Phosphor For Light-emitting Diodes Research Articles

Synthesis and Properties of Ca2La3(SiO4)2(PO4)O:Dy3+ Single-Phase Full-Color Phosphor

Novel single-phase white-light-emitting Ca2La3(SiO4)2(PO4)O:Dy3+ (CLSPO:Dy3+) phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reactions. The phases and luminescent properties of the obtained CLSPO:Dy3+ phosphors were well characterized. The results show that the excited bands of CLSPO:Dy3+ phosphor centered at wavelengths of 324 nm (6H15/2 → 4M17/2), 350 nm (6H15/2 → 4M15/2, 6P7/2), 366 nm (6H15/2 → 4I11/2), 387 nm (6H15/2 → 4I13/2, 4F7/2), 427 nm (6H15/2 → 4G11/2), and 448 nm (6H15/2 → 4I15/2). On excitation at 350 nm, the emission transitions of Dy3+ consisted of double emission bands, which can be assigned to the transition emissions of 4F9/2 → 6H15/2 (480 nm) and 4F9/2 → 6H13/2 (572 nm). The band gap energy of CLSPO and CLSPO : 0.45Dy3+ are 3.99 and 3.92 eV, respectively. The developed phosphor has great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.

New solid solution ceramics LixY1-yEuy(VO4)1-xF4x (0

New solid solutions, LixY(VO4)1-xF4x (0 ​< ​x ​≤ ​0.1), were successfully prepared via solid state reaction method by combination of orthovanadate YVO4 (Zircon structure) and LiYF4 fluoride (Scheelite structure). The structures were determined by X-ray diffraction and profil-matching refinements. Solid state nuclear magnetic resonance, Fourier transforms infrared and Raman spectroscopies with scanning electron microscopy were used to describe the microstructure and chemical composition of the as-prepared ceramics. It was found that solid solutions in the range 0 ​< ​x ​≤ ​0.1 are structurally similar to the zircon structure of YVO4. The luminescence properties of Eu3+ doped samples were investigated. Under excitation of 398 ​nm, the LixY1-yEuy(VO4)1-xF4x (x ​= ​0.05, 0.07, 0.1; y ​= ​0.05, 0.10, 0.15, 0.20) solid solution exhibited red emission originating from the strongest 5D0→7F2 transition. As the amount of Li+ and F− contents increases, the photoluminescence efficiency improved. So, the solid solution ceramics can be considered promising red phosphors for light-emitting diodes.

Intense green‐, red‐emitting Tb3+, Tb3+/Bi3+‐doped and Sm3+, Sm3+/La3+‐doped Ca2Al2SiO7 phosphors

This paper focuses on an optical study of a Tb3+ /Bi3+ -doped and Sm3+ /La3+ - doped Ca2 Al2 SiO7 phosphor synthesized using combustion methods. Here, Ca2 Al2 SiO7 :Sm3+ showed a red emission band under visible light excitation but, when it co-doped with La3+ ions, the emission intensity was further enhanced. Ca2 Al2 SiO7 :Tb3+ shows the characteristic green emission band under near-ultraviolet light excitation wavelengths, co-doping with Bi3+ ions produced enhanced photoluminescence intensity with better colour tunable properties. The phosphor exhibited better phase purity and crystallinity, confirmed by X-ray diffraction. Binding energies of Ca(2p), Al(2p), Si(2p), O(1s) were studied using X-ray photoelectron spectroscopy. The reported phosphor may be a promising visible light excited red phosphor for light-emitting diodes and energy conversion devices.

White-light-emitting triphasic fibers as a phosphor for light-emitting diodes.

