Ultrafast Photoluminescence from the Core and the Shell in CdSe/CdS Dot‐in‐Rod Heterostructures

Abstract

With an ultrafast time-resolved photoluminescence system utilizing a Kerr gate, the time-resolved photoluminescence of core and shell constituents within CdSe/CdS dot-in-rod heterostructures is studied as a function of heterostructure size. Measurements performed at low excitation fluence generating, on average, less than one exciton per nanorod, reveal photoluminescence from direct recombination of carriers in the CdS heterostructure rod with lifetime generally increasing from 0.4 ps to 1.3 ps as the rod length increases. Decay of the CdS rod photoluminescence is accompanied by an increase in emission from the CdSe core on comparable time scales, also trending towards larger values as the rod length increases. The observed kinetics can be explained without invoking a non-radiative trapping mechanism. We also present alloying as a mechanism for enhancing electron confinement and reducing fluorescence lifetime at nanosecond time scales.

Tailoring Hot Exciton Dynamics in 2D Hybrid Perovskites through Cation Modification

“…To investigate the dynamics of the hot carrier PL, we use ultrafast time-resolved PL (TRPL) measurements. 5,29 The TRPL spectrum at 16 K of 2-Cl is shown in Figure 2C. Each slice of the TRPL spectrum is fit to the sum of Gaussian functions ( Figure 2D), with the resonance centers shown in Figure 2E and areas in Figure 2F.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…In type-I 1/2 (or quasi-type-II) hetero-NCs one carrier is delocalized over the whole volume of the hetero-NC, while the other is localized in one of the segments (e.g., CdSe/CdS, ZnSe/CdSe). This allows the electron–hole spatial overlap to be tailored by controlling the size, shape, and composition of each segment of the hetero-NC, which has a dramatic impact on several properties (viz., quantum yields, stability, PL wavelength [15, 16, 21, 60, 61], reabsorption cross section [22, 29, 62–64], radiative lifetimes [60, 64–66], exciton-phonon coupling strength [67–69], Auger recombination [66, 70–72], hot carrier relaxation [51, 73], thermal quenching [74, 75]). The general trend is that the exciton lifetime, exciton-phonon coupling, and PL wavelength increase when going from the type-I to the type-II localization regimes, while Auger recombination rates and hot carrier relaxation rates are reduced.…”

“…Interband hot-carrier emission is due to recombination of a hot carrier in one band (e.g., an electron in the conduction band), with a carrier in the other band. This emission is blue-shifted with respect to that from the ground-state exciton, and decays on a timescale of picoseconds or faster [73, 172, 181]. In addition, the possibility of intraband hot-carrier emission has recently been demonstrated in Cd-based and Hg-based NCs [182, 183].…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…In type-I 1/2 (or quasi-type-II) hetero-NCs one carrier is delocalized over the whole volume of the hetero-NC, while the other is localized in one of the segments (e.g., CdSe/CdS, ZnSe/CdSe). This allows the electron-hole spatial overlap to be tailored by controlling the size, shape, and composition of each segment of the hetero-NC, which has a dramatic impact on several properties (viz., quantum yields, stability, PL wavelength [15,16,21,60,61], reabsorption cross section [22,29,[62][63][64], radiative lifetimes [60,[64][65][66], exciton-phonon coupling strength [67][68][69], Auger recombination [66,[70][71][72], hot carrier relaxation [51,73], thermal quenching [74,75]). The general trend is that the exciton lifetime, exciton-phonon coupling, and PL wavelength increase when going from the type-I to the type-II localization regimes, while Auger recombination rates and hot carrier relaxation rates are reduced.…”

“…Interband hot-carrier emission is due to recombination of a hot carrier in one band (e.g., an electron in the conduction band), with a carrier in the other band. This emission is blue-shifted with respect to that from the ground-state exciton, and decays on a timescale of picoseconds or faster [73,172,181]. In addition, the possibility of intraband hot-carrier emission has recently been demonstrated in Cd-based and Hgbased NCs [182,183].…”