Multicolor Light-emitting Diodes Research Articles

Phosphine-Capped Effects Enable Full-Color Clusteroluminescence in Nonconjugated Polyesters.

Full-color luminophores have advanced applications in materials and engineering, but constructing color-tunable clusteroluminescence (CL) from nonconjugated polymers based on through-space interactions remains a huge challenge. Herein, we develop phosphine-capped nonconjugated polyesters exhibiting blue-to-red CL (400-700 nm) based on phosphine-initiated copolymerization of epoxides and cyclic anhydrides, especially P1-0.5TPP, which exhibits red CL (610 nm) with a high quantum yield of 32%. Experiments and theoretical calculations disclose that the phosphine-capped effect in polyesters brings about conformational changes and induces phosphine-ester clusters by through-space (n,π*) interactions. Moreover, CL colors and efficiencies can be easily tailored by types of phosphines, compositions and structures of polyesters, and concentration. Significantly, the role of polymer motions (group, segmental, and chain motions) on CL originating from microregions inside polyesters is revealed. Further, phosphine-capped nonconjugated polyesters are demonstrated to be nonconjugated dyes and fluorescent fibers and are also used for multicolor light-emitting diodes including white light. This work not only provides an engineering strategy based on the end-group effect to prepare full-color clusteroluminogens but also broadens the prospects for material applications.

Tunable dual-emission of Sb3+, Ho3+ Co-doped Cs2NaScCl6 single crystals for light-emitting diodes

Lead-free halide double perovskites are considered as one of the most promising materials in optoelectronic devices, such as solar cells, photodetectors, and light-emitting diodes (LEDs), due to their environmental friendliness and chemical stability. However, the extremely low photoluminescence quantum yield (PLQY) of self-trapped excitons (STEs) emission from lead-free halide double perovskites impedes their applications. Herein, Sb3+ ions were doped into rare-earth-based double perovskite Cs2NaScCl6 single crystals (SCs), resulting in a large enhancement of PLQY from 12.57% to 87.37%. Moreover, by co-doping Sb3+ and Ho3+ into Cs2NaScCl6 SCs, the emission color can be tuned from blue to red, due to an efficient energy transfer from STEs to Ho3+ ions. Finally, the synthesized sample was used in multicolor LED, which exhibited excellent stability and optical properties. This work not only provides a new strategy for improving the optical properties of Cs2NaScCl6 SCs, but also suggests its potential application in multicolor LEDs.

Carbon Dot Based Multicolor Electroluminescent LEDs with Nearly 100% Exciton Utilization Efficiency.

Carbon dots (CDs) are promising nanomaterials for next-generation lighting and displays due to their tunable bandgap, high photoluminescence quantum yield (PLQY), and high stability. However, the exciton utilization efficiency (EUE) of CD-based films can only reach 25%, fundamentally limiting their application in electroluminescent light-emitting diodes (LEDs). Improving the EUE is therefore of great significance. Herein, we developed composite films containing CDs and poly(9-vinylcarbazole) (PVK). The films were then used to construct a series of high-performance electroluminescent LEDs with tunable emission colors covering the blue to green regions as the concentration of CDs in the films increased, delivering a maximum external quantum efficiency and current efficiency of 2.62% and 5.11 cd/A, respectively. Theoretical calculations and experiments established that the excellent performance at low film PLQY was due to a hot exciton effect in the CDs, achieving nearly 100% EUE. This work provides new design strategies toward high-performance CD-based electroluminescent LEDs.

One-pot synthesis of nitrogen-doped carbonized polymer dots with tunable emission for multicolor light-emitting diodes

Carbonized polymer dots (CPDs) have highly potential application value in the field of optoelectronic devices due to their preferable stability, excellent optical properties and low cost. Here, the nitrogen-doped carbonized polymer dots (HNCDs) with self-quenching-resistant fluorescence were prepared via a simple solvothermal method with citric acid, urea and 2-hydroxyethyl methacrylate (HEMA) as raw materials. The structure and optical properties of the HNCDs have been explored in detail by various contrast experiments. The results show that HEMA form the poly(HEMA) to modify on the surface of carbonized core, which can overcome the quenching effect of carbonized core. The nitrogen doping is crucial for the red shift emission of solid-state HNCDs. Furthermore, the HNCDs exhibit concentration-dependent emission and excellent compatibility with silicone sol, which lead to their emission red shifted from blue to red with increasing concentration. The HNCDs were further applied to construct the light-emitting diodes (LEDs), and the multicolor LEDs ranging from blue to red can be prepared by simply varying the type of chips and adjusting the concentration of HNCDs in encapsulating material.

