composition 23B 2 O 3 –5ZnO–72Bi 2 O 3 – x CuO (where, x =0.0003, 0.0012 and 0.003 at%, in excess) were prepared by a melt-quench technique. The effects of the copper ions on the structural and optical properties of ZnO–Bi 2 O 3 –B 2 O 3 glass matrix were analyzed using various spectroscopic techniques. The infrared spectra showed the presence of some bands that are assigned to vibrations of Bi–O bonds from BiO 6 octahedral units and B–O bonds from BO 3 and BO 4 units. The electron paramagnetic resonance spectra revealed the presence of Cu 2+ ions in the glass structure in an axially distorted octahedral environment. The number of Cu 2+ ions participating in resonance and its paramagnetic susceptibility has been evaluated. The UV–vis spectra show a broad absorption band at 785 nm and another band at 438 nm which are due to d-d transitions of Cu 2+ ions. These glasses are found to exhibit visible and near infrared luminescence bands centered at 548 and 652, and 804 nm when excited at 400 and 530 nm, respectively. The luminescence centers are supposed to be caused by the lower valence state of bismuth, such as Bi 2+ and Bi + ions, generated during in-situ redox reactions.

CoFe 2 O 4 nanoparticles were prepared by solution combustion method. The nanoparticle are characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). PXRD reveals single phase, cubic spinel structure with Fd 3 ¯ m (227) space group. SEM micrograph shows the particles are agglomerated and porous in nature. Electron paramagnetic resonance spectrum exhibits a broad resonance signal g =2.150 and is attributed to super exchange between Fe 3+ and Co 2+ . Magnetization values of CoFe 2 O 4 nanoparticle are lower when compared to the literature values of bulk samples. This can be attributed to the surface spin canting due to large surface-to-volume ratio for a nanoscale system. The variation of dielectric constant, dielectric loss, loss tangent and AC conductivity of as-synthesized nano CoFe 2 O 4 particles at room temperature as a function of frequency has been studied. The magnetic and dielectric properties of the samples show that they are suitable for electronic and biomedical applications.

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.

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.

α-Fe(2)O(3) 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 α-Fe(2)O(3) exhibits pure rhombohedral structure. SEM micrographs reveal the dumbbell shaped particles. The EPR spectrum shows an intense resonance signal at g≈5.61 corresponding to isolated Fe(3+) ions situated in axially distorted sites, whereas the g≈2.30 is due to Fe(3+) 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)→(4)T(1)(4 G)+(4)T(1)(4 G) excitation of an Fe(3+)-Fe(3+) pair. A prominent TL glow peak was observed at 140°C at heating rate of 5 °Cs(-1). The trapping parameters namely activation energy (E), frequency factor (s) and order of kinetics (b) were evaluated and discussed.

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 (I�) 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.

This work reports the preparation of CdSiO3:Sm3+ (1–7 mol%) nanophosphors by a low temperature solution combustion method. For the first time the effect of NaF flux on the crystallization behavior, morphology, and thermoluminescence property of 5 mol% Sm3+ doped CdSiO3 has been investigated. The nanopowders are well characterized by powder X-ray diffraction (PXRD), Fourier Transform Infra-Red (FT–IR), and scanning electron microscopy (SEM). PXRD results indicate that the powder calcined at 800 °C for 2 h has monoclinic phase. SEM results show that the powder is highly porous and the pore size and shape can be modified by the addition of NaF flux. Addition of NaF could lead to formation of particle type morphology and the increase in wt% of NaF changes crystallinity and phase. The thermoluminescence glow curves for 2–6 wt% NaF in CdSiO3:Sm3+ show a single, well resolved glow peak at 126, 130 and 150 °C, respectively. But for the sample prepared with 8 wt% of NaF flux shows two glow peaks at 148 and 220 °C. With the addition of NaF flux, TL intensity can be effectively enhanced.

