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Impact of t-butyl group on the singlet-triplet energy gap via weak orbital overlap of [1,2,5]-thiadiazolo[3,4-C]pyridine based TADF emitters: Structural modification
摘要： We theoretically investigated the combination of D-A and D-spacer (phenyl ring) -A with an electron donating alkyl (t-butyl) group. The strategy of twisting the geometry of the molecule with the alkyl substituents exclusion of strong electron withdrawing or donating groups leads to gain efficient deep blue-blue TADF emitter through maintaining the band gap while the reduction of singlet-triplet energy gap (EST). The t-butyl group strongly twisted the conformation of molecules by the steric hindrance resulted in weak HOMO and LUMO overlap (IH/L) and efficient spatial separation of HOMO and LUMO (rH/L) in the S0 state. In contrast, designed molecules S1 state own large HOMO and LUMO overlap of excited singlet state (IS) and inefficient spatial separation of HOMO and LUMO. The computed results indicated that introducing alkyl group into the phenyl ring of the acceptor of the designed molecules cannot affect the ΔEST. The ΔEST is mainly related to the IH/L, which can be adjusted by tuning the orbital IH/L. The large modular orbital overlap at S1 and T1 excited states resulted large ΔEST occurs in the range of 0.38 to 0.59eV whose dominant contribution switches from charge transfer (CT) to local excitation (LE). Our studied results reiterate (10.1038/srep10923) that modular orbital overlap of IS, HOMO and LUMO overlap of excited triplet state IT, spatial separation of HOMO and LUMO in the excited singlet state (rS) and spatial separation of HOMO and LUMO in the excited triplet state (rT) are the essential factors to determine ΔEST when inconsistencies between ΔEST and IH/L. Increasing the dihedral angle between D and A from molecule 1-4 (9-12), decrease the transition dipole moment which lowering the oscillator strength. When changing the connection position between D and A, molecules 5-8, the oscillator strength reduced to half with respect to molecules 1-4 and 9-12. The present work provides a theoretical understanding of the impact of alkyl substituents on the overlap of HOMO-LUMO resulting to tuning the ΔEST, as well as its influence on the oscillator strength may be a reliable idea to design efficient TADF emitters.
关键词： [1,2,5]-thiadiazolo[3,4-C]pyridine,HOMO-LUMO orbital overlap,fluorescence radiative decay rate,TADF,singlet-triplet energy gap
更新于2025-09-23 15:21:01
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Tailoring of graphene quantum dots for toxic heavy metals detection
摘要： The sensitivity of graphene quantum dots towards toxic heavy metals (THMs; Cd, Hg, Pb) can be improved through doping with nitrogen at the vacant site defects. Using density functional theory, we investigate the adsorption of THMs on the graphene quantum dots (GQDs) and nitrogen-coordinated defective GQDs (GQD@1N, GQD@2N, GQD@3N and GQD@4N) surfaces. Thermochemistry calculations reveal that the adsorption of Pb atom on the surfaces is more favorable than Cd and Hg adsorption. The decoration of the vacant defects with nitrogen on the GQD surface substantially increases the charge transfer and adsorption energy values of THMs on the GQD surface (GQD@4N > GQD@3N > GQD@1N > GQD@2N > GQD). The charge transfer and adsorption energy of lead on each of these surfaces are greater than those of cadmium and mercury (Pb > Cd > Hg). Quantum theory of atoms in molecules analysis and non-covalent interaction plots further validate this result while also confirming that Pb atom has a partially covalent and electrostatic nature of interaction at the nitrogen-coordinated vacant site defects. The electron density values—a criterion of bond strength—for the THM...N interactions are greater than for the THM…C interactions, confirming the observed adsorption energy trends of the THMs on the surfaces. The lowering of the HOMO–LUMO energy gap of the surfaces follows the order Pb > Cd > Hg and also results in increased electrical conductivity, which are consistent with the calculated adsorption energy trends. Significant changes in the energy gap and electric conductivity of the surfaces upon THMs adsorption make them promising sensors for metal detection. Finally, time-dependent density functional theory calculations showed that changes such as peak shifts, peak quenching and appearance of new peaks are seen in the UV–visible absorption spectra of the surfaces upon adsorption of THMs, wherein the shifts in peaks correspond to the magnitude of adsorption energy of THMs on the surfaces. These results should motivate the experimentalists towards using rational and systematic modulation of surfaces as sensors for heavy metal detection.
