Commission Internationale De L'Eclairage Coordinates Research Articles

Single-Molecule White Circularly Polarized Photoluminescence and Electroluminescence from Dual-Emission Enantiomers.

The strategy of integrating conformational isomerization donors and chiral acceptors in a single molecule was proposed to construct white circularly polarized luminescence (WCPL) materials in this work. Consequently, a pair of dual-emission enantiomers, namely (R/S)-DO-PTZ, were designed and synthesized, which displayed white emission with blue and yellow dual-emission bands in solution and solid films with Commission Internationale de l'Eclairage (CIE) coordinates of (0.30, 0.33) and (0.33, 0.35), respectively. Meanwhile, (R/S)-DO-PTZ exhibited a high PLQY of up to 67 % in doped films and clear mirror-image WCPL signals with a |glum| value of 3.0×10-3. Moreover, white circularly polarized electroluminescence (WCPEL) based on organic light-emitting diodes (OLEDs) with (R/S)-DO-PTZ as emitters were also achieved with CIE coordinates of (0.32, 0.37) and EQEmax of 4.7 %, representing the state-of-the-art level of white OLEDs based on single-molecule purely organic emitters. By optimizing the device structure, warm WCPEL devices were further obtained with a |gEL| value of 2.8×10-3, CIE coordinates of (0.37, 0.48) and EQEmax of up to 15.6 %. To our knowledge, this is the first report of CP-WOLEDs based on single-molecule purely organic emitters.

Fine tuning of excited states by trifluoromethylphenyl for blue-shifted color and enhanced EQEs in thermally activated delayed fluorescence emitters

3,6-di-tert-butyl-9H-carbazole and 3,6-diphenyl-9H-carbazole have been widely used to construct blue thermally activated delayed fluorescence (TADF) emitters. However, it is difficult for related emitters to achieve maximum external quantum efficiency (EQEmax) above 20 % with the Commission Internationale de l'Eclairage (CIE) y ≤ 0.12. A new type of donor was developed to construct blue TADF molecules, namely CF3P-BuCz-TRZ and CF3P-PhCz-TRZ. The weak electron-withdrawing trifluoromethylphenyl (CF3P) with moderate steric hindrance was introduced into the 1-site of carbazole donor for improving the color purity for blue TADF emitters. More importantly, the introduction of CF3P tightly compacts the energy levels for the significant excited states in RISC process. The energy gap between the lowest singlet excited (S1) state and the lowest triplet (T1) state (Δ E(S1−T1)), as well as between T1 and the higher triplet (Tn, n ≥ 2) states (Δ E(Tn−T1)) were reduced, so that Tn (n ≥ 2) could be effectively harvested to further promote reverse intersystem crossing (RISC). As a result, the OLEDs based on CF3P-BuCz-TRZ and CF3P-PhCz-TRZ displayed blue electroluminescence with CIE coordinates of (0.156, 0.107) and (0.155, 0.115). In particular, the maximum EQEs of the CF3P-PhCz-TRZ device reached 20.43 % without employing any light out-coupling enhancement or TADF-sensitized structure. This strategy should be valuable for designing more pure-blue and deep-blue TADF emitters.

Enhancing Light-Emitting Efficiency of Blue Through-Space Charge Transfer Emitters via Fixing Configuration Induced by Intramolecular Hydrogen Bonding.

Closely aligned configuration of the donor (D) and acceptor (A) is crucial for the light-emitting efficiency of thermally activated delayed fluorescence (TADF) materials with through-space charge transfer (TSCT) characteristics. However, precisely controlling the D-A distance of blue TSCT-TADF emitters is still challenging. Herein, an extra donor (D*) located on the side of the primary donor (D) is introduced to construct the hydrogen bonding with A and thus modulate the distance of D and A units to prepare high-efficiency blue TSCT emitters. The obtained "V"-shaped TSCT emitter presents a minimal D-A distance of 2.890 Å with a highly parallel D-A configuration. As a result, a high rate of radiative decay (>107 s-1) and photoluminescence quantum yield (nearly 90%) are achieved. The corresponding blue organic light-emitting diodes show maximum external quantum efficiencies (EQEmax) of 27.9% with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.16, 0.21), which is the highest device efficiency of fluorene-based blue TSCT-TADF emitters. In addition, the TSCT-TADF emitter-sensitized OLEDs also achieve a high EQEmax of 29.3% with a CIE coordinate of (0.12, 0.16) and a narrow emission.

