Barium molybdate nanoparticles exhibiting up-conversion luminescence were synthesized via the solvothermal method. Analysis revealed a prominent signal corresponding to the (112) plane in the XRD pattern, indicating the tetragonal structure of the synthesized nanoparticles. Raman spectroscopy detected the symmetric stretching frequencies of MoO4. When excited at 980 nm, the nanoparticles emitted a green spectrum with peaks at 532 and 553 nm. The luminescence intensity varied with the excitation light source, supporting the mechanism involving energy transfer from Yb-doped Er ions via the two-photon effect of the up-conversion phosphor. Moreover, the synthesized nanoparticles exhibited diminished luminous intensity with increasing temperature, suggesting potential for flexible composite sensor fabrication. Integration with a 980 nm LED chip yielded a green emission color. Furthermore, when applied to banknotes, plastic cards, fabrics, and artwork, the opaque solution mixed with polymers remained invisible to the naked eye; however, under 980 nm laser irradiation, the distinct green color became apparent, offering a viable approach for anti-counterfeiting measures.
Thermally stable SrWO4:[Er3+]/[Yb3+] upconversion phosphors were synthesized. X-ray diffraction analysis indicated a crystalline inorganic phosphor material with a tetragonal structure having a clear peak in the (112) phase, which is the main peak. The upconversion phosphor was synthesized using a precursor prepared by co-precipitation and sintered at 800 °C. When the phosphor was excited by a 980 nm laser with a pumping power of 200 mW, a strong green light was emitted. As the concentration of Er3+ ions increased, it was observed that the emission intensity decreased due to concentration quenching. The changes in the intensity of luminescence according to the pumping power are due to a two-photon process. As the temperature increased, the green emission intensity of the up-conversion phosphor increased. This was thought to be a phenomenon caused by efficient energy transfer between Yb3+ and Er3+ ions by the SrWO4 host with negative thermal expansion. A composite was prepared by mixing phosphor powder and PDMS, that could be used for temperature sensing.
Crystalline BaMoO4:Dy3+ and BaMoO4:Sm3+ phosphors were synthesized by co-precipitation at room temperature. The main peak (112) phase and tetragonal structure were confirmed using X-ray diffraction analysis. The lattice constant and Raman signal on d (112) were changed by the rare earth doping. A strong absorption wavelength appeared in the UV region, and BaMoO4:Dy3+ excited with UV wavelength showed a yellow spectrum. BaMoO4:Sm3+ showed a reddish orange spectrum. BaMoO4:[Sm3+]/[Dy3+] was synthesized for use as a white light phosphor, and the change in the emission characteristics of yellow, white, and reddish orange could be observed depending on the doping concentration of Sm3+ ions. The synthesized phosphor powder and PDMS polymer were mixed to form a flexible composite, and when applied on a UV-LED chip, the same color as the powder was realized, suggesting its use as an LED color filter.
The precursor prepared by co-precipitation method was sintered at various temperatures to synthesize crystalline manganese tungstate (MnWO4). Sintered MnWO4 showed the best crystallinity at a sintering temperature of 800 °C. Rare earth ion (Dysprosium; Dy3+) was added when preparing the precursor to enhance the magnetic and luminescent properties of crystalline MnWO4 based on these sintering temperature conditions. As the amount of rare earth ions was changed, the magnetic and luminescent characteristics were enhanced; however, after 0.1 mol.%, the luminescent characteristics decreased due to the concentration quenching phenomenon. In addition, a composite was prepared by mixing MnWO4 powder, with enhanced magnetism and luminescence properties due to the addition of dysprosium, with epoxy. To one of the two prepared composites a magnetic field was applied to induce alignment of the MnWO4 particles. Aligned particles showed stronger luminescence than the composite sample prepared with unsorted particles. As a result of this, it was suggested that it can be used as phosphor and a photosensitizer by utilizing the magnetic and luminescent properties of the synthesized MnWO4 powder with the addition of rare earth ions.
