Light-emitting Diode Chip Research Articles

Dual-shell protection enables highly efficient and stable all-inorganic perovskite composites for light-emitting-diodes

Lead-halide perovskite nanocrystals (NCs) present superior photoelectric properties, but the poor stability seriously hinders their practical application. The encapsulation of perovskite NCs inside mesoporous silica (m-SiO2) matrix is considered as one of the most feasible pathways to improve the stability of NCs. However, the challenges of loose encapsulation structure, aggregation of particles, high energy consumption during the preparation of CsPbX3@m-SiO2 composites have not yet been overcome, which throw a shadow over the large-scale commercial applications. Here, we present a dual-shell encapsulation strategy that enables the formation of highly emissive CsPbBr3@m-SiO2@SiO2 composites, achieving an exceptional photoluminescence quantum yield (PLQY) of 97.37 %. The reaction parameters for the preparation of composites are meticulous investigated. The CsPbBr3 NCs can be well formed inside the pores of m-SiO2 as the m-SiO2 is introduced into the precursor solution. The secondary SiO2 shells can effectively seal the open pores of m-SiO2. As a result, the as-prepared CsPbBr3@m-SiO2@SiO2 composites present excellent stability, in which the composites can maintain 93.16 % of initial intensity after storage for 84 days. Besides, a series of CsPbX3@m-SiO2@SiO2 composites with tunable emission wavelength in the range of 428.6–630.6 nm are prepared through facile designing the halide ratios of precursor solution, which present a wide color gamut (148.48 % of the National Television Standards Committee). In addition, a white light-emitting diode (LED) is fabricated by combining CsPbBr3@m-SiO2@SiO2 composites and K2SiF6:Mn4+ phosphors with a 455 nm LED chip, which exhibits good photoelectric performances. This facile low-temperature dual-shell encapsulation strategy reported here provides a new pathway for preparing high-performance perovskite composites, facilitating their practical photoelectric application.

A novel high-brightness red phosphor Ca4Nb2O9: Eu3+ for WLEDs

In this study, new phosphors Ca4Nb2O9 doped with Europium (Eu3+) ions were created using a high-temperature solid-state method. Characterizations with X-ray diffraction (XRD), Rietveld refinement, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and elemental mapping revealed successful doping and uniform elemental distribution. The band gap is 4.17 eV for Ca4Nb2O9 and 3.73 eV for Ca3.7Nb2O9: 0.3Eu3+, which is shown that the band gap decreases with increasing concentration. Subsequently, the samples underwent photoluminescence (PL) spectra testing, revealing that the Ca4Nb2O9: Eu3+ phosphors exhibited intense red emission when excited at 395 and 465 nm. Meanwhile, the principal emission peak resided at 613 nm, and the ideal doping concentration of Eu3+ was determined to be x = 0.3. In addition, at 420 K, the luminous intensity of Ca3.7Nb2O9: 0.3Eu3+ under 395 and 465 nm excitation is 60 % as well as 82 % of its strength at 300 K, respectively, indicating excellent thermal stability. Furthermore, the phosphor exhibits a relatively high quantum efficiency, reaching 45.47 % when excited with 395 nm light and 58.17 % when excited with 465 nm light. Finally, a white light-emitting diode (WLED) device with a Ra value of 86.3 and correlated color temperature (CCT) of 4450 K was fabricated. The results suggest that the prepared phosphor, in combination with a near-ultraviolet (NUV) light-emitting diode (LED) chip, has the potential for application in white light-emitting diodes.

Sorbent selection for the recovery of gallium and indium from aqueous solutions: a sustainable approach to the recovery of strategic metals from LED lamps.