Elastic Organic Crystals Exhibiting Amplified Spontaneous Emission Waveguides with Standard Red Chromaticity of the Rec.2020 Gamut.

The use of mechanically flexible molecular crystals as optical transuding media is demonstrated for a plethora of applications; however, the spectral peaks of optical outputs located mainly in the range of 400-600nm are insufficient for practical telecommunication and full-color display applications. Herein, two elastically bendable organic crystals are reported that show red emission of the rec.709 gamut under 365nm UV light irradiation yet generate rec.2020 gamut red optical waveguides and amplified spontaneous emissions when irradiated by a 355nm laser. Capitalizing on the extended π-conjugation and donor-acceptor character, as well as mechanical elasticity, these organic crystals exhibit flexible optical waveguides with Commission Internationale de L'Eclairage (CIE) coordinates of (0.70, 0.29), nearly identical to the red chromaticity of the rec.2020 gamut required for ultrahigh-definition (UHD) displays. Notably, one of the elastic crystals functions as a soft resonance cavity, resulting in amplified spontaneous emission waveguides with CIE coordinates of (0.71, 0.29) and the standard red chromaticity of the rec.2020 gamut, both in straight and bent states. This study presents a new avenue for the development of high-purity red-emissive crystalline materials to create all-organic, lightweight, and mechanically compliant optical telecommunication and UHD display devices.

A record-high EQE of 7.65%@3300 cd m-2 achieved in non-doped near-ultraviolet OLEDs based on novel D'-D-A type bipolar fluorophores upon molecular configuration engineering.

Developing a high-performance near-ultraviolet (NUV) material and its simple non-doped device with a small efficiency roll-off and good color purity is a promising but challenging task. Here, we proposed a novel donor'-donor-acceptor (D'-D-A) type molecular strategy to largely solve the intrinsic contradictions among wide-bandgap NUV emission, fluorescence efficiency, carrier injection and transport. An efficient NUV fluorophore, 3,6-mPPICNC3, exhibiting a hybridized local and charge-transfer state, is achieved through precise molecular configuration engineering, realizing similar hole and electron mobilities at both low and high electric fields. Moreover, the planarized intramolecular charge transfer excited state and steric hindrance effect endow 3,6-mPPICNC3 with a considerable luminous efficiency and good color purity in the aggregation state. Consequently, the non-doped device emitting stable NUV light with Commission Internationale de l'Eclairage (CIE) coordinates of (0.160, 0.032) and a narrow full width at half maximum of 44 nm exhibits a state-of-the-art external quantum efficiency (EQE) of 7.67% and negligible efficiency roll-off over a luminance range from 0 to 3300 cd m-2. This is a record-high efficiency among all the reported non-doped NUV devices. Amazingly, an EQE of 7.85% and CIE coordinates of (0.161, 0.025) are achieved in the doped device. This demonstrates that the D'-D-A-type molecular structure has great potential for developing high-performance organic light-emitting materials and their optoelectronic applications.

