Browsing by Author "Som, Sudipta"

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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.
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.