Browsing by Author "Ray, Sudeshna"

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Analysis of growth kinetics and impact of NH3 on the morphology evolution of hexagonal-prism shaped Y4O(OH)(9)NO3/Y2O3 single crystals
(2017-11-01)
Ray, Sudeshna
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Nair, Govind B.
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Dhoble, S. J.
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Kato, H.
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Kakihana, Masato
The effect of NH3 on the morphology evolution of single crystalline hexagonal-prism like Y4O(OH)(9)NO3 and Y2O3 has been systematically investigated, as a function of reaction time, by using a combination of powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Rational control over the morphology has been achieved by the choice of suitable electrolytes like NaNO3, KNO3, NH4NO3, KCl and NH4Cl in the presence of NH4OH. We report that the cross-sectional geometry of hydrothermally grown one-dimensional Y4O(OH)(9)NO3 crystals can be tuned from spherical to hexagonal-prism like shape by introducing a particular reagent like NH4NO3 in the presence of NH4OH. An 'oriented attachment' mediated growth process takes place along with the 'dissolution-recrystallization' route which eventually resulted in the generation of the single crystals with hexagonal-prism like morphology. (C) 2017 Elsevier Ltd. All rights reserved.
Broadband, site selective and time resolved photoluminescence spectroscopic studies of finely size-modulated Y2O3:Eu3+ phosphors synthesized by a complex based precursor solution method
(2014-01-01)
Ray, Sudeshna
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Fabian Leon-Luis, Sergio
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Javier Manjon, Francisco
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Alfonso Mollar, Miguel
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Gomis, Oscar
Undoped and Eu3+-doped cubic yttria (Y2O3) nanophosphors of good crystallinity, with selective particle sizes ranging between 6 and 37 nm and showing narrow size distributions, have been synthesized by a complex-based precursor solution method. The systematic size tuning has been evidenced by transmission electron microscopy, X-ray diffraction, and Raman scattering measurements. Furthermore, size-modulated properties of Eu3+ ions have been correlated with the local structure of Eu3+ ion in different sized Y2O3:Eu3+ nanophosphors by means of steady-state and time-resolved site-selective laser spectroscopies. Time-resolved site-selective excitation measurements performed in the F-7(0) -> D-5(0) peaks of the Eu3+ ions at C-2 sites have allowed us to conclude that Eu3+ ions close to the nanocrystal surface experience a larger crystal field than those in the nanocrystal core. Under the site-selective excitation in the F-7(0) -> D-5(0) peaks, energy transfer between the sites has also been observed. (C) 2013 Published by Elsevier B.V.
Enhanced photovoltaic performance of Y2O3:Ho3+/Yb3+ upconversion nanophosphor based DSSC and investigation of color tunability in Ho3+/Tm3+/Yb3+ tridoped Y2O3
(2020-04-25)
Tadge, Prachi
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Yadav, Ram Sagar
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Vishwakarma, Pradeep Kumar
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Rai, S. B.
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Chen, Teng-Ming
The present study reports the upconversion (UC) based color tuning in Y2O3:Ho3+/Yb3+, Y2O3:Tm3+/Yb3+ and Y2O3:Tm3+/Ho3+/Yb3+ phosphors synthesized through complex based precursor solution method. The Y2O3:Ho3+/Yb3+ phosphor emits intense green and weak red colors whereas the Y2O3:Tm3+/Yb3+ emits NIR and blue colors on excitation with 976 nm. The impact of the enhancement in the concentration of Yb3+ on the color point of codoped as well as tridoped phosphors has been studied in detail. When Y2O3:Tm3+/Ho3+/Yb3+ phosphor is excited by 976 nm laser, the phosphor emits dominant green color. This is due to energy transfer from Tm3+ to Ho3+ ions. The increase in the concentration of Yb3+ ion leads to a color tunability not only in the co-doped but also in the tridoped phosphors. Furthermore, we have incorporated Y2O3:Ho3+,Yb3+ UC phosphor into TiO2 electrode to form an UC based DSSC for converting near IR (NIR) light into visible where DSSCs typically have high sensitivity. The short-circuit current density (Jsc) as well as the open-circuit voltage (Voc) of the UC-TiO2 based cell was found to be 8.46% and 5.18% higher which in turn, resulted into a 10.33% enhancement in power conversion efficiency as compared to that of bare TiO2 based DSSC. Thus, the UC based Y2O3:Ho3+/Yb3+ may be useful in color tunability and DSSC applications. (C) 2019 Elsevier B.V. All rights reserved.
