A. Srinivasa Rao

Delhi Technological University, New Dilli, NCT, India

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Publications (16)34.55 Total impact

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    ABSTRACT: Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Ho3+ ions have been synthesized using the melt quenching method and characterized to understand their visible emission characteristic features using optical absorption and photoluminescence spectral studies. The Judd–Ofelt (JO) parameters measured from the absorption spectral features were used to evaluate radiative properties such as transition probability (AR), branching ratio (βR) and radiative lifetimes (τR) for the prominent fluorescent levels of Ho3+ ions in LTT glasses. The photoluminescence spectra recorded for all the Ho3+ doped LTT glasses at an excitation wavelength 452 nm gives three prominent emission transitions 5F4→5I8, 5F5→5I8 and 5F4→5I7, of which 5F4→5I8 observed in visible green region (546 nm) is relatively more intense than the other two transitions. The intensity of 5F4→5I8 emission transition in these glasses increases up to 1 mol% of Ho3+ ions and beyond concentration quenching is observed. Branching ratios (βR) and emission cross-sections (σse) were evaluated for the intense emission transition 5F4→5I8 in these glasses to understand the luminescence efficiency in visible green region (546 nm). The CIE chromaticity coordinates were also evaluated in order to understand the suitability of these glasses for visible luminescence. From the measured emission cross-sections and CIE coordinates, it was found that 1 mol% of Ho3+ ions in LTT glasses are most suitable for visible green luminescence in principle.
    Journal of Luminescence 07/2015; 163. DOI:10.1016/j.jlumin.2015.02.052 · 2.37 Impact Factor
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    ABSTRACT: Er3+ doped Zinc Alumino Bismuth Borate (ZnAlBiB) glasses with composition 20 ZnO+10 Al2O3+(10-x) Bi2O3+60 B2O3+xEr2O3 (where x=0.1, 0.5, 1.0 and 2.0 mol %) were prepared by using melt quenching technique to study their luminescence efficiency in different regions of electromagnetic spectrum using absorption, emission, up-conversion and time resolved photoluminescence spectral studies at room temperature. The Judd-Ofelt (JO) parameters evaluated by applying JO theory to the absorption spectra of Er3+ doped ZnAlBiB glasses were used to calculate the radiative properties such as transition probability (AR), Branching ratios (βR), radiative lifetimes (τR), stimulated emission cross-section ( ), gain band width ( ) and optical gain ( ) parameters for the prominent luminescent levels of Er3+. Visible and near infrared (NIR) emission spectra have been recorded by exciting the glass samples at 486 nm and 980 nm respectively. Quantum efficiency (η) values for the prepared glasses were evaluated from the decay curves recorded for the NIR transition 4I13/2→4I15/2. The up-conversion luminescence shown by these glasses were recorded and analysed to understand utility of these glasses as up-conversion lasers by exciting them with 980 nm laser diode. The visible, up-conversion and NIR luminescence studies indicates that Er3+ ions doped ZnAlBiB glasses are aptly suitable for solid state lasers and optical amplifiers.
    Journal of Luminescence 03/2015; 163. DOI:10.1016/j.jlumin.2015.02.036 · 2.37 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with terbium (Tb3+) ions with a chemical composition 20ZnO–10Al2O3–(10−x)Bi2O3–60B2O3−xTb2O3 (x=0.1, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol%) were prepared by a conventional melt quenching method and studied their optical absorption, photoluminescence and decay spectral properties. The Judd–Ofelt (J–O) parameters evaluated from the experimental oscillator strengths were used to measure the radiative properties for the prominent luminescent transitions of Tb3+ ions such as 5D4→7F6, 7F5, 7F4 and 7F3. The effect of Tb3+ ion concentration on the luminescence process observed in the visible region was discussed in detail. The emission spectra recorded for all the ZnAlBiB glasses doped with Tb3+ ions, show an intense peak in green region at 542 nm. The stimulated emission cross-section, branching ratios and quantum efficiency values evaluated for green emission (5D4→7F5) suggests the utility of these glasses for green luminescence applications. It was found that, within the concentration range investigated, 2.5 mol% of Tb3+ doped ZnAlBiB glass is most suitable for green luminescence applications at 542 nm in principle.
