Transition Energy Decreases Research Articles

Influence of electron-donating ability of ligand and pH value on MLCT properties of cyanido-bridged complexes

In this work, one mononuclear complex CH3CNFeII(eq-Py4PzMe2) (1) and two binuclear complexes Cp(dppe)MIICNFeII(eq-Py4PzMe2) (M = Ru 2, Fe 3; Cp = cyclopentadiene, dppe = 1,2-bis(diphenylphosphino)ethane, eq-Py4PzMe2 = 2-(1-(6-(1,1-di(pyridin-2-yl)ethyl)pyridin-2-yl)-1-(pyridin-2-yl)ethyl)pyrazine) were synthesized. Combined with the TDDFT calculations, the metal-to-ligand charge transfer (MLCT) properties of all the compounds were investigated. The results show that for the mononuclear complex, the MLCT originates from FeII to the pyrazine (Pz) component of the eq-Py4PzMe2 ligand. After the substitution of CH3CN in complex 1 by the half-sandwich fragment Cp(dppe)MIICN, the binuclear complexes 2 and 3 exhibit the MLCT transition from the neighboring FeII atom to the Pz component of the eq-Py4PzMe2 together with some contributions from the remote MII. With the increase of the electron-donating ability from CH3CN, Cp(dppe)RuIICN to Cp(dppe)FeIICN, the MLCT transition energy decreases. Furthermore, with the decrease of pH value, all the MLCT absorption bands are significantly redshifted by 160 nm or more, and the extent of these red shifts increases from complex 1 to 2, to 3.

Concentration, And Temperature Dependences Of Exciton Transition Energies In AlxGa1-xAs/GaAs/AlxGa1-xAs Nanofilms

The energy of transition into the ground excitonic state for a quasi-two-dimensional (nanofilm) semiconductor nanoheterostructure with single quantum well and its dependences on the thickness, temperature, and composition of the barrier medium are calculated in the dielectric continuum approximation using the Green’s function method. Specific calculations are made for a nanofilm containing a rectangular finite-depth quantum well created by the double hetero-junction GaAs/AlxGa1−xAs taken as an example. For the films narrower than 30–40 nm, the transition energy is shown to be mainly governed by the confinement effect and the aluminum content x. In particular, the energy decreases rapidly from 1.55 eV (at x = 0.2), 1.62 eV (at x = 0.3), or 1.69 eV (at x = 0.4) to 1.41 eV for all those x-values, as the film thickness grows. The further increase in the film thickness up to approximately 100 nm is accompanied by a slow growth of the energy to the value characteristic of bulk GaAs, which occurs due to the corresponding reduction in the exciton binding energy. The rate of this growth depends weakly on x. The temperature increase from 0 to 300 K results in a long-wave shift of the exciton band bottom. As a result, the transition energy decreases by a value weakly depending on the film thickness and ranging from 2 meV at x = 0.2 to 3 meV at x = 0.4. The temperature-induced variations are invoked by the interaction with phonons, which are mostly confined ones in nanofilms thicker than 30–40 nm or interface ones, if nanofilms are thinner.

Effect of a magnetic field on the energy levels of donor impurities in the ZnO parabolic quantum well

Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method. The binding energy of the ground state, the energies of 2p± state and 1s → 2p± transition energies of a hydrogenic donor in the ZnO parabolic quantum well are numerically calculated as a function of the strength of magnetic field for different parabolic potential fields. The results show that the external magnetic field has an obvious influence on the binding energies and the 1s → 2p± transition energies of a hydrogenic donor. The 1s to 2p± transition energy increases linearly with the strength of magnetic field, but the 1s to 2p− transition energy decreases when the strength of magnetic field increases for the small field strength. Compared to the GaAs parabolic well, the donors are more tightly bound to the ZnO parabolic well and the influence of external magnetic field on the binding energy of a donor is much stronger in the ZnO parabolic well.

