Liquid Crystal Display Backlight Research Articles

Tunable Narrowband to Wideband emission of Mn2+, Eu2+ Co-doped GdMgAl11O19 for multifunctional applications

As the widespread application of white light-emitting diodes (WLEDs) in lighting field and liquid crystal display (LCD) backlight, the development of phosphors toward multifunctional applications is considered to be an inevitable tendency. In this work, multi-color light emissions have been realized in Eu2+ and Mn2+-activated magnetoplumbite-type GdMgAl11O19 (GMAO) along with adjustable photoluminescence properties. Significantly, a promising narrow-band green light emission can be achieved by Mn2+-activated GMAO with the full width at half maximum (FWHM) of 27 nm, and such narrow emission band makes the as-prepared WLED device reach 121 % of National Television Standards Committee (NTSC), which can act as an ideal LCD backlight. On the other hand, the broad cyan light can be achieved in Eu2+-activated GMAO. Moreover, multi-color light emissions have been realized in Eu2+ and Mn2+ co-doped GMAO, and the energy transfer from Eu2+ to Mn2+ ions was established. Benefitting from the broad band cyan light emission of Eu2+ ion, a promising WLED device with high color rendering index (CRI) of 90 has been fabricated by using Eu2+ and Mn2+ co-doped sample. The result indicates the multifunctional applications of the GMAO modulated by Eu2+ and Mn2+ activators.

Design and fabrication of a porous prism film for display backlight applications

This study demonstrates a fabrication method of a porous brightness enhancement film (pBEF) that offers brightness enhancement, light diffusion, color shift reduction, and improved thermal stability. During the ultraviolet imprinting and solvent evaporation processes, the nano/submicron-sized air pores are generated within the polymer prism structure, and micropatterns spontaneously form on the prism surface. The inner pores ranging from 30 to 450 nm can effectively scatter light to mitigate color shift, which is caused by multiple internal reflections within the prism structure. The micropatterns have multiple rings formed one around another with 5–15-µm diameter on the prism surface improve visual quality. Moreover, the obtained functions are achieved in a single film solution, obviating the need for using multiple materials, and the fabrication process is relatively simple and fast as it is conducted under ambient conditions. When the pBEF is integrated into a liquid-crystal display backlight, it provides the brightness enhancement performance and comparable viewing angle distribution of a regular BEF combined with an additional diffuser (two films) and increases brightness by ∼8% compared to a bead prism (particle-based BEF). Additionally, it reduces the redshift (Δxy) from 0.1605 to 0.1415. Furthermore, the pBEF exhibits a lower coefficient of thermal expansion than the regular BEF.

Polarized emission of Cs3Cu2I5 nanowires embedded in nanopores of an anodic aluminum oxide template.

Due to the intrinsic polarized emission property, polarized emissive materials with anisotropic nanostructures are expected to be potential substitutes for polarizers. Herein, by the template-assisted strategy, well-aligned lead-free metal halide Cs3Cu2I5 nanowire (NW) arrays are fabricated by evaporating the precursor ink in the anodic aluminum oxide (AAO) for polarized emission. The Cs3Cu2I5/AAO composite film emits highly polarized light with a degree of polarization (DOP) of 0.50. Furthermore, by changing the molar ratio of CsI/CuI, the stability of Cs3Cu2I5 precursor inks is improved. Finally, an ultraviolet (UV) light-emitting diode (LED) is adopted to pump the composite film to achieve a blue LED device. The reported Cs3Cu2I5/AAO composite film with highly polarized light emissions will have great potential for polarized emission applications such as liquid crystal display backlights, waveguides, and lasers.

All-Inorganic Green Synthesis of Small-Sized and Efficient K2SiF6:Mn4+ Phosphor for Mini-LED Displays.