Synthesis, structure and optoelectronic properties of iridium(III) complexes bearing a four-membered Ir-N-C[sbnd]N chelate structure

Herein four novel iridium(III) complexes (tfpmd)2Ir(dpppy) (Ir1a, tfpmd = 2-(4-(trifluoromethyl) phenyl) pyrimidine, dpppy = P,P-diphenyl-N-(pyridin-2-yl)phosphinic amide), (tfpmd)2Ir(dppq) (Ir1b, dppq = P,P-diphenyl-N-(quinolin-2-yl)phosphinic amide), (tfpqz)2Ir(dpppy) (Ir2a, tfpzq = 4-(4-(trifluoromethyl) phenyl) quinazoline) and (tfpqz)2Ir(dppq) (Ir2b) were synthetized, and their structures, opto-physical, and electro-chemical properties were investigated in detail. The crystal structure shows that these complexes exhibit pseudo-octahedral geometry around iridium atom coordinated by C, N atoms from cyclometalated and ancillary ligands. Interestingly, two coordinated nitrogen atoms from the ancillary ligand form an unusual quaternary ring with the central iridium ion. Ir1a and Ir1b emit pure-green light with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.25, 0.67) and (0.22, 0.67), respectively, in CH2Cl2 solution. With the increase of the degree of conjugation of the cyclometalated ligand from tfpmd to tfpqz, the luminescence of complexes Ir2a and Ir2b is greatly red-shifted, and pure-red emission with CIE coordinates of (0.66, 0.34) and (0.66, 0.34), respectively, is obtained. The photophysical behaviors were reasonably explained by quantum chemical calculations. The calculation results shows that their emission is ascribed to the mixed 3MLCT (metal-ligand charge transfer, dπ(Ir)→π*(cyclometalated ligand)) and 3LLCT (ligand-ligand charge transfer, π(ancillary ligand)→π*(cyclometalated ligand)) states. Owing to their good thermal and electrochemical stabilities, organic light emitting diode (OLED) devices with dual-emitting layer structure and a space interlayer were fabricated and exhibited high electroluminescent properties and mild efficiency roll-off (14%-21%).

Triphenylamine-phenylimidazole based hybridized local and charge-transfer molecular as blue-green/ white light emission emitter for light-emitting diode application

In this work, a new triphenylamine-phenylimidazole derivative named (E)-N,N-diphenyl-4-(2-(4'-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1′-biphenyl]-4-yl)vinyl)aniline (DPAvlBPI) with hybridized local and charge-transfer (HLCT) characteristics was successfully developed. The undoped organic light-emitting diode (OLED) based on DPAvlBPI (XF-OLED) is prepared with a maximum external quantum efficiency (EQE) of 1.23 %, and the exciton utilization efficiency (EUE) can reach 41 %. The Commission Internationale de L'Eclairage (CIE) color coordinate of XF-OLED is (0.1925, 0.3975), indicating that the device is in the blue-green light region. Since the photoluminescence quantum efficiency (PLQY) of DPAvlBPI in neat film is only 0.12, the maximum brightness of the device is 545 cd m−2. However, by dispersing DPAvlBPI in silica gel at a low concentration, the PLQY can approach 1. Therefore, the DPAvlBPI-based organic/inorganic hybrid LED XF-HBLED is prepared, and the device can achieve a luminous efficacy of 18.64 lm/W and EQE of 9.98 % at an operating current of 64.90 mA. To broaden the application scope of DPAvlBPI, a “Halochromism” white light emission system based on DPAvlBPI has been prepared, and the solution type (XF-SWLED) and solid-state(XF-W2) white light emission device based on this system have been successfully realized. The luminous efficacy of XF-W2 with a CIE coordinate of (0.3205, 0.4363) can reach 14.92 lm/W with an EQE of 8.23 % under the operating current of 64.90 mA. This provides a reference for expanding the multifunctional/multi-device applications of HLCT molecules.

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.

