Gap Energy Levels Research Articles

Energy-level tuning of poly(p-phenylenebutadiynylene) derivatives by click chemistry-type postfunctionalization of side-chain alkynes

A series of poly(p-phenylenebutadiynylene) polymers substituted with electron-rich alkynes as the side chain were synthesized by homocoupling polymerization of asymmetric bifunctional monomers. The electron-rich alkynes underwent “click chemistry” with tetracyanoethylene (TCNE) to produce donor–acceptor chromophores. Optical and electrochemical characterizations clearly indicated that the energy level and band gap of P2 could be precisely controlled by the addition of acceptor molecules. One of the most important conclusions of this study is that a linear relationship between the lowest occupied molecular orbital (LOMO) and the amount of TCNE was observed. From the Z-scan measurement, all the compounds exhibited very special nonlinear optical properties, which suggested a tendency to transfer from saturable absorption (SA) to reverse saturable absorption (RSA).

SOLVENT FREE, ONE POT SYNTHESIS OF SYMMETRIC XANTHENE DYES AND THEIR ELECTROCHEMICAL STUDY

The present paper reports the synthesis of xanthene dyes derivatives from 4, 4’-oxydiphthalic anhydride and 1, 4, 5, 8-naphthalenetetracarboxylic dianhydride (3a-e and 6a-e ) with different substituted phenols via Friedel-Crafts acylation reaction in the presence of an ammonium chloride catalyst. The structures of all newly synthesized derivatives were confirmed by the chromatographic, spectral and microelemental data. Dianhydride derivatives with 3-N’, N’-dimethylaminophenol ( 3d and 6d ) and resorcinol (3e and 6e) have been found to be highly fluorescent. Electrochemical study was done to determine band gap energy, LUMO and HOMO level energy. Band gap and LUMO energy levels were found to be lowest in xanthene derivatives 3c and 6c . Dyes 3d, 3e, 6d and 6e were found useful for differential staining of plant cells.

Soft synthesis of potassium co-doped Al–ZnO nanocomposites: a comprehensive study on their visible-light driven photocatalytic activity on dye degradation

The present work reports on the, first of its kind, synthesis of potassium co-doped aluminum-doped ZnO nanoparticles (NPs) through thermo-sol gelation process. The co-doping of K on Al–ZnO NPs is found having a significant influence on the band gap narrowing of ZnO, to an extent that the entire light absorption is shifted towards the visible-light spectrum. The synthesized NPs are characterized using, XRD, TEM, SEM, EDX, UV–Vis–DRS, BET surface area analysis, TG/DTA, PL, and ICP–OES. The band gap energy levels for bare ZnO, Al-doped ZnO, and K co-doped Al–ZnO NPs are 3.26, 3.03 and 2.88 eV, respectively. A systematic study has been carried to evaluate the photocatalytic properties of K co-doped Al–ZnO photocatalyst through Direct Green 6 (a textile dye) degradation studies, and has been compared with well-known Al–ZnO NPs. The effect of various operational parameters such as, co-dopant/dopant stoichiometry, solution pH, catalyst dosage, dye concentration, kinetics, photosensitizers, light intensity, and matrix tolerance, on the dye degradation, has been systematically evaluated. The analytical data reveal that under optimized conditions, the K co-doped Al–ZnO photocatalyst can induce complete dye degradation within 0.5 h under visible light. A comprehensive mechanism has been proposed on the photocatalytic activity of K–Al–ZnO NPs.

