http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
- 中文 을 입력하시려면 zhongwen을 입력하시고 space를누르시면됩니다.
- 北京 을 입력하시려면 beijing을 입력하시고 space를 누르시면 됩니다.
RISS 인기검색어
- 검색키워드
- 저자 : B.V. Ratnam (검색결과 11 건)
- 무료
- 기관 내 무료
- 유료
-
Ratnam, B.V.,Jayasimhadri, M.,Bhaskar Kumar, G.,Jang, K.,Kim, S.S.,Lee, Y.I.,Lim, J.M.,Shin, D.S.,Song, T.K. Elsevier Sequoia 2013 JOURNAL OF ALLOYS AND COMPOUNDS Vol.564 No.-
<P>An efficient green emitting Tb3+ doped NaCaPO4 (NCP) phosphor was synthesized by using conventional solid-state reaction for solid-state lighting applications. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), FT-IR, emission and excitation properties were extensively investigated for NCP phosphors. X-ray diffraction analysis confirmed the formation of NaCaPO4 with orthorhombic structure. The excitation spectrum consists of strong 4f-4f transition at around 370 nm, which has higher intensity than the f-d transition. Emission spectra indicated that this phosphor can be efficiently excited by UV light in the range from 250 to 400 nm, and shows strong emission band centered at 547 nm. Analysis of the emission spectra with different Tb3+ concentrations revealed that the optimum dopant concentration for these NCP phosphors is about 5 mol% of Tb3+. Diminishing of D-5(3) level and increasing of D-5(4) level emission intensity with the Tb3+ concentration explained successfully. The emission color was analyzed and confirmed with the help of chromaticity coordinates and color temperature. The excellent luminescent properties of NaCaPO4: Tb3+ phosphor makes it as a potential green phosphor upon near-UV LED excitation. (C) 2013 Elsevier B.V. All rights reserved.</P>
-
Ratnam, B.V.,Sahu, Mukesh K.,Vishwakarma, Amit K.,Jha, Kaushal,Woo, Hyun-Joo,Jang, Kiwan,Jayasimhadri, M. North-Holland 2017 Journal of luminescence Vol.185 No.-
<P><B>Abstract</B></P> <P>Europium activated NaCaPO<SUB>4</SUB> phosphor has been synthesized by various synthesis techniques such as solid-state reaction (SSR), molten salt synthesis (MSS) and sol-gel combustion (SGC) method to optimize the synthesis procedure. The comparative investigations of structural and luminescent properties have been studied to know the best synthesis method. The XRD patterns and Rietveld refinement analysis of the synthesized phosphors confirmed the single phase orthorhombic structure of NaCaPO<SUB>4</SUB>. Excitation spectra indicate the strong absorption in near ultraviolet (n-UV) region and the emission spectra exhibit strong emission band at 595nm corresponds to <SUP>5</SUP>D<SUB>0</SUB>→<SUP>7</SUP>F<SUB>1</SUB> transition under n-UV (λ<SUB>ex</SUB>=392nm) excitation. The SGC route synthesized phosphor exhibit intense emission than that of the SSR and MSS method. Therefore, the effect of dopant (Eu<SUP>3+</SUP>) concentration on the emission intensity and concentration quenching mechanism has been discussed in detail for the Eu<SUP>3+</SUP> doped NaCaPO<SUB>4</SUB> phosphor synthesized by SGC method. The CIE chromaticity coordinates have been calculated for the phosphors synthesized by SSR, MSS and SGC methods to reveal the emitting color and also to know the utility of this phosphor for white LEDs.</P>
-
Jayasimhadri, M.,Jha, Kaushal,Ratnam, B.V.,Woo, Hyun-Joo,Jang, Kiwan,Rao, A.S.,Haranath, D. ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.711 No.-
<P><B>Abstract</B></P> <P>In this work, Tb<SUP>3+</SUP> ions doped lead-germanate-tellurite (LGT) glasses were prepared by conventional melt quenching technique with different dopant concentrations ranging from 0.5 to 3.5 mol %. X-ray diffraction (XRD) and FT-IR analysis were carried out to analyze the structural properties of LGT glass. The excitation spectra revealed a single band centered in the NUV region at 380 nm by monitoring emission at 545 nm. The emission spectra consist of four bands, which are attributed to the <SUP>5</SUP>D<SUB>4</SUB>→<SUP>7</SUP>F<SUB>J</SUB> (J = 3–6) transitions. Among these transitions, the strong emission band was observed at 545 nm corresponding to the <SUP>5</SUP>D<SUB>4</SUB>→<SUP>7</SUP>F<SUB>5</SUB> transition and the optimized doping concentration of Tb<SUP>3+</SUP> ions was 2 mol %. The Huang's theory and I-H model indicate the possibility of energy transfer via electric dipole-dipole interaction between Tb<SUP>3+</SUP> ions. The CIE chromaticity coordinates were (<I>x</I> = 0.282 and <I>y</I> = 0.614) and emits intense yellowish green light. The decay curves measured for <SUP>5</SUP>D<SUB>4</SUB> level for the samples with different doping concentrations and the lifetime for the optimized sample was 548 μs. The results indicate that these glasses have potential applications in solid state lighting and display devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optically transparent Tb<SUP>3+</SUP> doped PbO-GeO<SUB>2</SUB>-TeO<SUB>2</SUB> (LGT) glasses have been prepared. </LI> <LI> Excitation spectrum consists of single band in the NUV region at 380 nm. </LI> <LI> CIE coordinates indicate that Tb<SUP>3+</SUP> doped LGT glass emits yellowish green light. </LI> <LI> Huang's theory applied to reveal the energy transfer process between Tb<SUP>3+</SUP> ions. </LI> <LI> This glass may be potential to use in fabricating GaN based WLEDs. </LI> </UL> </P>
