High Color Stability Research Articles

Efficient co-doped white organic light-emitting diodes with high color stability and color rendering index

Efficient color-stable fluorescent white organic light-emitting diodes based on a blue fluorescent host 2-(t-butyl)-9,10-di(2-naphthyl)anthracene(TBADN) co-doped with a blue guest p-di( p- N, N-diphenyl-amino-styryl)benzene(DSA-ph) and a red guest 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) were reported. The luminance mechanism was explored by analyzing the characteristics of devices with different doping concentrations. It was found that DSA-ph showed effective assistant energy transfer ability in the system. When 1.5% DSA-ph and 0.5% DCJTB were doped, the energy of the system could be most effectively utilized, achieving a maximum luminance efficiency of 14.26 cd/A at 40 mA/cm 2, with a color rendering index of 80. The Commission International de L’Eclairage coordinates changed slightly from (0.3381, 0.3327) to (0.3336, 0.3203), as the applied current density increased from 20 mA/cm 2 to 200 mA/cm 2. The high efficiency could be attributed to effective utilization of host energy, as well as the depression of concentration quenching, and the color stability may be ascribed to the efficient energy transfer from host to both guests in direct and indirect ways and efficient exciton confinement.

Bi-layer non-doped small-molecular white organic light-emitting diodes with high colour stability

Bi-layer non-doped white organic light-emitting diodes (WOLEDs) with hole-transporting layer 4-(4-(1,2,2-triphenylvinyl)phenyl)-7-(5-(4-(1,2,2-triphenylvinyl)phenyl)thiophen-2yl)benzo[c][1,2,5]thiadiazole (BTPETTD) as a red emitter and electron-transporting layer 4,4′-bis(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (DDPi) as a blue emitter are demonstrated. The blue emission is due to direct recombination of excitons in DPPi, while the red emission originates not only from the direct recombination of excitons in BTPETTD but also from a colour down-conversion process by absorbing blue emission and re-emitting red photons. The combination of blue emission and red emission yields an efficient and extremely stable white colour, regardless of driving voltages. In our demonstration, a bi-layer WOLED with an efficiency of 4.2 cd A−1 at 1000 cd m−2, 1931 Commision International de L'Eclairage coordinates of (0.31, 0.31) and a high colour rendering index of 92 over a wide range of driving voltages is obtained.

Top-emitting white organic light-emitting diodes with a color conversion cap layer

We report top-emitting white organic light-emitting diodes (WOLEDs) by thermally evaporating non-doped (4-(4-(1,2,2-triphenylvinyl)phenyl)-7-(5-(4-(1,2,2-triphenylvinyl)phenyl)thiophen-2yl)benzo[c][1,2,5]thiadiazole) (BTPETTD) as a color conversion cap layer on top-emitting blue OLEDs. With a 240 nm cap layer, 74.5% of the blue photon energy are absorbed and converted to red emission with a conversion efficiency of 40%. By mixing the unabsorbed blue emission and red emission, the resulting top-emitting WOLEDs exhibit a broad band spectra with CIE coordinates of (0.34, 0.35), high color stability over a wide range of driving voltages, and peak efficiency of 17.7 cd/A and 8.7 lm/W.

In Situ Synthesis of Thiol-Capped CuInS2-ZnS Quantum Dots Embedded in Silica Powder by Sequential Ligand-Exchange and Silanization

Thiol-capped CuInS2-ZnS core-shell quantum dot (QD) embedded in silica powder is synthesized by in situ approach, which contributes to facileness, high reproducibility and mass-productivity. The proposed method is distinguished in that it uses intermediate ligand-exchange step with hydroxyl-terminated ligands during growth stage, which helps the QDs to be dispersed in polar silane matrix to form micron-sized silica powder. This results in well-dispersed QDs in the silica powder with luminescence efficiency of 34%. In addition, the QDs/silica composites are applied to white-LEDs, demonstrating high quality white light with high color stability under various operating currents. © 2011 The Electrochemical Society. [DOI: 10.1149/2.011202esl] All rights reserved.