Solar Photocatalytic Mineralization of Dye New Coccine in Aqueous Phase Using Different Photocatalysts

The objective of this study was to examine the effect of band gap of photocatalyst on the decolorization of dye new coccine (NC). The concentration of NC in the present of CuO, Fe2O3, TiO2, and ZnO reduced to 50.5, 23.3, 0.1, and 0 mg L−1, respectively, after 5 h solar light irradiation. The concentration of NC in dark condition only decreased to 48.140, 45.079, 35.269, and 31.045 mg L−1 with CuO, Fe2O3, TiO2, and ZnO as photocatalysts, respectively, after 5 h contact time. The absorbance peaks and chemical oxygen demand (COD) concentration of NC in the presence of TiO2 and ZnO decreased to baseline and zero compared to the CuO and Fe2O3. The COD concentration of NC with CuO, Fe2O3, TiO2, and ZnO as photocatalysts reduced to 21, 13, 0, and 0 mg L−1, respectively, after 12 h of solar irradiation. The surface morphology of photocatalysts was examined by scanning electron microscope (SEM), and it was found that the particle size of CuO, Fe2O3, TiO2, and ZnO ranging 250–375, 250–600, 40–100, and 60–500 nm, respectively. In summary, the higher band gap energy level indicated greater photocatalytic degradation and mineralization of NC.

Cr modified Raman, optical band gap and magnetic properties of SnO2 nanoparticles

Pure and Cr (1, 3, 5, 7 and 10 at.%) doped SnO2 nanoparticles were synthesized in aqueous solution by a low cost chemical co-precipitation method without using any stabilizing agent. The effects of Cr doping on Raman, optical band gap and magnetic properties of SnO2 nanoparticles were investigated. Particle size is found to decrease with Cr doping into the SnO2 matrix which was confirmed by TEM. Besides of the fundamental mode of vibration, two additional peaks are also observed in Raman spectra which are correlated to Cr. The absorption spectra showed two peaks at 340 and 454 nm. The absorbance peak at 340 nm is assigned to the transition from valence band (VB) to conduction band (CB) and the peak at 454 nm was due to the transition from VB to mid gap energy level introduced by Cr. The optical band gap of undoped SnO2 nanoparticles is calculated to be 3 eV. With the doping of Cr in SnO2, band gap increases due to the decrease in particle size. The emission intensity is found to decrease with the increase in Cr doping due to the emission from CB to mid gap energy levels introduced by Cr between CB and VB. Undoped SnO2 nanoparticles show room temperature ferromagnetism due to the presence of defects and oxygen vacancies. The heavily doped SnO2 nanoparticles show paramagnetic nature due to the antiferromagnetic coupling between Cr and its nearest neighbour.

Thiophene-S,S-dioxidized Indophenine: A Quinoid-Type Building Block with High Electron Affinity for Constructing n-Type Polymer Semiconductors with Narrow Band Gaps.

Three thiophene-S,S-dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most-stable 3 a by heating at 110 °C. An IDTO-containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n-type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm(2) V(-1) s(-1)), despite its rather disordered chain packing.

Thiophene‐S,S‐dioxidized Indophenine: A Quinoid‐Type Building Block with High Electron Affinity for Constructing n‐Type Polymer Semiconductors with Narrow Band Gaps

AbstractThree thiophene‐S,S‐dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most‐stable 3 a by heating at 110 °C. An IDTO‐containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n‐type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm2 V−1 s−1), despite its rather disordered chain packing.

Remarkable red-shift of upconversion luminescence and anti-ferromagnetic coupling in NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ bifunctional microcrystals

Lanthanide doped bifunctional materials are potentially important for developing multifunctional devices. Here, NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ optical-magnetic bifunctional microcrystals were successfully synthesized by hydrothermal method, which could emit ∼480 nm blue light from the 1G4→3H6 electronic transition and ∼800 nm infrared light from the 3H4→3H6 electronic transition of Tm3+ ion, under the excitation of 980 nm infrared light. By doping Sm3+ ion into NaLuF4:Yb3+/Tm3+/Gd3+, the infrared emission peak centered at 800 nm would shift obviously to longer wavelength. This indicated that Sm3+ ion could efficiently tune the energy level gaps of Tm3+ ions in NaLuF4 host which was demonstrated based on the crystal field theory. In addition, these NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ microcrystals presented unique ferromagnetic property instead of usually reported paramagnetic property. Importantly, the ferromagnetic property decreased with increasing the concentration of Gd3+ ion. This was in good agreement with Swift's theoretical investigation that the coexistence of light rare earth (Gd3+) and heavy rare earth (Yb3+/Tm3+) would lead to the anti-ferromagnetic coupling in the sub-lattices.