LaGaO3:Er3+, Yb3+ powder with different Er3+ contents (0.01~0.10 mol) was synthesized by a conventional solid-state reaction. The structure, morphology and photoluminescence properties of the as-prepared phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and fluorescence spectrophotometer techniques, respectively. The photoluminescence (PL) emissions based on the green emission near 522 and 544 nm were observed and the highest emission intensity occurred for the sample LaGaO3:Yb0.15, Er0.07. The green and red up-conversion emissions were observed in Er3+, Yb3+ co-doped LaGaO3 phosphors under the excitation of 980 nm laser diode.
A series of new double perovskite tungstate Ba2CaWO6:xDy(3+) (0.01⩽x⩽0.15) phosphors were synthesized via solid state reaction process. XRD analysis confirmed the phase formation of Ba2CaWO6:Dy(3+) materials. The photoluminescence excitation and emission spectra, concentration effect, thermal-quenching, and decay property were investigated. The phosphor could be excited by the UV light region from 250 to 400 nm, and it exhibits blue (493 nm) and yellow (584 nm) emission corresponding to (4)F(9/2)-(6)H(15/2) transitions and (4)F9/2-(6)H13/2 transitions, respectively. The optimum dopant concentration of Dy(3+) ions in Ba2CaWO6:xDy(3+) is around 5 mol% and the critical transfer distance of Dy(3+) is calculated as 14 Å. The thermal-quenching temperature is 436 K for Ba2CaWO6:0.05Dy(3+). The fluorescence lifetime is also determined in Ba2CaWO6:0.05Dy(3+).
Barium/chemistry , Calcium/chemistry , Dysprosium/chemistry , Luminescence , Phosphites/chemistry , Temperature , Tungsten Compounds/chemistry , Microscopy, Electron, Scanning , Spectrometry, Fluorescence , X-Ray Diffraction
Eu(3+)-activated novel alkaline earth metal (Sr and Ca) vanadate phosphors, Na(Sr(0.97-x), Ca(x))VO4:Eu0.03(3+) (x = 0 to 0.97) has been successfully synthesized using solid state reaction method and characterized by XRD, XPS, FE-SEM, luminescence (PLE, PL and CIE coordinate) and decay rate measurements as a function of Ca ion concentration. Phosphors show a broad excitation band (monitored for (5)D0 --> (7)F2 transition of Eu(3+)) in the 230-430 nm wavelength regions which make them highly suitable for LED chips. Material gives strong emission of Eu(3+) ion (λex = 323 nm) and intensity of this emission increases with increase in the doping concentration of Ca ions until a maximum is reached for Na(Sr0.22, Ca0.75)VO4:Eu0.03(3+) (x = 0.75) phase phosphor. The intensity ratio of (5)D0 --> (7)F2 to (5)D0 --> (7)F1 transition (monochromaticity, R) suggest that local symmetry around the Eu(3+) ion increases with increase in Ca ion concentration, which is responsible for enhanced emission.
A rare-earth metal ion (Eu3+) doped ZnO nanocomposites have been successfully synthesized by employing wet chemical procedure using multi-wall carbon nanotubes (MWCNT's) as removable template. The preparation was carried out by immersing empty and dried MWCNT's in a stoichiometric composition of zinc nitrate and europium nitrate solution followed by filtration and sintering. The synthesized Eu3+ doped ZnO nanocomposites were characterized by means of different characterization techniques namely XRD, SEM, EDS, FT-IR and Raman spectroscopy. The XRD profile of the Eu3+ doped ZnO nanocomposites indicated its hexagonal nature while the photoluminescent analysis reveals that the prepared nanocomposite exhibits a strong red emission peak at 619 nm due to 5D0 --> 7F2 forced electric dipole transition of Eu3+ ions. Such luminescent materials are expected to find potential applications in display devices.
