Spectroscopic investigations of Nd³⁺ doped gadolinium calcium silica borate glasses for the NIR emission at 1059 nm

Kesavulu, C.R.,Kim, H.J.,Lee, S.W.,Kaewkhao, J.,Wantana, N.,Kaewnuam, E.,Kothan, S.,Kaewjaeng, S. Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.695 No.-

<P><B>Abstract</B></P> <P>The Nd<SUP>3+</SUP>-doped gadolinium calcium silica borate (BSGdCaNd) glasses of composition (55-x) B<SUB>2</SUB>O<SUB>3</SUB> - 10 SiO<SUB>2</SUB> - 25 Gd<SUB>2</SUB>O<SUB>3</SUB> -10 CaO -x Nd<SUB>2</SUB>O<SUB>3</SUB>, where x = 0.0, 0.05, 0.5, 1.0, 1.5, 2.0 and 2.5 mol %, have been prepared by conventional melt quenching technique and are characterized through structural, thermal, absorption, emission and decay time measurements. Based on the Judd-Ofelt intensity parameters and radiative properties were determined from the absorption spectrum. The emission spectra recorded for BSGdCaNd glasses gives three emission transitions <SUP>4</SUP>F<SUB>3/2</SUB> → <SUP>4</SUP>I<SUB>9/2</SUB> (903 nm), <SUP>4</SUP>F<SUB>3/2</SUB> → <SUP>4</SUP>I<SUB>11/2</SUB> (1059 nm) and <SUP>4</SUP>F<SUB>3/2</SUB> → <SUP>4</SUP>I<SUB>13/2</SUB> (1334 nm) for which effective bandwidths (Δλ<SUB>eff</SUB>) and stimulated emission cross-section (σ(λp)) are evaluated. Branching ratios (β<SUB>R</SUB>) measured for BSGdCaNd0.5 glass show that <SUP>4</SUP>F<SUB>3/2</SUB> → <SUP>4</SUP>I<SUB>11/2</SUB> transition is quite suitable for lasing applications. The intensity of emission spectra increases with increase in the concentration of Nd<SUP>3+</SUP> ion up to 1.0 mol% and beyond that concentration, quenching is observed. The decay from <SUP>4</SUP>F<SUB>3/2</SUB> level is found to be non-exponential nature for concentrations of Nd<SUP>3+</SUP> ions. The non-exponential curve has been fitted to the Inokuti-Hirayama model to understand the nature of energy transfer process. Hence, the high emission cross-section (1.39 × 10<SUP>−20</SUP> cm<SUP>2</SUP>), branching ratio (0.58) and long lifetime (342 μs) indicate that the BSGdCaNd0.5 glass system could be considered as a good candidate for strong NIR lasers at 1059 nm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nd<SUP>3+</SUP>-doped gadolinium calcium silica borate glasses were prepared and characterized. </LI> <LI> Spectroscopic parameters were evaluated using Judd-Ofelt theory. </LI> <LI> Optical properties have been evaluated and compared to other host matrices. </LI> <LI> Strong NIR emission at 1059 nm (<SUP>4</SUP>F<SUB>3/2</SUB> → <SUP>4</SUP>I<SUB>11/2</SUB>) has been found for Nd<SUP>3+</SUP> ion in BSGdCaNd glasses. </LI> <LI> BSGdCaNd0.5 glass system could be considered as a good candidate for strong NIR lasers at 1059 nm. </LI> </UL> </P>

Influence of Er³⁺ ion concentration on optical and photoluminescence properties of Er³⁺-doped gadolinium-calcium silica borate glasses

Kesavulu, C.R.,Kim, H.J.,Lee, S.W.,Kaewkhao, J.,Wantana, N.,Kothan, S.,Kaewjaeng, S. Elsevier Sequoia 2016 JOURNAL OF ALLOYS AND COMPOUNDS Vol.683 No.-

The Er<SUP>3+</SUP>-doped gadolinium calcium silica borate glasses of composition (55-x) B<SUB>2</SUB>O<SUB>3</SUB> - 10 SiO<SUB>2</SUB> - 25 Gd<SUB>2</SUB>O<SUB>3</SUB> - 10 CaO - x Er<SUB>2</SUB>O<SUB>3</SUB>, where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol %, have been prepared by conventional melt quenching technique and are characterized through optical absorption, visible and near-infrared (NIR) emission spectra and decay time measurements. Judd-Ofelt (JO) intensity parameters (Ω<SUB>λ</SUB>, λ = 2, 4 and 6) have been derived from the absorption spectrum of 0.5 mol % Er<SUB>2</SUB>O<SUB>3</SUB> doped glass and in turn are used to calculate radiative properties for the important luminescent levels of Er<SUP>3+</SUP> ions. The studied glasses show intense and broad green (550 nm) and red (591 nm) visible emissions under at 379 nm excitation. Upon excitation at 980 nm laser diode, an intense 1.53 μm NIR emission has been observed with the maximum full width at half maximum (FWHM) and its value is found to be 106 nm for 2.5 mol % Er<SUP>3+</SUP>-doped gadolinium calcium silica borate glasses. This broad luminescence locates in the region of 1420-1635 nm and covers the S, C and L bands. The decay curves of the <SUP>4</SUP>I<SUB>13/2</SUB> level exhibit exponential nature for all the concentrations. The lifetime of the <SUP>4</SUP>I<SUB>13/2</SUB> level has found to be decrease from 1.46 to 1.35 ms with increase of Er<SUP>3+</SUP> ion concentration. Hence, these results clearly indicate that present glasses are suitable for efficient short and conventional-length optical amplifiers and tunable lasers.