Collisional broadening of Kr [formula omitted] transition with combustion species as collision partners

Collisional broadening of krypton 4p6S01→→5p[32]2 transition centered at 107.3nm caused by common combustion species is investigated in this work. The present work investigates the compositional and thermodynamic dependencies of the collisional parameters between collision partners with similar electronic energy level gaps. In this situation, the classical expression of dispersive energy during collisions cannot be simplified to obtain closed form equations for the collisional parameters. The broadening parameters, namely collisional full width at half maximum (wc) and collisional shift (δc) are obtained through a two-photon excitation scan of krypton (Kr) present in a mixture containing krypton and the collision partner at 295K and 101kPa. The compositional scaling of wc and δc are compared with scaling at situations corresponding to both large and small perturber electronic energy level gaps as compared to the absorber’s electronic energy level gap. In the Kr PLIF system, wc scaling corresponds to a situation where the perturber electronic energy level gap is significantly larger than absorber energy level gap, whereas δc scaling corresponds to when the absorber electronic energy level gap is significantly larger than the perturber electronic energy level gap. Further, contributions from non-dispersive forces are computed to be significantly smaller than dispersive forces, which results to the observed tight scaling. The observed compositional scaling is shown to be consistent with a different collisional partner system (NO as the absorber and combustion species as perturbers), indicating that the scaling obtained with the krypton system is general to situations with perturbers and absorbers having similar electronic energy level spacing.

The Influence of High-Power Ion Beams and High-Intensity Short-Pulse Implantation of Ions on the Properties of Ceramic Silicon Carbide

The paper is focused on the study of the structural, electrical and optical characteristics of the ceramic silicon carbide before and after irradiation in the regimes of the high-power ion beams (HPIB) and high-intensity short-pulse implantation (HISPI) of carbon ions. The dominant mechanism of transport of charge carriers, their type and the energy spectrum of localized states (LS) of defects determining the properties of SiC were established. Electrical and optical characteristics of ceramic before and after irradiation are determined by the biographical and radiation defects whose band gap (BG) energy levels have a continuous energetic distribution. A dominant p-type activation component of conduction with participation of shallow acceptor levels 0.05-0.16 eV is complemented by hopping mechanism of conduction involving the defects LS with a density of 1.2T017-2.4T018 eV-Am-3 distributed near the Fermi level.The effect of radiation defects with deep levels in the BG on properties change dominates after HISPI. A new material with the changed electronic structure and properties is formed in the near surface layer of SiC after the impact of the HPIB.

Synthesis and Characterization of New Xanthene Derivatives, and Their Electrochemical Study

AbstractThis work investigated the synthesis of biphenyl‐3,3′,4,4′‐tetracarboxylic dianhydride and benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride derivatives (3a–e and 6a–e) with different substituted phenols via Friedel‐Crafts acylation reaction in the presence of dilute sulfuric acid. Dianhydride derivatives with 3‐N,N′‐dimethylamino phenol (3d and 6d) and resorcinol (3e and 6e) have been found to be highly fluorescent. The structures of all newly synthesized compounds were confirmed by the chromatographic, spectral and elemental data. Electrochemical study was done to determine to band gap energy, LUMO and HOMO levels energy. Band gap and LUMO energy levels were found to be lowest in xanthene derivatives substituted with 3‐N,N′‐dimethylamino group having value 2.24 and 4.85 eV respectively.

