Integrating β‑Pb<sub>0.33</sub>V<sub>2</sub>O<sub>5</sub> Nanowires with CdSe Quantum Dots: Toward Nanoscale
Heterostructures with Tunable Interfacial Energetic Offsets for Charge
Transfer
Achieving directional charge transfer
across semiconductor interfaces
requires careful consideration of relative band alignments. Here,
we demonstrate a promising tunable platform for light harvesting and
excited-state charge transfer based on interfacing β-Pb<sub><i>x</i></sub>V<sub>2</sub>O<sub>5</sub> nanowires with
CdSe quantum dots. Two distinct routes are developed for assembling
the heterostructures: linker-assisted assembly mediated by a bifunctional
ligand and successive ionic layer adsorption and reaction (SILAR).
In the former case, the thiol end of a molecular linker is found to
bind to the quantum dot surfaces, whereas a protonated amine moiety
interacts electrostatically with the negatively charged nanowire surfaces.
In the alternative SILAR route, the surface coverage of CdSe nanostructures
on the β-Pb<sub><i>x</i></sub>V<sub>2</sub>O<sub>5</sub> nanowires is tuned by varying the number of successive precipitation
cycles. High-energy valence band X-ray photoelectron spectroscopy
measurements indicate that “mid-gap” states of the β-Pb<sub><i>x</i></sub>V<sub>2</sub>O<sub>5</sub> nanowires derived
from the stereoactive lone pairs on the intercalated lead cations
are closely overlapped in energy with the valence band edges of CdSe
quantum dots that are primarily Se 4p in origin. Both the midgap states
and the valence-band levels are in principle tunable by variation
of cation stoichiometry and particle size, respectively, providing
a means to modulate the thermodynamic driving force for charge transfer.
Steady-state and time-resolved photoluminescence measurements reveal
dynamic quenching of the trap-state emission of CdSe quantum dots
upon exposure to β-Pb<sub><i>x</i></sub>V<sub>2</sub>O<sub>5</sub> nanowires. This result is consistent with a mechanism
involving the transfer of photogenerated holes from CdSe quantum dots
to the midgap states of β-Pb<sub><i>x</i></sub>V<sub>2</sub>O<sub>5</sub> nanowires