White Light-emitting Diode Device Research Articles

Design of a broadband cyan-emitting phosphor with robust thermal stability for high-power WLED application

Due to the complicated production process and reabsorption problem, the development and application for white light-emitting diodes (WLEDs) are affected. A combination of cyan and red phosphors with near-ultraviolet (n-UV) LED chip has been proposed to solve these problems. Its key is developing cyan phosphor with broad emission band and excellent performances. In this work, we have developed a broadband cyan-emitting phosphor RbBa2(PO3)5: Eu2+ (RBP: Eu2+) by a solid-state method. The phase purity, crystal structure, luminescence properties and their relationship were investigated systematically. The RBP: Eu2+ phosphor can yield asymmetric broadband cyan emission upon 350 nm light excitation, which is ascribed to the occupation of Eu2+ for both the Ba1 and Ba2 sites. The measurement of temperature-dependent luminescence implies that the phosphor remains 89.5% of the initial value at 150 °C, which is much better than the commercial Ba2SiO4: Eu2+ phosphor. Furthermore, a WLED device has been obtained by composing the RBP: 0.01Eu2+ and CaAlSiN3: Eu2+ phosphors with a 365 nm LED chip. The emitted white light can show fabulous performances with the color coordinates of (0.3792, 0.3359), correlated color temperature of 3841 K and CRI of 90.8. The results suggest the RBP: Eu2+ phosphor to be a promising candidate for high-power WLEDs.

High-efficiency Ca2+ doping all-inorganic nanocrystals (CsPbBr3 and CsPbBr1I2) encapsulated in a superhydrophobic aerogel inorganic matrix for white light-emitting diodes

All-inorganic halide perovskite nanocrystals (NCs) have become the most promising next generation luminescent materials due to their excellent properties. However, there are many nonradiative recombination defects in colloidal perovskite NCs, which reduce their luminescent efficiency and stability. In this work, we incorporated the alkaline-earth (AE) metal ion Ca2+ into NCs to further improve the photoluminescence quantum yield (PLQY) of CsPbBr3 and CsPbBr1I2 NCs. The PLQY of green-emitting CsPbBr3 and red-emitting CsPbBr1I2 NCs can be boosted to 72.3% and 78.7%, respectively by doping the optimum amount of Ca2+. At the same time, we adopted a simple and low-cost one-pot method to integrate Ca2+-CsPbX3 (X3 = Br3, Br1I2) NCs and superhydrophobic silica aerogels (AG), not only retaining the high PLQY of NCs, but also greatly improving the water, heat and light stability. Finally, the green-emitting Ca2+-CsPbBr3@AG, red-emitting Ca2+-CsPbBr1I2@AG composites and the blue chip as the light sources show a wide color gamut that accounts for 129% of the NTCS 1953 value and nearly 100% of the Rec.2020 value. Additionally, we fabricated white light-emitting diode (WLED) devices by coupling Ca2+-CsPbBr1I2@AG composites with commercial YAG:Ce3+ phosphors on blue chips, obtaining bright white light with a color rendering index (CRI) up to 92.2.

Tailoring of White Luminescence in a NaLi3 SiO4 :Eu2+ Phosphor Containing Broad-Band Defect-Induced Charge-Transfer Emission.

Single-component materials with white-light emission are ideal for lighting applications. However, it is very challenging to achieve white luminescence in single-dopant activated solid phosphors. Herein, white NaLi3 Si1- x O4 :Eu2+ materials are designed via defect engineering and synthesized by reducing the Si content (0.15 ≤ x≤ 0.25). Stochiometric NaLi3 SiO4 :Eu2+ exhibits a narrow-band blue emission at 469nm, ascribed to the 5d → 4f transition of Eu2+ at highly symmetric cuboid Na sites, while samples with Si content reduced by 15-25% display white emission with two peaks at 472nm and 585nm. The newly appeared broadband yellow peak arises from charge-transfer transitions involving Eu2+ and nearby defects, as verified by an unusual bandwidth, a large Stokes shift, and a long decay time. A single-component white light-emitting diode device is fabricated by employing a white phosphor to demonstrate a color-rendering index of 82.9. This result provides a new design strategy for single-component white-light materials with broad-band defect-induced charge-transfer emission.