Tuning joint sequence for donor–acceptor polymers based on fluorinated benzothiadiazole with thiophene/furan bridecakes

Three new donor–acceptor (D–A) polymers, PTBDT-ffBT-FT12, PTBDT-ffBT-TT12 and PTBDT-ffBT-T12T, based on thiophene substituted benzene[1,2-b:4,5-b′] thiophene (TBDT) and fluorinated benzothiadiazole (ffBT) with thiophene/furan conjugated bridges were prepared. The joint sequence of alkyl thiophene/furan bridges has significant influence on the energy levels, band-gap and molecule stacking of the copolymers. All copolymers show broad absorption bands, and the energy level and band gap could be well fine-tuned by the introduction of thiophene/furan bridges to polymer backbone. The small atomic radius of oxygen atom on furan bridges resulted in the inferior co-planarity and torsion backbone for PTBDT-ffBT-FT12 with furan bridges, while the adjacent dodecyl on thiophene bridges close to TBDT led to a big steric hindrance. As a result, the polymer solar cell (PSC) based on PTBDT-ffBT-T12T achieves the better efficiency compared to PTBDT-ffBT-FT12 and PTBDT-ffBT-TT12.

The Effect of Doping on the Electrophysical Properties of Polycrystalline Diamond Films Deposited from an Abnormal Glow Discharge

The paper is focused on the study of the boron doping effect on the electrical characteristics, on the mechanism of charge carrier transfer, and on the energy spectrum of the localized defect states in the polycrystalline diamond films (PDF) deposited from an abnormal glow discharge. PDF doping enables to form the semiconductor layers of p-type conductivity, which have as good properties as those of PDF produced by the alternative methods. The doping reduces the degree of disorder in the film material brought by the growth defects, which determine the film electrical characteristics and electrotransfer mechanism. The PDF electrical characteristics and electrotransfer mechanism are determined by the defects of different nature, whose band gap energy levels have a continuous energy distribution. A p-type activation component is realized in the exchange of charge carriers between the valence band and shallow acceptor levels with the activation energy of 0.013-0.022 eV. Doping increases the effect of the hopping mechanism of the conductivity involving the localized states with a density of (1-6)·1020 eV-1 •cm-3 distributed near the Fermi level, which is in the low half of the band gap.

Aluminum doping tunes band gap energy level as well as oxidative stress-mediated cytotoxicity of ZnO nanoparticles in MCF-7 cells.

We investigated whether Aluminum (Al) doping tunes band gap energy level as well as selective cytotoxicity of ZnO nanoparticles in human breast cancer cells (MCF-7). Pure and Al-doped ZnO nanoparticles were prepared by a simple sol-gel method. Characterization study confirmed the formation of single phase of AlxZn1-xO nanocrystals with the size range of 33–55 nm. Al-doping increased the band gap energy of ZnO nanoparticles (from 3.51 eV for pure to 3.87 eV for Al-doped ZnO). Al-doping also enhanced the cytotoxicity and oxidative stress response of ZnO nanoparticles in MCF-7 cells. The IC50 for undoped ZnO nanoparticles was 44 μg/ml while for the Al-doped ZnO counterparts was 31 μg/ml. Up-regulation of apoptotic genes (e.g. p53, bax/bcl2 ratio, caspase-3 & caspase-9) along with loss of mitochondrial membrane potential suggested that Al-doped ZnO nanoparticles induced apoptosis in MCF-7 cells through mitochondrial pathway. Importantly, Al-doping did not change the benign nature of ZnO nanoparticles towards normal cells suggesting that Al-doping improves the selective cytotoxicity of ZnO nanoparticles toward MCF-7 cells without affecting the normal cells. Our results indicated a novel approach through which the inherent selective cytotoxicity of ZnO nanoparticles against cancer cells can be further improved.

