We show that the finite lateral sizes of ultrathin CdSe nanoplatelets strongly affect both their photoluminescence and optical absorption spectra. This is in contrast to the situation in quantum wells, in which the large lateral sizes may be assumed to be infinite. The lateral sizes of the nanoplatelets are varied over a range of a few to tens of nanometers. For these sizes excitons experience in-plane quantum confinement, and their center-of-mass motion becomes quantized. Our direct experimental observation of the discretization of the exciton center-of-mass states can be well understood on the basis of the simple particle-in-a-box model.
The in-plane coefficient of thermal expansion (CTE) for CdSe nanoplatelets with the zinc-blende structure containing from two to five monolayers is calculated from first principles within the quasiharmonic approximation. A comparison of the obtained results with those for bulk CdSe with both the zinc-blende and wurtzite structures finds a significant increase in the magnitude of negative CTE and the temperature range of its observation in nanoplatelets. The main contribution to the negative thermal expansion in CdSe nanoplatelets is given by the out-of-plane flexural ZA mode and in-plane optic…
Charge carrier dynamics essentially determine the performance of various optoelectronic applications of colloidal semiconductor nanocrystals. Among them, two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructure. Herein, we demonstrate that by fine-tuning the core size and the lateral quantum confinement, the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets. In addition, the transfer can be affected by a carrier blocking mechanism, i.e., the filled carriers…
We investigated the nonlinear optical properties of CdSe/CdS nanoplatelets in the vicinity of heavy hole and light hole exciton resonances. The two color pump-probe technique was applied. The first intense pulse created non-equilibrium exciton population, which was detected as a decrease of probe light absorption. We observed intense scattering of excitons between heavy- and light-hole excitonic states. We also studied experimentally saturation of absorption in nanoplatelets. Theoretical description of these phenomena allowed us to determine parameters of exciton dynamics in nanoplatelets.
Two-dimensional electron-hole gases in colloidal semiconductors have a wide variety of applications. Therefore, a proper physical understanding of these materials is of great importance. In this paper we present a detailed theoretical analysis of the recent experimental results by Tomar et al., that show an unexpected stability of excitons in CdSe nanoplatelets at high photoexcitation densities. Including the screening effects by free charges on the exciton properties, our analysis shows that CdSe nanoplatelets behave very differently from bulk CdSe, and in particular do not show a crossover t…
The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetism owing to the uncompensated spins of dangling bonds (DBSs). We reveal that by optical spectroscopy in high magnetic fields up to 15 Tesla using the exciton spin as probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the DBS and exciton spin polarization as well as by the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction can be adjusted by the nanoplatelet gr…
We report excited state emission from p-states at excitation fluences well below ground state saturation in CdSe nanoplatelets. Size dependent exciton ground state-excited state energies and dynamics are determined by three independent methods, time-resolved photoluminescence (PL), time-integrated PL and Hartree renormalized k$\cdot$p calculations -- all in very good agreement. The ground state-excited state energy spacing strongly increases with the lateral platelet quantization. Our results suggest that the PL decay of CdSe platelets is governed by an LO-phonon bottleneck, related to the rep…
We measured the intrinsic ground-state exciton dephasing and population dynamics in colloidal quasi two-dimensional (2D) CdSe nanoplatelets at low temperature (5-50K) using transient resonant four-wave mixing in heterodyne detection. Our results indicate that below 20K the exciton dephasing is lifetime limited, with the exciton population lifetime being as fast as 1ps. This is consistent with an exciton lifetime given by a fast radiative decay due to the large in-plane coherence area of the exciton center-of-mass motion in these quasi 2D systems compared to spherical nanocrystals.
