R. S. Ningthoujam

Induction heating studies of Fe3O4 magnetic nanoparticles capped with oleic acid and polyethylene glycol for hyperthermia

Fe3O4 magnetic nanoparticles (Fe3O4-MN) capped with either oleic acid (Fe3O4-OA-MN) or polyethylene glycol (Fe3O4-PEG-MN) were prepared by a co-precipitation method. From X-ray diffraction studies, the average crystallite sizes of Fe3O4-MN, Fe3O4-OA-MN and Fe3O4-PEG-MN were found to be 12, 6 and 8 nm, respectively. A reduction in the agglomeration of particles was observed when the magnetic nanoparticles (MN) were capped with oleic acid (OA) and polyethylene glycol (PEG), as confirmed by a transmission electron microscopy study. Magnetization of these MN was almost zero at room temperature in the absence of an applied magnetic field, indicating their superparamagnetic behavior. Magnetization was lower and the superparamagnetic fraction was higher for Fe3O4-OA-MN and Fe3O4-PEG-MN compared to Fe3O4-MN studied using a Mossbauer spectrometer. Compared to the control, an increased killing (35%) was observed in human breast cancer cells (MCF7) after Fe3O4-OA-MN treatment, which was further enhanced (65%) under induction heating conditions. However, MCF7 cells treated with Fe3O4-MN or Fe3O4-PEG-MN showed 5–10% killing after induction heating. These results showed the characterization of MN with different lipophilicity and suggests their suitability for hyperthermia applications in cancer therapy.

Disappearance and Recovery of Luminescence in Bi3+, Eu3+ Codoped YPO4 Nanoparticles Due to the Presence of Water Molecules Up to 800 °C

YPO(4) nanoparticles codoped with Eu(3+) (5 at. %) and Bi(3+) (2-10 at. %) have been synthesized by a simple coprecipitation method using a polyethylene glycol-glycerol mixture, which acts as capping agent. It has been found that the incorporation of Bi(3+) ions into the YPO(4):Eu(3+) lattice induces a phase transformation from tetragonal to hexagonal, and also a significant decrease in Eu(3+) luminescence intensity was observed. This is related to the association of the water molecules in the hexagonal phase of YPO(4) in which the nonradiative process from the surrounding water molecules around Eu(3+) is dominating over the radiative process. On annealing above 800 °C, luminescence intensity recovers due to significant removal of water. 900 °C annealed Bi(3+) codoped YPO(4):Eu(3+) shows enhanced luminescence (2-3 times) as compared to that of YPO(4):Eu(3+). When sample was prepared in D(2)O (instead of H(2)O), 4-fold enhancement in luminescence was observed, suggesting the extent of reduction of multiphonon relaxation in D(2)O. This study illustrates the stability of water molecules even at a very high temperature up to 800 °C in Eu(3+) and Bi(3+) codoped YPO(4) nanoparticles.

Behaviour of electric and magnetic dipole transitions of Eu3+, 5D0 → 7F0 and Eu–O charge transfer band in Li+ co-doped YPO4:Eu3+

The effect of Li+ co-doping on the photoluminescence properties of YPO4:Eu is discussed. Interesting behaviours, such as the presence of intermediate bands, shifting of the Eu–O charge transfer band (Eu–O CTB) to a lower wavelength, variation in intensities of magnetic (5D0 → 7F1) and electric dipole (5D0 → 7F2) transitions of Eu3+ and shift of 5D0 → 7F0 to higher energy with increasing excitation wavelengths are observed. The Eu3+ ion does not have an absorption band in the range 340–350 nm, but after excitation at these wavelengths, a broad emission band (370–570 nm), as well as sharp peaks of Eu3+, could be observed. This is due to strong energy transfer from the intermediate band of the host to the Eu3+ ion. X-ray photoelectron spectroscopy (XPS) study also confirms that intermediate band emission is not due to Eu2+ ion emission. The blue shifting of Eu–O CTB is because of the increase in the optical electronegativity of the Eu3+ ion on Li+ co-doping. The variation in intensities of the 5D0 → 7F2 and 5D0 → 7F1 dipole transitions is related to (i) overlapping interaction parameters within the ground and excited states, (ii) exchange interaction among atoms/ions and (iii) density of the incoming photons. Shift of 5D0 → 7F0 to a higher energy with increasing excitation wavelengths is because of change in the second order crystal field parameter B20 with excitation wavelength. The significant enhancement of luminescence intensity is found with Li+ co-doping due to the increase in crystallinity.

