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Results for “UV-LED”

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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11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

PVP capped CdS nanoparticles for UV-LED applications

Polyvinlypyrrolidone (PVP) capped cadmium sulphide (CdS) nanoparticles are synthesized by wet chemical method. The powder X-ray diffraction (XRD) result indicates that the nanoparticles are crystallized in cubic phase. The optical properties are characterized by UV-Vis absorption. The morphology of CdS nanoparticles are studied using Scanning electron microscope (SEM). The thermal behavior of the as prepared nanoparticles has been examined by Thermo gravimetric analysis (TGA). The optical absorption study of pvp capped CdS reveal a red shift confirms the UV-LED applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Luminescent properties of Eu{sup 2+}-doped BaGdF{sub 5} glass ceramics a potential blue phosphor for ultra-violet light-emitting diode

Eu{sup 2+} doped transparent oxyfluoride glass ceramics containing BaGdF{sub 5} nanocrystals were successfully fabricated by melt-quenching technique under a reductive atmosphere. The structure of the glass and glass ceramics were investigated by differential scanning calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The luminescent properties were investigated by transmission, excitation, and emission spectra. The decay time of the Gd{sup 3+} ions at 312 nm excited with 275 nm were also investigated. The results of XRD and TEM indicated the existence of BaGdF5 nanocrystals in the transparent glass ceramics. The excitation spectra of Eu{sup 2+} doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). Compared with the as-made glass, the emission of glass ceramics is much stronger by a factor of increasing energy transfer efficiency from Gd{sup 3+} to Eu{sup 2+} ions, the energy transfer efficiency from Gd{sup 3+} to Eu{sup 2+} ions was discussed. In addition, the chromaticity coordinates of glass and glass ceramics specimens were also discussed, which indicated that the Eu{sup 2+} doped BaGdF{sub 5} glass ceramics may be used as a potential blue-emitting phosphor for UV-LED.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

High efficiency single Ag nanowire/p-GaN substrate Schottky junction-based ultraviolet light emitting diodes

We report a high efficiency single Ag nanowire (NW)/p-GaN substrate Schottky junction-based ultraviolet light emitting diode (UV-LED). The device demonstrates deep UV free exciton electroluminescence at 362.5 nm. The dominant emission, detectable at ultralow (<1 μA) forward current, does not exhibit any shifts when the forward current is increased. External quantum efficiency (EQE) as high as 0.9% is achieved at 25 μA current at room temperature. Experiments and simulation analysis show that devices fabricated with thinner Ag NWs have higher EQE. However, for very thin Ag NWs (diameter < 250 nm), this trend breaks down due to heat accumulation in the NWs. Our simple device architecture offers a potentially cost-effective scheme to fabricate high efficiency Schottky junction-based UV-LEDs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Efficient Perovskite Solar Cells Achieved via Rapid Photonic Annealing of all Stacking Layers: Unveiling the Crystallization Energy Window

In this study, we report high-performance perovksite solar cells (PSCs) with rapid photonic annealing (RPA) of all stacking layers, enabled by ultraviolet (UV) light-emitting diode (LED) sources, to replace lengthy and energy-intensive thermal annealing (TA). The UV-LED annealing technique allows for layer-specific annealing, where the selected light source provides a precise UV wavelength for maximizing the amount of light absorption by the target layer. The disparity in optical absorption between the target layer and the underlying films allows the stack of the underlying films to remain relatively unaffected, making this process ideal for heating sensitive substrates. Along with a systematic investigation into the layer-specific annealing mechanism of RPA, the results demonstrated that this UV-LED-based photonic annealing of all stacking layers (7 s for perovskite absorber) can produce PSCs with the power conversion efficiency (PCE) of over 23%, the highest reported among optically annealed PSCs. Moreover, the RPA device retains over 80% of the initial PCE over 1000 h under continuous 1 sun illumination at 55 °C and 30%–60% relative humidity (RH), while TA control device drops to 50% of its initial efficiency. Furthermore, these findings represent significant strides toward achieving rapid, cost-effective, and scalable manufacturing of commercial perovskite photovoltaics (PV).

