Search results for: nanophosphors

Authors: Hyeon Mi Noh, Ju Hyun Oh, Jung Hyun Jeong, Haeyoung Choi, Jung Hwan Kim

Abstract:

The Er³⁺/Yb³⁺/Tm³⁺ tri-doped Y₂O₃ nanophosphors were synthesized by solvothermal method and its temperature dependence of the white upconversion emission has been studied by using 975 nm laser diode. The upconversion emission spectra in 1 mol% Er³⁺/5 mol% Yb³⁺/xTm³ tri-doped Y₂O₃ nanophosphors sintered at 1000 °C with x from 0 to 0.5 mol%. The blue emission intensity increase with Tm³⁺ concentration from 0 to 0.5 mol%, it is due to the 2F7/2→2F5/2 transition of Yb³⁺ around 10,000 cm-1 could easily reach the Tm³⁺ sates. The white light is composed with the blue (1G4→3H6 of Tm³⁺), green (2H11/2, 4S3/2→4I15/2 of Er³⁺), and red (4F9/2→4I15/2 of Er³⁺) upconversion radiations. The Y₂O₃: Er³⁺/Yb³⁺/Tm³⁺ nanophosphors show from white to green upconversion emission at power of 600 mW/cm² as sintering temperature increased. The calculated Commission Internationale de l’Eclairage (CIE) coordinates can be located in the white area with various sintering temperatures, in sintered at 1000 °C, and their color coordinates are very close to the standard white-light emission (0.33, 0.33). Their upconversion processes were explained by measuring the upconversion luminescence spectra and pump power dependence and energy level diagram.

Keywords: white upconversion emission, nanophosphors, energy transfer, solvothermal method

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Authors: Mohit Kalra, Varun S., Mayuri Gandhi

Abstract:

CeF3 nanophosphors has been extensively investigated in the recent years for lighting and numerous bio-applications. Down conversion emissions in CeF3:Eu3+/Tb3+ phosphors were studied with the aim of obtaining a white light emitting composition, by a simple co-precipitation method. The material was characterized by X-ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HR-TEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Photoluminescence (PL). Uniformly distributed nanoparticles were obtained with an average particle size 8-10 nm. Different doping concentrations were performed and fluorescence study was carried out to optimize the dopants concentration for maximum luminescence intensity. The steady state and time resolved luminescence studies confirmed efficient energy transfer from the host to activator ions. Different concentrations of Tb 3+, Eu 3+ were doped to achieve a white light emitting phosphor for UV-based Light Emitting Diodes (LEDs). The nanoparticles showed characteristic emission of respective dopants (Eu 3+, Tb3+) when excited at the 4f→5d transition of Ce3+. The chromaticity coordinates for these samples were calculated and the CeF3 doped with Eu 3+ and Tb3+ gave an emission very close to white light. These materials may find its applications in optoelectronics and various bio applications.

Keywords: white light down-conversion, nanophosphors, LEDs, rare earth, cerium fluoride, lanthanides

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Authors: Badis Kahouadji, Lakhdar Guerbous, Lyes Lamiri

Abstract:

For many years, the luminescent materials were investigated principally in the infrared and visible areas, because the ultraviolet (UV) and especially in vacuum Ultraviolet (VUV) are technically more difficult to explore, especially absence of applications requiring of materials suitable to short wavelengths.Recent necessary, related to the development of certain technologies, encouraged research in these spectra domains. It is in this context that the 4Fn-4Fn-1 5d transitions of rare earth in insulating materials, lying in the UV and VUV, are the aim of large number of studies. These studies relate in particular to search for new scintillator materials used for spectroscopy and X-ray, ɤ, as well as medical imaging. The 4Fn- 4Fn-15d transitions of the rare earth dependent to the host-matrix, several matrices ions were used to study these transitions, in this work we are suggeting to study on a very specific class of inorganic scintillators that are orthophosphate doped with rare earth ions, this study focused on the Pr3+ concentration on the structural and optical properties of Pr3+ doped YPO4 (yttriumorthophosphate) with powder form prepared by the Sol Gel method.