    Journal of Luminescence 12/2014; 156:180–187. DOI:10.1016/j.jlumin.2014.08.019 · 2.37 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of Eu3+ ions have been prepared by rapid melt quenching technique and characterized for their luminescence behavior through various spectroscopic techniques such as absorption, excitation, emission, decay profiles and confocal image measurements at room temperature. From the measured absorption spectra, the bonding parameters (δ) were evaluated to find the nature of bonding between Eu3+ ions with its surrounding ligands in these ZnAlBiB glasses. The emission spectra of Eu3+ ions in ZnAlBiB glasses excited at 410 nm (CW laser) show the characteristic of Eu3+ ions with more intense visible red emission corresponding to 5D0→7F2 transition. This intense visible red emission is further confirmed by the confocal luminescence images recorded for all the ZnAlBiB glasses. Judd–Ofelt (J–O) parameters estimated from the emission spectral information are used to estimate the important radiative properties such as transition probability (AR), branching ratios (βR) and emission-cross sections for the prominent emission levels. The large stimulated emission cross-sections and branching ratios observed for ZnAlBiB glasses suggest the utility of these glasses in visible red region of the electromagnetic spectrum. The CIE chromaticity coordinates evaluated from the emission spectra and the confocal images recorded for all the ZnAlBiB glasses also indicates that, these glasses at higher concentration of Eu3+ ions are aptly suitable for intense red emission at 613 nm corresponding to 5D0→7F2 transition.
    Journal of Luminescence 12/2014; 156:80–86. DOI:10.1016/j.jlumin.2014.07.022 · 2.37 Impact Factor
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    ABSTRACT: Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Nd3+ ions were prepared by using the melt quenching technique to study the absorption, emission and decay spectral profiles with an aim to understand the lasing potentialities of these glasses. From the absorption spectra, the Judd–Ofelt (J–O) parameters are evaluated and in turn used to calculate the transition probability (AR), total transition probability (AT), radiative lifetime (τR) and branching ratios (βR) for prominent emission levels of Nd3+. The emission spectra recorded for LTT glasses gives three emission transitions 4F3/2 → 4I9/2, 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 for which effective band widths (ΔλP) and stimulated emission cross-sections (σse) are evaluated. Branching ratios (βR) measured for all the LTT glasses show that 4F3/2 → 4I11/2 transition is quite suitable for lasing applications. The intensity of emission spectra increases with increase in the concentrations of Nd3+ up to 1.0 mol% and beyond concentration quenching is observed. Relatively higher emission cross-sections and branching ratios observed for the present LTT glasses over the reported glasses suggests the feasibility of using LTT glasses for infrared laser applications. From the absorption, emission and decay spectral measurements, it was found that 1.0 mol% of Nd3+ ion concentration is aptly suitable for LTT glasses to give a strong NIR laser emission at 1062 nm.
    Optical Materials 11/2014; DOI:10.1016/j.optmat.2014.10.031 · 2.08 Impact Factor
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    ABSTRACT: Oxy-fluoroborate (OFB) glasses doped with different concentrations of Sm3+ ions have been prepared using conventional melt quenching technique and characterised for their lasing potentialities using spectroscopic techniques such as FTIR, optical absorption, emission and emission decay measurements. The FTIR spectrum has been recorded to determine the various functional groups present in the OFB base glass. From the absorption spectra, the bonding parameters (δ) were evaluated to find the bonding nature present between Sm3+ ions with its neighbouring ligands. The Judd–Ofelt intensity (J–O) parameters (Ωλ, where λ=2, 4, and 6), measured from the experimental oscillator strengths of the absorption spectral futures, are used to evaluate the radiative parameters for the fluorescent transitions 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2 of Sm3+ ions in OFB glasses. The asymmetric ratio has been evaluated to understand the local disorder of Sm3+ ions in the glass network. The experimental lifetimes (τexp) measured from the decay curves are coupled with radiative lifetimes (τrad) to measure quantum efficiency (η) of the prepared glasses. The experimental lifetimes (τexp) for 4G5/2 emission state decrease with increase in Sm3+ ion concentration due to energy transfer. In order to elucidate the nature of energy transfer mechanism, the non-exponential decay curves are well fitted to the Inokuti–Hirayama model for S=6, which indicates that the energy transfer mechanism is of dipole–dipole type. The branching ratio (βR), stimulated emission cross-section (σse) and quantum efficiency (η) values measured for the most intense emission transition 4G5/2→6H7/2 (598 nm) optimise the concentration of Sm3+ ions as 1 mol% to produce bright visible orange lasing emission from these OFB glasses.
