Unusually Slow Electron Cooling to Charge-Transfer State in Gradient CdTeSe Alloy Nanocrystals Mediated through Mn Atom

Understanding the charge transfer dynamics of the Cu2WS4-CNT-FeOOH ternary composite for photo-electrochemical studies

Ternary transition metal chalcogenide (Cu2WS4) is a semiconductor with a band gap of 2.1 eV and could be a promising candidate for photoelectrochemical water splitting and solar energy conversion applications. Despite numerous reports on ternary transition metal chalcogenides, this semiconductor's ultrafast charge transfer dynamics remain unknown. Here, we report on charge carrier dynamics in a pristine Cu2WS4 system with the aid of ultrafast transient (TA) pump-probe spectroscopy and a hot carrier transfer process from Cu2WS4 to multi-walled carbon nanotubes (CNTs) and FeOOH has been observed. Furthermore, we have explored Cu2WS4-FeOOH having a type-II composite for photo-electrochemical (PEC) water oxidation and modified this with the addition of multi-walled carbon nanotubes to expedite the charge-transfer processes and photo-anodic performance. The photo-electrochemical studies demonstrate that the Cu2WS4-CNT, Cu2WS4-FeOOH, and Cu2WS4-CNT-FeOOH provide nearly 3-, 8- and 12-fold enhancement in photocurrent density relative to the bare Cu2WS4 photo-anode at 1.23 V vs. RHE. These photo-electrochemical studies support the results obtained from the TA investigation and further prove the higher charge separation in the ternary composite system. These studies probe the excited states and provide evidence of longer charge separation in the binary and ternary composites, responsible for their remarkable photo-electrochemical performance.

Effect of Mn2+ incorporation on the photoelectrochemical properties of BiVO4

Mn2+–BiVO4 photoanodes (Mn2+ = 0.2–1%) to improve the charge-carrier separation and electrical conductivity of BiVO4 are reported.

Concurrent Energy- and Electron-Transfer Dynamics in Photoexcited Mn-Doped CsPbBr3 Perovskite Nanoplatelet Architecture

Mn-doped perovskites have already been widely explored in the context of interesting optical, electronic, and magnetic properties. Such fascinating traits showcased by them explain the huge augmentation in the device efficiency, directing their widespread application in the field of solar cells, energy- harvesting sectors, and light-emitting diodes. However, the underlying photophysics governing the overall charge carrier dynamics in Mn-doped CsPbBr₃ nanoplatelets (NPLs) has never been discussed and therefore demands an in-depth investigation. Herein, fluorescence up-conversion and femtosecond transient absorption (TA) spectroscopy are employed for gaining a comprehensive understanding of the excited-state dynamics and the fundamental energy/charge-transfer processes for two-dimensional CsPbBr₃ nanoplatelets (NPLs) and their Mn-doped counterparts. The up-conversion measurement clearly suggests the possibility of energy-transfer pathways in the Mn-doped CsPbBr₃ NPLs. Interestingly, strong indication of charge transfer (CT) in Mn-doped CsPbBr₃ NPLs was unambiguously established by an ultrafast TA approach. Our investigation clearly suggests that both the probable processes viz. the ultrafast energy and electron transfers noticeable in the Mn²⁺-doped CsPbBr₃ NPLs are utterly competitive and rapid owing to the highly confined nature of the two-dimensional NPLs. This extensive probing of concurrent charge/energy-transfer processes may pave help clarify unresolved anomalies in Mn-doped perovskites, which may prove advantageous for a wide range of practical applicability.

Energetic hot electrons from exciton-to-hot electron upconversion in Mn-doped semiconductor nanocrystals

Generation of hot electrons and their utilization in photoinduced chemical processes have been the subjects of intense research in recent years mostly exploring hot electrons in plasmonic metal nanostructures created via decay of optically excited plasmon. Here, we present recent progress made in generation and utilization of a different type of hot electrons produced via biphotonic exciton-to-hot electron "upconversion" in Mn-doped semiconductor nanocrystals. Compared to the plasmonic hot electrons, those produced via biphotonic upconversion in Mn-doped semiconductor nanocrystals possess much higher energy, enabling more efficient long-range electron transfer across the high energy barrier. They can even be ejected above the vacuum level creating photoelectrons, which can possibly produce solvated electrons. Despite the biphotonic nature of the upconversion process, hot electrons can be generated with weak cw excitation equivalent to the concentrated solar radiation without requiring intense or high-energy photons. This perspective reviews recent work elucidating the mechanism of generating energetic hot electrons in Mn-doped semiconductor nanocrystals, detection of these hot electrons as photocurrent or photoelectron emission, and their utilization in chemical processes such as photocatalysis. New opportunities that the energetic hot electrons can open by creating solvated electrons, which can be viewed as the longer-lived and mobile version of hot electrons more useful for chemical processes, and the challenges in practical utilization of energetic hot electrons are also discussed.

Ultrafast charge carrier dynamics in CdSe/V2O5 core/shell quantum dots

Ultrafast transient absorption (TA) spectroscopy has been carried out to study the charge carrier dynamics of CdSe core and CdSe/V2O5 core/shell quantum dots (QDs). A significant redshift accompanied by broadening in the first excitonic peak was observed in the UV-Vis absorption spectra of the core/shell QDs as the shell thickness increases. This interesting observation is related to a quasi-type-II alignment characterized by the spatial separation of an electron into the core/shell and a hole into the core. The observed optical excitonic spectra have further been used to study the energetics of CdSe and charge separated states with the concept of Marcus theory and confirmed that electron transfer takes place in the Marcus inverted region (). Moreover, the growth kinetics of the CdSe core and CdSe/V2O5 core/shell QDs, studied with TA spectroscopy, exhibits slow electron cooling in core/shell QDs because of the de-coupling of the electronic wave functions with their hole counterpart. These exciting properties reveal a new paradigm shift from CdSe QDs to CdSe/V2O5 core/shell QDs for highly suitable applications in photovoltaics (PV) and optoelectronic devices.

Synthesis, properties, and formation mechanism of Mn-doped Zn2SiO4 nanowires and associated heterostructures

Charge transfer and energy transfer phenomena were observed and analyzed in heterostructure systems composed of CdSe QDs immobilized onto Mn-doped Zn₂SiO₄ nanowire host materials.

Ultrafast spectroscopic studies of composition-dependent near-infrared-emitting alloyed CdSeTe quantum dots

In this study, ultrafast optical properties of composition-dependent near infrared-emitting alloyed CdSeTe quantum dots are measured and analyzed.

Near-infrared emitting CdTeSe alloyed quantum dots: Raman scattering, photoluminescence and single-emitter optical properties

The synthesis of ternary core/shell zinc-blende CdTeSe/ZnSe quantum dots with optimal synthesis parameters is analyzed.