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Reddy A.A.,Indian Institute of Technology Delhi | Sekhar M.C.,Indian Institute of Technology Delhi | Pradeesh K.,Indian Institute of Technology Delhi | Babu S.S.,Laser Instrumentation Design Center | Prakash G.V.,Indian Institute of Technology Delhi
Journal of Materials Science | Year: 2011

Trivalent dysprosium (Dy3+)-doped sodium-aluminum-phosphate (NAP) glasses were prepared and characterized by their optical absorption, excitation, emission spectra, and decay time measurements. Judd-Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative lifetime and stimulated emission cross section of the 4F9/2 → 6H13/2 and 4F9/2 → 6H15/2 transitions. The luminescence intensity ratio of 4F9/2 → 6H13/2 to 4F9/2 → 6H15/2 transitions of Dy3+ in NAP glasses gives the feasibility of extracting white light. The lifetime and quantum efficiency of 4F9/2 level is found to be higher than other reported glasses. With increase in Dy3+ ion concentration, the decay from 4F9/2 level is found to be faster with decrease in lifetime due to cross relaxation between Dy3+ ions. © 2011 Springer Science+Business Media, LLC.


Das S.,Indian Institute of Technology Delhi | Amarnath Reddy A.,Indian Institute of Technology Delhi | Surendra Babu S.,Laser Instrumentation Design Center | Vijaya Prakash G.,Indian Institute of Technology Delhi
Journal of Materials Science | Year: 2011

Potassium calcium borate, KCaBO3:Eu3+ phosphors with various Dy3+ concentrations (0-3 wt%) were synthesized by solid state reaction and studied for the first time. Under various UV-violet excitations, the obtained single monoclinic phased Dy3+-Eu3+ co-doped KCaBO3 polycrystalline phosphors emit a combination of yellow-blue and red-orange wavelength giving intense white light, which can easily be controlled by varying the concentration of Dy3+. The increase in white light emission with the increase of Dy3+ concentration indicates the efficient energy inter-ion transfer from Dy3+ to Eu3+ ions. Furthermore, the observed emission lifetimes and the intense white light emission are suggestive exploration for the present phosphor for potential optoelectronic applications such as white light-emitting phosphor for blue LEDs chips. © 2011 Springer Science+Business Media, LLC.


Reddy A.A.,Indian Institute of Technology Delhi | Babu S.S.,Laser Instrumentation Design Center | Pradeesh K.,Indian Institute of Technology Delhi | Otton C.J.,Polytechnic University of Valencia | Vijaya Prakash G.,Indian Institute of Technology Delhi
Journal of Alloys and Compounds | Year: 2011

Erbium-doped Na3Al2P3O12 (NAP) glasses with compositions 92NAP-(8-x)Al2O3-(x)Er 2O3 (where x = 2-8) were prepared and characterized for absorption, visible and NIR emission and decay time properties. Judd-Ofelt analysis has been carried out to predict radiative properties of luminescent levels of Er3+ ions. Comparatively larger photoluminescence lifetimes (7.86 ms) and larger quantum efficiencies (74%) for the laser transition, 4I13/2 → 4I15/2 (at 1.54 μm) are observed. The moisture insensitivity, large Er3+ ion doping capability and relatively high-gain and broad emission at 1.5 μm are the most notable features of these glasses to realize efficient short-length optical amplifiers. © 2011 Elsevier B.V. All rights reserved.


Rayappan I.A.,Gandhigram Rural University | Rayappan I.A.,St. Josephs College | Maheshvaran K.,Gandhigram Rural University | Babu S.S.,Laser Instrumentation Design Center | Marimuthu K.,Gandhigram Rural University
Physica Status Solidi (A) Applications and Materials Science | Year: 2012

Dy 3+ doped lead fluoroborate (LFB) glasses (B 2O 3+PbO+PbF 2) have been prepared following conventional melt quenching technique by varying the concentration of Dy 2O 3 in the order 0.01, 0.1, 1, 2, and 3mol%. X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), optical absorption, fluorescence emission, and decay curves have been recorded and analyzed. From the optical measurements and based on the Judd-Ofelt (JO) theory, the JO intensity parameters were evaluated and in turn used to evaluate the radiative transition probabilities (A), stimulated emission cross-section (σ P E, radiative lifetimes (τ rad), and branching ratios (β R) for the various 4F 9/2→ 6H J (J=11/2, 13/2, 15/2) transitions of Dy 3+ ions in the LFB glasses and these values were compared with the other reported Dy 3+:glasses. The decay curves of the 4F 9/2 level were measured and found to be deviate from the exponential nature with the increase in Dy 3+ ion concentration. The luminescence quantum efficiency of the 4F 9/2 level was also determined and discussed. Differential scanning calorimetry (DSC) curves were used to evaluate the glass stability factor (S) and Hruby's parameter (H R) through the glass transition (T g), crystallization (T c), and melting (T m) temperatures and these results were discussed and reported. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Shanmuga Sundari S.,Gandhigram Rural University | Marimuthu K.,Gandhigram Rural University | Sivraman M.,Gandhigram Rural University | Babu S.S.,Laser Instrumentation Design Center
Journal of Luminescence | Year: 2010

Sodium borate and fluoroborate glasses doped with trivalent samarium (Sm3+) were prepared and their detailed spectroscopic analysis was carried out. The FTIR spectra reveal that, the glasses contain BO3, BO4, non-bridging oxygen and strong OH- bonds. From the optical absorption spectra, Judd-Ofelt intensity parameters (Ωλ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross section (σPE) and branching ratios (βR) for the excited levels of Sm3+ ions in sodium borate and sodium fluoroborate glasses. The dependence of the spectral characteristics of Sm3+ ions due to compositional changes have been examined and reported. The value is found to decrease with the decrease in the sodium content in the glass. The decay from the 4G5/2 level is found to be non-exponential indicating a cross-relaxation among the Sm3+ ions. © 2010 Elsevier B.V. All rights reserved.

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