Gallium and indium, metals present in light-emitting diode (LED) lighting technology, can be effectively recovered from aqueous solutions by sorption. For this purpose, carbonaceous materials, such as activated carbon, or low-cost biosorbents as beer bagasse, spent coffee grounds or peanut shells, and a low-cost zeolite as chabazite, were characterized by BET, FTIR, XRD, and SEM analysis prior use. Protonated chabazite, with high surface area (505m2/g) and a Si/Al molar ratio of 3.4, showed high sorption capacities for gallium (56mg/g) and indium (92mg/g), which is 10 to 30 times higher than those of our carbonaceous materials (T = 298K, pH < 3, dosage = 1g/L). Sorption experiments with both metals in solution showed a competitive effect between gallium and indium for the sorption sites of the chabazite, showing more affinity toward gallium than indium. Ga3+sorbed/In3+sorbed molar ratio above 2 was achieved for the same initial concentration of both metals, increasing to almost 3 when the initial gallium concentration increased, which was appropriate since gallium concentration tends to be higher in LED chips. However, the sorption capacity for both metals was always around 0.35mmol Ga + In/g. The selectivity of the chabazite was conditioned by different behavior of both metals in aqueous solution at the sorption pH (below 3.5) being the predominant species in solution Ga(OH)2+ for gallium and In3+ for indium. Sorption with protonated chabazite can be used in the treatment of spent LEDs leachate for the dual purpose of water purification and selective metal separation.

Bright Structural-Phase-Pure CsPbI3 Core-PbSO4 Shell Nanoplatelets With Ultra-Narrow Emission Bandwidth of 77 meV at 630 nm.

Achieving a narrow emission bandwidth islong pursued for display applications. Among all primary colors, obtaining pure red emission with high visual perception is the most challenging. In this work, CsPbI3 halide perovskite nanoplatelets (NPLs) with rigorously controlled 2D [PbI6]4- octahedron layer number (n) are demonstrated. A perovskite core-PbSO4 shell structure is designed to prevent aggregation and fusion between NPLs, enabling consistent thickness and quantum confinement strength for each NPL. Consequently, exact n = 4 CsPbI3NPLs are demonstrated, exhibiting emission peaks around 630nm, with very narrow spectral bandwidths of <24nm and high absolute photoluminescence quantum yields up to 85%. The emission of n = 4 NPLs falls exactly within the pure-red region, closely aligning with the International Telecommunication Union Recommendation BT.2020 standard. Measurements suggest predominant stability and color homogeneity compared to traditional red-emitting CsPbIxBr3- x nanocrystals. Finally, proof-of-concept pure-red emissive light-emitting diodes (LEDs) are demonstrated by integrating n = 4 CsPbI3 NPLs films with a blue LED chip, showing an excellent external quantum efficiency of 18.3% and high brightness exceeding 3 × 106 nits. Stringent requirements for future display technologies, are satisfied based on the high color purity, stability, and brightness of CsPbI3 NPLs.

Surface Vibration‐Mediated and Multiphonon Relaxation‐Assisted Antithermal‐Quenching Shortwave Infrared Emission in Ho‐Based Double Perovskite With Long Lifetime

AbstractThermal quenching generally predominates in Er3+ 1540 nm luminescence quenching at elevated temperatures, due to intensified lattice vibration and efficient overtone vibrational relaxation by O─H stretch. This issue impedes practical device applications of shortwave infrared Er‐doped phosphors. Herein, with the mediation of surface vibrational phonons, anti‐thermal quenching of Er3+ 1540 nm emission is reported in (220)‐dominated Er3+‐doped Cs2NaHoCl6 double perovskite. The downshifting emissions can be boosted with rising temperatures from 303 to 543 K, reaching 225%@483 K of the initial intensity at 303 K, accompanied with a long lifetime of 33.02 ms at 483 K. By combining temperature‐dependent in situ Raman and Fourier transform infrared spectroscopies with the excited‐state dynamics results, the coordination role of water molecules is verified, serving as promoters instead of quenchers on the (220) facet at high temperatures. Furthermore, efficient energy transfer from Ho3+ to Er3+ enables intense 1540 nm emission with a photoluminescence quantum yield of 78.1% under 450 nm excitation. Finally, a compact thermally stable phosphor‐converted light‐emitting diode (LED) is designed as a narrowband shortwave infrared light source with a blue LED chip. This work pushes the improved understanding of achieving thermal‐enhanced Er3+ luminescence for potential broad applications.

