Dynamics and spatial distribution of edge luminescence generators in CDS from time-resolved excitation spectroscopy

Jiang, H. X.; Baum, D.; Hönig, A.

doi:10.1016/0022-2313(88)90328-6

Cited by 4 publications

(1 citation statement)

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“…Here we extend the light absorption of the TiO 2 –Ni(OH) 2 photoelectrode through photosensitization with CdS nanocrystals. CdS-sensitized TiO 2 has been researched extensively as photoanode in quantum dot sensitized solar cells. − CdS was also an early candidate for solar water splitting, given its straddled conduction and valence band positions relative to the water reduction and oxidation potentials. − However, OER cannot compete with the water-mediated photocorrosion reaction at the electrode–electrolyte interface, leading to electrode disintegration and failure. − The current approach represents a maiden effort in developing a midband gap semiconductor-catalyst architecture (CdS–Ni(OH) 2 ) that can harness urea as sacrificial electron donor for the sustainable production of hydrogen by side-stepping OER. We probed the charge-carrier transfer and recombination kinetics to provide insight into the photoelectrochemical performance of the semiconductor-catalyst architecture.…”

Section: Introductionmentioning

confidence: 99%

Ni(OH)₂ as Hole Mediator for Visible Light-Induced Urea Splitting

et al. 2018

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Urea is a small molecule produced in millions of tons per day and is ubiquitous in nature. Biological treatment is commonly used to oxidize the urea wastewater produced each day across the world, which produces additional solid waste and eliminates any potential for utilizing the stored chemical energy within. A solar waste-to-fuels concept is presented to synergistically produce hydrogen fuel from visible sunlight while remediating urea wastewaters. A cascade semiconductor-catalyst electrode assembly was designed to drive the photoconversion of urea to hydrogen. Proper band energy alignment facilitates catalyst activation via hole transfer across the semiconductor–catalyst interface. Specifically CdS-sensitized TiO2 with Ni(OH)2 urea electrocatalyst on fluorine-doped tin oxide coated glass was employed as photoanode. The steady-state response of the semiconductor–catalyst electrode is investigated in a photoelectrochemical cell, and charge transfer and recombination kinetics are elucidated to identify limiting charge-transfer reactions within the electrode architecture. Back electron transfer from semiconductor to catalyst is found to be competitive with urea oxidation reaction, which hinders steady-state photoconversion efficiency. Furthermore, the photoanode rapidly decomposes in urea electrolyte solutions as a result of the water-mediated photocorrosion of chalcogenide electrodes. Passivation of CdS with ZnS prior to catalyst deposition significantly improves open-circuit potential and photostability.

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Section: Introductionmentioning

confidence: 99%

Ni(OH)₂ as Hole Mediator for Visible Light-Induced Urea Splitting

et al. 2018

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Dynamics of bound-exciton energy transformation to edge-luminescence centers in CdS

Lin

Baum

Zhu

et al. 1990

Journal of Luminescence

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Direct observation of edge luminescence excited by long-lived-exciton-polariton propagation in CdS

et al. 1989

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Low-temperature time-resolved edge-luminescence excitation spectroscopy has been used to probe the exciton-polariton transport properties in CdS crystals of up to 3 mm thickness. We report the first direct experimental observation of edge luminescence excited by long-lived polaritons with lifetimes exceeding 400 ns which propagate from their origin at the front sample surface to the rear surface, appearing as delayed peaks in the temporal response of edge luminescence. The A exciton-polariton group-velocity distribution is obtained. A group-velocity minimum of 6.8x105 cm/s corresponding to the "bottleneck" energy has been observed.Due to the photon-exciton interaction in semiconductors, there arise new elementary excitations, which are essentially mixed states of the photon and exciton: excitonic polaritons. Exciton polaritons are very important in understanding the optical properties of many semiconductors at low temperatures and their properties are still being investigated extensively. ' In this paper, dynamics of long-lived exciton polaritons in model substances, CdS crystals, have been investigated by using time-resolved edge-luminescence excitation spectroscopy. There are basically two series of edge emission bands present in CdS crystals. One is the low-energy series (LES) emission due to the radiative recombination between a hole bound to an ionized acceptor and an electron bound to an ionized donor, which is also referred to as the "bound-to-bound" or "donor-acceptor pair" transition; the other, denoted as the high-energy series (HES) emission, due to the recombination of a free electron in the conduction band and a neutral acceptor, is the "freeto-bound" transition. From edge-luminescence emission-intensity measurements on CdS, it was deduced that the edge emission from the rear surface is generated by polaritons propagating from their front surface origin.It was also shown by Itm) CuC1 single crystals, polariton propagation effects play an essential role in determining the temporal behavior of the free-exciton luminescence. In order to fully explore the polariton effect, we present experimental results of very monochromatic excitation measurements on bound-to-bound and free-to-bound transitions for excitation energies in the vicinity of the highly absorptive region of the A exciton resonance, which corresponds to the lower-polariton branch in the dispersion curve. We directly observed the delayed rear surface polaritongenerated edge luminescence in CdS crystals of thicknesses up to 3 mm.The uncompensated ultrahigh purity (UHP) CdS samples of cross-sectional area of approximately 30 mm and thicknesses d=2.6 and 0.83 mm, grown by vapor phase transport starting from high-purity powder, were obtained from Eagle-Picher Industries, Inc. Two laser excitation source configurations were employed in this work. They consist of (i) a high spectral resolution (0.01-nm) dye laser driven by a 3-ns pulsed Nz laser (Laser Science, O OO 2.6(mm), o 486.05 485.95 485.80 485.60 0 485.50~+ .2(K} nm Am nm nm nm 0 5X X X...

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Dynamics and spatial distribution of edge luminescence generators in CDS from time-resolved excitation spectroscopy

Cited by 4 publications

References 4 publications

Ni(OH)₂ as Hole Mediator for Visible Light-Induced Urea Splitting

Ni(OH)₂ as Hole Mediator for Visible Light-Induced Urea Splitting

Dynamics of bound-exciton energy transformation to edge-luminescence centers in CdS

Direct observation of edge luminescence excited by long-lived-exciton-polariton propagation in CdS

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Dynamics and spatial distribution of edge luminescence generators in CDS from time-resolved excitation spectroscopy

Cited by 4 publications

References 4 publications

Ni(OH)2 as Hole Mediator for Visible Light-Induced Urea Splitting

Ni(OH)2 as Hole Mediator for Visible Light-Induced Urea Splitting

Dynamics of bound-exciton energy transformation to edge-luminescence centers in CdS

Direct observation of edge luminescence excited by long-lived-exciton-polariton propagation in CdS

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Product

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Ni(OH)₂ as Hole Mediator for Visible Light-Induced Urea Splitting

Ni(OH)₂ as Hole Mediator for Visible Light-Induced Urea Splitting