Lifetime and quantum yield studies of Dy3+ doped GdVO4 nanoparticles: Concentration and annealing effect

GdVO4 nanoparticles doped with Dy3+ have been prepared using urea hydrolysis method in ethylene glycol medium. Linear decrease in the unit cell volume indicates the quantitative substitution of Gd3+ lattice sites by Dy3+ in GdVO4. The luminescence intensity of electric dipole transition at 573 nm is more than that of magnetic dipole transition at 483 nm. This has been attributed to the asymmetric environment of Dy3+ ion in GdVO4. Luminescence intensity decreases with increasing Dy3+ concentrations due to concentration quenching. This is supported by lifetime decay studies. There is no particle size effect on the peak positions of Dy3+ emission. There is an increase in the decay lifetime for F49/2 level with increase in heat treatment from 500 to 900 °C. This is attributed to the reduction in nonradiative process arose from surface inhomogeneities. The decay lifetime data follow the biexponential to monoexponential nature with increase of Dy3+ concentrations. There is an increase in the quantum yield with ...

Synthesis of oleic acid functionalized Fe3O4 magnetic nanoparticles and studying their interaction with tumor cells for potential hyperthermia applications.

In the present study, oleic acid (OA) functionalized Fe3O4 magnetic nanoparticles (MN) were synthesized following modified wet method of MN synthesis. The optimum amount of OA required for capping of MN and the amount of bound and unbound/free OA was determined by thermogravimetric analysis (TGA). Further, we have studied the effect of water molecules, associated with MN, on the variation in their induction heating ability under alternating current (AC) magnetic field conditions. We have employed a new approach to achieve dispersion of OA functionalized MN (MN-OA) in aqueous medium using sodium carbonate, which improves their biological applicability. Interactions amongst MN, OA and sodium carbonate were studied by Fourier transform infrared spectroscopy (FT-IR). Intracellular localization of MN-OA was studied in mouse fibrosarcoma cells (WEHI-164) by prussian blue staining and confocal laser scanning microscopy (CLSM) using nile blue A as a fluorescent probe. Results showed MN-OA to be interacting mainly with the cell membrane. Their hyperthermic killing ability was evaluated in WEHI-164 cells by trypan blue method. Cells treated with MN-OA in combination with induction heating showed decreased viability as compared to respective induction heating controls. These results were supported by altered cellular morphology after treatment of MN-OA in combination with induction heating. Further, the magnitude of apoptosis was found to be ~5 folds higher in cells treated with MN-OA in combination with induction heating as compared to untreated control. These results suggest the efficacy of MN-OA in killing of tumor cells by cellular hyperthermia.

Luminescence, lifetime, and quantum yield studies of redispersible Eu3+-doped GdPO4 crystalline nanoneedles: Core-shell and concentration effects

Crystalline nanoneedles of Eu3+-doped GdPO4 and Eu3+-doped GdPO4 covered with GdPO4 shell (core shell) have been prepared at relatively low temperature of 150 °C in ethylene glycol medium. From luminescence study, asymmetric ratio of Eu3+ emission at 612 nm (electric dipole transition) to 592 nm (magnetic dipole transition) is found to be less than one. Maximum luminescence was observed from the nanoparticles with Eu3+ concentration of 5 at. %. For a fixed concentration of Eu3+ doping, there is an improvement in emission intensity for core-shell nanoparticles compared to that for core. This has been attributed to effective removal of surface inhomogeneities around Eu3+ ions present on the surface of core as well as the passivation of inevitable surface states, defects or capping ligand (ethylene glycol) of core nanoparticles by bonding to the shell. Lifetime for D50 level of Eu3+ was found to increase three times for core-shell nanoparticles compared to that for core confirming the more Eu3+ ions with sym...