Synthesis and photoluminescence of Ba1-xSrxMgSi4O10:Eu2+ phosphors for warm white light-emitting-diodes

Efficient and thermally stable blue-cyan-emitting phosphors are urgently demanded to cover the “cyan gap” for high quality light-emitting-diodes (LEDs) lighting. This work provides a series of blue to cyan color-tunable Ba0.96-xSrxMgSi4O10:0.04Eu2+ phosphors developed via solid-solution method. The phase transformation, photoluminescence, quantum efficiency and thermal stability were investigated in detail. Notably, Sr2+ substitution is effective to red-shift the emission toward cyan emission (from 465 to 480 nm). Simultaneously, the quantum efficiency and thermal stability can be well maintained. Finally, using a 365 nm near-ultraviolet (NUV) LED chip combining with the as-prepared blue-cyan-emitting phosphor, β-SiAlON:Eu2+ green-emitting phosphor and CaAlSiN3:Eu2+ red-emitting phosphor, a warm-white LED device was fabricated with correlated color temperature (CCT) of 4329 K, and color-rendering index (CRI) of 92. These results indicate that the Ba1-xSrxMgSi4O10:Eu2+ blue-cyan-emitting phosphors may have potential applications for high quality NUV-pumped warm-white LED lighting.

Eco-friendly synthesis of red-emissive carbon dots for visual alcohol detection and light-emitting diodes

Red-emissive carbon dots (R-CDs) is highly desired in developing full-color solid-state lighting and display applications based on CDs. Developing simple and eco-friendly methods to produce R-CDs is extremely desirable. In this work, two types of R-CDs were obtained via simple and eco-friendly grinding-heating or solvothermal methods using fresh spinach leaves as the carbon source, respectively. The obtained R-CDs naturally possess surface functional groups. These R-CDs were effectively used as sensitive probes for detecting alcohol (including alcohol gas and liquor detection) due to the synergistic effect of the nitrogen-containing surface groups on the R-CDs and the oxhydryl groups in the alcohol solution. Finally, red electroluminescence was achieved by mixing the R-CDs with polyvinyl pyrrolidone as the phosphor layer on a blue light-emitting diode (LED) chip. This work paves the way for the further development of R-CDs in fluorescence probes and full-color LED applications.

Multi‐layer graphene nanosheets bridging binary aluminium oxide for the synergistic enhancement of thermal conductivity and electrical insulation of silicone resin composite

AbstractThe flexible polymer composites usually require high intrinsic thermal conductivity fillers for the applications in thermal management, such as the well‐known graphene, which can, in turn, compromise their electrical insulation properties. Here, the authors developed the silicone resin (SR) composites filled with multi‐layer graphene nanosheets (MGN) and binary alumina (Al2O3), and the microstructure of composites exhibits the dominant skeleton of large‐sized Al2O3 filler and branching of small‐sized Al2O3 fillers features by the size matching effect of optimal binary Al2O3. The introduction of supplementary MGN fillers further increases the face‐to‐face contact probability and bridges the isolated binary Al2O3, which contributes to the high thermal conductivity of 3.0 W·m−1·K−1 under these synergistic effects. The dense and connected ‘Al2O3‐MGN‐Al2O3’ thermal conductive pathway is successfully built, as supported by the numerical simulation and Agari model fitting. Meanwhile, the electrical conductivity caused by MGN can be blocked by the surrounding insulation Al2O3 filler network, exhibiting a high volume resistivity of 1.7 × 1015 Ω · cm. Moreover, the Al2O3/MGN/SR composite films effectively transfer the heat and diminish the hot‐spot temperature by 53.5°C in cooling light emitting diode chip module application.

Synthesis and properties of naphthylamine derivative functionalized spiro-[fluorene-9,9′-xanthene] for single-component white light-emitting diodes

White light-emitting diodes (LEDs) with high color purity and color-rendering index have elicited much interest in many fields. In this work, a spirotype molecule SFX-PNA was designed and synthesized by combining a spiro[fluorene-9,9′-xanthene] (SFX) core with naphthylamine derivative functionalized at the 2,3′,6′,7-positions. Studies revealed that the highly twisted configuration allowed SFX-PNA to exhibit good thermal stability and a broad blue-emissive band (λem = 466 nm) in the solid state. In combination with the intrinsic yellow luminescence (λem = 556 nm) of commercially available GaN ultraviolet LED chips, a white LED with SFX-PNA as the phosphor was successfully obtained, which showed high color purity with Commission Internationale de L’Éclairage coordinates of (0.30, 0.33) and a color-rendering index of 86.

