E. B. da Costa

Universidade Federal Rural de Pernambuco, Arrecife, Pernambuco, Brazil

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Publications (16)30.67 Total impact

  • Journal of Luminescence 12/2013; · 2.14 Impact Factor
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    ABSTRACT: Rare-earth doped oxyfluoride 75SiO2:25PbF2 nano-structured phosphors for white-light-emitting diodes were synthesized by thermal treatment of precursor sol–gel derived glasses. Room temperature luminescence features of Eu3+, Sm3+, Tb3+, Eu3+/Tb3+, and Sm3+/Tb3+ ions incorporated into low-phonon-energy PbF2 nanocrystals dispersed in the aluminosilicate glass matrix and excited with UV light emitting diode were investigated. The luminescence spectra exhibited strong emission signals in the red (600, 610, 625, and 646 nm), green (548 and 560 nm), and blue (485 nm) wavelength regions. White-light emission was observed in Sm/Tb and Eu/Tb double-doped activated phosphors employing UV-LED excitation at 395 nm. The dependence of the luminescence emission intensities upon annealing temperature and rare-earth concentration was also examined. The results indicated that there exist optimum annealing temperature and activator ion concentration in order to obtain intense visible emission light with high color rendering index. The study suggests that the nanocomposite phosphor based upon 75SiO2:25PbF2 host herein reported is a promising contender for white-light LED applications.
    Journal of Luminescence 01/2012; 132:299-304. · 2.14 Impact Factor
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    ABSTRACT: Multicolor visible light emitting near-infrared (NIR)-excited Tm/Ho/Yb-codoped tantalum oxide nanopowders were produced using the sol-gel method. The generation of wide color gamut fluorescence in glass-ceramic with orthorhombic Ta <sub>2</sub> O <sub>5</sub> nanocrystals dispersed into amorphous silica-based matrix is observed. The light emission spectroscopic properties of the rare-earth doped SiO <sub>2</sub>: Ta <sub>2</sub> O <sub>5</sub> nanocomposites as a function of the tantalum content and temperature of annealing is examined. Simultaneously emitted multicolor fluorescence consisting of blue (480 nm), green (540 nm), and red (650 nm) upconversion signals in the SiO <sub>2</sub>: Ta <sub>2</sub> O <sub>5</sub> system doped with holmium and thulium and sensitized with ytterbium, is demonstrated. It is also demonstrated that the proper choice of the rare-earth content and the NIR excitation power yielded the generation and control of the three primary colors and allows the emission of a balanced white overall luminescence from the glass-ceramic nanopowder samples.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
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    ABSTRACT: Temperature induced variable chromaticity lanthanide multidoped solid-state phosphors are presented. The phosphors are composed of ytterbium-sensitized multiple-doped (Tm, Er, Ho) PbGeO3–PbF2–CdF2 glass excited at 1.064 µm. The temperature induced color variation exploits the heat enhanced effective absorption cross-section of the ytterbium sensitizer under quasi-resonance excitation. The temperature enhancement of the energy-transfer mechanism between the sensitizer and the appropriate active light emitter allows the selective intensity control of the RGB emissions due to distinct excitation routes. The suitable combination of active ions generated variable chromaticity light with CIE-1931 coordinates changing from CIE-X = 0.283; Y = 0.288 at 20 °C to CIE-X = 0.349;Y = 0.412 at 190 °C, and CIE-X = 0.285; Y = 0.361 at 25 °C to CIE-X = 0.367; Y = 0.434 at 180 °C in Yb3+/Tm3+/Ho3+ and Yb3+/Tm3+/Er3+ samples, respectively.
    Proc SPIE 09/2009; 63(23):1999–2002.
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    ABSTRACT: Cooperative energy transfer upconversion luminescence is investigated in Tb3+/Yb3+-codoped PbGeO3–PbF2–CdF2glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473–490, 545, 587, and 623 nm are identified as due to the 5D3(5G6)→7FJ (J=6,5,4) and 5D4→7FJ (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.
    Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B. 01/2009; 50(1).
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    ABSTRACT: Energy transfer excited multiwavelength visible upconversion emission and white light generation is described in a single sample of PbGeO3–PbF2–CdF2 glass-ceramic triply doped with Ho/Tm/Yb under single infrared laser excitation. Blue (475 nm), green (540 nm), and red (650 nm), upconversion luminescence signals are generated, and the emissions are assigned, respectively, to thulium (1G4–3H6), and holmium (5S2;5F4)→5I8,5F5→5I8) ions transitions, both excited via successive energy transfers from ytterbium ions. It is experimentally shown that with a proper combination of the rare earth ions contents, white light may be produced, with the simultaneous generation of fluorescence with controllable intensities at the wavelengths of the three primary colours in a single sample and using a single near-infrared excitation source.
    Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B. 01/2009; 50(1).