Optical and upconversion properties of Er³⁺-doped oxyfluoride transparent glass-ceramics containing SrF₂ nanocrystals

Kesavulu, Culala Rajasekharaudayar,Yoo, Mi-Yeon,Lee, Jin-Ho,Lim, Ki-Soo,Dharmaiah, Peyala,Jayasankar, Chalicheemalapalli Kulala,Babu, Palamandala Cambridge University Press (Materials Research Soc 2013 Journal of materials research Vol.28 No.11

<▼1><B>Abstract</B><P/></▼1><▼2><P>Er<SUP>3+</SUP>-doped oxyfluoride transparent glass and glass-ceramics (GCs) containing SrF2 nanocrystals were prepared and their spectroscopic properties were investigated. The formation of SrF2 nanocrystals in GCs has been confirmed by x-ray diffraction (XRD) and transmission electron microscopy. The Judd-Ofelt (JO) parameters have been evaluated from absorption spectra of the Er<SUP>3+</SUP>-doped glass and GCs, which are used to predict radiative properties for some important luminescence levels of Er<SUP>3+</SUP> ions in glass and GCs. The XRD and JO parameters suggest that the Er<SUP>3+</SUP> ions are progressively incorporated into the SrF2 nanocrystals in the GCs compared with glass. The up-conversion luminescence intensity increases significantly in GCs with increase in time of thermal treatment. The lifetime of the <SUP>4</SUP>S3/2 level of the Er<SUP>3+</SUP> ions in GCs is found to be slightly higher than that in the glass due to the incorporation of Er<SUP>3+</SUP> ions into the lower phonon energy of SrF2 nanocrystals in the GCs.</P></▼2>

Enhanced visible emissions of Pr³⁺-doped oxyfluoride transparent glass-ceramics containing SrF₂ nanocrystals

Kesavulu, C.R.,Viswanath, C.S. Dwaraka,Karki, Sujita,Aryal, Pabitra,Kim, H.J.,Jayasankar, C.K. Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.2

<P><B>Abstract</B></P> <P>The Pr<SUP>3+</SUP>-doped oxyfluoride transparent glass and glass-ceramic (GC) with the composition of 41SiO<SUB>2</SUB> + 10Al<SUB>2</SUB>O<SUB>3</SUB> + 25.5LiF + 23SrF<SUB>2</SUB> + 0.5Pr<SUB>2</SUB>O<SUB>3</SUB> were prepared and investigated their optical and luminescence properties. The formation of SrF<SUB>2</SUB> nanocrystals in GC has been confirmed by X-ray diffraction (XRD) and transmission electron micrographs (TEM). The Fourier transform infrared spectroscopy (FT-IR) studies were used to examine the network structure characteristics of silicates in the glass matrices. The XRD and TEM results suggest that the Pr<SUP>3+</SUP> ions are progressively incorporated into the SrF<SUB>2</SUB> nanocrystals in the GC with increase in time of thermal treatment at 650°C, corresponding to the first crystallization temperature of the glass. The obtained visible emissions of Pr<SUP>3+</SUP>-doped GC are several times enhanced than that in the glass and the lifetime of the <SUP>3</SUP>P<SUB>0</SUB> level of the Pr<SUP>3+</SUP> ions in glass and GC are found to be 7 and 12μs, respectively. Therefore, the enhanced visible emission and lifetimes in GC are due to the incorporation of Pr<SUP>3+</SUP> ions into the lower phonon energy of SrF<SUB>2</SUB> nanocrystals in the GCs. Moreover, the smaller difference in ionic radius between the added trivalent ions (Pr<SUP>3+</SUP>) and Sr<SUP>2+</SUP> induces the larger enhancement of luminescence intensity in the GC. Hence, these enhanced visible luminescence properties indicate that the present glass and GC could be useful for photonic device applications.</P>

Spectroscopic properties of Na(Sr,Ba)VO₄:Eu³⁺ novel red-emitting phosphors for solid state lighting applications

