Time filter

Source Type

Sowjanya G.,Sri Venkateswara University | Sowjanya G.,Madanapalle Institute of Technology and Science | Basavapoornima Ch.,Sri Venkateswara University | Moorthy L.R.,Sri Venkateswara University | And 3 more authors.
Key Engineering Materials | Year: 2016

Red emitting new phosphor, YBO3 doped with Eu3+ ions, has been prepared by solid state reaction method. The excitation spectra were recorded by monitoring a red emission at 610 nm and observed very intense band in the lower wavelength region, 230 ∼ 280 nm, which could be attributed due to the Eu3+-O2-charge transfer band (CTB) lying in the band gap region of the host matrix. In addition to the CTB, strong absorption lines in the excitation spectrum is located at 395 nm and 465 nm which corresponds to the 7F0 → 5L6 and 7F0 → 5D2 transitions of Eu3+ ions, respectively. The decay curves are found to be single exponential at lower concentrations and tends to be non-exponential at higher concentrations with shortening of lifetime (2.74 ms to 0.86 ms). The systematic investigation indicates that this Eu3+-doped YBO3 phosphor is an ideal candidate for solid state lighting applications. © 2016 Trans Tech Publications, Switzerland.


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.


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.


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.


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.


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.


Sasikala T.,Sri Venkateswara University | Moorthy L.R.,Sri Venkateswara University | Moorthy L.R.,Chadalawada Venkata Subbaiah Engineering College | Pavani K.,Sri Venkateswara University | Chengaiah T.,Sri Venkateswara University
Journal of Alloys and Compounds | Year: 2012

Optical absorption, near infrared emission and FTIR studies were carried out for the glasses prepared with chemical composition of (61.5-x)TeO 2 + 25ZnO + 8K 2O + 5CaO + 0.5Er 2O 3 + xCe 2O 3 (TZKCEr05Cex; x = 0, 0.1, 0.5, 1.0 mol%) by the conventional melt quenching technique. Judd-Ofelt analysis has been adopted for the experimental oscillator strengths of the absorption bands of 0.5 mol% of Er 3+ ions in singly doped TZKC glass. From the Judd-Ofelt intensity parameters ( λ), different radiative parameters were evaluated and the effect of Ce 3+ ions concentration on the Er 3+ ion emission intensities of 4I 13/2 → 4I 15/2 transition has been discussed. © 2012 Elsevier B.V. All rights reserved.

Loading Chadalawada Venkata Subbaiah Engineering College collaborators
Loading Chadalawada Venkata Subbaiah Engineering College collaborators