Light Absorption, Carrier Recombination, and Luminescence

2017 ◽  
pp. 23-42
Author(s):  
Juan Bisquert
Keyword(s):  
Light Absorption ◽  
Carrier Recombination

scholarly journals Activation of Water on MnOx-Modified Rutile (110) and Anatase (101) TiO2 and the Role of Cation Reduction

2018 ◽  
Author(s):  
Michael Nolan ◽  
Stephen Rhatigan
Keyword(s):  
Oxygen Vacancy ◽  
Light Absorption ◽  
Density Functional ◽  
Vacancy Formation ◽  
Visible Range ◽  
Coulomb Interactions ◽  
Carrier Recombination ◽  
Oxygen Vacancy Formation ◽  
Surface Hydroxyls

Surface modification of titania surfaces with dispersed metal oxide nanoclusters has the potential to enhance photocatalytic activity. These modifications can induce visible light absorption and suppress charge carrier recombination which are vital in improving the efficiency. We have studied heterostructures of Mn<sub>4</sub>O<sub>6</sub> nanoclusters modifying the TiO<sub>2</sub> rutile (110) and anatase (101) surfaces using density functional theory corrected for on-site Coulomb interactions (DFT + U). Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. In our study we have considered partial hydroxylation of the rutile and anatase surfaces and the role of cation reduction, via oxygen vacancy formation, and how this impacts on a variety of properties governing the photocatalytic performance such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface and that modification extends light absorption into the visible range. MnO<sub>x</sub>-modified anatase can show an off-stoichiometric ground state, through oxygen vacancy formation and cation reduction spontaneously, and both modified rutile and anatase are highly reducible with moderate energy costs. Manganese ions are therefore present in a mixture of oxidation states. Photoexcited electrons and holes localize at cluster metal and oxygen sites, respectively. The interaction of water at the modified surfaces depends on the stoichiometry and spontaneous dissociation to surface bound hydroxyls is favoured in the presence of oxygen vacancies and reduced metal cations. Comparisons with bare TiO<sub>2</sub> and other TiO<sub>2</sub>-based photocatalyst materials are presented throughout.

Controllable synthesis of a 3D ZnS@MoO3 heterojunction via a hydrothermal method towards efficient NO purification under visible light

CrystEngComm ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 257-266 ◽  
Author(s):  
Ziyang Guo ◽  
Wangchen Huo ◽  
Tong Cao ◽  
Fangzheng Fan ◽  
Guangxu Ge ◽  
...  
Keyword(s):  
Charge Carrier ◽  
Visible Light ◽  
Hydrothermal Method ◽  
Light Absorption ◽  
Interface Reaction ◽  
Photocatalytic Efficiency ◽  
Controllable Synthesis ◽  
Carrier Recombination ◽  
Charge Carrier Recombination

Heterojunctions can deliver superior photocatalytic efficiency via modulating the surface-interface reaction, enhancing light absorption and hindering charge carrier recombination.

scholarly journals Activation of Water on MnOx-Modified Rutile (110) and Anatase (101) TiO2 and the Role of Cation Reduction

2018 ◽  
Author(s):  
Michael Nolan ◽  
Stephen Rhatigan
Keyword(s):  
Oxygen Vacancy ◽  
Light Absorption ◽  
Density Functional ◽  
Vacancy Formation ◽  
Visible Range ◽  
Coulomb Interactions ◽  
Carrier Recombination ◽  
Oxygen Vacancy Formation ◽  
Surface Hydroxyls

Surface modification of titania surfaces with dispersed metal oxide nanoclusters has the potential to enhance photocatalytic activity. These modifications can induce visible light absorption and suppress charge carrier recombination which are vital in improving the efficiency. We have studied heterostructures of Mn<sub>4</sub>O<sub>6</sub> nanoclusters modifying the TiO<sub>2</sub> rutile (110) and anatase (101) surfaces using density functional theory corrected for on-site Coulomb interactions (DFT + U). Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. In our study we have considered partial hydroxylation of the rutile and anatase surfaces and the role of cation reduction, via oxygen vacancy formation, and how this impacts on a variety of properties governing the photocatalytic performance such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface and that modification extends light absorption into the visible range. MnO<sub>x</sub>-modified anatase can show an off-stoichiometric ground state, through oxygen vacancy formation and cation reduction spontaneously, and both modified rutile and anatase are highly reducible with moderate energy costs. Manganese ions are therefore present in a mixture of oxidation states. Photoexcited electrons and holes localize at cluster metal and oxygen sites, respectively. The interaction of water at the modified surfaces depends on the stoichiometry and spontaneous dissociation to surface bound hydroxyls is favoured in the presence of oxygen vacancies and reduced metal cations. Comparisons with bare TiO<sub>2</sub> and other TiO<sub>2</sub>-based photocatalyst materials are presented throughout.

