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Counterfeiting is a major current concern throughout the world, and recent technological advances have made counterfeiting of sophisticated products easy. It is therefore essential to develop further means to combat counterfeiting, including the use of new luminescent materials for security inks. Here, we report the synthesis by a sol–gel technique of a highly luminescent YBO3:Eu3+ phosphor, which can be scaled up to 1 kg amounts in single batches. This phosphor is both structurally and chemically stable and has a particle size of 110 ± 10 nm. It emits strongly at a wavelength of 591 nm (orange–red) upon excitation at a wavelength of 245 nm and is also excitable by wavelengths in the 280–480 nm range. The structural and microstructural characteristics and the photoluminescence behavior of the phosphor were characterized by SEM, TEM/HRTEM, and fluorescent spectroscopy, respectively. The phosphor was used with a commercially available PVC gold medium to produce a luminescent security ink for printing security codes, and the results were investigated by photoluminescence mapping instruments. TheYBO3: Eu3+ phosphor-based security ink described here provides a low-cost material for use in printing security codes that are easy to detect but difficult to counterfeit.Counterfeiting is a major current concern throughout the world, and recent technological advances have made counterfeiting of sophisticated products easy. It is therefore essential to develop further means to combat counterfeiting, including the use of new luminescent materials for security inks. Here, we report the synthesis by a sol–gel technique of a highly luminescent YBO3:Eu3+ phosphor, which can be scaled up to 1 kg amounts in single batches. This phosphor is both structurally and chemically stable and has a particle size of 110 ± 10 nm. It emits strongly at a wavelength of 591 nm (orange–red) upon excitation at a wavelength of 245 nm and is also excitable by wavelengths in the 280–480 nm range. The structural and microstructural characteristics and the photoluminescence behavior of the phosphor were characterized by SEM, TEM/HRTEM, and fluorescent spectroscopy, respectively. The phosphor was used with a commercially available PVC gold medium to produce a luminescent security ink for printing securi...

Biocompatible nanoparticles, with magnetic cores and optically active shells, acting as multifunctional materials with a core size of 6 nm encapsulated in silver shells of varying thickness were synthesized through a novel single phase microemulsion method. Incorporation of silver shells onto the magnetite core enhances the intensity of the highest luminescence peak observed for magnetite by a significant luminescence enhancement factor. A blue photoluminescence peak observed in the visible region of spectrum brightens further with the increase in the thickness of silver shell. The magnetic properties of these core-shell nanomaterials show superparamagnetic behavior at room temperature, which is a mandatory criterion for MRI contrast enhancement agents. The hyperthermic response of synthesized magnetite nanoparticles elevates its temperature to 43 °C in a sharp span of time, which is above the desired temperature for the therapeutic application of these multifunctional nanomaterials. These excellent optical and magnetic properties, of the material having a size range suitable for cellular uptake, make it a potential candidate for both diagnostic and therapeutic uses in biomedical applications.Biocompatible nanoparticles, with magnetic cores and optically active shells, acting as multifunctional materials with a core size of 6 nm encapsulated in silver shells of varying thickness were synthesized through a novel single phase microemulsion method. Incorporation of silver shells onto the magnetite core enhances the intensity of the highest luminescence peak observed for magnetite by a significant luminescence enhancement factor. A blue photoluminescence peak observed in the visible region of spectrum brightens further with the increase in the thickness of silver shell. The magnetic properties of these core-shell nanomaterials show superparamagnetic behavior at room temperature, which is a mandatory criterion for MRI contrast enhancement agents. The hyperthermic response of synthesized magnetite nanoparticles elevates its temperature to 43 °C in a sharp span of time, which is above the desired temperature for the therapeutic application of these multifunctional nanomaterials. These excellent optic...

We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C) than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

We report photoluminescence and time-resolved spectroscopy in bismuth ferrite excited with a 325 nm source. The direct-bandgap recombinations near 2.55 eV and indirect-bandgap transitions near 2.67 eV are presented as functions of applied in-plane electric field with recombination time in the microsecond regime. The applied field moves some conduction electrons away from the Brillouin zone center, increasing significantly the intensity of indirect-gap recombination. An aging phenomenon is manifest in specimens stored for more than twelve months under ambient conditions. Effect of external magnetic field on the surface phase transition is negligible up to H = 0.5 T.

Carbon nanofiber (CNF) with springlike and double-helix structures has been synthesized by catalytic thermal pyrolysis of an acetylene precursor at 850–950 °C using iron nanopowder and thiophene as catalyst and promoter, respectively. High resolution electron microscopy revealed a higher d-spacing (∼3.46 A) of (002) crystal plane than customary multiwalled carbon nanotube (MWCNT) (3.37 A) that helps in sustaining mechanical shocks better than MWCNTs. The large surface to volume ratio of springlike CNF does provide many delocalized free electrons to enhance the photoluminescence activity. Electron paramagnetic resonance signal showed a single narrow line having g-value 2.0024±0.0002 and spin contribution 3.4956×10−16 spins/g.