Light-emitting diodes (LEDs) are excellent candidates for general lighting because of their rapidly improving efficiency, durability, and reliability, their usability in products of various sizes, ...and their environmentally friendly constituents. Effective lighting devices can be realized by combining one or more phosphor materials with chips. Accordingly, it is very important that the architecture of phosphors be developed. Although numerous phosphors have been proposed in the past several years, the range of phosphors that are suitable for LEDs is limited. This work describes recent progress in our understanding of the prescription, morphology, structure, spectrum, and packaging of such phosphors. It suggests avenues for further development and the scientific challenges that must be overcome before phosphors can be practically applied in LEDs.
Warm white LEDs with a high color rendering index and a low correlated color temperature have undergone rapid development. In this regard, red-emitting materialssuch as fluoride phosphors, namely, ...A2MF6:Mn4+ (A = K, Na, and Cs; M = Si, Ge, Zr, Sn, and Ti) and XSiF6:Mn4+ (X = Ba or Zn), nitridoaluminate phosphor (SrLiAl3N4:Eu2+), and nanocrystals of cesium lead iodide perovskite (CsPbI3)have been extensively investigated recently. These compounds generate narrow emissions in the visible red spectral region that are highly perceived by the human eye and lead to excellent chromatic saturation of the red spectra. This paper describes the structure, luminescence properties, morphologies, thermal features, and moisture resistance of critical red components, as well as their limitations for practical applications. This Perspective also provides a basis for future development and scientific challenges in optical research.
Light-emitting diodes (LEDs) are attracting considerable attention around the world. Phosphor materials, as crucial color-converted components, play central roles in LED development. The demands for ...phosphor materials have become increasingly stringent over the past decades, from high brightness to narrowband emission or function-dependent spectrum engineering. Although substantial progress has been made for currently developed phosphor materials, simultaneously satisfying all requirements for high-level applications remains challenging. In this review, we aim to provide a comprehensive understanding of the development of phosphor materials in different generations and to elucidate the key designed mechanisms concerning the activators and the host structures to fulfill the aforementioned aspects. We highlight the developments in phosphor materials through the classification of demands for high luminescence, high thermal stability, narrowband emission for high color gamut, and broadband emission for near-infrared. We also focus on elucidating the key designed mechanisms of phosphor materials in different generations. Furthermore, future perspectives about micro-LED applications and nanoluminescent materials are provided. This study opens up an avenue for designing the luminescent materials of the future.
A solvent‐vapor transport route produces centimeter‐sized single‐crystal red phosphors. The epitaxial growth route to yield its core–shell structure at ambient temperature was adopted. These red ...phosphors could be applied in all‐inorganic WLED devices. Cs2TiF6:Mn4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs2TiF6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three‐step photoluminescence intensity evolution mechanism has been proposed. By combining as‐prepared CTFM@CTF core–shell structured single crystal, YAG:Ce single crystal and blue‐chip, warm WLEDs with excellent color rendition (Ra=90, R9=94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins.
Single‐crystal red phosphors easily grown by solvent exchange exhibit considerably better efficiency and stability. To further improve the chemical stability, a core–shell CTFM@CTF single crystal was prepared through an epitaxial growth route and a unique three‐step PL intensity change has been proposed.
A facile approach for coating red fluoride phosphors with a moisture‐resistant alkyl phosphate layer with a thickness of 50–100 nm is reported. K2SiF6:Mn4+ particles were prepared by co‐precipitation ...and then coated by esterification of P2O5 with alcohols (methanol, ethanol, and isopropanol). This route was adopted to encapsulate the prepared phosphors using transition‐metal ions as cross‐linkers between the alkyl phosphate moieties. The coated phosphor particles exhibited a high water tolerance and retained approximately 87 % of their initial external quantum efficiency after aging under high‐humidity (85 %) and high‐temperature (85 °C) conditions for one month. Warm white‐light‐emitting diodes that consisted of blue InGaN chips, the prepared K2SiF6:Mn4+ phosphors, and either yellow Y3Al5O12:Ce3+ phosphors or green β‐SiAlON: Eu2+ phosphors showed excellent color rendition.
The moisture instability of fluoride phosphors has limited their application in optoelectronic devices. Their waterproof properties can be improved by a hydrophobic coating layer, such as an alkyl phosphate. The luminous efficacy of warm white‐light‐emitting diodes (WLEDs) based on such coated phosphors is remarkably stable even under high‐humidity and high‐temperature conditions.
