National Television System Committee Research Articles

Synthesis and luminescence properties of a novel narrow band green-emitting Na2MgAl10O17:Mn2+ phosphor for backlight display

An activator’s selective occupation of a host is of great significance for designing high-quality white light-emitting diodes (w-LEDs) phosphors, while achieving a full-spectrum single-phase white light emission phosphor is challenging. For developing high-performance and green-emitting phosphors with narrow bands used for backlight display, a series of Na2Mg1-xAl10O17:xMn2+ (NMAO:xMn2+) phosphors with high Mn2+ concentration were synthesized. The NMAO:0.65Mn2+ green phosphor exhibits an ultra-narrow band green emission with full width at half maximum (FWHM) about 27 nm and peak position at 513 nm when excited by the blue light with wavelength of 450 nm. The NMAO:0.65Mn2+ not only has a super narrow band which is narrower than β-SiAlON:Eu2+ (FWHM ∼ 55 nm) but also shows an exceptional thermal stability performance (77% peak intensity @423 K). A w-LED device was assembled with NMAO:0.65Mn2+, a blue GaInN chip and K2SiF6:Mn4+ phosphors, which represents a wide color-gamut of 112% National Television System Committee (NTSC) standard under the current of 50 mA. These results demonstrate the NMAO:0.65Mn2+ has potential superiority in application of backlight display.

Ultra‐Stable Yellow Monolithic Perovskite Quantum Dots Film for Backlit Display

AbstractPerovskite quantum dots (PeQDs) are seen as the credible alternative to traditional QDs ascolor converter in liquid crystal display (LCD). Unfortunately, PeQDs sufferfrom instability and color separation, and the prepared PeQDs enhanced films(PQDFs) need the protection of expensive barrier layers, which significantly increases price and limits their application. Herein, large‐area yellow monolithic PQDF is fabricated with both green CsPbBr3 and red CsPbBr1I2QDs encapsulated in the dual matrices of inorganic glass and polypropylene (PP) via an industrialized melt extruding & rolling method. The PQDF shows high photoluminescence quantum yield (PLQY) of 92% and narrow full width at half maximum (FWHM) of 19 nm (green) and 33 nm (red). Importantly, the bare PQDF without barrier layers can pass harsh aging test at 85 °C/85% RH and reach anoperating T90 lifetime over 1000 h. Finally, a white backlit unit is designed by coupling yellow monolithic PQDF with blue light guide panel, and the constructed prototype display shows superior color rendering performance forits narrow green/red emissions, reaching a color gamut of 110% National Television System Committee (NTSC). This work provides a novel and easy‐to‐industrialize route to prepare PQDFs to realize their commercial application in backlit display.

Photoluminescence characteristics of microwave synthesized La2(WO4)3:Eu3+ phosphor and evaluation of its radiative parameters

A series of Eu3+ doped La2(WO4)3 phosphors were synthesized by microwave-assisted co-precipitation technique and their properties were systematically characterized. The crystalline nature and the monoclinic structure were evidenced from the X–ray diffraction. In La2(WO4)3 host matrix, Eu3+ ions in non-centrosymmetric sites, resulting in strong and sharp peak at 615 nm (red) due to 5D0→7F2 electric dipole transition with an average short lifetime of 0.803 ms. The interesting feature of the phosphor is the delayed concentration quenching which is observed at 70 % Eu content. The radiative parameters of the phosphor analyzed in the light of Judd – Ofelt theory manifest its excellent spectral characteristics. The calculated CIE co-ordinates of the synthesized phosphors lie close to the commonly available red phosphor Y2O2S:Eu3+ and National Television System Committee (NTSC) red light standard. The above results validate the potential of Eu3+ doped La2(WO4)3 phosphor as a viable candidate for red-emitting devices.

Deep-blue narrow-band emissive cesium europium bromide perovskite nanocrystals with record high emission efficiency for wide-color-gamut backlight displays.

