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Ancillary ligand increases the efficiency of heteroleptic Ir-based triplet emitters in OLED devices
摘要： The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry. To improve future display technologies, higher electroluminescence efficiency is needed. Herein, the detailed study of the non-radiative decay mechanism employing density functional theory calculations is carried out and a simple, general strategy for the design of the ancillary ligand is formulated. It is shown that steric bulk properly directed towards the phenylisoquinoline ligands can significantly reduce the non-radiative decay rate.
关键词： photoluminescence quantum yield,non-radiative decay,OLED,Ir(III)-complexes,density functional theory
更新于2025-09-23 15:21:01
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Cyclometalated Ir(III) Complexes Towards Blue-Emissive Dopant for Organic Light-Emitting Diodes: Fundamentals of Photophysics and Designing Strategies
摘要： The main difficulties hindering development of a deep-blue phosphorescent cyclometalated Ir(III) complex are insufficient colour purity, i.e., failure to achieve ideal Commission Internationale de L’Eclairage (CIE) coordinates of (0.14, 0.09), and insufficient emission efficiency and stability. The latter problem is due to the highly energetic and hot excited states of these complexes, which yield faster decomposition. Therefore, control of the excited-state properties of cyclometalated Ir(III) complexes through systematic chemical modification of the ligands is being extensively investigated, with the aim of developing efficient and stable blue phosphorescent materials. The most common strategies towards achievement of a blue phosphorescent cyclometalated Ir(III) complex involve 1) substitution of electron-withdrawing F atoms at the cyclometalating ligands that stabilise the HOMO orbitals and 2) use of a heteropeltic system with electron-rich ancillary ligands bearing a 5-membered ring heterocycle to increase the LUMO energy level. However, the C–F bonds on the cyclometalating ligands have been found to be inherently unstable during device operation; thus, other types of electron-withdrawing groups (e.g., the cyano, trifluoromethyl, and sulfonyl groups) have been applied. Along with phosphorescence colour tuning to blue, the influence of the ligand structure on the photoluminescence quantum yield (PLQY) is also being intensively investigated. Two major PLQY lowering mechanisms for blue emissive Ir(III) complexes have been identified: 1) the vibronic-coupled non-radiative decay process and 2) crossing from the emissive state to an upper non-emissive 3MC excited state. To enhance the PLQY, mechanism 1) can be suppressed by employing rigid ligand frameworks to restrict intramolecular motion, whereas mechanism 2) can be prevented by destabilising the 3MC state using strong σ donor ligands such as N-heterocyclic carbenes. This review summarises the fundamental photophysics of cyclometalated Ir(III) complexes and surveys design strategies for efficient blue phosphorescent Ir(III) complexes, to provide a guide for future research in this field.
关键词： blue phosphorescent,3MC excited state,photoluminescence quantum yield,non-radiative decay,N-heterocyclic carbenes,cyclometalated Ir(III) complexes,OLEDs
更新于2025-09-23 15:21:01
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Morphological and optoelectronic investigations of CsPbBr3 nanocrystals chelating diphenylammonium halide ligands via low temperature synthesis
摘要： In this study, the low temperature method was adopted to synthesize all-inorganic cesium lead bromide CsPbBr3 nanocrystals (NCs) as the active layer in light-emitting devices. In order to improve film-forming and optoelectronic properties of CsPbBr3 NCs, a surface ligand diphenylammonium bromide (DPABr) was added from 0 to 0.15 mole fraction in proportion to the amount of oleylamine. The experimental results showed that introducing 0.1 mole fraction of DPABr in CsPbBr3 NCs brought the best performance. The SEM and AFM results revealed that smooth and pinhole-free films of CsPbBr3 NCs were formed by introducing DPABr with a low surface roughness of 4.6 nm. The introduced bromide ions can passivate the surface vacancies of CsPbBr3 NCs and improve photoluminescence quantum yield (PLQY) from 38% to 72% compared with the pristine CsPbBr3 NCs. Moreover, shorter and π electron-rich phenyl groups help to increase carrier injection into nanocrystalline core, preventing carriers from being hindered by oleic acid and oleylamine with longer alkyl chains. Therefore, the conductivity of the resulting CsPbBr3 NCs was augmented. The maximum brightness and current efficiency of the optimized device based on CsPbBr3 NCs with 0.1 mole fraction of DPABr were enhanced 2.3- and 3.3-fold, respectively, relative to the pristine one.