Synthesis and luminescence characterization of Dy3+/Sm3+ Co-doped Y2MgTiO6 double-perovskite phosphors for warm WLED

Y2MgTiO6:Dy3+/Sm3+ double-perovskite phosphors were synthesized using the high-temperature solid-state reaction method, and their luminescence properties were examined through various techniques, including Rietveld refinement, excitation and emission spectra, Commission Internationale de l'Eclairage (CIE) analysis, and band gap simulation. Ab initio calculations were performed to analyze the band gap and density of states, allowing for the prediction of the effect of Dy3+ and Sm3+ doping on emission intensity. The emission spectra of Y2MgTiO6 (YMTO) doped with Sm3+ and Dy3+ exhibited maximum peaks at 602 nm and 575 nm, respectively, when excited at 325 nm. Both YMTO:Sm3+ and YMTO:Dy3+ demonstrated excellent thermal stability. The CIE coordinates of YMTO doped with 1 mol% Dy3+ were determined to be (0.3771, 0.3804), with a correlated color temperature (CCT) of 4115 K, confirming its suitability for warm white light applications. Introducing 1 mol% and 3 mol% of Sm3+ ions into the Dy3+/Sm3+ co-doped YMTO allowed for adjustable CCT values of 3719 K and 3302 K, respectively, further enhancing their potential for use in warm white light-emitting diodes (WLEDs).

Cyan luminescence from Bi ions-doped borosilicate glass induced by the gradual substitution of MO (M=Ca, Sr, Ba)

At present, amorphous glasses that can give blue light, green light, and yellow light emission upon ultraviolet excitation have achieved good commercial prospect, but lacking of the high-efficiency cyan luminescence is still a challenging problem. To fill the lack of cyan light emission in the current white light LED technology spectrum excited by ultraviolet light, the effect of the substitution of CaO for SrO and BaO, and that of SrO for BaO on the optical properties, structure, DSC, and CIE (Commission International de L'Eclairage) coordinates of Bi ions-doped borosilicate glasses were systematically studied in this work. The emission spectra results reveal that the emission position of Bi ions-doped borosilicated glasses is observed from 482 nm to 492 nm when CaO is gradually replaced by SrO, from 482 nm to 502 nm when CaO is gradually replaced by BaO. In one word, the luminescent peak position of the Bi ions-doped borosilicate glass can be easily tuned by altering the concentration of basicity-earth oxide modifier, and the cyan light emission can be finally achieved.

Spectrally Stable Deep‐Blue Perovskite Light‐Emitting Diodes Enabled by a Deep Eutectic Solvent

AbstractFull‐color LED display requires Commission Internationale de l'Eclairage (CIE) 1931 coordinates of (0.14, 0.08), based on the National Television Standards Committee (NTSC) blue standard. However, such deep‐blue perovskite light‐emitting diodes (PeLEDs) still lag far behind in terms of device efficiency. Moreover, spectral stability remains a big challenge. To settle these issues, a kind of deep eutectic solvent (DES) is introduced as the perovskite precursor solvent additive, which is formed from a hydrogen bond acceptor (HBA) choline chloride and a hydrogen bond donor (HBD) urea via the hydrogen bond interaction. The incorporation of DES has multiple advantages, shown as follows: 1) improves the solubility of CsCl to yield dense perovskite morphology, 2) inhibits the growth of the perovskite crystal to achieve low‐n phases with narrow distribution, and 3) stabilizes the halide anions in the lattice to ensure stable electroluminescence (EL) spectra. As a result, the as‐prepared PeLED shows the maximum external quantum efficiency (EQEmax) of 2.71% with a CIE coordinate of (0.134, 0.055). With the increase in the DES concentration, the spectra stability is also obviously enhanced.

Novel “hot-exciton” material with high hole mobility for highly efficient deep red OLEDs