Lead halide perovskite nanocrystals (NCs) are highly promising for backlighting display applications due to their high photoluminescence quantum yields (PLQYs) and wide color gamut values. However, the practical applications of blue emitters are limited due to the toxicity of lead, unstable structure, and unsatisfactory PLQY. Herein, we report the successful synthesis of divalent europium-based perovskite CsEuBr3 NCs using a modified hot injection method. By optimizing the reaction conditions, the CsEuBr3 NCs display a deep-blue emission at 443 nm with a full width at half maximum (FWHM) of 28.5 nm, a color purity of 99.61%, and a record high PLQY of 93.51% for deep-blue narrow-band emissive lead-free perovskite NCs as far as we know. The emission mechanism of CsEuBr3 NCs is proved through first-principles calculations and spectral analysis. Notably, the CsEuBr3 NCs exhibit remarkable stability when exposed to high temperature, UV irradiation, and long-term sealed storage. The incorporation of CsEuBr3 NCs into polydimethylsiloxane (PDMS) serving as a converter is utilized for white light-emitting devices (WLEDs). WLEDs for backlight displays achieves a wide color gamut of 127.1% of the National Television System Committee standard (NTSC), 94.9% coverage of the ITU-R Recommendation BT.2020 (Rec.2020), and their half-lifetime is up to 1677 h, providing a promising pathway for highly efficient, environment-friendly and practical liquid crystal display backlights.

Efficient deep blue fluorescent emitters based on bipolar phenanthroimidazole-carbazole hybrid for non-doped electroluminescent device with small CIEy

In this work, four bipolar deep-blue emitting materials of 2-(4-(9H-carbazol-9-yl)phenyl)-1-(4-methylphenyl)-1H-phenanthro[9,10-d]imidazole (MePPIM-Cz), 2-(4-(9H-carbazol-9-yl)phenyl)-1-(4-chlorophenyl)-1H-phenanthro [9,10-d]imidazole (ClPPIM-Cz), 2-(4-(9H-carbazol-9-yl)phenyl)-1-(4-tert-butyl phenyl)-1H-phenanthro[9,10-d]imidazole (BuPPIM-Cz) and 2-(4-(9H-carbazol-9-yl) phenyl)-1-(4-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazole (TFMPPIM-Cz) based on phenanthroimidazole and carbazole group have been designed and synthesized by introducing different electron active substitutions into the N1 position of phenanthroimidazole. The thermal, photophysical, electrochemical and computational properties of four compounds were investigated. All compounds exhibited the deep blue emission and good thermal stability with glass transition temperature (Tg) in range of 126°C–137 °C. Single carrier devices were also fabricated and demonstrated that the four compounds have bipolar transporting properties. The non-doped organic light emitting diodes (OLEDs) based on MePPIM-Cz, ClPPIM-Cz, BuPPIM-Cz and TFMPPIM-Cz showed deep blue emission with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.07), (0.16, 0.06), (0.16, 0.05) and (0.16, 0.10) and the maximum external quantum efficiencies (EQEmax) of 2.67%, 2.24%, 1.81% and 1.09%, respectively. The CIE coordinates of MePPIM-Cz, ClPPIM-Cz and BuPPIM-Cz is extremely close to the National Television System Committee (NTSC) standard blue CIE of (0.14, 0.08), which is very significant for high color purity full-color display.

Ligand-Enhanced Neodymium Doping of Perovskite Quantum Dots for Superior Exciton Confinement.

In this study, all-inorganic perovskite quantum dots (QDs) for pure blue emission are explored for full-color displays. We prepared CsPbBr3 and Cs3NdCl6 QDs via hot injection methods and mixed in various ratios at room temperature for color blending. Nd-doped CsPb(Cl/Br)3 QDs showed a blueshift in emission, and the photoluminescence quantum yields (PLQY, ΦPL) were lower in the 460-470 nm range due to surface halogen and Cs vacancies. To address this, we introduced a silane molecule, APTMS, via a ligand exchange process, effectively repairing these vacancies and enhancing Nd doping into the lattice. This modification promotes the PLQY to 94% at 466 nm. Furthermore, combining these QDs with [1]Benzothieno[3,2-b][1]benzothiophene (BTBT), a conjugated small-molecule semiconductor, in a composite film reduced PLQY loss caused by FRET in solid-state QD films. This approach achieved a wide color gamut of 124% National Television System Committee (NTSC), using a UV LED backlight and RGB perovskite QDs in a BTBT-based organic matrix as the color conversion layer. Significantly, the photostability of this composite was enhanced when used as a color conversion layer (CCL) under blue-LED excitation.