White-light-emitting materials have received significant attention because of their potential application in lighting, displays, and sensors. However, it is a challenge to obtain white light from one phosphor, because the basic requirement of the white light emission spectrum is that it should be wide enough to cover the entire visible light region. In this study, we have designed and demonstrated a white-light-emitting PMMA–CBS-127/PVP–coumarin 6/PAN–rhodamine B (PSCR) fibrous membrane, which was prepared through a triphasic electrospinning method. Three luminescent organic dyes, CBS-127 (4.77 wt%, blue), coumarin 6 (0.1 wt%, green), and rhodamine B (0.42 wt%, red), were elaborately selected and doped into PMMA, PVP, and PAN, respectively. The resulting flexible PSCR membranes show white light emission (cover the entire visible-light region from 382 to 700 nm) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.31, 0.32), which is very close to ideal white light with CIE coordinates (0.33, 0.33). In addition, the PSCR membranes maintained high-quality white light emission after about 10 weeks of storage. The PSCR membranes can be used as the phosphor converting layer in white light-emitting diodes (WLEDs) through a remote membrane packaging method. A bright white emission is achieved at an applied voltage of 9 V. Therefore, the results indicate that PSCR membranes are potentially attractive candidates for application in WLEDs and displays.

Current Situation and Trend of the Phosphors for Full Spectrum LED Lighting

With the increase of the requirements for lighting quality, full spectrum light emitting diode (LED) lighting becomes the development hotspot. In this paper, the key materials for full spectrum LED phosphors are discussed and compared in detail. The advantages and disadvantages, research progress, and practical application of various color phosphors excited by violet and near ultraviolet light are emphasized, and then the existing problems, development trend, and industrial direction in this field are analyzed and prospected. Currently, there remain many problems in the phosphors excited by violet and near ultraviolet light, which can be applied in full spectrum. For example, the blue and cyan phosphors take on narrow emission spectrum, low light efficiency, and poor thermal stability; yellow phosphors and far-red phosphors have a low luminous efficiency due to their low absorption of violet or near ultraviolet light; and single matrix white phosphors have insufficient red light emission. Among them, luminous efficiency and thermal stability are the key factors restricting the application of the phosphors. Therefore, it is urgent to research the preparation and application technology of wide spectrum blue, cyan, yellow green, yellow, far-red, and single matrix white phosphors with high light efficiency and thermal stability, and develop the high-efficient and continuous preparation technology of the present phosphor products, to promote the further development of full spectrum LED.

Designing High‐Performance LED Phosphors by Controlling the Phase Stability via a Heterovalent Substitution Strategy

AbstractPhosphor‐converted white light‐emitting diodes (LEDs) are currently playing key roles in the lighting and display industries and trigger urgent demands for the discovery of “good” phosphors with high quantum efficiency, improved thermal stability, and controllable excitation/emission properties. Herein, a general and efficient heterovalent substitution strategy is demonstrated in K2HfSi3O9:Eu2+achieved by Ln3+(Ln = Gd, Tb, Dy, Tm, Yb, and Lu) doping to optimize luminescence properties, and as an example, the Lu3+substitution leads to improvement of emission intensity and thermal stability, as well as tunable emission color from blue to cyan. The structural stability and Eu2+occupation via Lu3+doping have been revealed by the structural elaboration and density functional theory calculations, respectively. It is shown that heterovalent substitution allows predictive control of site preference of luminescent centers and therefore provides a new method to optimize the solid‐state phosphors for LEDs.

Divalent europium-doped near-infrared-emitting phosphor for light-emitting diodes

Near-infrared luminescent materials exhibit unique photophysical properties that make them crucial components in photonic, optoelectronic and biological applications. As broadband near infrared phosphors activated by transition metal elements are already widely reported, there is a challenge for next-generation materials discovery by introducing rare earth activators with 4f-5d transition. Here, we report an unprecedented phosphor K3LuSi2O7:Eu2+ that gives an emission band centered at 740 nm with a full-width at half maximum of 160 nm upon 460 nm blue light excitation. Combined structural and spectral characterizations reveal a selective site occupation of divalent europium in LuO6 and K2O6 polyhedrons with small coordination numbers, leading to the unexpected near infrared emission. The fabricated phosphor-converted light-emitting diodes have great potential as a non-visible light source. Our work provides the design principle of near infrared emission in divalent europium-doped inorganic solid-state materials and could inspire future studies to further explore near-infrared light-emitting diodes.