CdSe colloidal nanoplatelets are studied by spin-flip Raman scattering in magnetic fields up to 5 T. We find pronounced Raman lines shifted from the excitation laser energy by an electron Zeeman splitting. Their polarization selection rules correspond to those expected for scattering mediated by excitons interacting with resident electrons. Surprisingly, Raman signals shifted by twice the electron Zeeman splitting are also observed. The theoretical analysis and experimental dependencies show that the mechanism responsible for the double flip involves two resident electrons interacting with a p…
We present the phase diagram of free charges (electrons and holes), excitons, and biexcitons in highly excited CdSe nanoplatelets that predicts a crossover to a biexciton-dominated region at easily attainable low temperatures or high photoexcitation densities. Our findings extend previous work describing only free charges and excitons by introducing biexcitons into the equation of state, while keeping the exciton and biexciton binding energies constant in view of the relatively low density of free charges in this material. Our predictions are experimentally testable in the near future and offe…
Recent experiments suggest that the photoluminescence line width of CdSe and CdSe/CdS nanoplatelets (NPLs) may be broadened by the presence of shakeup (SU) lines from negatively charged trions. We carry out a theoretical analysis, based on effective mass and configuration interaction (CI) simulations, to identify the physical conditions that enable such processes. We confirm that trions in colloidal NPLs are susceptible of presenting SU lines up to one order of magnitude stronger than in epitaxial quantum wells, stimulated by dielectric confinement. For these processes to take place trions mus…
We address spin properties and spin dynamics of carriers and charged excitons in CdSe/CdS colloidal nanoplatelets with thick shells. Magneto-optical studies are performed by time-resolved and polarization-resolved photoluminescence, spin-flip Raman scattering and picosecond pump-probe Faraday rotation in magnetic fields up to 30 T. We show that at low temperatures the nanoplatelets are negatively charged so that their photoluminescence is dominated by radiative recombination of negatively charged excitons (trions). Electron g-factor of 1.68 is measured and heavy-hole g-factor varying with incr…
We experimentally investigated for the first time the lowest four band structure of Cd Se nanoplatelets at the r point of Brillouin zone [heavy-hole (hh), light-hole (lh) and two spin-orbital bands] and its modification due to the changing of the CdS shell thickness. The results of an experimental and theoretical study of exciton dynamics in colloidal CdSe/CdS nanoplateles are presented in the case of stationary laser excitation. The excitation was performed by means of the powerful nanosecond laser and the pump and probe technique was utilized. The differential transmission spectra peculiarit…
Colloidal 2D semiconductor nanoplatelets are highly efficient light emitters, which exhibit large absorption and emission cross sections, and constitute promising laser gain media. However, if dispersed in solutions, such nanoplatelets lack a suitable optical platform for scalable and application-oriented integration into optical setups such as lasers. Here, we demonstrate the first successful integration of solution-processed 2D CdSe/CdS Core/Crown nanoplatelets in m-scale liquid core optical fibers. We compare the nanoplatelets' spectroscopic properties before and after filling them into the…
We report on the experimental and theoretical studies of optical alignment and optical orientation effects in an ensemble of core/shell CdSe/CdS colloidal nanoplatelets. The dependences of three Stokes parameters on the magnetic field applied in the Faraday geometry are measured under continuous wave resonant excitation of the exciton photoluminescence. Theoretical model is developed to take into account both bright and dark exciton states in the case of strong electron and hole exchange interaction and random in-plane orientation of the nanoplatelets in ensemble. The data analysis allows us t…
Excitons in diluted magnetic semiconductors represent excellent probes for studying the magnetic properties of these materials. Various magneto-optical effects, which depend sensitively on the exchange interaction of the excitons with the localized spins of the magnetic ions can be used for probing. Here, we study core/shell CdSe/(Cd,Mn)S colloidal nanoplatelets hosting diluted magnetic semiconductor layers. The inclusion of the magnetic Mn$^{2+}$ ions is evidenced by three magneto-optical techniques using high magnetic fields up to 15 T: polarized photoluminescence, optically detected magneti…
We study the band-edge exciton fine structure and in particular its bright-dark splitting in colloidal semiconductor nanocrystals by four different optical methods based on fluorescence line narrowing and time-resolved measurements at various temperatures down to 2 K. We demonstrate that all these methods provide consistent splitting values and discuss their advances and limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5 monolayers are chosen for experimental demonstrations. The bright-dark splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional to …
We demonstrate high quantum yield broad photoluminescence emission of ultrathin sub-nanometer CdSe nanoplatelets (two-monolayer). They also exhibit polarization-characterized lateral size dependent anomalous heavy hole and light/split-off hole absorption intensities.
