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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Optical studies in Er{sup 3+} doped BaMoO{sub 4} downconverting phosphor for blue LEDs

Erbium ion (Er{sup 3+}) doped BaMoO{sub 4} phosphor has been synthesized via co-precipitation technique. Phase formation of the prepared phosphor has been recognized by powder X-ray diffraction analysis. The photoluminescence emission spectrum has been recorded in 400-800nm wavelength range under 380nm excitation. The observed photoluminescence peaks are explained with the help of energy level structure. The prepared phosphor seems capable to produce efficient blue colour emission which can be useful for making blue light emitting diodes (LEDs).

36 MATERIALS SCIENCE↗
DOE OSTI2016

Photoluminescence studies of high-efficient red-emitting K{sub 2}Y(WO{sub 4})(PO{sub 4}):Eu{sup 3+} phosphor for NUV LED

Highlights: • Novel K{sub 2}Y(WO{sub 4})(PO{sub 4}):Eu{sup 3+} red phosphors were prepared by solid-state method. • Phosphors exhibit strong red light under NUV excitation with quantum efficiency of 70.5 %. • Judd–Ofelt analysis ascertains the presence of Eu{sup 3+} in a highly asymmetric environment. • The red LED prototype was fabricated with KYWP:Eu{sup 3+} phosphor and InGaN chip. - Abstract: A series of high-efficient red-emitting phosphors K{sub 2}Y(WO{sub 4})(PO{sub 4}):Eu{sup 3+} have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The phosphors can be excited efficiently by NUV light, then exhibit strong red emission with quantum efficiency of 70.5%. The concentration quenching takes place at relatively high concentration of Eu{sup 3+} (x = 0.70), which is further confirmed by the variation of decay curves of the entitled phosphors. Judd–Ofelt analysis ascertains the presence of Eu{sup 3+} in a highly asymmetric environment. The phosphor exhibits good thermal stability (92.5% at 100 °C and 84.1% at 180 °C). The red LED prototype fabricated by opyimized-composition K{sub 2}Y(WO{sub 4})(PO{sub 4}):0.70Eu{sup 3+} phosphor and 395 nm-emitting InGaN chips exhibit bright red emission. The results indicate that the K{sub 2}Y(WO{sub 4})(PO{sub 4}):Eu{sup 3+} phosphors are promising red phosphors for NUV LED.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Energy transfer and tunable luminescence of Na{sub 2}(Y,Eu)Mg{sub 2}V{sub 3}O{sub 12} phosphors for white LED applications

Highlights: • Iso-structural garnet-type Na{sub 2}(Y,Eu)Mg{sub 2}V{sub 3}O{sub 12} solid solution were synthesized. • Efficient energy transfer from [VO{sub 4}]{sup 3−} to Eu{sup 3+} ions in this phosphor is observed obviously. • Tuning the Y/Eu ratio generates the varied hues from yellowish-green to reddish-orange. • This kind of phosphor can be potentially used in UV pumped LEDs. - Abstract: A series of solid-solution phosphors Na{sub 2}(Y,Eu)Mg{sub 2}V{sub 3}O{sub 12} were prepared using solution combustion reaction. X-ray diffraction studies verified the formation of single phase Na{sub 2}(Y,Eu)Mg{sub 2}V{sub 3}O{sub 12} with garnet structure. Na{sub 2}(Y,Eu)Mg{sub 2}V{sub 3}O{sub 12} phosphors show not only a broad emission band with a maximum at 510 nm due to the [VO{sub 4}]{sup 3−} group but also several sharp emission lines due to the Eu{sup 3+} ions. The energy transfer from [VO{sub 4}]{sup 3−} to Eu{sup 3+} was discussed on the base of the spectral analysis. The color-tunable emissions of the Na{sub 2}(Y,Eu)Mg{sub 2}V{sub 3}O{sub 12} phosphor as a function of Y/Eu ratio are realized by continuously generating the varied hues from yellowish-green to reddish-orange. This indicates that the obtained phosphor may have potential applications in the field of UV-based white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Novel Transparent Phosphor Conversion Matrix with High Thermal Conductivity for Next Generation Phosphor-Converted LED-based Solid State Lighting

