White LED Applications Research Articles

Ultralow-loss Optical Waveguides through Balancing Deep-Blue TADF and Orange Room Temperature Phosphorescence in Hybrid Antimony Halide Microstructures.

Harnessing the potential of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is crucial for developing light-emitting diodes (LEDs), lasers, sensors, and many others. However, effective strategies in this domain are still relatively scarce. This study presents a new approach to achieving highly efficient deep-blue TADF (with a PLQY of 25 %) and low-energy orange RTP (with a PLQY of 90 %) through the fabrication of lead-free hybrid halides. This new class of monomeric and dimeric 0D antimony halides can be facilely synthesized using a bottom-up solution process, requiring only a few seconds to minutes, which offer exceptional stability and nontoxicity. By leveraging the highly adaptable molecular arrangement and crystal packing modes, the hybrid antimony halides demonstrate the ability to self-assemble into regular 1D microrod and 2D microplate morphologies. This self-assembly is facilitated by multiple non-covalent interactions between the inorganic cores and organic shells. Notably, these microstructures exhibit outstanding polarized luminescence and function as low-dimensional optical waveguides with remarkably low optical-loss coefficients. Therefore, this work not only presents a pioneering demonstration of deep-blue TADF in hybrid antimony halides, but also introduces 1D and 2D micro/nanostructures that hold promising potential for applications in white LEDs and low-dimensional photonic systems.

Ultralow‐loss Optical Waveguides through Balancing Deep‐Blue TADF and Orange Room Temperature Phosphorescence in Hybrid Antimony Halide Microstructures

AbstractHarnessing the potential of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is crucial for developing light‐emitting diodes (LEDs), lasers, sensors, and many others. However, effective strategies in this domain are still relatively scarce. This study presents a new approach to achieving highly efficient deep‐blue TADF (with a PLQY of 25 %) and low‐energy orange RTP (with a PLQY of 90 %) through the fabrication of lead‐free hybrid halides. This new class of monomeric and dimeric 0D antimony halides can be facilely synthesized using a bottom‐up solution process, requiring only a few seconds to minutes, which offer exceptional stability and nontoxicity. By leveraging the highly adaptable molecular arrangement and crystal packing modes, the hybrid antimony halides demonstrate the ability to self‐assemble into regular 1D microrod and 2D microplate morphologies. This self‐assembly is facilitated by multiple non‐covalent interactions between the inorganic cores and organic shells. Notably, these microstructures exhibit outstanding polarized luminescence and function as low‐dimensional optical waveguides with remarkably low optical‐loss coefficients. Therefore, this work not only presents a pioneering demonstration of deep‐blue TADF in hybrid antimony halides, but also introduces 1D and 2D micro/nanostructures that hold promising potential for applications in white LEDs and low‐dimensional photonic systems.

Pivotal role of Boron-doped graphene quantum dots in stretchable and Self-Healable red emission nanocomposite Film: One step advance for white light emitting diodes application

In this study, red-emitting BGQDs were prepared by a hydrothermal method derived from 1,3,6-Trinitropyrene (TNP) and boric acid. The luminescence properties of as-synthesized BGQDs were characterized through photoluminescence (PL), time-resolved photoluminescence (TRPL), and UV–Vis measurements. After the modification of boron doping, B-GQDs demonstrated superior optical properties and chemical stability compared to pristine ones. For the sake of continued stability in the luminescent layer performance derived from BGQDs, poly{(n-butyl acrylate)–co-[N-(hydroxymethyl)acrylamide]} (PBA0.8-co-PNMA0.2) as an amphiphilic copolymer matrix with tunable mechanical, elastic, and self-healing properties was introduced. Through the synergistic effects between BGQDs and amphiphilic copolymer side chain, the physical and mechanical properties of the red-emitting nanocomposite film were impressively improved. Furthermore, white light-emitting diodes (WLEDs) were successfully fabricated by combining a 450 nm GaN chip, a commercial green-emitting (Ba,Sr)2SiO4:Eu2+ phosphor, and a self-healable red-emitting nanocomposite film, generating a high color rendering index (CRI) value of 89.4.

