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Tetraphenylimidazole-based luminophores for explosive chemosensors and OLEDs: experimental and theoretical investigation
摘要： Four different small molecular weight tetraphenylimidazole (TPI) derivatives were synthesized and characterized. The photophysical properties, solvatochromism, ?uorescence decays and electrochemical behaviours were discussed. All luminophores showed very high selectivity towards picric acid (PA) among all other nitroaromatics. All synthesized TPI luminophores showing good selectivity and high sensitivity, not only can detect PA in solution but can also be used in the contact mode for PA in thin-layer chromatography plates. The sensing mechanism was carefully studied by using nuclear magnetic resonance and density functional theory (DFT) studies. The optimal geometries and singlettriplet levels were calculated theoretically by using DFT and time-dependent DFT methods. Furthermore, examinations were carried out to know the optical, electronic, charge transport and stability properties of TPI derivatives as emissive and charge transport materials for organic light-emitting devices (OLEDs). Furthermore, all the TPI derivatives were used as emissive component for fabrication of OLED devices (I and II types) with multilayer con?guration via solution process. The device con?gurations are ITO/PEDOT:PSS/CBP:TPI-1, TPI-2, TPI-3 and TPA-4/TPBi/LiF/Al and ITO/PEDOT:PSS/TPI-1, TPI-2, TPI-3 and TPA-4/TPBi/LiF/Al for doped (device II) and non-doped (device I) devices, respectively. Compared with all, the luminophores containing non-?uorinated linker (CH3-phenyl) showed deep-blue electroluminescence (Commission International de L'Eclairage [CIE], x ? 0.20, y ? 0.17), whereas the ?uorinated linker (CF3-phenyl) containing luminophores exhibited bright-blue emission (CIE, x ? 0.23, y ? 0.21) with 1.4% external quantum ef?ciency.
关键词： Organic light emitting diodes,Sensing,DFT and TD-DFT,Lifetime
更新于2025-09-12 10:27:22
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Equivalent Circuit of Quantum-Dot LED and Acquisition of Carrier Lifetime in Active Layer
摘要： We propose an equivalent circuit for a quantum-dot LED (QLED), where the resistances and the capacitances are expressed in terms of the physical parameters of the QLED. The validity of the equivalent circuit is verified by measurement results. From the measured frequency response of the QLED and the calculated frequency response of the equivalent circuit, we are able to deduce the carrier lifetime in the active layer of the QLED. The availability of the equivalent circuit can facilitate the analysis of the electrical characteristics of QLEDs.
关键词： Quantum-dot light-emitting diode,frequency response,carrier lifetime,equivalent circuit
更新于2025-09-12 10:27:22
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Broad tunability of emission wavelength by strain coupled InAs/GaAs <sub/>1???x</sub> Sb <sub/>x</sub> quantum dot heterostructures
摘要： Tuning of the photoluminescence emission over a wider range of optical telecommunication wavelength (1.38 μm–1.68 μm) has been achieved by employing a GaAs1 ? xSbx capping layer to the strain coupled bilayer InAs quantum dot (QD) heterostructures. It is shown that the modulation of strain between the two dot layers through variation in Sb-content and thickness of the capping layer strongly influence the dot size. The band alignment transformation from type-I to type-II is observed for high Sb-content in the capping layers. In addition, the carrier lifetime is improved by a factor of three in the QD heterostructures having type-II band alignment. This, we believe, is of importance for optoelectronic device applications.
关键词： GaAs1 ? xSbx capping layer,carrier lifetime,optoelectronic device applications,photoluminescence emission,strain coupled bilayer InAs quantum dot,type-I to type-II band alignment,optical telecommunication wavelength
更新于2025-09-12 10:27:22
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Studying the Effect of Doping with Nickel on Silicon-Based Solar Cells with a Deep p–n-Junction
摘要： It has been shown that the doping of the front side of a solar cell with a deep-level p–n junction with nickel atoms increases short-circuit current density Jsc by 89% and open-circuit voltage Voc by 19.7%. Additional thermal treatment at 700°C for 1 h increases Jsc by 98.4% and Voc by 13.18%. It is presumed that the IR radiation conversion efficiency grows because nickel atoms form clusters, these being getter centers for uncontrolled recombinant impurities.
关键词： photocell,silicon,nickel,lifetime,collection coefficient,thermal annealing,clusters,doping
更新于2025-09-12 10:27:22
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Detailed description of the transient effect of radiative carrier transition in the bulk of semiconductor: The case of gallium antimonide
摘要： Upon solving the differential equation related to the rate of accumulation of photo-generated carriers in the respective bands of GaSb that involve radiative generation-recombination mechanisms under constant illumination in the entire bulk of the material, the transient response (time dependence) of the photo-generated carrier density and the excess carrier lifetimes during illumination and after switching-off illumination are described for a system under different injection levels. The rates of variations of the photo-generated carrier density and the radiative excess carrier lifetimes at the initial stages of the illumination and after switching-off illumination are evaluated at different injection levels. The injection level dependences of the effective values of the photo-generated carrier density and the radiative excess carrier lifetimes are described. The competition of the thermal and the illumination effects in the band to band radiative recombination mechanism is also described thoroughly.