关键词： Adsorption energy,Toxic heavy metals,Charge transfer,UV–visible absorption spectra,Nitrogen doping,Density functional theory,HOMO–LUMO energy gap,Graphene quantum dots
更新于2025-09-16 10:30:52
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Efficiency enhancement in PbS/CdS quantum dot-sensitized solar cells by plasmonic Ag nanoparticles
摘要： Semiconductor quantum dots (Q-dots) are attractive nanomaterials to be used in numerous research areas and device fabrication such as sensors, transistors, and solar cells due to their unique optoelectronic properties. Quantum dot-sensitized solar cells (QDSSCs) have drawn considerable attention due to their cost-effectiveness and ability of multiple exciton generation and tunable energy gap of the quantum dots. In this study, plasmonic Ag colloidal nanoparticle-incorporated plasmonic TiO2 double-layer (nanofiber/nanoparticle) electrodes have been fabricated. These TiO2 electrodes were sensitized with PbS/CdS core-shell quantum dots by successive ionic layer adsorption and reaction (SILAR) technique, and QDSSCs were fabricated with polysulfide electrolyte. Cu2S was formed on brass plate and used as the counter electrode of the QDSSC. A higher power conversion efficiency of 4.09% has been obtained due to the plasmonic effect under the simulated light of 100 mW cm?2 with AM 1.5 spectral filter. The overall efficiency and short-circuit current density of the plasmonic QDSSC are enhanced by 15% and 23%, respectively, with respect to the QDSSC without Ag nanoparticles. The enhanced performance of the plasmonic QDSSC is evidently due to the enhanced optical absorption by localized surface plasmon resonance effect by the Ag nanoparticles in the TiO2 photoanode and the resulting increase in the short-circuit photocurrent.
关键词： Energy gap,Ag nanoparticles,Surface plasmon resonance,Quantum dots,Multiple exciton generation
更新于2025-09-16 10:30:52
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Designing dithienonaphthalene based acceptor materials with promising photovoltaic parameters for organic solar cells
摘要： Scientists are focusing on non-fullerene based acceptors due to their efficient photovoltaic properties. Here, we have designed four novel dithienonaphthalene based acceptors with better photovoltaic properties through structural modification of a well-known experimentally synthesized reference compound R. The newly designed molecules have a dithienonaphthalene core attached with different 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (H1), 2-(5,6-dicyano-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (H2), 2-(5-methylene-6-oxo-5,6-dihydrocylopenta[c]thiophe-4-ylidene)-malononitrile (H3) and 2-(3-(dicyanomethylene)-2,3-dihydroinden-1-yliden)malononitrile (H4) acceptor moieties (end-capped). The photovoltaic parameters of the designed molecules are discussed in comparison with those of the reference R. All newly designed molecules show a reduced HOMO–LUMO energy gap (2.17 eV to 2.28 eV), compared to the reference R (2.31 eV). Charger transfer from donor to acceptor is confirmed by a frontier molecular orbital (FMO) diagram. All studied molecules show extensive absorption in the visible region and absorption maxima are red-shifted compared to R. All investigated molecules have lower excitation energies which reveal high charge transfer rates, as compared to R. To evaluate the open circuit voltage, the designed acceptor molecules are blended with a well-known donor PBDB-T. The molecule H3 has the highest Voc value (1.88 V). TDM has been performed to show the behaviour of electronic excitation processes and electron hole location between the donor and acceptor unit. The binding energies of all molecules are lower than that of R. The lowest is calculated for H3 (0.24 eV) which reflects the highest charge transfer. The reorganization energy value for both the electrons and holes of H2 is lower than R which is indicative of the highest charge transfer rate.