Pink all-inorganic halide perovskite nanocrystals with adjustable characteristics: Fully reversible cation exchange, improving the stability of dopant emission and light-emitting diode application

In this work, we proposed a straightforward and effective strategy for preparing pink all-inorganic halide perovskite nanocrystal (NC) phosphors for light-emitting diode (LED) application. The pink perovskite NCs with varying Mn contents could be easily and steadily obtained via postsynthetic ion exchange at room temperature. The dependence of the size and optical properties of pink NCs on dopant content was systematically investigated. The reversible anion exchange processes of pink perovskite NCs were conducted with halide salts containing or excluding Pb. The contrasting results suggested that the irreversibility of Mn-emission was mainly affected by the fully reversible cation exchange between Pb2+ and Mn2+. The pink NCs with better stability of dopant emission and high monodispersity were successfully developed by compounding with silica. A pink LED was further made by using the pink NCs/silica composites as pink phosphors on a 395 nm InGaN LED chip. This work provides a feasible strategy for the fabrication of pink LEDs, which may have great application prospects in the field of special lighting, like neon lights and plant growth lights.

Highly Efficient and Stable White Light-Emitting Diodes Using Perovskite Quantum Dot Paper.

Perovskite quantum dots (PQDs) are a competitive candidate for next‐generation display technologies as a result of their superior photoluminescence, narrow emission, high quantum yield, and color tunability. However, due to poor thermal resistance and instability under high energy radiation, most PQD‐based white light‐emitting diodes (LEDs) show only modest luminous efficiency of ≈50 lm W−1 and a short lifetime of <100 h. In this study, by incorporating cellulose nanocrystals, a new type of QD film is fabricated: CH3NH3PbBr3 PQD paper that features 91% optical absorption, intense green light emission (518 nm), and excellent stability attributed to the complexation effect between the nanocellulose and PQDs. The PQD paper is combined with red K2SiF6:Mn4+ phosphor and blue GaN LED chips to fabricate a high‐performance white LED demonstrating ultrahigh luminous efficiency (124 lm W−1), wide color gamut (123% of National Television System Committee), and long operation lifetime (240 h), which paves the way for advanced lighting technology.

Redesign and manually control the commercial plasma green Zn2SiO4:Mn2+ phosphor with high quantum efficiency for white light emitting diodes

By reduce the stoichiometry ratio of ZnO raw materials, we successfully redesign and tailor the luminescence properties of commercial plasma green Zn2SiO4:Mn2+ phosphors for using as white light emitting diodes phosphors due to the strong absorption intensity at 420 nm. When excited at 420 nm, the quantum efficiency of the best redesigned Zn2SiO4:Mn2+ green phosphor can reach 76.2% which is much higher than 1.26% of the original Zn2SiO4:Mn2+ phosphor. To make clear the mechanism of the strong absorption at 420 nm as well as the increasing quantum efficiency, several classical methods of investigation including Rietveld refinement, X-ray diffraction patterns, Raman spectra and PL/PLE spectra are measured in this study. When reducing ZnO raw materials, the increased randomly distributed oxygen vacancies will induce the deviation from the inversion center of symmetry lattice site and then increase the quantum efficiency. Moreover, the FWHM of the best redesigned Zn2SiO4:Mn2+ is narrower that of β-SiAlON:Eu2+ and commercial green phosphor LMS-520B which indicates the redesigned Zn2SiO4:Mn2+ is more suitable for using as backlights for LCD. The redesigned Zn2SiO4:Mn2+ phosphor can also exhibit 81.2% color purity and excellent thermal stability with only 30% emission intensity loss at 140 °C. In addition, with reduced ZnO, the long decay times of Zn2SiO4:Mn2+ phosphor caused by the restriction of parity-forbidden and spin-forbidden 4T1-6A1 transition of Mn2+ can decrease from 4.168 ms to 3.268 ms. All the results suggest its great potential applications as backlights for LCD.

Tuning the Doping of Europium in Gadolinium Borate Microparticles at Mesoscale Toward Efficient Production of Red Phosphors.