High-resolution liquid crystal display (LCD) backlight requires a color conversion layer featuring micrometer light-emitting particles and a uniform morphology. The widely used commercial red-emitting K2SiF6:Mn4+ phosphor, showing promise as a light-conversion candidate, faces limitations due to its toxic synthesis process, large particle size, and poor moisture resistance. We successfully demonstrated an efficient substitution of the highly toxic HF/TEOS/KHF2 solvent system with a commonly used HCl/SiO2/KF solvent system to synthesize the small-sized K2SiF6:Mn4+ phosphor. Additionally, surface passivation was performed to enhance the luminescence intensity and resistance to moisture, denoted as K2SiF6:Mn4+@CaF2. Accordingly, the K2SiF6:Mn4+@CaF2 phosphor presents a high luminescence efficiency (99.87%/32.84% IQE/EQE) with an average particle size of ∼2.67 μm. Notably, after exposure to 85% humidity and 85 °C temperature for 3 h, the luminescence intensity remains at 47.4% for K2SiF6:Mn4+@CaF2, while 21.2% for pristine K2SiF6:Mn4+, and only 3.5% for K2SiF6:Mn4+ synthesized by TEOS. These advancements hold great potential for improving high-resolution LCD backlighting, particularly for displays with micron-level pixels, opening up new possibilities for enhanced display technology.

Quantum dots printing paste for display backlights: Preparation, characterization, and applications

AbstractQuantum dots (QDs) are one kind of photoluminescent materials with excellent properties, such as adjustable spectrum, narrow full width at half maximum (FWHM), and high color gamut. In this paper, a photoluminescent QDs printing paste suitable for light guide dots array applied in the backlight for liquid crystal display (LCD) was presented. The QDs printing paste was first prepared and characterized with different kinds of solvents. Then, triphenyl phosphite (TPP), a kind of antioxygen, was added into the QDs printing paste to improve the stability of the QDs printing paste. Finally, a QDs light guide plate (LGP) was fabricated by screen printing with QDs printing paste added with silicon dioxide (SiO2) light scattering particles. The color gamut of QDs LGP arrived 131.6%NTSC due to light scattering interaction between blue LED, red QDs, green QDs, and SiO2 particles. The results showed that the QDs‐chloroform printing paste had uniform light output and the highest photoluminescent peak intensity. Therefore, the composite screen printing paste has wide application prospects in the backlight of LCD, with the advantages of simple process, high production efficiency, and low cost.

High efficiency fluorescent perovskite quantum dots encapsulated in superhydrophobic silica aerogel for wide color gamut backlight displays

• A super-hydrophobic Silica Aerogels film for backlight display was prepared. • A wide gamut of 128% of color gamut of NTSC standard was achieved. • Excellent environmental stability was achieved through a composite strategy. Recently, all-inorganic cesium lead halide (CsPbX 3 ) perovskite quantum dots (PQDs) have been widely used in the photoelectric field. However, a major limitation of solution-processed PQDs for applications is inherent instability. Herein, we adopt strategy of passivation, CsPbX 3 (X = Cl, Br, I) PQDs are encapsulated into super-hydrophobic silica aerogels (SiO 2 AGs) to form a protective layer for resisting destruction by external forces. Importantly, the photoluminescence quantum yield (PLQY) of CsPbBr 3 @AGs composites achieves 71%, CsPbCl 2 Br 1 @AGs, CsPbBr 3 @AGs and CsPbBr 1 I 2 @AGs composites with narrow emissions can replace traditional phosphors as color converters. In addition, a high-performance liquid crystal display (LCD) with a wide color gamut (128% of National Television System Committee color space) is demonstrated using the prepared CsPbX 3 @AGs@PS composite film and blue light emitting diode (LED) chip as backlight. The combination of improved stability and wide color gamut of the perovskite material provides a viable approach for LCD backlight.

A highly efficient narrow-band blue phosphor of Bi3+-activated cubic borate Ba3Lu2B6O15 towards backlight display applications