关键词： absorption maxima,binding energies,reorganization energy,photovoltaic properties,open circuit voltage,charge transfer,dithienonaphthalene,HOMO–LUMO energy gap,non-fullerene based acceptors
更新于2025-09-12 10:27:22
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Micro-structural, optical and vibrational spectra analysis of Lead sulphide, Cadmium doped PbS and Strontium doped PbS nano-structured thin films synthesized through Successive Ionic Layer Adsorption and Reaction technique for solar cell and infrared detector sensor applications
摘要： Nanostructured skinny or thin films have captivated or fascinated the research network all over the entire world. Successive Ionic Layer Adsorption and Reaction technique is well suited for producing large area deposition and multilayer thin films especially for solar cell like Dipping time, precursor concentration and number of process cycle. In the present investigation lead Sulphide (PbS), cadmium and strontium doped PbS thin films are deposited on a glass substrate by SILAR process at room temperature to study the various morphological, structural and optical properties of them.
关键词： Cadmium doped PbS,SILAR technique,Lead sulphide,Strontium doped PbS thin films,Energy gap
更新于2025-09-11 14:15:04
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Influence of cobalt-doping on the optical properties of zinc tris–thiourea sulfate (ZTS) single crystal
摘要： Zinc tris-thiourea sulfate (ZTS) single crystals, pure and doped with different concentrations of cobalt, were synthesized and grown by the slow evaporation technique of supersaturated aqueous solutions at 315 K. Co2+ concentration in the solution was 2, 4 and 6 mol%. Optical transmittance was measured for the obtained crystals as a function of wavelength in the range of 190–900 nm. The present investigation shows that doping ZTS crystal with Co2+ changes the values of optical transmittance, cut off wavelength, absorption coefficient of ZTS crystal exhibits an exponential dependence on photon energy following Urbach relation. Doping ZTS crystal with Co2+ modifies its optical properties. The absorption coefficient, optical energy gap, Urbach tail energy and steepness parameter. The changes are systematic i.e. the mentioned optical parameters increase or decrease continuously with increasing Co2+ concentration in the growth solution. The electrical conduction of ZTS crystal is increased with cobalt doping. The Urbach tail energy changes reversely with the optical energy gap.
关键词： ZTS crystal,cobalt-doped,urbach tail energy,optical energy gap,steepness parameter
更新于2025-09-10 09:29:36
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Synthesis and Characterization of BaAl2O4 Catalyst and its Photocatalytic Activity Towards Degradation of Methylene Blue Dye
摘要： Hexagonal BaAl2O4 catalyst has been prepared using a gamma-ray irradiation assisted polyacrylamide gel method. The catalysts synthesized at different calcining temperatures were analyzed to insight into their effects on the structural, crystalline, surface morphology, color, optical, fluorescence and photocatalytic properties of the hexagonal BaAl2O4 catalyst. Increasing the calcining temperature has obvious influences on the crystallinity, color, optical properties and the formation of the hexagonal BaAl2O4 catalyst. The optical energy gap (Eg) value of the hexagonal BaAl2O4 catalyst increases with the increasing of calcining temperature. TEM image of the pure hexagonal BaAl2O4 catalyst shows a morphology of flake structure and aggregation. Raman spectroscopy of the pure hexagonal BaAl2O4 catalyst exhibits four luminescent background peaks at 400, 415, 428 and 445 nm mainly due to the oxygen vacancies (VO), Ba vacancies (VBa) and some color centers exists in the BaAl2O4 sample. A comparison of photocatalytic activity among samples for degradation of methylene blue (MB) dye indicates that the pure hexagonal BaAl2O4 catalyst exhibits highest photocatalytic activity under the irradiation of both visible and ultraviolet light. Based on the fluorescence experiment, electrochemical and active species tests, the high photocatalytic activity of the pure hexagonal BaAl2O4 catalyst to be related to hole (h+) and hydroxyl radical (·OH) and also to the defects in the sample.
