Stimulated Emission through an Electron–Hole Plasma in Colloidal CdSe Quantum Rings

Abstract

Colloidal CdSe quantum rings (QRs) are a recently developed class of nanomaterials with a unique topology. In nanocrystals with more common shapes, such as dots and platelets, the photophysics is consistently dominated by strongly bound electron–hole pairs, so-called excitons, regardless of the charge carrier density. Here, we show that charge carriers in QRs condense into a hot uncorrelated plasma state at high density. Through strong band gap renormalization, this plasma state is able to produce broadband and sizable optical gain. The gain is limited by a second-order, yet radiative, recombination process, and the buildup is counteracted by a charge-cooling bottleneck. Our results show that weakly confined QRs offer a unique system to study uncorrelated electron–hole dynamics in nanoscale materials.

Single Elementary Charge Fluctuations on Nanoparticles in Aqueous Solution

“…We first use the above method for nanoparticles with relatively low electric fields. We employ an electrostatic calculation − to estimate the amplitude of the electric field in the center of the gap between two ITO electrodes (Methods) as 0.16 MV m –1 for an applied voltage of 20 V (Supplementary Figure S2). For the applied 10 kHz sinusoidal voltage (Figure a), the drift component of the nanoparticle motion is expected to be also sinusoidal (Figure b).…”

“…We first use the above method for nanoparticles in relatively low electric fields. We employ an electrostatic calculation [33][34][35] to estimate the amplitude of the electric field in the center of the gap between two ITO electrodes (Methods) as 0.16 MV m -1 for an applied voltage of 20 V (Supplementary Fig. S2).…”

“…Calculation of the electric field. The electric field between the ITO electrodes is calculated using the commercially available finite-element solver COMSOL Multiphysics 5.6 (Electrostatics module) according to our previously published methods [33][34][35] . The flow cell with interdigitated electrodes is modelled as a 2D unit cell (Supplementary Fig.…”

“…The electric field between the ITO electrodes is calculated using the commercially available finite-element solver COMSOL Multiphysics 5.6 (Electrostatics module) according to our previously published methods. − The flow cell with interdigitated electrodes is modeled as a 2D unit cell (Supplementary Figure S2a,b) with a height h and Periodic Boundary Conditions (PBC) applied on the left and right sides of the geometry to simulate an infinite array of electrodes separated by the gap distance d gap . The medium inside the cell is water with a dielectric constant ε m = 80ε 0 .…”

Colloidal CdSe/CdS Core/Crown Nanoplatelets for Efficient Blue Light Emission and Optical Amplification

“…Figure d shows the τ g i values of core and core/crown 3.5 ML NPLs, measured for exciton densities between 0.1 and 0.16 nm –2 . Nonlinear carrier recombination in 2D materials is typically modeled using a mixed first-/second-order process, where the density of the carrier decays according to − − normald n normald t = k 1 n + k 2 n 2 Here, k 1 is the single-exciton rate constant and k 2 the rate constant accounting for biexciton recombination. In the case of green-emitting 4.5 ML CdSe NPLs, τ g i ≈ 100 ps, which is a value limited by biecxiton Auger recombination with a rate constant of k 2 = 9.7 × 10 –4 cm 2 /s .…”