The ideal product of rare-earth-doped phosphors should have uniform particle size distribution and homogeneous doping ions in each particle, and therefore, intensified micromixing at mesoscale is highly required. In this article, inspired by the concept of “mesoscience”, we demonstrate the tuning of Eu3+ doping in GdBO3 microparticles at mesoscale by a high-gravity-assisted reactive precipitation-coupled calcination process. The high-gravity environment and tiny droplets generated by the high-gravity rotating packed bed (RPB) reactor lead to significant intensification of mass transfer and micromixing, which are beneficial for the homogeneous doping of Eu3+ in the host material during reactive precipitation in liquid solution. Under excitation at 395 nm, the emission spectra of the Eu3+-doped phosphors exhibit a narrow-band red emission centered at 625 nm and the highest intensity was observed at x = 0.2. The RPB products show higher intensity than that of the control group even when the reaction time was shortened to 1/6. After calculation, the quenching in the sample most likely results from dipole–dipole interactions. The chromaticity coordinates for the RPB sample was measured as (0.598, 0.341) with a quantum yield of up to 78.11%, and the phosphors exhibit good thermal stability at 423 K. The phosphors were used as the luminescent materials for light-emitting diodes (LEDs), and the devices showed good performance. Our preliminary study illustrated that high-gravity-assisted approaches are promising for tuning the doping of rare-earth ions in microparticles at mesoscale toward efficient production of phosphors for LEDs.

A Robust TbIII-MOF for Ultrasensitive Detection of Trinitrophenol: Matched Channel Dimensions and Strong Host-Guest Interactions.

Host-Guest interaction is crucial to the sensitivity of heterogeneous sensors. Here, a series of isomorphic three-dimensional lanthanide metal-organic frameworks (Ln-MOFs), [Ln(TCBA)(H2O)2]2·DMF [H3TCBA = tris(3'-carboxybiphenyl)amine; Ln = Tb (1), Eu (2), and Gd (3); DMF = dimethylformamide] was synthesized and characterized, in which the propeller-like TCBA3- ligands adopt special torsional link between Tb(III) ions to form one-dimensional triangular channels. Optical experiments show that 1 exhibits bright green luminescence with an overall quantum yield of 26%, a 5D4 lifetime of 478 μs, and can act as an excellent heterogeneous fluorescent sensor to detect 2,4,6-trinitrophenol (TNP) explosive with an extremely low detection limit of 1.64 ppb. Because the confined channels within 1 exhibit matched dimensions toward TNP and feature multiple guest-response sites including rich π-conjugated groups, electron-donating N centers, and open metal nodes, strong host-guest interactions between 1 and TNP are captured and accurately determined by online microcalorimetry, which provides a distinctive thermodynamic perspective to understand the heterogeneous sensing behaviors. Additionally, the finely modulated heterometallic isomorphism [Tb0.816Eu0.184(TCBA)(H2O)2]2·DMF emits bright white light when excited at 380 nm and could potentially be used as single-phase white light-emitting diode phosphors materials.

Color-tunable luminescence and energy transfer properties of Dy3+/Tm3+ co-doped Sr9Mg1.5(PO4)7 phosphor for light-emitting diodes

A series of Sr9Mg1.5(PO4)7:Tm3+, Dy3+ phosphors were prepared by conventional sintering method. Rietveld refinement, X-ray diffraction patterns, PL/PLE spectra, lifetimes and thermal quenching spectra were measured and investigated in detail. All the prepared phosphors crystalized to single phase and consisted of micronized particles. When excited by 358 nm, the emission hue of Sr9Mg1.5(PO4)7:0.01 Tm3+, yDy3+ (0 ≤ y ≤ 0.20) turned from blue to white by modifying the Tm3+/Dy3+ ratio. The overlapped PL/PLE spectra and decreasing lifetimes of Sr9Mg1.5(PO4)7:Tm3+, yDy3+ indicated the energy transfer from Tm3+ to Dy3+. Moreover, the resonance type energy transfer from sensitizer (Tm3+) to activator (Dy3+), CIE chromaticity and energy transfer efficiency were confirmed and discussed, too. The energy transfer mechanism was determined as a resonant type via dipole-dipole mechanism with 53.05% energy transfer efficiency when the doping content y = 0.02. The CIE chromaticity coordinates of Sr9Mg1.5(PO4)7:0.01 Tm3+, 0.20Dy3+ was (0.3279, 0.3299) with 27.8% quantum efficiency. The sample also exhibited excellent thermal quenching performance with the remained 95% emission intensity at 150 °C compared with the original emission intensity at ambient temperature. The outstanding luminescence properties and excellent thermal stability suggested that Sr9Mg1.5(PO4)7:0.01 Tm3+, 0.20Dy3+ phosphor had a potential application in WLEDs.