Novel single phase warm white-emitting phosphor BaLaGaO4:Dy3+,Sm3+ with high thermal stability and color stability

In this study, new phosphors BaLaGaO4 (BLGO) doped with dysprosium (Dy3+) and samarium (Sm3+) ions were created using a high-temperature solid-state method. Characterizations with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and elemental mapping revealed successful doping and uniform elemental distribution. Then the samples were tested for photoluminescence (PL) spectra, the results indicated that the BaLaGaO4:xDy3+ (BLGO:xDy3+) phosphors emitted strong blue and yellow light upon excitation at 350 nm. The emission peaks were located at 480 and 572 nm, respectively. By introducing different proportions of Sm3+ ions, the BaLaGaO4:0.04Dy3+,ySm3+ (BLGO:0.04Dy3+,ySm3+) samples could be excited at 365 nm, and enhancing the red emission component of the phosphor. Meantime, with increasing Sm3+ content, the correlated color temperature (CCT) decreased from 5507 to 3767 K. And the emission spectrum and decay lifetime of BLGO:0.04Dy3+,ySm3+ confirmed the energy transfer from Dy3+ to Sm3+. Furthermore, at 423 K, the luminous intensity of BLGO:0.04Dy3+,0.04Sm3+ retained 86 % of its strength at 298 K, and the chromaticity shift (ΔS) was only 0.00574, which indicated that the sample had excellent thermal stability and excellent color stability. Finally, using the prepared sample and a 365 nm light-emitting diode (LED) chip, a white light-emitting diode (WLED) was fabricated. The CCT of the manufactured WLED also showed a corresponding reduction (from 3423 to 2814 K). Moreover, under the working conditions of 3.4 V and 0.6A, the thermal imaging obtained after 90 min of WLED operation shows the stability of the packaged WLED at high temperature. These researches show that the phosphor has potential application value in indoor lighting technologies.

Cr3+ and Yb3+ co-doped perovskite-like phosphor with improved thermal stability by efficient energy transfer

With the development of white light-emitting diode (LED) technology, near-infrared (NIR) phosphor-converted (pc) LED is becoming a new emerging light source. However, due to the lack of long wavelength components of the phosphors, the application of NIR pc-LED is restricted. In this work, a continuous ultra-broadband NIR emission without the emission gap in the 850–950 nm region has been realized in the Mg4Nb2O9 (MNO):Cr3+, Yb3+ phosphor. Meanwhile, when compared to MNO:Cr3+, an improved internal quantum efficiency (from 55.4% to 72.6%) and thermal stability (from 39% to 63% at 100 °C) have been obtained for MNO:Cr3+, Yb3+, which is attributed to the combined effect of the efficient energy transfer from Cr3+ to its nearest Yb3+ and the unique energy levels of Yb3+. The performances of the fabricated pc-LED devices by combining MNO:Cr3+, Yb3+ with 460 nm LED chips were also given, and the results demonstrate that the MNO:Cr3+, Yb3+ phosphor may have potential for practical application in the NIR pc-LED.

Preparation of BaAl2-xGaxSi2O8:Ce3+, M+ (Li, Na, K) blue-cyan phosphors based on charge compensation and cation substitution strategies and luminescence performance study

Highly efficient blue-cyan phosphors can fill the cyan gap in conventional white light-emitting diode (LED) devices to improve the spectral continuity while effectively increasing the white LED colour rendering index (Ra). In this study, Ba0·94Al2-xGaxSi2O8:0.06Ce3+, M+ (Li, Na, K, x = 0–0.8) blue-cyan phosphors with a feldspar structure were prepared by a high-temperature solid-phase method using charge compensation and cation substitution strategies. The barium (Ba) vacancy due to the charge-imbalance substitution of Ce3+ is compensated by the different charge compensators Li+, Na+, and K+. The charge compensators affect the luminescence performance of the samples, with the K+-compensated samples showing the greatest enhancement, with intensities up to 1.8 times that of the uncompensated samples. The cation substitution strategy using Ga3+ to partially replace Al3+ further improves the luminescence performance of the Ba0·94Al2Si2O8:0.06Ce3+, 0.04 K+ sample, and the excitation band is also improved. In this case, the luminescence intensity of the Ba0·94Al2Si2O8:0.06Ce3+ luminescent material is increased by a factor of 6, and a broadband blue-cyan phosphor with a full-width at half-maximum of 118 nm containing blue, cyan and green is obtained. The co-doping of charge compensators and partial cation substitution improved the luminescence performance of phosphors. The representative sample Ba0·94Al1.6Ga0.4Si2O8:0.06Ce3+, 0.04 K+ has a luminescence intensity at a temperature of 150 °C that is 83.2% of that at room temperature and good thermal stability. The combination of 365 nm near-ultraviolet (NUV) LED chips with Ba0·94Al1.6Ga0.4Si2O8:0.06Ce3+, 0.04 K+ and the commercial red powder (Ca, Sr)AlSiN3:Eu2+ yields a white LED device with an Ra of up to 93 and a correlated colour temperature (CCT) of 4825 K. These results show that the blue-cyan phosphor complements the cyan component while simplifying the manufacturing process of white LEDs.