Optical property evaluation of oxyfluoride glasses doped with different amounts of Y3 + ions

In present study, oxyfluoride glasses doped with different amounts of Y2O3 (0.5, 1 and 1.5wt.%) were prepared by the convenient melting process. Based on the density measurements and differential thermal analysis (DTA) results, the network-forming role of Y3+ ions was proved. In addition, Fourier transform infrared spectroscopy (FT-IR) study of the samples approved this claim by showing structural changes happening with the increase of Y2O3 content. Using the UV–Vis spectra, optical properties including Fermi energy level, direct and indirect optical band gaps and Urbach energy were determined. The mentioned optical properties were calculated using Fermi–Dirac distribution function, Tauc's plots and absorption coefficient diagrams, respectively. Increment of optical properties with the increase of Y2O3 content (i.e. decrease of Fermi energy level from 3.59 to 3.17eV, indirect band gap from 3 to 2.79eV and direct band gap from 3.57 to 3.42eV) confirms the better semiconducting behavior. Moreover, Urbach energy decreased from 0.27 to 0.23eV arising from the network forming role of Y3+ ions in the glass network.

Poly(benzodithiophene) Homopolymer for High-Performance Polymer Solar Cells with Open-Circuit Voltage of Near 1 V: A Superior Candidate To Substitute for Poly(3-hexylthiophene) as Wide Bandgap Polymer

Conjugated homopolymers can be synthesized more simply and reproducibly at lower cost than widely developing donor–acceptor (D–A) alternating copolymers. However, except for well-known poly(3-hexylthiophene) (P3HT), almost no successful homopolymer-based polymer solar cells (PSCs) have been reported because of their relatively wide band gap and unoptimized energy levels that limit the values of short circuit current (JSC) and open-circuit voltage (VOC) in PSCs. Herein, we report the development of poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene) (PBDTT) homopolymer that has high light absorption coefficients and nearly perfect energy alignment with that of [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Therefore, we were able to produce high-performance PSCs with the power conversion efficiency (PCE) of 6.12%, benefiting from both high VOC (0.93 V) and JSC (11.95 mA cm–2) values. To the best of our knowledge, this PCE value is one of the highest values reported for the homo...

Experimental optimal design of the Er3+/Yb3+ codoped BaGd2ZnO5 phosphor and its upconversion luminescence properties

In order to obtain the Er3+/Yb3+ co-doped BaGd2ZnO5 up-conversion phosphor which has the maximum green and red emission intensity, firstly, the method of homogeneous design rooted in the experimental optimal design is employed to search optimum Er3+/Yb3+doping concentration preliminarily. Next, the quadratic general rotary unitized design is adopted to further optimize the experiment, and the regression equation in green and red emission intensity is established as a function of the doping concentration of Er3+/Yb3+. Finally, the optimal solution, that is, the doping concentration of Er3+/Yb3+ corresponding to the maximum emission intensity, is calculated by genetic algorithm. The optimal Er3+/Yb3+co-doped BaGd2ZnO5 phosphor is synthesized by the conventional high temperature solid state method. The crystal structure of as-prepared products is characterized by X-ray diffraction (XRD), and the results show that all the Er3+/Yb3+co-doped BaGd2ZnO5 phosphors we synthesized are of pure phase. The steady-state up-conversion (UC) emission spectra of products are measured under the excitation of a continuous 980 nm laser diode at different working currents. From the UC luminescent spectra of Er3+/Yb3+co-doped BaGd2ZnO5 phosphor, we can see a red emission centered at 662 nm, two green emissions centered at 551 nm and 527 nm, which are assigned to 4F9/2→4I15/2, 4S3/2→4I15/2 and 2H11/2→$4I15/2 transitions of Er3+ ion, respectively. The dependences of green and red UC emission intensities of optimal samples on working current are investigated, indicating that the red emission and green emission of optimal samples both originate from two-photon process. From the normalized green UC emission spectra, it can be concluded that the experimental laser working current induced temperature variation of samples can be omitted. According to Boltzmann distribution law and the thermal equilibrium existing between the levels of 2H11/2 and 4S3/2, the relationship between green emission and temperature in the optimal green UC emission sample is discussed in depth, and the energy level gap between 2H11/2 level and 4S3/2 level is calculated to be 926.11 cm-1. Through the study of the temperature effect on the optimal green UC emission sample, we find that the emission intensity decreases with the increasing of the temperature, owing to the thermal quenching effect. Furthermore, we calculate the activation energies of the samples, the activation energies of the green emission, red emission, and the overall emission are deduced to be 0.45, 0.46, and 0.45 eV, respectively.