    Journal of Luminescence 09/2014; 154. DOI:10.1016/j.jlumin.2014.05.017 · 2.37 Impact Factor
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    ABSTRACT: Oxy-fluoroborate (OFB) glasses doped with different concentrations of Dy3+ ions were synthesized through melt quenching technique and characterized by using optical absorption, photoluminescence and decay analysis to understand the lasing potentialities and their utility for white light emitting diodes (LEDs). The XRD spectrum recorded for undoped OFB glass confirms the amorphous nature of the prepared glasses. Judd-Ofelt theory has been applied to the recorded absorption spectra to measure the radiative properties such as transition probability (A(R)), radiative lifetimes (tau(R)), branching ratios (beta(R)) and spectroscopic quality factor (chi) for the prominent fluorescent levels. The emission spectra recorded for these glasses gives four emission transitions F-4(9/2)-> H-6(15/2), H-6(13/2), H-6(11/2) and H-6(9/2) for which effective band widths (Delta lambda p), experimental branching ratios (beta(exp)) and stimulated emission cross-sections (sigma(se)) are evaluated. To know the lasing potentialities of these glasses, the quantum efficiency (eta) of these glasses are measured by recording the decay curves for the prominent emission levels F-4(9/2)-> H-6(15/2) and F-4(9/2) -> H-6(13/2). Among the observed emission transitions, a transition at 575 nm (F-4(9/2)-> H-6(13/2)) indicates the lasing potentialities. The CIE chromaticity co-ordinates and the confocal photoluminescence images of these glasses further suggests the near white light generation capabilities in principle.
    Journal of Luminescence 08/2014; 153. DOI:10.1016/j.jlumin.2014.03.009 · 2.37 Impact Factor
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    ABSTRACT: Lead tungsten tellurite (LTT) glasses doped with Pr3+ (0.01, 0.1, 0.5, 1.0 and 1.5 mol%) ions were prepared by the conventional melt quenching technique. The glasses were characterized by X-ray diffraction, optical absorption and photoluminescence spectra. The glassy nature of LTT host glass has been confirmed through XRD measurements. From the measured intensities of various absorption bands of these glasses, the three phenomenological Judd-Ofelt (J-O) intensity parameters (Ω2, Ω4 and Ω6) have been evaluated by using the standard as well as modified J-O theory. The J-O parameters measured from the modified J-O theory were used to characterize the absorption and luminescence spectra of these glasses. From this theory, various radiative properties like radiative transition probability (AR), total transition probability (AT), branching ratio (βR) and radiative lifetime (τR) have been evaluated for the fluorescent levels of Pr3+ in these glasses. The emission spectra show five emission bands in visible region for which the effective band widths (ΔλP) and emission cross-sections (σse) have been evaluated. Among all the five emission transitions, a transition 3P0→3F2 is more intense and falls in red region. The visible emission spectra, stimulated emission cross-sections and branching ratios observed for all these glasses suggest the feasibility of using these glasses as lasers in red region. The CIE chromaticity co-ordinates were also evaluated from the emission spectra to understand the suitability of these materials for red emission. From the absorption, emission and CIE chromaticity measurements, it was found that 1 mol% of Pr3+ ion concentration is quite suitable for LTT glasses to develop bright red lasers from these glasses.
    Ceramics International 05/2014; 40(4). DOI:10.1016/j.ceramint.2013.11.084 · 2.09 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of samarium (Sm(3+)) ions were prepared by using melt quenching technique and characterized for their lasing potentialities in visible region by using the techniques such as optical absorption, emission and emission decay measurements. Radiative properties for various fluorescent levels of Sm(3+) ions were estimated from absorption spectral information using Judd-Ofelt (JO) analysis. The emission spectra and con-focal photoluminescence images obtained by 410nm laser excitation demonstrates very distinct and intense orange-red emission for all the doped glasses. The suitable concentration of Sm(3+) ions in these glasses to act as an efficient lasing material has been discussed by measuring the emission cross-section and branching ratios for the emission transitions. The quantum efficiencies were also been estimated from emission decay measurements recorded for the (4)G5/2 level of Sm(3+) ions. From the measured emission cross-sections, branching ratios, strong photoluminescence features and CIE chromaticity coordinates, it was found that 1mol% of Sm(3+) ions doped ZnAlBiB glasses are most suitable for the development of visible orange-red lasers.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 05/2014; 125:53–60. DOI:10.1016/j.saa.2014.01.025 · 2.13 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth Borate (ZnAlBiB) glasses at different compositions doped with 1 mol% of Sm3+ ions were prepared by using the melt quenching technique and investigated by XRD, optical absorption, emission and decay curve analysis to understand the visible luminescence of these glasses. From the absorption spectra the JO parameters are evaluated and are used to calculate the radiative properties such as transition probability, radiative lifetime, branching ratio and absorption cross-sections for various fluorescent levels of Sm3+ ions. The emission spectra of Sm3+ ions doped ZnAlBiB glasses show two intense emission bands (4)G(5/2)-> H-6(7/2) (orange) and (4)G(5/2)-> H-6(9/2) (red) for which the stimulated emission cross-section and branching ratios are evaluated to understand the potentiality of these materials as visible lasers. The decay profiles for the (4)G(5/2) fluorescent level of Sm3+ doped ZnAlBiB glasses have been recorded to measure the quantum efficiency (77) of these glasses. The strong visible emissions, large stimulated emission cross-sections, high branching ratios and good quantum efficiencies observed for the present ZnAlBiB glasses suggest the suitability of these glasses as laser and photonic devices operating in visible region.