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    ABSTRACT: Upconversion luminescence in erbium-doped PbGeO3–PbF2–CdF2-based vitroceramic under 1540nm infrared excitation is investigated. Luminescence signals around 410, 525, 550, 660 and 850nm were generated and attributed to the 2H9/2, 2H11/2, 4S3/2 and 4F9/2 transitions to the 4I15/2 ground-state, and 4S3/2–4I13/2, respectively. The erbium ions excited-state emitting levels were populated through a combination of stepwise ground-state absorption, phonon-assisted excited-state absorption and cross-relaxation processes. The results also disclosed that all emission signals obtained with vitroceramic samples presented intensities three times higher when compared to the precursor glass samples. In addition, the red emission signal at 660nm for 1540nm pumping exhibited an expressively high intensity when compared to the green signal.
    Journal of Non-Crystalline Solids 01/2009; 355(8):488-491. · 1.72 Impact Factor
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    ABSTRACT: Transparent oxyfluoride glasses and β-PbF2 nanocrystals containing glass-ceramics were prepared with varying Eu3+ content (0.3, 0.4, 0.5 and 0.6%). The effect of Eu3+ content on the preparation of glass-ceramics was investigated. From differential scanning calorimetry, the Tx–Tg (Tx—temperature of the onset of crystallization; Tg—glass transition temperature) parameter for glasses has shown slight variation, and an exothermic peak near Tg called the ceramization temperature (Tc) has been observed. Heat treatments were performed at this temperature to obtain transparent glass-ceramics containing β-PbF2 nanocrystals, identified by x-ray diffraction. Heat treatments for different periods of time were performed and were observed to be very important in the control of the crystal size and of the crystallization rate. Based upon the absorption spectra, the scattering level due to the presence of β-PbF2 nanocrystals in the glass-ceramics was observed to be similar to that for the mother glasses. Detailed analysis of emission spectra and decay time measurements led to the identification of Eu3+ ions as the β-PbF2 crystalline phase. Excitation spectra at 70 K show the interaction of Eu3+ ions with the fluorogermanate network.
    Journal of Physics Condensed Matter 03/2008; 20(14):145201. · 2.22 Impact Factor
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    ABSTRACT: White light was produced exploiting an additive synthesis of red, green, and blue fluorescence through frequency upconversion in fluorolead-germanate glass codoped with Ho3+, Tm3+, and Yb3+. The 475, 540, and 650 nm signals were, respectively, assigned to thulium (1G4-3H6) and holmium (5S2;5F4)→5I8 and 5F5→5I8, excited via energy tranfer from ytterbium. The dopant concentrations were adjusted, yielding the emission of a wide color gamut in the visible spectrum and the production of white light using excitation at 975 nm. The spectral positions and purity (blue, 97%; green, 100%; red, 95%) of the three colors produced CIE-X = 0.3438 and CIE-Y = 0.3639 coordinates.
    Applied Physics Letters 08/2007; 91(9):091114-091114-3. · 3.52 Impact Factor
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    ABSTRACT: The effect of ytterbium ions upon energy transfer (ET) excited upconversion emission in Nd3+/Pr3+-codoped PbGeO3–PbF2–CdF2 glass under 810 nm diode laser excitation is investigated. The results revealed that the presence of Yb3+ ions in the Nd3+/Pr3+-doped sample yields a fourfold enhancement in the visible and near infrared upconversion luminescence. The dependence of the upconversion process upon the excitation power, Nd3+, and Yb3+ concentrations is examined. The results indicated that ytterbium plays a major role in the ET upconversion process by bridging the 810 nm neodymium excitation to praseodymium ions. The population of the Pr3+ ions 3P0 emitting level was accomplished through a multi-ion interaction involving ground-state and excited-state absorption of pump photons at 810 nm by the Nd3+ followed by successive ET involving the Nd3+–Yb3+ and Yb3+–Pr3+ pairs. There is also direct ET Nd3+–Pr3+.
    Journal of Luminescence 01/2006; 116:52-58. · 2.14 Impact Factor
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    ABSTRACT: Visible frequency upconversion emission through resonant energy-transfer involving neodymium and praseodymium ions in PbGeO3–PbF2–CdF2 glass excited by a semiconductor laser at 810nm is investigated. Luminescence emission centered around 485, 530, 610, and 645nm, which correspond to the 3P0→3H4, 3P1+1I6→3H5, 3P0→3H6 and 3P0→3F2 transitions of praseodymium ions, respectively, are observed. The upconversion excitation of the Pr3+ ions excited-state emitting levels was accomplished by means of an ion–pair interaction involving ground-state absorption, multiphonon relaxation, and excited-state absorption of pump photons at 810nm by the Nd3+ (4I9/2→2H9/2, 4F5/2; 4F3/2→2P1/2) and direct energy-transfer to Pr3+ (4G11/2+2K11/2, 3H4→4I9/2, 3P1+1I6). The dependence of the upconversion emission intensity upon the excitation power, and neodymium concentration are also examined.
    Journal of Alloys and Compounds 01/2005; 394(1):24-27. · 2.73 Impact Factor
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    ABSTRACT: We report a patient with discoid lupus erythematosus (DLE) and associated allergic contact dermatitis (ACD) in the eyelids. In women, ACD caused by nail varnish is frequent and often seen in the eyelids. ACD caused by drugs (e.g. neomycin) is also frequent in this region. However, DLE with periorbital presentation without evidence of systemic or other cutaneous involvement is rare.
