Greenish-Yellow Emission from Dy3+-Doped Y2O3 Nanophosphors

Jayasimhadri, M.,Ratnam, B. V.,Jang, K.,Lee, H. S.,Chen, B.,Yi, S. S.,Jeong, J. H.,Moorthy, L. R. Blackwell Publishing Ltd. 2010 Journal of the American Ceramic Society Vol.93 No.2

White light generation from Dy3+-doped ZnO-B2O3-P2O5 glasses

Jayasimhadri, M.,Jang, Kiwan,Lee, Ho Sueb,Chen, Baojiu,Yi, Soung-Soo,Jeong, Jung-Hyun American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.106 No.1

Combustion Synthesis and Luminescent Properties of Nano and Submicrometer-Size Gd2O3:Dy3+ Phosphors for White LEDs

Jayasimhadri, M.,Ratnam, B. V.,Jang, K.,Lee, H. S.,Chen, B.,Yi, S. S.,Jeong, J. H.,Rama Moorthy, L. Blackwell Publishing Ltd 2011 INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOG Vol.8 No.4

Single NUV band pumped PbO-GeO₂-TeO₂:Tb³⁺ yellowish green emitting glass material for tricolor white LEDs

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>

Optical and luminescent characteristics of thermally stable new Eu3+ doped potassium tungstate tellurite glasses for epoxy-free luminescent devices

Vikas,Jayasimhadri M.,Haranath D. 한국물리학회 2024 Current Applied Physics Vol.58 No.-

Transparent, Eu3+ doped potassium tungstate tellurite (TKWZBiEu) glass matrices were successfully synthesized via employing the traditional melt quenching method and their thermal, structural and photoluminescent characteristics were thoroughly investigated. To estimate the aggregate weight loss, glass transition temperature (Tg) and thermal stability factor (ΔT) of the prepared host glass matrix, thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) were utilized. The non-crystalline character of the prepared TKWZBiEu glass was studied via XRD profile. Various vibrational functional groups were revealed via employing Fourier transform infrared (FT-IR) spectroscopy. The optical bandgap (Eopt) values for all prepared TKWZBiEu glasses have been evaluated by employing the absorption spectra. Under n-UV and blue excitations, all the prepared TKWZBiEu glasses are demonstrating reddish emission at 614 nm ascribed to the 5D0 → 7F2 transition, in which the intensity is increasing continuously with Eu3+ ion content up to 5.0 mol%. The experimental lifetime (τ) profiles demonstrate the single-exponential nature of prepared TKWZBiEu glasses under n-UV excitation. Furthermore, temperature dependent photoluminescence (TDPL) spectra indicate excellent thermal stability of the TKWZBiEu glass matrix with the highest value of activation energy (ΔE). The prototype organic epoxy resin/ binder-free device has been developed using the 5.0 mol% Eu3+ doped with TKWZBi glass matrix and n-UV LED chip. All the aforementioned findings validate that the optimized TKWZBiEu glass is an auspicious candidate for the red component to fabricate organic epoxy-free w-LEDs.

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.

White Light Emission from NaCaPO4:Dy3+ Phosphor for Ultraviolet-Based White Light-Emitting Diodes : White Light Emission from NaCaPO4:Dy3+ Phosphor

Ratnam, B.V.,Jayasimhadri, M.,Jang, Kiwan,Sueb Lee, Ho,Yi, Soung-Soo,Jeong, Jung-Hyun Wiley (Blackwell Publishing) 2010 Journal of the American Ceramic Society Vol.93 No.11

Synthesis and luminescent features of NaCaPO₄:Tb³⁺ green phosphor for near UV-based LEDs

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>

Optical Spectroscopy and Luminescence Properties of Sm³+-Doped Lead-Germanate Glasses

Eun-Jin Cho,Jayasimhadri Mula,Ho-Sueb Lee,Hyo-Jin Seo,Il-Gon Kim,Ki-Wan Jang,Yanlin Huang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.3

Glasses of 1-mol% Sm³+-doped lead germanate glasses 49 PbO-50 GeO₂, 49 PbO-30 GeO₂-20 Ga₂O₃ and 49 PbO-30 GeO₂-20 B₂O₃ (in mol%) have been prepared by using the conventional melt quenching method. A Judd-Ofelt (JO) analysis for Sm³3+ ions in lead-germanate glasses has been performed on the basis of the absorption spectrum. Fluorescence and lifetime measurements have been carried out using an argon-ion laser. Efficient visible emissions were observed, and the stimulated emission cross sections, branching ratios and quantum efficiencies were determined. In the present work, the relatively high values of the emission cross sections (σe) suggest that these materials can be considered as interesting candidates for optical applications. A comparison of the lasing properties of these three lead germanate glasses and their utilities as laser active materials are shown and analyzed. Glasses of 1-mol% Sm³+-doped lead germanate glasses 49 PbO-50 GeO₂, 49 PbO-30 GeO₂-20 Ga₂O₃ and 49 PbO-30 GeO₂-20 B₂O₃ (in mol%) have been prepared by using the conventional melt quenching method. A Judd-Ofelt (JO) analysis for Sm³3+ ions in lead-germanate glasses has been performed on the basis of the absorption spectrum. Fluorescence and lifetime measurements have been carried out using an argon-ion laser. Efficient visible emissions were observed, and the stimulated emission cross sections, branching ratios and quantum efficiencies were determined. In the present work, the relatively high values of the emission cross sections (σe) suggest that these materials can be considered as interesting candidates for optical applications. A comparison of the lasing properties of these three lead germanate glasses and their utilities as laser active materials are shown and analyzed.

Luminescent properties of orange emissive Sm³⁺-activated thermally stable phosphate phosphor for optical devices

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.