Studies on a novel SrZr2 CaLa2 O8 :Eu3+ phosphor for lighting applications emitting direct white light.

Direct white light emitting phosphors play a significant role in the display industry due to their ability to improve the quality, efficiency, and versatility of lighting sources used in most of the displays. The currently investigated phosphor SrZr2 CaLa2 O8 :Eu3+ was prepared by a conventional solid-state reaction method. It has been observed that the stoichiometric ratio of all precursors plays an important role in determining the characteristics of the final phosphor. From X-ray diffraction (XRD) analysis, the phosphor was observed to have a hexagonal phase and a crystal size of ~28 nm. Scanning electron microscopy (SEM) observations revealed a cluster of rod-like structures with an average diameter of ~0.2 µm. The excitation peak maximum observed at 280 nm is due to charge transfer between Eu3+ -O2- ions. The energy transitions 7 F0 → 5 L6 and 7 F0 → 5 D2 are responsible for the appearance of other excitation peaks at ultraviolet (UV) (395 nm), blue (~467 nm), green (~540 nm), orange (~590 nm), and red (~627 nm) attributed to 5 D0 → 7 FJ (J = 0-4) transitions of europium ion (Eu3+ ). The Commercial International de I'Eclairage (CIE) chromaticity coordinates were estimated to be (0.37, 0.0.33) and (0.67, 0.33) for the emissions corresponding to 395 and 590 nm, respectively. The characteristic emissions of Eu3+ ions allow this novel phosphor to be used to generate direct white light in light-emitting diodes (LEDs), which is otherwise difficult to achieve in single-component systems.

Comparative Study of Impact of Gamma and MeV Ion Irradiations on Electrical and Optical Properties Polystyrene/Eu2O3 Nanocomposites.

In the present study, the effect of gamma irradiation and 90 MeV carbon ion beam irradiation on electrical properties and optical of Polystyrene/Eu2O3 nanocomposites at different fluences were examined. Modified electrical and optical responses of polymer nanocomposites were investigated using Impedance, Photoluminescence and UV-VIS spectroscopies. FTIR analysis shows a reduction of various modes of molecular vibrations caused by 90 MeV carbon ion beam irradiation. The polymer nanocomposites change into a graphite-like structure upon both kinds of irradiations as evidenced by the decrease in the optical band gap. The photoluminescence emission spectra show three characteristic peaks of Eu3+ ions, when excited at 247 nm wavelength. It emits intense red light suggesting its potential for usage in LED technology. The peak intensity of PL emission spectra is enhanced after ion beam irradiation and is because of the formation new radiative combination; however, it decreases upon gamma irradiation. Dielectric responses of pristine and irradiated polymer nanocomposites were studied over the frequency range of 100 Hz to 100 kHz using LCR meter. There appears a significant improvement in the dielectric response as a result of structural changes in both types of irradiations. AFM images show that the film becomes smoother upon both types of irradiations.

Luminescence studies of a Li2 Ca1-x SiO4 :xSm3+ phosphor for the generation of white light under NUV-excited phosphor converting LEDs.

In this paper, we present new aspects of Sm3+ -doped pure Li2 CaSiO4 as a suitable candidate for white light emitting diode (WLED) applications. The samples were mainly prepared using a conventional modified solid-state synthesis technique. The structural studies were done using X-ray diffraction and Rietveld refinement. Instruments such as a scanning electron microscope (SEM) were used to obtain information about the morphology of the as-prepared samples. Photoluminescence (PL) analysis of phosphor samples for variable concentrations of doping ions with variable excitations were presented. When doped with Sm3+ in host Li2 CaSiO4 it emitted intense blue, green and red emissions and a more intense red emission peak (605 nm) under 408 nm excitation (near-UV-blue). Our study shows that the as-prepared phosphor may be useful for optical devices and mainly for WLEDs. The corresponding transitions of doping ions and concentration quenching effect were studied in detail. The 1931 Commission Internationale de l'Eclairage (x, y) chromaticity coordinates showed the distribution of spectral regions calculated from PL emission spectra and this was found (0.63, 0.36) in the red region, so the phosphor may be useful for near-UV-blue excited WLED applications.