Preparation and photoluminescence properties of LaBMoO6:Dy3+ yellow-emitting phosphor for LEDs

LaBMoO6:Dy3+ phosphor is successfully synthesized in the air by the solid-state reaction method. The luminescence properties and crystal structures are researched. LaBMoO6:Dy3+ phosphor with excitation at 388, 398, 426, and 451 nm emits yellow light. The emission spectrum of LaBMoO6:Dy3+ phosphor in the range of 450–780 nm contains four emission bands peaking at ~ 480, 570, 658, and 750 nm because of the 4F9/2 → 6H15/2, 6H13/2, 6H11/2, and 6H9/2 transitions of Dy3+ ion, respectively. The optimal Dy3+ ion concentration is ~ 6 mol% in LaBMoO6:Dy3+ phosphor. The lifetime of LaBMoO6:Dy3+ phosphor decreases from 0.467 to 0.279 ms with increasing Dy3+ ion concentration from 2 to 10 mol%. The energy-level diagram of Dy3+ ion is used to explain the luminous mechanism of LaBMoO6:Dy3+ phosphor. The experimental results indicate a potential application of LaBMoO6:Dy3+ phosphor as yellow phosphor for light-emitting diode based on near ultraviolet and blue chips.

Synthesis, spectroscopic properties and applications of divalent lanthanides apart from Eu2+

Abstract In this review, modern insights into the synthesis and fundamental optical properties as well as applications of divalent lanthanides as spectral energy converters are discussed, which have especially evolved within the last two decades. An emphasis is put on the state-of-the-art knowledge about the luminescence of other divalent lanthanides than the most commonly applied representative Eu2+ and what special features in their luminescence arises due to the different number of 4fn electrons. In particular, the luminescence of Sm2+, Tm2+, Yb2+ and the less stable ions Nd2+ and Dy2+ will be regarded. A broad overview over the synthetic approaches to inorganic compounds based on divalent lanthanide ions will be conveyed as well and shall demonstrate the fascinating developments in the field of inorganic solid-state chemistry of the lanthanides. Besides their fundamental optical properties, also applications of the presented divalent lanthanide activators are discussed. Sm2+ is a well-known temperature and pressure sensor due to its interconvertible 4f‐4f and 5d-4f transitions. Moreover, nanocrystalline BaFCl:Sm2+ has an appreciable potential as novel X-ray storage phosphor. Tm2+ is interesting for upconversion in photovoltaic and lasing applications, whereas Yb2+ in halides may be a promising alternative to Eu2+ for scintillation materials and phosphors for light-emitting diodes (LEDs). Nd2+ and Dy2+ are currently emerging as novel near infrared (NIR)-absorbing and emitting activators that might become interesting as lasing ions. The spectroscopy of these unusual lanthanide ions provides many non-trivial features due to the excited two-open shell 4fn-15d1 configuration overlapping with the excited 4fn levels. Finally, a perspective for future developments will be given.

Red-emitting phosphor Na2Ca2Nb4O13:Eu3+ for LEDs: Synthesis and luminescence properties

Na2Ca2Nb4O13:Eu3+ phosphor is successfully synthesize by the high-temperature solid-state reaction method in air. The crystal structures, morphology, X-ray powder diffractions (XRPD) patterns, energy dispersive X-ray (EDX) spectrum, decay curves, and luminescence properties are investigated. Na2Ca2Nb4O13:Eu3+ phosphor emits red light with the chromaticity coordinates (0.6312, 0.3684) and the emission spectrum is observed in the range of 575–725 nm, which contains four emission bands because of the 5D0 → 7F1 (575–600 nm), 5D0 → 7F2 (600–650 nm), 5D0 → 7F3 (650–670 nm), 5D0 → 7F4 (680–725 nm) transitions of Eu3+ ion, respectively. The optimal Eu3+ ion concentration in Na2Ca2Nb4O13:Eu3+ phosphor is ~10 mol%. The lifetime decreases in turn from 736.5 μs to 431.8 μs with increasing Eu3+ ion concentration from 2 mol% to 12 mol%. Na2Ca2Nb4O13:Eu3+ phosphor has a good thermal stability according to the temperature-dependent emission spectra. Luminous mechanism is explained by energy level diagram of Eu3+ ion. The experimental results indicate that Na2Ca2Nb4O13:Eu3+ phosphor has a hope to be used as red phosphor for light-emitting diodes (LEDs) based on near ultraviolet (UV) and blue LED chips.