14 SOLAR ENERGY↗
DOE OSTI2013

Synthesis and photoluminescence of (Y{sub 0.9−x}La{sub x})Eu{sub 0.1}VO{sub 4} nano-crystal phosphors using a sol–gel method

Graphical abstract: Emission spectra and CIE chromaticity diagram of the (Y{sub 0.9−x}La{sub x})Eu{sub 0.1}VO{sub 4} phosphor. - Highlights: • The CIE chromaticity of (Y{sub 0.75}La{sub 0.15})Eu{sub 0.1}VO{sub 4} phosphor is (0.66, 0.34). • The D{sub 0} → {sup 7}F{sub 2} transition intensity increases about five times for the 15 mol% of La{sup 3+} ion doping. • The (Y{sub 0.75}La{sub 0.15})Eu{sub 0.1}VO{sub 4} may be suitable for use as a UV-LED converted phosphor. - Abstract: The (La, Eu) co-doped YVO{sub 4} with nano-crystal phosphors were prepared using a sol–gel method. The X-ray diffraction profiles show that all of the peaks are attributed to the YVO{sub 4} phase when co-doped with the (La{sup 3+}, Eu{sup 3+}) ions. The intensities of the diffraction peaks decreases when the La{sup 3+} ion concentrations increase. In addition, under an excitation of 318 nm, the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition intensity increased with increasing the La{sup 3+} ion concentration, and increased about five with the 15 mol% of La{sup 3+} ion doping. This is caused by the large difference in ion radius between the La{sup 3+} and Y{sup 3+} ions, which leads to a distorted lattice and a local nonuniform strain in the vicinity of the Eu{sup 3+} ions when La{sup 3+} ions substitute Y{sup 3+} ions in the (Y{sub 0.9−x}La{sub x})Eu{sub 0.1}VO{sub 4} system. The bright red emission of the (Y{sub 0.9}Eu{sub 0.1})VO{sub 4} phosphor has the CIE chromaticity coordinates of (0.66, 0.34) with 15 mol% La{sup 3+} ion doping, which is very close to the NTSC system standard red chromaticity coordinates of (0.67, 0.33)

36 MATERIALS SCIENCE↗
DOE OSTI2013

Novel yellowish-green emitting luminescence in Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} phosphor

Graphical abstract: The phosphor has two separated emission centers with the dependent emission intensity on Eu{sup 2+} doping. There is a red-shift in the emission due to energy transfer with increasing the Eu{sup 2+}-doping. - Highlights: • Green-origin-emitting phosphors of Eu{sup 2+}-doped Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16} were firstly prepared by chemical sol–gel method. • The tunable luminescence color was realized by the changing Eu{sup 2+}-doping in Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}. • Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} displays two typical luminescence centers with the emission depending on Eu{sup 2+} doping. • Eu{sup 2+}-doped Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16} phosphor has an excellent thermal stability on the temperature quenching. - Abstract: Color tunable green-origin-emitting phosphor of Eu{sup 2+}-doped phosphate-silicate Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16} was prepared by chemical sol–gel method. The X-ray powder diffraction, the photoluminescence excitation and emission spectra, time resolved spectra, and thermal stability were measured. The excitation spectra can well match with the emission light of near UV-LED chips (360–400 nm). The tunable luminescence was realized by changing Eu{sup 2+}-doping concentration. Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} displays two typical luminescence centers, which were suggested to originate from two Ca{sup 2+} sites in the host. With increasing Eu{sup 2+} doping concentrations, the green emission band shifts to long wavelength. Energy transfer between the two different Eu{sup 2+} ions is discussed by analyzing the photoluminescence excitation and emission spectra, concentration-dependent luminescence intensity, and lifetimes. The dependence of the luminescence intensity of Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} on temperatures was measured. The activation energy (ΔE) for thermal quenching was reported.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Luminescence properties of Eu-activated alkaline and alkaline-earth silicate Na{sub 2}Ca{sub 3}Si{sub 6}O{sub 16}

Highlights: • A novel yellow-emitting alkaline and alkaline-earth silicate Na{sub 2}Ca{sub 3}Si{sub 6}O{sub 16}:Eu{sup 2+} was first developed. • Under excitation with UV or near UV light the silicate presents broad emission band centered at 580 nm. - Abstract: Yellow-emitting phosphors of Na{sub 2}Ca{sub 3}Si{sub 6}O{sub 16}:Eu{sup 2+} was prepared by wet chemistry sol–gel method. X-ray powder diffraction and SEM measurements were applied to characterize the structure and morphology, respectively. The luminescence properties were investigated by the photoluminescence excitation and emission spectra, decay curve (lifetimes), CIE coordinates and the internal quantum efficiencies. The excitation spectra can match well with the emission light of near UV-LED chips (360–400 nm). Na{sub 2}Ca{sub 3}Si{sub 6}O{sub 16}:Eu{sup 2+} presents a symmetric emission band from 4f{sup 6}5d{sup 1} ⟶ 4f{sup 7}({sup 8}S{sub 7/2}) transitions of Eu{sup 2+} ions on doping below 3.0 mol%. On increasing Eu-doping levels, the sample contains two kinds of emission centers, i.e., Eu{sup 2+} and Eu{sup 3+} ions, which present the characteristic broad band (5d ⟶ 4f) and narrower (4f ⟶ 4f) luminescence lines, respectively. The energy transfer, the luminescence thermal stability (activation energy ΔE for thermal quenching) and luminescence mechanism of Na{sub 2}Ca{sub 3}Si{sub 6}O{sub 16}:Eu{sup 2+} phosphors were discussed by analyzing the relationship between the luminescence characteristics and the crystal structure.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Tunable and white light emitting AlPO{sub 4} mesoporous glass by design of inorganic/organic luminescent species