The low thermal conductivity of state-of-the-art polymer encapsulants (k ~ 0.15 Wm-1K-1) limits the efficiency and power density of current phosphor conversion light emitting diodes (pc-LEDs). The technical objective of this project was to demonstrate synthesis and processing schemes for the fabrication of polymer hybrid encapsulants with a thermal conductivity exceeding k = 0.4 Wm-1K-1 for LED applications. The ‘hybrid polymer’ approach encompasses the dispersion of high thermal conductivity particle fillers (zinc oxide, ZnO as well as the alpha-polymorph of alumina, Al2O3) within a polysiloxane matrix (poly(dimethylsiloxane), PDMS as well as poly(phenyl methyl siloxane), PPMS) to increase the thermal conductivity while maintaining optical transparency and photothermal stability at levels consistent with LED applications. To accomplish this goal, a novel synthesis method for the fabrication of nanosized ZnO particles was developed and a novel surface chemistry was established to modify the surface of zinc oxide particle fillers and thus to enable their dispersion in poly(dimethyl siloxane) (PDMS) matrix polymers. Molecular dynamics and Mie simulations were used to optimize ligand structure and to enable the concurrent mixing of particles in PDMS/PPMS embedding media while also minimizing the thermal boundary resistance as well as optical scattering of particle fillers. Using this approach the synthesis of PDMS/ZnO hybrid encapsulants exhibiting a thermal conductivity of 0.64 Wm-1K-1 and optical transparency > 0.7 mm-1 was demonstrated. A forming process based on micromolding was developed to demonstrate the forming of particle filled PDMS into film and lens shapes. Photothermal stability testing revealed stability of the materials for approximately 4000 min when exposed to blue light LED (450 nm, 30 W/cm2). One postgraduate and seven graduate students were supported by the project. The research performed within this project led to fifteen publications in peer-reviewed journals and one patent application. The grant stimulated a multi-investigator research collaborations among seven investigators at Carnegie Mellon University to address the challenge of encapsulants in pc-LED applications. The grant also catalyzed the future collaboration between researchers at Carnegie Mellon University and OSRAM Sylvania to address challenges associated with the use if polymers in LED applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Mg2+-Ge4+ substituting strategy for optimizing color rendering index and luminescence of YAG: Ce3+ phosphors for white LEDs

Highlights: • Mg{sup 2+}-Ge{sup 4+} ion pairs can partially substitute the Al{sup 3+} ions of YAG successfully. With the substitution, the garnet crystal structure remains unchanged. • With increasing Mg{sup 2+}-Ge{sup 4+} ions concentrations, the emission spectra show a progressive red-shift, from 528 to 552 nm (about 24 nm). • In white LEDs, with increasing Mg{sup 2+}-Ge{sup 4+} ions concentrations, the CCT decreased gradually from 6798 to 3261 K and the CRI increased from 76.5 to 89.3. - Abstract: Mg{sup 2+}-Ge{sup 4+} ions substituted YAG: Ce{sup 3+} phosphors (Y{sub 3}Al{sub 5-2x}Mg{sub x}Ge{sub x}O{sub 12}: Ce{sup 3+}) were prepared by high temperature solid state reaction method. X-ray diffraction (XRD), Scanning election microscope (SEM), Photoluminescence (PL) spectra and so on were used to characterize the samples. The effects of Mg{sup 2+}-Ge{sup 4+} concentrations on the morphology, structure, luminescence properties, fluorescence lifetime and white LED performance of YAG: Ce{sup 3+} phosphors were studied in detail. The results indicate that Mg{sup 2+}-Ge{sup 4+} ion pairs can partially substitute the Al{sup 3+} ions of YAG successfully. With the substitution, the garnet crystal structure remains unchanged. However the emission spectra show a progressive red-shift, from 528 to 552 nm (about 24 nm). The lifetime decreased rapidly from 84 to 26 ns. In particular, the correlated color temperature (CCT) decreases gradually from 6798 to 3261 K and the color rendering index (CRI) increases from 76.5 to 89.3 with the increasing of the incorporation content of Mg{sup 2+}-Ge{sup 4+} ion pairs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+}: A novel blue emitting phosphor for white LEDs

