Surface and interface effects on non-radiative exciton recombination and relaxation dynamics in CdSe/Cd,Zn,S nanocrystals

Walsh, Brenna; Saari, Jonathan I.; Krause, Michael; Nick, Robert; Coe‐Sullivan, Seth; Kambhampati, Patanjali

doi:10.1016/j.chemphys.2015.11.004

Cited by 16 publications

(22 citation statements)

References 28 publications

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“…In doing so, transient decay traces depend on the pump pulse fluence (all set of data SI2, Figure S2 ). The dependence of transient decay kinetics on the pump fluence due to the process of the multiexciton recombination and surface trapping was reported previously [ 1 , 21 , 28 , 29 , 31 , 35 ].…”

Section: Resultssupporting

confidence: 57%

Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence

et al. 2017

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The main goal of the present work is to study the coherent phonon in strongly confined CdSe quantum dots (QDs) under varied pump fluences. The main characteristics of coherent phonons (amplitude, frequency, phase, spectrogram) of CdSe QDs under the red-edge pump of the excitonic band [1S(e)-1S3/2(h)] are reported. We demonstrate for the first time that the amplitude of the coherent optical longitudinal-optical (LO) phonon at 6.16 THz excited in CdSe nanoparticles by a femtosecond unchirped pulse shows a non-monotone dependence on the pump fluence. This dependence exhibits the maximum at pump fluence ~0.8 mJ/cm2. At the same time, the amplitudes of the longitudinal acoustic (LA) phonon mode at 0.55 THz and of the coherent wave packet of toluene at 15.6, 23.6 THz show a monotonic rise with the increase of pump fluence. The time frequency representation of an oscillating signal corresponding to LO phonons revealed by continuous wavelet transform (CWT) shows a profound destructive quantum interference close to the origin of distinct (optical phonon) and continuum-like (exciton) quasiparticles. The CWT spectrogram demonstrates a nonlinear chirp at short time delays, where the chirp sign depends on the pump pulse fluence. The CWT spectrogram reveals an anharmonic coupling between optical and acoustic phonons.

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Section: Resultssupporting

confidence: 57%

Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence

et al. 2017

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“…We showed that there is a XX SS as well . This electronic structure of X and XX governs the gain threshold, as illustrated in Figure . , …”

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confidence: 54%

Understanding and Exploiting the Interface of Semiconductor Nanocrystals for Light Emissive Applications

2017

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Semiconductor nanocrystals have been extensively studied for optoelectronic applications including light emission, the focus of this review. Historically, the core of the nanocrystal was the main aspect of the system as it gives rise to the confined excitons and multiexcitons which absorb and emit light. In addition to the core, the surface or interface of these nanocrystals is also important by virtue of their small size. Yet, our understanding of the surface is in its early stages in terms of both chemical and electronic structure. Here, we review the ways in which the interface can control the excitonics, which gives rise to optoelectronic function. We focus our discussion on the ways in which the interface can control optical gain for nanocrystal lasers and white light generation for nanocrystal based light emitting diodes. These processes are connected to different interfacial structures. Finally, we discuss two new applications based on surface electronic structure control: optical switching and optical thermometry. The work here suggests that the interface of nanocrystals should be a profitable route for chemical control of the electronic structure which can yield both performance enhancements as well as qualitatively different functional behavior.

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“…[31][32][33] Hole trapping states also affect the AR lifetimes by altering the electronhole interactions and, therefore, significantly impacting the kinetic competition between hole transfer and AR dynamics. [34][35][36] Ultrafast transient absorption (TA) spectroscopy provides the time resolution required to directly track the population of holes in different states as they have established that phenothiazine derivatives can serve as a class of hole acceptors for CdS QDs or nanorods with both the high driving force and the necessary optical signature in TA to track hole transfer. 31,37,38 In these model systems, ultrafast hole trapping was observed within ~1 ps following photo-excitation, and trap-mediated hole transfer dynamics were investigated under single-excitonic or bi-excitonic conditions.…”

Section: Introductionmentioning

confidence: 99%

“…For metal chalcogenide QDs, hole trap states are prevalent on the surface due to underpassivated chalcogenide atoms. , The multitude of these relatively localized hole traps play an important role in mediating hole transfer from delocalized valence band (VB) states to surface bound acceptors. − Hole-trapping states also affect the AR lifetimes by altering the electron–hole interactions and, therefore, significantly impacting the kinetic competition between hole transfer and AR dynamics. − Ultrafast transient absorption (TA) spectroscopy provides the time resolution required to directly track the population of holes in different states as they migrate from QDs to acceptors. Previous works with TA methods by Lian et al and Weiss et al have established that phenothiazine derivatives can serve as a class of hole acceptors for CdS QDs or nanorods with both the high driving force and the necessary optical signature in TA to track hole transfer. ,, In these model systems, ultrafast hole trapping was observed within ∼1 ps following photoexcitation, and trap-mediated hole-transfer dynamics were investigated under single-excitonic or biexcitonic conditions.…”

Section: Introductionmentioning

confidence: 99%

Uncovering the Role of Hole Traps in Promoting Hole Transfer from Multiexcitonic Quantum Dots to Molecular Acceptors

et al. 2020

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Understanding electronic dynamics in multi-excitonic quantum dots (QDs) is important for designing efficient systems useful in high power scenarios, such as solar concentrators and multielectron charge transfer. The multiple charge carriers within a QD can undergo undesired Auger recombination events, which rapidly annihilate carriers on picosecond timescales and generate heat from absorbed photons instead of useful work. Compared to the transfer of multiple electrons, the transfer of multiple holes has proven to be more difficult due to slower hole transfer rates. To probe the competition between Auger recombination and hole transfer in CdSe, CdS, and CdSe/CdS QDs of varying sizes, we synthesized a phenothiazine derivative, with optimized functionalities for binding to QDs as a hole accepting ligand and for spectroscopic observation of hole transfer. Transient absorption spectroscopy was used to monitor the photoinduced absorption features from both trapped holes and oxidized ligands under excitation fluences where the averaged initial number of excitons in a QD ranged from ~1 to 19. We observed fluence-dependent hole transfer kinetics that last around 100 ps longer than the predicted Auger recombination lifetimes, and the transfer of up to 3 holes per QD. Theoretical modeling of the kinetics suggests that binding of hole acceptors introduces trapping states significantly different from those in native QDs passivated with oleate ligands. Holes in these modified trap states have prolonged lifetimes, which promotes the hole transfer efficiency. These results highlight the beneficial role of hole trapping states in devising hole transfer pathways in QD-based systems under multi-excitonic conditions.

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Surface and interface effects on non-radiative exciton recombination and relaxation dynamics in CdSe/Cd,Zn,S nanocrystals

Cited by 16 publications

References 28 publications

Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence

Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence

Understanding and Exploiting the Interface of Semiconductor Nanocrystals for Light Emissive Applications

Uncovering the Role of Hole Traps in Promoting Hole Transfer from Multiexcitonic Quantum Dots to Molecular Acceptors

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