关键词： perovskite nanocrystals,low temperature method,photoluminescence quantum yield,surface passivation,diphenylammonium bromide
更新于2025-09-23 15:21:01
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Annealing CsPbX <sub/>3</sub> (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention
摘要： Annealing perovskite nanocrystals at high reaction temperature changes their crystal phase, shape, and optical properties. Carrying out reactions between 180 and 250 °C, the impact of thermal annealing for CsPbCl3 and CsPbBr3 nanocrystals in a reaction ?ask was investigated here. At higher temperature, a phase change was observed instantly, which could not be trapped even with ice-bath cooling. Interestingly, using a calculated amount of preformed alkylammonium halides as dual passivating agents, the nanocrystals of both CsPbCl3 and CsPbBr3 could even be stabilized for hours of annealing at 250 °C. CsPbCl3, which was reported to be a poor emissive nanocrystal in comparison to CsPbBr3, could sustain even more than 5 h of annealing at 250 °C and recorded ～51% absolutely quantum yield. Details of the interface chemistry and the role of the used dual passivating agent for providing thermal stability are studied and reported in this Letter.
关键词： thermal annealing,quantum yield,phase change,dual passivating agents,perovskite nanocrystals
更新于2025-09-23 15:21:01
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Carbon Dots as Theranostic Agents || Carbon Dots for Cell Imaging and Diagnostics
摘要： Not only CDs, but many carbon allotropes showing graphitic structure, i.e., honeycomb-like arrangement of carbon atoms, have shown potential for various applications in electronic devices in biosensors and bioimaging agents. Some examples of these are 0D fullerene [274], diamond nanocrystals [123] and carbon dots (CDs), as well as 1D CNT [275], 2D graphene QD (GQDs) [276] and graphene [277]. However, it must be mentioned here that although CDs and GQDs have similar quantum-confined fluorescent carbon materials, CDs have been more used as biosensors and bioimaging agents [278]. Both CD and GQD are mainly composed of sp2 carbon, oxygen and nitrogen elements and other doped heteroatoms [24, 101]; the different spatial arrangements of carbon atoms exhibit distinctive physical and chemical properties [279]. Unlike GQD, the CDs do not have perfect crystal structures [42]. Moreover, CDs exhibit luminance at size < 10 nm, whereas GQDs have size up to 100 nm [280, 281] and are luminescent. Generally, CDs display strong optical absorption in the UV region, with a tail extending out into the visible range (Figure 5.1a), i.e., 280–360 nm. The absorption band could be regulated via surface passivation or modification. CDs show the excitation-dependent emission properties in wavelength and intensity (Figure 5.1b). Other properties that make CD more applicable for biomedical applications are their low cost, high quantum yield, abundant source, low cytotoxicity, and superior chemical and photo stability. Wang et al. [282] have evaluated the cytotoxicity of the CDs prepared by different combinations of precursor of CDs and molecules used for surface functionalization. It is found that in terms of their nanoscale structure and configuration CDs are not intrinsically cytotoxic. The cytotoxicity of CD depends on the selection of surface passivation molecules.
关键词： quantum yield,theranostic agents,bioimaging,carbon dots,photoluminescence,biosensors,cytotoxicity
更新于2025-09-23 15:21:01
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Regionalization and Dynamic Parameterization of Quantum Yield of Photosynthesis to Improve the Ocean Primary Production Estimates From Remote Sensing
摘要： Quantum yield of photosynthesis (φ) expresses the efficiency of phytoplankton carbon fixation given certain amount of absorbed light. This photophysiological parameter is key to obtaining reliable estimates of primary production (PPsat) in the ocean based on remote sensing information. Several works have shown that φ changes temporally, vertically, and horizontally in the ocean. One of the primary factors ruling its variability is light intensity and thereby, it can be modeled as a function of Photosynthetically Available Radiation (PAR). We estimated φ utilizing long time-series collected in the North Subtropical Oligotrophic Gyres, at HOT and BATS stations (Pacific and Atlantic oceans, respectively). Subsequently the maximum quantum yield (φm) and Kφ (PAR value at half φm) were calculated. Median φm values were ～0.040 and 0.063 mol C mol photons?1 at HOT and BATS, respectively, with higher values in winter. Kφ values were ～8.0 and 10.8 mol photons m?2 d?1 for HOT and BATS, respectively. Seasonal variability in Kφ showed its peak in summer. Dynamical parameterizations for both regions are indicated by their temporal behaviors, where φm is related to temperature at BATS while Kφ to PAR, in both stations. At HOT, φm was weakly related to temperature and its median annual value was used for the whole data series. Differences in the study areas, even though both belong to Subtropical Gyres, reinforced the demand for regional parameterizations in PPsat models. Such parameterizations were finally included in a PPsat model based on phytoplankton absorption (PPsat?aphy?based), where results showed that the PPsat?aphy?based model coupled with dynamical parameterization improved PPsat estimates. Compared with PPsat estimates from the widely used VGPM, a model based on chlorophyll concentration (PPsat?chl?based), PPsat?aphy?based reduced model-measurement differences from ～62.8 to ～8.3% at HOT, along with well-matched seasonal cycle of PP (R2 = 0.76). There is not significant reduction in model-measurement differences between PPsat?chl?based and PPsat?aphy?based PP at BATS though (37.8 vs. 36.4%), but much better agreement in seasonal cycles with PPsat?aphy?based (R2 increased from 0.34 to 0.71). Our results point to improved estimation of PPsat by parameterized quantum yield along with phytoplankton absorption coefficient at the core.
