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Emerging ultra-narrow-band cyan-emitting phosphor for white LEDs with enhanced color rendition.

ABSTRACT: Phosphor-converted white LEDs rely on combining a blue-emitting InGaN chip with yellow and red-emitting luminescent materials. The discovery of cyan-emitting (470-500?nm) phosphors is a challenge to compensate for the spectral gap and produce full-spectrum white light. Na_0.5K_0.5Li₃SiO₄:Eu²⁺ (NKLSO:Eu²⁺) phosphor was developed with impressive properties, providing cyan emission at 486?nm with a narrow full width at half maximum (FWHM) of only 20.7?nm, and good thermal stability with an integrated emission loss of only 7% at 150?°C. The ultra-narrow-band cyan emission results from the high-symmetry cation sites, leading to almost ideal cubic coordination for UCr₄C₄-type compounds. NKLSO:Eu²⁺ phosphor allows the valley between the blue and yellow emission peaks in the white LED device to be filled, and the color-rendering index can be enhanced from 86 to 95.2, suggesting great applications in full-spectrum white LEDs.

SUBMITTER: Zhao M

PROVIDER: S-EPMC6456736 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Combustion Synthesis and Photoluminescence Properties of Red-Emitting CaAlSiN₃:Eu2+ Phosphor for White-LEDs.

Project description:A combustion synthesis method has been developed for synthesis of Eu2+ doped CaAlSiN₃ phosphor and its photoluminescence properties were investigated. Ca, Al, Si, and Eu₂O₃ powders were used as the Ca, Al, Si and Eu sources. The addition of NaN₃, NH₄Cl and Si₃N₄ powders was found to increase significantly the product yield. These powders were mixed and pressed into a compact, which was then wrapped up with an igniting agent (i.e., Mg+Fe₃O₄). The compact was ignited by electrical heating under a N₂ pressure of ≤1.0 MPa. Effects of these experimental parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized CaAlSiN₃:Eu2+ phosphor absorbs light in the region of 200-600 nm and shows a broad band emission in the region of 500-800 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu2+. The sample doped with Eu2+ at the optimized molar ratio of 0.04 is efficiently excited by the blue light (460 nm) and generates emission peaking at ~650 nm with peak emission intensity ~106% of a commercially available phosphor, YAG:Ce3+(P46-Y3).The internal quantum efficiency of the synthesized phosphor was measured to be 71%, compared to 69% of the YAG:Ce3+ (P46-Y3).

| S-EPMC5456445 | biostudies-other

One-Pot Synthesis of Dual Color-Emitting CDs: Numerical and Experimental Optimization towards White LEDs.

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| S-EPMC6062429 | biostudies-literature

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| S-EPMC10131834 | biostudies-literature

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| S-EPMC4639743 | biostudies-literature

Effect of particle sizes and mass ratios of a phosphor on light color performance of a green phosphor thin film and a laminated white light-emitting diode.

Project description:Green phosphor thin films with different silica resin/phosphor mass ratios and phosphor particle sizes were prepared by the hot pressing method. A 405 nm near-ultraviolet light-emitting diode (LED) chip was used to package the laminated white LED (WLED), and the correlated color temperature, luminous efficiency of radiation, light color uniformity, and color coordinate of the laminated WLED were obtained. An increase in the mass ratio and decrease in particle size can effectively affect the scattering coefficient of phosphor photons and the efficiency of the absorption-excitation-emission process, increasing the efficiency and light color uniformity of phosphor thin films and laminated WLEDs. By comprehensive evaluation of various light color parameters, a laminate was prepared with a mass ratio of silica resin/phosphor = 6 : 0.75, and the optimum value of the WLED was obtained. According to the IES TM30 standard, its R f reached 92, R g reached 101, and R g and color distortion icons showed increased saturation for green color. Its luminous efficiency of radiation value of 270.21 lm W-1, correlated color temperature of 4423 K, and neutral white characteristics indicate that it is a device suitable for lighting applications.

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Color Shift Failure Prediction for Phosphor-Converted White LEDs by Modeling Features of Spectral Power Distribution with a Nonlinear Filter Approach.

Project description:With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to color quality. However, most of the current available research on the reliability of LEDs is still focused on luminous flux depreciation rather than color shift failure. The spectral power distribution (SPD), defined as the radiant power distribution emitted by a light source at a range of visible wavelength, contains the most fundamental luminescence mechanisms of a light source. SPD is used as the quantitative inference of an LED's optical characteristics, including color coordinates that are widely used to represent the color shift process. Thus, to model the color shift failure of white LEDs during aging, this paper first extracts the features of an SPD, representing the characteristics of blue LED chips and phosphors, by multi-peak curve-fitting and modeling them with statistical functions. Then, because the shift processes of extracted features in aged LEDs are always nonlinear, a nonlinear state-space model is then developed to predict the color shift failure time within a self-adaptive particle filter framework. The results show that: (1) the failure mechanisms of LEDs can be identified by analyzing the extracted features of SPD with statistical curve-fitting and (2) the developed method can dynamically and accurately predict the color coordinates, correlated color temperatures (CCTs), and color rendering indexes (CRIs) of phosphor-converted (pc)-white LEDs, and also can estimate the residual color life.

| S-EPMC5551862 | biostudies-other

Enhanced blue-light excited cyan-emitting persistent luminescence of BaLu2Al2Ga2SiO12:Ce3+, Bi3+ phosphors for AC-LEDs via defect modulation

Project description:Alternating current light-emitting diodes (AC-LEDs) have received significant attention from both academia and industry due to their remarkable benefits of more compact volume, cheaper manufacturing cost, greater energy usage efficiency, and longer service life. One of the most significant challenges for AC-LEDs is the flicker effect, which is mainly caused by the unavoidable 5–20 ms dimming time. Aiming to reduce the flicker effect, we designed a series of excellent blue-light excited cyan-emitting persistent luminescence (PersL) phosphors BaLu2Al2Ga2SiO12:Ce3+, Bi3+ via defect engineering of co-doping Bi3+. Interestingly, we found that co-doping Bi3+ not only effectively enhanced the PersL intensity, but also regulated the PersL lifetime of this phosphors. As the Bi3+ co-doping concentration increases to 0.01, the τ80 value (the time when the PersL intensity decreases to 80% of the initial intensity) increases from 0.24 to 19.61 ms, which proves to be effective in compensating the flicker effect of AC-LEDs. A new method of generating white light emission during the dimming time through adding the blue-light excited cyan PersL phosphor to the original orange-red PersL phosphor was proposed and an AC-LED lamp with a decreased percent flicker of 48.15% was fabricated, which is significantly better than the other currently reported AC-LED devices based on PersL phosphors. These results demonstrate that BaLu2Al2Ga2SiO12:Ce3+, Bi3+ might be an attractive material for low-flicker AC-LEDs. Efficient blue-light excited cyan-emitting persistent luminescence phosphor BaLu2Al2Ga2SiO12:Ce3+, Bi3+ is designed and synthesized to effectively compensate for the flicker effect of AC LEDs.

| S-EPMC9206004 | biostudies-literature

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