Graphical abstract: Under the 350 nm radiation excitation, Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} has a broad blue emission band. When the temperature turned up to 150 °C, the emission intensity of Ba{sub 1.97}B{sub 2}O{sub 5}:0.03Ce{sup 3+} is 63.4% of the initial value at room temperature. The activation energy ΔE is calculated to be 0.25 eV, which prove the good thermal stability of Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+}. All the properties indicate that Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} may have potential application in white LEDs. - Highlights: • Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} has a broad blue emission band under the 350 nm radiation excitation. • Emission intensity of Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} is 63.4% (150 °C) of the initial value (30 °C). • The activation energy ΔE for thermal quenching is 0.25 eV. - Abstract: A novel blue emitting phosphor Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} is synthesized by a high temperature solid state method. The luminescent property and the thermal stability of Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} are investigated. Under the 350 nm radiation excitation, Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} has a broad blue emission band, and the peak locates at 417 nm which is assigned to the 5d{sup 1}–4f{sup 1} transition of Ce{sup 3+}. It is further proved that the dipole–dipole interaction results in the concentration quenching of Ce{sup 3+} in Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+}. When the temperature turned up to 150 °C, the emission intensity of Ba{sub 1.97}B{sub 2}O{sub 5}:0.03Ce{sup 3+} is 63.4% of the initial value at room temperature. The activation energy ΔE is calculated to be 0.25 eV, which prove the good thermal stability of Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+}. All the properties indicate that Ba{sub 2}B{sub 2}O{sub 5}:Ce{sup 3+} may have potential application in white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High Performance Green LEDs for Solid State Lighting

The development of white LEDs for solid state lighting (SSL) has been driven in recent years by phosphor converted LEDs (pc-LEDs). However, losses (known as Stokes’ losses) between the blue pump LED and phosphor impose a fundamental efficiency limit of ~300 lm/W on pc-LEDs. White light can also be generated from color mixed LEDs (cm-LEDs), which employ red, green, blue, and amber LEDs and have a fundamental efficiency limit of ~400 lm/W. Efficient group III-nitride materials are used for the blue LED, while efficient group III-phosphide materials are used for the red LED component. Currently, the poor efficiency of green and amber LEDs (i.e. the “green gap”) is the primary limitation for cm-LEDs. Relative to nitride-based blue LEDs, green and amber nitride LEDs suffer from lower radiative recombination rates and higher nonradiative recombination rates, which ultimately lead to reduced internal quantum efficiency (IQE). The IQE represents the portion of all electron-hole recombination events that result in a photon. In addition, long-wavelength LEDs have lower electrical efficiency (EE) compared to their blue counterparts. Addressing the green gap, would ultimately enable cm-LEDs that rival or exceed the performance of pc-LEDs. Our project focused on III-nitride materials growth and characterization, device fabrication and testing, and semiconductor physics to understand efficiency limitations of green LEDs and develop solutions to these challenges. Insights gained during our research has led to novel long-wavelength LED designs which will enable efficient solid-state lighting.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2013

Phosphors for near UV-Emitting LED's for Efficacious Generation of White Light

1) We studied phosphors for near-UV (nUV) LED application as an alternative to blue LEDs currently being used in SSL systems. We have shown that nUV light sources could be very efficient at high current and will have significantly less binning at both the chip and phosphor levels. We identified phosphor blends that could yield 4100K lamps with a CRI of approximately 80 and LPWnUV,opt equal to 179 for the best performing phosphor blend. Considering the fact that the lamps were not optimized for light coupling, the results are quite impressive. The main bottleneck is an optimum blue phosphor with a peak near 440 nm with a full width half maximum of about 25 nm and a quantum efficiency of >95%. Unfortunately, that may be a very difficult task when we want to excite a phosphor at ~400 nm with a very small margin for Stokes shift. Another way is to have all the phosphors in the blend having the excitation peak at 400 nm or slightly shorter wavelength. This could lead to a white light source with no body color and optimum efficacy due to no self-absorption effects by phosphors in the blend. This is even harder than finding an ideal blue phosphor, but not necessarily impossible. 2) With the phosphor blends identified, light sources using nUV LEDs at high current could be designed with comparable efficacy to those using blue LEDs. It will allow us to design light sources with multiple wattages using the same chips and phosphor blends simply by varying the input current. In the case of blue LEDs, this is not currently possible because varying the current will lower the efficacy at high current and alter the color point. With improvement of phosphor blends, control over CRI could improve. Less binning at the chip level and also at the phosphor blend level could reduce the cost of SSL light sources. 3) This study provided a deeper understanding of phosphor characteristics needed for LEDs in general and nUV LEDs in particular. Two students received Ph.D. degrees and three undergraduates participated in this work. Two of the undergraduate students are now in graduate school. The results were widely disseminated – 20 archival journal publications (published, accepted or in preparation) and three conference proceedings resulted. The students presented their work at 11 different national/international conferences (32 oral or poster presentations) and the PI’s delivered 12 invited, keynote or plenary lectures.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Wide range yellow emission Sr8MgLa(PO4)7: Eu2+, Mn2+, Tb3+ phosphors for near ultraviolet white LEDs

