Blue-green Emission Research Articles

Efficient multi-component PL emission tunning in single emissive layer (SEL) by amino-functionalized graphene quantum dots in type-II ZnSe/af-GQDs soft core/shell interface as an efficient phosphor

This research demonstrates first report on successful formation of ZnSe/amino functionalized graphene quantum dots (af-GQDs), type-II core-shell structures. The structures having potential as a single emissive layer (SEL), were synthesized via a facile and eco-friendly hot injection method. We achieved a highly efficient tuning of PL emission spectral components in visible region ranging from (∼458 to 750nm). The functional groups attached with af-GQDs rendered soft shell feature to the structures and the soft core-shell interface significantly passivated the strain-induced defect states and reduced Auger recombination (AR). The PL emission properties of ZnSe/af-GQDs were studied through steady state and temperature dependent photoluminescence (TDPL) spectroscopy within the temperature range (80-300k), using 457nm excitation laser. Three samples including bare ZnSe QDs, bare af-GQDs and ZnSe/af-GQDs core/shell structures were prepared. The steady state PL emission spectra revealed a weak blue and pronounced green, yellow, orange and red emission, whereas the full width half maximum (FWHM) of PL spectra distinctly decreased in ZnSe/af-GQDs. The carrier activation and escape energies of radiative and non-radiative recombination respectively were estimated through Arhenious and Brethelot fitting functions for TDPL measurements. The calculated values clearly indicated a decrease in activation energies and an increase in escape energies in ZnSe/af-GQD X-ray photon spectroscopy (XPS) measurements revealed the presence of Zn 2p and Se (3d) O1s and NIs orbitals of constituent elements including Zn, Se, C, O and N. Tight binding model was applied to estimate the valance and conduction band energies that suggested formation of type-II core-shell band alignment in the structures. The relative PLQY was estimated using comparative method and Rhodamine-B was used as reference and calculated PLQY are 58%, 61% and 83% for ZnSe, af-GQDs and ZnSe/af-GQDs. A mechanism of formation of a soft core-shell interface for ZnSe/af-GQDs is clarified. We suggest that ZnSe-/af-GQDs structures synthesized in this report have a great potential for LEDs and display devices in which multi-color components are of paramount importance, such as white light emission. This report may open a gate way for more and vivid possibilities to apply af-GQDs for optoelectronic devices.

Synthesis of a dual-emissive pyrene-based fluorescent probe for imaging intracellular viscosity

A pyrene-based fluorescent molecular probe (Py2-5EG) was synthesized for optical detection of viscosity variation. Py2-5EG was synthesized by the reaction of two hydroxyl groups at the two ends of pentaethylene glycol with pyrene via a two-step reaction. Unlike typical pyrene compounds, the monomer fluorescence of Py2-5EG was not observed even in a dilute solution. Instead, the monomer fluorescence gradually increased with the increase in solvent viscosity. Blue fluorescent emission was observed from the monomer in a more viscous medium, and greenish blue emission from excimer was dominant in a less viscous medium in which dynamic excimer formation was involved. The observed fluorescence change of Py2-5EG was ratiometric and depended on the solution viscosity. A microscopic change in cellular viscosity was clearly observed inside and outside the mitochondria of living cells via different fluorescence colors of blue and green. The viscosity inside and outside mitochondria was determined using the fluorescence colors. Py2-5EG featured noticeable fluorescence emission shift in response to viscosity, and this phenomenon can be applied as a fluorescent probe, estimating the viscosity of various solutions as well as inside living cells.

Multifunctionality of rare earth doped 0.925Na0.5Bi0.5TiO3-0.075K0.5Na0.5NbO3 ferroelectric ceramics

Undoped and RE3+ (RE: Pr; Nd; Dy; Ho; Tm) doped 0.925Na0.5Bi0.5TiO3-0.075K0.5Na0.5NbO3 (NBTKN0.075/NBTKN0.075-RE) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed a pure perovskite structure without secondary phases. The Ho, Dy and Tm ions revealed a dielectric curve with a more diffused phase transition associated with a high value of the dielectric constant, while the lowest diffusivities were found for the Nd and Pr ions doped NBTKN0.075. The ferroelectric hysteresis loops show the significant increase of polarization and electric breakdown strengths (BDS) in all doped samples, accompanied by P–E shape changes under the influence of the different RE3+ ions. In the optical studies, the conversion of near- infrared light to visible light was investigated for Ho3+ and Dy3+ doped NBTKN0.075. The sample with Ho3+ produced a strong green-yellow up-conversion (UC) emission. At an excitation of λex = 800 nm, the blue-green UC emission of the Dy ion showed that the UC is due to the energy transfer interaction. CIE diagram with the corresponding (x, y) coordinates were used to clearly identify the overall color of the multichromatic spectral emissions in each spectrum. The additional functionality of up-conversion emission in the ferroelectric NBTKN0.075-RE material, and its positive effects on the electrical proprieties, open the possibility to realize multifunctionality in a wide range of applications.