Properties of white organic electroluminescent devices based on a new organic metal complex with quantum well structure

A series of white organic electroluminescent devices with a quantum well structure were fabricated based on a new type of organic metal complex bis(2-(4-trifluoromethyl-2-hydroxyphenyl) benzothiazolate) zinc (Zn(4-TfmBTZ)2) by electroplex at NPB/Zn(4-TfmBTZ)2 interface. The results show that the introduction of the hetero-junction quantum well structure can increase effectively the efficiency of electroplex emission, color rendering index(CRI),and the color coordination stability. The optimized device ITO/NPB (60 nm)/Zn(4-TfmBTZ)2(3.0 nm)/NPB (4.0 nm)i> /Zn(4-TfmBTZ)2(30 nm) /Alq3 (30 nm)/LiF(1.5 nm)/Al(150 nm) is obtained with color coordinates of (0.324, 0.337), the highest CRI of 92.5, a maximal brightness of 2013 cd/m2, and a maximal efficiency of 1.03 cd/A,. This device shows very high color stability when the driving voltage is varied from 10 V to 14 V.

Nearly non-roll-off high efficiency fluorescent yellow organic light-emitting diodes

This paper demonstrates the employment of a multi-emissive-layer device architecture with smooth cascading energy levels to improve markedly the efficiency, roll-off, and color-stability of a fluorescent yellow organic light-emitting diode. As a tri-emissive layer structure was used in lieu of neat film, for example, the resultant external quantum efficiency was increased from 2.2 and 1.8% to 8.2 and 8.6% between 100 and 1000 cd m−2, while current efficiency increased from 5.8 and 4.6 cd A−1 to 26.5 and 27.2 cd A−1 and efficacy from 4 and 2.4 lm W−1 to 20.6 and 18.3 lm W−1. Moreover, the color stability of the tri-emissive layer structure has become of even higher quality than the neat film counterpart has. The reason why the multi-emissive-layer device exhibits both high efficacy and high color-stability may be attributed to the stepwise energy levels that enable a significant reduction in injection barriers, a wider recombination zone, and a more effective carrier confinement. Additionally, the paired host and guest energy-levels in two of the emissive layers allow excitons to generate on the host to facilitate the occurrence of host-to-guest energy transfer and, thus, high device efficiency. The little roll-off may be due to the different paired host and guest energy-levels in the third emissive layer allowing excitons to generate predominantly on the guest at low voltage, but with increasing excitons generating on the host as the voltage increases, fully utilizing all the possible recombination sites.

A carbazole–phenylbenzimidazole hybrid bipolar universal host for high efficiency RGB and white PhOLEDs with high chromatic stability

A novel bipolar molecule CNBzIm comprised of electron-donating carbazole and electron-accepting phenylbenzimidazole is designed, synthesized and characterized for RGB phosphorescent organic light emitting diodes (PhOLEDs). CNBzIm exhibits promising properties such as high triplet energy (ET = 2.71 eV) due to disrupted π-conjugation, bipolar and balanced charge transport ability (μh ≈ μe ≈ 10−5 cm2 V−1s−1), and high morphological stability (Tg = 185 °C). PhOLEDs adopted CNBzIm as a host respectively doped with Os(bpftz)2(PPh2Me)2, (PPy)2Ir(acac) and FIrpic under the same device structure show excellent performance with external quantum efficiencies (ηext) as high as 19.1% for red, 17.8% for green, and 12.7% for blue. A two-color, all-phosphor and single-emitting-layer WOLED hosted by CNBzIm was achieved with a maximum ηext of 15.7%, current efficiency (ηc) of 35 cd A−1, and power efficiency (ηp) of 36.6 lm W−1. Utilizing a bipolar host with balanced mobilities, WOLED can effectively broaden its recombination zone and show high color stability. The Commission Internationale de L'Eclairage (CIE) coordinates of the WOLED remain almost constant when the brightness goes from 1700 cd m−2 (0.32, 0.41) to 49 900 cd m−2 (0.31, 0.41).