Kesavulu, C.R.,Lee, D.G.,Yi, S.S.,Jang, K.,Park, J.H.,Leem, J.S.,Choi, Y.H.,Jang, Y.J.,Choi, J.G. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.561 No.-

Eu<SUP>3+</SUP>-activated novel alkaline earth metal (Sr and Ba) vanadate phosphors, Na(Sr<SUB>0.97-x</SUB>,Ba<SUB>x</SUB>)VO<SUB>4</SUB>:Eu<SUB>0.03</SUB><SUP>3+</SUP> (x=0-0.97) have been successfully synthesized using solid state reaction method and characterized through structure, morphology, elemental analysis, luminescence (excitation, emission and CIE coordinate) and decay rate properties as a function of Ba ion concentration. Phosphors show a broad excitation band (monitored for <SUP>5</SUP>D<SUB>0</SUB>→<SUP>7</SUP>F<SUB>2</SUB> transition of Eu<SUP>3+</SUP>) in the 230-430nm wavelength regions which make them highly suitable for GaN-based LED chips. These phosphors can be efficiently excited by near UV light and exhibit a dominant red emission at 613nm (<SUP>5</SUP>D<SUB>0</SUB>→<SUP>7</SUP>F<SUB>2</SUB>). The decay lifetime and color coordinates were evaluated for Na(Sr,Ba)VO<SUB>4</SUB>:Eu<SUP>3+</SUP> phosphors. Hence, these phosphors could be a potential candidate for light emitting diodes and display applications.

The use of parabolic arc in matching curved boundary by point transformations for septic order triangular element and its applications

V. Kesavulu Naidu,K.V. Nagaraja 장전수학회 2010 Advanced Studies in Contemporary Mathematics Vol.20 No.3

This paper is concerned with curved boundary triangular element having one curved side and two straight sides. The curved element considered here is the 36-node (septic) triangular ele-ment. On using the isoparametric coordinate transformation, the curved triangle in the global (x; y) coordinate system is mapped into a standard triangle: f{ξ, Ƞ)/0≤ξ, Ƞ≤1,ξ+Ƞ≤1}in the local coordinate system (ξ, Ƞ). Under this transformation curved boundary of this triangular element is implicitly replaced by septic arc. The equation of this arc involves parameters, which are the coordinates of points on the curved side. This paper deduces rela-tions for choosing the parameters in septic arc in such a way that the arc is always a parabola which passes through four points of the original curve, thus ensuring a good approximation. The point transformations which are thus determined with the above choice of parameters on the curved boundary and also in turn the other parameters inthe interior of curved triangle will serve as a powerful subparametric coordinate transformation for higher order curved triangular elements with one curved side and two straight sides. We have considered an ap-plication example, which consists of the quarter ellipse: { n(x, y)/x = 0, y = 0, x2/36 + y2/4 = 1}We take this as a curved triangle in the physical coordinate system (x, y). We have demon-strated the use of point transformations to determine the points along the curved boundary of the triangle and also the points in the interior of the curved triangle. We have next demon-strated the use of point transformation to determine the arc length of the curved boundary. An additional demonstration which uses the point transformation and the Jacobian is con-sidered. We have thus evaluated certain integrals, for example, ∬Atαdxdy, (t = x, y, α= 0, 1)and found the physical quantities like area and centroid of the curved triangular elements. We hope that this study gives us the required impetus in the use of higher order curved triangular elements under the subparametric coordinate transformation.

OPTIMAL SUBPARAMETRIC FINITE ELEMENT METHOD FOR ELLIPTIC PDE OVER CIRCULAR DOMAIN

V. KESAVULU NAIDU,DIPAYAN BANERJEE,K. V. NAGARAJA 장전수학회 2018 Proceedings of the Jangjeon mathematical society Vol.21 No.1

This paper gives us an insight into the usefulness of the proposed method in Finite Element Analysis (FEM) for solving an el- liptic Partial Dierential Equation (PDE) over circular domain. We are using quadratic and cubic order curved triangular elements to solve the problem of stress concentration on a circular plate, which is governed by Poisson's equation. The proposed FEM solution matches very well with the exact solution. This shows the eciency and effectiveness of the method in various mechanical applications.

