Jennifer Ann Hollingsworth

A time-dependent likelihood distribution for analyzing time correlated single photon counting data from a four-pixel time-resolved single molecule localization microscopy experiment is discussed. It is generated by accounting for the probabilities to record photons from two emitters, background counts, and dark counts during two different time channels relative to each incident laser pulse in the experiment. Maximizing the distribution enables localization of each emitter in a dual emitting nanostructure based on the disparate photoluminescence lifetimes of the emitters, even when both emitters are simultaneously in an emissive state. The technique is demonstrated using simulated photon counting data from a hypothetical non-blinking dual-emitter nanostructure in which the distance between the two emitters is less than 10-nm.

Photoluminescence images can be acquired with detection schemes that have both single-photon sensitivity and nanosecond scale temporal resolution, enabling the study of possible structural bases for photoluminescence lifetimes and other features of the photon arrival statistics. Within the context of super-resolution (SR) imaging, this has been demonstrated with detection schemes that collect images with a bundle of optical fibers that are coupled to individual single-photon counting avalanche photodiode detectors. Recently, our group used a bundle of four optical fibers to collect these "time-resolved photon arrival" images. Despite the paucity of information contained in a four-pixel image, we precisely located the emission centroid of quantum dots (QDs) and observed correlations between centroid location, photoluminescence lifetime, and intensity within clusters of QDs that were suggestive of electronic interactions among them. This proceedings paper details the approach that we used to locate the emission centroid based on the counts in the four detectors.

Semiconductor quantum dots (QDs) in small clusters can exchange excited state energy via various transfer mechanisms such as Forster resonant energy transfer (FRET). Such energy transfer enables excitons to move from larger bandgap donors to smaller bandgap acceptors. Clusters of mixed donor/acceptor QD species consequently have a spectral signature that is dependent on which QDs in the clusters are responsible for the emission. Using a dual-color super-resolution imaging approach, we report on the spectral characteristics of interacting QDs in clusters with nanometer spatial resolution. Higher emission intensities from clusters are shown to emanate from sub-regions of the clusters and have spectral signatures that indicate the emission is dominated by the acceptor region of the spectrum. Thus, energy transferring interactions among QDs in clusters funnel excitons primarily to acceptor particles. Acceptor particles are responsible for the majority of the emission from the clusters with an emission spectra corresponding to the spectral profiles of the acceptor species.

Quantum light and in particular single photons have become essential resources for a growing number of quantum applications including quantum computing, quantum key distribution and quantum metrology. Solid-state atom-like systems such as semiconductor quantum dots and color defects in crystals have become the hallmark of highly pure single photon emitters in the past two decades. A particular interest has been developed in nanocrystal quantum dots (NQDs) and color centers in diamond as potential compact room-temperature emitters. There are however several challenges that inhibit the use of such sources in current technologies including low photon extraction efficiency, low emission rates and relatively low single photon purities. In this work we will review our efforts in overcoming these technical difficulties using several complementary methods including designing several nanoantenna devices that enhance the directionality and emission rate of the nanoemitter. In addition, we developed several temporal heralding techniques to overcome the hurdle of low single photon purity in NQDs in an effort to produce a highly pure, bright and efficient single photon source on-chip.

Particle-size or ‘quantum-confinement’ effects have been used for decades to tune semiconductor opto-electronic properties. More recently, particle size control as the primary means for properties control has been succeeded by nanoscale hetero-structuring. In this case, the nanosized particle is modified to include internal, nanoscale interfaces, generally defined by compositional variations that induce additional changes to semiconductor properties. These changes can entail enhancements to the size-induced properties as well as unexpected or ‘emergent’ behaviors. Common structural motifs include enveloping a spherical semiconductor nanocrystal, i.e., a quantum dot, within a shell of a different composition. In this talk, I will discuss how solution-phase synthesis can be used to create these structures with precisely ‘engineered’ complexity. Most notably, I will review our experiences with so-called ‘giant’ quantum dots that, due to their internal nanoscale structure, exhibit a range of novel behaviors, including being non-blinking and non-photobleaching (Chen et al. J. Am. Chem. Soc. 2008, 130, 5026; Ghosh et al. J. Am. Chem. Soc. 2012, 134, 9634; Dennis et al. Nano Lett. 2012 12, 5545; Acharya et al. J. Am. Chem. Soc. 2015, 137, 3755), and remarkably efficient emitters of ‘multi-excitons’ due to extreme suppression of Auger recombination (Mangum et al. Nanoscale 2014, 6, 3712; Gao et al. Adv. Optical Mater. 2015, 3, 39). I will discuss recent work extending non-blinking behavior to the blue/green and “dual-color” emission, and show how correlated optical/structural characterization can reveal new information regarding structure-property relations to guide new nanomaterials development (Orfield et al. ACS Nano, Article ASAP).

Thick-shell or “giant” core/shell nanocrystal quantum dots (gQDs) are efficient and stable emitters. Their characteristic properties of non-blinking and non-photobleaching emission, as well as suppressed non-radiative Auger recombination and minimal self-reabsorption (due to a large effective Stokes shift) make them relevant to both single-emitter and many-emitter applications, e.g., live-cell single-molecule tracking in the biosciences and down-conversion phosphors for solid-state lighting. Here, I will discuss how gQDs are also ideal “building blocks” for achieving additive functionalities through synthesis and modified emission properties through integration with fabricated photonic structures. gQDs have been synthetically incorporated into the interior of a gold shell, resulting in “plasmonic gQDs” that exhibit efficient photoluminescence combined with efficient photothermal transduction and thermometry. Furthermore, through direct patterning of gQDs into all-dielectric antennas, we show an approach for realizing emitter-antenna couples (toward controlling the motion of photons) that is both deterministic and reproducible.

Hybrid semiconductor-metal nanoparticles are of both fundamental and practical interest. CdSe semiconductor nanocrystal quantum dots (NQDs) are emissive following direct absorption of photons, while nanosized metal structures exhibit plasmonic absorption and light scattering. In a hybrid nanoscale architecture, both optical phenomena can be integrated as metal-semiconductor coupling via non-radiative energy transfer and modifications of the radiative decay rates through Purcell effect, alter the emission mechanism resulting in a range of effects from photoluminescence (PL) quenching to enhancement.

  Conference Title: 2013 Conference on Lasers and Electro-Optics (CLEO) Conference Start Date: 2013, June 9 Conference End Date: 2013, June 14 Conference Location: San Jose, CA, USA We describe the development and characterization of two novel non-blinking "giant" nanocrystal quantum dot (g-NQD) systems and their application to single-particle tracking in live cells real-time and in three dimensions. The two g-NQDs -- CdSe/CdS and InP/CdS -- are characterized by a thick shell layer (>10 monolayers of CdS), a quasi-type-II or type-II electronic structure, and extremely suppressed non-radiative Auger recombination and photobleaching, in addition to suppressed blinking. We show that these unique traits make this new class of NQD ideal molecular probes for observing spatio-temporal dynamics of cellular processes.