photoluminescence of a single quantum emitter in a strongly inhomogeneous chemical environment

A comprehensive photoluminescence study of defect centers in single SiO2 nanoparticles provides new insight into the complex photo-physics of single quantum emitters embedded into a random chemical environment

Electrodynamic coupling of electric dipole emitters to a fluctuating mode density within a nano-cavity

We investigate the impact of rotational diffusion on the electrodynamic coupling of fluorescent dye molecules (oscillating electric dipoles) to a tunable planar metallic nanocavity. Fast rotational diffusion of the molecules leads to a rapidly fluctuating mode density of the electromagnetic field along the molecules' dipole axis, which significantly changes their coupling to the field as compared to the opposite limit of fixed dipole orientation. We derive a theoretical treatment of the problem and present experimental results for rhodamine 6G molecules in cavities filled with low and high viscosity liquids. The derived theory and presented experimental method is a powerful tool for determining absolute quantum yield values of fluorescence.Comment: 5 pages, 3 figures, accepted by Physical Review Letter

Characterizing the Quantum Confined Stark Effect in Semiconductor Quantum Dots and Nanorods for Single-Molecule Electrophysiology

We optimized the performance of quantum confined Stark effect QCSE based voltage nanosensors. A high throughput approach for single particle QCSE characterization was developed and utilized to screen a library of such nanosensors. Type II ZnSe CdS seeded nanorods were found to have the best performance among the different nanosensors evaluated in this work. The degree of correlation between intensity changes and spectral changes of the excitons emission under applied field was characterized. An upper limit for the temporal response of individual ZnSe CdS nanorods to voltage modulation was characterized by high throughput, high temporal resolution intensity measurements using a novel photon counting camera. The measured 3.5 us response time is limited by the voltage modulation electronics and represents about 30 times higher bandwidth than needed for recording an action potential in a neuron.Comment: 36 pages, 6 figure

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit ‘cold’ electroluminescence in percolation films1,2, tunnel diodes3, electromigrated nanoparticle aggregates4,5, optical antennas6 or scanning tunnelling microscopy7,8,9. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET–light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides10. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes11 in on-chip optical interconnects

Modifizierung der Fluoreszenz einzelner Quantenemitter: einzelne Farbstoffmoleküle und SiO2-Nanopartikel in einem durchstimmbaren Subwellenlängen-Mikroresonator

In dieser Arbeit untersuchen wir die kontrollierte Änderung der Strahlungsübergangsrate und des Fluoreszenzspektrums eines einzelnen Farbstoffmoleküls und SiO2-Nanopartikels (NP) durch Einbetten in eine durchstimmbare plane Mikrokavität mit Subwellenlängenabstand. Wir haben ein theoretisches Modell entwickelt und finden hervorragende Übereinstimmungen zwischen theoretischen Voraussagen und experimentellen Ergebnissen. Während die Fluoreszenz einzelner Farbstoffmoleküle in Glas-Luft-Grenzfläche (d.h. im freien Raum) sehr gut bekannt ist, sind die Einzelheiten der optischen Eigenschaften individueller SiO2-NP immer noch unklar. Daher widmet sich ein Teil dieser Arbeit der Untersuchung ihrer Fotolumineszenz im freien Raum. Einleitend präsentieren wir die Konstruktion der durchstimmbaren Mikrokavität, die für die Messungen verwendet wurde.In this thesis we study controlled modification of the radiative transition rate and fluorescence spectrum of a single dye molecule and SiO2 nanoparticle (NP) by embedding it within a tunable planar microcavity with subwavelength spacing. We develop a theoretical model and find excellent agreement between theoretical prediction and experimental results. Whereas fluorescence of single dye molecules in glass-air confinement (i.e., in free space) is fairly well known, the details of optical properties of individual SiO2 NPs are still unclear. Therefore, a part of this thesis is dedicated to investigation of their photoluminescence in free space. In introduction of the thesis we present a tunable microcavity construction, which has been used for the measurements

Microstructure and mechanical behaviour of additive manufactured Ti–6Al–4V parts under tension

Metal-based additive manufacturing technologies using electron or laser beams as a heat source for melting a metal powder or wire have been the subject of keen interest in recent years. At present paper a comparative analysis of the microstructure, strain response during tensile test and mechanical properties of Ti–6Al–4V samples produced by selective laser melting, electron beam melting or electron beam free-form fabrication were performed. A microstructural study using transmission electron microscopy revealed columnar prior β grains transformed into a lamellar α-morphology in the samples. According to X-ray diffraction study, the volume fractions of the β-Ti phase in the samples were equal to 2, 4 and 6 % respectively. It has been shown that the Vickers microhardness of SLM and EBM Ti–6Al–4V samples was similar (~5.4 GPa) while the hardness of EBF3 parts was significantly lower (4.5 GPa). The uniaxial stress-strain response of the Ti–6Al–4V samples fabricated by different additive manufacturing technologies were compared. Crystallographic (dislocation motion) and non-crystallographic (shear banding) deformation mechanisms of the loaded samples were studied by scanning electron microscopy and optical profilometry

Metal-induced energy transfer

Since about a decade, metal-induced energy transfer (MIET) has become a tool to measure the distance of fluorophores to a metal-coated surface with nanometer accuracy. The energy transfer from a fluorescent molecule to surface plasmons within a metal film results in the acceleration of its radiative decay rate. This can be observed as a reduction of the molecule’s fluorescence lifetime which can be easily measured with standard microscopy equipment. The achievable distance resolution is in the nanometer range, over a total range of about 200 nm. The method is perfectly compatible with biological and even live cell samples. In this review, we will summarize the theoretical and technical details of the method and present the most important results that have been obtained using MIET. We will also show how the latest technical developments can contribute to improving MIET, and we sketch some interesting directions for its future applications in the life sciences