-
-
Luminescent Properties of Tb<SUP>3+</SUP>- Doped NaCaPO<SUB>4</SUB> Phosphor
B. V. Ratnam,,M. Jayasimhadri,Jaeho Yoon,Kiwan Jang,Ho-Sueb Lee,Soung-Soo Yi,Sung Hoon Kim,Jung Hyun Jeong 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6
Trivalent-terbium-doped NaCaPO4 powder phosphors were prepared with different processes by using a conventional solid state reaction method. The phase and the structure of the as-prepared samples were characterized by using X-ray diffraction. The excitation and the emission spectra were measured to characterize the luminescent properties of the NaCaPO4:Tb3+ phosphors. The excitation spectrum exhibited one strong band located in the UV region at 274 nm and was assigned to 4f8 → 4f75d1 transition, and some other excitation bands in the longer wavelength region were attributed to the f-f transitions within the Tb3+ (4f8) configuration. The emission spectra were measured upon 370-nm excitation, and the most intense peak was observed in the green region at 547 nm, corresponding to the 5D4 → 7F5 transition. The emitting color of Tb3+- doped NaCaPO4 phosphor is discussed based on the CIE diagram. The lifetime of the 5D4 energy level of Tb3+ ions in the NaCaPO4 phosphor was measured upon 355-nm excitation. From this study, we have successfully optimized the preparation and emission process of the Tb-doped NaCaPO4 green phosphor for use in white- light- emitting diodes. Trivalent-terbium-doped NaCaPO4 powder phosphors were prepared with different processes by using a conventional solid state reaction method. The phase and the structure of the as-prepared samples were characterized by using X-ray diffraction. The excitation and the emission spectra were measured to characterize the luminescent properties of the NaCaPO4:Tb3+ phosphors. The excitation spectrum exhibited one strong band located in the UV region at 274 nm and was assigned to 4f8 → 4f75d1 transition, and some other excitation bands in the longer wavelength region were attributed to the f-f transitions within the Tb3+ (4f8) configuration. The emission spectra were measured upon 370-nm excitation, and the most intense peak was observed in the green region at 547 nm, corresponding to the 5D4 → 7F5 transition. The emitting color of Tb3+- doped NaCaPO4 phosphor is discussed based on the CIE diagram. The lifetime of the 5D4 energy level of Tb3+ ions in the NaCaPO4 phosphor was measured upon 355-nm excitation. From this study, we have successfully optimized the preparation and emission process of the Tb-doped NaCaPO4 green phosphor for use in white- light- emitting diodes.
-
Eswaraiah, S.,Kim, Yong Ha,Hong, Junseok,Kim, Jeong-Han,Ratnam, M. Venkat,Chandran, A.,Rao, S.V.B.,Riggin, Dennis Elsevier 2016 Journal of Atmospheric and Solar-Terrestrial Physi Vol.140 No.-
<P><B>Abstract</B></P> <P>A minor stratospheric sudden warming (SSW) event was noticed in the southern hemisphere (SH) during September (day 259) 2010 along with two episodic warmings in early August (day 212) and late October (day 300) 2010. Among the three warming events, the signature of mesosphere response was detected only for the September event in the mesospheric wind dataset from both meteor radar and MF radar located at King Sejong Station (62°S, 59°W) and Rothera (68°S, 68°W), Antarctica, respectively. The zonal winds in the mesosphere reversed approximately a week before the September SSW event, as has been observed in the 2002 major SSW. Signatures of mesospheric cooling (MC) in association with stratospheric warmings are found in temperatures measured by the Microwave Limb Sounder (MLS). Simulations of specified dynamics version of Whole Atmosphere Community Climate Model (SD-WACCM) are able to reproduce these observed features. The mesospheric wind field was found to differ significantly from that of normal years probably due to enhanced planetary wave (PW) activity before the SSW. From the wavelet analysis of wind data of both stations, we find that strong 14–16 day PWs prevailed prior to the SSW and disappeared suddenly after the SSW in the mesosphere. Our study provides evidence that minor SSWs in SH can result in significant effects on the mesospheric dynamics as in the northern hemisphere.