Investigation on the application of ZnO nanostructures to improve the optical performance of white light-emitting diodes

Though combining blue LED chips with yellow phosphor has been the most common method in white light-emitting diode (WLED) production, the attained angular correlated color temperature (CCT) uniformity is still poor. Thus, this article proposes to add ZnO nanostructures to WLED packages to promote the color uniformity of the WLEDs. The outcomes of the research demonstrate that utilizing ZnO at different amount can affect the scattering energy and the CCT deviations in WLEDs packages in different extents. Particularly, adding the node-like (N-ZnO), sheet-like (S-ZnO), and rod-like (R-ZnO) leads to the corresponding decreases of CCT deviations from 3455.49 K to 96.30 K, 40.03 K, and 60.09 K, respectively. Meanwhile, with 0.25% N-ZnO, 0.75% S-ZnO, and 0.25 % R-ZnO, WLED devices can achieve both better CCT homogeneity and lower reduction in luminous flux. The results of this article can be a valuable document for the manufacturer to use as reference in improving their WLED products.

Design of a novel WLED structure based on the non-rare-earth Ca2Y(Nb,Sb)O6:Mn4+ materials

Herein, the novel white light-emitting diode (WLED) structures based on the Ca2Y(Nb,Sb)O6:Mn4+ materials were presented. The crystal structure, morphology, elemental composition, luminescent behavior, thermal stability, quantum yield, decay curve, and color purity of Ca2YSbO6:Mn4+ (CYS:Mn4+) and Ca2YNbO6:Mn4+ (CYN:Mn4+) phosphors were investigated and compared in detail. For these phosphors, the concentration quenching (CQ) mechanism is different. For CYS:Mn4+ phosphors, the dipole-dipole interaction dominates the CQ while the dipole-quadrupole interaction is dominant in CYN:Mn4+ phosphors. The emission intensity of the optimal CYN:Mn4+ phosphors was stronger than that of the CYS:Mn4+ phosphors. Meanwhile, the color purities of the optimal CYS:0.003Mn4+ and CYN:0.003Mn4+ phosphors were calculated to be as high as 96.40% and 96.91%, respectively. Eventually, it is interesting that the packaged novel WLED structure would improve the color rendering index and correlated color temperature values. From the above results, non-rare-earth Ca2Y(Nb,Sb)O6:Mn4+ materials with high color purities could be proposed for WLED devices.

Utilizing energy transfer strategy to produce efficient green luminescence in Ca2LuHf2Al3O12:Ce3+,Tb3+ garnet phosphors for high-quality near-UV-pumped warm-white LEDs

White light-emitting diodes (LEDs) are widely used in lighting and display devices, and the exploration of phosphors with excellent luminescence performance and good stability is the key to the development of white LEDs. In this work, we reported novel near-UV-excited green-emitting Ca2LuHf2(AlO4)3:Ce3+,Tb3+ garnet phosphors with efficient Ce3+ → Tb3+ energy transfer. The CLHA:Ce3+,Tb3+ green phosphors were successfully synthesized by a high-temperature solid-state method, and the phosphors were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence excitation and photoluminescence spectra, the Commission International de I’Eclairage (CIE) chromaticity coordinates, quantum efficiency and temperature-dependent emission spectra. Due to the spin-allowed 4f → 5d transition of Ce3+ ions, the CLHA:Ce3+,Tb3+ phosphors exhibited a strong broad excitation band in the 300–470 nm near-ultraviolet (near-UV) range. Under 408 nm excitation, the CLHA:Ce3+,Tb3+ phosphors showed strong green light with emission center at 543 nm. The mechanism of energy transfer from Ce3+ to Tb3+ ions was attributed to quadruple-quadruple interaction. Impressively, the internal quantum efficiency and external quantum efficiency of the optimal CLHA:0.02Ce3+,0.5Tb3+ green phosphors were measured to be 77.1% and 55.8%, respectively. Finally, using the CLHA:0.02Ce3+,0.5Tb3+ phosphors as green-emitting color converter, a near-UV-pumped white LED device was fabricated, and under 80 mA driving current the LED device demonstrated bright warm-white light with high color rendering index (93.7), low correlated color temperature (3574 K), CIE chromaticity coordinates (0.3922, 0.3633), and high luminous efficacy (29.35 lm/W).