Spectroscopic investigation of K5La(MoO4)4:Sm3+ red phosphor with excellent thermal stability and color purity for white LEDs

In this study, a series of innovative red-emitting Sm3+-doped K5La(MoO4)4 phosphors were synthesized using the solid-state reaction method. The X-ray powder diffraction patterns and Rietveld refinement confirmed the single-phase structure of the synthesized K5La(MoO4)4:Sm3+ samples with trigonal system (space group R3‾m (#166)). The phosphors demonstrated a strong red emission at 644 nm, corresponding to the electric dipole transition 4G5/2 → 6H9/2 of Sm3+ ions. The optimal doping concentration for K5La(1-x) (MoO4)4:xSm3+ was found to be approximately 5 mol%. The temperature-dependent emission of phosphors was examined and found that the luminescence intensity remained at 86 % even at 480 K, showing the exceptional thermal stability of this material. K5La(1-x) (MoO4)4:xSm3+ phosphors displayed remarkable color stability with chromaticity coordinates falling within the red region in 1931 CIE diagram. K5La(MoO4)4:5 mol%Sm3+ exhibited a high color purity of 99.9 % and internal quantum efficiency (IQE) was measured as 66.8 %. Light-emitting diodes (LEDs) were constructed using InGaN chips and the synthesized red phosphors. The chromaticity coordinates of the fabricated w-LED (white light-emitting diode) were (0.330, 0.351), closely resembling the typical white point of the National Television System Committee (NTSC) at (0.333, 0.333). The color rendering index (CRI, Ra) and correlated color temperature (CCT) of w-LED were 87 and 5627 K. These findings strongly suggest the potential use of K5La(MoO4)4:Sm3+ phosphors as red phosphors in LEDs.

Ultrastable quantum dot composites with dense barrier layer for wide color gamut display

Quantum dots (QDs) have showed great potential for next-generation lighting and display technologies. However, its stability is still one of the key problems that limit its practical application. In this paper, by comparing the specific surface area (SSA) and pore width of aluminum oxide (AlOx) and silicon oxide (SiO2) barrier layers, the relationship between the porosity of barrier layers and the stability of QDs was studied. The results showed that the synthesized SiO2-QD-AlOx, which has the smallest SSA in the synthesized QD composites, exhibited the best stability on the quantum dot diffuser plate (QD-DP). Moreover, the operational lifetime (T80) at 450 nm blue light excitation was increased by a factor of 3.41 compared to that of bare QDs. Meanwhile, the prepared QD-DP containing dense SiO2-QD-AlOx composites significantly improved the resistance to light, heat, moisture and oxygen. Finally, the prepared QD-DP was assembled into a Mini-LED TV with a wide color gamut and excellent display performance (a color gamut of 157.4 % for commercial normal TV, and 107.19 % for the National Television System Committee (NTSC 1931)). This technique provides favorable guide for effectively enhancing the stability of QDs in lighting and display technologies.

Temperature-dependent photoluminescent behavior of millimeter-scale Cs4PbBr6/CsPbBr3 bulk crystals and their application to white light-emitting diodes

