Luminescence properties of Eu3+-doped Na3Gd(PO4)(2) red-emitting nanophosphors for LEDs

Eu3+-doped Na3Gd(PO4)(2) phosphors were synthesized by the modified citrate gel combustion technique. From the XRD pattern, structure of the compound was found to be orthorhombic with a particle size of 10-20 nm. The emission spectra revealed that the Na3Gd(PO4)(2):Eu3+ phosphors can be excited effectively by 394 nm pump wavelength. From the concentration dependent photoluminescence studies, the optimum concentration for efficient luminescence of Eu3+ ions in Na3Gd(PO4)(2) phosphor has been found to be 1.5 mol%. Decay curves of the D-5(0) level of Eu3+ ions were recorded by monitoring the emission at 596 nm corresponding to D-5(0) -> F-7(1) transition and are found to be single exponential for all the concentrations. The chromaticity properties for different concentrations of Na3Gd(PO4)(2):Eu3+ nanophosphors were calculated from emission spectra and analyzed in the frame work of CIE color diagram. (C) 2014 Elsevier B.V. All rights reserved

Enhanced white light emission and energy transfer studies of Dy3+/Ce3+ co-doped YAl3(BO3)4 phosphors for white light emitting diodes

We reported the structure, photoluminescence and energy transfer studies of Dy3+/Ce3+ co-doped YAl3(BO3)4 (YAB) phosphors prepared by solid-state reaction method at 1200°C/3h. Upon 273 nm UV excitation, the YAB:Ce3+ phosphor exhibits a sharp emission band with peak maximum at 380 nm related to the parity and spin allowed Ce3+:5d ? 4f transition. When excited with 352 nm, the broad emission band of Ce3+ contains two components at 390 and 417 nm due to the electric dipole transitions from 5d excited state to the two splitting ground 2F5/2,7/2 states, respectively. The incorporation of Ce3+ enhances the luminescence intensity of Dy3+ due to efficient energy transfer from Ce3+ to Dy3+. The emission spectra of Dy3+/Ce3+ co-doped phosphors under 273 nm excitation display the Dy3+:4F9/2 ? 6H15/2,13/2,11/2 and the Ce3+:5d ? 4f transitions. The emission colour can be tuned from blue-to-white as a function of Ce3+ concentration and/or excitation wavelength. Colour perception has been analyzed by evaluating the Commission International de I'Eclairagein (CIE) chromaticity coordinates. The YAB:Dy3+/Ce3+ phosphors can be significant for current generation UV excited white light emitting diodes. © 2013 VBRI press

Preparation, structural and luminescent properties of YAl3(BO3)(4):Dy3+ phosphor for white light-emission under UV excitation

A series of YAl3(BO3)(4) phosphors doped with different concentrations of Dy2O3 (0.1 H-6(15/2) at 485 nm and F-4(9/2)-> H-6(13/2) at 576 nm were observed in the emission spectra. The luminescence quenching noticed at higher Dy203 concentrations is due to the exchange interaction among the excited Dy3+ ions. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Optical characterization of YAl3(BO3)(4):Dy3+-Tm3+ phosphors under near UV excitation

Dy3+ and Tm3+ co-doped YAl3(BO3)(4) (YAB) phosphors were prepared by solid-state reaction method at 1200 degrees C/3 h. The average crystallite size was determined as 52.09 nm from the X-ray diffraction measurements. Upon 352 and 359 nm near ultra violet excitation, the YAB:Dy3+-Tm3+ phosphors exhibit Dy3+:F-4(9/2) --> H-6(J) = (J = 15/2, 13/2, 11/2) and Tm3+:D-1(2) --> F-3(4) transitions with different luminescence intensity. The photoluminescence emission and decay measurements revealed the energy transfer from Dy3+ to Tm3+ ions under 359 nm excitation only. The energy transfer between Dy3+ and Tm3+ takes place in Dy3+-Tm3+ clusters through exchange interaction mechanism. The Commission International de I'Eclairage chromaticity coordinates of YAB:Tm3+ phosphor (lambda(ex) = 359 nm) were found very close to the European Broadcasting Union and National Television Standard Committee illuminants. The emission color of the studied phosphors could be tuned from blue-to-white as a function of excitation wavelength. The YAB:Dy3+-Tm3+ phosphors can be used as potential candidates in display technology. (C) 2013 Elsevier B.V. All rights reserved