Enhancing the conversion efficiency of red emission by spin-coating CdSe quantum dots on the green nanorod light-emitting diode

A hybrid structure of CdSe quantum dots (QDs) (λ = 640 nm) spin-coated on the indium gallium nitride (InGaN) nanorod light-emitting diode (LED, λ = 525 nm) is successfully fabricated. Experimental results indicate that the randomness and the minuteness of nanorods scatter the upcoming green light into the surrounding CdSe QDs efficiently, subsequently alleviating the likelihood of the emitted photons of red emission being recaptured by the CdSe QDs (self-absorption effect), and that increases the coupling probability of emission lights and the overall conversion efficiency. Moreover, the revealed structure with high color stability provides an alternative solution for general lighting applications of next generation.

Association of Indigo with Zeolites for Improved Color Stabilization

The durability of an organic color and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidizing conditions, using Raman and ultraviolet-visible (UV-Vis) spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In the absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high color stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment.

Survey of Currently Used Materials for Fabrication of Extraoral Maxillofacial Prostheses in North America, Europe, Asia, and Australia

The purpose of this survey was to review the extraoral maxillofacial materials currently used as well as the advantages and disadvantages of the materials in the fabrication of facial prostheses. Results of this survey will enhance scientific knowledge, generate research study ideas, and possibly lead to production of alternative or new maxillofacial materials. A 47-question survey was delivered via e-mail to all members (combined total of 260 members) of the American Anaplastology Association (AAA) and American Academy of Maxillofacial Prosthetics (AAMP) for evaluation of personal preference involving maxillofacial prosthetic materials (intrinsic/extrinsic silicone elastomers and pigments/colorants used, polymerization/curing process, advantages and disadvantages of the most often used materials, most important characteristic of material/technique used). The views of 43 (16%) respondents indicated that the majority surveyed were using room temperature-vulcanized (RTV) silicone products. Silicone pigments for intrinsic and silicone pastes for extrinsic coloring were favored over artist's oil colors and dry earth pigments. The polymerization process and/or curing times and temperatures for the same silicone material varied between users. The top five advantages of most often used materials were good esthetics, ease of coloring, easy manipulation, thin margins possible, and adhesive compatibility. The top five disadvantages were discoloration over time, technique-sensitivity, lack of repairability, extrinsic colors peel/fade, and lack of longevity. Nontoxic/nonallergenic materials with high edge strength and color stability were the most important features when choosing a maxillofacial prosthetic material/technique. The responses to this survey indicate that the majority of AAA and AAMP members are using or have used a variety of RTV silicones, pigments, and colorants in the quest to provide the best possible facial prosthetic service. Further research is needed to further refine and improve extraoral maxillofacial materials/techniques based on the results of this study.

Emitting layer thickness dependence of color stability in phosphorescent organic light-emitting devices

We investigated the strong influence of the thickness of iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C 2′] picolinate (FIrpic) doped N, N′-dicarbazolyl-3, 5-benzene (mCP) blue-emitting layer (B-EML) on color stability. The large voltage drop across the B-EML resulted in a higher sensitivity of the carrier transport and injection properties to the applied external voltage. According to carrier mobility measurements by the time-of-flight method, the electron mobility of the mCP exhibited a strong dependence on the electric field. Therefore, at a higher driving voltage, the more rapidly increasing electron mobility of the mCP and the decreasing energy barrier height on the electron transport path would extend the recombination zone from the B-EML to the tris(phenylpyridine)iridium (Ir(ppy) 3) doped mCP green-emitting layer (G-EML) in devices with thinner B-EMLs. Coupled with the fluctuations of the recombination zone, stronger triplet–triplet exciton annihilation occurring in the thinner B-EMLs led to an even more evident deterioration of the color stability. After circumventing these two negative factors, a green–blue organic light-emitting device (OLED) with ultra-high color stability was demonstrated, with the CIE coordinates slightly shifted from (0.256, 0.465) to (0.259, 0.467) with increased luminance from 48.7 to 12,700 cd/m 2. Further adding a red phosphorescent dopant into this green–blue EML backbone, we successfully fabricated a white OLED with high color stability, which exhibited a nearly invariant CIE coordinate throughout the practical luminance range from 1050 (0.310, 0.441) to 9120 cd/m 2 (0.318, 0.446) and maximum efficiencies of 26.4 cd/A and 19.8 lm/W.