Synthesis and photoluminescence properties of AlPO4:Ln (Ln = Dy3+, Eu3+ and Sm3+) phosphors for near UV-based white LEDs application

Synthesis and photoluminescence properties of AlPO4:Ln (Ln = Dy3+, Eu3+ and Sm3+) phosphors for near UV-based white LEDs application

A review of fluorescent carbon dots: Synthesis, photoluminescence mechanism, solid-state photoluminescence and applications in white light-emitting diodes

A review of fluorescent carbon dots: Synthesis, photoluminescence mechanism, solid-state photoluminescence and applications in white light-emitting diodes

Energy transfer induced colour tunable photoluminescence performance of thermally stable Sm3+/Eu3+ co-doped Ba3MoTiO8 phosphors for white LED applications

Energy transfer induced colour tunable photoluminescence performance of thermally stable Sm3+/Eu3+ co-doped Ba3MoTiO8 phosphors for white LED applications

Synthesis and photoluminescence properties of Ce3+ and Tb3+ doped Na3Gd(PO4)2 phosphors for white LEDs

Na3Gd(PO4)2 phosphors doped with rare-earth metal ions Ce3+ and Tb3+ were fabricated by the solid-state reaction method. Under the excitation of 340 nm light, the Ce3+-doped Na3Gd(PO4)2 phosphors exhibit a broad emission band ranging from 370 nm to 480 nm, which emitted blue light centered at 405 nm. When excited at 373 nm, the Tb3+-doped Na3Gd(PO4)2 phosphors presented a green light emission, including a strong peak located at 547 nm. In addition, both of the Na3Gd(PO4)2: Ce3+ and Na3Gd(PO4)2: Tb3+ phosphors showed excellent thermal stability at different temperatures, be specific in the Na3Gd(PO4)2: Ce3+ emission intensities at 150 °C could maintain about 84 % and the Na3Gd(PO4)2: Tb3+ could maintain about 92.9 % of those at room temperature. A prototype of the white light-emitting diodes lamp exhibiting bright white light was fabricated by using a 365 nm near-ultraviolet-emitting LED chip, combined with Na3Gd(PO4)2: Ce3+ blue phosphors, Na3Gd(PO4)2: Tb3+ green phosphors, and Na3Gd(PO4)2: Eu3+ red phosphors, which produced a high color rendering index of 89.4, and a relatively low correlated color temperature of 5496 K. Moreover, the CIE point was calculated to be at (0.3332, 0.3438), locating in the white light region. These results indicate that the as-prepared phosphors can be considered as potential candidates for ultraviolet/near-ultraviolet light-excited white light-emitting diodes applications.

Energy transfer behavior and tunable spectroscopic properties of Ba3Lu4O9:Dy3+,Eu3+ phosphors for white LEDs

Ba3Lu4O9:Dy3+,Eu3+ phosphors were developed through the conventional solid-state reaction. Luminescent performance including the energy transfer from dysprosium to europium, spectral tunability, fluorescent lifetime and thermal quenching behavior of the as-studied phosphors was studied. The characteristic emission of Dy3+ and Eu3+ were detected in Ba3Lu4O9:Dy3+,Eu3+ upon the excitation at various ultraviolet–visible wavelengths. The critical distance between dysprosium and europium ions was evaluated to be about 16.05 Å. The energy transfer from dysprosium to europium in Ba3Lu4O9 can be attributed to the dipole-quadruple mechanism, and the efficiency was evaluated to be 81.8% for Ba3Lu3.52O9:0.16Dy3+,0.32Eu3+. The tunable warm-white emission and high thermal stability reveal that the as-studied phosphor can be an auspicious alternative for white LEDs application.

A porous Eu-PTA/Tb-SSA/ZrO2/ZnZrO3 light color adjustable phosphor: Luminescent property and application of warm white LED

Light emitting diode (LED) is the fourth generation lighting source, but it has some shortcomings such as complex chip packaging process and the unbalanced light color of phosphor in long-time application. In this study, a kind of Eu-terephthalic acid/Tb-sulfosalicylate/ZrO2/ZnZrO3 (Eu-PTA/Tb-SSA/ZrO2/ZnZrO3) phosphor with warm white light emission properties was prepared, and the warm white light LED (w-WLEDs) was successfully prepared by encapsulating Eu-PTA/Tb-SSA/ZrO2/ZnZrO3 phosphors together with 270 nm UV-chip. The ZrO2/ZnZrO3, Tb-SSA/ZrO2/ZnZrO3 and Eu-PTA/ZrO2/ZnZrO3 samples show blue emission, green emission and red emission under deep ultraviolet (UV, 270 nm) excitation, respectively. The Tb-SSA and Eu-PTA are co-doped into ZrO2/ZnZrO3 matrix with blue emission to achieve the warm white light emission, and the light color can be adjusted by controlling the doping amount of Eu3+ and Tb3+. Through the excitation method of single-component phosphor by the single chip, the complex chip packaging process of w-LED can be solved. By doping rare earth organic complexes into porous ZrO2/ZnZrO3 matrix, the problems of the light color unbalanced of phosphor and the low luminescence intensity of rare earth doped metal oxides composites can be solved.