The zero-dimensional perovskite composite Cs4PbBr6/CsPbBr3 has attracted significant attention for its remarkable photoluminescence (PL), which remains highly effective even in solid state. This work presents a detailed analysis of the steady-state and time-resolved PL (TRPL) behavior of millimeter-scale Cs4PbBr6/CsPbBr3 crystals over a temperature range of 80 to 360 K, which covers exciton binding energy, phonon energy, and PL peak energy shifting with increasing temperature. According to the results, Cs4PbBr6/CsPbBr3 exhibits high exciton binding energy and phonon energy, with calculated values of 358.7 and 94.8 meV, respectively. Specifically, when the temperature is below ∼235 K, thermal expansion dominates to influence the TRPL and peak energy, whereas electron-phonon interaction becomes the dominant factor as temperature rises from 235 to 325 K. It is found that Cs4PbBr6/CsPbBr3 has a PL behavior similar to CsPbBr3, and characterization and TRPL results demonstrate that nanometer-scale CsPbBr3 crystals embed in the Cs4PbBr6 bulk matrix. Meanwhile, a white light-emitting diode (WLED) device based on Cs4PbBr6/CsPbBr3 with luminous efficiency of 64.56 lm/W is fabricated, and its color coordinate is measured as (0.34, 0.31) under 20 mA, which is in close proximity to the standard white color coordinate. Moreover, the color gamut of the device is measured as 128.66% of the National Television Systems Committee (NTSC). The WLED electroluminescence (EL) spectra show high Correlated Color Temperature (CCT) stability for the working current varying from 5 to 100 mA, and after continuous operation for 12 h, the EL intensity decreases and stabilizes at ∼70% of the initial EL intensity. These findings suggest that Cs4PbBr6/CsPbBr3 crystals are a promising candidate for WLEDs.

Efficient and tunable emission CsPbClxBr3-x quantum dot glass for overcoming the lack of cyan gap in WLED.

Recently, the photoluminescence (PL) performance and stability of cyan emission perovskite quantum dot (PQD) were found to be inferior to other color emitting PQDs, which greatly limits their practical applications. In this Letter, CsPbClxBr3-x PQD glass with excellent hydrothermal stability is successfully synthesized by a high-temperature melting method. Results review that the vacancy defects in [PbBr6]4- octahedra can be effectively compensated by excessive halogen doping, resulting in an improvement in the photoluminescence quantum yield (PLQY) of PQDs from 24.73% to 65.62%. In addition, compared to white light emitting diode (WLED) synthesized with commercial fluorescent powders, the introduction of CsPbCl2Br1 PQD glass effectively fills the cyan gap. Moreover, the WLED displays the color-rendering index (CRI) of 87 at correlated color temperature (CCT) of 5257 K, and the color gamut area reaches 126% of the National Television System Committee (NTSC). This work provides an effective way for improving the PL performance of PQDs and brings CsPbClxBr3-x PQD glass significant prospect in the optoelectronic applications.

High-Efficiency Narrow-Band Green-Emitting Manganese(II) Halide for Multifunctional Applications.

Zero-dimensional (0D) Mn2+-based metal halides used as luminescent materials and scintillators have become a research hotspot in the field of photoelectric materials and devices due to their unique composition, structure, and fluorescence properties. It is of great value to explore new Mn2+-based metal halides to achieve multifunctional applications. Herein, the novel 0D Mn2+-based metal halide single crystal (BPTP)2MnBr4 is synthesized by a simple solvent-antisolvent recrystallization method. Under excitation at 468 nm, the (BPTP)2MnBr4 single crystal shows a pronounced narrow-band green luminescence centered at 515 nm derived from the d-d transition of the Mn2+ ion. This emission has a relatively narrow full width at half maximum of 43 nm and a high photoluminescence quantum yield (PLQY) of 82%. In addition, (BPTP)2MnBr4 exhibits good thermal stability at 393 K with a retention of 79% of the initial photoluminescence intensity at 298 K. Benefiting from its strong blue light excitation, high PLQY, and good thermal stability, we manufacture an ideal white light-emitting diode (LED) device using a 460 nm blue LED chip, green-emitting (BPTP)2MnBr4, and commercial K2SiF6:Mn4+ red phosphor. Under 20 mA drive current, the LED shows a high luminous efficiency of 112 lm/W and a wide color gamut of 110.8%, according to the National Television System Committee standard. In addition, (BPTP)2MnBr4 crystals show a strong X-ray absorption. Based on the commercial Lu3Al5O12:Ce3+ scintillator, the calculated light yield of (BPTP)2MnBr4 reaches up to about 136,000 photons/MeV and the detection limit reaches 0.282 μGyair s-1. Additionally, a melt quenching approach is used to construct a (BPTP)2MnBr4 clear glass scintillation screen, realizing a spatial resolution of 10.1 lp/mm. The proper performances of (BPTP)2MnBr4 as phosphor-converted LED materials and the X-ray scintillator with the addition of eco-friendly, low-cost solution processability make 0D Mn2+-based metal halides potential luminescent materials for multifunctional applications.