利用复合色彩转换膜实现白色有机电致发光

A novel white organic light-emitting device (WOLED) using a strategy of exciting organic/inorganic color conversion film with a blue organic light-emitting diode (OLED) is reported.The luminescent layer of the blue OLED is prepared by using of CBP host blended with a blue highly fluorescent dye N-BDAVBi.The organic/inorganic color conversion film is prepared by dispersing a mixture of red pigment VQ-D25 and YAG phosphor in PMMA.A novel WOLED with the high color stability by optimizing the thickness and fluorescent pigment concentration of the color conversion film are achieved.When the driving voltage varied between 6 V to 14 V,the color coordinates varied slightly from (0.354,0.304) to (0.357,0.312) and the maximum current efficiency is about 5.8 cd/A(4.35 mA/cm2),the maximum brightness is 16 800 cd/m2 at the operating voltage of 14 V.

Preparation and Performance of Ag<sup>+</sup>-Zn<sup>2+</sup>-Zeolite Antimicrobial and Antibacterial Plastic

Ag+-Zn2+-zeolite antimicrobial (AZZA) with high antibacterial efficiency and good color stability was prepared by ion-exchange method in water phase, followed by surface modification. Taking the modified AZZA as raw material, antibacterial polyethylene (PE) master batch was prepared and applied in PE plastic. In this paper, the technological parameters to prepare AZZA were optimized, and the effect of antimicrobial addition on the mechanical property and antibacterial property of PE plastic was studied as well. As shown in SEM analysis, AZZA particles were distributed homogeneously in PE plastic, and was compatible with the PE matrix well. The mechanical property of PE sample was not influenced notably when the adding amount of modified AZZA was less than 6%.

Contributions of Muscles of Various Color Stabilities to the Overall Color Stability of Ground Beef

Ground high (HCS), intermediate (ICS), and low color stability (LCS) cow muscles were used to investigate effects of blending muscles of different color stabilities on ground beef display color. Six formulations at 90% and 80% lean points combining HCS, ICS, and LCS muscles were: 50% HCS + 50% ICS; 50% HCS + 50% LCS; 50% ICS + 50% LCS; 33.3% HCS + 33.3% ICS + 33.3% LCS; 75% HCS + 25% LCS; and 25% HCS + 75% LCS. Patties were packaged in a high oxygen (80% O(2), 20% CO(2)) modified atmosphere, held in dark storage for 5 d, then displayed for 4 d. The 80% lean patties containing >or= 50% HCS had the brightest red initial visual color. During display 75% HCS + 25% LCS at both lean points had the most cherry-red display color. Patties containing a greater proportion of HCS had greater metmyoglobin reducing ability throughout display. HCS, ICS, and LCS muscle can be mixed without adverse color affects, provided LCS muscle is <or= 25%, and HCS muscle is >or= 50% of the blend.

Single molecule color controllable light emitting organic field effect transistors for white light emission with high color stability

The authors report on color controllable white light emission from a unipolar organic light emitting transistor. We demonstrate light emission with two distinct peaks: a spectrally narrow blue emission from monomers and a yellow broadband emission created close to the interface of the organic film and SiO2. Due to the functionality of Mg/Au stacked electrodes, we are able to position the recombination zone via gate voltage control. Therefore, we are able to shift the spectral peak position and change the emission intensity independently by the drain voltage. The emission color is tunable from CIE coordinates (0.27, 0.28) to (0.40, 0.41).

