Synthesis of Nanocrystals of Long Persisting Phosphor by Modified Combustion Technique

Synthesis and characterization of Nanocrystalline long persistent SrAl2O4:Eu2+, Dy3+ phosphor via a modified combustion process has been presented in the paper. In this synthesis process, a mixture of respective metal nitrates, flux and combustible agent (urea/camphor) were thermally treated with slight modification at 400-600oC for about 5 minutes. It resulted in low-density voluminous mass in contrast to a solid lump by conventional solid-state method. The present work reports the changes made in the combustion process to achieve the homogenous incorporation of dopants and large-scale production of the nanophosphor in a short interval of time. The samples have been characterized for nanophase, structural and luminescent properties. PACS Code: 33.50.-j, 33.50.Dq, 78.55.-m, 68.37.HkComment: 15 pages with figures. Submitted to Journal of Crystal Growt

Fabrication and Electro-optic Properties of MWCNT Driven Novel Electroluminescent Lamp

We present a novel, cost-effective and facile technique, wherein multi-walled carbon nano-tubes (CNTs) were used to transform a photoluminescent material to exhibit stable and efficient electroluminescence (EL) at low-voltages. As a case study, a commercially available ZnS:Cu phosphor (P-22G) was combined with a very low concentration of CNTs dispersed in ethanol and its alternating current driven electroluminescence (AC-EL) is demonstrated. The role of CNTs has been understood as a local electric field enhancer and facilitator in the hot carrier injection inside the ZnS crystal to produce EL in the hybrid material. The mechanism of EL is discussed using an internal field emission model, intra-CNT impact excitation and the recombination of electrons and holes through the impurity states.Comment: 9 Figure

Highly emissive and low refractive index layers from doped silica nanospheres for solar cell applications

Confinement of europium (Eu3+) ions in silica (SiO2) nanospheres yields efficient red-emitting nanophosphors when excited via charge transfer states (CTS) absorption in UV (393 nm) radiation. This is explained on the basis of modulation of f–f transition due to quantum confinement of rare-earth ion in a nanosize host. It is also evidenced that the short range crystallanity and confinement effects provided by the nanospheres increases the Eu3+ emission intensity by almost ten times at the expense of CTS. Coating of organically modified SiO2 nanospheres resulted in low refractive index layers that are highly useful as cover glazing for solar collectors

Fabrication and electro-optic properties of a MWCNT driven novel electroluminescent lamp

We present a novel, cost-effective and facile technique, wherein multi-walled carbon nanotubes (CNTs) were used to transform a photoluminescent material to exhibit stable and efficient electroluminescence (EL) at low voltages. As a case study, a commercially available ZnS:Cu phosphor (P-22G having a quantum yield of 65 +/- 5%) was combined with a very low (similar to 0.01 wt%) concentration of CNTs dispersed in ethanol and its alternating current driven electroluminescence (AC-EL) is demonstrated. The role of CNTs has been understood as a local electric field enhancer and facilitator in the hot carrier injection inside the ZnS crystal to produce EL in the hybrid material. The mechanism of EL is discussed using an internal field emission model, intra-CNT impact excitation and the recombination of electrons and holes through the impurity states

Synthesis and Characterization of Highly Fluorescent Water Dispersible ZnO Quantum Dots

We report the synthesis of stable and water dispersible fluorescent zinc oxide (ZnO) quantum dots (QDs). Hydrophilic polyethyleneimine (PEI) was used to stabilize QDs in water and trisodiumcitrate was used as linker between ZnO and PEI. X-ray diffraction reveals the nanocrystalline nature and hexagonal wurtzite structure of as synthesized ZnO QDs. High-resolution transmission electron micrograph suggests nearly spherical particles of size 3-6 nm and lattice spacing of 0.28 nm corresponding to the (100) plane of zinc oxide. Water dispersed ZnO QDs exhibit efficient yellow-green fluorescence centered at 555 nm (2.23 eV) with an excitation wavelength of 360 nm, which is found to be stable for two month revealing the high stability of QDs in water

Mean particle size determination of ground sugar using near infrared diffuse reflectance spectroscopy

Near infrared (NIR) diffuse reflectance spectroscopy is used for the measurement of size of sugar granules. Commercially available sugar samples were procured from the market and were ground using a home grinder to yield samples with varying particle size. The lot was subjected to differential sieving to create a set of hundred and ten samples. The mean particle size values of all the samples were determined using laser particle size analyzer and were used as reference values for calibration. NIR spectra of all the samples were recorded in diffuse reflectance mode. Partial least squares (PLS) chemometric method was applied for calibration. A separate set of twelve samples was created in a similar manner for prediction. Mean particle size values of all the samples in prediction set was also determined using laser technique and their near Infrared spectra were recorded. The mean particle size values of these samples were predicted using the derived calibration curve and were compared with laser reference values. A good correlation was obtained between NIR predicted values and laser reference values. The present work demonstrates that the near infrared diffuse reflectance spectroscopic technique can be successfully applied for determination of particle size of sugar

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ∼170% and attained a saturation value after ∼100 min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200 °C) and pressures (∼120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation

Intense red-emitting Y4Al2O9:Eu3+phosphor with short decay time and high color purity for advanced plasma display panel

A new phosphor Y4Al2O9:Eu3+ (YAM:Eu3+) emitting intense monochromatic red at 612 nm under vacuum ultraviolet (VUV) and ultraviolet (UV) excitations has been developed for application in next generation plasma display panels (PDPs). The developed phosphor has better luminescence efficiency, colour purity and shorter decay time than commercial (Y,Gd)BO3:Eu3+ red emitting PDP phosphor. High color purity (x = 0.67, y = 0.32) under VUV excitation with short decay time (1.03 msec) and excellent stability against degradation during PDP panel preparation suggest that YAM:Eu3+ is a potential candidate for present and future PDPs. Surface coating by SiO2 further improved phosphor characteristics