Cooperative Energy Transfer and Frequency Upconversion in Yb3+–Tb3+ and Nd3+–Yb3+–Tb3+ Codoped GdAl3(BO3)4 Phosphors
ABSTRACT Polycrystalline GdAl3(BO3)4 phosphors codoped with Yb3+/Tb3+ and/or Nd3+/Yb3+/Tb3+ have been synthesized by combustion method. Upon excitation with a 980 nm laser diode, an intense green upconversion luminescence has been observed in GdAl3(BO3)4:Yb,Tb phosphor. The quadratic dependence of the luminescence on the pump-laser power indicating a cooperative energy transfer process. Meanwhile, it is noticed that upon excitation with 808 nm laser diode, intense luminescence has clearly been detected in GdAl3(BO3)4:Nd,Yb,Tb phosphor. The luminescence intensity exhibits also a quadratic dependence on incident pump-laser power. However, no green-emission has been observed in GdAl3(BO3)4 phosphors codoped with Yb3+/Tb3+ or Nd3+/Tb3+ respectively upon excited at 808 nm laser diode. A proposed upconversion mechanism involving energy transfer from Nd3+ to Yb3+, and then a cooperative energy transfer process from two excited Yb3+ to Tb3+ has been presented.
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ABSTRACT: GdAl3(BO3)4 polycrystals co-doped with Yb3+ and Eu3+ has been synthesised by combustion method with urea. Upon the excitation at 465 nm (Eu3+/7F6-->5D2 transition), emission bands centered at 590, 613, 697 and 702 nm in the wavelength region of 550-750 nm have clearly been observed, assigned to the electronic transitions of 5D0-->7FJ (J=1, 2, 4 and 5) of Eu3+ ions, respectively. Meanwhile, an intense emission centred at 980 nm along with a shoulder at 1,040 nm has also been observed by exploiting a cross-relaxation process between the transitions of Eu3+/5D0-->7F6 and Yb3+/2F7/2-->2F5/2. On the contrary, an intense red up-conversion emission centred at 613 nm originated from the 5D0-->7F2 transition of Eu3+ has been observed upon excitation with 980 nm laser diode. The quadratic dependence of the red up-conversion intensity on the pump-laser power reveals a cooperative energy transfer mechanism from a pair of Yb3+ ions to one Eu3+ ion.Journal of Fluorescence 08/2008; 19(1):105-9. DOI:10.1007/s10895-008-0389-z · 1.67 Impact Factor
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ABSTRACT: In an attempt to take full advantage of near-infrared part of the solar spectrum, Gd(2)(MoO(4))(3):Er(3+) nanophosphors have been proposed as potential luminescent materials to enhance the response of the silicon solar-cell. Upon excitation with low-energy near-infrared photons, intense upconverted emissions at 545, 665, 800, and 980 nm, for which energies higher than the bandgap of silicon solar-cell, have been achieved with conversion efficiencies of 0.12%, 0.05%, 0.83%, and 1.35%, respectively. Development of nanophosphors for photovoltaic purposes could open up an approach in achieving high-efficiency silicon-based solar-cell by means of the up-conversion of the sub-bandgap near-infrared part of the solar spectrum (E < 1.12 eV) to visible/near-infrared photons.Journal of Fluorescence 09/2008; 19(2):285-9. DOI:10.1007/s10895-008-0414-2 · 1.67 Impact Factor
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ABSTRACT: We demonstrate a facile approach for the synthesis of Zn <sub>2</sub> SiO <sub>4</sub>: Tb <sup>3+</sup>, Yb <sup>3+</sup> transparent thin films. The thin film phosphor was characterized by various methods including x-ray diffraction, atom force microscope, and photoluminescence studies. Upon excitation with a UV-blue photon in the range of 350–485 nm, an intense near-infrared (NIR) emission at around 900–1100 nm has been obtained, which is assigned to the electronic transition <sup>2</sup>F<sub>7/2</sub>→<sup>2</sup>F<sub>5/2</sub> of Yb <sup>3+</sup> upon exploring the cooperative down conversion mechanism from Tb <sup>3+</sup> to Yb <sup>3+</sup> . The dependence of Yb <sup>3+</sup> doping concentration on the visible- and NIR-emissions, decay lifetime, and quantum efficiencies of the thin-films has been investigated. The optimal internal NIR quantum efficiency could be as high as 154.1%.Journal of Applied Physics 04/2009; 105(5-105):053521 - 053521-4. DOI:10.1063/1.3088890 · 2.19 Impact Factor