Encapsulating copper nanoclusters in 3D metal-organic frameworks to boost fluorescence for bio-enzyme sensing, inhibitor screening, and light-emitting diode fabrication

Herein, copper nanoclusters (CuNCs) were encapsulated with metal-organic framework based on the confinement effect to fabricate a sensitive fluorescence probe for xanthine oxidase activity monitoring and inhibitor screening. Compared with CuNCs, the yielded fluorescent composite exhibits long fluorescence lifetime, high quantum yield, and strong stability. The fluorescence intensity of the sensor is efficiently quenched by H2O2 (λem = 566 nm), which is a product of the oxidation of xanthine by dissolved oxygen in the presence of xanthine oxidase. On this basis, a fluorescent sensor was reported for xanthine oxidase detection with a detection limit of 0.034 U/L, and a good linear range from 0.4 to 28 U/L. This method is capable of screening xanthine oxidase inhibitors as potential drugs for the treatment of diseases such as hyperuricemia. Moreover, the composite was used to manufacture orange and white light-emitting diodes. Taken together, the present work provides a new heuristic strategy for the monitoring of xanthine oxidase and the screening of its inhibitors, and exhibits some insights into the construction of multicolor light-emitting diodes.

Monolithic Multicolor Emissions of InGaN-Based Hybrid Light-Emitting Diodes Using CsPbBr3 Green Quantum Dots.

To address the increasing demand for multicolor light-emitting diodes (LEDs), a monolithic multicolor LED with a simple process and high reliability is desirable. In this study, organic-inorganic hybrid LEDs with violet and green wavelengths were fabricated by depositing CsPbBr3 perovskite green quantum dots (QDs) as the light-converting material on InGaN-based violet LEDs. As the injection current was increased, the total electroluminescence (EL) intensities of the hybrid LEDs increased, whereas the light-converted green emission efficiency of the CsPbBr3 QDs decreased. The maximum green-to-violet EL spectral intensity ratio of the hybrid LEDs with CsPbBr3 QDs was achieved with the injection current of <10 mA. Moreover, the EL spectral ratio of the green-to-violet emission decreased at an injection current of 100 mA. The light-conversion intensity of the CsPbBr3 QDs decreased linearly as the junction temperature of the hybrid LEDs was increased with increasing injection current, similar to the temperature-dependent photoluminescence degradation of CsPbBr3 QDs. In addition, the junction temperature of the hybrid LED was minimized by pulse injection to suppress the thermal degradation of QDs and increase the light conversion efficiency to green emission. Therefore, the overall emission spectrum color coordinates of the hybrid LEDs exhibited a red shift from violet to blue in the low-current region and a blue shift toward violet as the green emission of the QDs was decreased above 10 mA.

Synthetic wavelength scanning interferometry for 3D surface profilometry with extended range of height measurement using multi-colour LED light sources

We report three-dimensional surface profilometry with extended range of height measurements using synthetic wavelength scanning interferometry without tunable filters, wavelength-tuning lasers, grating elements. We have used inexpensive multiple colour light emitting diodes (LEDs) and operate them sequentially one by one or combination of two or more colours simultaneously to visualize synthetic wavelength light source. Multiple colour LED light source was synthesized and entire visible range from violet to deep red colour was covered. A wide range of synthetic wavelengths were obtained. Five step phase shifting algorithm was used to recover phase maps with Mirau type interferometer which can be further utilized for 3D height measurements. A simple phase subtraction method was used to reconstruct the phase map at synthetic wavelength. The present system provides extended range of height measurements from sub-wavelength to tens of wavelengths. Experimental results of 3D-surface profile measurements of Si-IC chip and standard step object are presented.

