Chadalawada Ramanamma Engineering College

Tirupati, India

Chadalawada Ramanamma Engineering College

Tirupati, India
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Pavani K.,Sri Venkateswara University | Suresh Kumar J.,University of Aveiro | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College
Journal of the American Ceramic Society | Year: 2014

Dy3+-Tm3+ ions codoped SrMg2La 2W2O12 (strontium magnesium lanthanum tungstate) phosphors were synthesized by conventional high-temperature solid-state reaction method. X-ray analysis of the end products revealed the well-crystallized phases with orthorhombic structure. The functional groups present in the phosphors were studied by the Fourier transform infrared measurements. To know the potential applicability of these phosphors for white light emission, the excitation and emission spectra were recorded. The excitation spectra exhibited an intense broad band at 313 nm, pertaining to the O → W ligand-to-metal charge-transfer state (LMCT) of the host. With the excitation of LMCT band (313 nm), the decay curves of singly doped SrMg 2La2W2O12:Dy phosphors exhibited single exponential, where as the codoped SrMg2La2W 2O12:DyTm phosphors exhibited double exponential nature. The luminescence colors of these phosphors were estimated from Commission Internationale de L'Eclairage (CIE) coordinates using the photoluminescence data. The color of singly doped SrMg2La2W 2O12:Dy phosphor has been tuned by codoping with Tm 3+ ions. It has been noticed that the CIE chromaticity coordinates (x,y) determined from the luminescence spectrum of singly Dy3+ doped SrMg2La2W2O12 phosphor shifted toward the white light region, when codoped with Tm3+ ions. The increase in correlated color temperatures (Tcct) has been noticed with the increase of Tm3+ ions concentration in SrMg 2La2W2O12:DyTm phosphors. © 2014 The American Ceramic Society.


Pavani K.,Sri Venkateswara University | Suresh Kumar J.,University of Aveiro | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College
Journal of Alloys and Compounds | Year: 2014

In this paper, we report a series of Tb3+ and Eu3+ activated SrMg2La2W2O12 phosphors synthesized by the solid state reaction method. The structural and photoluminescence properties have been characterized and analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, photoluminescence and decay measurements. X-ray diffraction pattern confirms that the SrMg 2La2W2O12 powders were well indexed to orthorhombic structure (JCPDS card No. 35-0259). The excitation spectra monitored at 547 and 617 nm consist of a broad band in the region 250-370 nm pertaining to O → W ligand to metal charge transfer transition and several narrow bands related to Tb3+ and Eu3+ ions absorptions, respectively. The emission spectra of singly Tb3+ and Eu3+ doped SrMg2La2W2O12 phosphors consist of narrow bands from 4f-4f emission transitions of 5D 4 and 5D0 excited levels to several lower lying levels of Tb3+ and Eu3+ ions, respectively. The emission color of phosphors doped with Tb3+ and Eu3+ ions has been changed by varying concentrations and excitation wavelengths to obtain white light emission. The Commission Internationale de L'éclairage (CIE) chromaticity coordinates and correlated color temperatures (Tcct) show that the SrMg2La2W2O12:TbEu phosphors can be tuned to exhibit white light emission ranging from 450 to 750 nm, when they are excited by ultraviolet (UV) light. © 2013 Elsevier B.V. All rights reserved.


Pavani K.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College | Suresh Kumar J.,University of Aveiro | Mohan Babu A.,Chadalawada Ramanamma Engineering College
Journal of Luminescence | Year: 2013

Calcium fluoroborate glasses doped with Tm2O3 (CFBTm) were prepared by the conventional melt quenching method. Optical absorption and the photoluminescence spectra were recorded in UV-vis-NIR regions. Free-ion and Judd-Ofelt (J-O) parameters have been evaluated from the energy level positions and the intensities of the absorption bands. Using the J-O parameters, several radiative parameters were calculated for different excited states of Tm 3+ ions in CFB glasses. Stimulated emission cross-sections (σe) and effective bandwidths (Δλeff) were determined for the observed emission bands. The intensities of the emission peaks in the visible region increase with the increase of Tm2O 3 concentration and then decrease at higher concentrations. The quenching of emission intensities has been attributed to the energy transfer through cross-relaxation mechanisms. The NIR emission spectrum recorded with the excitation of 808 nm laser diode (LD) exhibited an emission peak at 1.47 μm corresponding to the 3H4→3F4 transition. The intensity of NIR emission peak increases with increase of Tm2O3 concentration. Beer Lambert and McCumber theories were also implemented to evaluate the absorption and emission cross-sections for the prominent 3F4→3H6 transition at 1.82 μm emission wavelength. © 2012 Elsevier B.V. All rights reserved.