Schiff base-type Cu(I) complexes containing naphthylpyridyl-methanimine ligands featuring higher light-absorption capability: Synthesis, structures, and photophysical properties

Herein, the three novel copper (I) complexes bearing Schiff base ligands of the types [Cu(Methoxyphenyl-NaphthylPyridyl-Meth-Aniline)(POP)]PF6 (P1), [Cu(NaphthylPy-Methylene-Adam-Amine)(POP)]PF6 (P2), and [Cu(Dipp-NaphthylPyridyl-Meth-Aniline)(POP)]PF6 (P3) (Methoxyphenyl-NaphthylPyridyl-Meth-Aniline = 4-methoxyphenyl-N-((5-(naphthalen-1-yl)pyridin-2-yl)methylene)aniline, NaphylPy-Methylene-Adam-Amine = N-((5-(naphthalen-1-yl)pyridin-2-yl)methylene)adamantan-1-amine, Dipp-NaphylPyridyl-Meth-Aniline = 2,6-diisopropylphenyl-N-((5-(naphthalen-1-yl)pyridin-2-yl)methylene)aniline, POP = bis[2-diphenylphosphino]-phenyl)ether) have been prepared and investigated. The different groups such as methoxyphenyl, adamantyl and diisopropylphenyl were functionalized onto the azomethine unit of the Schiff base ligands to tune the photophysical behaviors of the resulting Schiff base Cu(I) complexes. All the complexes exhibit the lowest energy metal-to-ligand charge transfer (MLCT) characters in the visible region with higher molar extinction coefficients on the order of 104 M−1 cm−1, making them much attractive as photosensitizers in optoelectronic and light-harvesting applications. Blue-green emissions in the region of 479–513 nm with photoluminescence quantum yields (PLQY) of 0.8–1.2 % can be observed in CH2Cl2 solution. Additionally, the photophysical properties are also investigated theoretically using density functional theory (DFT) and time dependent DFT.

A comparative analysis on electrical and nonlinear optical properties of pure and Co–Ni co-doped SnO2 nanoparticles

Compared to bulk materials, nanostructured materials possess ultrafast optical response and strong two-photon absorption which leads to the utility of materials in various laser related applications. Hence, Cobalt (Co)-Nickel (Ni) co-doped SnO2 nanoparticles were synthesized via co-precipitation technique and its optical limiting behavior was studied. PXRD confirms the formation of tetragonal rutile SnO2with space group P42/mnm with decrease in crystallite size due to co-doping. Shift in PXRD peak position towards higher angle and suppression of Sn–O–Sn vibrational peaks confirm the intervention of Co2+ and Ni2+ ions into the SnO2 lattice. Upon co-doping, the band gap decreases (3.35, 3.28 and 3.20 eV) and the PL intensity of blue-green emission increases due to the increase in density of oxygen vacancies on the surface of SnO2. Low dielectric constant, dielectric loss and ac conductivity indicates the prepared materials are having lesser defects. Nonlinear optical (NLO) absorption and optical limiting behavior of developed NPs were recorded by Z-scan method (open aperture) using nano pulsed green laser excitation. Open aperture Z-scan curves with a valley-like pattern indicate the presence of reverse saturable nonlinear absorption due to the sequential two-photon absorption (2PA) process. The 2PA coefficient increases (0.27–0.56 ×10−10W/m) and onset optical limiting threshold decreases (4.5 –1.7 ×10−12W/m2) with increasing dopant concentration of Co–Ni (2 & 4 wt%) in SnO2 NPs. These results demonstrate that Co–Ni (4 wt%) NPs have virtuous dielectric and efficient NLO absorption and limiting properties which suggest that it could be an eminent candidate for the potential applications such as high-performance dielectric material and optical limiting components in optical devices.

