Effects of crystallization and dopant concentration on the emission behavior of TiO2:Eu nanophosphors

Uniform, spherical-shaped TiO2:Eu nanoparticles with different doping concentrations have been synthesized through controlled hydrolysis of titanium tetrabutoxide under appropriate pH and temperature in the presence of EuCl3·6H2O. Through air annealing at 500°C for 2 h, the amorphous, as-grown nanoparticles could be converted to a pure anatase phase. The morphology, structural, and optical properties of the annealed nanostructures were studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy [EDS], and UV-Visible diffuse reflectance spectroscopy techniques. Optoelectronic behaviors of the nanostructures were studied using micro-Raman and photoluminescence [PL] spectroscopies at room temperature. EDS results confirmed a systematic increase of Eu content in the as-prepared samples with the increase of nominal europium content in the reaction solution. With the increasing dopant concentration, crystallinity and crystallite size of the titania particles decreased gradually. Incorporation of europium in the titania particles induced a structural deformation and a blueshift of their absorption edge. While the room-temperature PL emission of the as-grown samples is dominated by the 5D0 - 7Fj transition of Eu+3 ions, the emission intensity reduced drastically after thermal annealing due to outwards segregation of dopant ions

Disappearance and recovery of luminescence in GdPO4:Eu3+ nanorods: Propose to water/OH center dot release under near infrared and gamma irradiations

Luminescence intensity of rare-earth doped materials can be varied depending on shape of particles, capping agent, and heat-treatment. This is related to the non-radiative rate possessed by the material. Here, we observed the high quenching of the luminescence intensity of Eu3+ doped GdPO4 prepared in water (H2O) medium. On the contrary, in ethylene glycol (EG) medium, it shows high luminescence. Luminescence intensity is recovered when Eu3+ doped GdPO4 nanorods prepared in H2O medium is heated above 700 degrees C. This transforms hexagonal to monoclinic structure following the removal of water. Luminescence intensity is enhanced by changing the medium from H2O to D2O and also if core-shell formation occurs. Also, we found significant variation in bending and stretching vibrations of O-H and microstructure in this material prepared in H2O and EG. Two types of O-H stretching frequencies are observed at 3450 and 3520cm(-1) in H2O medium prepared sample which are assigned to the O-H having the hydrogen bonding (surface water) and the confined water, respectively. The formation of nanorods is due to the presence of water on the surface of particles or/and inside the pores of compound. The available water in the nanoparticles pores can be utilized for the efficient killing of mass cells tumor by generating reactive free radicals (H-center dot and OH center dot) through the application of laser near infrared (NIR) source and the subsequent irradiation of gamma ray. This proposed mechanism is quite different from the conventional treatment of mass cell/malignant tumor using gamma ray radiation. Sample is highly paramagnetic and it will be useful for magnetic resonance imaging contrast agent. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731644

Ce3+-Sensitized GdPO4:Tb3+ Nanorods: An Investigation on Energy Transfer, Luminescence Switching, and Quantum Yield

Herein we report the enhanced green emission from Tb3+-doped GdPO4 nanorods sensitized with Ce3+. The increase in the rate of nonradiative transition processes in sensitizer due to efficient energy transfer to activator is realized from steady-state and dynamic luminescence studies. Luminescence quenching due to cross relaxation is least significant up to 20 at. % Ce3+ and 7 at. % Tb3+ concentration. The quantum yield of the sample with maximum luminescence, i.e., GdPO4:Tb3+ (5 at. %)/Ce3+ (7 at. %), is found to be 28%. Also, samples are readily redispersible in water and could be easily incorporated in polymer-based films that show strong green light emission under UV excitation. The luminescence switching (ON and OFF) behavior is examined using alternately an oxidizing agent (KMnO4) and then a reducing agent (ascorbic acid) through a redox reaction (Ce3+/Ce4+). Both GdPO4:Tb3+ and GdPO4:Tb3+/Ce3+ are observed to be paramagnetic

Enhanced specific absorption rate in silanol functionalized Fe3O4 core-shell nanoparticles: Study of Fe leaching in Fe3O4 and hyperthermia in L929 and HeLa cells

Core-shell Fe3O4-SiO2 magnetic nanoparticles (MNPs) have been synthesized using a simple synthesis procedure at different temperatures. These MNPs are used to investigate the effect of surface coating on specific absorption rate (SAR) under alternating magnetic field. The temperature achieved by silica coated Fe3O4 is higher than that by uncoated MNPs (Fe3O4). This can be attributed to extent of increase in Brownian motion for silica coated MNPs. The sample prepared at optimized temperature of 80 degrees C shows the highest SAR value of 111 W/g. It is found that SAR value decreases with increase in shell thickness. The chemical stability of these samples is analyzed by leaching experiments at pH 2-7. The silica coated samples are stable up to 7 days even at pH 2. Biocompatibility of the MNPs is evaluated in vitro by assessing their cytotoxicity on L929 and human cervical cancer cells (HeLa cells) using sulforhodamine-B assay. Their hyperthermic killing ability is also evaluated in HeLa cells using the same method. Cells treated with MNPs along with induction heating show decrease in viability as compared to that without induction heating. Further, cell death is found to be similar to 55% more in cells treated with silica coated MNPs under induction heating as compared to untreated control. These results establish the efficacy of Fe3O4-SiO2 prepared at 80 degrees C in killing of tumor cells by cellular hyperthermia. (C) 2014 Elsevier B.V. All rights reserved