Rapid Synthesis of Red‐Emitting Sr2Sc0.5Ga1.5O5:Eu2+ Phosphors and the Tunable Photoluminescence Via Sr/Ba Substitution

AbstractDiscovering new Eu2+‐doped red‐emitting phosphors in oxide‐based materials is a challenge for white light‐emitting diode (WLED) applications. Herein, a highly efficient high‐frequency induction heating method is employed to rapidly prepare the red‐emitting Sr2Sc0.5Ga1.5O5:Eu2+ phosphors peaking at 614 nm and exhibiting a high photoluminescence quantum yield of 78.4% under the excitation of 440 nm. The structural and spectral analyses suggest that Eu2+ ions tend to enter the [Sc1/Ga1O6] and [Ga2O6] polyhedrons with small coordination numbers, leading to the broadband red emission originated from large crystal field splitting of Eu2+ 5d level. The chemical substitution of Ba in the Sr site enhances the thermal stability and helps to the photoluminescence tuning from 614 to 728 nm in SrBaSc0.5Ga1.5O5:Eu2+. The WLED device fabricated by blending the red Sr1.7Ba0.3Sc0.5Ga1.5O5:Eu2+ and yellow Y3(Al, Ga)5O12:Ce3+ phosphors shows a high color‐rendering index (Ra = 91.1), and low color‐correlated temperature (CCT = 4750 K). This study aims to provide a new synthesis method and design principle for guiding the development of Eu2+‐doped oxide‐based red phosphors with low preparation cost; moreover, the photoluminescence tuning strategy via cation substitutions is essential to achieve tunable emission, even the near‐infrared luminescence.

Novel CsPbX3@mica composites with excellent optical properties for high efficiency and wide color gamut white light-emitting diode

All inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have been widely reported. However, the poor stability of CsPbX3 QDs limits their application in the field of optoelectronics. In this work, CsPbX3 QDs were prepared by the hot injection strategy. We compounded CsPbX3 QDs with mica to improve stability. A series of novel CsPbX3@mica composites with high thermal stability and light radiation stability were successfully fabricated and the narrow full width at half maximum (FWHM) of blue, green and red emissions are ~17 nm, ~21 nm and ~37 nm, respectively. What's more, the photoluminescence quantum yield (PLQY) of CsPbBr3@mica composite is 38.5%. Notably, the white light-emitting diodes (wLED) device can be manufactured by coupling the red-emitting CsPbBr1I2@mica composite material and commercial phosphor YAG: Ce3+ with the InGaN chip to produce bright natural white light. Meanwhile, CsPbX3@mica composites can be used as color conversion materials to construct a LED device, which exhibits a wide color gamut covering up 115.7% of National Television System Committee (NTSC). This present work provided novel CsPbX3@mica composites and could bring the potential inspiration in backlit display and lighting applications.

