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RISS 인기검색어
- 검색키워드
- 저자 : Unithrattil Sanjith (검색결과 16 건)
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Phase formation and luminescence properties of ternary solid-solution among tetragonal systems
Unithrattil, Sanjith,Kim, Ha Jun,Im, Won Bin ELSEVIER SCIENCE 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.798 No.-
<P><B>Abstract</B></P> <P>A new strategy for developing solid-solution compounds from three constituent compounds was analyzed. Using this strategy, a series of yellow-light-emitting phosphors derived from ternary solid-solution host compositions were prepared using solid-state synthesis. Three vertex members, Sr<SUB>3</SUB>SiO<SUB>5</SUB> (space group <I>P</I>4/<I>ncc</I>), Sr<SUB>3</SUB>AlO<SUB>4</SUB>F (space group <I>I</I>4/<I>mcm</I>), and LaSr<SUB>2</SUB>AlO<SUB>5</SUB> (space group <I>I</I>4/<I>mcm</I>), were selected from similar crystal structures with slightly different symmetries. The crystallization space group of the composition was found to be dependent on the end members, and from the vertex of the ternary plot to the centroid, the composition assumed the space group that was more tolerant toward substitutions. All the compositions, except those lying at the periphery of the ternary plot, formed a single phase and emitted yellow light when activated with Ce<SUP>3+</SUP> ions. The luminescence properties of the 28 selected compositions on the ternary plot were analyzed. The compound that was formed from a 1:2:1 ratio of end members assumed a <I>I</I>4/<I>mcm</I> structure and showed the highest-intensity emission. Phosphor derived from the developed host lattice was analyzed for application in solid-state lighting devices by preparing a white-light emitting device.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phase formation in ternary solid-solutions of tetragonal systems. </LI> <LI> Tetragonal structure Sr<SUB>3</SUB>SiO<SUB>5</SUB>, LaSr<SUB>2</SUB>AlO<SUB>3</SUB> and Sr<SUB>3</SUB>AlO<SUB>4</SUB>F are investigated in the preparation of ternary solid solution. </LI> <LI> Structural analysis of all the selected compositions was carried out using the Le Bail method. </LI> <LI> The detailed structural analysis of selected compositions was performed via Rietveld refinement. </LI> <LI> Ternary solid solution present great color tunability in wLED fabrication. </LI> </UL> </P>
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Unithrattil, Sanjith,Arunkumar, Paulraj,Kim, Yoon Hwa,Kim, Ha Jun,Vu, Ngoc Hung,Heo, Jaeyeong,Chung, Woon Jin,Im, Won Bin American Chemical Society 2017 Inorganic Chemistry Vol.56 No.24
<P>NaCa<SUB>3</SUB>PSiO<SUB>8</SUB> was synthesized in a microwave-assisted solid-state reaction. The crystal structure of the synthesized compound was solved using a least-squares method, followed by simulated annealing. The compound was crystallized in the orthorhombic space group <I>Pna</I>2<SUB>1</SUB>, belonging to Laue class <I>mmm</I>. The structure consisted of two layers of cation planes, each of which contained three cation channels. The cation channels in each of the layers ran antiparallel to that of the adjacent layer. All the major cations together constituted four distinct crystallographic sites. The Rietveld refinement of the powder X-ray diffraction data, followed by the maximum-entropy method analysis, confirmed the obtained structure solutions. The electronic band structure of the compound was analyzed through density function theory calculations. Luminescence properties of the compound, upon activating with Eu<SUP>2+</SUP> ions, were analyzed through photoluminescence measurements and decay profile analysis. The compound was found to exhibit green luminescence centered at ∼502 nm, with a typical broadband emission due to the transition from the crystal-field split 4<I>f</I><SUP>6</SUP>5<I>d</I> to 4<I>f</I><SUP>7</SUP> levels.</P><P>A new phosphosilicate composition with diverse cation sites for activator substitution leads to a broadband emitting phosphor with peak emission wavelengths located in the green region of the spectrum.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2017/inocaj.2017.56.issue-24/acs.inorgchem.7b02456/production/images/medium/ic-2017-024568_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic7b02456'>ACS Electronic Supporting Info</A></P>
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Unithrattil, Sanjith,Kim, Ha Jun,Gil, Kyeong Hun,Vu, Ngoc Hung,Hoang, Van Hien,Kim, Yoon Hwa,Arunkumar, Paulraj,Im, Won Bin American Chemical Society 2017 Inorganic chemistry Vol.56 No.10