Keywords: rare earth, scintillator, YPO4:Pr3+ nanophosphors, sol gel, 4Fn-4Fn-15d transitions

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Authors: Celestine Mbakaan, Iorkyaa Ahemen, A. D. Onoja, A. N. Amah, Emmanuel Barki

Abstract:

Rice husk (RH) is a natural sheath that forms and covers the grain of rice. The husk composed of hard materials, including opaline silica and lignin. It separates from its grain during rice milling. RH also contains approximately 15 to 28 wt % of silica in hydrated amorphous form. Nanosilica was derived from the husk of different rice varieties after pre-treating the husk (RH) with HCl and calcination at 550°C. Nanosilica derived from the husk of Osi rice variety produced the highest silica yield, and further pretreatment with 0.8 M H₃PO₄ acid removed more mineral impurities. The silica obtained from this rice variety was selected as a host matrix for doping with Sm³⁺ ions. Rice husk silica (RH-SiO₂) doped with samarium (RH-SiO₂: xSm³⁺ (x=0.01, 0.05, and 0.1 molar ratios) nanophosphors were synthesized via the sol-gel method. The structural analysis by X-ray diffraction analysis (XRD) reveals amorphous structure while the surface morphology, as revealed by SEM and TEM, indicates agglomerates of nano-sized spherical particles with an average particle size measuring 21 nm. The nanophosphor has a large surface area measuring 198.0 m²/g, and Fourier transform infrared spectroscopy (FT-IR) shows only a single absorption band which is strong and broad with a valley at 1063 cm⁻¹. Diffuse reflectance spectroscopy (DRS) shows strong absorptions at 319, 345, 362, 375, 401, and 474 nm, which can be exclusively assigned to the 6H5/2→4F11/2, 3H7/2, 4F9/2, 4D5/2, 4K11/2, and 4M15/2 + 4I11/2, transitions of Sm³⁺ respectively. The photoluminescence excitation spectra show that near UV and blue LEDs can effectively be used as excitation sources to produce red-orange and yellow-orange emission from Sm³⁺ ion-doped RH-SiO₂ nanophosphors. The photoluminescence (PL) of the nanophosphors gives three main lines; 568, 605, and 652 nm, which are attributed to the intra-4f shell transitions from the excited level to ground levels, respectively under excitation wavelengths of 365 and 400 nm. The result, as confirmed from the 1931 CIE coordinates diagram, indicates the emission of red-orange light by RH-SiO₂: xSm³⁺ (x=0.01 and 0.1 molar ratios) and yellow-orange light from RH-SiO₂: 0.05 Sm³⁺. Finally, the result shows that RH-SiO₂ doped with samarium (Sm³⁺) ions can be applicable in display applications.

Keywords: luminescence, nanosilica, nanophosphors, Sm³⁺

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Authors: G. Swati, D. Haranath

Abstract:

