Wide Color Gamut Research Articles

Subjective video quality for 4K HDR-WCG content using a browser-based approach for “at-home” testing

The paper describes a design of a subjective experiment for testing the video quality of High Dynamic Range, Wide Color gamut (HDR-WCG) content at 4K resolution. Due to Covid, testing could not use a lab, so an at-home test procedure was developed. To aim for calibration despite not fully controlling the conditions and settings, we limited subjects to those who had a specific TV model, which we had previously calibrated in our labs. Moreover, we performed the experiment in the Dolby Vision mode (where the various enhancements of the TV are turned OFF by default). A browser approach was used which took control of the TV, and ensure the content was viewed at the native resolution of the TV (e.g., dot-on-dot mode). In addition, we know that video imagery is not ergodic, and there is wide variability in types of low levels features (sharpness, noise, motion, color volume, etc.) that affect both TV and visual system performance. So, a large number of test clips was used (30) and the content was specifically chosen to stress key features. The obtained data is qualitatively similar to an in-lab study and is subsequently used to evaluate several existing objective quality metrics.

Multicolored structural coloration of carbon nanotube fibers

AbstractCarbon nanotube fibers (CNTFs) are endowed with excellent mechanical, electrical, and thermal properties and are considered promising candidates in numerous cutting‐edge fields. However, the inherent black color of CNTFs hinders their practical application in fields with high aesthetic requirements such as wearable devices and smart textiles. Due to the smooth surface and chemical inertness, CNTFs are hard to be dyed by conventional chemical dyes or colorful inks. Herein, we realize a structural coloration of CNTFs by coating them with two metal oxide layers via atomic layer deposition. The three elements of color, that is, hue, saturation, and brightness, can be controlled by adjusting the types and thickness of each oxide layer. Colorful CNTFs with wide color gamut and high saturation are achieved through different combinations. A film interference model is also established to reveal the mechanism of the structural coloration, which is a comprehensive result of thin‐film interference and surface roughness briefly. The calculated reflectance well fits the measured results by introducing surface roughness parameters. Moreover, the colored CNTFs are not iridescent because of retinal signal delay, which will further expand their applications.

Highly Stable and Photoluminescent CsPbBr3/Cs4PbBr6 Composites for White-Light-Emitting Diodes and Visible Light Communication

Inorganic lead halide perovskite is one of the most excellent fluorescent materials, and it plays an essential role in high-definition display and visible light communication (VLC). Its photochromic properties and stability determine the final performance of light-emitting devices. However, efficiently synthesizing perovskite with high quality and stability remains a significant challenge. Here, we develop a facile and environmentally friendly method for preparing high-stability and strong-emission CsPbBr3/Cs4PbBr6 composites using ultrasonication and liquid paraffin. Tuning the contents of liquid paraffin, bright-emission CsPbBr3/Cs4PbBr6 composite powders with a maximum PLQY of 74% were achieved. Thanks to the protection of the Cs4PbBr6 matrix and liquid paraffin, the photostability, thermostability, and polar solvent stability of CsPbBr3/Cs4PbBr6-LP are significantly improved compared to CsPbBr3 quantum dots and CsPbBr3/Cs4PbBr6 composites that were prepared without liquid paraffin. Moreover, the fabricated CsPbBr3/Cs4PbBr6-LP-based WLEDs show excellent luminescent performance with a power efficiency of 129.5 lm/W and a wide color gamut, with 121% of the NTSC and 94% of the Rec. 2020, demonstrating a promising candidate for displays. In addition, the CsPbBr3/Cs4PbBr6-LP-based WLEDs were also demonstrated in a VLC system. The results suggested the great potential of these high-performance WLEDs as an excitation light source to achieve VLC.

Challenges and developments for the blue perovskite nanocrystal light-emitting diodes.

Perovskite nanomaterials have been highly thought as next-generation light emitters after recent development owing to their benefits of simple synthesis, low-cost, large-area, and wide color gamut. Encouragingly, the external quantum efficiencies (EQEs) of green, red, and near-infrared perovskite light-emitting diodes (PeLEDs) have exceeded more than 20%. However, the performance of the blue PeLEDs is still lower than other analogs, which severely limits the applications of PeLEDs in future full-color displays. Herein, we have reviewed the advances in blue perovskite NCs and their applications in blue PeLEDs. Promising blue perovskite emitters and strategies for fabricating highly efficient blue PeLEDs based on perovskite NCs are investigated and highlighted. Moreover, we point out the main challenges in blue perovskite NC LEDs including low electroluminescence efficiency (EL), spectral instability, the difficulty of charge injection, and device optimization. The perspectives for the further development of blue PeLEDs are also presented.