Analysis of trap distribution in polysilicon channel transistors using the variable amplitude charge pumping method

The trap distribution of a polysilicon (poly-Si) channel in a metal–oxide–semiconductor field effect transistor (MOSFET) was extracted successfully using a variable amplitude charge pumping method (VACP) and an energy band bending model. Compared to single crystal Si channels, the poly-Si channels exhibited a high density of bulk channel traps due to the presence of grain boundaries. The densities of the trap states existing in the poly-silicon channel with various grain sizes and channel thicknesses were extracted and compared. The grain size of poly-Si was found to have a stronger impact on the trap distribution than the channel thickness. After hot carrier stress, the trap density in the poly-silicon channel increases and the generated traps are located both at mid gap energy level and near the conduction band energy level.

Solution‐Processable Hosts Constructed by Carbazole/PO Substituted Tetraphenylsilanes for Efficient Blue Electrophosphorescent Devices

Two new solution‐processable wide bandgap materials, bis(4‐((4‐(9‐H‐carbazol‐9‐yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (CS2PO) and bis(4‐((4‐(9‐H‐(3,9′‐bicarbazol)‐9‐yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (DCS2PO), have been developed for blue phosphorescent light‐emitting diodes by coupling an electron‐donating carbazole moiety and an electron‐accepting PO unit together via double‐silicon bridges. Both of them have been characterized as having high glass transition temperatures of 159–199 °C, good solubility in common organic solvent (20 mg mL−1), wide optical gap (3.37–3.55 eV) and high triplet energy levels (2.97–3.04 eV). As compared with their corresponding single‐silicon bridged compounds, this design strategy of extending molecular structure endows CS2PO and DCS2PO with higher thermal stability, better solution processability and more stable film morphology without lowering their triplet energies. As a result, DCS2PO/FIrpic doped blue phosphorescent device fabricated by spin‐coating method shows the best electroluminescent performance with a maximum current efficiency of 26.5 cd A−1, a maximum power efficiency of 8.66 lm W−1, and a maximum external quantum efficiency of 13.6%, which is one of the highest efficiencies among small molecular devices with the same deposition process and device configuration.

Energy Spectrum and Phase Transition of Superfluid Fermi Gas of Atoms on Noncommutative Space

Based on the Bogoliubov non-ideal gas model, we discuss the energy spectrum and phase transition of the superfluid Fermi gas of atoms with a weak attractive interaction on the canonical noncommutative space. Because the interaction of a BCS-type superfluid Fermi gas originates from a pair of Fermionic quasi-particles with opposite momenta and spins, the Hamiltonian of the Fermi gas on the noncommutative space can be described in terms of the ordinary creation and annihilation operators related to the commutative space, while the noncommutative effect appears only in the coefficients of the interacting Hamiltonian. As a result, we can rigorously solve the energy spectrum of the Fermi gas on the noncommutative space exactly following the way adopted on the commutative space without the use of perturbation theory. In particular, different from the previous results on the noncommutative degenerate electron gas and superconductor where only the first order corrections of the ground state energy level and energy gap were derived, we obtain the nonperturbative energy spectrum for the noncommutative superfluid Fermi gas, and find that each energy level contains a corrected factor of cosine function of noncommutative parameters. In addition, our result shows that the energy gap becomes narrow and the critical temperature of phase transition from a superfluid state to an ordinary fluid state decreases when compared with that in the commutative case.