关键词： BaAl2O4,photocatalytic activity,methylene blue,polyacrylamide gel method,calcining temperature,optical energy gap
更新于2025-09-10 09:29:36
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Optical Properties of Fe <sub/>3</sub> O <sub/>4</sub> Thin Films Prepared from the Iron Sand by Spin Coating Method
摘要： Research on magnetic oxide is growing very rapidly. This magnetic oxide can be found in nature that is in iron sand. One of the beaches in Sumatera Barat containing iron sand is Tiram Beach, Padang Pariaman District, Sumatera Barat. The content of iron sand is generally in the form of magnetic minerals such as magnetite, hematite, and maghemit. Magnetite has superior properties that can be developed into thin films. The purpose of this research is to investigate the optical properties of transmittance, absorbance, reflectance and energy gap from Fe3O4 thin films. This type of research is an experimental research. The iron sand obtained from nature is first purified using a permanent magnet, then made in nanoparticle size using HEM-E3D with milling time for 30 hours. After that, the process of making thin film with sol-gel spin coating method. In this research, variation of rotation speed from spin coating is 1000 rpm, 2000 rpm and 3000 rpm. Based on XRD results indicated that the iron sand of Tiram beach contains magnetite minerals and the SEM results show that the thickness of the thin films formed is 25μm, 24μm and 11μm. The characterization tool used for characterizing optical properties is the UV-VIS Spectrophotometer. So it can be concluded that the greater the speed of rotation the thickness of the thin layer will be smaller, resulting in the transmittance and reflectance will be greater, while the absorbance will be smaller. Energy gap obtained from this research is 3,75eV, 3,75eV and 3,74eV. So the average energy gap obtained is 3,75eV.
关键词： Fe3O4,energy gap,optical properties,thin films,spin coating
更新于2025-09-10 09:29:36
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Fabrication and analysis of the structural phase transition of ZrO <sub/>2</sub> nanoparticles using modified facile sol–gel route
摘要： The synthesis of zirconia nanoparticles is achieved through a modified facile sol–gel route. The as-prepared gel is analyzed thermally using TGA and DTA techniques to spot the crystallization process of zirconia nanoparticles. The prepared gel is then annealed at different temperatures and the structure was found to change between tetragonal and monoclinic crystal systems. The first stable tetragonal phase is achieved after annealing for 2 h at 400°C. The annealed powders between 600°C and 800°C demonstrate mixed tetragonal/monoclinic phases. Annealing at 1000°C and higher temperatures up to 1200°C resulted in pure monoclinic phase. Cubic phase was not detected within the annealing temperature range in this study. The elemental analysis of the annealed powder confirmed the formation of zirconia nanoparticles with the chemical formula ZrO2. The FTIR spectra of the annealed samples introduced a variation in the vibrational bands especially around the phase transition temperature. HR-TEM images reported the formation of nano-zirconia crystals with apparently large particle sizes. The optical energy gap of zirconia nanoparticles is investigated and determined.
关键词： ZrO2 nanoparticles,HR-TEM,sol–gel synthesis,EDAX,optical energy gap
更新于2025-09-09 09:28:46
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The Correlation between the Energy Gap and the Pseudogap Temperature in Cuprates: The YCBCZO and LSHCO Case
摘要： The paper analyzes the influence of the hole density, the out-of-plane or in-plane disorder, and the isotopic oxygen mass on the zero temperature energy gap (2Δ(0)) Y1???Ca??Ba2(Cu1???Zn??)3O7??? (YCBCZO) and La1.96???Sr??Ho0.04CuO4 (LSHCO) superconductors. It has been found that the energy gap is visibly correlated with the value of the pseudogap temperature (???). On the other hand, no correlation between 2Δ(0) and the critical temperature (????) has been found. The above results mean that the value of the dimensionless ratio 2Δ(0)/???????? can vary very strongly together with the chemical composition, while the parameter 2Δ(0)/??????? does not change significantly. In the paper, the analytical formula which binds the zero temperature energy gap and the pseudogap temperature has been also presented.
关键词： energy gap,pseudogap temperature,superconductors,cuprates,electron-phonon interaction,electron-electron correlations
更新于2025-09-09 09:28:46