Colloidal semiconductor nanoplatelets combine weak lateral confinement with strong Coulomb interactions, enhanced by dielectric confinement. When the platelets are charged with carriers of the same sign, this results in severe Coulomb repulsions which shape the electronic structure. To illustrate this point, the shell filling of type-I (CdSe/CdS) and type-II (CdSe/CdTe) core/crown nanoplatelets with up to 4 electrons or holes is investigated theoretically. We find that Coulomb repulsions enable addition energies exceeding room temperature thermal energy and promote the occupation of high-spin …
The optoelectronic properties of metal chalcogenide colloidal nanoplatelets are often interpreted in terms of excitonic states. However, recent spectroscopic experiments evidence the presence of trion states, enabled by the slow Auger recombination in these structures. We analyze how the presence of an additional charge in trions modifies the emission energy and oscillator strength as compared to neutral excitons. These properties are very sensitive to dielectric confinement and electronic correlations, which we describe accurately using image-charge and variational Quantum Monte Carlo methods…
Using semi-analytical models we calculate the energy, effective Bohr radius and radiative lifetime of neutral excitons confined in CdSe colloidal nanoplatelets (NPLs). The excitonic properties are largely governed by the electron-hole in-plane correlation, which in NPLs is enhanced by the quasi-two-dimensional motion and the dielectric mismatch with the organic environment. In NPLs with lateral size $L \gtrsim 20$ nm the exciton behavior is essentially that in a quantum well, with superradiance leading to exciton lifetimes of 1 ps or less, only limited by the NPL area. However, for $L < 20$ nm…
We present a theoretical description of excitons and positively and negatively charged trions in "giant" CdSe/CdS core-shell nanocrystals (NCs). The developed theory provides the parameters describing the fine structure of excitons in CdSe/CdS core/thick shell NCs as a function of the CdSe/CdS conduction band offset and the CdSe core radius. We have also developed a general theory describing the fine structure of positively charged trions created in semiconductor NCs with a degenerate valence band. The calculations take into account the complex structure of the CdSe valence band and inter-part…
The dephasing time of the lowest bright exciton in CdSe/ZnS wurtzite quantum dots is measured from 5 K to 170 K and compared with density dynamics within the exciton fine structure using a sensitive three-beam four-wave-mixing technique unaffected by spectral diffusion. Pure dephasing via acoustic phonons dominates the initial dynamics, followed by an exponential zero-phonon line dephasing of 109 ps at 5 K, much faster than the ~10 ns exciton radiative lifetime. The zero-phonon line dephasing is explained by phonon-assisted spin-flip from the lowest bright state to dark exciton states. This is…
Recently, the fabrication of CdSe nanoplatelets became an important research topic. Nanoplatelets are often described as having a similar electronic structure as 2D dimensional quantum wells and are promoted as colloidal quantum wells with monolayer precision width. In this paper, we show, that nanoplatelets are not ideal quantum wells, but cover depending on the size: the strong confinement regime, an intermediate regime and a Coulomb dominated regime. Thus, nanoplatelets are an ideal platform to study the physics in these regimes. Therefore, the exciton states of the nanoplatelets are numeri…
Theory of electronic and optical properties of exciton and bi-exciton complexes confined in CdSe spherical nanocrystals is presented. The electron and hole states are computed using atomistic $sp^3d^5s^*$ tight binding Hamiltonian including an effective crystal field splitting, spin-orbit interactions, and model surface passivation. The optically excited states are expanded in electron-hole configurations and the many-body spectrum is computed in the configuration-interaction approach. Results demonstrate that the low-energy electron spectrum is organized in shells ($s$, $p$, ...), whilst the …
Semiconductor nanoparticles of cadmium chalcogenides are known to exhibit pronounced thickness-dependent $E_0$ series of exciton transitions at the $Γ$ point of the Brillouin zone (BZ). In this work, we report an experimental evidence for high-energy series of exciton transitions, which originates from BZ points different from the $Γ$ point, in the family of cadmium chalcogenide quasi-2D nanoplatelets (NPLs). Intensive UV absorption bands demonstrating a pronounced size effect are observed for CdTe, CdSe, and CdS NPLs in addition to the $E_0$ exciton bands in the visible region. These new band…