A novel narrow-band blue emitting phosphor of Bi 3+ -activated cubic borate Ba 3 Lu 2 B 6 O 15 is synthetized by solid state reaction, which benefited from a highly symmetrical crystal structure. Ba 3 Lu 2 B 6 O 15 :Bi 3+ shows great application potential in LCD backlight display attributed to its extreme color purity of 97.76%, high internal quantum efficiency of 90.6% and weak chromaticity drift. • FWHM = 35.5 nm. • IQE = 90.6%. • Excellent thermal stability. • Energy level scheme. • 90.06% NTSC. Developing innovative efficient phosphors featured with a narrow-band emission is essential for present white light-emitting diodes (wLEDs) towards high-performance liquid–crystal display (LCD) backlights applications, especially for Bi 3+ -activated phosphors. Herein, we synthesized a near-ultraviolet (n-UV) excitable narrow-band blue-emitting Ba 3 Lu 2 B 6 O 15 :Bi 3+ (BLB:Bi 3+ ) phosphor. It exhibits a narrow band emission (full-width at half-maximum, FWHM = 35.5 nm), high color purity of 97.76%, surprisingly high internal quantum efficiency (IQE) which reached up to 90.6%, excellent thermal stability (85%@150 °C of the integrated emission intensity at room temperature) and reversibility and high consistency. The outstanding photoluminescence properties of Bi 3+ are attributed to a highly symmetrical crystal field environment and tightly connected polyhedral network of Ba 3 Lu 2 B 6 O 15 . In addition, the energy level scheme is constructed from the calculated electronic structure to explore the difference in luminescence stability of Ce and Bi doped BLB phosphors. The pc-wLED device fabricated using commercial green β -Sialon:Eu 2+ , red K 2 SiF 6 :Mn 4+ , and as-prepared blue BLB:Bi 3+ phosphor on a 365 nm n-UV chip covered 90.06% of the color space of National Television System Committee (NTSC) standard, suggesting great potential for industrial applications as LCD backlighting.

High-performance narrow-band green-emitting phosphor enabled by substituting Na with Rb

Exploring green phosphors with satisfactory peak position (525–535 nm) and full width at half-maximum (FWHM) to replace the commercial narrow-band green β-SiAlON:Eu2+ phosphor (λem = 540 nm, FWHM = 54 nm) is crucial for realizing wide-gamut full-color liquid crystal display (LCD) devices. Here, taking the UCr4C4-type tetragonal phase RbNa3(Li3SiO4)4:3%Eu2+ (RN3(LSO)4:Eu2+) blue phosphor as starting model, we substitute Na+ with Rb+ to synthesize a series of Rb1+xNa2.97-x(Li3SiO4)4:3%Eu2+ (0.1 ≤ x ≤ 2.5) (R1+xN2.97-x(LSO)4:Eu2+) phosphors that exhibit tunable emission from blue to green. We demonstrate that Rb+-substitution triggers tetragonal-to-monoclinic phase transition, making Eu2+ ions enter two new, cuboid-like Rb and Na sites and resultant green emission. With optimized content of Rb+, Rb3Na(Li3SiO4)4:3%Eu2+ (R3N(LSO)4:Eu2+) green phosphor not only shows appropriate peak position (∼526 nm) and FWHM (∼43 nm) compared to β-SiAlON:Eu2+ phosphor, but also high internal quantum efficiency (IQE) of 90.2% and superior thermal stability (integrated emission intensity at 150 °C is 105.7% of room-temperature performance). Using the green R3N(LSO)4:Eu2+ phosphor, white light-emitting diode prototype shows a wide-color-gamut (111.2% National Television System Committee, NTSC). This work demonstrates that as-prepared green R3N(LSO)4:Eu2+ phosphor has a potential application in LCD backlight display, and may stimulate more researches on exploring high-performance narrow-band UCr4C4-type phosphors.

62‐9: Invited Paper: Hybrid Composite Films with Perovskite Quantum Dots and Red Phosphors for LCD Display Backlights

Perovskite quantum dots films (PQDF) are emerging as low‐cost alternatives to improve the color gamut of liquid crystal display (LCD) backlights due to their narrow half peak width. In this paper, hybrid composite films with green perovskite quantum dots (PQDs) and red rare earth phosphors were combined in a dual layer film for LCD backlight display applications. By combining the in‐situ fabricated green emissive PQDF with KSF phosphor or red nitride phosphor (NP), we prepared hybrid composite films of green PQDF and red phosphors with high brightness and wide color gamut. The color gamut of PQDs‐KSF is 83.1% of Rec. 2020 due to the narrow full‐width‐at‐half‐maximum of PQDs and KSF phosphors. These composite films have great potential in the application of LCD backlights.