Proton Beam Induced Modification of Luminescence Properties of Polystyrene/Al2O3 Polymer Nanocomposites.

Polystyrene polymer (PS)/Al2O3 nanocomposite films were synthesized from PS:Al2O3 (1-x):x mixtures (x = 3 wt%) via solution casting method. These nanocomposite films were exposed to 5 MeV proton beam of different fluences. The proton beam induced changes in optical and luminescence properties of PS and PS:Al2O3 films have been investigated using FTIR, UV-visible, Photoluminescence and thermoluminescence studies. FTIR studies concede reduction in the peak intensity due to doping of Al2O3 and proton irradiation. The UV-visible spectra show shifting of absorption edge with increasing fluence. This can be attributed to creation of conjugated system of bonds. The band gap of PS and 3 wt% Al2O3 doped PS is observed to be 4.38 eV and 4.34 eV, respectively, whereas the band gaps of proton irradiated 3 wt% Al2O3 doped PS films are found to be 4.28 eV and 4.23 eV at the fluences of 1 × 1012 ions/cm2 and 1 × 1013 ions/cm2, respectively. The photoluminescence emission spectra show three peaks, wavelength at 411 nm, 435 nm and 462 nm corresponding to the PS in violet-blue region when excited with near UV wavelength of 380 nm. The intensity of emission peaks was found to increase with increasing fluence. The thermoluminescence curves of PS/Al2O3 were analysed using glow curve deconvolution method (GCD). The increase in TL peak intensity of the glow curve was observed as fluence increase.

Studies on the luminescence properties of cerium co-doping on Ca2 MgSi2 O7 :Eu2+ phosphor by solid-state reaction method.

Ca2 MgSi2 O7 :Ce3+ , Ca2 MgSi2 O7 :Eu2+ and Ca2 MgSi2 O7 :Eu2+ ,Ce3+ phosphors were prepared using the solid-state reaction method. The crystal structures of the sintered phosphors were of melilite type, which has a tetragonal crystallography. The chemical compositions of the sintered phosphors was confirmed by energy dispersive X-ray spectroscopy. The different thermoluminescence kinetic parameters [activation energy (E), frequency factor (s) and order of the kinetics (b)] of these phosphors were evaluated and compared using the peak shape method. Under ultraviolet excitation, the emission spectra of both Ca2 MgSi2 O7 :Eu2+ and Ca2 MgSi2 O7 :Eu2+ ,Ce3+ phosphors were composed of a broad emission band peaking at 530 nm. When the Ca2 MgSi2 O7 :Eu2+ phosphor is co-doped with Ce3+ ions, photoluminescence, afterglow and mechanoluminescence intensity was strongly enhanced. Ca2 MgSi2 O7 :Eu2+ showed some afterglow with a short persist time. On incorporation of Ce3+ , efficient energy transfer from Ce3+ to Eu2+ was found and the emission intensity of Eu2+ was enhanced. The mechanoluminescence intensities of Ca2 MgSi2 O7 :Ce3+ , Ca2 MgSi2 O7 :Eu2+ and Ca2 MgSi2 O7 :Eu2+ ,Ce3+ phosphors increased proportionally increased with the increase in impact velocity, which suggests that these phosphors can be used as sensors to detect stress in an object.

Preparation and Photoluminescence of Sm (3+) Doped YAlO 3 Phosphor.

YAlO3: Sm(3+) phosphor has been synthesized by the solid state reaction method with calcium flouride used as a flux. The resulting YAlO3: Sm(3+) phosphor was characterized by X-ray diffraction (XRD) technique, Fourier transmission infrared spectroscopy (FTIR), photoluminescence . . PL excitation spectrum was found at 254,332,380,400,407, 603 and 713 nm. Under excitation of UV(713 nm) YAlO3: Sm(3+) (0-3 %) broad band emission were observed from 400 to 790 nm with a maximum around 713 nm of YAlO3 host lattice accompanied by weak emission of Sm(3+) ((4)G5/2 - (6)H5/2, (6)H7/2,(6)H9/2) transitions. The results of the XRD show that obtained YAlO3: Sm(3+) phosphor has a orthorhombic structure. The study suggested that Sm(3+) doped phosphors are potential luminescence material for laser diode pumping and inorganic scintillators.