Nd2O3:Co2+ (1–4 mol%) nanophosphors (15–25 nm) have been prepared via low temperature solution combustion method. Scanning electron micrograph (SEM) shows that the product is highly porous in nature. The stokes line in the Raman spectrum at ∼2000 cm−1 is assigned to Fg mode and the anti-stokes lines are assigned to a combination of Ag + Eg modes. With increase of Co2+ concentration, the intensity of Fg mode decreases, whereas the combination of Ag + Fg modes completely disappears. Electron paramagnetic resonance (EPR) spectrum exhibits two resonance signals with effective g values at g = 2.25 and g = 2.03. Thermoluminescence (TL) response of Nd2O3:Co2+ nanopowders with γ dose 0.23–2.05 kGy was studied. The activation energy (E) and frequency factor (s) are estimated using Chen's glow peak shape method and obtained to be in the range 0.45–1.67 eV and 1.8 × 104 to 4.0 × 1012 s−1, respectively. It is observed that the TL glow peak intensity at 430 K increases linearly with γ dose which is suitable for radiation dosimetry.

Red light emitting cubic Y1.95Eu0.05O3 nanophosphors have been synthesized by a low temperature solution combustion method using ethylene diamine tetra acetic acid (EDTA) as fuel. The systematic studies on the effect of calcination temperature on its structural, photoluminescence (PL), and thermoluminescence (TL) properties were reported. The crystallinity of the samples increases, and the strain is reduced with increasing calcination temperature. SEM micrographs reveal that samples lose their porous nature with an increase in calcination temperature. PL spectra show that the intensity of the red emission (611 nm) is highly dependent on the calcination temperature and is found to be 10 times higher when compared to as-formed samples. The optical band gap (E-g) was found to reduce with an increase of calcination temperature due to reduction of surface defects. The thermoluminescence (TL) intensity was found to be much enhanced in the 1000 degrees C calcined sample. The increase of PL and TL intensity with calcination temperature is attributed to the decrease of the nonradiative recombination probability, which occurs through the elimination of quenching defects. The trap parameters (E, b, s) were estimated from Chen's glow peak shape method and are discussed in detail for their possible usage in dosimetry.

CdSiO 3 :Co 2+ (1–7 mol %) nanophosphors have been prepared via solution combustion method with post calcination at 800 °C for 2 h for the first time. The formation of expected monoclinic phase was investigated by Powder X-ray diffraction (PXRD) measurements. The effect of different fluxes like NaF, NaCl, NH 4 F and NH 4 Cl on the crystallinity, phase and morphology of CdSiO 3 was investigated in detail. The crystallinity of the samples can be greatly enhanced by using fluxes rather than increasing the calcination temperature. Scanning electronic micrograph (SEM) image shows that the powder morphologies are highly influenced by flux addition. The addition of 2 wt% of fluxes would drastically enhance the crystallinity when NaCl, NH 4 F and NH 4 Cl fluxes are used. A well resolved single thermoluminescent glow peak at ∼170 °C was recorded for all the samples. Among all the halide fluxes, NaCl flux was found to be the potential one in enhancing the TL peak intensity along with crystallinity.

YAlO(3):Cr(3+) (0.1 mol%) nanophosphor has been synthesized by low temperature solution combustion method. The X-ray diffraction studies reveal an orthorhombic structure. Transmission electron microscopy reveals that the particles are spherical in shape with nano-size ~40-65 nm. Electron paramagnetic resonance (EPR) spectrum shows a resonance signal with effective g value at g=1.978 which can be attributed to the exchange coupled Cr(3+) ion pairs in weakly distorted sites. The photoluminescence spectrum shows an intense doublet at 677 nm and 694 nm (R lines) assigned to spin-forbidden (2)E(g)→(4)A(2)(g) transition of Cr(3+) ions. EPR and PL studies reveal that the Cr(3+) ions occupy Al(3+) sites in YAlO(3). The interesting feature reported in this work concerns the linearity with gamma dose in the wide range (0.1-6 kGy). Prominent TL glow peaks at 226 °C and 346 °C were observed for both γ and UV-rays respectively. It is observed that the peaks at 226 °C and 346 °C eventually show a linear response up to 5 kGy which makes them a candidate for high dose dosimetry of ionizing radiation. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped and Cr doped samples were determined using Chens glow peak shape method and the results are discussed in detail.