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The mesosphere response to 2010 minor SSW over the Antarctica was observed. </LI> <LI> The mesospheric wind field is found to significantly differ from normal years. </LI> <LI> Mesospheric cooling (MC) in association with SSWs are found. </LI> <LI> 14–16 day planetary waves are noticed in mesosphere before the onset of SSW. </LI> <LI> SD-WACCM simulations are able to reproduce observed MC and wind reversal. </LI> </UL> </P>
-
Ratnam, B.V.,Jayasimhadri, M.,Jang, K. Pergamon 2014 Spectrochimica acta. Part A, Molecular and biomole Vol.132 No.-
Rare earth ion activated orthophosphates have a great deal of interest due to their thermal stability for white light emitting diodes. In this regard, thermally stable Sm<SUP>3+</SUP> doped NaCaPO<SUB>4</SUB> (NCP) phosphor was synthesized by conventional solid state reaction technique. The phase and the structure of the as prepared powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), FT-IR, emission and excitation properties were extensively investigated for NCP phosphors. X-ray diffraction analysis confirmed the formation of NaCaPO<SUB>4</SUB> with orthorhombic structure. The excitation spectra indicate that this phosphor can be effectively excited by UV light from 350 to 500nm. All the transitions in the excitation spectrum of Sm<SUP>3+</SUP> start from the ground state <SUP>6</SUP>H<SUB>5/2</SUB> to various excited states. The emission spectra indicated that the emitted radiation was dominated by the emission peak wavelength at 599nm originated from the transition of <SUP>4</SUP>G<SUB>5/2</SUB>→<SUP>6</SUP>H<SUB>7/2</SUB>. The optimum concentration of Sm<SUP>3+</SUP> is determined as 1.0mol% based on the concentration dependent emission spectra. These results suggest that the NaCaPO<SUB>4</SUB>:Sm<SUP>3+</SUP> phosphor is a promising orange emitting phosphor under 404nm excitation with CIE coordinates of x=0.545, y=0.41, which might be used in the development of materials for LED's and other optical devices in the visible region.
-
NaCaPO₄모체물질에 첨가된 Eu(²+,³+)에 대한 광학적 성질
윤제호,B.V. Ratnam,Jayasimhadri,장기완,이호섭,이성수,정중현 한국물리학회 2010 새물리 Vol.60 No.9
NaCaPO₄:Eu(²+,³+)powdered phosphors were prepared by using wet and dry solid-state reaction methods, followed by heat treatment in different atmospheres (i.e., air, argon, oxygen, 10 % H₂+90% N₂gas), and the effect of sample preparation condition and heat treatment atmosphere on the luminescent properties of the Eu³+ or the Eu²+ ions in the NaCaPO₄phosphors were studied. The NaCaPO₄:Eu³+ samples prepared by using the wet solid-state reaction method and then heat treated in air showed the strongest emission intensity of the Eu³+ ions. To reduce the Eu³+ to the Eu²+ ion in NaCaPO₄, we calcined the samples prepared in air and oxygen atmospheres again in a reducing atmosphere. Contrary to the emission intensity in NaCaPO₄:Eu³+, the sample prepared by using the wet solid-state reaction method, followed by sintering in an oxygen atmosphere, showed the strongest emission intensity of the Eu²+ ions. Unlike the usual oxide phosphors, the sample prepared by using the dry solid-state reaction method showed better emission efficiency than that prepared by using the wet solid-state reaction method for the NaCaPO₄:Eu³+ phosphors. The emission and the excitation spectra of the NaCaPO₄:Eu²+ phosphors exhibited a strong emission band in the wavelength region of 425-625 nm, with a peak at 507 nm, and an excitation band in the wavelength region of 275-500 nm, with a peak at 422 nm. We found that the optical and the luminescence properties of Eu²+/Eu³+ doped in NaCaPO₄ lattices to be highly dependent on the conditions of sample preparation and on the heat-treatment atmospheres. Eu(²+,³+)가 첨가된 NaCaPO₄분말형광체를 습식 또는 건식고상반응법으로 제조하여 제조조건 및 열처리 분위기의 변화에 따른 Eu(²+,³+)이온들의 광학적 특성을 조사하였다. 공기, 아르곤 및 산소 분위기에서 1차 열처리한 NaCaPO₄:Eu³+시료들의 발광효율은 습식고상반응법으로 제조하여 공기 분위기에서 열처리한 시료가 가장 높은 발광효율을 보였고 산소 분위기에서 열처리한 시료가 가장 낮은 발광효율을 보였으나, 환원분위기에서 2차 열처리 했을때의 NaCaPO₄:Eu²+에 대해서는 정반대의 결과를 보였다. 일반적으로 알려진 사실과는 달리 건식법으로 제조한 시료가 습식법으로 제조한 시료보다 우수한 발광효율을 보였다. NaCaPO₄:Eu²+시료들의 발광스펙트럼은 507nm에서 최대효율을 보였으며, 최대 여기파장은 422nm에서 나타났다. 실험결과들은 NaCaPO₄모체에 첨가된 Eu(²+,³+)이온들의 광학적 특성이 열처리 분위기 및 시료의 제조방법에 매우 의존적이라는 사실을 보여주고 있다.
-
-
연관 검색어 추천
이 검색어로 많이 본 자료
활용도 높은 자료