Red-emitting phosphors of BaSr2(PO4)2: 4 %Eu3+, 4 %A (A = Li+, Na+, K+) for white LEDs

Abstract BaSr2(PO4)2: 4 %Eu3+, 4 %A (A = Li+, Na+, K+) phosphors were prepared by high-temperature solid-phase method. The crystal structure, photoluminescence properties, thermal stability, chromaticity coordinates, and fluorescence lifetime of the samples were investigated. The excitation and emission spectra of the samples are broadbands and the maximum peak of the emission spectrum is located at 619 nm. Among three charge compensators, the luminescence intensity is optimal for Li+ co-doping case, and the quenching temperature of the typical sample is about 500 K. the fluorescence lifetime τ $\left\langle \tau \right\rangle $ is 1469.6 ns, and the chromaticity coordinates exhibit a strong red emission. The present phosphor has a potential application for white light-emitting diodes (LEDs) under the near-ultra violet (n-UV) light excitation.

Improved Luminous Efficiency of AgInS2 Quantum Dots and Zeolitic Imidazolate Framework-70 Composite for White Light Emitting Diode Applications.

The application of multiple quantum dots (QDs) in the field of white light emitting diodes (WLEDs) is still an important challenge due to their low luminous efficiency and quenching phenomenon. In this paper, we prepared AgInS2 QDs/zeolitic imidazolate framework-70 (AIS/ZIF-70) composite by a microwave hydrothermal method. Owing to the high porosity and stability of ZIF-70, it could effectively prevent quenching issues due to the aggregation of QDs. Since the ZIF-70 and QDs were chemically bonded, the formation of the ZnS layer could effectively passivate the surface defect and thus the quantum yield reached 21.49 % in aqueous solution. The luminous efficiency (LE) of the assembled AIS/ZIF-based WLED was reinforced by 6.8 times with a molar ratio of AgIn/Zn=18, i. e. at 5.26 % molar fraction of ZIF-70. Moreover, the color rendering index (CRI) and correlated color temperature (CCT) of AIS/ZIF-based WLED were 84.3 and 3631 K, respectively, indicating its potential application in solid-state lighting.

Excitation wavelength altered PL study of Co doped ZnO nanoparticles suitable for white LED application

Abstract ZnO nanoparticles doped with Co at different concentration (Zn1−x Co x O) were synthesized by sol–gel auto combustion method and are characterized by using various characterization tools. Structural study using X-ray diffraction technique (XRD) analysis showed the crystalline nature with hexagonal wurtzite geometry and the composition analysis using energy dispersive X-ray spectroscopy (EDX) confirmed the incorporation of Co in the ZnO lattice in the case of doped nanoparticles. Scanning electron-microscopy (SEM) and transmission electron microscopy (TEM) analysis showed the prepared nanoparticles as spherical, loosely agglomerated and having dimension of nanoscale. UV–vis DRS studies indicated a red shift in optical band gap with Co doping. PL spectra exhibits emission in the UV and visible region and the analysis revealed information about the presence of various types of defects in the ZnO lattice. An increase in the excitation wavelength gives intense emission in the high wavelength region for doped nanoparticles confirming the presence of divalent and monovalent oxygen as main defects. The Zn0.93Co0.07O nanoparticles records CIE coordinates lying in the white region of CIE color space at 350 nm with CCT of 5561.4 K suggesting their suitability in fabrication of white light emitting diodes.

Structural, optical, elemental and photometric properties of Sm3+ activated Ca3Ga4O9 oxide phosphors for WLEDs

Solid-state lighting systems rely on the exceptional characteristics of phosphor-converted LEDs, including long lifetime, low energy consumption, and high brightness. This study focuses on the synthesis of Sm3+ activated Ca3Ga4O9 (CGO: Sm3+) orange-red emitting oxide phosphors using the solid-state reaction method. X-ray photoelectron spectroscopy was used to analyze the nature of bonding with the dopant ion and oxidative states of the elements in the structure. Scanning electron microscopy and energy dispersive spectroscopy revealed agglomerated particles with a flake-like structure in the Sm3+ doped sample. The optical properties of the samples were investigated using UV-Visible diffuse reflectance and photoluminescence excitation and emission analyses. The Sm3+ doped samples showed maximum excitation at 404 nm and 479 nm, with corresponding energy level transitions of 6H5/2 - 6P3/2 and 6H5/2 - 4I11/2, respectively. Emission spectra exhibited four emission maxima at 564, 601, 645, and 708 nm, representing the 4G5/2 - 6H5/2, 4G5/2-6H7/2, 4G5/2-6H9/2, and 4G5/2-6H11/2 transitions of Sm3+ ions. The Kubelka-Munk function was used to calculate the optical energy gap values. Photometric parameters, including color coordinates, correlated color temperature, and color purity, were determined. The CIE chromaticity coordinates of CGO: Sm3+ were found in the orange-red region, indicating its potential as a promising candidate for use in phosphor-converted white LEDs applications. The study concludes that Sm3+ activated CGO phosphors have great potential for use in solid-state lighting systems.