Robust Nanofiber Films Prepared by Electro‐Microfluidic Spinning for Flexible Highly Stable Quantum‐Dot Displays

AbstractQuantum dot (QD)‐based liquid crystal displays (LCDs) are emerging as a new generation of LCDs due to their good performance. However, the QD fluorescent materials in LCDs are vulnerable to water and high temperatures, severely limiting their practical and long‐term use. Here, flexible and ultrastable QD‐based color‐converting films for LCD backlights are fabricated using robust poly(styrene‐methyl‐methacrylate‐acrylic acid) (poly(St‐MMA‐AA)) nanoparticle/polyamide 66 nanofiber (NPs@PA66) film with unique fiber–particle–fiber microstructure as protective substrate. Through an emerging strategy called electro‐microfluidic spinning technology (EMST), the nanofiber film not only exhibits excellent flexibility but also remarkably improves the mechanical property via the in situ particle‐mediated enhancement mechanism. An LCD backlight using the NPs@PA66 nanofiber film as QD loading substrate shows a wide color gamut of 116% and long‐term fluorescence stability under high temperature of 200 °C. More importantly, the fluorescence lifetime of NPs@PA66/QDs backlight reaches up to ≈64500 h, ≈22 times higher than that using encapsulated sandwiched polyethylene terephthalate (PET) QD film. These findings offer a promising method toward high‐strength nanofiber manufacturing, high‐stability flexible electronics and optoelectronic display devices.

Facile In Situ Fabrication of Cs4PbBr6/CsPbBr3 Nanocomposite Containing Polymer Films for Ultrawide Color Gamut Displays

AbstractA modified supersaturated recrystallization method for in situ fabrication of Cs4PbBr6/CsPbBr3 nanocomposite containing polymer films is reported. This facile and efficient strategy can be easily carried out at room temperature, and minimizes the contact time between CsPbBr3 nanocrystals and water and oxygen molecules during the formation of perovskite film, passivating the perovskite nanocrystals. Through the approach, the dual protection of Cs4PbBr6 and polymer matrix enhances the water stability and photostability of emitting CsPbBr3. Even after being immersed in water for 30 days, the Cs4PbBr6/CsPbBr3@PMMA film still retains a bright green fluorescence. Moreover, combining the as‐prepared green‐emitting Cs4PbBr6/CsPbBr3@PMMA and a red‐emitting CdSe/ZnS based quantum dots (QDs) polymer film with blue light emitting diode (LED) chips as the backlight, a high performance liquid crystal display (LCD) is demonstrated. The color gamut of the demonstrated display is 131% and 98% that of the NTSC 1953 and Rec.2020, respectively. The combination of better stability and improved color purity of the perovskite material intuitively provides a viable approach for LCD backlights.

Swelling-Deswelling Microencapsulation-Enabled Ultrastable Perovskite-Polymer Composites for Photonic Applications.

Metal halide perovskite nanocrystals are emerging as novel optoelectronic materials. Owing to their excellent optical and electronic properties such as tunable band gap, narrow-band emission and high charge mobility, they are quite promising in various fields including liquid-crystal display backlighting, solid-state lighting and other energy conversion applications. However, the intrinsic low formation energy makes them vulnerable to external stimulus, e. g. water, oxygen, heat, etc. Among many methods, swelling-deswelling microencapsulation emerges as one of the most promising strategies to improve their stability. Herein, recent developments and future research directions in swelling-deswelling microencapsulation-enabled ultrastable perovskite-polymer composites are summarized. We believe this strategy has great potential to deliver successful perovskite-based commercial products for many photonics applications.

Luminescent thermal stability and electronic structure of narrow-band green-emitting Sr-Sialon:Eu2+ phosphors for LED/LCD backlights