Study of formation of deep trapping mechanism by UV, beta and gamma irradiated Eu(3+) activated SrY2O4 and Y4Al2O9 phosphors.

This paper reports the thermoluminescence properties of Eu(3+) doped different host matrix phosphors (SrY2O4 and Y4Al2O9). The phosphor is prepared by high temperature solid state reaction method. The method is suitable for large scale production and fixed concentration of boric acid using as a flux. The prepared samples were characterized by X-ray diffraction technique and the crystallite size calculated by Scherer's formula. The prepared phosphor characterized by Scanning Electron Microscopic (SEM), Fourier Transform Infrared (FTIR), Energy Dispersive X-ray analysis (EDX), thermoluminescence (TL) and Transmission Electron Microscopic (TEM) techniques. The prepared phosphors for different concentration of Eu(3+) ions were examined by TL glow curve for UV, beta and gamma irradiation. The UV 254nm source used for UV irradiation, Sr(90) source was used for beta irradiation and Co(60) source used for gamma irradiation. SrY2O4:Eu(3+)and Y4Al2O9:Eu(3+) phosphors which shows both higher temperature peaks and lower temperature peaks for UV, beta and gamma irradiation. Here UV irradiated sample shows the formation of shallow trap (surface trapping) and the gamma irradiated sample shows the formation of deep trapping. The estimation of trap formation was evaluated by knowledge of trapping parameters. The trapping parameters such as activation energy, order of kinetics and frequency factor were calculated by peak shape method. Here most of the peak shows second order of kinetics. The effect of gamma, beta and UV exposure on TL studies was also examined and it shows linear response with dose which indicate that the samples may be useful for TL dosimetry. Formation of deep trapping mechanism by UV, beta and gamma irradiated Eu(3+) activated SrY2O4 and Y4Al2O9 phosphors is discussed in this paper.

Synthesis and Photoluminescence Studies of Eu(III), Er(III) Doped Strontium Gadolinium Tantalum Oxide.

The luminescence properties of Sr2GdTaO6 have been studied by keeping Eu(3+) as constant concentration and varying Er(3+) concentration. Sr2GdTaO6 phosphor doped with rare earth ions of Eu and Er having monoclinic phase of space group P21/n was synthesized, and their photoluminescence properties have been examined under UV excitation of wavelength 265 nm and 275 nm. PL emission exhibited around 468, 475, 580, 596, and 610 nm wavelength subsequently for various concentrations of Er(3+) for two different excitation wavelengths. By using xenon lamp as source and corresponding wavelength having excitation wavelength 265 and 275 nm, it is observed that the maximum light emission yield in region presenting a color-correlated temperature in the range of 1500-1900 K and 3000-6000 K.

Blue excitable green emitting Ce(3+) doped CaS phosphor for w-LEDs.

CaS:Ce(3+) is an efficient green-emitting (535 nm) phosphor, excitable with blue light (450-470 nm) and was synthesized via a solid-state reaction method by heating under a reducing atmosphere. The luminescent properties, photoluminescent (PL) excitation and emission of the phosphor were analyzed by spectrofluorophotometry. The excitation and emission peaks of the CaS:Ce(3+) phosphor lay in the visible region, which made them relevant for light-emitting diode (LED) application for the generation of white light. Judd-Oflet parameters were calculated and revealed that green light emitted upon blue illumination. The prepared phosphor had strong blue absorption at 470 nm and a broad green emission band range from 490-590 nm with the peak at 537 nm. The characteristics of the CaS:Ce(3+) phosphor make it suitable for use as a wavelength tunable green emitting phosphor for three band white LEDs pumped by a blue LED (470 nm). The Commission International de l'Eclairage co-ordinates were calculated by a spectrophotometric method using the spectral energy distribution (0.304, 0.526) and confirm the green emission. The potential application of this phosphor is as a phosphor-converted white light-emitting diode.

Luminescence study and dosimetry approach of Ce on an α-Sr2 P2 O7 phosphor synthesized by a high-temperature combustion method.