    Journal of Luminescence 02/2014; 146:288-294. DOI:10.1016/j.jlumin.2013.09.035 · 2.37 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of Holmium were prepared by conventional melt quenching technique. The glassy nature of these glasses has been confirmed through the XRD spectral measurements. The FTIR spectra recorded for undoped glass revealed the information related to the functional groups involved in the host glass. Optical absorption, excitation and photoluminescence spectra of these glasses have been recorded at room temperature. The Judd–Ofelt theory has been applied successfully to characterize the absorption spectra of the ZnAlBiB glasses. From this theory various radiative properties such as radiative transition probability (AR), radiative lifetimes (τR), branching ratios (βR) and spectroscopic quality factor (χ) for the prominent emission levels 5F5 → 5I7, 5F5 → 5I8 and 5I7 → 5I8 have been evaluated. The photoluminescence spectra revealed the quenching of luminescence intensity beyond 1.0 mol% of Ho3+ ion concentration in ZnAlBiB glasses. To investigate the lasing potentiality of 5F5 → 5I7, 5F5 → 5I8 and 5I7 → 5I8 transitions, the effective band width (Δλp) and the stimulated emission cross-section (σse) were determined. The CIE chromaticity co-ordinates were also evaluated from the emission spectra for all the glasses to understand the suitability of these materials for visible red laser emission in principle.
    Optical Materials 12/2013; 36(2):362–371. DOI:10.1016/j.optmat.2013.09.023 · 2.08 Impact Factor
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    ABSTRACT: Praseodymium doped Zinc Alumino Bismuth Borate (ZnAlBiB) glasses were prepared by melt quenching technique and characterized by optical absorption and emission studies. The glassy nature of these glasses has been confirmed through XRD spectral measurements. From the absorption spectra, the Judd-Ofelt intensity parameters Ωλ (λ=2, 4 and 6) and other radiative properties like transition probability (AR), radiative lifetimes (τR) and branching ratios (βR) have been evaluated. Emission spectra were measured for different concentrations of Pr3+ ions doped glasses by exciting the glasses at 445 nm. The intensity of Pr3+ emission spectra increases from 0.1 to 1 mol% and beyond 1 mol% concentration quenching is observed. The suitable concentration of Pr3+ ions in ZnAlBiB glasses to act as a good lasing material at reddish-orange wavelength (604 nm) region has been discussed by measuring the emission cross-sections for the intense emission transition 1D2→3H4. The CIE chromaticity co-ordinates were also evaluated from the emission spectra for all the glasses to understand the suitability of these materials for reddish-orange emission. From the measured emission cross-sections and CIE chromaticity co-ordinates, it was found that 1 mol% of Pr3+ is aptly suitable for the development of visible reddish-orange lasers.
    Physica B Condensed Matter 11/2013; 428:36-42. DOI:10.1016/j.physb.2013.07.010 · 1.28 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of neodymium are prepared by using the melt quenching technique to study their physical, absorption and luminescence properties to understand the lasing potentialities of these glasses. From the absorption spectra various spectroscopic parameters and Judd–Ofelt (JO) parameters are evaluated. These JO parameters are used to calculate the transition probability (A), radiative lifetime (τR), and branching ratios (βR) for most of the fluorescent levels of Nd3+. The emission spectra recorded for these glasses gives three prominent transitions 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2 for which effective band widths (ΔλP) and stimulated emission cross-sections (σse) are evaluated. Branching ratios and stimulated emission cross-sections measured for all these glasses show that the 4F3/2→4I11/2 transition under investigation has the potential for laser applications. The intensity of Nd3+ emission spectra increases with increasing concentrations of Nd3+ up to 1 mol% and beyond 1 mol% the concentration quenching is observed. The high stimulated emission cross-section and branching ratios from the present glasses suggests their potential for infrared lasers. From the absorption and emission spectral studies it was found that, 1 mol% of Nd3+ ion concentration is optimum for Zinc Alumino Bismuth Borate glasses to generate a strong laser emission at 1060 nm.