Highlights: • The wide range of the emission spectra of Sr{sub 8}MgLa(PO{sub 4}){sub 7}: Eu{sup 2+}{sub 0.03} were clarified by Van Uitert equation and the crystal field strength equation. • The Mn{sup 2+} and Tb{sup 3+} had enhanced the total PL intensity up to 30% comparing to only Eu{sup 2+} doped phosphor. • W-LEDs using Sr{sub 8}MgLa(PO{sub 4}){sub 7}: Eu{sup 2+}{sub 0.03}, Mn{sup 2+}{sub 0.06}, Tb{sup 3+}{sub 0.06} and BAM: Eu{sup 2+} resulted in an excellent CRI of 89 and CIE coordinates of (0.3463, 0.3898). - Abstract: A series of single phased phosphors Sr{sub 8}MgLa(PO{sub 4}){sub 7}: Eu{sup 2+}, Mn{sup 2+}, Tb{sup 3+} were synthesized by solid state reaction methods for applications of white light emitting diodes(w-LEDs). The broad absorption band at the near ultraviolet (NUV) region of 250–450 nm was obtained, which is ascribed to the 4f{sup 7}→ 4f{sup 6}5d{sup 1} electronic transition of the Eu{sup 2+} ions. Under NUV excitation, the broad yellow emission was obtained from tri-activated Sr{sub 8}MgLa(PO{sub 4}){sub 7} phosphors via combining three emission bands centered at 500, 550, and 600 nm contributed by Eu{sup 2+}, Tb{sup 3+} and Mn{sup 2+}, respectively. The optimized concentrations of Mn{sup 2+} and Tb{sup 3+} were 6 mol%, respectively, which enhanced the total PL intensity up to 30% comparing to only Eu{sup 2+} doped phosphor. Moreover, the quantum efficiency of Sr{sub 8}MgLa(PO{sub 4}){sub 7}: Eu{sup 2+}, Mn{sup 2+}, Tb{sup 3+} phosphor had achieved up to 52%. The combination of a NUV chip with compound of Sr{sub 8}MgLa(PO{sub 4}){sub 7}: Eu{sup 2+}, Mn{sup 2+}, Tb{sup 3+} and BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} achieved tunable w-LEDs with high CRI. The results suggest that this single phased Sr{sub 8}MgLa(PO{sub 4}){sub 7}: Eu{sup 2+}, Mn{sup 2+}, Tb{sup 3+} phosphor can be a key for the phosphor converted w-LEDs for warm white light emission.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Efficient and bright white light-emitting diodes based on single-layer heterophase halide perovskites

At present, electric lighting accounts for ~15% of global power consumption and thus the adoption of efficient, low-cost lighting technologies is important. Here, halide perovskites have been shown to be good emitters of pure red, green and blue light, but an efficient source of broadband white electroluminescence suitable for lighting applications is desirable. Here, we report a white light-emitting diode (LED) strategy based on solution-processed heterophase halide perovskites that, unlike GaN white LEDs, feature only one broadband emissive layer and no phosphor. Our LEDs operate with a peak luminance of 12,200 cd m –2 at a bias of 6.6 V and a maximum external quantum efficiency of 6.5% at a current density of 8.3 mA cm –2 . Systematic in situ and ex situ characterizations reveal that the mechanism of efficient electroluminescence is charge injection into the α phase of CsPbI 3 , α to δ charge transfer and α–δ balanced radiative recombination. Future advances in fabrication technology and mechanistic understanding should lead to further improvements in device efficiency and luminance.

36 MATERIALS SCIENCE↗
DOE OSTI2014

LED lamp or bulb with remote phosphor and diffuser configuration with enhanced scattering properties

An LED lamp or bulb is disclosed that comprises a light source, a heat sink structure and an optical cavity. The optical cavity comprises a phosphor carrier having a conversions material and arranged over an opening to the cavity. The phosphor carrier comprises a thermally conductive transparent material and is thermally coupled to the heat sink structure. An LED based light source is mounted in the optical cavity remote to the phosphor carrier with light from the light source passing through the phosphor carrier. A diffuser dome is included that is mounted over the optical cavity, with light from the optical cavity passing through the diffuser dome. The properties of the diffuser, such as geometry, scattering properties of the scattering layer, surface roughness or smoothness, and spatial distribution of the scattering layer properties may be used to control various lamp properties such as color uniformity and light intensity distribution as a function of viewing angle.