Encapsulation of AIEgens within Metal–Organic Framework toward High‐Performance White Light‐Emitting Diodes

AbstractWhite light‐emitting diodes (WLEDs) have a wide range of applications in display and illumination, however, it is still challenging to achieve efficient solid‐state white light‐emitting (WLE) materials due to the conventional quenching effect. Herein, a strategy of encapsulating aggregation‐induced emission luminogens (AIEgens) into the pores of metal–organic framework (MOF) to achieve high‐performance WLED is proposed. Two cationic dyes, 2,3,4,5‐tetrakis(4‐methoxyphenyl)oxazol‐3‐ium (MOTPO) and 1‐methyl‐4‐(4‐(1,2,2‐triphenylvinyl)phenyl)pyridin‐1‐ium (TPEPy) with bright blue and yellowish green emissions, respectively, are synthesized and successfully incorporated into the pore of anionic MOF ZJU‐28. The synergy of AIE characteristics and confinement effect within hybrid material result in an enhanced emission signal in comparison to each of the individual components. The single‐phase WLE material with Commission International de L'Eclairage coordinates of (0.35, 0.34) and the quantum efficiency of 64.9% is realized by optimizing the ratio between the two guests, which is almost the best among the reported WLE MOF composites to date. The resulting WLED demonstrates the maximum external quantum efficiency of 12.67% accompanied by the excellent color‐rendering index and correlated color temperature of 86 and 4076 K, respectively. Moreover, the WLE flexible film is also achieved. This work will provide new insights and strategies for the design of efficient WLEDs in the future.

Rare earth (RE: La and Ce) elements doped ZnWO4 nanoparticles for enhanced photocatalytic removal of methylene blue dye from aquatic environment

In the present study, the enhanced photocatalytic behaviour of La:ZnWO4 and Ce:ZnWO4 nanoparticles produced by a simple co-precipitation technique is reported. The X-ray diffraction study suggested that La and Ce ions are harmoniously incorporated into the Zn2+ sites or interstitial sites within the ZnWO4 lattice without altering the monoclinic wolframite phase. The field emission scanning electron microscopic study showed the formation of spherical particles and nanorod-like morphology for La:ZnWO4 and Ce:ZnWO4 samples. The shrinkage in optical band gap energy of La and Ce doped ZnWO4 nanoparticles was realized owing to the effect of dopant concentration induced microstructural defects. The broad blue-green emission peak perceived at 350–600 nm regions is ascribed to the electronic transition from O2p to W5d orbitals. The highest surface area of 283.272 m2/g was obtained for 2% La doped ZnWO4 sample. The elemental composition of samples was ascertained by x-ray photoelectron spectroscopic study. La:ZnWO4 and Ce:ZnWO4 nanophotocatalysts showed an excellent dye removal efficiency towards the degradation of methylene blue than the pure ZnWO4 catalyst. This may be due to the fact that the RE ions (La and Ce) endorse the separation of photo-induced electron-hole pairs in ZnWO4.

A dual-emission Ba6Ca3Al2Si6O24: Eu2+, Mn2+ phosphor with energy transfer for plant-protecting LED lamps and ratiometric temperature

A series of dual-emitting Eu2+-Mn2+ co-doped Ba6Ca3Al2Si6O24 (BCASO) phosphors were prepared by a solid phase method at high temperature. The phosphors show a blue-green emission peaking at 500 nm and a red emission peaking at 600 nm under a single UV excitation, which facilitates the absorption of Chlorophyll a/b and Phytochrome PR, while avoiding excessive blue light damage to plants and energy wastage. The reason for the simultaneous appearance of blue-green and red light is the energy transfer from Eu2+ to Mn2+. The corresponding process has been investigated by analyzing the spectrum and the decay lifetime variations. In addition, we have explored the thermal stability of the phosphors, which is also an important parameter especially in plant lighting. We have unexpectedly found that Eu2+ and Mn2+ ions have different thermal reactions during the stability study, which has opened up the possibility for temperature detection. Therefore, we have discussed temperature measurement characteristics, such as the relationship between FIR and T, absolute sensitivity (Sa) and relative sensitivity (Sr). The results confirmed that the BCASO: Eu2+, Mn2+ phosphor might have great applicational potential in plant-protecting and optical temperature measurement.

