Universal emission intermittency in quantum dots, nanorods and nanowires

Abstract

Virtually all known fluorophores exhibit mysterious episodes of emission intermittency. A remarkable feature of the phenomenon is a power law distribution of onand off-times observed in colloidal semiconductor quantum dots (QDs), nanorods, nanowires and some organic dyes. For nanoparticles the resulting power law extends over an extraordinarily wide dynamic range: nine orders of magnitude in probability density and five to six orders of magnitude in time. Exponents hover about the ubiquitous value of -3/2. Dark states routinely last for tens of seconds, which are practically forever on quantum mechanical time scales. Despite such infinite states of darkness, the dots miraculously recover and start emitting again. Although the underlying mechanism responsible for this phenomenon remains a mystery and many questions persist, we argue that substantial theoretical progress has been made.

Collective fluorescence enhancement in nanoparticle clusters

“…The fluorescence intensity stochastically changes between bright and dark regimes, commonly referred to as onand off-states. Furthermore, this blinking does not follow a simple two-level quantum jump model, but instead displays approximately power-law (Lévy) statistics over many decades in time [3][4][5][6][7][8] . Similar non-Poissonian statistics have been observed in electron transport through colloidal nanocrystal (NC) arrays 9 .…”

“…In correlated electron systems, measurements of the statistics of backscattered current (quantum shot noise) have established the elusive fractional quasiparticle charge 1,2 , a result of strong electron interactions in the quantum Hall regime. In chemical systems, complexity of the environment produces the fluorescence intermittency or 'blinking' displayed by many types of single emitters, such as single molecules, green fluorescent proteins, lightharvesting complexes, organic fluorophores and semiconductor nanoparticles 3,4 . The fluorescence intensity stochastically changes between bright and dark regimes, commonly referred to as onand off-states.…”

“…The origin of the observed Lévy statistics has been investigated extensively, with several models proposed in the 15 years since the first observation of power-law blinking [3][4][5] . Although the details of the mechanism are still poorly understood, it is thought that NCs become 'dark' , cease emitting light, when one of the charge carriers in a photoexcited exciton becomes trapped at the surface of the NC or tunnels off the NC into the environment, leaving a net charge delocalized in the NC core.…”

“…In the charged core, highly efficient Auger processes lead to rapid nonradiative recombination of subsequent photoexcited excitons. The NC is 'dark' in this 'charge-separated' state; fluorescence resumes once the core regains electrical neutrality [3][4][5][10][11][12][13][14] . Recently, the Krauss and Klimov groups observed near-complete suppression of blinking in NCs synthesized with graded shells that greatly reduce the efficiency of Auger recombination, providing strong support for the proposal that dark states involve Auger recombination 10,15 .…”

“…Recently, the Krauss and Klimov groups observed near-complete suppression of blinking in NCs synthesized with graded shells that greatly reduce the efficiency of Auger recombination, providing strong support for the proposal that dark states involve Auger recombination 10,15 . Other mechanisms based on fluctuating nonradiative rates have also been proposed 4,16,17 .…”