Colloidal semiconductor nanoplatelets exhibit quantum size effects due to their thickness of only few monolayers, together with strong optical band-edge transitions facilitated by large lateral extensions. In this article we demonstrate room temperature strong coupling of the light and heavy hole exciton transitions of CdSe nanoplatelets with the photonic modes of an open planar microcavity. Vacuum Rabi splittings of $66 \pm 1$ meV and $58 \pm 1$ meV are observed for the heavy and light hole excitons respectively, together with a polariton-mediated hybridisation of both transitions. By measuri…
Colloidal semiconductor nanoplatelets (NPLs) with electronic structure as quantum wells have recently emerged as exciting materials for optoelectronic applications. Here we investigate how morphology affects important photoluminescence (PL) properties of single CdSe and core/shell CdSe/CdZnS nanoplatelets. By analyzing PL intensity-lifetime correlation and second-order photon correlation results, we demonstrate that, irrespective of morphology, Auger recombination cannot be responsible for PL blinking of single NPLs. We propose that hot carrier trapping plays a significant role in blinking and…
We present a theory of highly excited interacting carriers confined in a semiconductor nanostructure, incorporating Auger coupling between excited states with different number of excitations. The Coulomb matrix elements connecting exciton, bi-exciton and tri-exciton complexes are derived and an intuitive picture of breaking neutral multi-exction complexes into positively and negatively charged multi-exciton complexes is given. The general approach is illustrated by analyzing the coupling of biexciton and exciton in CdSe spherical nanocrystals. The electron and hole states are computed using at…
Exciton-exciton annihilation (EEA) and Auger recombination are detrimental processes occurring in semiconductor optoelectronic devices at high carrier densities. Despite constituting one of the main obstacles for realizing lasing in semiconductor nanocrystals (NCs), the dependencies on NC size are not fully understood, especially for those with both weakly and strongly confined dimensions. Here, we use differential transmission spectroscopy to investigate the dependence of EEA on the physical dimensions of thickness-controlled 2D halide perovskite nanoplatelets (NPls). We find the EEA lifetime…
Colloidal semiconductor nanoplatelets, in which carriers are strongly confined only along one dimension, present fundamentally different excitonic properties than quantum dots, which support strong confinement in all three dimensions. In particular, multiple excitons strongly confined in just one dimension are free to re-arrange in the lateral plane, reducing the probability for multi-body collisions. Thus, while simultaneous multiple photon emission is typically quenched in quantum dots, in nanoplatelets its probability can be tuned according to size and shape. Here, we focus on analyzing mul…
We study the low-temperature magneto-photoluminescence (PL) from individual CdSe nanocrystals. Nanocrystals having a small "bright" exciton fine structure splitting ($<$0.5 meV) exhibit a conventional left- and right-circularly polarized Zeeman PL doublet in applied magnetic fields. In contrast, nanocrystals with large fine structure splitting ($>$1 meV) show an anomalous magneto-PL polarization, wherein the lower-energy peak becomes circularly polarized with increasing field, while the higher-energy peak remains linearly polarized. This unusual behavior arises from strong mixing between the a…
The picosecond dynamics of excitons in colloidal CdSe nanorods are directly measured via their 1s to 2p-like internal transitions by ultra-broadband terahertz spectroscopy. Broadened absorption peaks from both the longitudinal and transverse states are observed at 8.5 and 11 THz, respectively. The onset of exciton-LO phonon coupling appears as a bleach in the optical conductivity spectra at the LO phonon energy for times > 1 ps after excitation. Simulations show a suppressed exciton temperature due to thermally excited hole states being rapidly captured onto ligands or unpassivated surface sta…
Magnetic doping of semiconductor nanostructures is actively pursued for applications in magnetic memory and spin-based electronics. Central to these efforts is a drive to control the interaction strength between carriers (electrons and holes) and the embedded magnetic atoms. In this respect, colloidal nanocrystal heterostructures provide great flexibility via growth-controlled `engineering' of electron and hole wavefunctions within individual nanocrystals. Here we demonstrate a widely tunable magnetic sp-d exchange interaction between electron-hole excitations (excitons) and paramagnetic manga…