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 °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 °C along with relatively resolved glow peak at 180 °C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115 °C along with two well defined peaks at ∼215 and 275 °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.

Nanocrystalline Nd(2)O(3):Ni(2+) (2 mol%) phosphor has been prepared by a low temperature (∼400°C) solution combustion method, in a very short time (

The LaAl11O18:Mn2+ powder phosphor has been prepared using a self-propagating synthesis. Formation and homogeneity of the LaAl11O18:Mn2+ phosphor has been verified by X-ray diffraction and energy dispersive X-ray analysis respectively. The EPR spectra of Mn2+ ions exhibit resonance signals with effective g values at g≈4.8 and g≈1.978. The signal at g≈1.978 exhibits six-line hyperfine structure and is due to Mn2+ ions in an environment close to tetrahedral symmetry, whereas the resonance at g≈4.8 is attributed to the rhombic surroundings of the Mn2+ ions. It is observed that the number of spins participating in resonance for g≈1.978 increases with decreasing temperature obeying the Boltzmann law. Upon 451 nm excitation, the photoluminescence spectrum exhibits a green emission peak at 514 nm due to 4T1 (G)→6A1 (S) transition of Mn2+ ions. The crystal field parameter Dq and Racah inter-electronic repulsion parameters B and C have been evaluated from the excitation spectrum.

The red emitting Cr3+ activated α-Al2O3 powder phosphor has been prepared by easy combustion reactions from mixed metal nitrate reactants and urea with ignition temperatures of 500 °C. The as-synthesized powder was characterized by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared techniques. The X-ray diffraction pattern reveals that the phosphor crystallized in the hexagonal α-Al2O3 phase directly from the combustion reaction. The EPR spectrum exhibits an intense resonance signal with effective g value at g=3.33 along with a few weak resonance signals with effective g values at g=13.7, 2.34, 1.95, 1.49, and 1.26. The spin concentration (N) and its paramagnetic susceptibility (χ) have been evaluated. The excitation spectrum consists of two broad intense bands at 415 nm and 555 nm and are assigned to 4A2g (F)→4T1g (F) and 4A2g (F)→4T2g (F) transitions, respectively. The intense fluorescence peak around 691 nm is attributed to 2E g →4A2g transition of Cr3+ ion. By correlating EPR and optical data, the crystal field splitting parameter (Dq), Racah inter-electronic repulsion parameter (B) have been evaluated and discussed. The EPR and optical studies reveal that Cr3+ ions are occupying in Al3+ sites in octahedral coordination.

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 ≈ 2.0 with a sextet hyperfine structure (hfs) besides a weak signal at g ≈ 4.13. The signal at g ≈ 2.0 with a sextet hyperfine structure might be due to manganese impurity where as the resonance signal at g ≈ 4.13 is due to iron. The optical band gap Eg was found to decrease with increase of Fe content. Raman spectra exhibit two non-polar optical phonon (E2) 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 dopant concentration. TL measurements of γ-irradiated (1–5 kGy) samples show a main glow peak at 368 °C at a warming rate of 6.7 °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.

