scholarly journals Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO2 reduction

2016 ◽  
Vol 113 (50) ◽  
pp. E8011-E8020 ◽  
Author(s):  
Laura B. Hoch ◽  
Paul Szymanski ◽  
Kulbir Kaur Ghuman ◽  
Le He ◽  
Kristine Liao ◽  
...  
Keyword(s):  
Photocatalytic Activity ◽  
Excited State ◽  
Oxygen Vacancy ◽  
Band Gap ◽  
Gas Phase ◽  
Density Functional ◽  
Carrier Dynamics ◽  
Valuable Insight ◽  
Relaxation Dynamics ◽  
Excitation Energies

In2O3-x(OH)y nanoparticles have been shown to function as an effective gas-phase photocatalyst for the reduction of CO2 to CO via the reverse water–gas shift reaction. Their photocatalytic activity is strongly correlated to the number of oxygen vacancy and hydroxide defects present in the system. To better understand how such defects interact with photogenerated electrons and holes in these materials, we have studied the relaxation dynamics of In2O3-x(OH)y nanoparticles with varying concentration of defects using two different excitation energies corresponding to above-band-gap (318-nm) and near-band-gap (405-nm) excitations. Our results demonstrate that defects play a significant role in the excited-state, charge relaxation pathways. Higher defect concentrations result in longer excited-state lifetimes, which are attributed to improved charge separation. This correlates well with the observed trends in the photocatalytic activity. These results are further supported by density-functional theory calculations, which confirm the positions of oxygen vacancy and hydroxide defect states within the optical band gap of indium oxide. This enhanced understanding of the role these defects play in determining the optoelectronic properties and charge carrier dynamics can provide valuable insight toward the rational development of more efficient photocatalytic materials for CO2 reduction.

scholarly journals Designing small organic non-fullerene acceptor molecules with diflorobenzene or quinoline core and dithiophene donor moiety through density functional theory

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ghulam Bary ◽  
Lubna Ghani ◽  
Muhammad Imran Jamil ◽  
Muhammad Arslan ◽  
Waqar Ahmed ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Solar Cells ◽  
Band Gap ◽  
Gas Phase ◽  
Organic Solar Cells ◽  
Density Functional ◽  
Excitation Energies ◽  
Functional Theory ◽  
Reorganization Energies ◽  
Donor Moiety

AbstractThe non-fullerene acceptors A1–A5 with diflourobenzene or quinoline core (bridge) unit, donor cyclopenta[1,2-b:3,4-b′]dithiophene unit and 2-(2-methylene-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile as acceptor unit with additional phenyl, fulvene or thieno[3,2-d]pyrimidinyl 5-oxide groups have been designed through DFT calculations. The optimization of molecular geometries were performed with density functional theory (DFT) at B3LYP 6-31G (d,p) level of theory. The frontier molecular orbital (FMO) energies, band gap energies and dipole moments (ground and excited state) have been calculated to probe the photovoltaic properties. The band gap (1.42–2.01 eV) and dipole moment values (5.5–18. Debye) showed that these designed acceptors are good candidates for organic solar cells. Time-Dependent Density Functional Theory (TD-DFT) results showed λmax (wave length at maximum absorption) value (611–837 nm), oscillator strength (f) and excitation energies (1.50–2.02 eV) in gas phase and in CHCl3 solvent (1.48–1.89 eV) using integral equation formalism variant (IEFPCM) model. The λmax in CHCl3 showed marginal red shift for all designed acceptors compared with gas phase absorption. The partial density of states (PDOS) has been plotted by using multiwfn which showed that all the designed molecules have more electronic distribution at the donor moiety and lowest at the central bridge. The reorganization energies of electron (λe) (0.0007 eV to 0.017 eV), and the hole reorganization energy values (0.0003 eV to − 0.0403 eV) were smaller which suggested that higher charged motilities. The blends of acceptors A1–A5 with donor polymer D1 provided open circuit voltage (Voc) and ∆HOMO off-set of the HOMO of donor and acceptors. These blends showed 1.04 to 1.5 eV values of Voc and 0 to 0.38 eV ∆HOMO off set values of the donor–acceptor bends which indicate improved performance of the cell. Finally, the blend of D1–A4 was used for the study of distribution of HOMO and LUMO. The HOMO were found distributed on the donor polymer (D1) while the A4 acceptor was found with LUMO distribution. Based on λmax values, and band gap energies (Eg), excitation energies (Ex), reorganization energies; the A3 and A4 will prove good acceptor molecules for the development of organic solar cells.

Multiconfiguration pair-density functional theory for doublet excitation energies and excited state geometries: the excited states of CN

2017 ◽  
Vol 19 (44) ◽  
pp. 30089-30096 ◽  
Author(s):  
Jie J. Bao ◽  
Laura Gagliardi ◽  
Donald G. Truhlar
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Excited States ◽  
Density Functional ◽  
Excitation Energies ◽  
Functional Theory ◽  
Pair Density

MC-PDFT is more accurate than CR-EOM-CCSD(T) or TDDFT when averaged over the first four adiabatic excitation energies of CN.

Structural and Electronic Properties of Oxygen Vacancies in Monoclinic HfO2

2007 ◽  
Vol 996 ◽  
Author(s):  
Peter Broqvist ◽  
Alfredo Pasquarello
Keyword(s):  
Oxygen Vacancy ◽  
Optical Absorption ◽  
Total Energy ◽  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Structural And Electronic Properties ◽  
Defect Levels ◽  
Hybrid Density Functional

AbstractWe study structural and electronic properties of the oxygen vacancy in monoclinic HfO2 for five different charge states. We use a hybrid density functional to accurately reproduce the experimental band gap. To compare with measured defect levels, we determine total-energy differences appropriate to the considered experiments. Our results show that the oxygen vacancy can consistently account for the defect levels observed in optical absorption, direct electron injection, and trap-assisted conduction experiments.