Preparation and broadband white emission of Ce3+-doped transparent glass-ceramics containing ZnO nanocrystals for WLEDs applications

Ce3+-doped transparent glass-ceramics containing ZnO nanocrystals were successfully prepared. The optimal heat treatment condition was determined by DSC, XRD, SEM, and fluorescence spectrum analysis. The transmittances of all the glass-ceramics can reach about 70% in the visible region. With the increase of Ce3+ ions concentration, the stability of the precursor glass decreased slightly. The broadband emission spectrum of the glass-ceramics consists of Ce3+ ions characteristic emission peak at 471 nm (5d → 2F5/2), 524 nm (5d → 2F7/2), blue emission (431 nm), and yellow emission (580 nm) caused by defect emission of ZnO nano-crystalline. As the concentration of doped Ce3+ ions increased, the emission intensity of these glass-ceramics shows an increasing trend. Moreover, the luminescent color from warm white light to cool white light can be achieved by changing the excitation conditions. The chromaticity coordinate (0.312, 0.342) of 1.0 mol% CeO2 doped glass-ceramics is close to the standard white light. The results indicate that luminescent glass-ceramics are promising potential candidate materials for WLEDs (white light-emitting diodes) devices.

Novel and wide-ranging color tuning photoluminescence properties of Tb3+/Eu3+ doped garnet-type Li3Lu3Te2O12 phosphor: Energy transfer and enhanced thermal stability

In order to promote the development of white light emitting diodes (WLEDs) with improved color reproduction, the challenge by discovering novel photoluminescence color tuning phosphors via energy transfer (ET) is essential. However, the mechanism of energy transfer among dopants and its effect on ET efficiency have not been fully understood. Therefore, the photoluminescence color tuning in a variety of matrix structures based on energy transfer always needs to be discussed further. Herein, a series of wide-ranging color tunable Li3Lu3Te2O12 phosphors doped with Tb3+/Eu3+ were synthesized by high-temperature solid-state reaction for the first time. The crystalline structure, morphology and chemical composition of as-prepared phosphors were characterized. The excitation and emission spectra, fluorescence decay curve, and the relationship among emission intensity, doping concentration of dopants and CIE coordinates were investigated in detail. The results indicate that photoluminescence color tuning from green to red was realized by designing the Tb3+→Eu3+ energy transfer in Li3Lu3Te2O12:Tb3+, Eu3+ phosphors. The approximation theory of Reisfeld and the electric multipole interaction theory of Dexter were used to analyze the ET mechanism, which reveals that the dipole-dipole and dipole-quadrupole interaction is responsible for the ET process of Tb3+→Tb3+ and Tb3+→Eu3+. In addition, the thermal stability of the as-prepared phosphors was also revealed. Unforgettably, the samples with reasonable design ratio of Tb3+/Eu3+ exhibits a wider color tuning range, excellent luminescence intensity under n-UV excitation and outstanding thermal stability comparable to commercial Y2O3:Eu3+ phosphor after surface treatment, whose emission intensity at 150 °C exceeds 70% of the initial value. In addition, a prototype WLED device was fabricated with representative phosphor and commercial blue phosphor BaMgAl10O17: Eu2+ (BAM: Eu2+), which emitted warm-white light with great color rendering index (CRI) of 84.8, softer correlated color temperature (CCT) of 3989 K and the chromaticity coordinates of (0.3647,0.3178). All the results suggest that Li3Lu3Te2O12:Tb3+, Eu3+ phosphors can be conducted as potential alternative for near ultraviolet (n-UV) pumped phosphor-converted white light-emitting diodes (pc-WLEDs).

High-Performance NaK2Li[Li3SiO4]4:Eu Green Phosphor for Backlighting Light-Emitting Diodes

Narrowband green phosphors with high quantum efficiency are required for backlighting white light-emitting diode (WLED) devices. Materials from the A[Li3SiO4]4:Eu2+ family have recently been propos...

