Blue-emitting Light-emitting Diodes Research Articles

Controllable Synthesis of Cadmium-Free Blue-Emitting Cu-Ga-Zn-S-Based Nanocrystals for Solution-Processed Quantum-Dot Light-Emitting Diodes.

The utility of semiconductor nanocrystals (NCs) in light-emitting diodes (LED) has shown great potential in the field of display, whereas the challenge remains in developing efficient and stable cadmium-free blue-emitting LED devices due to the poor photophysical properties of blue-emitting NCs. Herein, we develop a controllable synthesis of Cu-Ga-Zn-S (CGZS) semiconductor NCs that show blue light emission with a relative photoluminescence quantum yield exceeding 90%. Furthermore, we have successfully fabricated a solution-processed quantum-dot LED (QLED) using CGZS NCs, achieving a notable maximum external quantum efficiency (EQE) of 1.00% at a luminance of 100 cd/m2. Our work lays a foundational framework for advancing cadmium-free blue-emitting QLEDs and facilitates the development of quantum dot electroluminescent panchromatic displays.

One-Step Extrusion Preparation for Low-Cost Multicolored Carbon Dot Fluorescent Films.

Carbon dots (CDs), an emerging class of environmentally friendly luminescent materials, have been extensively applied in full-color display of light-emitting diodes (LEDs). However, the synthesis of CDs usually requires high pressure, and the conventional preparation of CD-based LED films involves intricate manufacturing techniques. The resulting security risk and high cost restrict the further application of CD-based LEDs. Here, we present a cost-effective method to obtain CD-based LED films via in situ extrusion in a twin-screw extruder. By fine-tuning the extrusion temperature, we created blue-emitting LEDs. The resulting fluorescent films exhibited remarkable stability, retaining 94% fluorescence intensity after 180 days of storage. We also prepared yellow, pure white, and cool white LEDs with malleable shapes, validating the versatility of the in situ extrusion method. More importantly, the manufacturing cost for CD-based films amounts to only about 0.8 RMB/g, which is substantially lower than that of the reported preparation methods. This work offers a cost-effective, safe, and massive approach to preparing photoluminescent LEDs, paving the way for the development of more sustainable and efficient CD-based LEDs.

Sustainable next-generation color converters from P. harmala seed extracts for solid-state lighting.

Traditional solid-state lighting heavily relies on color converters, which often have a significant environmental footprint. As an alternative, natural materials such as plant extracts could be employed if their low quantum yields (QYs) in liquid and solid states were higher. With this motivation, here, we investigate the optical properties of aqueous P. harmala extract, develop efficient color-converting solids through a cost-effective and environmentally friendly method, and integrate them with light-emitting diodes (LEDs). To achieve high-efficiency solid hosts for P. harmala-based fluorophores, we optically and structurally compare two crystalline and two cellulose-based platforms. Structural analyses reveal that sucrose crystals, cellulose-based cotton, and paper platforms enable a relatively homogeneous distribution of fluorophores compared to KCl crystals. Optical characterization demonstrates that the extracted solution and the extract-embedded paper possess QYs of 75.6% and 44.7%, respectively, whereas the QYs of the cotton, sucrose, and KCl crystals remain below 10%. We demonstrated that the paper host with the highest efficiency causes a blueshift in the P. harmala fluorescence, whereas the cotton host induces a redshift. We attribute this to the passivation of nonradiative transitions related to the structure of the hosts. Subsequently, as a proof-of-concept demonstration, we integrate the as-prepared efficient solids of P. harmala for the first time with a light-emitting diode (LED) chip to produce a color-converting LED. The resulting blue-emitting LED achieves a luminous efficiency of 21.9 lm Welect -1 with CIE color coordinates of (0.139, 0.070). These findings mark a significant step toward the utilization of plant-based fluorescent biomolecules in solid-state lighting, offering promising environmentally friendly organic color conversion solutions for future lighting applications.

Highly Efficient Broad-Band Green-Emitting Cerium(III)-Activated Garnet Phosphor Allows the Fabrication of Blue-Chip-Based Warm-White LED Device with a Superior Color Rendering Index.