We report synthesis of a cerium-activated strontium pyrophosphate (Sr2 P2 O7 ) phosphor using a high-temperature combustion method. Samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and thermoluminescence (TL). The XRD pattern reveals that Sr2 P2 O7 has an α-phase with crystallization in the orthorhombic space group of Pnam. The IR spectrum of α-Sr2 P2 O7 displays characteristic bands at 746 and 1190 cm(-1) corresponding to the absorption of (P2 O7 )(-4) . PL emission spectra exhibit a broad emission band around 376 nm in the near-UV region due to the allowed 5d-4f transition of cerium and suggest its applications in a UV light-emitting diode (LED) source. PL also reveals that the emission originates from 5d-4f transition of Ce(3+) and intensity increases with doping concentration. TL measurements made after X-ray irradiation, manifest a single intense glow peak at around 192°C, which suggests that this is an outstanding candidate for dosimetry applications. The kinetic parameters, activation energy and frequency factor of the glow curve were calculated using different analysis methods.

Development and validation of new discriminative dissolution method for carvedilol tablets.

The objective of the present study was to develop and validate a discriminative dissolution method for evaluation of carvedilol tablets. Different conditions such as type of dissolution medium, volume of dissolution medium and rotation speed of paddle were evaluated. The best in vitro dissolution profile was obtained using Apparatus II (paddle), 50 rpm, 900 ml of pH 6.8 phosphate buffer as dissolution medium. The drug release was evaluated by high-performance liquid chromatographic method. The dissolution method was validated according to current ICH and FDA guidelines using parameters such as the specificity, accuracy, precision and stability were evaluated and obtained results were within the acceptable range. The comparison of the obtained dissolution profiles of three different products were investigated using ANOVA-based, model-dependent and model-independent methods, results showed that there is significant difference between the products. The dissolution test developed and validated was adequate for its higher discriminative capacity in differentiating the release characteristics of the products tested and could be applied for development and quality control of carvedilol tablets.

Synthesis, characterization and photoluminescence properties of CaSiO3:Eu3+ red phosphor.

CaSiO3:Eu3+ (1-5 mol%) red emitting phosphors have been synthesized by a low-temperature solution combustion method. The phosphors have been well characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical spectroscopy. PXRD patterns reveal monoclinic CaSiO3 phase can be obtained at 900°C. The SEM micrographs show the crystallites with irregular shape, mostly angular. Upon 254 nm excitation, the phosphor show characteristic fluorescence 5D0→7FJ (J=0, 1, 2, 3, 4) of the Eu3+ ions. The electronic transition located at 614 nm corresponding to 5D0→7F2 of Eu3+ ions, which is stronger than the magnetic dipole transition located at 593 nm corresponding to 5D0→7F1 of Eu3+ ions. Different pathways involved in emission process have been studied. Concentration quenching has been observed for Eu3+ concentration>4 mol%. UV-visible absorption shows an intense band at 240 nm in undoped and 270 nm in Eu3+ doped CaSiO3 which is attributed to oxygen to silicon (O-Si) ligand-to-metal charge-transfer (LMCT) band in the SiO3(2-) group. The optical energy band gap is widened with increase of Eu3+ ion dopant.

Tablet formulation studies on nimesulide and meloxicam-cyclodextrin binary systems.

The objective of this work was to develop tablet formulations of nimesulide-beta-cyclodextrin (NI-beta-CD) and meloxicam-gamma-cyclodextrin (ME-gamma-CD) binary systems. In the case of nimesulide, 3 types of binary systems--physical mixtures, kneaded systems, and coevaporated systems--were studied. In the case of meloxicam, 2 types of binary systems--physical mixtures and kneaded systems--were investigated. Both drug-CD binary systems were prepared at 1:1 and 1:2 molar ratio (1:1M and 1:2M) and used in formulation studies. The tablet formulations containing drug-CD binary systems prepared by the wet granulation and direct compression methods showed superior dissolution properties when compared with the formulations of the corresponding pure drug formulations. Overall, the dissolution properties of tablet formulations prepared by the direct compression method were superior to those of tablets prepared by the wet granulation method. Selected tablet formulations showed good stability with regard to drug content, disintegration time, hardness, and in vitro dissolution properties over 6 months at 40 degrees C +/- 2 degrees C and 75% relative humidity.