Tunable white light photoluminescence of a single phase Tm3+/Tb3+/Eu3+ codoped GdPO4 phosphor

The present study describes the production of triply-doped GdPO4 and its optical characteristics. Structural information of the prepared material has been investigated by using X-ray diffraction and Fourier transform infrared spectroscopy. The material synthesized crystallizes into a single monoclinic crystal of space group P 21/n. The excitation curves of photoluminescence of single doped GdPO4: Tm3+, Tb3+, and Eu3+ are recorded and their emission spectra are analyzed. Triple-doped material emits multi colour light after a single UV stimulation. White light emission was seen in both triply-doped GdPO4 with variable Tm3+ concentration and triply-doped GdPO4 with variable Eu3+ concentration. GdPO4 doped with Tb3+ (7 mol%), Tm3+ (1.5 mol%), and Eu3+ (2 mol%) has colour coordinates (x = 0.3290, y = 0.3291) approximately near the value of typical white colour coordinates (x = 0.333, y = 0.3333). Furthermore, the transfer of energy in Tm3+, Tb3+ and Eu3+ in triple doped phosphor with varying Eu3+ concentrations was explained. Electric dipole-dipole interaction is used to justify and describe the process of energy transfer from Tb3+ to Eu3+. Decay time measurements were performed to explain energy transfer. Colour rendering index (CRI), Corelated colour temperature (CCT), Quantum efficiency and thermal stability of the prepared phosphor was calculated. All these parameters infer that GdPO4 doped with Tm3+, Tb3+ and Eu3+ may have potential application in white LEDs.

Towards efficient blue Eu2+ activated pyrophosphate phosphor for warm white LED applications

A blue-emitting LiCsBaP2O7:Eu2+(LCBPO:Eu2+) pyrophosphate phosphor prepared by solid-state synthesis that emits bright blue light with a first-rate internal quantum efficiency and high color purity is reported. Furthermore, when heated from 298 K to 473 K, LCBPO:0.015Eu2+ phosphor exhibits excellent color stability. Impressively, LCBPO:0.015Eu2+ blue phosphor exhibits exceptional stability against air exposure over a month. Fabricating a near-ultraviolet (n-UV) pumped pc-wLED using LCBPO:0.015Eu2+ along with green (Sr,Ba)2SiO4:Eu2+ and red (Ca,Sr)AlSiN3:Eu2+ phosphors demonstrates a well distributed warm white light with a high color-rendering index (Ra) of 91.7, a low correlated color temperature (CCT) of 3382 K and a high luminous efficiency (LE) of 26.1 l m/W. The high-performance optical characteristics, straightforward synthesis procedures and economical initial materials cost of LCBPO:Eu2+ support the potential of this material for usage in warm white LED-based lighting systems.

Synthesis and optical properties of Y3Al5O12:Ce3+,Cr3+ nano-phosphor for white LED

In this paper, Y3Al5O12:Ce3+,Cr3+ (YAG:Ce3+,Cr3+) nano-phosphors are prepared by the co-precipitation method, the average particle size of the phosphor is ∼100 nm. In addition, two surface treatments are introduced to improve the homogeneity of the nanoparticles. One is the addition of an appropriate amount of sodium dodecyl sulfate, and the other is coating a carbon layer on the surface of the nanoparticles by a solvothermal method using glucose as the carbon source. The optical properties and mechanisms of the synthesized YAG:Ce3+,Cr3+ nano-phosphors are detailed analyzed in the text. The CIE color coordinates (0.30, 0.36) of the nanoscale YAG:Ce3+,Cr3+ phosphor combined with the 450 nm blue chip is close to standard white light, which has potential application in white LED.