Stable and high-efficiency narrow-band green phosphor is a key component for wide color gamut liquid crystal display (LCD) backlights. In this paper, narrow-band green-emitting Sr3-3xSi13Al3O2N21:3xEu2+ (0.001 ≤ x ≤ 0.09) (Sr-Sialon:Eu2+) phosphor with a full-width at half maximum of 66 nm has been successfully synthesized by using the solid-state reaction method. All the samples are the pure phase with Sr3Si13Al3O2N21-type structure. Their emission band maximum can be tuned from 495 to 523 nm by increasing Eu2+ content. The compound with x = 0.03 possesses the highest luminescence intensity with the peak position around 510 nm. Luminescent thermal stability gets better with Eu2+ concentration decreasing. The integrated intensity of the sample with x = 0.01 at 425 K remains about 80% of the intensity at room temperature. The host referred binding energy (HRBE) and vacuum referred binding energy (VRBE) schemes are constructed to further explain its luminescent thermal quenching mechanism. White light-emitting-diode (w-LED) device using optimized Sr2.91Si13Al3O2N21:0.09Eu2+ phosphor demonstrates its potential application for LCD backlights.

Polyhedron Transformation toward Stable Narrow‐Band Green Phosphors for Wide‐Color‐Gamut Liquid Crystal Display

AbstractA robust and stable narrow‐band green emitter is recognized as a key enabler for wide‐color‐gamut liquid crystal display (LCD) backlights. Herein, an emerging rare earth silicate phosphor, RbNa(Li3SiO4)2:Eu2+ (RN:Eu2+) with exceptional optical properties and excellent thermal stability, is reported. The resulting RN:Eu2+ phosphor presents a narrow green emission band centered at 523 nm with a full width at half maximum of 41 nm and excellent thermal stability (102%@425 K of the integrated emission intensity at 300 K). RN:Eu2+ also shows a high quantum efficiency, an improved chemical stability, and a reduced Stokes shift owing to the modified local environment, in which [NaO8] cubes replace [LiO4] squares in RbLi(Li3SiO4)2:Eu2+ via polyhedron transformation. White light‐emitting diode (wLED) devices with a wide color gamut (113% National Television System Committee (NTSC)) and high luminous efficacy (111.08 lm W−1) are obtained by combining RN:Eu2+ as the green emitter, K2SiF6:Mn4+ as the red emitter, and blue‐emitting InGaN chips. Using these wLEDs as backlights, a prototype 20.5 in. LCD screen is fabricated, demonstrating the bright future of stable RN:Eu2+ for wide‐color‐gamut LCD backlight application.

Highly Polarized Fluorescent Film Based on Aligned Quantum Rods by Contact Ink-Jet Printing Method

Fluorescent quantum rods (QRs) have received much attention recently because of their properties of polarized light emission with narrow full width at half-maximum. Therefore, QRs can be used in liquid crystal display (LCD) backlight, as an active polarizer. In order to emit light with a high degree of polarization (DOP), QRs need to be controlled and aligned along one direction on large-scaled devices. However, most of the proposed effective alignment approaches cannot be applied to a large area. In this paper, we report for the first time the contact ink-jet printing (CIJP) method to align CdSe/CdS core/shell QRs. With the ink being printed, the QRs can align along the fluid ink flow direction resulting in aligned QRs along printing direction and forming a film with a high DOP of 42%. Furthermore, CIJP can realize arbitrarily large area fabrication without reducing DOP value. It is expected that this method can be utilized to print on large-scaled substrates directly to fabricate polarized optoelectronic devices, and further applied to LCD backlights and any other applications where polarized light is needed.

Tilted light coupling structure for the thickness reduction of a liquid crystal display backlight.

It is hard to design a traditional edge-lit light guide plate (LGP) as an ultrathin structure, because the LGP thickness will be limited by the luminescence regional width of the LED source. In this paper, a tilted light coupling structure (TLCS) for a liquid crystal display (LCD) backlight is proposed that allows an inclined layout of an edge LED array to significantly reduce the LGP thickness. The design process and optical conditions of the TLCS are first discussed, and the effect of structural parameters on the coupling efficiency is also analyzed. After that, a fundamental model and an improved model are designed: namely, the planar TLCS and the curved TLCS. Design results show that the light coupling efficiency of the proposed TLCS can reach 95%, while the LGP thickness is reduced to 7% thinner than the luminescence regional width of the LED source. The proposed TLCS will have broad applications in light guiding devices.

Beyond OLED: Efficient Quantum Dot Light-Emitting Diodes for Display and Lighting Application.