Lokeswara Reddy G.V.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College | Jamalaiah B.C.,University of Aveiro | Sasikala T.,Sri Venkateswara University
Ceramics International | Year: 2013

A series of YAl3(BO3)4 phosphors doped with different concentrations of Dy2O3 (0.1≤x≤5 mol%) were prepared by solid-state reaction method. The crystallization process of the precursor has been examined by differential thermal analysis (DTA) measurements. The phase purity and surface morphological features were characterized by X-ray diffraction (XRD) and scanning electron microscopic (SEM) investigations. The YAl3(BO3)4 nanocrystals obtained were found to be about 45 nm in size and have the trigonal structure with some agglomeration. Fourier transform infrared (FTIR) and energy dispersive X-ray spectra (EDS) measurements were carried out to understand the compositional and elemental analysis. The characteristics emission peaks of Dy3+ ion corresponding to the transitions of 4F 9/2→6H15/2 at 485 nm and 4F9/2→6H13/2 at 576 nm were observed in the emission spectra. The luminescence quenching noticed at higher Dy2O3 concentrations is due to the exchange interaction among the excited Dy3+ ions. © 2012 Elsevier Ltd and Techna Group S.r.l.


Chengaiah T.,Sri Venkateswara University | Jayasankar C.K.,Sri Venkateswara University | Pavani K.,Sri Venkateswara University | Sasikala T.,Sri Venkateswara University | And 2 more authors.
Optics Communications | Year: 2014

Different concentrations of Dy3+ ions activated ZnMoO 4 luminescent phosphors were prepared using the solid-state reaction method by sintering at 900 C. Phase purity features of the prepared phosphors were characterized by X-ray diffraction (XRD) patterns and the particle size has been found to be about 40 nm. The compositional and structural details were carried out using Fourier transform infrared (FTIR) spectrum. The characteristic emission peaks of Dy3+ ions were observed due to the 4F9/2→6H15/2 (490 nm) and 4F9/2→6H13/2 (580 nm) transitions. The variation of luminescence intensity with Dy3+ ions concentrations as well as with different excitation wavelengths has been discussed. The CIE chromaticity color coordinates (x, y) were calculated from the luminescent characteristics of ZnMoO4: Dy3+ phosphors, which fall in the white light region of the chromaticity diagram. The lifetime of 4F9/2 excited level has been quenched due to the energy transfer among Dy3+ ions at higher concentrations. © 2013 Elsevier B.V.


Sasikala T.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College | Mohan Babu A.,Chadalawada Ramanamma Engineering College
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

Glasses with chemical composition of (62-x) TeO2 + 25 ZnO + 8 K2O + 5 CaO + x Sm2O3 (TZKCSmx; x = 0.1, 0.5, 1.0, 1.5 mol%) were prepared by melt quenching technique. The absorption spectrum was recorded in the UV-visible and NIR regions. The oscillator strengths of absorption bands were obtained by measuring the area under the bands. Judd-Ofelt analysis has been carried out to estimate the host dependent J-O intensity ωλ (λ = 2, 4, 6) parameters by least squares fitting approach. Photoluminescence spectra recorded in the visible region revealed intense green, orange and red emission bands in all the glasses, corresponding to the 4G5/2→ 6H5/2, 4G5/2→6H 7/2 and 4G5/2→6H9/2 transitions respectively. From the emission spectra and J-O intensity parameters, various radiative parameters were calculated from the excited 4G5/2 to the lower lying 6HJ (J = 5/2, 7/2, 9/2, 11/2) multiplet. Quenching of luminescence with the increase of Sm3+ ions concentration has been observed. Decay times of excited 4G5/2 state decrease with the increase of the Sm 3+ ions concentration. The energy transfer mechanism that leads to the quenching of 4G5/2 state lifetime has been discussed. Inokuti-Hirayama (I-H) model was used to evaluate various energy transfer parameters, which are the qualitative indicators for the interaction among Sm3+ ions. © 2012 Elsevier B.V. All rights reserved.