In situ and General Multidentate Ligand Passivation Achieves Efficient and Ultra-Stable CsPbX3 Perovskite Quantum Dots for White Light-Emitting Diodes.

Inorganic CsPbX3 perovskite quantum dots (PeQDs) show great potential in white light-emitting diodes (WLEDs) due to excellent optoelectronic properties, but their practical application is hampered by low photoluminescence quantum yield (PLQY) and especially poor stability. Herein, we developed an in-situ and general multidentate ligand passivation strategy that allows for CsPbX3 PeQDs not only near-unit PLQY, but significantly improved stability against storage, heat, and polar solvent. The enhanced optical property arises from high effectiveness of the multidentate ligand, diethylenetriaminepentaacetic acid (DTPA) with five carboxyl groups, in passivating uncoordinated Pb2+ defects and suppressing nonradiative recombination. First-principles calculations reveal that the excellent stability is attributed to tridentate binding mode of DTPA that remarkably boosts the adsorption capacity to PeQD core. Finally, combining the green and red PeQDs with blue chip, we demonstrated highly luminous WLEDs with distinctly enhanced operation stability, a wide color gamut of 121.3% of national television system committee, standard white light of (0.33,0.33) in CIE 1931, and tunable color temperatures from warm to cold white light readily by emitters' ratio. This study provides an operando yet general approach to achieve efficient and stable PeQDs for WLEDs and accelerates their progress to commercialization.

Low fluorescence crosstalk patterning of quantum dots based on laser drilling and micropore filling

In this study, a dual-color patterned perovskite quantum dot color conversion layer with a light-blocking matrix was created by combining laser drilling with micropore filling technology. When the blue micro-LED and the quantum dot color conversion layer make contact, the fluorescence crosstalk effect can be simulated to be near zero. The color conversion layers with high color gamut (111.2% of the National Television System Commission) were further confirmed to have outstanding optical isolation performance through experimental observations. This work may have significant advantages for its applications in photonic integration, micro-LED, and near-field displays due to simple operation process, maskless, harmlessness to quantum dots, short process period, and low crosstalk effect.

Designing ultra-highly efficient Sm3+ activated SrLaAlO4 orange-red emitting phosphor towards security encoding, hydro-gels, flexible displays and personal identification

SrLaAlO4:Sm3+ (1–5 mol %) nanophosphors (SLAO:Sm3+ NPs) has been developed. Under stimulation at 402 nm, the Sm3+ ions shows the transition of 4G5/2→ 6H7/2 enabled the phosphor to emit a powerful orange-red light at 602 nm. Based on the photoluminescence emission (PLE) profiles, the International Commission on Illumination calculated the colour coordinates (CC), correlated colour temperature (CCT) and colour purity (CP) values. Comparisons were made between the acquired CC and the normal National Television System Committee (NTSC) coordinates. Additionally, the applicability of the SLAO:2Sm3+ NPs was evaluated to visualize the latent fingerprints on smooth surfaces using the powder dusting method. The obtained latent fingerprint images exhibited good sensitivity, high contrast, and appreciable ridge details. To develop anti-counterfeiting inks that mark on multiple surfaces with high resolution without spreading and tracing, fluorescent phosphor was fabricated with the required thickening agent. The created pattern in the ink above immediately formed and lighted with bright orange and red fluorescence emission when exposed to UV light. The findings showed that the optimized NPs can generate a lot of interest for application in security encoding and personal identification.

RGB Thermally Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes toward Realizing the BT.2020 Standard.

With the surging demand for ultra-high-resolution displays, the International Telecommunication Union (ITU) announce the next-generation color gamut standard, named ITU-R Recommendation BT.2020, which not only sets a seductive but challenging milestone for display technologies but also urges researchers to recognize the importance of color coordinates. Organic light-emitting diodes (OLEDs) are an important display technology in current daily life, but they face challenges in approaching the BT.2020 standard. Thermally activated delayed fluorescence (TADF) emitters have bright prospects in OLEDs because they possess 100% theoretical exciton utilization. Thus, the development of TADF emitters emitting primary red (R), green (R), and blue (B) emission is of great significance. Here, a comprehensive overview of the latest advancements in TADF emitters that exhibit Commission Internationale de l'Éclairage (CIE) coordinates surpassing the National Television System Committee (NTSC) and approaching BT.2020 standards is presented. Rational strategies for molecular designs, as well as the resulting photophysical properties and OLED performances, are discussed to elucidate the underlying mechanisms for shifting the CIE coordinates of both donor-acceptor and multiple resonance (MR) typed TADF emitters toward the BT.2020 standard. Finally, the challenges in realization of the wide-color-gamut BT.2020 standard and the prospects for this research area are provided.