Effects of electronegative substitution on the optical and electronic properties of acenes and diazaacenes

Large acenes, particularly pentacenes, are important in organic electronics applications such as thin-film transistors. Derivatives where CH units are substituted by sp(2) nitrogen atoms are rare but of potential interest as charge-transport materials. In this article, we show that pyrazine units embedded in tetracenes and pentacenes allow for additional electronegative substituents to induce unexpected redshifts in the optical transitions of diazaacenes. The presence of the pyrazine group is critical for this effect. The decrease in transition energy in the halogenated diazaacenes is due to a disproportionate lack of stabilization of the HOMO on halogen substitution. The effect results from the unsymmetrical distribution of the HOMO, which shows decreased orbital coefficients on the ring bearing chlorine substituents. The more strongly electron-accepting cyano group is predicted to shift the transitions of diazaacenes even further to the red. Electronegative substitution impacts the electronic properties of diazaacenes to a much greater degree than expected.

Influence of wetting layers on the electric potentials and optical properties of InGaN quantum dots

This study investigates the influence of wetting layers (WLs) on the electric potentials and electronic structures of InGaN quantum dots (QDs). The single particle electron and hole energies of QDs with different thicknesses and indium compositions of the WLs are calculated using the four-band k ⋅ p Hamiltonian. Numerical results show that there is an average of 60 mV increase in the maximum electric potential drop per every 0.2 nm increment in the thickness of the WL or per every 0.05 increase in indium composition α of the WL. Consequently, the transition energy decreases significantly with increasing thickness and/or indium composition of the WL. We find that the strained bandgap shifts down by 125 meV leading to a 128 meV decrease in the transition energy per every 0.4 nm increment in the thickness of the WL, which corresponds to 5.6% and 4.8% of the strained bandgap and the transition energy, respectively, for the cases without the WL. Furthermore, there is also a 32.5 meV transition energy decrease per every 0.025 increase in indium composition α of the WL. Hence, it is important to consider the thickness and indium composition of the WL in the analysis of InGaN QDs.

Electronic structure and optical gain of InAsSbN/InAs quantum dots

The electronic structure and optical gain of InAsSbN/InAs QDs are investigated in the framework of effective-mass envelope function theory. The strain distribution is calculated using the valence force field (VFF) method. When the composition of Sb increases, both the conduction and valence bands offset and the compressive strain increase, and the transition energy decreases and the strained band alignment may change from type I to type II. The added nitrogen can reduce the compressive strain in QD, and it reduces the C1-HH1 transition energy due to the strong repulsion between nitrogen resonant band and conduction band. When the Sb composition increases, the overlapping of wave-functions of electrons and holes are less efficient, the optical transition matrix element decreases. For the optical gain, we should consider the factors including the transition matrix element, the matrix element of Kane’s theory, the refractive index and Fermi-Dirac distributions for electrons f c in the conduction bands and holes f v in the valence bands. So depending on the specific application requirements, we should select the appropriate compositions of Sb and N accordingly.

109 Expression and activation of protein kinases in Triple Negative Breast Cancer (TNBC)

We investigate InAs self-assembled quantum dots (SAQD) by resonant inelastic light scattering. By applying a gate voltage between a metallic front gate and a back electrode, we can charge the quantum dots with single electrons (1–6). With resonant inelastic light scattering, we can directly observe the elementary electronic excitations of the few-electron quantum-dot atoms, which are formed by the SAQD. We observe excitations which we identify as transitions of electrons from the s- to the p-shell (s–p transitions) and from the p- to the d-shell (p–d transitions) of the quasiatoms. We find that the s–p transition energy decreases when the p-shell is filled with 1–4 electrons. This can be explained as an effect of Coulomb interaction, which is confirmed by calculations of the few-electron system, using exact numerical diagonalization.