<P>A series of britholite compounds were synthesized by simultaneous introduction of trivalent La3+ and Si4+ ions into an apatite structure. The variations in the average structure, electronic band structure, and microstructural properties resulting from the introduction of cation pairs were analyzed as a function of their concentration. The effects of the structural variance and microstructural properties on the broad-band-emitting activator ions were studied by introducing Eu2+ ions as activators. For the resulting compound, which had dual emission bands in the blue and yellow regions of the spectrum, the emission peak position And strength were dependent upon the concentration of La3+-Si4+ pairs. By engineering the relative sizes of the two possible activator sites in the structure, 4f and 6h, through the introduction of a combination of trivalent La3+ and a polyanion, the preferential site occupancy of the activator ions was favorably altered. Additionally, the activator ions responsible for the lower-Stokes-shifted blue component of the emission functioned as a sensitizer of the larger-Stokes-shifted yellow emitting activators, and predominantly yellow-emitting phosphors were achieved. The feasibility of developing a white light emitting Sad-state device using the developed phosphor was also demonstrated.</P>
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황승현,Sanjith Unithrattil,이현준,송재선,이혜정,아눕,이상한,조지영 한국물리학회 2019 Current Applied Physics Vol.19 No.8
Superlattice comprising of ferroelectric (FE) and non-ferroelectric (non-FE) material has been developed to induce a ferroelectric response in the non-ferroelectric layer. In this study, a superlattice thin film comprising of BiFeO3 (BFO) as FE oxide and La0.85Ce0.15MnO3 (LCMO) as semiconducting non-FE oxide is fabricated and investigated the FE and piezoelectric responses in LCMO. We observed the piezoelectric response of individual layers using time-resolved X-ray microdiffraction experiment under an external electric field. Piezoelectric response of individual layers was resolved by comparing it with the values obtained from kinematic diffraction calculation. Piezoelectric coefficient (d33) of LCMO monolayer is found to be approximately 27 pm/V, which is a similar value as that of the BFO layer.
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Yim, Chul Jin,Unithrattil, Sanjith,Chung, Woon Jin,Im, Won Bin American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.12
<P>Red emitting nanofibers, KGdTa2O7:Eu3+ were synthesized by electrospinning technique followed by heat treatment. As-prepared uniform fiber precursor with diameter ranging from about 700 nm to about 900 nm were calcined after removing organic species by calcination. The fiber surface become rough and diameter decreased to about 250-340 nm range due to decomposition of organic species and formation of inorganic phase. Morphology, structural and photoluminescent properties of fibers were analyzed using thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). TG-DTA analysis indicates that KGdTa2O7:Eu3+ began to crystalize at 520 degrees C. Fibers annealed at 900 degrees C formed well crystallized uniform fibers. Under ultraviolet excitation KGdTa2O7:Eu3+ exhibits red emission due to transitions in 4f states of Eu3+. The excitation band is dominated by the Eu(3+)--O2-charge transfer band peaked at 289 nm. The emission peak is in the region that is ideal for red light emission.</P>
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Vu, Ngoc Hung,Unithrattil, Sanjith,Hoang, Van Hien,Chun, Sangeun,Im, Won Bin Elsevier Sequoia 2017 Journal of Power Sources Vol. No.
<P><B>Abstract</B></P> <P>Spinel-layered composites of Li<SUB>1.5</SUB>MnTiO<SUB>4+<I>δ</I> </SUB> were studied for their use as high-energy, low-cost, and environmentally benign cathode materials. The bulk particles showed an attractive specific capacity of up to 250 mAh g<SUP>−1</SUP> at C/10. To improve the performance of this cathode at a high C-rate, a spinel-layered Li<SUB>1.5</SUB>MnTiO<SUB>4+<I>δ</I> </SUB> nanorod was successfully synthesized using a β-MnO<SUB>2</SUB> nanorod template. The nanorod, which had an average diameter of 200 nm and a length of 1 μm, showed specific capacity as high as the bulk particle at C/10. However, owing to a one-dimensional nanostructure with a large effective contact area for Li<SUP>+</SUP> diffusion, the nanorod sample exhibited enhanced capacities 11% (170 mAh g<SUP>−1</SUP>) and 167% higher (80 mAh g<SUP>−1</SUP>) at 1C and 10C rates, respectively, compared to the bulk particles. Moreover, both samples showed good cycle stability and capacity retention of over 85% after 100 cycles at 1C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A promising Li<SUB>1.5</SUB>MnTiO<SUB>4+<I>δ</I> </SUB> cathode: spinel-layered structure with high capacity. </LI> <LI> A Li<SUB>1.5</SUB>MnTiO<SUB>4+<I>δ</I> </SUB> nanorod was synthesized by using a β-MnO<SUB>2</SUB> nanorod template. </LI> <LI> The Li<SUB>1.5</SUB>MnTiO<SUB>4+<I>δ</I> </SUB> nanorods exhibit improved rate performance at high C-rate. </LI> <LI> The structure and electrochemical performances of Li<SUB>1.5</SUB>MnTiO<SUB>4+<I>δ</I> </SUB> were studied. </LI> </UL> </P>
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Sohn, In Seong,Unithrattil, Sanjith,Im, Won Bin American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.8
