Ultrafast Hole Transfer in CdSe/ZnTe Type II Core−Shell Nanostructure

Abstract

We have synthesized thiol-capped CdSe/ZnTe quantum dot core−shell nanostructures by colloidal methods, have characterized them by steady-state absorption and photoluminescence (PL) spectroscopy and further confirmed by high resolution transmission electron microscopy and X-ray diffraction measurements. Clear red shift on shell formation was observed in optical absorption and photoluminescence studies. Time-resolved emission studies indicate longer emission lifetime of CdSe/ZnTe core−shell as compared to CdSe QD material where in both cases only CdSe gets excited, which indicates spatial charge separation in type-II core−shell. Ultrafast photoinduced charge transfer dynamics in type-II CdSe/ZnTe donor−acceptor core−shell were studied in real-time using femtosecond broadband pump−probe spectroscopy. Our transient absorption studies suggests that on photoexcitation core−shell hole transfer from CdSe core to ZnTe shell takes place in pulse-width limited time scale as evidenced by an increase in cooling dynamics of the charge carriers from 150 fs for CdSe to 300 fs for thickest CdSe/ZnTe core−shell. Increase in cooling dynamics in core−shell has been explained due to decoupling of electron and hole in photoexcited core−shell. Trapping dynamics play a major role in the excited dynamics of the photoexcited charge carriers of quantum dot materials. Bleach recovery kinetics of the photoexcited QD materials fitted multi-exponentially where 2.5 ps (first component) has been attributed to the electron trapping dynamics and the longer components (30−50 ps and >400 ps) attributed to the charge recombination dynamics.

State‐of‐the‐Art Progress in Diverse Heterostructured Photocatalysts toward Promoting Photocatalytic Performance

“…[ 87 ] Zamkov and co-workers reported the mecha-nism of holes extraction from the ZnSe core to the surface of the CdS shell in a ZnSe/CdS core shell system. The indirect-type exciton was also observed in CdTe/CdSe [ 90,91 ] and CdSe/ZnTe [ 90,92 ] core/shell QDs. Moreover, the transfer of photoinduced electrons and holes from the core to the surface of the shell was approximately an order of magnitude faster than electron-hole recombination time, indicating that most of the absorbed energy in ZnSe/CdS could be used to drive photocatalytic reactions.…”

Charge Transfer Dynamics and Auger Recombination of CdTe/CdS Core/Shell Quantum Dots

“…5,11 A relatively small lattice mismatch for epitaxial growth and a large conduction-/valence-band offset for band-alignment tuning are two important factors for the manipulation of nanoheterostructures, such as CdS/ZnSe, CdSe/ZnTe, CdSe/CdS, InP/CdS, and CdTe/CdS core/shell QDs. [11][12][13][14][15] The lattice parameters of bulk CdTe and CdS are 6.481 and 5.838 Å, respectively. 16 CdTe conduction-and valence-band energies (about 3.5 and 5.2 eV, respectively, below vacuum) are higher than those of CdS (about 3.7 and 6.3 eV, respectively, below vacuum) by 0.2 and 1.1 eV, respectively.…”

Preparation and characterization of SrTiO3–ZnTe nanocomposites for the visible-light photoconversion of carbon dioxide to methane

“…29 Because of its very negative conduction band position, ZnTe has a large driving force for the interfacial electron transfer from the semiconductor to the acceptor. 30 As a result, ZnTe is considered an attractive material for designing novel photocatalysts. SrTiO 3 -ZnTe nanocomposites have been synthesized via the hydrothermal method.…”