Polymer-derived preparations of the blue-excited greenish-yellow-emitting calcium-containing β-Si3N4:Eu-like phosphors

Polymer-derived greenish-yellow emitting silicon (oxy)nitride phosphors excited by blue light were prepared by using polycarbonsilane, europium (Eu) and calcium (Ca) acetylacetonates as raw materials. The chemical compositions, crystal phases, particle morphologies and microstructures of the samples prepared with Eu, and/or Ca, and none of any metal ions were studied and are compared. It was found that the Ca-containing Eu-activated silicon (oxy)nitride sample prepared with the atomic ratios of Eu/Si and Ca/Si being 0.06 and 0.12, respectively, was composed mainly of single crystallized particles in the β-Si3N4-like phase with Eu2+/3+ and Ca2+ ions locating at interstices of the β-Si3N4-like lattices. This sample demonstrated a substantial increment in the intensity of its broad and spike-less emission spectrum excited at 468 nm as compared to that for the Ca-free sample with its major emission peak being at 570 nm, and recorded a CIE coordinate (0.3386, 0.3474) near the equal energy white point with a Ra value of 71.4 when employed as the phosphor for a white light emitting diode device with blue chip of 460 nm. The emission mechanisms of Eu-activated for the Ca-free sample and the Ca-containing sample, the later res-shifted the major excitation band from the near-ultraviolet to blue, are discussed based on the experimental data.

Highly Photoluminescent CsPbBr3/CsPb2Br5 NCs@TEOS Nanocomposite in Light-Emitting Diodes.

All-inorganic halide perovskite (CsPb2Br5) nanocrystals (NCs) have received widespread attention owing to their unique photoelectric properties. This work reports a novel strategy to control the phase transition from CsPbBr3 to CsPb2Br5 and investigates the effects of different treatment times and treatment temperatures on perovskite NCs formation. By controlling the volume of tetraethoxysilane (TEOS) added, the formation of different phases of perovskite powder can be well controlled. In addition, a white light-emitting diode (WLED) device is designed by coupling the CsPbBr3/CsPbBr3-CsPb2Br5 NCs@TEOS nanocomposite and CaAlSiN3:Eu2+ commercial phosphor with a 460 nm InGaN blue chip, exhibiting a high luminous efficiency of 57.65 lm/W, color rendering index (CRI) of 91, and a low CCT of 5334 K. The CIE chromaticity coordinates are (0.3363, 0.3419). This work provides a new strategy for the synthesis of CsPbBr3/CsPbBr3-CsPb2Br5 NCs@TEOS nanocomposite, which can be applied to the field of WLEDs and display devices.

Design of Novel Highly Efficient Yellow-Orange Color-Tunable Luminescence in Rb2Sr1-yCayP2O7:xEu2+ Solid Solutions for White Light-Emitting Diodes.

Traditional white light-emitting diodes (WLEDs) are limited by the energy loss due to reabsorption. Integrating binary complementary color phosphors with near-ultraviolet (n-UV) LED chips can be a good solution, and the core of it is to develop yellow-emitting phosphors. In this work, we have designed Rb2Sr1-yCayP2O7:xEu2+ solid solutions with yellow-orange color-tunable luminescence. The crystal structure, luminescence properties, and potential applications for WLEDs were explored systematically. Under n-UV light excitation, the phosphors efficiently emit broadband yellow-orange emission. The reasons and mechanisms of the variation of the PL/PLE spectra have been investigated. The optimal Rb2SrP2O7:0.5% Eu2+ sample exhibits a high quantum efficiency of 72.96% with a good color purity of 87.1%. Upon combination of the BAM:Eu2+ and Rb2SrP2O7:0.5% Eu2+ phosphors with a 380 nm n-UV chip, a WLED device is fabricated and can emit white light with good performance.