Meta-Fluorophores: an uncharted ocean of opportunities.

meta-Fluorophores (MFs) are unique ultra-light (in terms of molecular weight (MW)) fluorophores exhibiting luminescence with a wide colour gamut ranging from blue to the NIR. Single benzenic MFs are easy to synthesize, are quite bright (with photoluminescence quantum yield (PLQY) as high as 63%) and exhibit very large Stokes shift (as high as 260 nm (8965 cm-1)), with large solvatochromic shift (as high as 175 nm), and very long excited-state-lifetime (as high as 26 ns) for such ultra-light fluorophores. An emission maximum of ≥600 nm has been achieved with an MF in a polar medium having a MW of only 177 g mol-1 and in a nonpolar medium having MW of only 255 g mol-1; therefore, a large-sized π-conjugated para-fluorophore is no longer a prerequisite for red/NIR emission. Structurally varied MFs pave the way for creating an ocean of opportunities and are thus promising for replacing para-fluorophores for different applications, ranging from bioimaging to LEDs.

Dynamically tunable multicolor emissions from zero-dimensional Cs3LnCl6 (Ln: europium and terbium) nanocrystals with wide color gamut.

This study demonstrates dynamically tunable multicolor emissions from a single component, zero-dimensional (0-D) cesium europium chloride (Cs3EuCl6) and cesium terbium chloride (Cs3TbCl6) nanocrystals (NCs). Highly uniform colloidal Cs3EuCl6 and Cs3TbCl6 NCs are synthesized via the heating-up method. Excitation-wavelength-dependent multicolor emissions from Cs3EuCl6 and Cs3TbCl6 NCs are observed. Under excitation of 330-400 nm, both NCs exhibit blue photoluminescence (PL). Under wavelengths shorter than 330 nm, characteristic red and green emissions are observed from Cs3EuCl6 and Cs3TbCl6, respectively, owing to the atomic emissions from the f-orbitals in trivalent europium (Eu3+) and terbium (Tb3+) ions. Cs3EuCl6 and Cs3TbCl6 NCs exhibit broadband excitation spectra and enhanced absorption properties. Particularly, Cs3EuCl6 NCs exhibit a very narrow full-width at half-maximum in both blue and red PL and no overlap between the two spectra. The photophysical properties of these NCs are further investigated to understand the multicolor PL origins by time-resolved and temperature-dependent PL measurements. Finally, the potential applications of Cs3EuCl6 and Cs3TbCl6 NCs as anti-counterfeiting inks for high-level security are demonstrated. Given their broadband excitation with enhanced absorption properties and dynamically tunable colors with a wide color gamut, Cs3EuCl6 and Cs3TbCl6 NCs have great potential as novel multicolor NC emitters for many emerging applications.

Cellulose-Based Ultralong Room-Temperature Phosphorescence Nanomaterials with Tunable Color and High Quantum Yield via Nano-Surface Confining Effect.

How to achieve multicolor organic room-temperature phosphorescence (RTP) is still challenging and striking. Herein, we discovered a new principle to construct eco-friendly color-tunable RTP nanomaterials based on the nano-surface confining effect. Cellulose nanocrystal (CNC) immobilized cellulose derivatives (CX) containing aromatic substituents via hydrogen-bonding interactions, which effectively inhibit the motion of cellulose chains and luminescent groups to suppress the nonradiative transitions. Meanwhile, CNC with a strong hydrogen-bonding network can isolate oxygen. CX with different aromatic substituents regulate the phosphorescent emission. After mixing CNC and CX directly, a series of polychromatic ultralong RTP nanomaterials were obtained. The RTP emission of the resultant CX@CNC can be finely adjusted through the introduction of various CX and the regulation of the CX/CNC ratio. Such a universal, facile, and effective strategy can be used to fabricate various colorful RTP materials with wide color gamut. Because of the complete biodegradability of cellulose, the multicolor phosphorescent CX@CNC nanomaterials can be used as eco-friendly security inks to fabricate disposable anticounterfeiting labels and information-storage patterns via conventional printing and writing processes.

Eu2+:CsCaX3 (X = Cl, Br, I) perovskite nanocrystals in glasses for blue light-emitting applications

Eu2+:CsCaX3 (X = Cl, Br, I) nanocrystals in glass show tunable blue emission, excellent chemical-, thermal- and photo-stability, high photoluminescence quantum yield of 81.9% and external quantum efficiency of 24.6% when excited with a UV LED chip.

An up-conversion Ba3In(PO4)3:Er3+/Yb3+ phosphor that enables multi-mode temperature measurements and wide-gamut 'temperature mapping'.