42 ENGINEERING↗
DOE OSTI2018

White LED based on CsPbBr3 nanocrystal phosphors via a facile two-step solution synthesis route

Highlights: • The work shows a simple and effective strategy to synthesize perovskite materials. • A LED with CsPbBr{sub 3} nanocrystals as green phosphors was fabricated. • Notable stability of the CsPbBr{sub 3} nanocrystals was verified. - Abstract: All-inorganic CsPbBr{sub 3} perovskite nanocrystals with mean size of ∼300 nm were synthesized via a facile two-step solution synthesis route. High-resolution transmission electron microscopy and X-ray diffraction characterizations confirm the as-prepared CsPbBr{sub 3} nanoparticles are single-crystals with good crystallinity, although a CsPb{sub 2}Br{sub 5} impure phase also exists in the final product. Power-/temperature-dependent and time-resolved photoluminescence measurements reveal the notable and stable excitonic emission feature of these CsPbBr{sub 3} nanocrystals. As a proof-of-concept demonstration, a LED with p-GaN/n-ZnO heterojunction as blue-violet excitation chip and CsPbBr{sub 3} nanocrystals as green phosphors, was fabricated and a white electroluminescence was achieved from this perovskite nanocrystals decorated LED.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Facile synthesis, structural characterization, and photoluminescence mechanism of Dy{sup 3+} doped YVO{sub 4} and Ca{sup 2+} co-doped YVO{sub 4}:Dy{sup 3+} nano-lattices

Light plays a vital role in the evolution of life. From sunlight to candle-light and then to other form of lighting devices, human beings are utilizing light since time immemorial. Lighting devices such as conventional incandescent lamp and fluorescent lamp have been replaced by Light Emitting Diodes (LEDs) for the later is cheap, durable, etc. Now-a-days, phosphor converted LEDs have been burning issues in the fabrication of lighting devices. Especially, lanthanide ion(s) doped phosphors are of great interest for the same. However, doped phosphors have a limitation of luminescence quenching, i.e., instead of increasing luminescence on increasing dopant concentration, the luminescence decreases. Therefore, it must be rectified by one or other means so as to get maximum desirable intensity for uses in display or lighting devices. In the present work, YVO{sub 4}:Dy{sup 3+} and YVO{sub 4}:Dy{sup 3+}/Ca{sup 2+} nano-lattices are synthesized by a facile technique. Structural characterizations such as x-ray diffraction, SEM, TEM, HRTEM, and Selected Area Electron Diffraction (SAED) of the samples are reported. Photoluminescence (PL) excitation and emission, enhanced mechanism, and lifetime are thoroughly discussed. PL intensity of the quenched YVO{sub 4}:Dy{sup 3+} is made increased up to 432.63% by Ca{sup 2+} co-doping. Role of the Ca{sup 2+} on the luminescence enhanced mechanism of YVO{sub 4}:Dy{sup 3+}/Ca{sup 2+} is elucidated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Phosphor-converted white light emitting diodes having narrow-band green phosphors

In one aspect, a phosphor converted white light LED comprising a narrow green phosphor rather than a conventional broad green phosphor may simultaneously exhibit high R9, and high Luminance Efficacy of Radiation, optionally without use of a deep red phosphor to maintain desired red color rendering. In another aspect, a phosphor converted white light LED comprising a narrow green phosphor rather than a conventional broad green phosphor may provide an emission spectrum exhibiting a significant dip in the yellow region of the spectrum and thereby provide high red-green contrast without use of a filter. The yellow dip may be shallower than in conventional devices, and the device may therefore be brighter, while maintaining desired CRI and R9.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Engineered core/shell quantum dots as phosphors for solid-state lighting

Light-emitting diodes (LEDs) for solid state light ing (SSL) typically combine a blue or near- ultraviolet drive LED with one or more dow nconverting phosphors to produce “white” light. Further advances in both efficiency and wh ite-light quality will re quire new phosphors with narrow-band, highly efficient emission, particul arly in the red. A team led by principal investigator Dr. Victor Klim ov of Los Alamos National Labo ratory proposes to develop engineered semiconductor nanocrystal quantum dots (QDs) that combine optimal luminescent properties with long-term stability under ty pical downconverting conditions to enable new performance levels in SSL. The white LED phosphor industry is estimated to have sales of roughly $400 million in 2018 and would significantly benefit from the development of bright and narrow red-emitting QD phosphors because they woul d enable warmer whites without wasting energy by emission of light beyond the response of the human eye. In order to capitalize on the market opportunity, the LANL team is partnering with a local company called UbiQD that will facilitate US manufacturing.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