Deconstructing the photon stream from single nanocrystals: from binning to correlation

Abstract

Prior to the advent of single-molecule fluorescence spectroscopy, many of the fundamental optical properties of colloidal semiconductor nanocrystal quantum dots were obscured by ensemble averaging over their inherent inhomogeneities. Single quantum dot spectroscopy has become a leading technique for the unambiguous determination of the governing excitonic physics of these quantum-confined systems. The analysis and interpretation of the timing and energies of photons emitted from individual nanocrystals have uncovered unexpected and fundamental electronic processes at the nanoscale. We review several different paradigms for deconstructing the photon stream from single nanocrystals, ranging from intensity "binning" techniques to more sophisticated methods based on single-photon counting. In particular, we highlight photon correlation - a powerful developing paradigm in single-nanocrystal studies. The application of photon-correlation techniques to single nanocrystals is changing the study of multiexcitonic recombination dynamics, uncovering the basic processes governing spectral linewidths and spectral diffusion, and enabling the extraction of single-nanocrystal properties directly from an ensemble with high statistical significance. These single-molecule techniques have proven invaluable for understanding the physics of nanocrystals and can provide unique insight into other heterogeneous and dynamical systems.

Measurement of Emission Lifetime Dynamics and Biexciton Emission Quantum Yield of Individual InAs Colloidal Nanocrystals

“…16 This understanding has also driven improvements in the quality of these materials. 11 Single-molecule methods to study effects such as blinking, multiexciton dynamics, 17 and spectral diffusion 18,19 have been implemented for visible-emitting nanocrystals using silicon single-photon avalanche photodiodes (SPAD).…”

Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals

“…Fused polycrystalline grains also exhibit this intriguing phenomenon, whichi sr ationalized by correlated and efficient migration of carriers to af ew transient nonradiative traps,t he nature and population of whichd etermine blinking propensity.O bservation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving longrange (mesoscopic) electronic communication.Fluorescence intermittencyo rb linking, which refers to temporally random discrete jumps in intensity between bright and dark levels,has been considered as one of the main pieces of evidence for the detection of single nano-sized quantum emitters. [1][2][3][4][5][6][7][8] Apart from single molecules,b linking is commonly observed in various individual quantum-confined systems such as semiconductor nanocrystals (NCs), in which excitons/charge carriers are spatially restricted in more than one dimension. [4][5][6][7][8][9][10][11][12][13] In NCs,photoluminescence (PL) blinking is attributed to intermittent Auger ionization-recombination processes leading to charging-discharging of NCs or longlived carrier trapping in surface (defect) states.…”

“…[1][2][3][4][5][6][7][8] Apart from single molecules,b linking is commonly observed in various individual quantum-confined systems such as semiconductor nanocrystals (NCs), in which excitons/charge carriers are spatially restricted in more than one dimension. [4][5][6][7][8][9][10][11][12][13] In NCs,photoluminescence (PL) blinking is attributed to intermittent Auger ionization-recombination processes leading to charging-discharging of NCs or longlived carrier trapping in surface (defect) states. [4,5,14,15] However,P Li ntermittencyi ss eldom observed beyond the nanoscale (approaching bulk), as temporally uncorrelated intensity fluctuations from various emitters average out over the ensemble and contribution of surface states in radiative recombination becomes less significant compared to that of free carriers in the bulk.…”

Surface Photochemistry of Quantum Dot-Porphyrin Nanoassemblies for Singlet Oxygen Generation

“…However, capping organic shells (including surfactants and dyes as organic ligands) have considerable impact on the optical properties of QDs (e.g. hot carrier relaxation, PL quantum yield and energy) as has been successfully studied experimentally and theoretically for several systems (75)(76)(77)(78)(79)(80)(81)(82)(83)(84)(85). QD PL efficiency has shown to be sensitive to the surrounding matrix also (86).…”