Photoluminescence Blinking from Single CdSeS/ZnS Quantum Dots in a Conducting Polymer Matrix

Quantum dot nanocrystals (NQDs) present within organic conducting (polymer) host environments form hybrid organic–inorganic materials that are applied in a range of technologies such as light emitting diodes or solar cells. Understanding hole-transport and exciton dynamics in these hybrid materials is central to device performance and efficiency. Integral to hole-transport is the understanding of multiexciton processes such as charged excitons as well as neighbor–neighbor NQD interactions (on the nano and micrometer length scales). Studied here are the photoluminescence dynamics of single alloyed NQDs in conducting (or insulating) polymer environments. We find that conducting polymers (through hole transport) affect the presence and dynamics of charged excitons relative to insulating environments. The presence of such charged excitons induces a change in blinking dynamics with a corresponding increase in photoluminescence correlation between neighboring NQDs found using spatiotemporal statistical analysis. Understanding such phenomena advances the understanding of photoluminescence processes central to device design

Plasmon Enhanced Raman from Ag Nanopatterns Made Using Periodically Poled Lithium Niobate and Periodically Proton Exchanged Template Methods

We study Ag nanopattern arrays formed using ferroelectric lithography based on two separate approaches, i.e., periodically poled lithium niobate (PPLN) and periodically proton exchanged (PPE) template methods. We demonstrate that such nanoarrays are plasmon active. Raman spectroscopy was applied to study molecular probe 4-aminothiophenol (4-ABT) absorbed onto a silver nanostructured array. The observed Raman spectra show peaks arising from b₂ modes, which occur for plasmon enhanced Raman from 4-ABT in place of a₁ modes, which occur in normal Raman scattering. We demonstrate that the PPLN and PPE substrates possess different plasmonic properties with PPE creating a stronger SERS signal relative to PPLN substrates

Single-Molecule Nonresonant Wide-Field Surface-Enhanced Raman Scattering from Ferroelectrically Defined Au Nanoparticle Microarrays

Single-molecule detection by surface-enhanced Raman scattering (SERS) is a powerful spectroscopic technique that is of interest for the sensor development field. An important aspect of optimizing the materials used in SERS-based sensors is the ability to have a high density of “hot spots” that enhance the SERS sensitivity to the single-molecule level. Photodeposition of gold (Au) nanoparticles through electric-field-directed self-assembly on a periodically proton-exchanged lithium niobate (PPELN) substrate provides conditions to form well-ordered microscale features consisting of closely packed Au nanoparticles. The resulting Au nanoparticle microstructure arrays (microarrays) are plasmon-active and support nonresonant single-molecule SERS at ultralow concentrations (<10^–9–10^–13 M) with excitation power densities <1 × 10^–3 W cm^–2 using wide-field imaging. The microarrays offer excellent SERS reproducibility, with an intensity variation of <7.5% across the substrate. As most biomarkers and molecules do not support resonance enhancement, this work demonstrates that PPELN is a suitable template for high-sensitivity, nonresonant sensing applications