Two-step sintered phosphor ceramics for high-power LED applications: Fine microstructure and luminescent property

With the development of the high-power solid-state lighting (SSL) industry, there is an urgent demand for low-cost color converters with good luminescent performance and thermal robustness. Conventional phosphor ceramics face the problems of high sintering energy consumption and low light extraction efficiency. In the present work, a two-step sintering (TSS) method has been developed to obtain a series of YAG:Ce and YAG:Ce-Al2O3 samples at a lower temperature of 1600 °C, where the operating power is reduced to 67% of the traditional one-step process. The TSS samples have a fine microstructure, which leads to a better scattering enhancement effect. The impacts of grain size and composition on optical and thermal properties were investigated in detail. The luminous characteristics and stability were analyzed by packaging phosphor ceramics with blue LEDs, with a maximum LE of 188.72 lm/W, CRI of 58.7, and CCT in the range of 3628–5048 K, respectively. Such suitable properties of the TSS material make it a promising candidate for high-power white LEDs applications.

Novel Mn4+-Activated K2Nb1-xMoxF7 (0 ≤ x ≤ 0.15) Solid Solution Red Phosphors with Superior Moisture Resistance and Good Thermal Stability.

Nowadays, Mn4+-activated fluoride red phosphors with excellent luminescence properties have triggered tremendous attentions for enhancing the performance of white light-emitting diodes (WLEDs). Nonetheless, the poor moisture resistance of these phosphors impedes their commercialization. Herein, we proposed the dual strategies of "solid solution design" and "charge compensation" to design K2Nb1-xMoxF7 novel fluoride solid solution system, and synthesized the Mn4+-activated K2Nb1-xMoxF7 (0 ≤ x ≤ 0.15, x represents the mol % of Mo6+ in the initial solution) red phosphors via co-precipitation method. The doping of Mo6+ not only significantly improve the moisture resistance of the K2NbF7: Mn4+ phosphor without any passivation and surface coating, but also effectively enhance the luminescence properties and thermal stability. In particular, the obtained K2Nb1-xMoxF7: Mn4+ (x = 0.05) phosphor possesses the quantum yield of 47.22% and retains 69.95% of its initial emission intensity at 353 K. Notably, the normalized intensity of the red emission peak (627 nm) for the K2Nb1-xMoxF7: Mn4+ (x = 0.05) phosphor is 86.37% of its initial intensity after immersion for 1440 min, prominently higher than that of the K2NbF7: Mn4+ phosphor. Moreover, a high-performance WLED with high CRI of 88 and low CCT of 3979 K is fabricated by combining blue chip (InGaN), yellow phosphor (Y3Al5O12: Ce3+) and the K2Nb1-xMoxF7: Mn4+ (x = 0.05) red phosphor. Our findings convincingly demonstrate that the K2Nb1-xMoxF7: Mn4+ phosphors have a good practical application in WLEDs.

Realizing thermal and moisture stability in the K2Ge1-xTixF6:Mn4+ red phosphors with high efficiency for WLEDs

Developing red light-emitting phosphors with high performances is an imperative issue for achieving high-quality warm white light-emitting diodes. Here, red light-emitting K2Ge1-xTixF6:Mn4+ phosphors with high luminescence performances are obtained. Benefiting from the Ti4+-doping in K2GeF6, a high internal quantum yield of 96% can be obtained. The emission intensity at 423 K keeps 83% of the initial value at 298 K in K2Ge0.6Ti0·4F6:Mn4+. The moisture resistance property of K2Ge0.6Ti0·4F6:Mn4+ is significantly enhanced and can keep 71% of the original luminescence intensity after immersing in deionized water for 180 min. A warm white light-emitting diode with high color rendering index of 92.4, low correlated color temperatures of 3113 K, and high luminous efficiency of 123.1 l m/W is simultaneously obtained by encapsulating K2Ge0.6Ti0·4F6:Mn4+ with commercial yellow phosphor on blue chips. This work proves the prospects of K2Ge1-xTixF6:Mn4+ as promising red phosphors for potentially viable application in warm white light-emitting diodes.

Photoluminescence and thermoluminescence study of Ca1.02Sr1.98Al2O6: Dy phosphor synthesized by combustion method

In the present work, we have synthesized Ca1.02Sr1.98Al2O6 phosphors with different doping concentrations of Dy3+ (0.5 mol% to 4.0 mol%) by simple combustion method. The phase purity of the prepared phosphor has been confirmed by X-ray diffraction (XRD). Detailed investigations have been carried out to study the photoluminescence (PL) and thermoluminescence (TL) properties of the synthesized phosphors. Under 348 nm excitation, the PL emission spectrum shows two intense emission bands at blue and yellow color region due to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transition of Dy3+ ions. In addition, the TL properties of gamma-irradiated Dy3+ doped Ca1.02Sr1.98Al2O6 phosphors were investigated. According to the obtained PL and TL results, the synthesized phosphors have good prospects for future investigations on white LED and TLD applications.