Due to the limitation of the energy gap rule, the development of highly efficient deep red hot-exciton material (λEL ≥ 650 nm) remains a great challenge. Here, we designed and synthesized a novel D-A-D type deep red fluorescent molecule, 4,7-bis(10-phenyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazole (2PPOXBZ), which is not only efficient deep red emitter but also has high hole mobility (2.56 × 10−3 cm2 V−1 s−1). The excited-state characteristics were investigated through photophysical experiments and theoretical calculations, it had been demonstrated the hot-exciton properties. The optimized non-doped OLED using 2PPOXBZ simultaneously act as a light-emitting layer and the hole transport layer exhibits the maximum external quantum efficiency (EQE) as high as 3.38% with a deep red emission peak at 678 nm, corresponding to the Commission International de L'Eclairage (CIE) coordinates (0.70, 0.30). More importantly, the optimized doped deep red OLED based on 2PPOXBZ as dopant exhibits an EQE up to 7.52% with electroluminescence (EL) peak of 658 nm and CIE coordinates of (0.67, 0.33), which is among the best results based on “Hot-exciton” deep red fluorescent OLEDs at present. The results of this study not only realize highly efficient deep red OLEDs with high color purity but also provide an effective molecular strategy for efficient deep red EL emitters.

Intrinsically Flexible and Aging Resistant Fluorene‐Based Rod‐Coil Copolymer for Bendable Deep‐Blue PLEDs

AbstractIn the field of flexible light‐emitting display, goal‐oriented intelligent molecular design is used to control various behaviors of molecules, which provides potential for the development of flexible light‐emitting conjugated polymers (LCPs). The introduction of non‐conjugated units into polymer molecules is a key prerequisite for realizing the intrinsic flexibility, but its easy interchain slip will also lead to the formation of interchain excited states, which is detrimental to the efficiency of light‐emitting diodes. Herein, two kinds of fluorene‐based rod‐coil copolymer with stable deep blue emission characteristics is presented and with Commission Internationale de L'Eclairage (CIE) coordinates of (0.18, 0.14) and (0.15, 0.09), respectively. Surprisingly, the copolymer films show efficient blue emission even at 100% tension. Meanwhile, the rod‐coil copolymer possesses better aging resistance compared to rigid π‐conjugated counterparts. Finally, both rigid and flexible light‐emitting diodes based on rod‐coil copolymer exhibit stable deep blue emission, and the G2‐based PLED with CIE coordinates of (0.16, 0.08), which approach National Television System Committee standard blue specification. These results confirm the validity of rod‐coil copolymer design strategy in constructing inherently flexible polymers with deep blue emission, which have great application potential in flexible PLEDs.

Spectrally Stable Pure Red CsPbI3 Quantum Dots Light‐Emitting Diodes via Effective Low Temperature Gradient Centrifugation Separation and Surface Modification

AbstractDevelopment of high‐performance and stable pure red perovskite light‐emitting devices (LEDs) promotes commercialization of perovskite. Benefiting from the quantum confinement effect, pure red CsPbI3 quantum dots (QDs) can avoid the color drift issue for mixed halide systems. Herein, a facile temperature‐dependent hot‐injection method combined with low temperature gradient centrifugation is employed to prepare 5.60 ± 0.05 nm pure red QDs. The QDs exhibit 642 nm photoluminescence (PL) with 37 nm full width at half maximum, and their Commission Internationale de l'Eclairage (CIE) coordinates located at (0.708, 0.292) match well with standard pure red for Rec. 2020. The PL half‐lifetime for pure red QDs solution is 210 days under ambient conditions, and both the X and Y coordinates of CIE only fluctuate within (0.002, 0.002). Finally, a simple NH4I post‐treatment to decrease ligand length further boosts the QDs conductivity, and the pure red LED exhibits 9.4% maximum external quantum efficiency. The electroluminescence spectra exhibits a sharp peak at 645 nm, and their CIE coordinates are located at (0.707, 0.290). Furthermore, the pure red LED exhibits both good working and color stability. Its half‐lifetime is 25.1 min and color drifts are only (0.002, 0.002) after 30.0 min of continuous working at 60 cd m−2 with a constant current density of 3.5 mA cm−2.

