Ultrafast intraband Auger process in self-doped colloidal quantum dots

•Self-doped ?-HgS QDs, a platform to monitor the electron dynamics only•The intraband Auger process occurring in conduction band•Mechanism of relaxation processes n-type self-doped CQDs Excess charge accumulation quantum dots is unavoidable when running electronic devices. Since it an instant phenomenon happening randomly, there have not been many systematic approaches investigate it. Also, excess charge-accumulated state adequate model for exploration higher states. n-Type provide excellent from which study electron-accumulated band. In combination with femtosecond mid-infrared spectroscopy, we were able selectively photoexcite electrons lowest energy band and that never directly experimentally measured. particular, ultrafast are revealed by this method such as process, helping us comprehend blinking single dots, disproportionate charging light-emitting diodes, hot states coupled surface colloidal dots. Investigating separate holes has challenging, although critical fundamental understanding semiconducting nanomaterials. (CQDs) occupying low-lying (CB) attracted great deal attention because only their potential applications infrared optoelectronics but also intrinsic system offers investigating without elusive contributions valence Here, show unprecedented between spin-orbit coupling states, exciton-to-ligand vibrational transfer all occur exclusively CB CQDs. The obtained spectroscopy will pave way further phenomenon, High-energy (e.g., recombination process), trapping, multi-exciton generation, trion formation, unbalanced injection interest dot (CQD) research field.1Pan J.L. Reduction rate semiconductor dots.Phys. Rev. B Condens. Matter Mater. Phys. 1992; 46: 3977-3998Crossref Scopus (21) Google Scholar, 2Park Y.S. Bae W.K. Pietryga J.M. Klimov V.I. biexcitons negative positive trions individual dots.ACS Nano. 2014; 8: 7288-7296Crossref PubMed (179) 3Pandey A. Guyot-Sionnest P. 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Unexpectedly, addition inter-sublevel (IST) ligand vibrations, direct evidence picosecond (IAP) CQDs, new type CB.28Melnychuk suppression HgSe 13: 10512-10519Crossref (19) experimental findings along result density functional theory (DFT) calculation invaluable information excited manifold.25Choi Figure 1A schematic illustration levels populations broad absorption peak at ?2,650 cm?1 (Figure 1B), energetically much lower than usual band-gap corresponds 1Pe frequency range. We no (1Sh-1Se) ?9,700 cm?1, shows fully (see S1 Fourier transform [FTIR] spectrum). bands low-frequency side FTIR spectrum other main associated 1Se-1Pe indicate empty. full-width-at-half-maximum values peaks passivated dodecanethiol (DDT) oleylamine (OLAm) 1,024 1,121 respectively. Such linewidths can attributed non-degenerate transitions, i.e., 1Se-1Pe3/2 1Se-1Pe1/2, where 1Pe3/2 1Pe1/2 shape asymmetry, well size heterogeneity (Figures 1, S2, S3).29Kovalenko Manna Cabot Hens Talapin D.V. Kagan C.R. Rogach Reiss Milliron al.Prospects nanoscience 9: 1012-1057Crossref (826) Gaussian fitting analyses spectra both ?-HgS-DDT ?-HgS-OLAm, 313 413 similar those HgTe CQDs.28Melnychuk Scholar,30Hudson M.H. Kamysbayev Janke E.M. Lan Allan G. Delerue Conduction fine structure 12: 9397-9404Crossref agreement DFT calculations Perdew-Burke-Ernzerhof (PBE) projector-augmented-wave (PAW) pseudopotentials Data S1; Figures S4 S5).4Bae calculated energies three breaking degeneracy into Their (1Se-1Pe), 2,524, 2,581, 2,702 close maximum spectrum. 1E depicts frontier molecular orbitals (electronic states) 1Sh near gap resemble H-atomic p-orbitals, appears more isotropic spherically symmetric, like s-orbital. Interestingly, 1Se, high-lying substantially delocalized compared VB. This morphology turns out important affected ligands spatially these To elucidate used centered 2,650 do induce any (VB-to-CB) transitions. Note pump should least ?12,400 transition. center pulse was selected avoid absorptions tetrachloroethylene (TCE) solvent or molecules. 2A profiles normalized signals S6 whole set frequency-resolved signals). broader spectral width (?250 cm?1) our S3 S2). subensemble optically selected, mainly populated field-CQD interaction, resulting negligible dependence S7). significant polarization due bulky nature population S8 probe frequencies). With increase excitation 56 747 ?J cm?2, becomes faster. It converges constant 2A) 378 cm?2. first carried multi-exponential identify scales involved (solid lines 2A). exponentially decaying components needed fit decay signal S9), indicating distinguishable pathways taken consideration establish kinetic scheme mechanism. First all, could rule possibility relaxations originate radiative processes. case approximately estimated following equation (in cgs unit),kR=TR?1=(3?m?HgS+2?m)22e2?1Se1Pe2fn3m0c2,(Equation 1) ?HgS ?m relative permittivity medium, respectively, e elementary charge, ?1Se1Pe frequency, f oscillator strength, n refractive index, m0 mass free electron, c speed light. From Equation lifetime ?0.9 ?s. Assuming yield (QY = kR/(kR + kNR)) range ?1.0 × 10?3–10?4 ?s, non-radiative excitons ?90 900 ps.22Jeong Indeed, constants slow component (?400 ps) range, suggesting observed measured clear density. 