The microstructure, mechanical, EPR and optical properties of transparent MnO 2 doped lithium disilicate (LDS) glass–ceramics prepared by melt quenching and controlled crystallization, have been studied. The microstructure of the glass–ceramics has been characterized using FE-SEM, TEM, FT-IR and XRD techniques. FE-SEM micrographs show elongated, highly interlocked, dense (∼80 vol.%) nanocrystals of LDS with an average size ∼100 nm. XRD and FT-IR studies reveal that the only crystalline phase formed after heat-treatment at 700 °C for 1 h is LDS. A good combination of average microhardness ∼5.6 GPa, high fracture toughness ∼2.8 MPa m 1/2 , 3-point flexural strength ∼250 MPa and moderate elastic modulus 65 GPa has been obtained. The EPR spectra of both LDS glasses and glass–ceramics exhibit resonance signals with effective g values at g = 4.73, g = 4.10, g = 3.3, and g = 1.98. The resonance signal at g = 1.98 is found to be more intense than the other signals and exhibits hyperfine structure at lower concentration of manganese. From the observed spectrum, the spin-Hamiltonian parameters have been evaluated. In glass samples the optical absorption spectrum exhibits a broad band around ∼20,320 cm −1 which has been assigned to the transition 6 A 1g (S) → 4 A 1g (G) 4 E g (G)-of Mn 2+ ions. The cerammed samples upon 394 nm excitation emit a green luminescence (565 nm, 4 T 1g → 6 A 1g (G) transition of Mn 2+ ions), and a weak red emission (710 nm). From the ultraviolet absorption edges, the optical bandgap energies ( E opt ) were evaluated and are discussed.

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 Zni and Vo+ 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 ∼343 °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 γ-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.

Copper dodecanoate films prepared by emulsion method exhibit superhydrophobic property with water contact angle of 155 degrees and sliding angle of 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.

A blue phosphor, BaMgAl 10 O 17 :Eu 2+ , has been synthesized in the furnace at a temperature of 500 °C by solution combustion method. The formation of the as-prepared BaMgAl 10 O 17 :Eu 2+ phosphor was confirmed by the powder X-ray diffraction technique. The EPR spectrum exhibited an intense resonance signal centered at g =4.63 at 150 mT along with a number of resonances in the vicinity of g>2.0 and g g =4.63 have been calculated as a function of temperature. The excitation spectrum of BaMgAl 10 O 17 :Eu 2+ phosphor showed a strong peak near 336 nm (4f 7 ( 8 S)→5d 1 (t 2g ) transition) with a staircase like structure in the region 376–400 nm owing to crystal field splitting of the Eu 2+ d-orbital. The 336 nm excitation produced a broad blue emission at 450 nm corresponding to 4f 6 5d→4f 7 transition. PL studies reveal the two emission centers one at 450 nm and the other at 490 nm in this phosphor.

Cu (0.1 mol%) doped ZnO nanopowders have been successfully synthesized by a wet chemical method at a relatively low temperature (300 degrees C). Powder X-ray diffraction (PXRD) analysis, scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectroscopy, UV-Visible spectroscopy, Photoluminescence (PL) and Electron Paramagnetic Resonance (EPR) measurements were used for characterization. PXRD results confirm that the nanopowders exhibit hexagonal wurtzite structure of ZnO without any secondary phase. The particle size of as-formed product has been calculated by Williamson-Hall (W-H) plots and Scherrer's formula is found to be in the range of similar to 40 nm. TEM image confirms the nano size crystalline nature of Cu doped ZnO. SEM micrographs of undoped and Cu doped ZnO show highly porous with large voids. UV-Vis spectrum showed a red shift in the absorption edge in Cu doped ZnO. PL spectra show prominent peaks corresponding to near band edge UV emission and defect related green emission in the visible region at room temperature and their possible mechanisms have been discussed. The EPR spectrum exhibits a broad resonance signal at g similar to 2.049, and two narrow resonances one at g similar to 1.990 and other at g similar to 1.950. The broad resonance signal at g similar to 2.049 is a characteristic of Cu2+ ion whereas the signal at g similar to 1.990 and g similar to 1.950 can be attributed to ionized oxygen vacancies and shallow donors respectively. The spin concentration (N) and paramagnetic susceptibility (X) have been evaluated and discussed. (C) 2011 Elsevier B. V. All rights reserved.