Near‐unity quantum efficiency wavelength‐tunable NIR phosphors (Sr2−yCay)Sc1−xSbO6: xFe3+ with excellent thermal stability

AbstractFe3+ ions as near‐infrared (NIR) activators are emerging as an alternative to Cr3+.1–5 However, it is a challenge to develop Fe3+‐activated NIR phosphors featuring tunable optical properties, high efficiency, and thermal stability. Herein, we present a series of near‐unity internal quantum efficiency (IQE), wavelength‐tunable and thermal stability NIR‐emitting phosphors Sr2−yCaySc1−xSbO6:xFe3+ (S2−yCyS1−xS:xFe3+). Sr2ScSbO6:1%Fe3+ (SSS:1%Fe3+) phosphor shows broadband NIR emission at 904 nm and near‐unity IQE under excitation at 300 nm. Experimental and theoretical calculation results demonstrate that introduced Ca ions could increase the bandgap value and Debye temperature (ΘD) of host from Eg = 3.702 eV, ΘD = 609 K of y = 0 to Eg = 3.801 eV, ΘD = 692 K of y = 2. Significantly, the resultant S2−yCyS1−xS:1%Fe3+ NIR phosphors show wavelength‐tunable emission from 904 to 952 nm and high IQE of 84.6%–97.5% as well as enhanced thermal stability (I423K/I298K = 76.9%) of Ca2ScSbO6:1%Fe3+ (CSS:1%Fe3+) in comparison with that (I423K/I298K = 70.6%) of pristine sample. We fabricated an NIR light‐emitting diodes (LED) device by using CSS:1%Fe3+ NIR phosphors with ultraviolet LED chip and demonstrated its potential applications in anticounterfeiting, information encryption, and night vision.

A new yellowish‐green‐emitting phosphor: Eu2+‐doped Ba3YAl2O7.5

AbstractA yellowish‐green emitting phosphor Ba3YAl2O7.5:Eu2+ was synthesized by a solid‐state method. The crystal structure, luminescence, concentration quenching, fluorescence decay, and thermal quenching properties were systematically investigated. Under blue light (440 nm) excitation, Ba3YAl2O7.5:Eu2+ phosphors exhibit a yellowish‐green emission peaking at 550 nm with a full width at half maximum ∼ 69 nm, and The Commission Internationale de l'Eclairage (CIE) coordinates of Ba3YAl2O7.5:Eu2+ are (0.4064, 0.5811). Structural analysis and Van Uitert equation along with fluorescence lifetime analysis reveal that Eu2+ ions occupy 6‐coordinated Y and 9‐coordinated Ba sites in Ba3YAl2O7.5, and therefore generate two emission sub‐bands at 582 and 548 nm. In addition, Ba3YAl2O7.5:Eu2+ phosphor remaining 43% photoluminescence emission intensity at 125°C with an activation energy of 0.372 eV. Utilizing the title phosphor (Ba3YAl2O7.5:3%Eu2+), commercial red (Ca,Sr)AlSiN3:Eu2+ (CSAlSi:Eu2+) phosphor, and InGaN‐based blue light emitting diode (LED) chip, a proof‐of‐concept warm white LEDs (WLEDs) with a color rendering index of 80.1, CIE chromaticity coordinates of (0.411, 0.381), luminous efficacy of ∼ 22.13 lm/W, and correlated color temperature of ∼ 3288 K is achieved. Thus, Eu2+ activated Ba3YAl2O7.5 phosphors have the potential application in WLEDs pumped by a blue LED chip for solid‐state lighting application.

