  Photoluminescence (PL) intermittency is a ubiquitous phenomenon detrimentally
reducing the temporal emission intensity stability of single colloidal quantum
dots (CQDs) and the emission quantum yield of their ensembles. Despite efforts
for blinking reduction via chemical engineering of the QD architecture and its
environment, blinking still poses barriers to the application of QDs,
particularly in single-particle tracking in biology or in single-photon
sources. Here, we demonstrate the first deterministic all-optical suppression
of quantum dot blinking using a compound technique of visible and mid-infrared
(MIR) excitation. We show that moderate-field ultrafast MIR pulses (5.5 $\mu$m,
150 fs) can switch the emission from a charged, low quantum yield 'grey' trion
state to the 'bright' exciton state in CdSe/CdS core-shell quantum dots
resulting in a significant reduction of the QD intensity flicker.
Quantum-tunneling simulations suggest that the MIR fields remove the excess
charge from trions with reduced emission quantum yield to restore higher
brightness exciton emission. Our approach can be integrated with existing
single-particle tracking or super-resolution microscopy techniques without any
modification to the sample and translates to other emitters presenting
charging-induced PL intermittencies, such as single-photon emissive defects in
diamond and two-dimensional materials.