Thermoluminescence dosimetric characteristics of beta irradiated salt.

The thermoluminescence (TL) characteristics of sodium chloride (NaCl), known as common salt, used for cooking purposes (iodised salt), have been studied in the present paper considering its usage as an 'accidental dosemeter' in the case of a nuclear fallout. TL characteristics of common salt have been examined under excitation with a beta dose of 20 Gy from a 90Sr beta source. The salt specimens are used in the form of discs. The average salt grain that sticks to the disc is measured to be approximately 1 mg. The TL of the beta irradiated salt is recorded in the conventional TL apparatus. Initially three peaks were observed at 133, 205 and 238 degrees C. All three peaks are well resolved, having maximum intensity at 238 degrees C. The material under investigation, i.e. 'common salt' possesses many good dosimetric properties and therefore this can be considered as an 'accidental dosemeter'.

Compact fluorescent lamp phosphors in accidental radiation monitoring.

The application of lamp phosphors for accidental dosimetry is a new concept. Since the materials used in fluorescent lamps are good photo luminescent materials, if one can either use the inherent defects present in the phosphor or add suitable modifiers to induce thermoluminescence (TL) in these phosphors, then the device (fluorescent lamp) can be used as an accidental dosemeter. In continuation of our search for a suitable phosphor material, which can serve both as an efficient lamp phosphor and as a good radiation monitoring device, detailed examination has been carried out on cerium and terbium-doped lanthanum phosphate material. A (90)Sr beta source with 50 mCi strength (1.85 GBq) was used as the irradiation source for TL studies. The TL response as a function of dose received was examined for all phosphors used and it was observed that the intensity of the TL peak vs. dose received was a linear function in the dose range 0.1-200 Gy in each case. Incidentally LaPO(4): Ce,Tb is a component of the compact fluorescent lamp marketed recently as an energy bright light source. Besides having very good luminescence efficiency, good dosimetric properties of these phosphors render them useful for their use in accidental dosimetry also.

Physicochemical characterization and dissolution properties of meloxicam-cyclodextrin binary systems.

The objective of the work is physicochemical characterization of meloxicam (ME)-cyclodextrin (CD) binary systems both in solution and solid states and to improve the dissolution properties of meloxicam via complexation with alpha-, beta- and gamma-cyclodextrins. Detection of inclusion complexation was done in solution state by means of phase solubility analysis, mass spectrometry and 1H nuclear magnetic resonance (NMR) studies, and in solid state using differential scanning calorimetry (DSC), powder X-ray diffractometry, and in vitro dissolution studies. Phase solubility, mass spectrometry and 1H NMR studies in solution state revealed 1:1M complexation of meloxicam with all CDs. A true inclusion of ME with gamma-CD at 1:1 and 1:2M in solid state was confirmed by DSC, powder XRD and scanning electron microscopy (SEM) studies. Dissolution properties of ME-CDs binary systems were superior when compared to pure ME.

Physicochemical characterization and dissolution properties of nimesulide-cyclodextrin binary systems.

The objective of this work is physicochemical characterization of nimesulide-cyclodextrin binary systems both in solution and solid state and to improve the dissolution properties of nimesulide (N) via complexation with alpha-, beta, and gamma-cyclodextrins (CDs). Detection of inclusion complexation was done in solution by means of phase solubility analysis, mass spectrometry, and 1H nuclear magnetic resonance (1H-NMR) spectroscopic studies, and in solid state using differential scanning calorimetry (DSC), powder x-ray diffractometry (X-RD), scanning electron microscopy (SEM), and in vitro dissolution studies. Phase solubility, mass spectrometry and 1H-NMR studies in solution revealed 1:1 M complexation of N with all CDs. A true inclusion of N with beta-CD at 1:2 M in solid state was confirmed by DSC, powder X-RD and SEM studies. Dissolution properties of N-CD binary systems were superior when compared to pure N.