Luminescence from individual dislocations in II-VI and III-V semiconductors

1991 ◽  
Vol 49 ◽  
pp. 834-835
Author(s):  
J W Steeds
Keyword(s):  
Group Iv ◽  
Luminescence Properties ◽  
Carrier Recombination ◽  
Transmission Electron ◽  
Wide Range ◽  
Basic Physics ◽  
Semiconducting Compounds ◽  
Diamond Group ◽  
Non Destructive ◽  
Technological Significance

There is a wide range of experimental results related to dislocations in diamond, group IV, II-VI, III-V semiconducting compounds, but few of these come from isolated, well-characterized individual dislocations. We are here concerned with only those results obtained in a transmission electron microscope so that the dislocations responsible were individually imaged. The luminescence properties of the dislocations were studied by cathodoluminescence performed at low temperatures (~30K) achieved by liquid helium cooling. Both spectra and monochromatic cathodoluminescence images have been obtained, in some cases as a function of temperature.There are two aspects of this work. One is mainly of technological significance. By understanding the luminescence properties of dislocations in epitaxial structures, future non-destructive evaluation will be enhanced. The second aim is to arrive at a good detailed understanding of the basic physics associated with carrier recombination near dislocations as revealed by local luminescence properties.

Degradation Analysis and Degradation Suppression Technology Caused by Light Absorption at Active Layer Facet of GaInAsP Laser Diode

2008 ◽  
Vol 128 (5) ◽  
pp. 732-737
Author(s):  
Hiroyuki Ichikawa ◽  
Masashi Ito ◽  
Chie Fukuda ◽  
Kotaro Hamada ◽  
Akira Yamaguchi ◽  
...  
Keyword(s):  
Active Layer ◽  
Laser Diode ◽  
Light Absorption ◽  
Degradation Analysis

Lifetime Regime in the Electrically-Detected Transient Grating Method Applied to Amorphous and Microcrystalline Silicon Films

2002 ◽  
Vol 715 ◽  
Author(s):  
P. Sanguino ◽  
M. Niehus ◽  
S. Koynov ◽  
P. Brogueira ◽  
R. Schwarz ◽  
...  
Keyword(s):  
Carrier Transport ◽  
Analytical Calculation ◽  
Chemical Vapor ◽  
Silicon Films ◽  
Dielectric Relaxation Time ◽  
Transient Grating ◽  
Minority Carrier Diffusion Length ◽  
Carrier Recombination ◽  
Thin Silicon ◽  
Good Agreement

AbstractThe minority-carrier diffusion length in thin silicon films can be extracted from the electrically-detected transient grating method, EDTG, by a simple ambipolar analysis only in the case of lifetime dominated carrier transport. If the dielectric relaxation time, τdiel, is larger than the photocarrier response time, τR, then unexpected negative transient signals can appear in the EDTG result. Thin silicon films deposited by hot-wire chemical vapor deposition (HWCVD) near the amorphous-to-microcrystalline transition, where τR varies over a large range, appeared to be ideal candidates to study the interplay between carrier recombination and dielectric response. By modifying the ambipolar description to allow for a time-dependent carrier grating build-up and decay we can obtain a good agreement between analytical calculation and experimental results.

Recombination of Optically Excited Carriers in a-Si:H at Low temperatures and Intermediate Times

2002 ◽  
Vol 715 ◽  
Author(s):  
J. Whitaker ◽  
T. Su ◽  
P. C. Taylor
Keyword(s):  
Electron Spin Resonance ◽  
Low Temperatures ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Dipolar Relaxation ◽  
Spin Lattice ◽  
Carrier Recombination ◽  
Nmr Data ◽  
Spin Resonance ◽  
Time Regime

AbstractOptically induced electron spin resonance (LESR) studies on time scales in between the previously published PL and LESR results (approximately 10 ms to 10 s) allow one to examine the cross over between energy-loss (downward) hopping of carriers and carrier recombination via tunneling. In addition, data in this time regime are directly compared in the same sample with NMR data on the dipolar spin-lattice relaxation of the bonded hydrogen where light induced electrons and holes are responsible for dipolar relaxation of bonded hydrogen. The LESR results confirm the interpretation of the NMR measurements.

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