At present, most fluorescent materials that can be used for optical temperature measurement exhibit poor thermochromic performance, which limits their applications. In this study, the phosphor Ba3In(PO4)3:Er/Yb was synthesized with a high doping concentration of Yb3+, and it emitted composition- and temperature-induced wide color gamut up-conversion luminescence from red to green. Four modes of fluorescence thermometry can be realized in the temperature range of 303-603 K, which is based on the ratio of fluorescence intensity between thermally coupled energy levels and non-thermally coupled energy levels, color coordinate shift, and fluorescence decay lifetime, respectively. The highest Sr value obtained was 0.977% K-1. Taking advantage of the fact that temperature can significantly change the luminous color of the phosphor Ba3In(PO4)3:0.02Er3+/0.05Yb3+, we demonstrated 'temperature mapping' on a smooth metal surface with multiple optical encryptions. These results indicate that the Ba3In(PO4)3:Er/Yb phosphor is an excellent fluorescent material for thermal imaging and has great application potential in temperature visualization measurement and optical encryption.

Flexible remote phosphor color converter based on ultra-thin glass and CsPbBr3 perovskite nanocrystal-embedded glass for a wide-color-gamut white LED

CsPbBr3 perovskite nano-crystal embedded glass and an ultra-thin glass substrate comprise a flexible white LED color converter with enhanced thermal stability and a wide color gamut reaching ∼130% of the NTSC area.

Reflective high-efficiency color filters for wide color gamut LCD

Reflective high-efficiency color filters for wide color gamut LCD

A novel red phosphor Cs2NaGaF6:Mn4+ with ultra-strong zero-phonon lines and long wavelength phonon sidebands for high-quality WLEDs.

For high-efficiency lighting and wide color gamut backlight display, high-quality narrow-band red phosphors for WLEDs are still in high demand. Herein, a novel red-emitting fluoride phosphor Cs2NaGaF6:Mn4+ was successfully synthesized by a simple two-step co-precipitation method and exhibits ultra-intense zero-phonon lines (ZPLs) and long wavelength phonon sidebands under 468 nm blue light irradiation. The ZPL emission peak of Cs2NaGaF6:Mn4+ was located at 627 nm, which is much stronger than its υ6 vibration peak, more matchable with the eye-sensitive region of humans, and beneficial for obtaining higher luminous efficiency of WLEDs. Interestingly, the υ6 vibration peak of this red phosphor is at 636.5 nm, which is larger than that of the common fluoride phosphor A2BF6:Mn4+ (usually at about 630 nm, represented by K2SiF6:Mn4+) at about 6.5 nm. Thanks to the longer wavelength of the υ6 vibration peak, the chromaticity coordinates (0.7026, 0.2910) with a larger x-coordinate value were realized, leading to a potentially wider color gamut of WLEDs. In addition, this phosphor has high thermal stability and its emission intensity at 423 K remains 93.7% of the initial intensity at room temperature. The lumen efficiency of WLED1 packaged with a mixture of Cs2NaGaF6:Mn4+ and YAG:Ce3+ on the InGaN blue chip is 115.7 lm W-1 with the color temperature (Tc) = 3390 K and the colour rendering index (Ra) = 92.5 under 20 mA driving current. The chromaticity coordinates of WLED2 packaged with Cs2NaGaF6:Mn4+ and β-SiAlON:Eu2+ on the InGaN blue chip are (0.3149, 0.3262) and the calculated color gamut is up to 118.4% (NTSC). These results indicate that Cs2NaGaF6:Mn4+ red phosphors have promising applications in the high-quality lighting and display fields.

A tunable color palette of electrochromic materials achieved through an ingenious stacking of ordinary conducting polymers

A wide color gamut of electrochromic polymers (ECPs), presenting controllable color switching, is described here based on a selective combination of transparent films of polythiophene, polyaniline and poly(3,4-ethylenedioxythiophene) (PEDOT).

Monolithically integrated high-resolution full-color GaN-on-Si micro-LED microdisplay

Full-color micro-LED displays are being widely developed and regarded as a primary option in current microdisplay technologies to fulfill the urgent demands of metaverse applications in the next decade. In this paper, a monolithic full-color micro-LED microdisplay with a resolution of 423 pixels per inch is demonstrated through the integration of a blue GaN-on-Si display module and a quantum dots photoresist (QDs-PR) color conversion module. The 400 × 240 active-matrix blue micro-LED display with a dominant wavelength of 440 nm was monolithically fabricated using GaN-on-Si epiwafers and flip-chip bonded on a custom-designed complementary metal-oxide semiconductor backplane. A color conversion module was independently fabricated on a 4-in. sapphire substrate by applying red and green QDs-PR arrays and a color filter array through the standard lithography process. Combining the blue GaN-on-Si micro-LED display module and the lithography-based QDs-PR color conversion module, a full-color micro-LED display was achieved with a wide color gamut up to 104% of the standard red, green, and blue and a maximum brightness of over 500 nits. The influence of blue light leakage resulting from the possible misalignment of flip-chip bonding and crosstalk in the bottom GaN-on-Si display was investigated in which the percentages of efficient pumping light for the blue, green, and red subpixels are around 95%, 89%, and 92%, respectively. This prototype demonstrates potential scalability and low-cost volume production of high-resolution full-color micro-LED microdisplays soon.