Eu3+ doped Ca3LiZnV3O12 phosphors for four-mode optical thermometry

Optical thermometer has brought about the widespread attention on account of non-contact and high-sensitive advantages. In this work, a novel optical thermometry with four modes was designed in Ca3LiZnV3O12:Eu3+ (CLZVO:Eu3+) phosphors. Benefitting from energy transfer of VO43− to Eu3+, CLZVO:Eu3+ phosphors (irradiated by 342 nm light) generate emissions from VO43− and Eu3+ simultaneously. As temperature increases, luminescent intensities of VO43− and Eu3+ show different downward trends, resulting in luminescent color changing with temperature. Besides, the excitation spectra of VO43− show a red shift with temperature boosting. Based on above luminescent characteristics, FI (fluorescence intensity), FIR (fluorescence intensity ratio), CIE (Commission Internationale de L'Eclairage) coordinate, and EIR (excitation intensity ratio) modes of CLZVO:Eu3+ thermometry were obtained. The maximum SR (relative sensitivity) values of each modes attain 2.56 %K−1 (340 K, FI), 2.18 %K−1 (320 K, FIR), 0.492 %K−1 (400 K, CIE coordinate), and 1.60 %K−1 (303 K, EIR). The minimal SR of FI and FIR modes are higher than 1.38 %K−1 and 1.08 %K−1 in 303–513 K temperature range. Above outstanding properties manifest the potentiality of CLZVO:Eu3+ for monitoring temperature.

Deep-Blue Organic Light-Emitting Diodes Employed Traditional Hole Transporting Material as Emitter for 31-Inch 4K Flexible Display

High-efficiency deep-blue organic light-emitting diodes (OLEDs) play a crucial role in realizing ultra-high-definition (UHD) flat-panel displays and reducing power consumption. Generally, most reported OLEDs with a Commission Internationale de L’Eclairage (CIE) y coordinate < 0.06 are achieved by traditional fluorescent deep-blue emitters. However, it is challenging to obtain deep-blue fluorescent OLEDs with a high external quantum efficiency (EQE) (reaching the theoretical limit of 5%). In this work, we have successfully employed a hole-transporting material for an emitter, which can increase the efficiency in deep-blue OLEDs. The device employed with the proposed hole-transporting material exhibits deep-blue emission peaks at 427.0 nm with CIE coordinates of (0.155, 0.051), a turn-on voltage (Von) of 4.5 V, and an EQE of 4.5%. The performance of the OLED can be improved by 5.0% by optimizing the device structure. Finally, the flexible display when using the OLED devices exhibited a high image quality.

White-light emission from yttrium iron garnet (YIG)

Single-phase phosphors that emit broadband white-light are needed for white-light-emitting diodes (wLEDs) to reach their full potential. However, it is challenging to achieve broad white-light emission from single-phase materials. Consequently, polycrystalline inorganic bulk compounds that emit white-light sans doping are rare. We report on broadband white-light emission from a well-known garnet compound, i.e., yttrium iron garnet (YIG), without activator-ion doping. Upon near-UV excitation at 370 nm, polycrystalline bulk YIG emits broadband white-light with (1931) Commission Internationale de L’Eclairage (CIE) coordinates as (0.28, 0.35) and correlated color temperature (CCT) as 8029 K. Variable excitation wavelengths ranging from 280 to 600 nm enable color-tunable emission as cyan-white-blue-green-yellow-orange-red, including near-white-light emission for a broad range of excitation from 325 to 390 nm. Moreover, a short lifetime (sub-nanosecond) is obtained, which is desirable for LED and other applications. We demonstrated the propriety of YIG as a single-phase converting phosphor for illumination by fabricating prototype wLEDs using commercial InGaN UV-LED chips (λ = 380 nm) for excitation. The CIE coordinates and CCT of prototype wLEDs were obtained as (0.34, 0.37) and 5284 K, respectively. We believe that the reported findings signify the great potential of YIG as a single-phase white-light-emitting phosphor for broadband emission, which offers a new perspective and a viable approach for the development of wLEDs.