High-performance warm-white light-emitting diode (LED) devices are in great demand toward green and comfortable solid-state lighting. Herein, we report a creative green-emission CaY2HfGa(AlO4)3:Ce3+ phosphor. CaY2HfGa(AlO4)3:Ce3+ compounds with different cerium ion doping contents have been successfully prepared through a conventional high-temperature solid-state method, and their phase and crystal structure have been revealed via the powder X-ray diffraction and Rietveld refinement. Impressively, the CaY2HfGa(AlO4)3:Ce3+ phosphors exhibit a broad-band excitation, which well covers the wavelength region from the 300 to 500 nm, corresponding to the commercial blue-emitting LED chip. Upon 450 nm excitation, the optimal CaY2HfGa(AlO4)3:2%Ce3+ sample shows an intense broad-band green emission (the corresponding testing spectral range: 460-750 nm) with a strongest peak about 534 nm. In addition, the CaY2HfGa(AlO4)3:2%Ce3+ sample possesses a broad full width at half-maximum equal to 120 nm; moreover, its CIE chromaticity coordinate and the internal quantum efficiency are determined to be (0.3541, 0.5427) and 72.8%, respectively. A high-quality warm-white LED has been fabricated through incorporating our CaY2HfGa(AlO4)3:2%Ce3+ green phosphors and commercial red phosphors with the 450 nm blue LED chip. When upon the 20 mA bias driving current, the LED device demonstrates a bright warm-white light emission, which possesses a satisfactory color rendering index of 91, a low correlated color temperature of 4080 K, as well as a good luminous efficacy of 85.14 lm W-1. The creative green-emitting CaY2HfGa(AlO4)3:Ce3+ garnet phosphor has a bright application prospect toward high-quality warm-white LED lighting.

Enhancement of the Modulation Response of Quantum-Dot-Based Down-Converted Light through Surface Plasmon Coupling.

In this paper, we first elaborate on the effects of surface plasmon (SP) coupling on the modulation responses of the emission of a light-emitting diode (LED) and its down-converted lights through colloidal quantum dots (QDs). The results of our past efforts for this subject are briefly discussed. The discussions lay the foundation for the presentation of the new experimental data of such down-converted lights in this paper. In particular, the enhancement of the modulation bandwidth (MB) of a QD-based converted light through SP coupling is demonstrated. By linking green-emitting QDs (GQDs) and/or red-emitting QDs (RQDs) with synthesized Ag nano-plates via surface modifications and placing them on a blue-emitting LED, the MBs of the converted green and red emissions are significantly increased through the induced SP coupling of the Ag nano-plates. When both GQD and RQD exist and are closely spaced in a sample, the energy transfer processes of emission-reabsorption and Förster resonance energy transfer from GQD into RQD occur, leading to the increase (decrease) in the MB of green (red) light. With SP coupling, the MB of a mixed light is significantly enhanced.

Chirality Transfer from Chiral Mesoporous Silica to Perovskite CsPbBr 3 Nanocrystals: The Role of Chiral Confinement

Chirality Transfer from Chiral Mesoporous Silica to Perovskite CsPbBr ₃ Nanocrystals: The Role of Chiral Confinement

Bright Blue Light Emission of Ni2+ Ion-Doped CsPbClxBr3-x Perovskite Quantum Dots Enabling Efficient Light-Emitting Devices.

In recent years, significant advances have been achieved in the red and green perovskite quantum dot (PQD)-based light-emitting diodes (LEDs). However, the performances of the blue perovskite LEDs are still seriously lagging behind that of the green and red counterparts. Herein, we successfully developed Ni2+ ion-doped CsPbClxBr3-x PQDs through the room-temperature supersaturated recrystallization synthetic approach. We simultaneously realized the doping of various concentrations of Ni2+ cations and modulated the Cl/Br element ratios by introducing different amounts of NiCl2 solution in the reaction medium. Using the synthetic method, not only the emission wavelength from 508 to 432 nm of Ni2+ ion-doped CsPbClxBr3-x QDs was facially adjusted, but also the photoluminescence quantum yield (PLQY) of PQDs was greatly improved due to efficient removal of the defects of the PQDs. Thus, the blue emission at 470 nm with PLQY of 89% was achieved in 2.5% Ni2+ ion-doped CsPbCl0.99Br2.01 QDs, which increased nearly three times over that of undoped CsPbClBr2 QDs and was the highest for the CsPbX3 PQDs with blue emission, fulfilling the National Television System Committee standards. Benefiting from the highly luminous Ni2+ ion-doped PQDs, the blue-emitting LED at 470 nm was obtained, exhibiting an external quantum efficiency of 2.4% and a maximum luminance of 612 cd/m2, which surpassed the best performance reported previously for the corresponding blue-emitting PQD-based LED.

Further reduction of efficiency droop effect by adding a lower-index dielectric interlayer in a surface plasmon coupled blue light-emitting diode with surface metal nanoparticles

Further reduction of the efficiency droop effect and further enhancements of internal quantum efficiency (IQE) and output intensity of a surface plasmon coupled, blue-emitting light-emitting diode (LED) by inserting a dielectric interlayer (DI) of a lower refractive index between p-GaN and surface Ag nanoparticles are demonstrated. The insertion of a DI leads to a blue shift of the localized surface plasmon (LSP) resonance spectrum and increases the LSP coupling strength at the quantum well emitting wavelength in the blue range. With SiO2 as the DI, a thinner DI leads to a stronger LSP coupling effect, when compared with the case of a thicker DI. By using GaZnO, which is a dielectric in the optical range and a good conductor under direct-current operation, as the DI, the LSP coupling results in the highest IQE, highest LED output intensity, and weakest droop effect.