Improvement of self-activated luminescence properties of Ca2KZn2(VO4)3 down-conversion materials by SSR method based on co-doped Eu3+,Dy3+ rare earth ions concentrations

In this study, a self-activated and co-doped Eu, Dy with Ca2KZn2(VO4)3 (CKZVO) phosphors were synthesized by conventional solid state reaction method. The powder X-Ray diffraction study confirm the formation of single phase cubic crystal structure with space group Ia3̅d. The surface morphology of as-synthesized phosphor was verified by SEM analysis. The FTIR spectrum shows characteristic bonds, for bending vibration and asymmetric stretching vibration. In photoluminescence under the UV excitations the CKZVO phosphor display greenish blue emission due to the VO4 transitions ions in host matrix. The PL characteristic of CKZVO: Dy3+ phosphors exhibits intense emission centred at 480 nm (blue) and 573 nm (yellow color). Moreover, CKZVO: Eu3+ phosphor exhibits strong emission at 500 nm (green) and 615 nm (Red) under UV excitation. Further co-doping of Dy3+, Eu3+ in the host matrix reveals a strong emission in blue, green, yellow and red region. The chromaticity coordinates of the samples were in near white region. All the results exhibit that CKZVO: Dy3+, Eu3+ phosphor might be a potential material for NUV-based white light-emitting diodes.

Highly luminescent copper nanoclusters as temperature sensors and “turn off” detection of oxytetracycline

Polyethyleneimine (PEI), playing roles as a templating agent, has been successfully applied to prepare blue-green-emitting copper nanoclusters (Cu NCs@PEI) on the basis of a rapid chemical reduction synthesis method. Some characterization methods, such as fluorescence spectrophotometer, UV spectrophotometer, Fourier transform infrared instrument (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and fluorescence lifetime, were used for the analysis of physical, chemical and optical properties of Cu NCs@PEI. The Cu NCs@PEI displayed a blue-green emission wavelength at 485 nm and the corresponding quantum yield (QY) was 2.24%. Subsequently, the as-synthesized Cu NCs@PEI were applied for the trace analysis of oxytetracycline on the basis of the inner filter effect (IFE) and static quenching, which caused the fluorescence to be effectively quenched. Additionally, this proposed platform based on the Cu NCs@PEI for oxytetracycline sensing possessed an excellent linear range from 0.5 to 300 μM with a lower detection limit of 0.032 μM (S/N = 3) and correlation coefficient R2 of 0.9972. Surprisingly, as the temperature increased, the fluorescence intensities of Cu NCs@PEI decreased gradually. Thence, the Cu NCs@PEI could be applied for the sensing of temperature. Finally, the practicability of the detection method have been successfully verified by analyzing oxytetracycline in real samples, enlarging its applicable fields for oxytetracycline sensing.

Structure, optical and magnetic properties of the pyridinium cobaltate (C6H9N2)2[CoCl4

The reaction of 2-amino-4-methylpyridine (L) with CoCl2·6H2O in hydrochloric acid gave the chlorocobaltate (HL)2[CoCl4] in 82% yield. X-ray diffraction of the blue crystalline material showed isolated [CoCl4]2– tetrahedra in the structure, connected to the aromatic 2-amino-4-methyl pyridinium cations through H bonding while the cations show π-stacking. FT-IR spectroscopy in conjunction with Hirshfeld surface analysis confirmed the importance of the 2-amino function in the cations for the hydrogen bonding. The material is thermally stable up to 270 °C. Intense UV–vis absorptions in the range 200–400 nm were assigned to π–π* transitions in the pyridinium cation, weaker features in the range 600–750 nm were due to ligand-field transitions in the d7 high-spin system [CoCl4]2–. Excitation at 370 nm led to an intense blue-green emission at λem = 473 nm attributable to excited π–π* states. The molar susceptibility measured over a range of 5–300 K reveals paramagnetic behavior at high temperature range with an effective magnetic moment of µeff = 4.74 µB indicating a significant spin–orbit coupling contribution adding to the spin-only value of 3.87 µB expected for Co(II) with 3d7 high spin configuration.

The blue-green emission color of Ag+, Gd3+ co-activated CdWO4 phosphor via energy transfer for luminescence applications

Ag+, Gd+3-doped CdWO4 (co-doped CWO) phosphor nanopowders were synthesized by an eco-friendly method and then embedded into the polymer matrix to produce a flexible and transparent thin film. A novel phosphor for the excitation by an ultraviolet source, 980 nm diode laser, and proton radiation was reported at room temperature and crystal structure, luminescent properties, and energy transfer between Ag+ and Gd+3 ions were thoroughly investigated. Elemental composition and chemical state analyses were measured using X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy studies. Crystal structure and phase identification were confirmed using powder X-ray diffraction measurement. Based on all results, the flexible phosphor film prepared has good thermal stability and efficient blue-green emission under UV light, laser, and proton excitation used in emissive displays applications.