Perovskite quantum dots (PQDs) attract significant interest in recent years because of their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence quantum ...efficiency (PLQY). Recent studies report new types of formamidinium (FA) PbBr3 PQDs, PQDs with organic–inorganic mixed cations, divalent cation doped colloidal CsPb1−xMxBr3 PQDs (M = Sn2+, Cd2+, Zn2+, Mn2+) featuring partial cation exchange, and heterovalent cation doped into PQDs (Bi3+). These PQD analogs open new possibilities for optoelectronic devices. For commercial applications in lighting and backlight displays, stability of PQDs requires further improvement to prevent their degradation by temperature, oxygen, moisture, and light. Oxygen and moisture‐facilitated ion migration may easily etch unstable PQDs. Easy ion migration may result in crystal growth, which lowers PLQY of PQDs. Surface coating and treatment are important procedures for overcoming such factors. In this study, new types of PQDs and a strategy of improving their stabilities are introduced. Finally, this paper discusses future applications of PQDs in light‐emitting diodes.
Perovskite quantum dots (PQDs) have attracted much attention in recent years due to their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence. They show amazing optical properties in two types of light‐emitting diode (LED) such as PQDs based white‐light LEDs and PQD‐QLED. It is hoped that the PQDs based LED can be used in next generation display and lighting applications.
Silicon has long been regarded as a prospective anode material for lithium-ion batteries. However, its huge volumetric changes during cycling are a major obstacle to its commercialization, as these ...changes result in irreversible cracking and disconnection of the active mass from the current collector, as well as an excessive formation of a highly resistive solid electrolyte interphase. Multiple mechanical stress relief strategies that primarily use silicon nanostructurization have been previously developed. However, despite the significant improvements on the active material cycle life, using nanomaterials still results in complications, such as low conductivity, reduced volumetric energy density, and increased side reactions. This work provides a historical context for the development of silicon anodes and focuses on the surface chemistry and structural integrity of the electrode, thereby highlighting the most effective strategies reported recently for their optimization.
We present a novel composite strategy to enhance the stability of water-sensitive CsPbBr3 quantum dots (QDs) by embedding the QDs into the super-hydrophobic porous organic polymer frameworks ...(CPB@SHFW). The CPB@SHFW composites not only preserve a high photoluminescence quantum yield (PLQY ≈ 60%) and narrow band emission (full width at half-maximum ≈ 16 nm) but also inherit the outstanding water-resistant property of SHFW to protect the QDs from hydrolytic degradation. The PLQY of the composites was maintained at 91% (PLQY ≈ 54.3%) of the initial one (PLQY ≈ 60%) after being immersed in water for 31 days. Even after being immersed in water for 6 months, the CPB@SHFW composites still retain a bright green emission. In addition, super-hydrophobic perovskite QD-polymer composites (IPQDs@SHFW) with tunable and bright emission were prepared by using suitable halide salts. A white light-emitting diode (WLED) device was prepared by combining green-emitting CPB@SHFW composites and red-emitting K2SiF6:Mn4+ phosphors with a blue LED chip. The device exhibits a high luminous efficiency of 50 lm/W and a wide color gamut (127% of the National Television System Committee and 95% Rec. 2020). This work provides an alternative approach to solve the challenging stability issue of perovskite QDs; therefore, it has a positive implication for their practical application in liquid crystal display backlights.
Half a century after its initial emergence, lanthanide photonics is facing a profound remodeling induced by the upsurge of nanomaterials. Lanthanide‐doped nanomaterials hold promise for ...bioapplications and photonic devices because they ally the unmatched advantages of lanthanide photophysical properties with those arising from large surface‐to‐volume ratios and quantum confinement that are typical of nanoobjects. Cutting‐edge technologies and devices have recently arisen from this association and are in turn promoting nanophotonic materials as essential tools for a deeper understanding of biological mechanisms and related medical diagnosis and therapy, and as crucial building blocks for next‐generation photonic devices. Here, the recent progress in the development of nanomaterials, nanotechnologies, and nanodevices for clinical uses and commercial exploitation is reviewed. The candidate nanomaterials with mature synthesis protocols and compelling optical uniqueness are surveyed. The specific fields that are directly driven by lanthanide doped nanomaterials are emphasized, spanning from in vivo imaging and theranostics, micro‐/nanoscopic techniques, point‐of‐care medical testing, forensic fingerprints detection, to micro‐LED devices.
Lanthanide doped nanomaterials are promising light transducers, integrating the features originating from lanthanide electronic behaviors and nanoscale size effects. Cutting‐edge technologies and devices have recently arisen from this association and are in turn promoting nanomaterials for diverse high‐technology applications. Here, recent progress in developing lanthanide‐containing nanomaterials, nanotechnologies, and nanodevices for clinical employment use and commercial exploitation is reviewed.
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