Browsing by Author "Dutta, Somrita"

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An efficient green-emitting Ba5Si2O6Cl6:Eu2+ phosphor for white-light LED application
(2017-01-01)
Dutta, Somrita
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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 series of novel green-emitting Ba5Si2O6Cl6:Eu2+ (BSOC:Eu2+) phosphors were synthesized via the high-temperature solid-state reaction route. The phase identification, elemental distribution, reflectance spectra, luminescence, and thermal stability of the BSOC:Eu2+ phosphor and its applicability in white light-emitting diodes (WLEDs) were investigated in detail. The broad excitation spectrum was observed from UV to blue light which generated a broadband emission peaking at 510 nm for the present phosphor with a good quantum efficiency of 44% and thereby it is promising for solid-state lighting applications. Temperature-dependent luminescence measurements of the BSOC:Eu2+ phosphor from 25 degrees C to 250 degrees C were performed to obtain the thermal stability of the present phosphor. Finally, a WLED was fabricated using the green-emitting BSOC:Eu2+ phosphor and commercially available red and blue phosphors pumped with a 400 nm blue chip. The CIE parameters such as color coordinate, color rendering index, color correlated temperature and luminous efficacy of radiation of the fabricated LED were measured. The suitable excitation spectra, efficient and broad emission band and excellent color parameters suggest that the synthesized phosphor could be a potential material for WLED application.
La6Si4S17:Ce3+: luminescence and lighting applications of a novel green-emitting phosphor
(2018-11-14)
Yang, Jiun-Yih
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Dutta, Somrita
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Chen, Teng-Ming
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應用化學系
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Department of Applied Chemistry
An efficient green-emitting La6Si4S17:Ce3+ phosphor was synthesized using a solid-state method. The phosphor exhibits a triclinic structure as the main phase. A broad green emission is observed upon excitation at 420 nm with a quantum efficiency of 83%. A white LED fabricated with the phosphor is promising for use in solid-state lighting applications.
Multisite-Occupancy-Driven Intense Narrow-Band Blue Emission from Sr5SiO4Cl6:Eu2+ Phosphor with Excellent Stability and Color Performance
(2020-02-03)
Dutta, Somrita
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Som, Sudipta
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Meena, Mohan Lal
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Chaurasiya, Rajneesh
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Chen, Teng-Ming
The development of an efficient blue phosphor with remarkable thermal stability required for high-quality white-lightemitting diodes (WLEDs) remains an exigent task and mainly concerned BaMgAl10O17:Eu2+ (BAM:Eu). Despite the outstanding performance of BAM:Eu, the reduction in luminescence efficiency under long-term operation results in numerous researches on new hosts having lattice rigidity with symmetrical coordination environment. Therefore, we have synthesized a competent blue-emitting Eu2+-activated Sr5SiO4Cl6 (SSC) phosphors. The admirable rigidity of these phosphors with three Sr polyhedra Sr(I)O-9, Sr(II)O-7, and Sr(III)O-8 assessed from Rietveld refinement indicate the dense connectivity in the crystal structure, and the ab initio calculations further support the firm electronic band structure. The broad excitation from 250 to 450 nm suitably matches the absorption band of a near-UV (n-UV) LED chip. The phosphor exhibited bright blue emission with internal quantum yield and color purity > 90% which contribute to the slender fwhm of 33 nm. The first-principle calculation indicates the most stable site for Eu2+ substitution as Sr(III)O-8, and the experimental results agreed with this fact as well. The synthesized phosphor displayed an excellent thermal stability which is superior to that of the commercial BAM:Eu phosphor. The excellent thermal stability may be owed to the highly symmetric coordination environment of Eu2+ in the SSC host that are revealed from the distortion and charge density distribution calculation by density functional theory. The blue phosphor was further utilized for WLEDs and displayed white light with a high color-rendering index and suitable correlated color temperature, which is ideal for practical applications in warm WLEDs.