Manganese-doped BaAl12O19 green phosphor was prepared using a self-propagating (combustion) synthesis. Powder X-ray diffraction and scanning electron microscopy were used to characterize the as-prepared combustion product. A room temperature photoluminescence study shows an emission line at 513 nm corresponding to a transition from the upper 4T1 → 6A1 ground state of Mn2+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits six line hyperfine structure at g = 1.981. From the EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The g value indicates that the site symmetry around Mn2+ ions is distorted tetrahedral. The number of spins (N) participating in the resonance for g = 1.981 is measured as a function of temperature. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures. From the plot 1/χ versus T, the Curie constant (C) and Curie paramagnetic temperature (θp) have been evaluated and discussed.

Europium doped LaMgAl11O19 phosphor was prepared by the combustion method. The as-prepared and post-treated (1350 °C 10 h 5% H2+95% N2) phosphors were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. XRD patterns show that LaMgAl11O19:Eu phosphors have hexagonal structure. FT-IR spectrum exhibits absorption bands corresponding to the stretching vibration of AlO4 and AlO6. Morphological studies reveal that this phosphor has faceted plates of varying sizes and shapes. The as-prepared LaMgAl11O19:Eu phosphor consists of both Eu3+ and Eu2+ ions. The phosphor exhibits a bright blue emission at 450 nm (4f65d→4f7 transition of Eu2+). On post-treating the phosphor we are able to enhance the blue emission efficiency by 330%. The process was detected from the evolution of excitation, emission and EPR spectra and the results are discussed.

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe3+ ions doped sodium borophosphate glasses (NaH2PO4–B2O3–Fe2O3). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe3+ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe3+ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123–295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θp) have been evaluated from the 1/χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe3+ ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed.

An efficient red emitting ZnAl2O4:Cr3+ powder phosphor material was prepared at furnace temperatures as low as 500 °C by using the combustion method. The prepared powders were analyzed by X-ray diffraction and scanning electron microscopy techniques. The optical properties were studied using photoluminescence technique. The EPR spectra exhibit an intense resonance signal at g = 3.74 which is attributed to Cr3+–Cr3+ pairs, and the weak resonance signal of at g = 1.97 is attributed to Cr3+ single ion transition. The spin population (N) has been evaluated as a function of temperature. The excitation spectrum exhibits two broad bands in the visible region which are characteristic of Cr3+ ions in octahedral symmetry and the emission spectrum exhibits zero-phonon line frequencies along with vibronic frequencies. The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed.

Gadolinium-activated Y2O3 phosphor has been prepared by combustion process in a short time of 5 min. The phosphors are well characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis of X-ray. The as-prepared Y2O3:Gd powder shows that all the peaks are due to the Y2O3 cubic phase. Upon UV light excitation (276 nm), the phosphor exhibits a strong and sharp UV emission at 314 nm and is ascribed to $$ ^{ 6} {\text{P}}_{ 7/ 2} \, {\to}\, ^{ 8} {\text{S}}_{ 7/ 2} $$ transition of Gd3+ ions. The EPR spectrum of Y2O3:Gd phosphor exhibits resonance signals with effective g values at g = 1.96, g = 2.88, and g = 6.08 and are attributed to Gd3+ ions located at sites with weak, intermediate, and strong cubic symmetry fields, respectively. It is observed that the population of spin levels (N) and linewidth depends on temperature. The paramagnetic susceptibility (χ) is also evaluated as a function of temperature and discussed.

Gd2O3:Eu3+ (0.5-8.0 mol%) nanophosphors have been prepared by low temperature solution combustion method using metal nitrates as oxidizers and oxalyl dihydrazide (ODH) as a fuel. The phosphors are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence (PL) techniques. PXRD patterns of as-formed and calcined (800 degrees C, 3 h) Gd2O3 powders exhibit monoclinic phase with mean crystallite sizes ranging from 20 to 50 nm. Eu3+ doping changes the structure from monoclinic to mixed phase of monoclinic and cubic. SEM micrographs shows the products are foamy, agglomerated and fluffy in nature due to the large amount of gases liberated during combustion reaction. Upon 254 nm excitation the photoluminescence of the Gd2O3:Eu3+ particles show red emission at 611 nm corresponding to D-5(0)-> F-7(2) transition. It is observed that PL intensity increases with calcination temperature. This might be attributed to better crystallization and eliminates the defects, which serve as centers of non-radiative relaxation for nanomaterials. It is observed that the optical energy gap (E-g) is widened with increase Eu3+ content. (C) 2010 Elsevier B.V. All rights reserved.