Europium/chemistry , Luminescent Measurements/methods , Metal Nanoparticles/chemistry , Metal Nanoparticles/ultrastructure , Zinc Oxide/chemistry , Materials Testing , Particle Size , Surface Properties
Y6(WMo)(0.5)O12 activated with Eu(3+) ions was investigated as a red-emitting conversion phosphor for white light emitting diodes (WLEDs). The phosphors were synthesized by calcining a citrate-complexation precursor at different temperatures. The photoluminescence properties of the phosphors and the energy transfer mechanisms involved were studied as a function of structure evolution. It was found that the host lattices were crystallized in a cubic or a hexagonal phase depending on the synthesis conditions. Although all the phosphors showed intensive red emission under an excitation of near-UV or blue light due to energy transfer from the host lattices to Eu(3+) ions, the photoluminescence spectra and temporal decay features were found to vary significantly with the structure and crystallinity of the host lattice. The mechanisms of the energy transfer from the host lattices to Eu(3+) ions and energy quenching among Eu(3+) ions were discussed on the basis of structure evolution of the host lattice. Phosphors calcined at 800 and 1300 °C were suggested to be promising candidates for blue and near-UV light excited WLEDs, respectively.
Eu3+ activated NaSr(P,V)O4 phosphors have been synthesized using solid state reaction method and further characterized for their structure and optical properties using different techniques such as X-ray diffraction, scanning electron microscopy, photolumniscenec excitation, emission, and chromaticity coorrdinate analysis, etc. Material shows a broad excitation peak (monitored for lambda(ems) = 613 nm) lying in the 300-360 nm region and gives intense transitions (lambda(exc) = 320 nm) namely 5D0 --> 7F1 at 590 nm, 5D0 --> 7F2 at 613 nm, 5D0 --> 7F3 at 650 nm, and 5D0 --> 7F4 at 700 nm due to Eu3+ ion. Our results show that replacement of the PO4(3-) ions with isomorphic VO4(3-) ions improves the structural stability and the overall intensity of the emission. The maxium emission intensity is achieved for the NaSr(P0.4, V0.6)O4:Eu3+ phosphor. An estimated increase of an order is attained for the NaSr(P0.4, V0.6)O4:Eu3+ phosphor as compared to NaSrPO4:Eu3+ or NaSrVO4:Eu3+ phosphor. The chromaticity coordinate of the phosphor (0.68, 0.31) lies well within the red region and suggest that the material could be an alternative red phosphor for lighting and display applications.
Al contents have been doped as a sensitizer to improve the luminescent brightness, and the conventional solid state reaction method has been used to synthesize the phosphors. Al doping effects on the microstructures of YVO4:Eu3+ phosphors were measured by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The luminescent characteristics were characterized by photoluminescence excitation (PLE) and emission (PL) measurements. Incorporation of Al3+ ions into the YVO4:Eu phosphors has greatly enhanced the crystallinity, particle size and hence the luminescence properties and the optimum concentration in Al dopants are found to be 0.05 mol. The photoluminescence intensity of 0.05 mol Al(3+)-doped YVO4:Eu3+ phosphors was improved by a factor of 1.41, in comparison with undoped Y0.95Eu0.05VO4 phosphor. The improvement in photoluminescence properties with Al doping may result from the improved crystallinity and from the enlarged grain sizes inducing lower scattering loss.
By SF6 gas incorporation for relatively short time during the initial deposition stage, carbon coils could be formed on nickel catalyst layer-deposited silicon oxide substrate using C2H2 and H2 as source gases under thermal chemical vapor deposition system. The characteristics (formation density and morphology) of as-grown carbon coils were investigated as a function of SF6 flow injection time. 5-min SF6 flow injection time is appropriate to produce the dominant microsized geometry for carbon coils without the appearance of the nanosized carbon coils. The geometry for the microsized carbon coils follows a typical double-helix structure and the shape of the rings constituting the coils is a flat-type. Fluorine's intrinsic etching characteristics for the nanosized carbon coils during the initial deposition stage seems to be the cause for the dominant formation of the microsized carbon coils in the case of 5-min SF6 flow injection time.