Fluorene‐Based Copolymers Containing Dinaphtho‐s‐indacene as New Building Blocks for High‐Efficiency and Color‐Stable Blue LEDs

By incorporating a new building block, 7,7,15,15-tetraoctyldinaphtho-s-indacene (NSI), into the backbone of poly(9,9-dioctylfluorene) (PFO), a novel series of blue light-emitting copolymers (PFO-NSI) have been developed. The insertion of the NSI unit into the PFO backbone leads to the increase of local effective conjugation length, to form low-energy fluorene-NSI-fluorene (FNF) segments that serve as exciton trapping sites, to which the energy transfers from the high-energy PFO segments. This causes these copolymers to show red-shifted emissions compared with PFO, with a high efficiency and good color stability and purity. The best device performance with a luminance efficiency of 3.43 cd · A(-1) , a maximum brightness of 6 539 cd · m(-2) , and CIE coordinates of (0.152, 0.164) was achieved.

Para-sexiphenyl-CdSe Nanocrystals Hybrid Light Emitting Diodes with Optimized Layer Thickness and Interfaces

AbstractCdSe/ZnS nanocrystals are embedded in para-sexiphenyl (p-6P) based hybrid light emitting diode devices providing red, green and blue (RGB) emission compatible to the HDTV color triangle. By structural and optical investigations the device parameters are optimized. The device performance is analyzed in respect to electrical and spectral response resulting in current-voltage characteristics with small leakage currents and low onset voltages. Furthermore the devices provide high color purity and stability which is demonstrated by their narrow emission line widths. All these results underline the ability of the presented device configuration to act as a future candidate for display applications.

Steady full colour white organic light-emitting devices consisting of an ultrathin red fluorescent layer

White organic light-emitting devices were fabricated using an ultrathin red fluorescent dye of 3-(dicyanomethylene)-5, 5-dimethyl-1-(4-dimethylamino-styryl)cyclohexene inserted in tris(8-quinolinolato) aluminium layer as a red and green emitting layer (EML) and a thin 4, 4′-bis(2, 2′-diphenylvinyl)-1, 1′-diphenyl (DPVBi) layer as blue EML. A maximum power efficiency of 2.4 lm W−1 at 5.5 V and a maximum luminance of 16 690 cd m−2 at 18.5 V were obtained. Pure white emission with a good colour rendering index of 80 was achieved as low as 5 V. The Commission Internationale de l'Eclairage (CIE) coordinates near (0.330, 0.300) show a slight variation of (−0.020, +0.002) in a wide range of voltages. The achievement of full colour white emission at low-operation voltages and high-colour stability is attributed to the confining emission zone function of the thin EML and direct carrier trapping in the ultrathin layer.

High efficiency, color stability, and stable efficiency roll off in three color hybrid white organic light emitting diodes

High efficiency, good color stability, and stable efficiency roll off were achieved in three color white organic light emitting diodes by developing a device architecture with red and green phosphorescent materials codoped in a mixed host emitting structure. A fluorescent blue material was used in a blue emitting layer and a mixed interlayer structure was applied. A high quantum efficiency of 9.7% was obtained and color coordinate of (0.40, 0.40) was kept constant up to luminance of 10000cd∕m2. In addition, efficiency decrease at 10000cd∕m2 was only 2% of the maximum quantum efficiency.

Effect of pre‐treatment with carbon monoxide and film properties on the quality of vacuum packaging of beef chops

AbstractBeef chops (longissimus dorsi) were pre‐treated with 5% carbon monoxide (CO) − 95% N2 for 24 h, vacuum packed in thermo‐contractile bags and stored at 0 ± 2°C. Shelf life, as determined by the viable aerobic bacterial load, was 11 weeks. Vacuum‐packed chops with heat‐contractile film produced a smaller drip loss, had a more intense red colour and higher colour stability under storage than chops with non‐heat‐contractile film. Chops pre‐treated with CO were redder during all the storage period than controls without CO. The pre‐treatment did not affect pH, water‐holding capacity, drip loss or rancidity of the meat stored in vacuum. Copyright © 2008 John Wiley &amp; Sons, Ltd.