The synthesis and properties of Ca3 Sc2 Si3 O12 :Ce3+ (CSSG) phosphor are utilized for the development of human-centric lighting light-emitting diodes (HCL-LEDs).

In this study, cerium ion (Ce3+ )-doped calcium scandium silicate garnet (Ca3 Sc2 Si3 O12 , abbreviated CSSG) phosphors were successfully synthesized using the sol-gel method. The crystal phase, morphology, and photoluminescence properties of the synthesized phosphors were thoroughly investigated. Under excitation by a blue light-emitting diode (LED) chip (450 nm), the CSSG phosphor displayed a wide emission spectrum spanning from green to yellow. Remarkably, the material exhibited exceptional thermal stability, with an emissivity ratio at 150°C to that at 25°C reaching approximately 85%. Additionally, the material showcased impressive optical performance when tested with a blue LED chip, including a color rendering index (CRI) exceeding 90, an R9 value surpassing 50, and a biological impact ratio (M/P) above 0.6. These noteworthy findings underscore the potential applications of CSSG as a white light-converting phosphor, particularly in the realm of human-centered lighting.

Tunable cold/warm white light emission from Bi3+/Te4+ co-doped Cs2ZrCl6 perovskite phosphors

Combining a single-component white-light phosphor with ultraviolet light emitting diode chips emerges as a promising method to produce white-light-emitting diodes (WLEDs). Nevertheless, it is still a challenge for synthesizing single-component white-light phosphors with a high color rendering index (CRI). Herein, Bi3+/Te4+ co-doped Cs2ZrCl6 perovskite white-light phosphor is presented with a high CRI of 91.7 and good stability against oxygen, water, and heat. The Cs2ZrCl6 microcrystals were prepared using an ultrasound-assisted hydrochloric acid method with controllable Bi3+ and Te4+ dopant contents. By manipulating the excitation wavelength, the emission light can be altered between cold and warm white. The Bi3+/Te4+ co-doped Cs2ZrCl6 phosphor can also emit the warm-white light, showing a high photoluminescence quantum yield of 82.9%. The presented Bi3+/Te4+ co-doped Cs2ZrCl6 perovskite phosphors with a high CRI and great environmental stability offer a new approach for the synthesis of single-phase white-light phosphors and have high potentiality for the application of WLEDs.

Ti-B-O System for Catalyzing Boron Nitride Nanotube Growth.

Chemical vapor deposition (CVD) stands out as the most promising method for cost-effective production of high-quality boron nitride nanotubes (BNNTs). Catalysts play a crucial role in BNNT synthesis. This work delves into the impact of oxygen (O) on Ti-based catalysts during the CVD growth of BNNTs. In contrast to the B/TiB2 nanoparticles (NPs) and B/TiN NPs systems, the oxygen-containing precursor B/TiO2 NPs remarkably catalyzes the growth of high-quality and high-purity BNNTs across a wider range of synthesis parameters. Subsequent analyses reveal that TiBO3 acts as an active catalyst, facilitating BNNT growth in Ti-based catalyst systems. Moreover, the nanocomposite film synthesized from BNNTs and PVDF-HFP exhibits excellent mechanical properties and heat dissipation capabilities. Utilizing the nanocomposite film as a thermal interface material effectively enhances the heat dissipation for a 5 W light-emitting diode (LED) chip. Consequently, our research confirms the effectiveness of the Ti-B-O system in catalyzing BNNT growth.

Blue-emitting fluorophosphate phosphor to enhance color rendition of near-ultraviolet LED white light

&lt;span&gt;This work presents a novel blue phosphor, Na&lt;sub&gt;2&lt;/sub&gt;MgPO&lt;sub&gt;4&lt;/sub&gt;F: Eu&lt;sup&gt;2+&lt;/sup&gt; (NMPF: Eu) for violet 405-nm light-emitting diode (LED) devices. The compound is synthesized via a simple one-step sintering process using readily available precursors. Notably, NMPF: Eu exhibits highly efficient and thermally stable blue emission when excited by violet light. The NMPF: Eu is applied to produce a white LED device driven by a 405 nm LED chip and Y3Al5O12: Ce3+ (YAG: Ce) yellow phosphor. The impacts of NMPF: Eu phosphors are investigated by varying their particle size while maintaining consistent doping concentrations. Impressively, the LED prototype displays a substantial reduction in blue light emission while generating white light with enhanced color rendering and luminous properties. These results highlight the suitability and potential of NMPF: Eu as a promising phosphor for widening violet LED applications, especially in generating white light perceptible to the human eyes.&lt;/span&gt;