Commercially available long afterglow /persistent phosphors are proprietary materials and hence the exact composition and phase responsible for their luminescent characteristics such as initial intensity and afterglow luminescence time are not known. Further to generate various emission colors, commercially available persistence phosphors are physically blended with fluorescent organic dyes such as rodhamine, kiton and methylene blue etc. Blending phosphors with organic dyes results into complete color coverage in visible spectra, however with time, such phosphors undergo thermal and photo-bleaching. This results in the loss of their true emission color. Hence, the current work is dedicated studies on inorganic based thermally and chemically stable primary color emitting nanophosphors namely SrAl2O4:Eu2+, Dy3+, (CaZn)TiO3:Pr3+, and Sr2MgSi2O7:Eu2+, Dy3+. SrAl2O4: Eu2+, Dy3+ phosphor exhibits a strong excitation in UV and visible region (280-470 nm) with a broad emission peak centered at 514 nm is the characteristic emission of parity allowed 4f65d1→4f7 transitions of Eu2+ (8S7/2→2D5/2). Sunlight excitable Sr2MgSi2O7:Eu2+,Dy3+ nanophosphors emits blue color (464 nm) with Commercial international de I’Eclairage (CIE) coordinates to be (0.15, 0.13) with a color purity of 74 % with afterglow time of > 5 hours for dark adapted human eyes. (CaZn)TiO3:Pr3+ phosphor system possess high color purity (98%) which emits intense, stable and narrow red emission at 612 nm due intra 4f transitions (1D2 → 3H4) with afterglow time of 0.5 hour. Unusual property of persistence luminescence of these nanophoshphors supersedes background effects without losing sensitive information these nanophosphors offer several advantages of visible light excitation, negligible substrate interference, high contrast bifurcation of ridge pattern, non-toxic nature revealing finger ridge details of the fingerprints. Both level 1 and level 2 features from a fingerprint can be studied which are useful for used classification, indexing, comparison and personal identification. facile methodology to extract high contrast fingerprints on non-porous and porous substrates using a chemically inert, visible light excitable, and nanosized phosphorescent label in the dark has been presented. The chemistry of non-covalent physisorption interaction between the long afterglow phosphor powder and sweat residue in fingerprints has been discussed in detail. Real-time fingerprint development on porous and non-porous substrates has also been performed. To conclude, apart from conventional dark vision applications, as prepared primary color emitting afterglow phosphors are potentional candidate for developing high contrast latent fingerprints.

Keywords: fingerprints, luminescence, persistent phosphors, rare earth

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Authors: Ravindra P. Singh, Drupad Ram, Dinesh K. Gupta

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Rare earth ions doped metal oxides are a class of luminescent materials which have been proved to be excellent for applications in field emission displays and cathode ray tubes, plasma display panels. Under UV irradiation Eu+++ doped Y2O3 is a red phosphor and Tb+++ doped Y 2O3 is a green phosphor. It is possible that, due to their high quantum efficiency, they might serve as improved luminescent markers for identification of biomolecules, as already reported for CdSe and CdSe/ZnS nanocrystals. However, for any biological applications these particle powders must be suspended in water while retaining their phosphorescence. We hereby report synthesis and characterization of Eu+++ and Tb+++ doped yttrium oxide nanoparticles by sol-gel and hydrothermal processes. Eu+++ and Tb+++ doped Y2O3 nanoparticles have been synthesized by hydrothermal process using yttrium oxo isopropoxide [Y5O(OPri)13] (crystallized twice) and it’s acetyl acetone modified product [Y(O)(acac)] as precursors. Generally the sol-gel derived metal oxides are required to be annealed to the temperature ranging from 400°C-800°C in order to develop crystalline phases. However, this annealing also results in the development of aggregates which are undesirable for bio-conjugation experiments. In the hydrothermal process, we have achieved crystallinity of the nanoparticles at 300°C and the development of crystalline phases has been found to be proportional to the time of heating of the reactor. The average particle sizes as calculated from XRD were found to be 28 nm, 32 nm, and 34 nm by hydrothermal process. The particles were successfully suspended in chloroform in the presence of trioctyl phosphene oxide and TEM investigations showed the presence of single particles along with agglomerates.

Keywords: nanophosphors, Y2O3:Eu+3, Y2O3:Tb+3, sol-gel, hydrothermal method, TEM, XRD

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Authors: Mitsunobu Iwasaki, Akifumi Iseda

Abstract:

