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Spectroscopic Studies of Semiconduct...

Hasham, Minhal,

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Spectroscopic Studies of Semiconductor Nanocrystals: From Core, to Surface, and Beyond /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Spectroscopic Studies of Semiconductor Nanocrystals: From Core, to Surface, and Beyond // Minhal Hasham.
Author:	Hasham, Minhal,
Description:	1 electronic resource (211 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-01, Section: B.
Contained By:	Dissertations Abstracts International85-01B.
Subject:	Chemistry. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30243155
ISBN:	9798379765927

Spectroscopic Studies of Semiconductor Nanocrystals: From Core, to Surface, and Beyond /
Hasham, Minhal,

Spectroscopic Studies of Semiconductor Nanocrystals: From Core, to Surface, and Beyond /Minhal Hasham. - 1 electronic resource (211 pages)

Source: Dissertations Abstracts International, Volume: 85-01, Section: B.

Semiconductor nanocrystals (NCs) have been actively investigated for the past 40 years due to their easily-tunable optical properties and rich, size-dependent photophysics. While technologies using NCs as the active material have already been commercialized, fundamental photophysical puzzles endure. Particularly, their optical properties often diverge from simple theoretical predictions. In this thesis, we explore the fundamental photophysics of two NC materials, CdSe and PbS. We begin by briefly reviewing canonical models for the electronic structure and optical properties of CdSe NCs. Then, we explore single-particle photophysics by developing a novel spectroscopic technique to interact with NC excited states. We show that all-optical modulation can perturb the ubiquitous 'blinking' phenomenon in CdSe/ZnS core-shell NCs. We demonstrate that this perturbation is timescale-free, characteristic, and selective for the ON-state. Next, we probe the kinetics of triplet energy transfer from core-only CdSe NCs to surface-bound anthracene moieties. Tailoring the energy level alignment between NC band-edges and frontier molecular orbitals, we find that sequential, hole-first carrier transfer outpaces correlated, Dexter-like exciton transfer when the barrier to the former is comparable to a few kBT. In tandem, measurements of energy transfer from surface-oriented trap states in the same NCs support a hypothesis where band-edge and trap states remain in dynamic equilibrium. From the known energy of the lowest-lying spin-triplet exciton, we infer a lower bound on the chemical potential of the surface state. Finally, we investigate the fundamental photophysics of ultrasmall PbS NCs, motivated by recent synthetic advances that have yielded smaller ensemble absorption linewidths. Our spectroscopic studies provide tests of models constructed from observations on larger PbS NCs. We discuss our observations in the context of prior descriptions for PbS electronic structure and propose that direct extrapolation from previous models is unsatisfactory-leading to a call for dedicated theoretical calculations in this size regime. We conclude by looking forward to studies which extend the present work and discuss key experiments to continue shedding light on the photophysics of semiconductor nanocrystals.

English

ISBN: 9798379765927Subjects--Topical Terms:

516420
Chemistry.
Subjects--Index Terms:

Photophysics

Spectroscopic Studies of Semiconductor Nanocrystals: From Core, to Surface, and Beyond /
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520 $a Semiconductor nanocrystals (NCs) have been actively investigated for the past 40 years due to their easily-tunable optical properties and rich, size-dependent photophysics. While technologies using NCs as the active material have already been commercialized, fundamental photophysical puzzles endure. Particularly, their optical properties often diverge from simple theoretical predictions. In this thesis, we explore the fundamental photophysics of two NC materials, CdSe and PbS. We begin by briefly reviewing canonical models for the electronic structure and optical properties of CdSe NCs. Then, we explore single-particle photophysics by developing a novel spectroscopic technique to interact with NC excited states. We show that all-optical modulation can perturb the ubiquitous 'blinking' phenomenon in CdSe/ZnS core-shell NCs. We demonstrate that this perturbation is timescale-free, characteristic, and selective for the ON-state. Next, we probe the kinetics of triplet energy transfer from core-only CdSe NCs to surface-bound anthracene moieties. Tailoring the energy level alignment between NC band-edges and frontier molecular orbitals, we find that sequential, hole-first carrier transfer outpaces correlated, Dexter-like exciton transfer when the barrier to the former is comparable to a few kBT. In tandem, measurements of energy transfer from surface-oriented trap states in the same NCs support a hypothesis where band-edge and trap states remain in dynamic equilibrium. From the known energy of the lowest-lying spin-triplet exciton, we infer a lower bound on the chemical potential of the surface state. Finally, we investigate the fundamental photophysics of ultrasmall PbS NCs, motivated by recent synthetic advances that have yielded smaller ensemble absorption linewidths. Our spectroscopic studies provide tests of models constructed from observations on larger PbS NCs. We discuss our observations in the context of prior descriptions for PbS electronic structure and propose that direct extrapolation from previous models is unsatisfactory-leading to a call for dedicated theoretical calculations in this size regime. We conclude by looking forward to studies which extend the present work and discuss key experiments to continue shedding light on the photophysics of semiconductor nanocrystals.
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