关键词： generation,recombination,Excess carriers,lifetime,transient effect,effective values
更新于2025-09-12 10:27:22
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Fluorescence coupled with electrochemical approach at the bulk and the interface region of hydrogen-bonding self assemblies of urea derivatives with DDP dye in aqueous solution
摘要： Photophysical and electrochemical techniques were employed to hydrogen-bonding self assemblies forming solutes (Urea, Dimethylurea and Tetramethylurea) in the presence of 4-dicyanomethylene 2, 6-dimethyl-4H-pyran (DDP) dye. Addition of urea derivatives to DDP dye (Intramolecular Charge Transfer (ICT)) results in a fluorescence enhancement accompanied with a significant shift. Fluorescence lifetime behavior exhibits a tri-exponential decay with a large variation in the fluorescence lifetime and relative amplitude distribution. The co-existence of three different fluorescence lifetime components of DDP with urea derivatives signifies the existence of heterogeneous micro environment. The dye is surrounded by varying proportion of solute and water molecules are established from fluorescence lifetime studies. Urea derivatives govern the excited state characteristics of DDP dye resulting in the formation and promotion of different microenvironment which are clearly distinguishable. The existence of multi environment attributed to urea-water structural behaviour is authenticated by electrochemical impedance spectral studies (EIS). A large variation in the contour pattern, shape and intensity in 3D fluorescence contour spectra of dye with urea validate the existence of dye in a heterogeneous micro environment. The hydrophobicity of urea derivatives along with the hydrogen-bonding properties of urea-water and urea-urea influence the photophysical and electrochemical nature of dye is emphasized.
关键词： Hydrogen-bonding,Urea derivatives,Fluorescence lifetime,Electrochemical impedance spectra,Fluorescence emission,DDP dye
更新于2025-09-12 10:27:22
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Preparation and luminescence properties of Dy3+-doped Na3Gd(PO4)2 nanophosphor for solid state white LEDs
摘要： White emitting Na3Gd(PO4)2 nanocrystalline phosphors doped with trivalent dysprosium (Dy3+) ions were synthesized by using citrate gel combustion technique. The structure of the compound is found to be orthorhombic with a particle size is 10 nm. Luminescence properties have been characterized using photoluminescence (PL), excitation, emission spectra and decay time measurements. In emission spectrum sharp emission peaks were observed 4F9/2 → 6H15/2 (blue) and 4F9/2 → 6H13/2 (yellow) transition of Dy3+ ions. From the concentration dependent PL studies, the optimum concentration of Dy3+ ions in Na3Gd(PO4)2 is found to be 1.0 mol %, where intense near white light for 352 nm pump wavelength. The yellow to blue intensity ratios, CIE chromaticity coordinates and correlated color temperature studies has shown the possibility of using this phosphor for W-LEDs.
关键词： Spectroscopic,Dy2O3,Color coordinates,Lifetime,White light emission
更新于2025-09-12 10:27:22
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The spectroscopic properties of the low-lying excited states and laser cooling scheme of SrBr molecule
摘要： The potential energy curves and the transition dipole moments for seven electronic states of SrBr molecule are obtained via the multi-reference configuration interaction method and the all-electron basis sets. The Davidson and relativistic corrections are also included. Based on the obtained potential energy curves, the rotational and vibrational energy levels of each electronic state are determined by solving the nuclear motion equation of the molecule. The spectroscopic parameters are fitted from the obtained energy levels by using Dunham expression. Moreover, the spin-orbit coupling splits of the A2Π state are considered to construct the optical laser cooling scheme. The Frank-Condon factors, radiation lifetimes, radiation widths between the ground electronic state and 2Π1/2, 3/2/B2Σ+ states are calculated. Then, the feasibility of laser cooling is explored and the optical scheme is proposed. The results demonstrate that the SrBr molecule is a promising candidate for laser cooling.
关键词： Frank-Condon factors,optical scheme,laser cooling,Radiative lifetime,Spectroscopic parameter
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 12th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives (SDEMPED) - Toulouse, France (2019.8.27-2019.8.30)] 2019 IEEE 12th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives (SDEMPED) - Parametric degradation model of OLED using Design of Experiments (DoE)
摘要： This article presents an original parametric degradation model using Design of Experiments. This method is based on the estimation of a Weibull function under accelerated conditions. It is applied on cold white organic light emitting diodes OLEDs from Philips with a 10000 hrs theoretical lifetime. Accelerated degradation using thermal and electrical stress is tested. The predicted degrading model is a function of time, temperature, current density and their interaction. It illustrates the behaviour of the degradation of the OLED using multiple stress factors without really knowing the physics of these degradations. The proposed model is tested on experimental data for different luminances. The average error of the predicted model compared to real values is around 3 %. The proposed model is then compared to a previously developed lifespan model. The results obtained with the present approach are closer to the real values.
关键词： Degradation,Electrical stresses,Modeling,Thermal stresses,Design for Experiments,Accelerated aging,Organic light emitting diodes,Weibull distribution,Lifetime estimation
更新于2025-09-12 10:27:22
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45.2: Long Lifetime Electron Transporting Materials for AMOLED
摘要： A series of new electron transporting materials with good thermal stability were designed and developed. The devices of this ET-1 applied in top fluorescent blue devices, top green phosphorescent device and top phosphorescent red device, exhibited high efficiency and long lifetime with blue index of 162 and the LT95 lifetime is around 2100 h under 500 cd/m2.
关键词： long lifetime,high efficacy,electron transport
更新于2025-09-12 10:27:22