Quantum Optoelectronics

Abstract:

The spectral diffusion of singlet and triplet excitons in 9,9-dioctylfluorene-based conjugated copolymers is investigated using photoluminescence spectroscopy at both low (5 K) and room temperature (300 K). Inclusion of a N,N-diphenyl-4-(pyridin-2-yl)aniline moiety into the polymer backbone allows subsequent cyclometalation with platinum acetylacetonate to increase the spin-orbit coupling and yield radiative decay from the triplet state. For suitably low fractions (≤5%) of bulky ligand inclusion, cyclometalated or not, the resulting longer sequences of fluorene units are able to adopt the chain-extended β-phase conformation. Comparison between the phosphorescence spectral diffusion in glassy- and β-phase Pt-copolymer samples provide insight into the triplet exciton transfer in more- or less-disordered conjugated polymer films. It is found in the glassy-phase samples with shorter conjugation lengths that the triplet exciton relaxation becomes frustrated at low temperature due to a freezing out of the thermally activated hops required to move from one conjugated segment to another. In contrast, for films containing β-phase chain segments, with increased conjugation lengths, this frustration is lifted as more hopping sites remain accessible through intra-segment motion. This work demonstrates controlled use of changes in molecular conformation to optimize triplet diffusion properties in a member of the widely deployed fluorene-based conjugated copolymers.

Abstract:

We investigate cavity-assisted Stimulated Raman Adiabatic passage (STIRAP) schemes in semiconductor quantum dots (QDs) embedded in an optical cavity as a route for generation of high-quality single photons with programmable waveform. This work addresses the need for high-purity, indistinguishable photons in linear quantum computing, boson sampling, and quantum communications. We develop a time-dependent Maxwellpseudospin model of single-photon generation through cavity-assisted adiabatic passage in a Λ-system isolated in a neutral InAs QD in a realistic GaAs/AlGaAs micropillar cavity. As a model Λ-system, we consider QD biexciton triplet states coupled to dark-exciton states by a circularly polarised pulse and a cavity field. Our simulations demonstrate control of the emitted single-photon pulse waveform by the driving pulse characteristics: shape, duration, intensity and detuning.

Abstract:

The self-assembly phenomenon plays a significant role in atomic, molecular, and biological self-assemblies. This phenomenon has also been found in colloidal nanocrystals (NCs). Self-assembly of colloidal NCs into superstructures is a flexible and promising approach for manipulating nanometre-sized particles and exploiting physical and chemical properties that are distinct from both individual nanoparticles and bulk assemblies. The development of superlattices (SLs) of colloidal perovskite NCs through self-assembly has recently attracted remarkable attention; it is quickly developing as a new frontier in nanotechnology. This review presents the different driving forces, crucial factors for self-assembly of perovskite NCs, recent developments in the synthesis, and properties of self-assembled colloidal perovskite NCs. We also discuss the formation of various SLs from perovskite NCs with different morphologies. Finally, we shed light on multiple challenges in developing numerous perovskite SLs for optoelectronic devices.