Enhanced Hygrothermal Stability of In-Situ-Grown MAPbBr3 Nanocrystals in Polymer with Suppressed Desorption of Ligands.

Currently, the intrinsic instability of organic-inorganic hybrid perovskite nanocrystals (PNCs) at high temperature and high humidity still stands as a big barrier to hinder their potential applications in optoelectronic devices. Herein, we report the controllable in-situ-grown PNCs in polyvinylidene fluoride (PVDF) polymer with profoundly enhanced hygrothermal stability. It is found that the introduced tetradecylphosphonic acid (TDPA) ligand enables significantly improved binding to the surface of PNCs via a strong covalently coordinated P-O-Pb bond, as evidenced by density functional theory calculations and X-ray photoelectron spectroscopy analyses. Accordingly, such enhanced binding could not only make efficient passivation of the surface defects of PNCs but also enable the remarkably suppressed desorption of the ligand from the PNCs under high-temperature environments. Consequently, the photoluminescence quantum yield (PL QY) of the as-fabricated MAPbBr3-PNCs@PVDF film exhibits almost no decay after exposure to air at 333 K over 1800 h. Once the temperatures are increased from 293 to 353 K, their PL intensity can be kept as 88.6% of the initial value, much higher than that without the TDPA ligand (i.e., 42.4%). Moreover, their PL QY can be maintained above 50% over 1560 h (65 days) under harsh working conditions of 333 K and 90% humidity. As a proof of concept, the as-assembled white light-emitting diodes display a large color gamut of 125% National Television System Committee standard, suggesting their promising applications in backlight devices.

Efficient blue and deep blue fluorescent OLEDs based on anthracene with upper-level intersystem crossing

Two new emitters based on anthracene core, 6-(10-phenylanthracen-9-yl)nicotinonitrile (CNPyAnPh) and 4-(10-(pyridin-2-yl)anthracen-9-yl)benzonitrile (CNPhAnPy) are designed and synthesized for realizing blue and deep blue organic light-emitting diodes (OLEDs). Both CNPyAnPh and CNPhAnPy show nearly orthogonal structures and the suppressed π-conjugation is favorable for blue and even deep blue emission. According to the theoretical calculations, small energy differences between T2 and S1 are observed in these two isomers, endowing the “hot exciton” channel. Furthermore, the S1 of CNPyAnPh possesses both locally excited (LE) and charge transfer (CT) components. By employing CNPyAnPh and CNPhAnPy as the emissive guests in the devices, their maximum external quantum efficiencies (EQEmaxs) are 4.15% and 3.71%, respectively. Thanks to the “hot exciton” and hybrid local and charge transfer (HLCT) properties, the exciton utilization efficiencies (EUEs) of the two molecules are higher than 25%, namely, 42% for CNPyAnPh and 34% for CNPhAnPy. The Commission International de l’Eclairage (CIE) coordinate of CNPhAnPy is (0.15, 0.08), approaching the National Television System Committee (NTSC) standard index for pure blue emission.