Deep blue fluorescent emitters based imidazole and carbazole for non-doped organic light emitting diodes with CIEy≤0.05

Two fluorescent emitters based imidazole and carbazole were synthesized for deep blue emission organic light-emitting diodes (OLED) with non-doped structure. The photophysical, thermal and electrochemical properties are investigated with high decomposition temperature up to 391 and 380 °C, and strong deep blue emission. Single carrier devices were also fabricated to show that two compounds have good bipolar carrier transport characteristic. The non-doped fluorescent OLED devices using the two compounds as emitting layers are designed among which the devices achieved the maximum external quantum efficiency of 1.66% and 1.56%, respectively. Besides, the deep blue emission peak of 412 nm with Commission Internationale de l’Eclairage (CIE) coordinate of (0.16, 0.04), and 420 nm with CIE coordinate of (0.16, 0.05) were also realized. The small CIEy value of 0.04 and 0.05 obtained in this work are very significant for high color purity full-color display, which is also among the best CIEy value results ever reported as deep blue bipolar emitters.

Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1−xCaLa0.5Er0.05Yb0.45(MoO4)3 Upconversion Scheelite-Type Phosphors

New triple molybdates LixNa1−xCaLa0.5(MoO4)3:Er3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) were manufactured successfully using the microwave-assisted sol-gel-based technique (MAS). Their room-temperature crystal structures were determined in space group I41/a by Rietveld analysis. The compounds were found to have a scheelite-type structure. In Li-substituted samples, the sites of big cations were occupied by a mixture of (Li, Na, La, Er, Yb) ions, which provided a linear cell volume decrease with the Li content increase. The increased upconversion (UC) efficiency and Raman spectroscopic properties of the phosphors were discussed in detail. The mechanism of optimization of upconversion luminescence upon Li content variation was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. The UC luminescence maximized at lithium content x = 0.05. The mechanism of UC optimization was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. Over the whole spectral range, the Raman spectra of LixNa1−xCaLa0.5(MoO4)3 doped with Er3+ and Yb3+ ions were totally superimposed with the luminescence signal of Er3+ ions, and increasing the Li+ content resulted in the difference of Er3+ multiple intensity. The density functional theory calculations with the account for the structural disorder in the system of Li, Na, Ca, La, Er and Yb ions revealed the bandgap variation from 3.99 to 4.137 eV due to the changing of Li content. It was found that the direct electronic transition energy was close to the indirect one for all compounds. The determined chromaticity points (ICP) of the LiNaCaLa(MoO4)3:Er3+,Yb3+ phosphors were in good relation to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.

Thermally stable novel double perovskite orange-red emitting Sr2InTaO6:Sm3+ phosphors with high CRI for WLEDs

Novel double perovskite Sr2InTaO6:Sm3+ phosphors were synthesized by the high-temperature solid-state reaction. The phase purity, luminescent properties, and thermal stability were systematically investigated in this work. When monitoring the emission peak at 649 nm, Sr2InTaO6:Sm3+ phosphors present an absorption band due to the O2−→Sm3+ charge transfer. Under 407 nm excitation, Sr2InTaO6:5 mol%Sm3+ phosphor presents four emission peaks at 565, 603, 649, and 717 nm corresponding to the electron transition from 6G5/2 level to 6H5/2, 6H7/2, 6H9/2 and 6H11/2 levels, respectively. The best doping concentration of Sr2InTaO6:xSm3+ is optimized as x = 5 mol%. The chromaticity coordinates of Sr2InTaO6:xSm3+ show high color stability and are located in the orange-red region. The residual luminescence intensity at 480 K reaches 86.64%, proving it has excellent thermal stability. Internal quantum efficiency (IQE) is measured as 67.1%. The prepared WLED (white light emitting diode) has a low correlation color temperature (CCT = 4853 K) and an excellent color rendering index (CRI, Ra = 93) with CIE (Commission International de L′ Eclairage) coordinates (0.346, 0.349). Therefore, Sr2InTaO6:Sm3+ phosphors have excellent luminescent properties and promising application prospects.