Multi-Color Light-Emitting Diodes

Multi-color light-emitting diodes (LEDs) with various advantages of color tunability, self-luminescence, wide viewing angles, high color contrast, low power consumption, and flexibility provide a wide range of applications including full-color display, augmented reality/virtual reality technology, and wearable healthcare systems. In this review, we introduce three main types of multi-color LEDs: the organic LED, colloidal quantum dots (CQDs) LED, and CQD–organic hybrid LED. Various strategies for realizing multi-color LEDs are discussed including red, green, and blue sub-pixel side-by-side arrangement; vertically stacked LED unit configuration; and stacked emitter layers in a single LED. Finally, according to their status and challenges, we present an outlook of multi-color devices. We hope this review can inspire researchers and make a contribution to the further improvement of multi-color LED technology.

Aggregation-induced emission solid-state multicolor fluorescent carbon dots for LEDs and fingerprints applications

At present, most of the reported carbon dots (CDs) are still dispersed in the solvent in liquid state. However, solid-state CDs cannot fundamentally prevent the aggregation-caused quenching effect (ACQ), which seriously affects their application. Herein, hydrophobic solid-state luminescent CDs with typical aggregation-induced emission (AIE) behavior were synthesized by simple solvothermal method using dithiosalicylic acid (DSTA) and acetic acid. The AIE behavior of CDs is mainly due to the presence of disulfide bonds, which restrict the intramolecular rotation of CDs surface groups around them, thus generating solid-state fluorescence (SSF) in long-wave emission. In addition, by using MA, urea and sulfonamide to tune the emission behavior of CDs, red, yellow and green AIE CDs named R-CDs, Y-CDs and G-CDs were obtained successfully. The as-prepared CDs powder was further applied to fabricate multi-color light-emitting diodes (LEDs) on UV chips. The fabricated tri-color LED devices can maintain high color purity and color rendering index (CRI). More importantly, the Correlated color temperature (CCT) of the three LED devices was located in the warm light area, which could effectively reduce visual fatigue. Finally, we applied three kinds of AIE CDs in fingerprint detection and effectively displayed the details.

Lanthanide ions doped rare earth-based double perovskite single crystals for light-emitting diodes

Lead-free double perovskites have become the research hotspot in the optoelectronic fields. Then, it is a challenge to utilize the lattice doping by different rare earth ions with rich energy level and unique luminescence for emerging photonic applications. Here, we successfully prepared Sb3+ and Ln3+ ions doped Cs2NaYCl6 single crystals (SCs), bringing tunable bright luminescent emissions of blue, red, and white light, the highest photoluminescence quantum yield (PLQY) is up to 58.33%. Based on excellent and tunable luminescent properties, the multicolor light-emitting diodes (LEDs) applications for the rare earth-based double perovskite SCs were designed. These findings indicate that rare earth-based double perovskite will provide a broader application space for lighting.

Nickel-doped carbon dots with enhanced and tunable multicolor fluorescence emission for multicolor light-emitting diodes

Carbon dots (CDs) are a new type of carbon-based fluorescent nanomaterials, which have received a lot of interest because of their excellent properties, simple synthesis and wide applications. However, facial and fast synthesis of CDs with tunable multicolor emission that can be used for lighting still remains a challenge. Here, through a simple one-step solvothermal method, nickel-doped CDs with tunable fluorescence emission are successfully prepared. By optimizing the experimental conditions, fluorescence emission of the as-prepared CDs can be adjusted within a certain wavelength range (513 nm–612 nm), that is, from green to red. The particle size of the CDs also increases from 2 nm to 8 nm. The introduction of Ni can successfully enhance the fluorescence intensity and cause an obvious redshift. In addition, by mixing polyvinylpyrrolidone (PVP) with the multicolor nickel-doped CDs (Ni-MCDs), the self-quenching effect of solid-state fluorescence can be effectively avoided. Based on this, green, yellow and red light-emitting diodes (LEDs) with high performance can be constructed by integrating CDs/PVP composites with different colors on top of the UV chip, demonstrating their superior potential for solid-state lighting applications.