2B plot exponential respect intermediate around 1 ps (black) 12 (red), strongly dependent intensity. On hand, (blue) decreases ?400 ?250 parameters pathways, they depend shall return issue later paper proposed numerical simulation results. amplitudes strong power dependences 2C). They reach asymptotic increases, saturation beam large strengths. At high powers, state, results two-photon nanocrystal, created. regime change 2B). 2C contributes densities, manifest rapidly upon increasing Our (?fast) does corresponding amplitude (Afast) increases suggest IAP 3A). known one transferred create another exciton. Unlike cases excitonic before, even its strictly matter doubt controversy. undoped e.g., CdSe, studied employing pump-push-probe method.19Hendry Scholar,31Rabouw F.T. Vaxenburg Bakulin A.A. Van Dijk-Moes R.J.A. Bakker H.J. Rodina Lifshitz Efros Koenderink A.F. Dynamics core-shell 10366-10376Crossref (40) optical pumping produces had proceed before probing particles. then whereby high-energy loses simultaneously created filled vacant involving makes complicated interpret measurements. contrast, only, so interfere purely reflect Quite unexpectedly, faster example, scaling coefficient (p=?BXr3=1 ps(1.6 nm)3) coefficients (CA=V2?BX) 0.24 nm?3 3.82 10–31 cm6 s?1, r, ?BX, V radius, lifetime, volume, order magnitude smaller reported (p 5.5 nm?3) 1.9 nm?3).20Guyot-Sionnest 31Rabouw 32Melnychuk Slow 2208-2211Crossref (20) suggests self-doping overall cases, collision probability carriers, holes, surface-delocalized.32Melnychuk cm?2 zero 0.29 biexcitonic negligibly small low again consistent fact strength high.24Deng Next, explanations interpretations components. Because exciton modes accept one-excitonic biexciton. initial filling (or quenching) after 1-ps Among few possible scenarios assignments components, ignore transfers average distance nearest enough. very useful adopt recently suggested group.28Melnychuk time-resolved emission showed IST 5–30 ps. (>100 time-dependent assigned 1Se-1Pe1/2 modes. identified (1Pe3/2 1Pe1/2), coupling. (?inter) similarly 3B). contribute ?2,250 cm?1. 250 400 explained terms phonon-bottleneck effect. confirm electronic-to-ligand (electronic-to-vibrational [EVET], exciton-to-vibrational transfer, near-field transfer), same experiments amine molecules, OLAm. If EVET, would ligand. (states), significantly surface-delocalized S5), implying unlike IST, notable passivating ligands. ?-HgS-OLAm triexponential pattern, 4A). lengthy aliphatic chain OLAm inefficient provides solvation environment CQD. exchange DDT make difference 4B 4C; Table S1). either. Its Afast density, 136 infers previous finding second (1Pe-1De) ?-HgS-OLAm.27Yoon contrast ?500 ps, 0.17 0.1 HgS-DDT component, dashed line 4B). fractions decrease stronger. However, account effect support hypothesis slowly vibrations. expectation interactions molecules EVET IAP-produced highly CQD-ligand interactions. Time-resolved measurements varying provided origins (Data S3). extract quantitative data rates, analysis assumes fitted represent completely independent shed light intricately correlated need describe entire pathway. shown 5. ground denoted 1Se(2)1Pe(0), number parentheses represents incident produce either (1Se(1)1Pe3/2(1)) (1Se(0)1Pe3/2(2)). considered 1B). power, 1Se(1)1Pe3/2(1) populated, undergo 1Se(1)1Pe1/2(1) QD measurements, produced dark between1Pe1/2 As consequence, ground-state bleaching (GSB) term only. requires 2,000 bath degrees freedom. lack frequencies, 1Se(2)1Pe(0) efficient, Melnychuk vibrations scale hundred picoseconds.32Melnychuk Scholar,33Pandey cooling 2008; 322: 929-932Crossref (436) believe recovery caused process. next consider 1Se(0)1Pe3/2(2). stimulated emissions GSBs. IAP, (1Se(1)1Pe3/2(0)1Xe(1)) ?1 spatial diameter about 3.2 nm enhance causes rapid (not interband) 1Se(1)1Pe3/2(0)1Xe(1), GSB term. Now, 1Xe(1) dump 2,500 phonons effectively 1Xe S5) exist assist cascading-type internal conversion (IC) After IC, 1Se(1)1Pe1/2(1), relax back An additional aspect ignored local heating signal. Strong light-matter followed dissipations cause temperature temperature-dependent S11). absorbance window increases. decreased long delay times (?microseconds) safely effect, offset. numerically solved equations determined four constants, ?IAP, ?IST, ?IC, ?EVET, finite-difference method. calculate seen 6A 6B , reproduces multi-exponentially patterns power-dependent almost perfectly, supports validity ?IC neither nor 6C). interpretation IC induced electron-QD couplings, electron-ligand vibration couplings. depends ligand; thiol group usually stronger QD.34Martell A.E. Smith R.M. Critical Stability Constants. Plenum 1974Google Scholar,35Wright J.G. Natan M.J. MacDonnel F.M. Ralston D.M. O’Halloran T.V. Mercury (II)—Thiolate chemistry biosensor MerR.Prog. Inorg. 1990; 38: 323-412Crossref weakly interacting slow, clue designing longer ?EVET unexpectedly One deviation contribution times. Unfortunately, scanning limited (<300–400 mechanical translational stage. microseconds materials. (PP up 300 sufficient enough resolve HgS-OLAm 6C) include processes, making value effects passivation layers. analysis, estimate branching (x) (1 ? x) excitations 6D). fraction x indicates OLAm, reflecting ?-HgS-DDT. studies particles manifold occurs 10 coupling-induced 60 irrespective picoseconds reflects binding here creating open avenue efficient photovoltaic devices operating relatively photon regime. work, anticipate insights previously unresolved observations disproportionately charged diode, nanocrystals’