Biexciton Dynamics in Single Colloidal CdSe Quantum Dots

Abstract

The investigation of biexciton dynamics in single colloidal quantum dots (QDs) is critical to biexciton-based applications. Generally, a biexciton exhibits an extremely low photoluminescence (PL) quantum yield as well as very fast PL decay due to strong nonradiative Auger recombination, making it difficult to investigate the biexciton dynamics. Here, we develop a quantitative method based on intensity- and time-resolved photon statistics to investigate the biexciton dynamics in single colloidal QDs. This robust method can be used under high-excitation conditions to determine the absolute radiative and Auger recombination rates of both neutral and charged biexciton states in a single QD level, and the corresponding ratios between the two states agree with the theoretical predictions of the asymmetric band structures of CdSe-based QDs. Furthermore, the surface traps are found to provide additional nonradiative recombination pathways for the biexcitons, and their contributions are quantified by the method.

Efficient, Stable, and Photoluminescence Intermittency-Free CdSe-Based Quantum Dots in the Full-Color Range

“…We found that PPD with a reasonable highest occupied molecular According to the PL intensities and lifetimes of these three states, the scaling β of radiative rates between the bright state and the dark state (or the gray state) is found to be 1.98 (or 1.70) by using I X + (X − ) /I X = βτ X + (X − ) /τ X , which are close to the theoretical value of 2. 49,50 Therefore, the bright, gray, and dark states correspond to the single exciton, negative trion, and positive trion states, respectively, which is consistent with previous works. 26,27 Figure 1d presents the corresponding second-order photon correlation function (g (2) (τ)) curve with a low g (2) (0) value, indicating that the investigated QD is indeed a single nanoparticle.…”

Photoluminescence Blinking and Biexciton Auger Recombination in Single Colloidal Quantum Dots with Sharp and Smooth Core/Shell Interfaces

“…Colloidal semiconductor quantum dots (QDs) show superior optical properties including high photoluminescence (PL) quantum yields (QYs), broad absorption, and narrow emission spectra, − making them promising materials for light-emitting diodes, , lasers, photovoltaic devices, − single-photon sources, and biomedical labels. − Nonetheless, almost all single colloidal QDs exhibit PL blinking, − the random switching between bright (on) and dim/dark (off) states, which is a considerable drawback in QD-based applications, e.g., degrading the performance of lasers and light-emitting diodes, interrupting the photon emission of quantum light sources, and causing difficulty in single-particle tracking …”

Influence of Shape Anisotropy on the Emission of Low-Dimensional Semiconductors

“…These states may take the form of multiexcitons or charged excitons (trions). The rates of processes such as intraband relaxation, multiple exciton generation, nonradiative Auger recombination, and emission from biexcitons ,,,− increase with decreasing size in the quantum-confined regime . In strongly confined spherical QDs, sub-100 ps Auger-type annihilation of biexcitons and recombination of trions gives both of these species a much lower PL quantum yield than single excitons in the same material, such that emission from these species is generally only observable when their radiative rates are enhanced ( e.g ., by an external field) or when the Auger rate is slowed at low temperature. − …”

“…The rates of processes such as intraband relaxation, 4 multiple exciton generation, 5 nonradiative Auger recombination, 6 and emission from biexcitons 34,35,48,50−52 increase with decreasing size in the quantum-confined regime. 95 In strongly confined spherical QDs, sub-100 ps Auger-type annihilation of biexcitons and recombination of trions gives both of these species a much lower PL quantum yield than single excitons in the same material, such that emission from these species is generally only observable when their radiative rates are enhanced (e.g., by an external field) or when the Auger rate is slowed at low temperature. 96−108 Anisotropic NPLs provide the quantum confinement needed to realize narrow optical spectra but are also more likely to emit from multiparticle states like trions and excitons because of their large lateral areas and high exciton binding energies.…”