Ramachari D.,Sri Venkateswara University | Moorthy L.R.,Sri Venkateswara University | Moorthy L.R.,Chadalawada Ramanamma Engineering College | Jayasankar C.K.,Sri Venkateswara University
Ceramics International | Year: 2014

Singly doped Dy3+, Tb3+ and co-doped Dy 3+/Tb3+ ions in oxyfluorosilicate glass-ceramics were prepared by conventional melt quenching technique to study their luminescence properties for the development of white light emitting diodes. The X-ray diffraction measurements confirmed the amorphous and KNbO3 crystalline nature of precursor glass and glass-ceramics, respectively. The effect of increasing the concentration of Tb3+ ions on the green emission from the 5D4 excited level has been investigated. The decay profiles of 4F9/2 excited level of Dy 3+ ion were fitted to double exponential function and Inokuti-Hirayama (IH) model to determine the energy transfer rates from Dy 3+ to Tb3+ ions. All the chromaticity (x, y) color co-ordinates determined from the emission spectra were found to be within the white light region of the CIE chromaticity color diagram. © 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Ramachari D.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College | Jayasankar C.K.,Sri Venkateswara University
Materials Research Bulletin | Year: 2013

Sm2O3-doped oxyfluorosilicate glasses were prepared by melt-quenching method. The differential thermal analysis and X-ray diffraction were carried out to investigate the glass transition temperature and structure of precursor glass. Infrared spectroscopy, Raman, optical absorption, photoluminescence and decay measurements were carried out for Sm 3+-doped oxyfluorosilicate glasses. From the absorption spectrum, the Judd-Ofelt intensity parameters have been evaluated to predict the radiative properties for the emission levels of Sm3+ ions. The lifetimes of 4G5/2 level are found to decrease from 1.17 to 0.93 ms due to the energy transfer, when the concentration of Sm3+ ions increases from 0.1 to 2.0 mol%. The optical gain parameter (18.13 × 10-25 cm2 s) of the investigated glass is found to be higher than the other Sm2O3-doped glass systems. © 2013 Elsevier Ltd. All rights reserved.


Chengaiah T.,Sri Venkateswara University | Jayasankar C.K.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College
Physica B: Condensed Matter | Year: 2013

Ce-Eu co-activated Na3Gd(PO4)2 phosphors of high luminescence efficiency were prepared by the solid state reaction method. Emission properties and the partical size of the synthesized phosphors have been explored by the photoluminescence (PL) and X-ray diffraction measurements. The CIE chromaticity color coordinates (x, y) were calculated from the emission spectra of Na3Gd(PO4)2:Ce 3+/Eu3+ phosphors, which fall in the white light region of the chromaticity diagram. The energy transfer from the excited Ce3+ to Eu3+ ions has been explained. © 2013 Published by Elsevier B.V.


Ramachari D.,Sri Venkateswara University | Rama Moorthy L.,Sri Venkateswara University | Rama Moorthy L.,Chadalawada Ramanamma Engineering College | Jayasankar C.K.,Sri Venkateswara University
Optical Materials | Year: 2014

Structural and spectral properties of erbium-doped niobium oxyfluorosilicate glasses were characterized by the differential thermal analysis, Raman, infrared, photoluminescence and lifetime measurements. With the increase of Er3+ ions concentration, the lifetime of 4I13/2 level has been decreased due to the concentration quenching effect. The McCumber's theory was adopted to predict the emission cross-section (σemiM) of 4I13/2 → 4I15/2 transition from the absorption cross-section (σabs) of 4I15/2 → 4I13/2 transition of Er3+ ions. The gain parameters such as optical gain, gain bandwidth and gain coefficient for amplification were evaluated for the 4I13/2 → 4I15/2 emission transition (1.54 μm). The Er 3+ -doped niobium oxyfluorosilicate glass covers both C (1530-1565 nm) and the L (1565-1625 nm) band regions in the optical communication window. From the results of these investigations, it is concluded that the Er 3+-doped niobium oxyfluorosilicate glasses are more useful for photonic device applications. © 2013 Elsevier B.V. All rights reserved.

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