Circularly polarized optical excitation is used to demonstrate the efficient injection of spin-polarized excitons to individual self-assembled CdSe quantum dots in ZnSe barrier. The exciton spin-transfer is studied by means of polarization-resolved single dot spectroscopy performed in magnetic field applied in Faraday configuration. Detailed analysis of the neutral exciton photoluminescence spectra reveals the presence of exciton spin relaxation during its lifetime in a quantum dot. This process is seen for both nonmagnetic dots and those containing single Mn$^{2+}$ ions. Taking this into acco…
We present a polarization-resolved photoluminescence study of the exchange interaction effects in a prototype system consisting of an individual Fe2+ ion and a single neutral exciton confined in a CdSe/ZnSe quantum dot. Maximal possible number of eight fully linearly-polarized lines in the bright exciton emission spectrum is observed, evidencing complete degeneracy lifting in the investigated system. We discuss conditions required for such a scenario to take place: anisotropy of the electron-hole interaction and the zero-field splitting of the Fe2+ ion spin states. Neglecting of either of thes…
We present a comparative study of two self-assembled quantum dot (QD) systems based on II-VI compounds: CdTe/ZnTe and CdSe/ZnSe. Using magneto-optical techniques we investigated a large population of individual QDs. The systematic photoluminescence studies of emission lines related to the recombination of neutral exciton X, biexciton XX, and singly charged excitons (X$^+$, X$^-$) allowed us to determine average parameters describing CdTe QDs (CdSe QDs): X-XX transition energy difference 12 meV (24 meV); fine-structure splitting $δ_{1}=$0.14 meV ($δ_{1}=$0.47 meV); $g$-factor $g=$2.12 ($g=$1.71…
Exciton luminescence of a CdSe quantum dot (QD) inserted in a ZnSe nanowire is strongly influenced by the dark exciton states. Because of the small size of these QDs (2-5nm), exchange interaction between hole and electron is highly enhanced and we measured large energy splitting between bright and dark exciton states ($ΔE\in [4, 9.2 ]$ meV) and large spin flip rates between these states. Statistics on many QDs showed that this splitting depends on the QD size. Moreover, we measured an increase of the spin flip rate to the dark states with increasing energy splitting. We explain this observatio…
Doping a semiconductor quantum dot with just a single impurity atom can completely transform its physical properties. Here, we report and analyze the magnetic circular dichroism (MCD) spectra of colloidal CdSe quantum dot samples containing on average fewer than one Mn2+ per quantum dot. Even at this sub-single-dopant level, the low-temperature low-field data are dominated by impurity-induced Zeeman splittings caused by dopant-carrier sp-d exchange. Unlike in more heavily doped quantum dots, however, the MCD intensity at the first CdSe exciton shows a field-induced sign flip as the field stren…
Large surface to volume ratios of semiconductor nanocrystals cause susceptibility to charge trapping, which can modify luminescence yields and induce single-particle blinking. Optical spectroscopies cannot differentiate between bulk and surface traps in contrast to spin-resonance techniques, which in principle avail chemical information on such trap sites. Magnetic resonance detection via spin-controlled photoluminescence enables the direct observation of interactions between emissive excitons and trapped charges. This approach allows the discrimination of two functionally different trap state…
Strongly quantum-confined 2D colloidal PbS nanoplatelets (NPLs) are highly interesting materials for near-infrared optoelectronic applications. Here, we use ultrafast transient optical absorption spectroscopy to study the characteristics and dynamics of photoexcited excitons in ultrathin PbS NPLs with a cubic (rock-salt) structure. The NPLs are synthesized at near room temperature from lead oleate and thiourea precursors and show an optical absorption onset at 680 nm (1.8 eV) as well as photoluminescence at 720 nm (1.7 eV). By treating PbS NPLs with CdCl2 in a post-synthetic step, their photol…
A theory of electron spin-flip Raman scattering (SFRS) is presented that describes the Raman spectral signals shifted by both single and twice the electron Zeeman energy under nearly resonant excitation of the heavy hole excitons in semiconductor nanoplatelets. We analyze the spin structure of photoexcited intermediate states, derive compound matrix elements of the spin-flip scattering and obtain polarization properties of the one- and two-electron SFRS common for all the intermediate states. We show that, in the resonant scattering process under consideration, the complexes "exciton plus loca…