Solid-state lighting with wide band gap semiconductors

ABSTRACTLight-emitting diodes (LEDs) made from wide band gap semiconductors, such as gallium nitride, are undergoing rapid development. Solid-state lighting with these LEDs is transforming patterns of energy usage and lifestyle throughout the world.With solid-state lighting gradually taking over from incandescent and fluorescent lighting, light-emitting diodes (LEDs) are very much the focus of research nowadays. This compact review takes a look at LEDs for lighting applications made from wide band gap semiconductors. A very brief history of electric lighting is included for completeness, followed by a description of blue-emitting LEDs that serve as pump sources for all ‘white’ LEDs. This is followed by a discussion on techniques to extract more light from the confines of LED chips through surface patterning. The thermal management of LEDs is perhaps the most important consideration in designing and using LED-based luminaires. This topic is discussed with regard to recent studies on LED reliability. The very promising development of gallium nitride-on-silicon LEDs is examined next followed by a discussion on phosphors for color conversion in LEDs. LED lighting has positively influenced both upscale and downscale illumination markets worldwide. Its societal impact is examined, with the review concluding with a look at efforts to produce LEDs from zinc oxide – a material that holds much promise for the future of solid-state lighting.

Synthesis of color-tunable Cu–In–Ga–S solid solution quantum dots with high quantum yields for application to white light-emitting diodes

Synthesis and application of I–III–VI type Cu–In–Ga–S (CIGS) quantum dots (QDs) with varied In : Ga ratios to a white light-emitting diode (LED) are reported. The band gap and emission energies of CIGS QDs are found to be systematically higher with increasing Ga content as a result of an appropriate formation of CIS–CGS solid solution. ZnS shell-capped QDs of the CIGS/ZnS core–shell emit quite tunable wavelengths of 520–578 nm with exceptionally high photoluminescence quantum yield of 72–83%, depending on the composition. By combining highly fluorescent CIGS/ZnS QDs as color converters with a blue-emitting LED, efficient white QD-based LEDs with high luminous efficacies of 69.1–75.0 lm W−1 at a forward current of 20 mA are fabricated. A white QD-LED with an enhanced color rendering property is further developed by choosing and blending two kinds of CIGS/ZnS QDs, and its electroluminescent properties are characterized in detail as a function of applied current.

Green GaInN photonic-crystal light-emitting diodes with small surface recombination effect

We have fabricated green GaInN light-emitting diodes (LEDs) containing two-dimensional photonic crystals (PCs). The PC structure is comprised of air holes that penetrate through the active layer. The observed emission intensity at room temperature was enhanced by a factor of ∼3 when a PC was introduced, which is close to the theoretical enhancement calculated without taking into account surface recombination at the air-hole edges. The carrier lifetime changes little when a PC is incorporated due to the low surface recombination. In contrast, the carrier lifetime in blue-emitting LEDs decreased by a factor of 4 when a PC was introduced. The surface-recombination velocity in green-emitting devices is estimated to be 3×102 cm/s, an order of magnitude smaller than in blue-emitting devices. This is due to the strong carrier localization effect in green-emitting GaInN.

Control of Spectral Properties of Strontium-Alkaline Earth-Silicate-Europium Phosphors for LED Applications

-based phosphors doped by were studied for use in white light emitting diodes (LEDs). Variations of excitation and emission spectra by changes in the alkaline earth ions in host lattice were studied. It was found that the system was excellent for white LED applications with excitation in the 380-465 nm region. Specially, the yellow light intensity from was comparable to yttrium aluminum garnet:Ce phosphors for excitation at 465 nm (blue-emitting LED). The peak excitation wavelength could be controlled by the ratio in the host lattice. Also, it was found that phosphors efficiently emit blue light at 405 nm excitation.

Light-emitting diodes based on poly(methacrylates) with distyrylbenzene and oxadiazole side chains

We report investigations on the use of singly and doubly functionalised poly(methacrylates) (PMA) for the fabrication of polymeric light-emitting diodes (LEDs). The functional groups we used were distyrylbenzene (DSB) as blue chromophore and 2-phenyl-5-phenyl-1,3,4-oxadiazole (PPD) or 2-phenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as charge-transport groups to produce three homopolymers (with one functional group only) and a copolymer bearing both DSB and PBD groups (PMA-DSB-PBD). The polymers have been used alone or blended together in single-layer devices or in double-layer devices, for which a thin poly( p-phenylene vinylene) (PPV) layer was used as a hole-transporting material. Despite the high photoluminescence yield of these DSB-based materials, successful fabrication of blue-emitting LEDs has only been achieved by using the copolymer, both in single- and double-layer devices.