Enhanced color rendering index of organic/inorganic hybrid white light-emitting diodes with trans-1-(9-anthryl)-2-phenylethene derivatives as organic blue-green emitting materials

Abstract The organic light-emitting materials have made certain development in organic/inorganic hybrid white light-emitting diodes (WLED) devices, which can reduce the reliance on rare earth metal materials to some extent. However, there is an urgent need to improve the color rendering index (CRI) of the hybrid WLED. Herein, the organic blue-green emitting materials mixed with green and red phosphors are used to construct the hybrid WLED. The device W19 is prepared by using the blue-green emitting material (E)-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-1-yl)anthracene (APEAn1N) mixed with green (BaSi2N2O2: Eu2+) and red (Sr, Ca)2AlSiN3: Eu2+ phosphors coated on near ultraviolet (NUV) LED chips (380 nm). The device W19 exhibits luminance efficiency of 17.78 lm W−1 (at 19.90 mA), CCT of 4658 K, CRI of 86.7, and CIE chromaticity coordinate of (0.3633, 0.4125), respectively. The CRI of device W22 based on tri-primary color phosphors and blue-green phosphor is 79.4 which is inferior to W19. The WLED device based on organic blue-green emitting materials blended with green and red phosphors has evident advantages for reducing of the reliance on rare earth metals and improving the CRI of hybrid device, which will greatly inspire us to design and synthesize new blue-green materials and facilitate the development of hybrid WLEDs in future.

Enhanced Stabilities and Production Yields of MAPbBr3 Quantum Dots and Their Applications as Stretchable and Self-Healable Color Filters.

Organic-inorganic hybrid CH3NH3PbBr3 (MAPbBr3) perovskite quantum dots (PQDs) are considered as promising and cost-effective building blocks for various optoelectronic devices. However, during centrifugation for the purification of these PQDs, commonly used polar protic and aprotic non-solvents (e.g., methanol and acetone) can destroy the nanocrystal structure of MAPbBr3 perovskites, which will significantly reduce the production yields and degrade the optical properties of the PQDs. This study demonstrates the use of methyl acetate (MeOAc) as an effective non-solvent for purifying as-synthesized MAPbBr3 PQDs without causing severe damage, which facilitates attainment of stable PQD solutions with high production yields. The MeOAc-washed MAPbBr3 PQDs maintain their high photoluminescence (PL) quantum yields and crystalline structures for long periods in solution states. MeOAc undergoes a hydrolysis reaction in the presence of the PQDs, and the resulting acetate anions partially replace the original surface ligands without damaging the PQD cores. Time-resolved PL analysis reveals that the MeOAc-washed PQDs show suppressed non-radiative recombination and a longer PL lifetime than acetone-washed and methanol-washed PQDs. Finally, it is demonstrated that a composite of the MAPbBr3 PQDs and a thermoplastic elastomer (polystyrene-block-polyisoprene-block-polystyrene) is feasible as a stretchable and self-healable green color filter for a white light-emitting diode device.

Composite structure Cr:YAG/Ce:YAG and (Ce,Cr):YAG/Ce:YAG transparent ceramics with high color rendering index for white LEDs/LDs

Transparent ceramics (TCs) with high color rendering index (CRI) are considered as excellent color converters for white light-emitting diode (LED) and laser diode (LD) devices. In this study, by utilizing the component and structural designs between layers, composite structure (Ce,Cr):YAG/Ce:YAG and Cr:YAG/Ce:YAG TCs with high CRI were fabricated by vacuum sintering. Microstructural and luminescence properties, as well as energy transfer from Ce3+ to Cr3+ ions of as-fabricated TCs were explored systematically. Simultaneously, TC based white LEDs/LDs were assembled via the remote excitation mode. Under 460 nm excitation, a high CRI value of 75.2 was realized in (Ce,Cr):YAG/Ce:YAG TC based white LEDs. As increasing the thickness of the Cr:YAG layer in Cr:YAG/Ce:YAG TC, its red emission intensity could be enhanced distinctly. The optimized CRI and CCT values could reach 74.4 and 4146 K, respectively. In addition, the optimized luminous flux (LF) and CRI of Cr:YAG/Ce:YAG TC based LD device were 160.6 lm and 69.1, respectively. Therefore, the composite structure design is an effective approach to realize the essential promotion of CRI value in TC based white LED/LD devices.