Multicolor Luminescent Carbon Dots: Tunable Photoluminescence, Excellent Stability, and Their Application in Light-Emitting Diodes

Carbon dots (CDs) are attracting much interest due to their excellent photoelectric properties and wide range of potential applications. However, it is still a challenge to regulate their bandgap emissions to achieve full-color CDs with high emissions. Herein, we propose an approach for producing full-color emissive CDs by employing a solvent engineering strategy. By only tuning the volume ratio of water and dimethylformamide (H2O/DMF), the photoluminescence (PL) emission wavelengths of the CDs can be changed from 451 to 654 nm. Different fluorescence features of multicolor CDs were systematically investigated. XRD, SEM, TEM, Abs/PL/PLE, XPS, and PL decay lifetime characterizations provided conclusive evidence supporting the extent to which the solvent controlled the dehydration and carbonization processes of the precursors, leading to a variation in their emission color from red to blue. The as-prepared CDs exhibited excellent and stable fluorescence performance even after being heated at 80 °C for 48 h and with UV light continuously irradiated for 15 h. Based on their excellent fluorescent properties and photothermal stability, bright multicolor light-emitting diodes with a high CRI of up to 91 were obtained. We anticipate that these full-color emissive CDs are beneficial for applications in lighting, display, and other fields.

Thermal modelling of multicolor LED luminaire via scaling of a heat sink to aid user wellness

Light Emitting Diode (LED) based lighting luminaires with efficient thermal management deliver high color renderance and inherit longevity. Thermal management is associated with the design of heat sink to extract the heat. This paper focuses on scaling heat sink baseplate and fin height to enhance the thermal management of multicolor LED luminaire. The heat sink fin height is scaled at three levels 10 mm, 15 mm and 20 mm with its base plate characterized at 1 mm, 1.5 mm and 2 mm. This two-dimensional scaling showed that the base plate thickness of 2 mm and fin height of 20 mm delivered high heat dissipation of 70.2828 °C on LED chip and Color Rendering Index (CRI) Ra 94.83 at correlated color temperature 4500 K, 500 lux. In addition to it the conceptual design demonstrated color point stability with low lumen degradation. This progressive study on thermal and color performance by scaling luminaire heat sink is an epoch to build energy and thermal efficient luminaire.

Closed Form Approximation of the Actual Spectral Power Emission of Commercial Color LEDs for VLC

Multi-color Light-Emitting Diode (LED) technology enables a simple approach to increase the throughput of a Visible Light Communications (VLC) system, by using Wavelength-Division Multiplexing (WDM) to transmit independent data streams on different <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">colors</i> . However, to compute the data rate that is achievable in such WDM VLC link, the optical power that leaks between the different colors needs to be estimated accurately, especially when low-cost optical filters are used in reception. So far, the approximations that have been reported in the literature to model the spectral power emission of different color LEDs are not good enough to perform these calculations. Starting from the theoretical spectral emission of a color LED, a closed form expression is derived based on an asymmetric Pearson type VII function, which is shown to approximate accurately the measured spectra of the color LEDs at different working regimes. In addition, the effect that the DC-bias current has on the key parameters of the approximated spectral power emissions, namely the peak and half-maximum wavelengths, as well as the peak spectral emission, are studied. Finally, a new approach is proposed to assess the level of fitness of the derived closed form approximations, using for this purpose the step-size of the MacAdam ellipses that corresponds to the different color LED spectral emissions in the CIE 1931 chromaticity diagram.

A pH-controlled synthetic route to violet, green, and orange fluorescent carbon dots for multicolor light-emitting diodes

• We develop a pH-controlled route to violet, green, and orange emissive CDs. • The sp 2 conjugated domains and content of graphite N tune the PL wavelength of CDs. • We embed CDs in starch to realize solid-state fluorescence toward multicolor LEDs. Carbon dots (CDs) with tunable photoluminescence (PL), especially with long wavelength PL, offer great potential for various applications including sensing, bioimaging, photomedicine, and optoelectronic devices. Here, we use 2,3-diaminopyridine as a single precursor to synthesize colorful CDs in different pH conditions. By simply regulating the reaction media from alkali to neutral to acid, bright CDs emitting violet, green, and orange fluorescence are prepared, respectively. Detailed characterizations reveal that the red-shift of PL is caused by the growing size of sp 2 conjugated domain and increasing content of graphite nitrogen. We embed CDs in starch to suppress self-quenching and enhance the PL quantum yields. The CD/starch composites, possessing efficient solid-state fluorescence, can be coated on the ultraviolet chips (365 nm) to fabricate multicolor light-emitting diodes toward indoor illumination. This work presents a new strategy to adjust the PL wavelength of CDs in a wide range, and clarifies the emission mechanism.