Identification of a narrow band red light-emitting phosphor using computational screening of ICSD: Its synthesis and optical characterization

We searched the inorganic crystal structure database (ICSD) for entries involving cuboid local structures around activator ion sites, which were believed to be potential candidates for red phosphor light-emitting diode (LED) applications. In addition to the UCr4C4-type structures that are quite familiar to phosphor scientists and engineers, density functional theory (DFT) suggested that other cuboid structures could serve as phosphor hosts based on formation energy and band-gap calculation. As a result, we found 37 cuboid-involved structures that were plausible phosphor candidates. Among these, only Sr2[MgAl5N7]:Eu2+ and (Sr,Ca)2[MgAl5N7]:Eu2+ solid solutions actually produced viable phosphors that exhibited a narrow band of red light emission. All the other novel phosphor candidates pinpointed through the suggested discovery protocol at the current stage of development were secured for further experimental studies. The applicability of the discovery protocol suggested here could be extended to all other materials discovery approaches.

Quantum confined peptide assemblies with tunable visible to near-infrared spectral range

Quantum confined materials have been extensively studied for photoluminescent applications. Due to intrinsic limitations of low biocompatibility and challenging modulation, the utilization of conventional inorganic quantum confined photoluminescent materials in bio-imaging and bio-machine interface faces critical restrictions. Here, we present aromatic cyclo-dipeptides that dimerize into quantum dots, which serve as building blocks to further self-assemble into quantum confined supramolecular structures with diverse morphologies and photoluminescence properties. Especially, the emission can be tuned from the visible region to the near-infrared region (420 nm to 820 nm) by modulating the self-assembly process. Moreover, no obvious cytotoxic effect is observed for these nanostructures, and their utilization for in vivo imaging and as phosphors for light-emitting diodes is demonstrated. The data reveal that the morphologies and optical properties of the aromatic cyclo-dipeptide self-assemblies can be tuned, making them potential candidates for supramolecular quantum confined materials providing biocompatible alternatives for broad biomedical and opto-electric applications.

Optical design of dental light using a remote phosphor light-emitting diode package for improving illumination uniformity

The projection-type dental lighting based on the remote phosphor light-emitting diode (LED) package is designed to enhance uniformity of illuminance and correlated color temperature (CCT) on a target plane and to remove glare in the eyes of the patient. This dental lighting enables dentists to illuminate effectively the patient's mouth by increasing the inner area (50 mm×25 mm) described in ISO 9680. The optical module comprised of the LED package and optical lens is modeled to satisfy the inner area wider than 100 mm×50 mm and illuminance over 5,000lx per the designed optical module. The fabricated prototype dental lighting contains four optical modules, and the maximum illuminance is 22,786lx. The measured inner area is 105 mm×74 mm, and the ratio of inner area to outer area is about 76%. Also, the CCT variation is below 450K in total illuminance pattern.

High-efficiency and thermally stable far-red-emitting NaLaMgWO6:Mn4+ phosphorsfor indoor plant growth light-emitting diodes.

In this Letter, we report a novel NaLaMgWO6:Mn4+ double-perovskite phosphor. Under the excitation at 342nm, this phosphor showed a high-efficiency far-red emission at approximately 700nm with internal quantum efficiency of up to 60%. Moreover, it exhibited a high thermal stability; the emission intensity at 423k was approximately 57% of that at room temperature. Finally, a prototype light-emitting diode (LED) device was fabricated using the combination of a NaLaMgWO6:Mn4+ far-red-emitting phosphor and 365-nm LED chip.