    Journal of the European Academy of Dermatology and Venereology 10/2004; 18(5):577-9. · 2.69 Impact Factor
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    ABSTRACT: Intense red upconversion emission around 650nm in PbGeO3–PbF2–CdF2 transparent glass ceramic containing β-PbF2:Ho3+ nanocrystals, is presented. The holmium-doped vitroceramic samples were excited by a 980nm diode laser source. The 650nm upconversion signal was assigned to the 5F5→5I8 transition of holmium ions. Very low intensity signals around 490 and 540nm corresponding to the 5F2,3→5I8 and 4S2,5F4→5I8 transitions, respectively, were also detected. The upconversion excitation mechanism was achieved through a combination of stepwise phonon-assisted multiphoton absorption, cross-relaxation processes involving pairs of holmium ions, and excited-state absorption. Using a diode laser pump source around 850nm green upconversion emission around 540nm was the observed predominant signal.
    Journal of Luminescence 10/2004; 110(1):79-84. · 2.14 Impact Factor
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    ABSTRACT: Blue, green, red, and near-infrared upconversion luminescence in the wavelength region of 480–740 nm in Pr3+/Yb3+-codoped lead–cadmium–germanate glass under 980 nm diode laser excitation, is presented. Upconversion emission peaks around 485, 530, 610, 645, and 725 nm which were ascribed to the 3P0–3HJ (J=4, 5, and 6), and 3P0–3FJ (J=2, 3, and 4), transitions, respectively, were observed. The population of the praseodymium upper 3P0 emitting level was accomplished through a combination of ground-state absorption of Yb3+ ions at the 2F7/2, energy-transfer Yb3+(2F5/2)–Pr3+(3H4), and excited-state absorption of Pr3+ ions provoking the 1G4–3P0 transition. The dependence of the upconversion luminescence upon the Yb3+-concentration and diode laser power, is also examined, in order to subsidize the proposed upconversion excitation mechanism.
    Optical Materials 08/2004; · 2.08 Impact Factor
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    ABSTRACT: Frequency upconversion luminescence in erbium-doped PbGeO3–PbF2–CdF2-based transparent glass ceramics (TGC) under 980nm infrared excitation is investigated. Upconversion emission signals around 410, 525, 550, 660, and 850nm were generated and identified as due to the 2H9/2, 2H11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground-state, and 4S3/2–4I13/2, respectively. The erbium ions excited-state emitting levels were populated via a combination of stepwise ground-state absorption (GSA), excited-state absorption (ESA), and cross-relaxation processes. The results also disclosed that both blue (410nm) and red (660nm) upconversion emission signals in the transparent glass ceramic sample presented twice as much intensity as compared to its vitreous counterpart.
    Journal of Alloys and Compounds 01/2004; 375(1):224-228. · 2.73 Impact Factor
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    ABSTRACT: Bright blue upconversion emission by thulium ions in PbGeO <sub>3</sub>– PbF <sub>2</sub>– CdF <sub>2</sub> glass triply doped with Nd <sup>3+</sup>– Tm <sup>3+</sup>– Yb <sup>3+</sup> under diode laser excitation around 800 nm is reported. The results revealed that the Nd <sup>3+</sup>/ Tm <sup>3+</sup>/ Yb <sup>3+</sup> -codoped sample generated ten times more 475 nm blue upconversion fluorescence than the Yb <sup>3+</sup> -sensitized Tm <sup>3+</sup> -doped one, under the same excitation power. The upconversion process also showed a strong dependence upon the Yb <sup>3+</sup> concentration. The results also indicated that the neodymium ions played a major role in the upconversion process by transfering the 800 nm excitation to thulium ions. The population of the Tm <sup>3+</sup> ions <sup>1</sup>G<sub>4</sub> emitting level was accomplished through a multiion interaction involving ground-state absorption of pump photons around 800 nm by the Nd <sup>3+</sup>(<sup>4</sup>I<sub>9/2</sub>→<sup>2</sup>H<sub>9/2</sub>, <sup>4</sup>F<sub>5/2</sub>) and Tm <sup>3+</sup>(<sup>3</sup>H<sub>6</sub>→<sup>3</sup>F<sub>4</sub>) ions followed by energy-transfer processes involving the Nd <sup>3+</sup>– Yb <sup>3+</sup>(<sup>4</sup>F<sub>3/2</sub>, <sup>2</sup>F<sub>7/2</sub>→<sup>4</sup>I<sub>11/2</sub>, <sup>2</sup>F<sub>5/2</sub>) and Yb <sup>3+</sup>– Tm <sup>3+</sup>(<sup>2</sup>F<sub>5/2</sub>, <sup>3</sup>- F<sub>4</sub>→<sup>2</sup>F<sub>7/2</sub>, <sup>1</sup>G<sub>4</sub>) pairs. © 2003 American Institute of Physics.
    Journal of Applied Physics 12/2003; · 2.21 Impact Factor