The unique features of solution-processed quantum dots (QDs) including emission tunability in the visible range, high-quality saturated color and outstanding intrinsic stability in environment are highly desired in various application fields. Especially, for the preparation of wide color gamut displays, QDs with high photoluminescence quantum yield are deemed as the optimal fluorescent emitter that has been utilized in the backlight for liquid crystal display. Nevertheless, the commercialization of electrically driven self-emissive quantum dot light-emitting diode (QLED) display is the ultimate target due to its merits of high contrast, slim configuration and compatibility with flexible substrate. Through the great efforts devoted to material engineering and device configuration, astonishing progresses have been made in device performance, giving the QLED technology a great chance to compete with other counterparts for next-generation displays. In this review, we retrospect the development roadmap of QLED technology and introduce the essential principles in the QLED devices. Moreover, we discuss the key factors that affect the QLED efficiency and lifetime. Finally, the advances in device architectures and pixel patterning are also summarized.

Effects of short-time plasma treatment in the magnetron sputtering equipment on various carbon nanotubes for applied to LCD backlight unit

The field emission and luminescent properties of various (single-walled CNTs, double-walled CNTs, multi-walled CNTs, and carbon nanofibers) screen-printed carbon nanotubes (SP-CNTs) that were straightened using plasma treatment in the magnetron sputtering equipment (MSE) for a short time were investigated. The SP-CNTs investigated CNT field emitter arrays for back light unit (BLU) in liquid crystal display (LCD). The plasma treatment in the MSE enhanced the emission properties of the single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs): the emission uniformity and number of emission sites increased. Recurring problems associated with SW and DW SP-CNTs such as bent and/or buried CNTs and degradation of binder–residue-induced emission were ameliorated by inducing protrusion from the binder and permanent straightening of the SW and DW SP-CNTs as a result of treatment. The multi-walled CNTs (MWCNTs) and carbon nanofibers (CNFs) had partial emission sites with poor emission factors. The results of the present study suggest that plasma treatment in the MSE of SW and DW SP-CNTs is an effective method for achieving uniform field emission and reducing the aging.

One-Step Synthesis of FA-Directing FAPbBr3 Perovskite Nanocrystals toward High-Performance Display

Hybrid organic-inorganic and all-inorganic metal halide perovskite nanocrystals (PNCs) have aroused extensive attention from both academic and industrial researchers, considering their excellent performance in optoelectronic applications. Herein, we develop a facile and time-saving strategy to synthesize NH2CH═NH2PbBr3 (NH2CH═NH+, FA) PNCs at room temperature. Benefiting from this facile method, high-quality FAPbBr3 PNCs with photoluminescence quantum yield up to 76% and narrow full width at half-maxima of 20 nm can be produced on a large scale. Moreover, anion-exchange reactions run by using FAPbBr3 as a template, producing various PNCs with different anion constituents. By manipulating the ratios of two different anions, a series PNCs with various bright photoluminescence ranging from 452 to 646 nm could be done. On account of superior and adjustable photoluminescence over the visible spectral region, FAPbBr3 PNCs can be applied as a promising color-converting material in liquid-crystal display (LCD) backlight, white light-emitting diode (WLED), and inkjet printing pattern. As a proof of concept, FAPbBr3 PNCs with green emission were integrated in WLED and LCD backlight, accomplishing a color rendering index of 87.5 and a wide color gamut of 116%, respectively.

Edge-lit LCD backlight unit for 2D local dimming.

Local dimming technology has been highly desired for integration with liquid crystal displays (LCDs) in order to improve their contrast ratios (CRs) as well as to overcome power efficiency bottlenecks. In this paper, we propose and demonstrate a slim (~1 mm) edge-lit LCD backlight unit (BLU) capable of 2D local dimming. We designed a semi-partitioned light guide plate (LGP) patterned with inverse-trapezoidal microstructures, which allows the ultra-slim BLU to function without prism sheets. Since light emitting diodes (LEDs) are placed in the middle of the LGP, the BLU can freely define illuminated areas and the whole BLU can be modularly expanded like a tile canvas. The fabricated BLU achieves uniformity in both local and global luminance distributions, as well as in high local dimming performance. Experimentally, the BLU increases the CR of the display up to two orders of magnitude compared to conventional BLUs.