Wearable, freezing-tolerant, and self-powered electroluminescence system for long-term cold-resistant displays

Tremendous efforts in wearable optoelectronics have recently harnessed considerable advances in intrinsically stretchable electroluminescence (EL) devices. However, developing wearable optoelectronics that maintain long-term stability in harsh cold environments is still challenging. Here, a wearable, freezing-tolerant, and self-powered EL system is developed based on organohydrogel-based EL (OH-EL) device integrated with liquid electrolyte-based single-electrode triboelectric nanogenerator (LE-TENG), in which the OH-EL device based on self-healing and highly conductive organohydrogel electrodes can be directly lit by the LE-TENG. The stretchable OH-EL device demonstrates a bright and uniform light emission under 140% tension stretching as well as severe mechanical deformations of bending, rolling, and twisting. Moreover, the optical performances of the OH-EL device exhibit excellent repeatability and durability after continuous 2000 cycles. More importantly, bright blue-green light emission of the self-powered EL system stored at 253 K can maintain for six months, demonstrating extremely long-term freezing-tolerant capability. Furthermore, while harvesting the biomechanical energy of hand slapping and knee/elbow bending, the self-powered EL system worn on different parts of human body can achieve real-time visualized displays. Consequently, the simple fabrication and unique operation of the self-powered EL system demonstrate potential application in cold-resistant displays, wearable self-powered photoelectric devices, soft robotics, and other fields.

Supercapacitor behaviors of carbon quantum dots by green synthesis method from tea fermented with kombucha

Quantum dots have good optical and electronic behaviors due to their smaller size and having changeable properties depending on the size owing to quantum confinement effect. They can be used in various applications such as solar cells, drug delivery, displays and supercapacitors. In this study, carbon quantum dots (CQD) with nitrogen containing have been synthesized by green synthesize technique from the Kombucha fungus and characterized by HRTEM, XRD, XPS, particle sizer, luminescence and UV–Vis spectrometers. While the XRD results confirmed the crystalline structure of the CQDs, HRTEM results revealed the size of CQDs as 5 nm. The luminescence spectroscopy results showed blue-green emission. The UV–Vis spectrometer affirmed absorption peaks of the carbon at around 250–330 nm wavelengths. The CQDs were used as electrode materials for supercapacitor structure and characterized by electrochemical analysis to determine charge-discharge profiles and capacity. The results revealed that the green synthesized CQDs can be employed and improved for supercapacitor applications.

Green Synthesis of Phosphorescent Carbon Dots for Anticounterfeiting and Information Encryption.

Room-temperature phosphorescent (RTP) carbon dots (CDs) have promising applications in bioimaging, anticounterfeiting, and information encryption owing to their long lifetimes and wide Stokes shifts. Numerous researchers are interested in developing highly bright RTP CDs using environmentally friendly and safe synthesis processes (e.g., natural raw materials and zero-pollution production pathways). In this study, we successfully synthesized RTP CDs using a hydrothermal process employing natural vitamins as a raw material, ethylenediamine as a passivator, and boric acid as a phosphorescent enhancer, which is referred to as phosphorescent CD (PCD). The PCDs exhibit both bright blue fluorescence emission and green RTP emission, with a phosphorescence lifetime as long as 293 ms and an excellent green afterglow visible to the naked eye for up to 7.0 s. The total quantum yield is 12.69%. The phosphorescence quantum yield (PQY) is up to 5.15%. Based on the RTP performance, PCDs have been successfully employed for anticounterfeiting and information protection applications. The results of this study provide a green strategy for the scalable synthesis of RTP materials, which is a practical method for the fabrication of RTP materials with high efficiency and long afterglow lifetimes.

Blue-green emitting LuASG:Ce phosphor ceramics with high luminous efficacy for high-power LEDs

Phosphor-converted blue-green emitting high-power LEDs (hp-LEDs) are essential for marine fishery and ocean optical communication. Here the blue-green emitting Sc3+-doped LuAG:Ce (LuASG:Ce) phosphor ceramics (PCs), as the phosphor converter of high-power LEDs (hp-LEDs), were successfully prepared by vacuum solid-state sintering based on the engineering of ion substitution. The influences of Sc3+ doping on the structure, optical and luminescence properties of LuAG:Ce were studied in detail. LuASG:Ce PCs owned blue-green emission from 510 nm to 501 nm. The emission intensity at 100 °C maintained more than 85% of the initial one, which exhibited significant thermal stability. Finally, the luminous efficacy (LE) as high as 127.59 lm/W and the emission peak at 503 nm were achieved from the LED encapsulated by Lu2.998Al4ScO12:Ce3+ with 50 W driving power. Thus, the blue-green emitting LuASG:Ce PCs will be promising phosphor converters for hp-LEDs.