1109 Direct cell entry of gold/iron-oxide magnetic nanoparticles in adenovirus mediated gene delivery

We investigate InAs self-assembled quantum dots (SAQD) by resonant inelastic light scattering. By applying a gate voltage between a metallic front gate and a back electrode, we can charge the quantum dots with single electrons (1–6). With resonant inelastic light scattering, we can directly observe the elementary electronic excitations of the few-electron quantum-dot atoms, which are formed by the SAQD. We observe excitations which we identify as transitions of electrons from the s- to the p-shell (s–p transitions) and from the p- to the d-shell (p–d transitions) of the quasiatoms. We find that the s–p transition energy decreases when the p-shell is filled with 1–4 electrons. This can be explained as an effect of Coulomb interaction, which is confirmed by calculations of the few-electron system, using exact numerical diagonalization.

AlxGa1−xN/GaN multi-quantum-well ultraviolet detector based on p-i-n heterostructures

We report on characterization of a set of AlGaN/GaN multiple-quantum-well (MQW) photodetectors. The model structure used in the calculation is the p–i–n heterojunction with 20 AlGaN/GaN MQW structures in i-region. The MQW structures have 2nm GaN quantum well width and 15nm AlxGa1−xN barrier width. The cutoff wavelength of the MQW photodetectors can be tuned by adjusting the well width and barrier height. Including the polarization field effects, on increasing Al mole fraction, the transition energy decreases, the total noise increases, and the responsivity has a red shift, and so the detectivity decreases and has a red shift.

Ab initio calculations on π‐stacked thiophene dimer, trimer, and tetramer: Structure, interaction energy, cooperative effects, and intermolecular electronic parameters

Pi-stacked complexes formed by two, three, and four thiophene rings have been investigated using abinitio quantum mechanical calculations. The relative orientation between the rings was investigated for each complex by exploring the corresponding potential energy surface at the MP2/6-31+G(d,p) level, the inter-ring distance, and the degree of tilting being examined in each case. Interaction energies were calculated at the MP2, MP3, MP4, and CCSD, levels of theory. Negligible or even slightly positive n-body effects have been predicted for the stacked thiophene arrangements studied in this work. This is consequence of the cancellation of favorable induction contribution by the destabilizing dispersion component. On the other hand analysis of the optimized geometries obtained for the trimer and tetramer revealed that the orientation of the rings presents a preferred degree of periodicity. Finally, we found that the lowest transition energy decreases when the size of the complex increases, this feature being attributed to desestabilization of the HOMO and stabilization of the LUMO that occur simultaneously.

Inelastic light scattering on few-electron quantum-dot atoms

We investigate InAs self-assembled quantum dots (SAQD) by resonant inelastic light scattering. By applying a gate voltage between a metallic front gate and a back electrode, we can charge the quantum dots with single electrons (1–6). With resonant inelastic light scattering, we can directly observe the elementary electronic excitations of the few-electron quantum-dot atoms, which are formed by the SAQD. We observe excitations which we identify as transitions of electrons from the s- to the p-shell (s–p transitions) and from the p- to the d-shell (p–d transitions) of the quasiatoms. We find that the s–p transition energy decreases when the p-shell is filled with 1–4 electrons. This can be explained as an effect of Coulomb interaction, which is confirmed by calculations of the few-electron system, using exact numerical diagonalization.

Spectroscopy of few-electron collective excitations in charge-tunable artificial atoms.

We report the investigation of electronic excitations in InGaAs self-assembled quantum dots using resonant inelastic light scattering. The dots can be charged via a gate by N=1, em leader,6 electrons. We observe excitations, which are identified as transitions of electrons, predominantly from the s to the p shell (s-p transitions) of the quasiatoms. We find that the s-p transition energy decreases and the observed band broadens, when the p shell is filled with 1 to 4 electrons. By a theoretical model, which takes into account the full Coulomb interaction in the few-electron artificial atom, we can confirm the experimental results to be an effect of the Coulomb interaction in the quantum dot.