ZnTe/CdSe/(Zn,Mg)Te core/double-shell nanowires are grown by molecular beam epitaxy by employing the vapor-liquid-solid growth mechanism assisted with gold catalysts. A photoluminescence study of these structures reveals the presence of an optical emission in the near infrared. We assign this emission to the spatially indirect exciton recombination at the ZnTe/CdSe type II interface. This conclusion is confirmed by the observation of a significant blue-shift of the emission energy with an increasing excitation fluence induced by the electron-hole separation at the interface. Cathodoluminescenc…
We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The p…
The recombination dynamics and spin polarization of excitons in CdSe nanocrystals synthesized in a glass matrix are investigated using polarized photoluminescence in high magnetic fields up to 30 Tesla. The dynamics are accelerated by increasing temperature and magnetic field, confirming the dark exciton nature of the low-temperature photoluminescence (PL). The circularly polarized PL in magnetic fields reveals several unusual appearances: (i) a spectral dependence of the polarization degree, (ii) its low saturation value, and (iii) a stronger intensity of the Zeeman component which is higher …
Coupling to phonon modes is a primary mechanism of excitonic dephasing and energy loss in semiconductors. However, low-energy phonons in colloidal quantum dots and their coupling to excitons are poorly understood, since their experimental signatures are weak and usually obscured by unavoidable inhomogeneous broadening of colloidal dot ensembles. We use multi-dimensional coherent spectroscopy at cryogenic temperatures to extract the homogeneous nonlinear optical response of excitons in a CdSe/CdZnS core/shell colloidal quantum dot ensemble. Comparison to simulation provides evidence that the ob…
The exciton spin dynamics and polarization properties of the related emission are investigated in colloidal CdSe/CdS dot-in-rod (DiR) and spherical core/shell nanocrystal (NC) ensembles by magneto-optical photoluminescence (PL) spectroscopy in magnetic fields up to 15 T. It is shown that the degree of circular polarization (DCP) of the exciton emission induced by the magnetic field is affected by the NC geometry as well as the exciton fine structure and can provide information on nanorod orientation. A theory to describe the circular and linear polarization properties of the NC emission in mag…
We study the effect of Coulomb correlation on the emission properties of the ground state exciton in zincblende CdSe/ZnS core-shell and in wurtzite ZnO quantum dots. We validate our theory model by comparing results of computed exciton energies of CdSe/ZnS quantum dots to photoluminescence and scanning near-field optical microscopy measurements. We use that to estimate the diameter of the quantum dots using a simple model based on infinitely deep quantum well and compare the results with the statistics of the atomic force microscopy scans of CdSe/ZnS dots, obtaining excellent agreement. Therea…
Colloidal Cadmium Selenide (CdSe) nanoplatelets (NPLs) are a recently developed class of efficient luminescent nanomaterial suitable for optoelectronic device applications. A change in temperature greatly affects their electronic bandstructure and luminescence properties. It is important to understand how-and-why the characteristics of NPLs are influenced, particularly at elevated temperature, where both reversible and irreversible quenching processes come into picture. Here we present a study on the effect of elevated temperature on the characteristics of colloidal CdSe NPLs. We used an effec…
The $k\cdot p$ effective mass approximation (EMA) predicts large, nearly size-independent exciton oscillator strengths in quantum confined semiconductors. Yet, experimental reports have concluded that the total oscillator strength of the lowest-energy (1S$_{3/2}$1S$_{\text{e}}$) excitons in strongly confined CdSe NQDs is small and strongly size-dependent. Using the optical Stark effect, we show that the oscillator strength of the 1S$_{3/2}$1S$_{\text{e}}$ excitonic absorption peak in CdSe NQDs follows the predictions of the EMA. These oscillator strengths enable helicity-selective unsaturated …
The multiplication rates of hot carriers in CdSe quantum dots are quantified using an atomistic pseudopotential approach and first order perturbation theory. Both excited holes and electrons are considered, and electron-hole Coulomb interactions are accounted for. We find that holes have much higher multiplication rates than electrons with the same excess energy due to the larger density of final states (positive trions). When electron-hole pairs are generated by photon absorption, however, the net carrier multiplication rate is dominated by photogenerated electrons, because they have on avera…