    Journal of Physics and Chemistry of Solids 09/2013; 74(9):1308–1315. DOI:10.1016/j.jpcs.2013.04.009 · 1.59 Impact Factor
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    ABSTRACT: Zinc Alumino Bismuth borate (ZnAlBiB) optical glasses of different compositions doped with 1 mol% of Dy3+ ions were prepared by the conventional melt quenching technique and investigated by the XRD, optical absorption, photoluminescence and decay curve analysis. The glassy nature of ZnAlBiB host has been confirmed through XRD measurements. From the absorption spectral measurements, the three phenomenological intensity parameters Ωλ (λ=2,4 and 6) have been determined from the Judd-Ofelt (J-O) theory. By using JO intensity parameters, several radiative properties such as transition probability (AR), branching ratio (βR) and radiative lifetimes (τR) have been determined. The room temperature photoluminescence spectra of Dy3+ ions doped ZnAlBiB glasses gave two relatively intense emission bands 4F9/2→6H15/2 (blue), 4F9/2→6H13/2 (yellow) along with one faint band. The higher values of branching ratios and stimulated emission cross-sections for the 4F9/2→6H13/2 transition suggest the utility of these glasses as potential laser materials. The decay curves have been recorded for all the ZnAlBiB glasses to measure the quantum efficiency of these glasses by measuring the experimental lifetime (τexp). The radiative properties and CIE chromaticity co-ordinates have been evaluated from the emission spectra to understand the feasibility of these glasses for optoelectronic devices.
    Ceramics International 09/2013; 39(7):8459-8465. DOI:10.1016/j.ceramint.2013.04.028 · 2.09 Impact Factor
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    ABSTRACT: a b s t r a c t Good optical quality Dy 3 þ doped Zinc Alumino Bismuth Borate (ZnAlBiB) glasses were prepared by the conventional melt quenching technique and characterized by optical absorption and luminescence studies. The glassy nature of these materials has been confirmed through XRD measurements. From the absorption spectra, the three phenomenological JO parameters O l (l¼ 2,4 and 6) have been determined from the absorption spectral intensities by using the JO theory. Luminescence spectra were measured for different concentrations of Dy 3 þ ions doped glasses by exciting the glasses at 387 nm. The intensity of Dy 3 þ emission spectra increases from 0.5 mol% to 1 mol % and beyond 1 mol % the concentration quenching is observed. The suitable concentration of Dy 3 þ ions for ZnAlBiB glassy material to act as good lasing material has been discussed by measuring the branching ratios and emission cross-sections for two strong emission transitions such as 4 F 9/2 -6 H 15/2 and 4 F 9/2 -6 H 13/2 observed in visible region. By exciting these glassy materials at various excitation wavelengths in n-UV region, the CIE chromaticity coordinates were evaluated for the two sharp emissions observed in blue (4 F 9/2 -6 H 15/2) and yellow (4 F 9/2 -6 H 13/2) regions to understand the suitability of these materials for white light generation. & 2013 Elsevier B.V. All rights reserved.
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    ABSTRACT: Dy3+-doped alkali lead tellurofluoroborate (RLTB) glasses (R=Li, Na and K) were prepared by melt quenching technique. Judd–Ofelt theory has been used to evaluate the three intensity parameters Ω2, Ω4 and Ω6 from the experimental oscillator strengths. The photoluminescence spectra obtained by the excitation wavelength of 385nm show four emission bands at 454, 483, 575 and 665nm corresponding to the 4I15/2→6H15/2 and 4F9/2→6HJ/2 (J=15/2, 13/2 and 11/2) transitions, respectively. The laser characteristic parameters like fullwidth at half maxima (FWHM), stimulated emission cross-sections (σe), optical gain parameters (σe×τexp) and gain bandwidth parameters (σe×FWHM) were determined. From the visible emission spectra, yellow to blue (Y/B) intensity ratios and chromaticity coordinates were also estimated. The lifetimes of 4F9/2 metastable state were also measured and discussed.
    Journal of Quantitative Spectroscopy and Radiative Transfer 01/2011; 112(1):78-84. DOI:10.1016/j.jqsrt.2010.08.017 · 2.29 Impact Factor