Multi-color emission tunability and energy transfer studies of YAl3(BO3)(4):Eu3+/Tb3+ phosphors

A series of YAB:Eu3+/Tb3+ co-activated phosphors of composition Y(1-x-y)Al3(BO3)(4)xEu(3+)/yTb(3+) (x=0, 0.3, 0.5, 1, 2% and y=0.5%) were prepared by solid-state reaction method and their photoluminescence properties were characterized. Eu3+/Tb3+ co-doped phosphors have shown their excellent luminescent properties in their respective emission regions. The YAB:2%Eu3+ phosphor under 395 nm excitation exhibited red luminescence with Commission International de I'Eclairagein chromaticity coordinates (x=0.627, y=0.334) which are close to an ideal red and commercial Y2O3:Eu3+ red phosphor chromaticity coordinates. The emission color of Eu3+/Tb3+ co-doped phosphors has been tuned from pale-green to white as a function of Eu3+/Tb3+ concentration. Moreover, the Tb3+ acts as an efficient sensitizer and enhances the luminescence of Eu3+ by transferring absorbed excitation energy. The overlapping F-7(0)-> D-5(3,2,1,0) (Eu3+); F-7(1)->>D-5(1,0)(Eu3+); F-7(2)-> D-5(1)(Eu3+) excitation and D-5(3)-> F-7(5,4,3) (Tb3+); D-5(4)-> F-7(5,4)(Tb3+) emission transitions revealed the transfer of energy from Tb3+ to Eu3+ through exchange interaction mechanism in Eu3+-Tb3+ clusters instead of from these ions randomly distributed in YAB lattice. The YAB:Eu3+/Tb3+ phosphors have potential in the field of display technology. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved

A convenient noninjection one-pot synthesis of Cds nanoparticles and their studies

Water-dispersible CdS quantum dots (QDs) were synthesized in a simple one-pot noninjection route. The X-ray diffraction (XRD) pattern of the nanoparticles shows the cubic structure with particle size of the order 5-7 nm which was in good agreement with the transmission electron microscopic (TEM) studies. Selected area electron diffraction (SAED) recognized the cubic structure of CdS. The energy dispersive X- ray spectroscopy (EDAX) analysis confirms the presence of Cd and S elements in the samples. The optical properties are characterized by Ultraviolet-Visible (UV-Vis) absorption and Photoluminescence (PL) spectra. The synthesis parameters of this simple and rapid approach, including the reaction temperature and time, the pH of the reaction solution and the molar ratio of the 3-mercaptopropionic acid (MPA) stabilizer to Cd2+, have considerable influence on the particle size and photoluminescence of the CdS quantum dots. The 3-mercaptopropionic acid (MPA) stabilized CdS QDs can be used in solar cells, light emitting diodes, biological imaging etc © 2013 VBRI press

Photoluminescence and energy transfer studies of YAl3(BO3)(4):Sm3+/Tb3+ phosphors for solid state lighting applications

Trivalent samarium (Sm3+)/terbium (Tb3+) co-doped YAl3(BO3)(4) (YAB) phosphors were prepared by solid-state reaction method. The phase, structure, optical and energy transfer studies were systematically characterized through X-ray diffraction, Fourier transform infrared spectroscopy, photoluminescence (PL) and decay measurements, respectively. Upon 406 nm excitation, both Sm3+ single- and Sm3+/Tb3+ co-doped YAB phosphors emit orange-red luminescence with peak maximum at 602 nm. The YAB:Tb3+ phosphor emits green luminescence at 546 nm when excited with 375 nm near UV wavelength. The YAB:Sm3+/Tb3+ phosphors emit green-to-white luminescence as a function of Sm3+ concentration upon an excitation wavelength of 375 nm. The Tb3+ acts as an efficient sensitizer of luminescence of Sm3+ under 375 nm excitation in YAB phosphors. Doped Sm3+ and Tb3+ ions were located at the inversion symmetry sites of YAB lattice. The Commission International de l'Eclairage chromaticity coordinates were calculated from the PL spectra. The energy transfer from Tb3+ to Sm3+ ions was described in detail. The YAB:Sm3+/Tb3+ phosphors can be used as a promising material for solid state lighting devices