KSrScSi2O7:Eu2+: a novel near-UV converting blue-emitting phosphor with high efficiency and excellent thermal stability
(2013)
Ray, Sudeshna
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Fang, Ying-Chien
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Chen, Teng-Ming
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應用化學系
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Department of Applied Chemistry
A novel blue-emitting phosphor KSrScSi2O7:Eu2+, synthesized from a water-soluble propylene glycol modified silane (PGMS) silicon precursor by a solution approach, exhibits high internal quantum efficiency and remarkable thermal stability, which are attributed to the rigid structural network of the host and weak electron-phonon coupling strength.
Structural and spectroscopic characterizations of a new near-UV-converting cyan-emitting RbBaScSi3O9:Eu2+ phosphor with robust thermal performance
(2017-08-05)
Ray, Sudeshna
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Tadge, Prachi
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Dhoble, S. J.
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Nair, Govind B.
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Singh, Akash
To facilitate the next generation of White Light Emitting Diodes (WLEDs) with higher color rendering and warm lighting, the development of inorganic phosphor for efficient conversion of photons from blue/near-UV light to other visible wavelengths is essential. In this regard, we demonstrate a systematic, cost effective, solution-processable, easily scalable and fully controllable synthesis of a series of RbBaScSi3O9:xEu(2+) (x = 0.2, 0.5, 2, 5, 7), a new cyan emitting scandium silicate based phosphor with 79% internal quantum efficiency under n-UV excitation with robust thermal performance. The concept as well as the methodology of using a "Mineral Inspired Approach" emerges as a new blueprint for the rational design of novel phosphor for phosphor converted WLEDs. The structural refinement, electronic structural calculation using "Density Functional Theory", characteristic photoluminescence study, lifetime measurement as well as the thermal quenching properties of the phosphor has been investigated in detail. Owing to the highly efficient cyan emission at lambda(max) similar to 492 nm a full-width at half-maximum of 63 cm(-1) that shows only very low thermal quenching (89.28% relative to the PL intensity at 150 degrees C with respect to that of measured at room temperature), reflects the great potential for the industrial application of this particular phosphor. (C) 2017 Elsevier B.V. All rights reserved.
Synthesis, luminescence and application of BaKYSi2O7:Eu2+ : A new blue-emitting phosphor for near-UV white-light LED
(2018-05-01)
Ray, Sudeshna
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Tadge, Prachi
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Dutta, Somrita
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Chen, T. M.
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Nair, Govind B.
A series of new silicate phosphors, Ba1-xEuxKYSi2O7 (BKY: Eu2+) (x = 0.005, 0.01, 0.02, 0.05, 0.07) have been synthesized from a water-soluble propylene glycol modified silane (PGMS) based silicon precursor by a solution approach. This phosphor can be efficiently excited by near-UV light and generates a broadband bright blue emission with internal Quantum Efficiency 34%. The detailed crystal structure of monoclinic BKY:Eu2+ was determined from the XRD profile using Rietveld refinement. Band gap was determined from Diffuse Reflectance Spectra using Kubelka Munk function. Steady state and time resolved Photoluminescence measurement as well as the thermal quenching properties of the phosphor have been investigated in detail. A highly efficient broadband blue emission centered lambda(max) similar to 460 nm with a full-width at half-maximum of 72 nm shows very low thermal quenching; 83.2% at 150 degrees C with respect to that measured at room temperature. Moreover, a white LED device has been fabricated by coating the as-synthesized phosphor with a standard red emitting CaAlSiN3:Eu2+ phosphor and a standard green emitting Ba2SiO4:Eu2+ phosphor. The LED device exhibited an excellent color-rendering index CRI of 84.0564 at a correlated color temperature of 3752.4 K with CIE color coordinates of (0.363, 0.293) under a 350 mA forward-bias current. The interesting excitation profile and robust thermal performance reflect the potential application of this phosphor for near UV- LED driven solid state lighting.