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Lokeswara Reddy G.V.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Venkata Subbaiah Engineering College | Pavani K.,Sri Venkateswara University | And 2 more authors.
Optoelectronics and Advanced Materials, Rapid Communications | Year: 2013

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 I'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. Source


Lokeswara Reddy G.V.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Venkata Subbaiah Engineering College | Chengaiah T.,Sri Venkateswara University | And 2 more authors.
Advanced Materials Letters | Year: 2013

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. Source


Lokeswara Reddy G.V.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Venkata Subbaiah Engineering College | Packiyaraj P.,Indian Institute of Technology Delhi | And 2 more authors.
Optical Materials | Year: 2013

Dy3+ and Tm3+ co-doped YAl3(BO 3)4 (YAB) phosphors were prepared by solid-state reaction method at 1200 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 Dy 3+:4F9/2 → 6HJ (J = 15/2, 13/2, 11/2) and Tm3+:1D2 → 3F4 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 (λex = 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:Dy 3+-Tm3+ phosphors can be used as potential candidates in display technology. © 2013 Elsevier B.V. All rights reserved. Source


Reddy G.V.L.,Sri Venkateswara University | Moorthy L.R.,Sri Venkateswara University | Moorthy L.R.,Chadalawada Venkata Subbaiah Engineering College | Chengaiah T.,Sri Venkateswara University | And 2 more authors.
Ceramics International | Year: 2014

A series of YAB:Eu3+/Tb3+ co-activated phosphors of composition Y(1-x-y)Al3(BO3) 4:xEu3+/yTb3+ (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 Eu 3+/Tb3+ concentration. Moreover, the Tb3+ acts as an efficient sensitizer and enhances the luminescence of Eu3+ by transferring absorbed excitation energy. The overlapping 7F 0→5D3,2,1,0(Eu3+); 7F1→5D1,0(Eu3+); 7F2→5D1(Eu3+) excitation and 5D3→7F5,4,3 (Tb3+); 5D4→7F 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. © 2013 Elsevier Ltd and Techna Group S.r.l. Source


Krishnapuram P.,Sri Venkateswara University | Jakka S.K.,University of Aveiro | Thummala C.,Sri Venkateswara University | Lalapeta R.M.,Sri Venkateswara University | Lalapeta R.M.,Chadalawada Venkata Subbaiah Engineering College
Journal of Molecular Structure | Year: 2012

The present work reports the preparation and characterization of calcium fluoroborate (CFB) glasses doped with different concentrations of Eu 2O3. The spectroscopic free-ion parameters are evaluated from the experimentally observed energy levels of Eu3+ ions in CFB glasses by using the free-ion Hamiltonian model (HFI). The phenomenological Judd-Ofelt (J-O) parameters, Ω2, Ω4 and Ω6, are evaluated from the intensities of Eu3+ ion absorption bands by various constraints. From these J-O parameters (Ωλ), the radiative parameters such as transition probabilities (AR), branching ratios (βR), stimulated emission cross sections (σe) and radiative lifetimes (τR) are evaluated for 5D 0→7FJ(J=0-6) transitions. From the decay curves of 5D0 emission level, the experimental lifetimes (τexp) are obtained for different Eu3+ ion concentrations. The variation of emission intensities and experimental lifetimes with concentration is analyzed/discussed to optimize the Eu2O 3 concentration in CFBEu glasses for device applications. © 2012 Elsevier B.V. All rights reserved. Source

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