Highly fluorescent carbon nitride oligomer with aggregation-induced emission characteristic for plastic staining

Polymeric carbon nitride often displays weak photoluminescence in solid state due to the aggregation-caused quenching effect. Herein, highly fluorescent carbon nitride oligomer (CNO) with aggregation-induced emission (AIE) characteristic was prepared via one-step solid-phase thermal condensation of 2,4-diamino-6-phenyl-1,3,5-triazine (DPT) at 350 °C. CNO is mainly composed of DPT dimer connected by rotatable imine groups, and exhibits weak fluorescence in the dispersed state and strong blue-green emission in the aggregated state and solid state. Density functional theory calculations indicate that the restriction of phenyl and triazine ring twisting motions is the main origin of the AIE phenomenon of CNO. Finally, CNO was preliminarily applied for fluorescent staining of plastic pellets. This work not only provides a solid-state strategy to synthesize fluorescent material with AIE characteristic but also extends the application of polymeric carbon nitride.

Mechanochemical synthesis of stable, quantum-confined CsPbBr3 perovskite nanocrystals with blue-green emission and high PLQY

Cesium lead halides are a family of bright, visible-light emitting materials with near-unity photoluminescence quantum yield (PLQY) in nanocrystals (NCs). The usual way to achieve visible light-emission tunability is by mixing halides, which often leads to phase separation and poor stability. While the NCs should also show size-dependent PL emission, reports on strong quantum confinement in these materials are scarce. Here, we report the synthesis of quantum-confined cesium lead bromide (CsPbBr3) NCs via a facile, environment-friendly, and scalable high-energy mechanochemical synthesis route. The PLQY measured is ∼85%, even after 90 days of synthesis, and the emission wavelength is shifted from green, 520 nm, to blue, 460 nm by quantum confinement in NCs of size 3–5 nm. Micro-PL optical spectroscopy and atomic force microscopy confirm the size tunability of PL on a single-dot scale. Our work demonstrates the potential of mechanochemical synthesis in the medium-scale production of bright luminescent quantum-confined NCs that could be extended to other materials as well.

Multi-conformational Luminescence and Phosphorescence of Few Phenazine 1,2,3-triazole Molecules.

Dropcast films produced from blends solutions of phenazine 1,2,3-triazole molecules in very lowconcentrations in a 1,3-Bis (N-carbazolyl) benzene (mCP) matrix were investigated at room tem-perature. The mCP acts as an optically inert matrix, having no influence on the emission propertiesof the guest molecules. Its conductive properties ensure the blend films as completely organic active layers. The fluorescent and phosphorescent emissions of the guest molecules in blue, green, red and also in white are relatively intense, without the need to mix different organic materials. The excitation of the system occurs directly by the incident laser beam on the films. The steady-state spectroscopy for the blue monomer and green dimer singlet fluorescence emissions were investigated. The analysis of their temporal decays was done using a different approach based on the Exponentially Modified Gaussian function. The phosphorescent emissions of the triplet steady-states, in the orange or in the red wavelength regions, were observed to be correlated, respectively, to the formation of guest monomers or to the guest dimers singlet states.

Highly efficient orange and white OLEDs based on ultrathin phosphorescent emitters with double reverse intersystem crossing system

Actualizing highly efficient organic light-emitting diodes (OLEDs) based on multiple doping technique is still a complicated manufacturing process and difficult to control precisely. In this paper, we reported high-efficiency and simplified orange and white OLEDs by combining ultrathin emitting layer with double reverse intersystem crossing (RISC) system. By doping thermally activated delayed fluorescence material into acceptor of interfacial exciplex as a sensitizer, the resulting orange OLEDs showed a maximum external quantum efficiency of 20.4%, which remained 18.7% at a luminance of 1000 cd/m2. In addition, the exciton quenching mechanism was explored by theoretical method, and the significance of novel design was understood by investigating excitons density experimentally. Furthermore, white OLED was achieved by restraining energy transfer between bluish-green emission layer and orange ultrathin layer, reaching maximum current efficiency and power efficiency of 52.4 cd/A and 60.9 lm/W with the Commission Internationale de L'Eclairage (CIE) coordinates variation of (0.002, 0.016) over a wide luminance range, which is one of the best performance in hybrid white OLED based on ultrathin-layer architecture.