title: Impact of D2O/H2O Solvent Exchange on the Emission of HgTe and CdTe Quantum Dots: Polaron and Energy Transfer Effects.
abstract: We have studied light emission kinetics and analyzed carrier recombination channels in HgTe quantum dots that were initially grown in H2O. When the solvent is replaced by D2O, the nonradiative recombination rate changes highlight the role of the vibrational degrees of freedom in the medium surrounding the dots, including both solvent and ligands. The contributing energy loss mechanisms have been evaluated by developing quantitative models for the nonradiative recombination via (i) polaron states formed by strong coupling of ligand vibration modes to a surface trap state (nonresonant channel) and (ii) resonant energy transfer to vibration modes in the solvent. We conclude that channel (i) is more important than (ii) for HgTe dots in either solution. When some of these modes are removed from the relevant spectral range by the H2O to D2O replacement, the polaron effect becomes weaker and the nonradiative lifetime increases. Comparisons with CdTe quantum dots (QDs) served as a reference where the resonant energy loss (ii) a priori was not a factor, also confirmed by our experiments. The solvent exchange (H2O to D2O), however, is found to slightly increase the overall quantum yield of CdTe samples, probably by increasing the fraction of bright dots in the ensemble. The fundamental study reported here can serve as the foundation for the design and optimization principles of narrow bandgap quantum dots aimed at applications in long wavelength colloidal materials for infrared light emitting diodes and photodetectors.
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.
authors.forename: Qiannan
authors.initials: Q
authors.lastname: Wen
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Kershaw
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.
authors.forename: Sergii
authors.initials: S
authors.lastname: Kalytchuk
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.
authors.forename: Olga
authors.initials: O
authors.lastname: Zhovtiuk
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.
authors.forename: Claas
authors.initials: C
authors.lastname: Reckmeier
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.|Centro de Fisica, Universidade do Minho, Campus de Gualtar , Braga 4710-057, Portugal.
authors.forename: Mikhail I
authors.initials: MI
authors.lastname: Vasilevskiy
authors.affiliation: Department of Physics and Materials Science and Centre for Functional Photonics (CFP), City University of Hong Kong , Kowloon, Hong Kong S.A.R.
authors.forename: Andrey L
authors.initials: AL
authors.lastname: Rogach
keywords: IR quantum dots; energy transfer mechanisms; exciton-polaron interactions; isotopic solvent effects; ligand and solvent vibrational modes; recombination rate effects