The effects of Sc doping and O vacancy on the electronic states and optical properties of m-BiVO4

2020 ◽  
Author(s):  
Yuhong Huang ◽  
Xiaqing Zhang ◽  
Jingnan Wang ◽  
Jianmin Zhang ◽  
Xiumei Wei ◽  
...  
Keyword(s):  
Optical Properties ◽  
Oxygen Vacancy ◽  
Band Gap ◽  
Density Functional ◽  
Electronic States ◽  
Dft Method ◽  
Defect Concentration ◽  
Direct Band Gap ◽  
Direct Band ◽  
The Ideal

Based on density functional theory (DFT), the effects of scandium (Sc) doping and oxygen vacancy (VO) on the electronic states and optical properties of BiVO4 are investigated. GGA+U method is adopt during the calculation of the electronic properties to compensate the limitation of DFT method. The ideal BiVO4 has a direct band gap of 2.400 eV, and if Bi in BiVO4 is substituted by Sc (sub Sc-Bi), the direct band gap will be reduced to 2.393 eV. However, if V is replaced by Sc (sub Sc-V) as well as that with oxygen vacancy induced (sub Sc-V+Vo), the band gap will become indirect one with values of 1.913 eV and 2.198 eV, respectively. The reduction capability is in the sequence of sub Sc-Bi > ideal > sub Sc-V+Vo > sub Sc-V, while the oxidation capability is in the order of ideal > sub Sc-Bi > sub Sc-V+Vo > sub Sc-V. The ε<sub>1</sub> (0) of the ideal, sub Sc-Bi, subSc-V and sub Sc-V+Vo defective BiVO4 is 8.290, 8.293, 12.791 and 8.285, respectively. The optical absorptions of ideal and sub Sc-Bi BiVO4 show anisotropy and they are nearly independent on the defect concentration. Sub Sc-V BiVO4 exhibits stronger absorption than the other three semiconductors. The absorptions of sub Sc-V+Vo BiVO4 vary obviously with the defect concentrations, where 3.906% defect concentration of BiVO4 has the strongest absorptions. The estimated optical band gaps are smaller than for ideal and defective BiVO4.

Ultrafast excited-state relaxation of a binuclear Ag(i) phosphine complex in gas phase and solution

2017 ◽  
Vol 19 (34) ◽  
pp. 22785-22800 ◽  
Author(s):  
S. V. Kruppa ◽  
F. Bäppler ◽  
W. Klopper ◽  
S. P. Walg ◽  
W. R. Thiel ◽  
...  
Keyword(s):  
Excited State ◽  
Gas Phase ◽  
Relaxation Dynamics ◽  
Phosphine Complex

The [Ag2(dcpm)2]2+ phosphine complex displays multiexponential excited-state relaxation dynamics both in the gas phase and in solution.

scholarly journals A wavelength dependent investigation of the indole photophysics via ionization and fragmentation pump–probe spectroscopies

2015 ◽  
Vol 17 (38) ◽  
pp. 25197-25209 ◽  
Author(s):  
T. J. Godfrey ◽  
Hui Yu ◽  
Michael S. Biddle ◽  
Susanne Ullrich
Keyword(s):  
Excited State ◽  
Gas Phase ◽  
Spectroscopic Techniques ◽  
Relaxation Dynamics ◽  
Pump Probe ◽  
State Involvement

Using a variety of gas-phase pump–probe spectroscopic techniques, this work investigates indole excited-state relaxation dynamics at several pump wavelengths with a particular focus on 1πσ*-state involvement.

STUDY OF THE S1 AND S2 EXCITED STATES OF GAS-PHASE PROTONATED SCHIFF BASE RETINAL CHROMOPHORES IN ONE AND TWO PHOTON ABSORPTION

2011 ◽  
Vol 10 (02) ◽  
pp. 121-132 ◽  
Author(s):  
YUANZUO LI ◽  
PENG SONG ◽  
YING SHI ◽  
YONG DING ◽  
FENGJIE ZHOU ◽  
...  
Keyword(s):  
Schiff Base ◽  
Excited State ◽  
Charge Transfer ◽  
Gas Phase ◽  
Excited States ◽  
Density Functional ◽  
Three Dimensional ◽  
Photon Absorption ◽  
Two Photon ◽  
The One

The S1 and S2 excited states of gas-phase protonated Schiff base retinal chromophores in the one- and two-photon absorptions (TPAs) are investigated with time-dependent density functional theory. In one-photon absorption, the two-dimensional (2D) site and three-dimensional (3D) cube representations reveal that S1 and S2 excited states of gas-phase protonated Schiff base retinal chromophores are all charge transfer excited states. To better study the weak S2 excited states of gas-phase protonated Schiff base retinal chromophores, we investigated theoretically excited state properties of them in TPA. For 11-cis dimethyl retinal, it is found that the cross section of S2 excited state is 51.04 GM in PTA, which is only slightly smaller than that of S1 (77.04 GM) in TPA. Therefore, the S2 excited state of 11-cis dimethyl retinal can be clearly observed in TPA experiment. The 2D site and 3D cube representations reveal that electronic transition from S1 to S2 excited state of gas-phase protonated Schiff base retinal chromophores in TPA are also of charge transfer character.

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