Transient Optical Properties of CsPbX3/Poly(maleic anhydride‐alt‐1‐octadecene) Perovskite Quantum Dots for White Light‐Emitting Diodes

Poly(maleic anhydride‐alt‐1‐octadecene) (PMAO)‐coated green CsPbBr3 and red CsPbBr0.6I2.4 quantum dots (QDs), as the phosphor materials for white light‐emitting diodes (WLEDs), are reported. The anhydride groups of PMAO can be bound to the surface ligands of perovskite QDs and act as a protective layer. The results show that CsPbX3/PMAO (X = Cl, Br, I) presents good crystallinity and excellent luminescence properties. Time‐resolved photoluminescence (TRPL) shows that the PL lifetime of CsPbX3/PMAO is prolonged, and the transient absorption (TA) results show that intraband hot‐exciton relaxation and exciton recombination can be slowed down when the CsPbX3 QDs are coated with PMAO. However, the PL quantum yields (PLQYs) increase for both the green‐emitting QDs and the red‐emitting QDs after PMAO coating. WLED devices are fabricated by integrating the green CsPbBr3/PMAO QDs and red CsPbBr0.6I2.4/PMAO QDs on the blue GaN chips. The devices show stable white light emission with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.314, 0.291). The results indicate that CsPbX3/PMAO QDs can be an ideal downconversion fluorescent material for WLED devices.

Enhancing the Water Resistance and Stability of CsPbBr3 Perovskite Quantum Dots for Light-Emitting-Diode Applications through Encapsulation in Waterproof Polymethylsilsesquioxane Aerogels.

Highly stable all-inorganic perovskite quantum dot/polymethylsilsesquioxane aerogel (CsPbBr3/PMSQ AG) composites were first produced using two-step hot-injection and encapsulation processes by embedding green-emitting CsPbBr3 PQDs into modified hydrophobic mesoporous silica AGs. The unique structure of the composites not only considerably enhances the chemical stability of CsPbBr3 PQDs against moisture, humidity, and blue-light irradiation in air but also prevents anion exchange reactions during light-emitting diode (LED) manufacturing processes. In addition, the composition-optimized CsPbBr3/PMSQ AG exhibited excellent stability when soaked in water for more than 14 days and retained half of its initial intensity. Finally, white LED devices were fabricated by combining a blue-emitting GaN-based chip, green-emitting CsPbBr3/PMSQ AG, and red-emitting K2SiF6:Mn4+ phosphors.

White Light Emitting CdS Quantum Dot Devices Coated with Layers of Graphene Carbon Quantum Dots

AbstractCadmium sulfide quantum dots (CdS QDs) are semiconductor nanoparticles having sizes in the order of nanometers. They are materials that have outstanding properties for down conversion applications. These nanostructures have been used in the fabrication of white light emitting diodes (WLEDs) in the last years. However, inhomogeneous deposition of CdS QD conversion materials allows unwanted UV light escape. In addition, low efficiency due to strong self-quenching effect, incompatibility between CdS QD solution/crystal polyester resin matrix and reabsorption are common problems that need to be solved. In this work, we try to address the incompatibility between the CdS QD solution/crystal polyester resin matrix by using a solvent exchange procedure. To block the unwanted UV-light escape, we coated our devices with a mixture of graphene carbon quantum dot (GCQD) solution/crystal polyester resin matrix. The QDs and the WLED prototypes were characterized by absorption and photoluminescence (PL) spectroscopy. The QDs embedded in the matrix shown a good homogeneous dispersion. On the other hand, the mixture shown a rapid solidification. These facts indicate a good compatibility between the CdS QDs and the crystal polyester resin. We also observed a considerable reduction of unwanted near UV-light. White light emission from WLED devices with common crystal polyester resin and low-cost materials has been achieved.