A novel phosphor namely CaLa2ZnO5 doped with Eu3+ ions were prepared by conventional solid state reaction method. We have studied and optimized various constraints like sintering temperature, sintering time and dopant concentration. XRD, SEM profiles have been studied to explore its structural properties. Luminescence properties of these phosphors have been characterized by means of their photoluminescence (PL) spectra. We have noticed that the emission intensity of CaLa2ZnO5:Eu3+ phosphors strongly depend on its sintering temperature and Eu3+ concentration. Moreover, their PL spectra reveals that CaLa2ZnO5:Eu3+ phosphors exhibits a strong luminescence of 5D(0)_7F(2) transition at 627 nm under the excitation of 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The obtained results of the prepared Eu3+ doped phosphors are very much encouraging and they are potentially useful in the development of new solid-state lightning devices.
Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Nickel catalyst layer deposition and then hydrogen plasma pretreatment were performed prior to the carbon coils deposition reaction. According to the different reaction processes, the injection time of SF6 gas flow was varied. The characteristics (formation density, morphology, and geometry) of the deposited carbon coils on the substrates were investigated according to the different reaction processes. Finally, the large-scale synthesis of carbon coils and their geometry control could be achieved merely by manipulating SF6 gas flow injection time. Three cases growth aspects were proposed according to SF6 gas flow injection time in association with the fluorine's characteristics for etching the materials or enhancing the nucleation sites.
Lu(6)WO(12) and Lu(6)MoO(12) doped with Eu(3+) ions have been prepared by using a citrate complexation route, followed by calcination at different temperatures. The morphology, structure, and optical and photoluminescence properties of the compounds were studied as a function of calcination temperature. Both compositions undergo transitions from a cubic to a hexagonal phase when the calcination temperature increases. All the compositions have strong absorption of near-UV light and show intense red luminescence under a near-UV excitation, which is related to the transfer of energy from the host lattices to dopant Eu(3+) ions. Density functional theory calculations have also been performed. The calculation reveals that hexagonal Lu(6)WO(12) and Lu(6)MoO(12) are indirect bandgap materials, and the near-UV excitations are due to the electronic transitions from the O-2p orbitals to W-5d and Mo-4d orbitals, respectively. The lattice parameters and bandgap energies of hexagonal Lu(6)WO(12) and Lu(6)MoO(12) were determined.
Eu(3+)-doped tetragonal and monoclinic ZrO2 (called t-ZrO2:Eu and m-ZrO2:Eu, respectively) nanoparticles were prepared using the Pechini sol-gel process. The samples were characterized via X-ray diffraction (XRD) and field-emission-scanning electron microscopy (FE-SEM), and with photoluminescence spectra. The influences of the Eu3+ concentration and the fired temperature on the crystal phase composition of the tetragonal and monoclinic ZrO2:Eu were reported. The typical interesting photoluminescence (PL) properties of the t-ZrO2:Eu and m-ZrO2:Eu nanoparticles were presented. In the t-ZrO2:Eu and m-ZrO2:Eu, the main emission peaks were at 607 and 615 nm, respectively, both of which originated from the 5D0-7F2 transition. The excitation band of the t-ZrO2:Eu powder with a lower Eu3+ doping concentration that was obtained at a low temperature (450 degrees C) consisted of a broad band of 230-500 nm. Both broad excitation bands in the t-ZrO2:Eu and m-ZrO2:Eu were ascribed to the O(2-) - Eu3+ charge transfer (CT) transition. The reason was discussed based on the relationship between the CT energy and its crystal structure. The CT energy of m-ZrO2:Eu is higher than that of t-ZrO2:Eu. A detailed chemical bond analysis was performed to explore the CT energy difference between t-ZrO2: Eu and m-ZrO2:Eu.