Re-dispersion and film formation of GdVO4 : Ln3+ (Ln3+ = Dy3+, Eu3+, Sm3+, Tm3+) nanoparticles: particle size and luminescence studies

GdVO(4) : Ln(3+) (Ln(3+) = Dy(3+), Eu(3+), Sm(3+), Tm(3+)) nanoparticles are prepared by a simple chemical route at 140 °C. The crystallite size can be tuned by varying the pH of the reaction medium. Interestingly, the crystallite size is found to increase significantly when pH increases from 6 to 12. This is related to slower nucleation of the GdVO(4) formation with increase of VO(4)(3-) present in solution. The luminescence study shows an efficient energy transfer from vanadate absorption of GdVO(4) to Ln(3+) and thereby enhanced emissions are obtained. A possible reaction mechanism at different pH values is suggested in this study. As-prepared samples are well dispersed in ethanol, methanol and water, and can be incorporated into polymer films. Luminescence and its decay lifetime studies confirm the decrease in non-radiative transition probability with the increase of heat treatment temperature. Re-dispersed particles will be useful in potential applications of life science and the film will be useful in display devices.

SnO2:Eu3+ nanoparticles dispersed in TiO2 matrix: Improved energy transfer between semiconductor host and Eu3+ ions for the low temperature synthesized samples

SnO2:Eu3+ nanoparticles uniformly dispersed in TiO2 matrix were prepared at 185°C in ethylene glycol. Unlike in SnO2:Eu3+, significant improvement in the exciton mediated energy transfer between SnO2 and Eu3+ ions was observed when SnO2:Eu3+ nanoparticles are dispersed in TiO2 matrix, and this is attributed to effective shielding of surface Eu3+ ions present in SnO2:Eu3+ nanoparticles from the vibrations of stabilizing ligand by TiO2 matrix. Annealing the samples at high temperatures leads to formation of Sn1−xTixO2, without significantly affecting the energy transfer process between Eu3+ ions and semiconductor host.

Observation of intermediate bands in Eu3+ doped YPO4 host: Li+ ion effect and blue to pink light emitter

This article explores the tuning of blue to pink colour generation from Li+ ion co-doped YPO4:5Eu nanoparticles prepared by polyol method at ∼100-120 °C with ethylene glycol (EG) as a capping agent. Interaction of EG molecules capped on the surface of the nanoparticles and/or created oxygen vacancies induces formation of intermediate/mid gap bands in the host structure, which is supported by UV-Visible absorption data. Strong blue and pink colors can be observed in the cases of as-prepared and 500 °C annealed samples, respectively. Co-doping of Li+ enhances the emission intensities of intermediate band as well as Eu3+. On annealing as-prepared sample to 500 °C, the intermediate band emission intensity decreases, whereas Eu3+ emission intensity increases suggesting increase of extent of energy transfer from the intermediate band to Eu3+ on annealing. Emission intensity ratio of electric to magnetic dipole transitions of Eu3+ can be varied by changing excitation wavelength. The X-ray photoelectron spectrosc...

Luminescence study of Eu3+ doped GdVO4 nanoparticles: Concentration, particle size, and core/shell effects

Nanoparticles of GdVO4 doped with Eu3+ and core/shell of GdVO4:Eu3+/GdVO4 are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130 °C. Unit cell volume increases when GdVO4 is doped with Eu3+ indicating the substitution of Gd3+ lattice sites by Eu3+. From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu3+. Optimum luminescence intensity is found to be in 5–10 at. % Eu3+. Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu3+ surroundings by bonding to GdVO4 shell. The lifetime for D50 level increases with annealing and core/shell formation.