关键词： quantum yield of photosynthesis,ocean color,phytoplankton primary production,in situ measurements,dynamical parameterization,marine seasonal variability
更新于2025-09-23 15:21:01
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Highly luminescent and stable CH3NH3PbBr3 quantum dots with 91.7% photoluminescence quantum yield: Role of guanidinium bromide dopants
摘要： Although perovskite quantum dots (PQDs) have received considerable attention, defects in PQDs can significantly degrade the properties and device performance. In this study, we report on an effective strategy for synthesizing highly luminescent CH3NH3PbBr3 quantum dots (QDs) by a simple doping. To remove such defects, guanidinium bromide (GuBr) was doped into the CH3NH3PbBr3 QDs synthesized by the ligand-assisted reprecipitation technique. From XRD and TEM studies, the doping of GuBr into the QD lattices was verified. In addition, the surfaces of PQDs with and without GuBr dopants were analyzed by XPS to trace the metallic Pb acting as a major recombination center. The GuBr doping resulted in the size uniformity of QDs and effectively eliminated defects and metallic Pb, which enhanced the photoluminescence quantum yield (PLQY) through the inhibition of the non-radiative recombination pathway. Furthermore, the recombination dynamics in the QDs were examined by using time-resolved photoluminescence and fluorescence lifetime imaging to verify the role of GuBr dopants. By optimizing the amount of GuBr doping, the CH3NH3PbBr3 QDs with strong green emission achieved a maximum PLQY of 91.7%.
关键词： Photoluminescence quantum yield,Fluorescence lifetime imaging,CH3NH3PbBr3 quantum dots,Guanidinium bromide,Recombination centers
更新于2025-09-23 15:19:57
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Evaluation of the optical absorption/emission spectral behavior of the Cd1-xDyxSe quantum dots synthesized via cation exchange approach
摘要： Cd1-xDyxSe nanocrystalline quantum dots were synthesized via cation exchange approach for the first time. The as-synthesized Cd1-xDyxSe nanocrystals showed a cubic phase at all Dy ion contents. The formed nanoparticles of the as-synthesized Cd1-xDyxSe nanocrystals were spherical like shape and their diameters increased from 2.1–7.3 nm with increasing the amount of Dy ions. The doping of CdSe with Dy atoms comprises a read shift of the optical absorption spectral curves. Therefore, a decrease of the optical band gap from 2.58 eV to 2.15 eV owing to the increase of Dy atoms took place. The partial substitute of the Cd atoms by Dy atoms instigated remarkable enhancing of the of luminescent intensities by eight order of magnitudes, made the PL peaks more sharper by four orders and achieved enlargement of the quantum yield to reach to value of 93 %. A decrease of the Stokes shift due to the doping by the Dy atoms was reasoned to the passivation of the defects. The enlargement of luminescence intensity, the creation of narrow emission band and the high quantum yield value empowered the as-synthesized Cd1-xDyxSe nanocrystals to be employed as laser materials for the manufacturing of multicolor laser diodes.
关键词： Absorption,Crystal structure,Quantum yield,Quantum dots,Luminescence
更新于2025-09-23 15:19:57
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Influence of photoactivation on luminescent properties of colloidal InP@ZnS quantum dots
摘要： The use of photo- and thermoactivation during the liquid-phase synthesis of colloidal quantum dots was found to yield luminescing InP@ZnS quantum dots with a luminescence quantum yield close to unity. Activation mode was found to have little or no influence on the maximal luminescent efficiency but affect particle size distribution. Compared to thermal activation, photoactivation ensures the formation of more monodispersed particles.
关键词： Colloidal quantum dots,Thermoactivation,Indium phosphide,Luminescence quantum yield,Photoactivation
更新于2025-09-23 15:19:57
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Highly Efficient Orange Emissive Graphene Quantum Dots Prepared by Acid-Free Method for White LEDs
摘要： Graphene quantum dots (GQDs) have wide prospective applications for optoelectronic fields owing to their unique characteristics, such as tunable bandgaps, high chemical and optical stability, as well as good biocompatibility. In this work, we offered a convenient proposal to obtain uniform blue-green emissive GQDs and modified efficient orange-emitting graphene quantum dots (D-GQDs) derived from fullerene (C60) under acid-free condition. The as-prepared D-GQDs demonstrate remarkable conversion efficiency which quantum yield is up to 52.4% with the emission peak of 617 nm. Also, GQDs and D-GQDs were blended with poly(vinyl alcohol) (PVA) to prepare transparent photo-luminescent films, which show excellent flexibility and preferable white emission property meeting the requirements of commercial white LEDs.
关键词： Graphene quantum dots,Quantum yield,Acid-free condition,WLEDs
更新于2025-09-23 15:19:57