Fully Enclosed Composite Micro/Nano‐Package for High‐Quality Micro‐LED Display Pixels and In Situ Nanoimprint Technology

AbstractMicro/mini‐light emitting diode (LED) arrays are regarded as the most promising next generation of display devices. However, the inherent Lambertian radiation of LED chips results in a significant pixel crosstalk. To improve the display quality, high‐quality micro/mini‐LED display pixels with fully enclosed composite micro/nano‐packages and in situ nanoimprint technology are proposed and demonstrated in this work. The nanoimprint template is designed as a composite structure comprising an intermediate sandwich cavity array and thin‐bottom nanostructure layer. Contact is maintained between the template and LED chips array substrate. By vacuuming the sealed sandwich cavities, the thin‐bottom nanostructure layer is deformed to drive the upward protrusion of the liquid optical polymer. Moreover, the nanocavities on the thin nanostructure layer are fully filled by the polymer, forming a composite micro/nano‐package. The characteristics of the composite micro/nano‐package, such as the aperture and protrusion height, can be flexibly adjusted by changing the template structure or process parameters. A 6 × 8 array LED chips display device enclosed by a composite micro/nanopackage is developed. The divergence angle of the single LED chip decreases to 72° from the original 138°, the light‐extraction efficiency increases18.4%, and the luminescence spectrum and current‐voltage characteristics changes only minimally.

Thermally-stable and color-tunable novel single phase phosphor Ca2GaTaO6:Dy3+, Sm3+ for indoor lighting applications

This study successfully synthesized novel phosphors Ca2GaTaO6:xDy3+ (CGTO:xDy3+) and Ca2GaTaO6:0.06Dy3+, ySm3+ (CGTO:0.06Dy3+, ySm3+) using the high temperature solid-phase reaction preparation. The microstructure, optical properties, and energy transfer mechanism of the phosphors were studied through X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and fluorescence lifetimes. XRD and corresponding refinement results indicate that Dy3+ and Sm3+ ions were effectively doped into the Ca2GaTaO6 (CGTO) lattice. The SEM graphs show that the elements in CGTO:0.06Dy3+, 0.5Sm3+ phosphors are uniformly distributed. PL spectra analysis show the CGTO:xDy3+ phosphors display two strong emission peaks located at 482 nm for blue emission and 575 nm for yellow emission when excited with 350 nm light. Under uniform conditions, when excited with 365 nm of light, the CGTO:0.06Dy3+, ySm3+ phosphors emit light that can be tuned with adjustable color coordinates and correlated color temperature (CCT) by incorporating varying proportions of Sm3+ ions. This tunability is achieved through the effective energy migration from Dy3+ to Sm3+ ions within the phosphor material. Furthermore, the emission spectra and weaken lifetimes of the CGTO:0.06Dy3+, ySm3+ confirm the energy transport between Dy3+ and Sm3+, and the energy transfer efficiency reached to 76 %. At 423 K, the luminescence intensity of CGTO:0.06Dy3+, 0.05Sm3+ phosphor retains 87 % of the intensity observed at 298 K, signifying its excellent thermal durability. Finally, the electroluminescent performance of the CGTO:0.06Dy3+ and CGTO:0.06Dy3+, 0.05Sm3+ phosphors packaged on 365 nm light-emitting diode (LED) chips respectively were studied to investigate the capability applications of the phosphors in white light-emitting diodes (WLEDs) field. The CCT of the packaged LEDs decline from 3396 to 2825 K, indicating CGTO:0.06Dy3+, 0.05Sm3+ phosphor shifts to warmer white light. At a voltage input of 3.4 V and a current of 600 mA, the thermal sensing shows that the WLEDs maintain aptitude for 90 min, showing that the packaged WLEDs can function consistently under elevated temperatures. These studies indicated the phosphors have potential applications in indoor lighting.