<P>Application of quantum dots as a color converter in white light-emitting diodes (WLEDs) has been highly restrained because of its lower stability under the operating conditions of LEDs. The feasibility of using quantum dots in WLEDs has been studied and demonstrated by developing a non-conventional packing technique. Multiple core shell CuInS<SUB>2</SUB>/ZnS quantum dots were coated by silica, and the silica-coated quantum dots were dispersed in ethoxylated trimethylolpropane triacrylate to form a color conversion film. This along with phosphor in a glass plate made of Y<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB>:Ce<SUP>3+</SUP> phosphor was stacked in different configurations, and its effect on color rendering of WLEDs was studied. In addition, the configuration developed here protects the color converter from thermal strain and moisture.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-8/am500429c/production/images/medium/am-2014-00429c_0007.gif'></P>
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Park, Seung Hyok,Lee, Kyoung Hwa,Unithrattil, Sanjith,Yoon, Ho Shin,Jang, Ho Gyeom,Im, Won Bin American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.51
<P>A red-emitting phosphor, CaY<SUB>1-<I>x</I></SUB>Eu<SUB><I>x</I></SUB>Al<SUB>3</SUB>O<SUB>7</SUB> (CYA:Eu<SUP>3+</SUP>), was prepared by conventional solid-state reaction, and its structural properties were investigated by means of Rietveld refinement method and maximum entropy method using an X-ray source. XRD patterns confirm the tetragonal phase of CYA:Eu<SUP>3+</SUP> phosphors. The photoluminescence properties of the samples were investigated for application to white light-emitting diodes (WLEDs). The emission spectrum is dominated by a red peak located at 616 nm due to the <SUP>5</SUP>D<SUB>0</SUB> → <SUP>7</SUP>F<SUB>2</SUB> electric dipole transition of Eu<SUP>3+</SUP> ions. Concentration quenching occurs when the Eu<SUP>3+</SUP> concentration is about 0.35 and the critical transfer distance of the phosphor is also calculated. A white LED fabricated with blue, green, and CYA:Eu<SUP>3+</SUP> red phosphor incorporated with an encapsulant in ultraviolet LEDs (λ<SUB>max</SUB> = 396 nm) is discussed.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-51/jp307192y/production/images/medium/jp-2012-07192y_0011.gif'></P>
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Kim, Yoon Hwa,Viswanath, Noolu S. M.,Unithrattil, Sanjith,Kim, Ha Jun,Im, Won Bin The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.1
<P>In the past decades, solid-state lighting based on phosphors as energy converters has been a fast-growing industry. Phosphor-converted white light-emitting diodes (pc-wLEDs) enable high-power applications and miniaturization; for this, the phosphor must have good stability and high efficiency. In order to satisfy this demand, phosphor plates have been proposed instead of conventional organic-based phosphor binders. In this review, such phosphor plates are categorized according to their synthesis methods, and the advantages and disadvantages of each category are detailed. In addition, we describe the major aspects of phosphor plates that require improvement for applications in high-power devices. For the fabrication of high-power LEDs, the phosphor configuration, color purity, porosity, and particle size of glass powders are key properties to enhance the luminescence efficiency and reduce the generation of heat inside wLED packages, thereby improving thermal stability.</P>
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Vu, Ngoc Hung,Im, Jong Chan,Unithrattil, Sanjith,Im, Won Bin The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.5
<P>An integrated layered-spinel material with a nominal composition of (1 − <I>x</I>)Li1.2Mn0.6Ni0.2O2·<I>x</I>LiMn1.5Ni0.5O4 (0.15 < <I>x</I> < 0.3) and crystal defects has been found to be a promising cathode material with a high capacity of 280 mA h g<SUP>−1</SUP>. However, capacity fading arising from Mn<SUP>2+</SUP> dissolution occurred at low voltages and long cycling times. To improve the cycling stability while preserving the advantages of this cathode material, a synergic coating and doping approach was studied. This method yields a coating with a similar, but more stable, structure to that of the pristine sample. This coating is achieved by the bulk doping of the surface while maintaining the ratio of layered to spinel phases. The coating layer had a thickness of 12 to 18 nm, which increased with increasing Ti doping, and protected the sample at low voltages while maintaining the ion and charge transport channels on the surface. The Ti-doped sample enhanced the capacity retention by up to 97% after 100 cycles at C/10 and 89% after 200 cycles at 1C compared to 75% and 74% of the pristine sample, respectively. The optimized sample delivered a stable capacity of 270, 250, and 145 mA h g<SUP>−1</SUP> at C/20, C/10, and 1C respectively. This study provides an effective approach to improve the cycling performance of integrated spinel-layered cathode materials.</P>
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