Physical, optical and luminescence properties of B₂O₃-SiO₂-Y₂O₃-CaO glasses with Sm³⁺ions for visible laser applications

Karki, Sujita,Kesavulu, C.R.,Kim, H.J.,Kaewkhao, J.,Chanthima, N.,Ruangtaweep, Y. Elsevier 2018 Journal of luminescence Vol.197 No.-

<P><B>Abstract</B></P> <P>Silicoborate glasses with composition of (BSYCaSm:(55-x)B<SUB>2</SUB>O<SUB>3</SUB>+ 10SiO<SUB>2</SUB> +25Y<SUB>2</SUB>O<SUB>3</SUB> +10CaO + xSm<SUB>2</SUB>O<SUB>3</SUB>), (where, x= 0.05, 0.10, 0.20, 0.25, 0.30, 0.40, 0.50, mol%) have been synthesized by using the well-known melt quenching technique. The present work deals with physical, optical, photoluminescence, X-ray luminescence and decay time studies of silicoborate glasses. Judd-Ofelt (JO) intensity parameters (Ω<SUB>2,</SUB> Ω<SUB>4</SUB> and Ω<SUB>6</SUB>) and radiative properties for the important luminescent level of Sm<SUP>3+</SUP> ions were derived by using the absorption spectrum of 0.3mol% Sm<SUB>2</SUB>O<SUB>3</SUB> doped glass. The luminescence spectra in the visible region was obtained due to <SUP>4</SUP>G<SUB>5/2</SUB> → <SUP>6</SUP>H<SUB>J</SUB> (5/2, 7/2, 9/2 and 11/2) transition of Sm<SUP>3+</SUP> ion under 401nm excitation. The decay profile for the <SUP>4</SUP>G<SUB>5/2</SUB> level of Sm<SUP>3+</SUP> ions was analyzed and found that for lower concentration (≤ 0.20mol%) it is single exponential in nature whereas for higher concentration (≥ 0.25mol%), it turns in to non-exponential due to the transfer of energy between donor (excited state Sm<SUP>3+</SUP>ion) and acceptor (ground state Sm<SUP>3+</SUP> ion). As the concentration of Sm<SUP>3+</SUP> ions increases the decay time of <SUP>4</SUP>G<SUB>5/2</SUB> state decreases. The well-known Inokuti-Hirayama (IH) model was used for fitting the non-exponential decay curves where S = 6 indicates that energy transfer process is of dipole-dipole type. Hence, in the present work, intense transition of <SUP>4</SUP>G<SUB>5/2</SUB> → <SUP>6</SUP>H<SUB>7/2</SUB> (601nm) is found to be suitable for reddish-orange laser emission. CIE chromaticity diagram has been performed for verifying the results of fluorescence in visible laser applications at 601nm.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Optical and luminescence characteristics of Eu 3+ -doped B 2 O 3 :SiO 2 :Y 2 O 3 :CaO glasses for visible red laser and scintillation material applications

Aryal, Pabitra,Kesavulu, C.R.,Kim, H.J.,Lee, S.W.,Kang, Sang Jun,Kaewkhao, J.,Chanthima, N.,Damdee, B. Elsevier 2018 Journal of rare earths Vol.36 No.5

<P>Europium (Eu3+) doped glasses of chemical compositions (55-x)B2O3:10SiO(2):25Y(2)O(3):10CaO:xEu(2)O(3), where x denotes mol% and ranges 0 <= x <= 2.5, were synthesized by adopting conventional melt quenching technique. Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of EU2O3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence, X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt (JO) intensity parameters (omega(lambda)) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability (A(R)), branching ratio (beta(R)), stimulated cross section emission (sigma) and radiative lifetime (tau(R)) for D-5(0) -> F-7(J) (J = 0,1,2,3 and 4) transitions. The decay rate of D-5(0) fluorescent level for all the glass samples was single exponential. Lifetimes of the D-5(0) level were decreased with increasing concentrations of Eu(3+)ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates (x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu3+ doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications. (C) 2017 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.</P>

Photoluminescence properties of Na(Sr,Ca)VO4:Eu(3+) phosphors.

Lee, Dong Gi,Kesavulu, C R,Yi, Soung Soo,Cho, Shinho,Jang, Kiwan,Kim, Sung Hoon,Jeong, Jung Hyun American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.8

<P>Eu3+-activated novel alkaline earth metal (Sr and Ca) vanadate phosphors, Na(Sr0.97-x, Ca-x)VO4:Eu-0.03(3+) (x = 0 to 0.97) has been successfully synthesized using solid state reaction method and characterized by XRD, XPS, FE-SEM, luminescence (PLE, PL and CIE coordinate) and decay rate measurements as a function of Ca ion concentration. Phosphors show a broad excitation band (monitored for D-5(0) -> F-7(2) transition of Eu3+) in the 230-430 nm wavelength regions which make them highly suitable for LED chips. Material gives strong emission of Eu3+ ion (lambda(ex) = 323 nm) and intensity of this emission increases with increase in the doping concentration of Ca ions until a maximum is reached for Na(Sr-0.22, Ca-0.75)VO4:Eu-0.003(3+) (x = 0.75) phase phosphor. The intensity ratio of D-5(0) -> F-7(2) to D-5(0) -> F-7(1) transition (monochromaticity, R) suggest that local symmetry around the Eu3+ ion increases with increase in Ca ion concentration, which is responsible for enhanced emission.</P>