Novel Eu2+-activated thiogallate phosphors for white LED applications: structural and spectroscopic analysis
(2018-01-01)
Lee, Szu-Ping
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Chan, Ting-Shan
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Dutta, Somrita
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Chen, Teng-Ming
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應用化學系
Novel Eu2+-activated BaGa2SiS6 and Ba2Ga8SiS16 thiogallate phosphors were prepared by solid-state reaction route. The BaGa2SiS6:Eu2+ phosphor generated a green emission upon excitation at 405 nm, whereas the Ba2Ga8SiS16:xEu(2+) phosphor could be tuned from cyan to green range with increasing Eu2+ concentration upon excitation at 365 nm. Additionally, the thermal luminescence properties of the thiogallate phosphors were investigated in the temperature range of 25 to 250 degrees C. A warm-white LED is fabricated using the combination of a 405 nm blue InGaN-based LED chip with the green-emitting BaGa2SiS6:0.01Eu(2+) phosphor, and red-emitting Sr2Si5N8:Eu2+ commercial phosphor with the CRI value of approximate to 88 and the CCT of 4213 K.
Promising Er3+/Yb3+-Codoped GdBiW2O9 Phosphor for Temperature Sensing by Upconversion Luminescence
(2018-09-01)
Dutta, Somrita
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Som, Sudipta
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Chen, Teng-Ming
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應用化學系
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Department of Applied Chemistry
Yb3+/Er3+-codoped GdBiW2O9 phosphors are prepared via the solidstate route for application in upconversion temperature sensors. The structural analyses indicate that all phosphors possess a single-phased orthorhombic structure. Upon the excitation of a laser wavelength of 980 nm, Yb3+/Er3+-codoped GdBiW2O9 phosphors emanate green emission peaks, endorsed to the emission to the I-4(15/2) state from the S-4(3/2) and H-2(11/2) states, respectively, and the weak emission (red) from the F-4(9/2) state to the I-4(15/2) state of Er3+ ion. The upconversion mechanism has been elucidated via the scheme of energy levels conferred from the pump power-induced upconversion characteristics. The temperature-dependent upconversion of GdBiW2O9 phosphors was investigated in detail along with the estimation of the stability and repeatability of the measurement. The obtained sensitivity data for the present materials with the corresponding sensing parameters show their probable outlook in temperature sensing applications.
Rapid and room temperature synthesis of MAPb(1-x)Sn(x)Br(3-2x)Cl(2x) perovskite quantum dots with enhanced lifetime in warm WLEDs: A step towards environmental friendly perovskite light harvester
(2020-07-01)
Singh, Rajan Kumar
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Som, Sudipta
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Dutta, Somrita
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Jain, Neha
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Singh, Jai
In this work, a facile approach to develop nontoxic CH3NH3PbBr3 perovskite quantum dots (PQDs) by substituting tin (Sn2+) ion instead of lead (Pb2+) ion and chloride (Cl-) ion instead of bromide (Br-) ion has been reported. Synchronized cation and anion substitution in CH3NH3Pb1-xSnxBr3-2xCl2x PQDs has resulted in commercial-friendly properties like fine-tuning of bandgap, shifting of color emission from green to cyan region (523 nm-490 nm), enhancing structural stability, excitonic lifetime, and color gamut. Presence of Sn2+ cations in +2 state, Cl- anions in -1 state, and ion exchange was confirmed from various spectroscopic and morphological analyses. Photoluminescence quantum yield (PLQY) for unsubstituted CH3NH3PbBr3 was observed as 97.50% and it is reduced to > 50% for 15% SnCl2 substituted CH3NH3PbBr3 PQDs because of the presence of defect-related nonradioactive recombination centres while cation and anion changeover. Warm white LED prototype with 123% color gamut encircling as per National Television System Committee Standard was achieved using as prepared CH3NH3Pb1-xSnxBr3-2xCl2x PQDs and commercial red phosphor on the blue LED chip. The inflated colour-gamut, promising PLQY, and slender FWHM of as-synthesized CH3NH3Pb1-xSnxBr3-2xCl2x PQDs illustrate great prospect to explore their utilization in display applications. Reduction in toxicity in perovskite material was confirmed by the biological study.
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.