The realization of tunable and white light emitting sources employed by UV-LED with single-host phosphors has been an exciting development in the search for high luminous efficiency and excellent color rendering index white-light source. A tunable and white light emitting mesoporous glass was prepared by utilizing both inorganic/organic (Europium/coumarin) luminescent species in the meso-structure. The tunable and white light emission was deliberately designed by CIE calculation based on the individual emission spectra, which was realized by tailoring the emission of Eu{sup 2+}/Eu{sup 3+} ions and coumarin 535 in sol-gel AlPO{sub 4} mesoporous glass. This simple and versatile procedure is not limited in the combination of rare earth and organic dye and is therefore extendable to other luminescent species in meso-structure for color-tunable efficient solid-state lighting sources.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Ultraviolet-enhanced light emitting diode employing individual ZnO microwire with SiO{sub 2} barrier layers

This paper details the fabrication of n-ZnO single microwire (SMW)-based high-purity ultraviolet light-emitting diodes (UV-LEDs) with an added SiO{sub 2} barrier layer on the p-Si substrate. However, the current-voltage (I-V) curve exhibited non-ideal rectifying characteristics. Under forward bias, both UV and visible emissions could be detected by electroluminescence (EL) measurement. When bias voltage reached 60 V at room temperature, a UV emission spike occurred at 390 nm originating from the n-ZnO SMW. Compared with the EL spectrum of the n-ZnO SMW/p-Si heterojunction device without the SiO{sub 2} barrier layer, we saw improved UV light extraction efficiency from the current-blocking effect of the SiO{sub 2} layer. The intense UV emission in the n-ZnO SMW/SiO{sub 2}/p-Si heterojunction indicated that the SiO{sub 2} barrier layer can restrict the movement of electrons as expected and result in effective electron-hole recombination in ZnO SMW.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Luminescent carbon quantum dots with high quantum yield as a single white converter for white light emitting diodes

Carbon quantum dots (CQDs) with high quantum yield (51.4%) were synthesized by a one-step hydrothermal method using thiosalicylic acid and ethylenediamine as precursor. The CQDs have the average diameter of 2.3 nm and possess excitation-independent emission wavelength in the range from 320 to 440 nm excitation. Under an ultraviolet (UV) excitation, the CQDs aqueous solutions emit bright blue fluorescence directly and exhibit broad emission with a high spectral component ratio of 67.4% (blue to red intensity to total intensity). We applied the CQDs as a single white-light converter for white light emitting diodes (WLEDs) using a UV-LED chip as the excitation light source. The resulted WLED shows superior performance with corresponding color temperature of 5227 K and the color coordinates of (0.34, 0.38) belonging to the white gamut.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Vertical and Lateral Etch Survey of Ferroelectric AlN/Al 1-x Sc x N in Aqueous KOH Solutions

Due to their favorable electromechanical properties, such as high sound velocity, low dielectric permittivity and high electromechanical coupling, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al 1-x Sc x N) thin films have achieved widespread application in radio frequency (RF) acoustic devices. The resistance to etching at high scandium alloying, however, has inhibited the realization of devices able to exploit the highest electromechanical coupling coefficients. In this work, we investigated the vertical and lateral etch rates of sputtered AlN and Al 1-x Sc x N with Sc concentration x ranging from 0 to 0.42 in aqueous potassium hydroxide (KOH). Etch rates and the sidewall angles were reported at different temperatures and KOH concentrations. We found that the trends of the etch rate were unanimous: while the vertical etch rate decreases with increasing Sc alloying, the lateral etch rate exhibits a V-shaped transition with a minimum etch rate at x = 0.125. By performing an etch on an 800 nm thick Al 0.875 Sc 0.125 N film with 10 wt% KOH at 65 °C for 20 min, a vertical sidewall was formed by exploiting the ratio of the {$10\overline{11}$ planes and {$1\overline{1}00$ planes etch rates. This method does not require preliminary processing and is potentially beneficial for the fabrication of lamb wave resonators (LWRs) or other microelectromechanical systems (MEMS) structures, laser mirrors and Ultraviolet Light-Emitting Diodes (UV-LEDs). It was demonstrated that the sidewall angle tracks the trajectory that follows the {$\overline{1}2\overline{12}$ of the hexagonal crystal structure when different c/a ratios were considered for elevated Sc alloying levels, which may be used as a convenient tool for structure/composition analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