One-Pot Synthesis of Nitrogen-Doped Carbonized Polymer Dots with Tunable Emission for Multicolor Light-Emitting Diodes

One-Pot Synthesis of Nitrogen-Doped Carbonized Polymer Dots with Tunable Emission for Multicolor Light-Emitting Diodes

Tunable fluorescence emission for multi-color light-emitting diodes and voice-activated intelligent lighting applications

A simple push-pull system is presented to control the energy gap of organic luminescent molecules; the latter have been employed in voice activated LED devices.

Multicolor Graphene Quantum Dots via Solvatochromic Tuning and Sulfur Doping for Light-Emitting Diodes

Recently, graphene quantum dots (GQDs) with polychrome emission capability have attracted much attention due to their multifarious applications. In this study, we report a facile and green approach for rapid preparation of multicolor emission GQDs. Experimentally, UV light was used to drive the low-temperature synthesis, and a tunable emission wavelength of the GQDs was achieved through the synergistic effect of solvatochromic tuning and sulfur doping. Results show that multicolor emission wavelengths of green-GQDs (G-GQDs) from blue to yellow are obtained by simply controlling the polarity of the surrounding solutions. Moreover, red-GQDs with the emission wavelengths extended from green to red are further obtained by sulfur doping. Thereafter, G-GQDs were used to develop a trace water-detecting platform, ascribed to the high sensitivity of water-quenchable fluorescence, and a low detection limit of 0.061% was achieved. Meanwhile, based on the outstanding multicolor tunability of as-prepared GQDs, we successfully manufactured multicolor solid fluorescence films to fabricate multicolor light-emitting diode (LED) devices. Furthermore, high-quality white LEDs (WLEDs) are fabricated with the CIE coordinates of (0.341, 0.354) and a color temperature of 5161 K. This study highlights the potential of GQDs in various applications, including solid-state fluorescence films, optoelectronics, and optical molecular sensing.

The correlation between limiting efficiency of indoor photovoltaics and spectral characteristics of multi-color white LED sources

The correlation between the optimal performance of indoor photovoltaics (IPVs) and spectral characteristics of white light-emitting diode (LED) sources has been investigated theoretically. We calculated the Schockley–Queisser limit of IPVs under multi-color white LEDs with different correlated color temperature (CCT), color rendering index (CRI) and luminous efficacy of radiation (LER). It is found that the optimal bandgap for an IPV cell is not only influenced by CCT, but also by LER and CRI. However, the main factor that affects the maximum power conversion efficiency (PCE) is CCT, and the maximum PCE is relatively independent of the CRI and LER under the same condition of CCT. The maximum PCE decreases with the increase of CCT. Based on the analysis of the energy loss within IPVs, it is found that the value of the optimal bandgap is sensitive to the fraction of red light in the spectrum of white LEDs. The maximum PCE is primarily limited by the relaxation to band edge loss, which is caused by the high-energy blue or cyan light in the spectrum of white LEDs.

Compact Modelling of Electrical, Optical and Thermal Properties of Multi-Colour Power LEDs Operating on a Common PCB

This paper concerns the problem of modelling electrical, thermal and optical properties of multi-colour power light-emitting diodes (LEDs) situated on a common PCB (Printed Circuit Board). A new form of electro-thermo-optical model of such power LEDs is proposed in the form of a subcircuit for SPICE (Simulation Program with Integrated Circuits Emphasis). With the use of this model, the currents and voltages of the considered devices, their junction temperature and selected radiometric parameters can be calculated, taking into account self-heating phenomena in each LED and mutual thermal couplings between each pair of the considered devices. The form of the formulated model is described, and a manner of parameter estimation is also proposed. The correctness and usefulness of the proposed model are verified experimentally for six power LEDs emitting light of different colours and mounted on an experimental PCB prepared by the producer of the investigated devices. Verification was performed for the investigated diodes operating alone and together. Good agreement between the results of measurements and computations was obtained. It was also proved that the main thermal and optical parameters of the investigated LEDs depend on a dominant wavelength of the emitted light.