This paper reports the results on mixed alkali effect (MAE) in x Li 2 O–(30– x )Cs 2 O–69.25B 2 O 3 (5 ⩽ x ⩽ 25) glasses doped with 0.75 mol% of Cr 3+ ions studied by Electron Paramagnetic Resonance (EPR), optical absorption and luminescence techniques. The EPR spectra exhibit two resonance signals with effective g values at g ≈ 4.82 and g ≈ 1.99. These two resonance signals are attributed to isolated Cr 3+ ions and exchange coupled Cr 3+ pairs respectively. In addition to this, two more resonance signals with effective g values at g ≈ 4.12 and g ≈ 1.97 are also observed. The resonance signal at g ≈ 4.12 is due to Fe 3+ ions impurity and the resonance signal at g ≈ 1.97 is due to Cr 5+ ions. The population of spin levels ( N ) for the resonance signal at g ≈ 1.99 has been calculated at room temperature. It is interesting to observe that N exhibits a non-linear behavior with change in composition showing the mixed alkali effect. The magnetic susceptibility ( χ ) was calculated from the EPR data at various temperatures. The exchange coupling constant J between Cr 3+ ions is calculated from relative intensities of g ≈ 1.99 resonance line. The optical absorption spectrum exhibits three bands characteristic of Cr 3+ ions in octahedral symmetry. From the optical absorption spectral data, the crystal field (Dq) and Racah parameters ( B and C ) have been evaluated. From ultraviolet absorption edges, the optical band gap and Urbach energies have been calculated. The luminescence spectrum exhibits a red emission peak observed at 640 nm which is assigned to a transition 2 E g → 4 A 2g of Cr 3+ ions.

Single-step low-temperature solution combustion (LCS) synthesis was adopted for the preparation of LaMnO3+ (LM) nanopowders. The powders were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),surface area and Fourier transform infrared spectroscopy (FTIR). The PXRD of as-formed LM showed a cubic phase but, upon calcination (900degrees C, 6 h), it transformed into a rhombohedral phase. The effect of fuel on the formation of LM was examined, and its structure and magnetoresistance properties were investigated. Magnetoresistance (MR) measurements on LM were carried out at 0, 1, 4 and 7 T between 300 and 10 K. LM (fuel-to-oxidizer ratio; = 1) showed an MR of 17% at 1 T, whereas, for 4 and 7 T, it exhibited an MR of 45 and 55%, respectively, near the TM-I. Metallic resistivity data below TM-I showed that the double exchange interaction played a major role in this compound. It was interesting to observe that the sample calcined at 1200 degrees C for 3 h exhibited insulator behavior.

Electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), optical absorption and photoluminescence (PL) spectroscopic measurements are performed on Mn2+ doped high bismuth containing zinc–bismuth–borate glasses. TEM images reveal homogeneously dispersed Bio nanoparticles (NPs) of spherical shape with size about 5 nm. EPR spectra exhibit predominant signals at g≈2.0 and 4.3 with a sextet hyperfine structure. The resonance signal at g≈2.0 is due to Mn2+ ions in an environment close to octahedral symmetry, where as the resonance at g≈4.3 is attributed to the rhombic surrounding of the Mn2+ ions. The hyperfine splitting constant (A) indicates that Mn2+ ions in these glasses are moderately covalent in nature. The zero-field splitting parameter D has been calculated from the allowed hyperfine lines. The optical absorption spectrum exhibits a single broad band centered at 518 nm (19,305 cm−1) is assigned to the 6A1g(S)→4T1g(G) transition of Mn2+ ions. The visible and near infrared (NIR) luminescence bands at 548, 652 and 804 nm have been observed when excited at 400 and 530 nm, respectively. These luminescence centers are supposed to be caused by the lower valence state of bismuth, such as Bi2+ and Bi+ ions, generated during melting process.