Effects of tensile strain in barrier on optical gain spectra of GaInNAs/GaAsN quantum wells

The band structures, optical gain spectra, and transparency radiative current densities of compressive-strained GaInNAs quantum wells (QWs) with different tensile-strained GaAsN (N composition from 0 to 3%) barriers are systematically investigated using a modified 6×6 k⋅p Hamiltonian including the heavy hole, light hole, and spin-orbit splitting bands. We found that the transition energy decreases when increasing the N composition in the barrier. The optical gain spectra and maximum optical gain as a function of carrier density and radiative current density are obtained for the GaInNAs/GaAsN QWs with well width of 5 nm, InW=28%, and NW=2.66% emitting around 1.55 μm. The transparency carrier density increases with the nitrogen composition in the GaAsN barrier. The transparency radiative current density decreases with more nitrogen being added into the barrier, which is in agreement with the recent experimental observation.

Excited States of InAs/GaAs Quantum Dots

Exciton properties of self-organized InAs/GaAs QDs are investigated. Size-selective spectroscopy reveals the excited single-exciton transition spectrum and enhanced polar exciton-LO-phonon coupling. A good qualitative understanding of the experimental results is achieved by eight-band k.p calculations. Renormalization of the single-exciton spectrum in highly populated QDs shows the importance of many-particle interactions in the strong confinement limit. The ground state transition energy decreases by ∼16 meV for QDs occupied with ∼18 excitons.

Many-body effects on the optical spectra of InAs/GaAs quantum dots

Many-body effects on the exciton spectra of self-organized InAs/GaAs quantum dots (QD's) are investigated in high-density photoluminescence experiments. Opposite renormalization of the ground- and excited-state transition energies is observed with increasing exciton occupation of the QD's. The ground-state transition energy decreases by \ensuremath{\sim}16 meV whereas the excited-state transition energies increase up to \ensuremath{\sim}26 meV for an average occupation with 18 excitons corresponding to a volume density of $\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}.$ The shrinkage of the ground-state transition energy normalized to the exciton binding energy is significantly smaller than band-gap renormalization in higher dimensional systems supporting the strong confinement in the self-organized InAs/GaAs QD's.

Fluorescence and photoinversion reactions in solutions of chiral diaryl sulfoxides with various sizes of aromatic rings

Chiral aryl 4-tolyl sulfoxides substituted with several sizes of aromatic rings, (S)-(−)-phenyl 4-tolyl sulfoxide (PHSO), (R)-(+)-1-naphthyl 4-tolyl sulfoxide (NASO), (R)-(+)-9-phenanthryl 4-tolyl sulfoxide (PNSO), and (R)-(+)-1-pyrenyl 4-tolyl sulfoxide (PYSO), were prepared. It has turned out for the first time that there are n–σ*, π–σ* and π–π* states in excited states of these molecules by MO calculation. Fluorescence spectra and quantum yields of fluorescence, Φ fl, were measured in polar and non-polar solvents. Quantum yields of photoinversion, Φ inv, and photolysis, Φ dec, were also obtained with CD and HPLC measurements. Aromatic-ketone like characteristics have been noticed in the fluorescence measurements, i.e., fluorescence has been observed from sulfoxides substituted with large aromatic rings and their fluorescence becomes strong in a polar solvent. We attributed these characteristics to the decrease in π–π* transition energy as the degree of conjugation increases, while n–σ* and π–σ* transition energy does not decrease so much. The values of Φ inv and Φ dec for PHSO, NASO and PNSO were found to be 0.3–0.4 (Φ inv) and 0.03–0.05 (Φ dec). The quantum yields for PYSO were measured as Φ inv = 0.02–0.03 in methanol and hexane, and Φ dec = 0.002–0.003 in methanol and 0.012–0.016 in hexane. It was found that quantum yields of photoinversion and photolysis decrease as the π–π* transition energy decreases. We concluded that photoinversion occur during change in electronic states from n–σ* states to the ground state.