Achieving chip-matched high purity red emission by Bi3+ sensitization in Ca3MgTiGe3O12:Pr3+

Phosphor-converted light emitting diodes (pc-LEDs) are essential for current lighting and display areas because of their unique properties of being uncomplicated, durable and economical. In previous studies, Pr3+ doped red-emitting phosphors have attracted enormous research interest due to their high color purity. However, their photoluminescence excitation (PLE) spectra are always hard to be combined with LED chips. This mismatch is a great obstacle to achieve Pr3+ phosphors utilizing in LED devices. Here, to circumvent this issue, Pr3+-doped Ca3MgTiGe3O12 (CMTG) red-emitting phosphor was optimized with PLE band shifting from 330 nm to 360 nm after tuning with Bi3+ co-doping based on the structure and phosphorescence properties. The chip-matched excitation makes it a good candidate for white LEDs (wLEDs) fabrication to improve the output quality of device. Meanwhile, the high color purity of 93.02 % was obtained, which is conducive to widening the color gamut of backlight display applications. The photoluminescence (PL) spectra, fluorescence lifetime, and X-ray photoelectron spectroscopy (XPS) analysis were employed and discussed in detail to explain the role of Bi3+ played in the system. Finally, wLEDs were fabricated with CMTG:Pr3+, Bi3+, showing a high color rendering index (Ra) of 94.4. And the color gamut covers ∼80 % of the National Television System Committee (NTSC) standard, suggesting great potential for applications of wLEDs and backlight display.

Fabrication of Photostable Siloxane-Coated Quantum Dots for White-Light-Emitting Diodes

Quantum dots (QDs) are considered as excellent candidate materials for light-emitting diode (LED)-based lighting and display applications due to their excellent optical properties. However, the intrinsic unstable properties of QDs under external environments or the incompatibility between QDs and polymer composites hindered the QD-related applications. Herein, a universal modification method based on the optimization of QDs was developed for device applications. The highly dispersible and photostable QDs/siloxane composite was constructed by using the dual silica-encapsulated strategy of core/multishell CdSe/CdS/ZnCdS QDs to improve the performance of QDs. First, core/multishell QD’s size and components were optimized to enhance stability. Then, QDs@SiO2-OTMS was prepared by a combination of the reverse micro-emulsion method and surface modification. Such a double silica surface modification strategy is found to be very effective in improving the dispersion by matching the surface energy of QDs@SiO2-OTMS with that of siloxane resins. The as-prepared QDs@SiO2-OTMS/siloxane films had long-term (10 days) stability against heat and moisture and corrosive solution (HCl and NaOH). For the first time, the surface photovoltage (SPV) technique was used to study the in situ thermal stability of QDs@SiO2-OTMS, and it was found that surface defects were greatly suppressed at high temperatures. Taking these advantages, a white LED (WLED) with a color coordinate of (0.336, 0.325), color temperature of 5287 K, color gamut 123% National Television Systems Committee (NTSC,1931), and long-time stability at 20 mA had been fabricated by integrating green and red QDs@SiO2-OTMS/siloxane. These results make QDs@SiO2-OTMS/siloxane excellent candidates for QD lighting and display applications.

Cation defects succeed in triggering super stability of narrow-band blue-emitting phosphors Ca3Sc2Si3O12: Bi3+ for backlighting display application

High-performance white light-emitting diodes (WLEDs) used for backlighting display applications require innovative and thermally stable narrow-band emission phosphors, particularly non-rare-earth Bi3+-activated phosphors. In this study, we demonstrate a defect-engineering strategy to create novel anti-thermal quenching phosphors Ca3Sc2Si3O12: xBi3+ (CSSO: xBi3+). Through structure refinement of CSSO: 0.06Bi3+ phosphor, we found that Bi occupies both Ca and Sc sites in the CSSO lattice. Direct visualization of atomic-resolution TEM and thermoluminescence spectra confirmed the formation of point defects due to the non-equivalent substitution of Ca2+ for Bi3+. Fluorescent-decay analysis revealed that two luminescence sites contribute to the blue-emitting of CSSO:Bi3+ phosphors. CSSO: 0.06Bi3+ phosphor exhibits outstanding thermal stability, with an integrated emission intensity of 103.6% at 423 K compared to that at 298 K. However, the addition of Li or Na as charge compensators reduced cationic defects, leading to a decrease in thermal stability. We believe that VCa″ defects are primarily responsible for the anti-thermal quenching behavior of CSSO: xBi3+ phosphors. An optimized CSSO: 0.06Bi3+ phosphor-based WLED displays a high color rendering index (CRI) of 90 and a wide color gamut (90% National Television System Committee (NTSC) standard), indicating its potential for use in industrial applications as a backlighting display.