Enstatite (MgSiO3) ceramic powders were synthesised by a low-temperature initiated self-propagating, gas-producing solution combustion process. The prepared powders were characterised by powder X-ray diffraction, scanning electron microscopy and Brunauer-Emmer-Teller specific surface area measurements. Defect centres induced by radiation were studied using the techniques of thermoluminescence (TL) and electron spin resonance (ESR). A well-resolved glow with peak at 178 degrees C and a shouldered peak at 120 degrees C were observed. Two defect centres were identified by ESR measurements, which were carried out at room temperature, and these were assigned to an O- ion and F+ centre. The O- ion (hole centre) appears to correlate with the main TL peak at 178 degrees C.

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence studies of Cr 3+ ions in lithium borophosphate glasses have been studied. The EPR spectra exhibit two resonance signals with effective g values at g = 4.56 and g = 1.96. These resonance signals are attributed to isolated Cr 3+ ions and exchange coupled Cr 3+ pairs, respectively. The EPR spectra have also been studied at various low temperatures. The population of spin levels ( N ) participating at resonance signal g = 1.96 has been calculated as a function of temperature. The spin-population ( N ) is found to be increasing with decrease in temperature. The magnetic susceptibility ( χ ) was calculated from the EPR data. It is observed that as temperature decreases, χ increases in accordance with Curie–Weiss law. The exchange coupling constant J between Cr 3+ ions is calculated from the relative intensities of g = 1.96 resonance line at various temperatures. The optical absorption spectrum exhibits four bands characteristic of Cr 3+ ions in octahedral symmetry. From the optical absorption spectral data, the crystal field (Dq) and Racah parameters ( B and C ) have been evaluated. The luminescence spectrum exhibits a red emission peak, which is assigned to a transition from the upper 4 T 2g (F) → 4 A 2g (F) ground state of Cr 3+ ions. The optical band gap is evaluated from the ultraviolet absorption edges.

Europium doped BaAl 12 O 19 powder phosphors have been synthesized by combustion process within few minutes. The phosphors have been characterized by XRD, SEM, FT-IR, EPR and PL techniques. The EPR spectrum exhibits an intense resonance signal at g =1.96 characteristic of Eu 2+ ions. In addition to this two weak resonance signals have been observed at g =2.28 and g =4.86. The population of the spin levels ( N ) for the resonance signal at g =1.96 is calculated as a function of temperature. By post-treating the phosphor at 1350 °C under a reducing atmosphere, it is observed that the population of spin levels has been increased five times. The excitation spectrum shows a peak at 326 nm with a shoulder at 290 nm. Upon excitation at 326 nm, the emission spectrum exhibits a well defined broad band with maximum at 444 nm emitting a blue light corresponding to 4f 6 5d→4f 7 transition. The luminescence intensity also has been enhanced to 60% by post-treating the phosphor at 1350 °C under a reducing atmosphere.

Glasses containing heavy metal oxide of the composition (wt.%) 23B 2 O 3 –5ZnO–72Bi 2 O 3 – x Fe 2 O 3 /CeO 2 (0 ≤ x ≤ 0.0058 at.% in excess) were prepared by melt quenching technique. The glass formation was confirmed by XRD. FTIR spectra exhibit characteristic absorption bands for B 2 O 3 and Bi 2 O 3 for their various structural units. The EPR spectra exhibit two resonance signals at g ≈ 6.4 and g ≈ 4.2 for Fe 2 O 3 doped glasses. The resonance signals at g ≈ 4.2 and g ≈ 6.4 are attributed to Fe 3+ ions in rhombic and axial symmetry sites, respectively. The number of spins participating in resonance ( N ) and its paramagnetic susceptibility ( χ ) with composition has been evaluated. The effect of CeO 2 and Fe 2 O 3 on optical and structural properties of zinc bismuth borate glass was investigated. From EPR and optical studies it is observed that iron ions are present in trivalent state with distorted octahedral symmetry. The cerium is present in Ce 4+ state. Upon 400 nm excitation the emission at 548 and 652 nm are attributed to the Bi 2+ species. The emission at 804 nm upon 530 nm excitation suggests that Bi + ions are present in the sample. It is interesting to observe that the optical band gap energy ( E opt ) decreases with the increase of transition metal and rare-earth ion doping.