Yttrium aluminum garnet doped with cerium (Ⅲ) ions (Y3Al5O12:Ce3+, YAG:Ce3+) has attracted a great attention because it can efficiently convert the blue light into a very broad yellow emission band, which produces white light emitting diodes and is applied for panel displays. To improve the brightness and resolution of the display, a considerable attention has been directed to develop fine phosphor particles. We have prepared YAG:Ce3+ nanophosphors by environmental-friendly wet process. The peak maximum of absorption spectra of surface plasmon of Ag nanopaticles are close to that of the excitation spectra (460 nm) of YAG:Ce3+. It can be expected that Ag nanoparticles supported onto the surface of YAG:Ce3+ (Ag-YAG:Ce3+) enhance the absorption of Ce3+ ions. In this study, we have prepared Ag-YAG:Ce3+ nanophosphors and investigated their photoluminescent properties. YCl3･6H2O and AlCl3･6H2O with a molar ratio of Y:Al=3:5 were dissolved in ethanol (100 ml), and CeCl3•7H2O (0.3 mol%) was further added to the above solution. Then, NaOH (4.6×10-2 mol) dissolved in ethanol (50 ml) was added dropwise to the mixture under reflux over 2 hours, and the solution was further refluxed for 1 hour. After cooling to room temperature, precipitates in the reaction mixture were heated at 673 K for 1 hour. After the calcination, the particles were immersed in AgNO3 solution for 1 hour, followed by sintering at 1123 K for 1 hour. YAG:Ce3+ were confirmed to be nanocrystals with a crystallite size of 50-80 nm in diameter. Ag nanoparticles supported onto YAG:Ce3+ were single nanometers in diameter. The excitation and emission spectra were 454 nm and 539 nm at a maximum wavelength, respectively. The emission intensity was maximum for Ag-YAG:Ce3+ immersed into 0.5 mM AgCl (Ag-YAG:Ce (0.5 mM)). The absorption maximum (461 nm) was increased for Ag-YAG:Ce3+ in comparison with that for YAG:Ce3+, indicating that the absorption was enhanced by the addition of Ag. The external and internal quantum efficiencies became 11.2 % and 36.9 % for Ag-YAG:Ce (0.5 mM), respectively. The emission intensity and absorption maximum of Ag-YAG:Ce (0.5 mM)×n (n=1, 2, 3) were increased with an increase of the number of supporting times (n), respectively. The external and internal quantum efficiencies were increased for the increase of n, respectively. The external quantum efficiency of Ag-YAG:Ce (0.5 mM) (n=3) became twice as large as that of YAG:Ce. In conclusion, Ag nanoparticles supported onto YAG:Ce3+ increased absorption and quantum efficiency. Therefore, the support of Ag nanoparticles enhanced the photoluminescent properties of YAG:Ce3+.

Keywords: plasmon, quantum efficiency, silver nanoparticles, yttrium aluminum garnet

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Authors: B. Kahouadji, L. Guerbous, L. Lamiri, A. Mendoud

Abstract:

Recently, nanomaterials are developed in the form of nano-films, nano-crystals and nano-pores. Lanthanide phosphates as a material find extensive application as laser, ceramic, sensor, phosphor, and also in optoelectronics, medical and biological labels, solar cells and light sources. Among the different kinds of rare-earth orthophosphates, yttrium orthophosphate has been shown to be an efficient host lattice for rare earth activator ions, which have become a research focus because of their important role in the field of light display systems, lasers, and optoelectronic devices. It is in this context that the 4fn- « 4fn-1 5d transitions of rare earth in insulating materials, lying in the UV and VUV, are the aim of large number of studies .Though there has been a few reports on Eu3+, Nd3+, Pr3+,Er3+, Ce3+, Tm3+ doped YPO4. The 4fn- « 4fn-1 5d transitions of the rare earth dependent to the host-matrix, several matrices ions were used to study these transitions, in this work we are suggesting to study on a very specific class of inorganic material that are orthophosphate doped with rare earth ions. This study focused on the effect of Ce3+ concentration on the structural and optical properties of Ce3+ doped YPO4 yttrium orthophosphate with powder form prepared by the Sol Gel method.

Keywords: YPO4, Ce3+, 4fn- <->4fn-1 5d transitions, scintillator

Procedia PDF Downloads 343