Highly luminescent and narrow-band-emitting InP/ZnSe/ZnS quantum dot synthesis by halide modified shell reaction

Indium phosphide (InP) quantum dots (QDs) are attractive materials as cadmium- and lead-free emitters for wide-color gamut displays. However, the wider emission full-width at half-maximum (FWHM) of InP-QDs has been the obstacle to replacing cadmium selenide QDs. Here, we report that the presence of ZnCl2 during shell formation drastically improves the emission properties of InP-QDs. Scanning transmission electron microscope observation revealed that uniform and spherical particles were formed in the presence of ZnCl2. By combining the flow reaction of InP core QDs, kilogram-scale synthesis was achieved while maintaining excellent emission properties.

Precise Functionalization of a Multiple-Resonance Framework: Constructing Narrowband Organic Electroluminescent Materials with External Quantum Efficiency over 40.

It is of important strategic significance to develop high-efficiency narrowband organic electroluminescent materials that can be employed to fabricate ultrahigh-definition displays with wide color gamut. This topic implies a great challenge to molecular design and synthesis, especially for the development of universality, diversity, scalability, and robustness of molecular architectonics. In this work, a synthetic methodology is demonstrated for functionalizing brominated BN-containing multiple-resonance (MR) frameworks with multifarious functional groups, such as donors, acceptors, and moieties without obvious push-pull electron properties. The m-DPAcP-BNCz-based organic light-emitting diode (OLED) exhibits green emission with a full-width at half-maximum (FWHM) of 28nm and a maximum external quantum efficiency (EQE) of 40.6%. The outstanding performance of m-DPAcP-BNCz is attributed to the perfect integration of the inherent advantages of the MR framework and the donor-acceptor configuration, which can not only achieve bathochromic shift and narrowband emission, but also obtain high photoluminescence (PL) quantum yield (ΦPL ) and horizontal emitting dipole orientation ratio (Θ// ). This straightforward and efficient approach provides insightful guidance for the construction and enrichment of more high-efficiency narrowband emitters.

Spectra stable deep-blue light-emitting diodes based on cryolite-like cerium(III) halides with nanosecond d-f emission.

Next-generation wide color gamut displays require the development of efficient and toxic-free light-emitting materials meeting the crucial Rec. 2020 standard. With the rapid progress of green and red perovskite light-emitting diodes (PeLEDs), blue PeLEDs remain a central challenge because of the undesirable color coordinates and poor spectra stability. Here, we report Cs3CeBrxI6-x (x=0to 6) with the cryolite-like structure and stable and tunable color coordinates from (0.17, 0.02) to (0.15, 0.04). Further encouraged by the short exciton lifetime (26.1ns) and high photoluminescence quantum yield (~76%), we construct Cs3CeBrxI6-x-based rare-earth LEDs via thermal evaporation. A seed layer strategy is conducted to improve the device's performance. The optimal Cs3CeI6 device achieves a maximum external quantum efficiency of 3.5% and a luminance of 470 cd m-2 with stable deep-blue color coordinates of (0.15, 0.04). Our work opens another avenue to achieving efficient and spectrally stable deep-blue LEDs.

Characteristics of GaN-on-Si Green Micro-LED for Wide Color Gamut Display and High-Speed Visible Light Communication

Characteristics of GaN-on-Si Green Micro-LED for Wide Color Gamut Display and High-Speed Visible Light Communication

Design for High Efficiency and Wide Color Gamut BT.2020 OLEDs

Design for High Efficiency and Wide Color Gamut BT.2020 OLEDs

Ultra‐High‐Resolution Perovskite Quantum Dot Light‐Emitting Diodes

AbstractPerovskite quantum dots (PQDs) have been widely used to realize light‐emitting diodes (LEDs) with high color purity, efficiency, and wide color gamut. Due to the demand for huge amount of display information, development on high‐resolution PQD LEDs (PQLEDs) with massive pixel density are highly desired. Herein, high‐resolution PQLEDs are fabricated by using nanoimprint technique. By preparing a honeycomb‐insulating polymer polymethyl methacrylate (PMMA) film, the high‐resolution pixelated quantum dot emissive layer is formed. In addition, the leakage current of the device is significantly reduced because the direct contact between electron transport layer and hole transport layer is avoided. The PQLEDs based on nanoimprint technology show a resolution of 9072 pixels per inch (PPI), and a maximum external quantum efficiency (EQE) and brightness of 7.81% and 146 400 cd m−2, respectively. The results demonstrate that high‐resolution PQLEDs can be realized by using nanoimprint technology, holding great commercial potential for next‐generation near‐eye displays.