Yttrium aluminum garnet (Y3Al5O12) and Mn activated Y3Al5O12 phosphors have been prepared by urea combustion route in less than 5 min. The phosphors are well characterized by powder X-ray diffraction, Scanning electron microscopy and Fourier-transform infrared spectroscopic techniques. Photoluminescence tests on the pure Y3Al5O12 showed a strong green emission at 525 nm (2.36 eV) attributed to the strongly allowed transition of F+ center whereas in Mn2+ activated YAG the green emission at 519 nm is due to the 4T1 (G)→6A1 (S) transition of Mn2+ ions. EPR studies have been carried out on Mn2+ activated Y3Al5O12 phosphor at 300 and 110 K. From EPR spectra the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting (A) indicates that the Mn2+ ions are in a moderately ionic environment. The spin concentration (N) and paramagnetic susceptibility (χ) have been evaluated and discussed.

EPR spectral investigations have been carried out on four edible leafy vegetables of India, which are used as dietary component in day to day life. In Rumex vesicarius leaf sample, EPR spectral investigations at different temperatures indicate the presence of anti-ferromagnetically coupled Mn(IV)–Mn(IV) complexes. EPR spectra of Trigonella foenum graecum show the presence of Mn ions in multivalent state and Fe3+ ions in rhombic symmetry. EPR spectra of Basella rubra indicate the presence of Mn(IV)–O–Mn(IV) type complexes. The EPR spectra of Basella rubra have been studied at different temperatures. It is found that the spin population for the resonance signal at g = 2.06 obeys the Boltzmann distribution law. The EPR spectra of Moringa oliefera leaves show the presence of Mn2+ ions. Radiation induced changes in free radical of this sample have also been studied. The FT-IR spectra of Basella rubra and Moringa oliefera leaves show the evidences for the protein matrix bands and those corresponding to carboxylic C O bonds.

Structural properties of natural jasper from Taroko Gorge (Taiwan) have been investigated by means of powder X-ray diffraction, electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopic techniques. The EPR spectrum at room temperature exhibits a sharp resonance signal at g = 2.007 and two more resonance signals centered at g ≈ 4.3 and 14.0. The resonance signal at g = 2.007 has been attributed to the E′ center and is related to a natural radiation-induced paramagnetic defect. Two more resonance signals centered at g ≈ 4.3 and 14.0 are characteristic of Fe3+ ions. The EPR spectra recorded at room temperature of jasper samples, heat-treated at temperatures ranging from 473 to 1,473 K exhibit marked temperature dependence. The resonance signal corresponding to E′ center disappears at elevated temperatures. A broad, intense resonance signal centered at g ≈ 2.0 appears at elevated temperatures. This resonance signal is a characteristic of Fe3+ ions, which are present as hematite in the jasper sample. The intensity of the resonance signal becomes dominant at elevated temperatures at ≥873 K, masking g ≈ 4.3 and g ≈ 14.0 resonance signals. The EPR spectra of jasper heat-treated at 673 K have been recorded at temperatures between 123 and 296 K. The population of spin levels (N) has been calculated for the broad g ≈ 2.0 resonance signal. It is found that N decreases with decreasing temperature. The linewidth (ΔH) of g ≈ 2.0 resonance signal of the heat-treated jasper is found to increase with decreasing temperature. This has been attributed to spin–spin interaction of the Fe3+ ions present in the form of hematite in the studied jasper sample.