Nanometalliliste struktuuride poolt põhjustatud muutused fotostabiilsete fluorofooride kiirguses ja spektri kujus

Väitekirja elektrooniline versioon ei sisadla publikatsioone.Uurimus kuulub uudsesse ja kiiresti arenevasse plasmoonika valdkonda, mis tegeleb plasmonitega ehk elektrontiheduse lainetega seotud nähtustega. Doktoritöös selgitati, kuidas mõjutavad metallist (kullast ja hõbedast) nano-osakesed ja struktuurid helendavatest materjalidest pärinevat valgust. Peamiselt analüüsiti samaariumit sisaldava titaanoksiidi ja lämmastikku sisaldavate 140 nanomeetri suuruste teemantide kiirguse muutumist. Uurimuses rakendati peamiselt fluorestsents-mikroskoopia ja spektroskoopia meetodeid. Katsete tulemused näitasid, et kullast ja hõbedast nano-osakesed suudavad teatud tingimustel helendavatest materjalidest pärinevat valgust võimendada. Peale selle selgus, et peale valguse võimendamise on nende plasmonlainetega võimalik kontrollida ka valguse teisi omadusi, nagu näiteks valguse polarisatsiooni või spektri kuju ehk värvi. Doktoritöö uudsus seisnes selles, et seal näidati, et plasmonlainete kasulike omadusi saab rakendada ka helendavate materjalide peal, millel on kõrge murdumisnäitaja ja mis ei kaota võimet valgust kiirata. Kuigi need fluorestseerivad materjalid on kõrgtehnoloogiatööstusele väga olulised, oli plasmonite mõju seda tüüpi materjalidele varem vähe uuritud. Neid materjale saab näiteks kasutada valgustites, laserites, biotehnoloogias, optikatööstuses ja optiliste elektroonikaseadmete valmistamise juures ning isegi katseliste kvantarvutite ehitamisel.The dissertation studied the effects of small metallic nanoparticles and nanostructures on the emission of fluorescent materials. Special type of metallic particles and structures were used in the experiments, which could support electron density waves also known as plasmons. How these waves are excited and how these plasmon waves can be applied in practice falls under the new and quickly growing scientific research field called plasmonics. The study analysed the fluorescent properties of samarium containing titanium oxide and 140 nanometre sized nitrogen containing fluorescent nanodiamonds. The study employed various microscopic and spectroscopic measurements. The results of the experiments showed that it is possible to apply metallic nanostructures to enhance the emission of high refractive index photostable fluorescence materials. It was also demonstrated that plasmonic nanostructures can modify other properties of the emission such as the polarization and spectral shape. The work was focused to these high refractive index photostable fluorescent materials as they possess great importance to the high-tech industry, but there were only a few studies dealing with the emission and spectral modifications effects induced by metallic nanostructures in similar materials. The results of the study help us to better understand the interactions of metallic nanostructures with fluorophores which can lead to engineering of more efficient fluorescent materials and new composite optical devices

Plasmonic nanostructures through DNA-assisted lithography

Programmable self-assembly of nucleic acids enables the fabrication of custom, precise objects with nanoscale dimensions. These structures can be further harnessed as templates to build novel materials such as metallic nanostructures, which are widely used and explored because of their unique optical properties and their potency to serve as components of novel metamaterials. However, approaches to transfer the spatial information of DNA constructions to metal nanostructures remain a challenge. We report a DNA-assisted lithography (DALI) method that combines the structural versatility of DNA origami with conventional lithography techniques to create discrete, well-defined, and entirely metallic nanostructures with designed plasmonic properties. DALI is a parallel, high-throughput fabrication method compatible with transparent substrates, thus providing an additional advantage for optical measurements, and yields structures with a feature size of ~10 nm. We demonstrate its feasibility by producing metal nanostructures with a chiral plasmonic response and bowtie-shaped nanoantennas for surface-enhanced Raman spectroscopy. We envisage that DALI can be generalized to large substrates, which would subsequently enable scale-up production of diverse metallic nanostructures with tailored plasmonic features.Peer reviewe

Effect of molecular Stokes shift on polariton dynamics

When the enhanced electromagnetic field of a confined light mode interacts with photoactive molecules, the system can be driven into the regime of strong coupling, where new hybrid light–matter states, polaritons, are formed. Polaritons, manifested by the Rabi split in the dispersion, have shown potential for controlling the chemistry of the coupled molecules. Here, we show by angle-resolved steady-state experiments accompanied by multi-scale molecular dynamics simulations that the molecular Stokes shift plays a significant role in the relaxation of polaritons formed by organic molecules embedded in a polymer matrix within metallic Fabry–Pérot cavities. Our results suggest that in the case of Rhodamine 6G, a dye with a significant Stokes shift, excitation of the upper polariton leads to a rapid localization of the energy into the fluorescing state of one of the molecules, from where the energy scatters into the lower polariton (radiative pumping), which then emits. In contrast, for excitonic J-aggregates with a negligible Stokes shift, the fluorescing state does not provide an efficient relaxation gateway. Instead, the relaxation is mediated by exchanging energy quanta matching the energy gap between the dark states and lower polariton into vibrational modes (vibrationally assisted scattering). To understand better how the fluorescing state of a molecule that is not strongly coupled to the cavity can transfer its excitation energy to the lower polariton in the radiative pumping mechanism, we performed multi-scale molecular dynamics simulations. The results of these simulations suggest that non-adiabatic couplings between uncoupled molecules and the polaritons are the driving force for this energy transfer process.peerReviewe

Time-resolved luminescence spectroscopy of ultrafast emissions in BaGeF6

Phase-pure crystalline micropowder samples of BaGeF6 were prepared and studied under excitation by tuneable synchrotron radiation and 10 keV electron beam. Time-resolved photoluminescence emission and excitation spectra and a set of single emission decay curves were recorded at 7 K for the exciting photon energy region of 4.3–45 eV. Several intrinsic emissions were revealed in BaGeF6 and their origin investigated. A single broad emission band peaking at 455 nm is assigned to be of excitonic origin due to its long decay time in the μs range and due to the presence of an intense excitation peak at 10.1 eV right in the region of the host absorption onset. The energy gap width of BaGeF6 was determined experimentally from the photoluminescence excitation spectra of the 455 nm emission to be 10.9 eV. Several emission bands, including distinct peaks at 270 and 455 nm, with the main decay component of ∼180 ps were revealed across the wavelength range of 200–500 nm. The revealed ultrafast emissions were studied by means of time-resolved photoluminescence spectroscopy and their origin was assigned to cross-luminescence resulting from radiative transitions between the Ba 5p core level and sub-bands of the valence band (Ge 4s, Ge 4p and F 2p hybridized states) and to intraband luminescence between the valence band sub-bands. Photoluminescence excitation spectra of the ultrafast emissions revealed a gently sloping onset at 17 eV, related to transitions from the Ge 4s states. It is followed by a distinct peak at 19.4 eV, which corresponds to the ionization of the Ba 5p cation states and is related to the excitation threshold of cross-luminescence

Deep Deconvolution of Object Information Modulated by a Refractive Lens Using Lucy-Richardson-Rosen Algorithm

A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances satisfy the imaging conditions. However, static imaging is limited to the depth of focus, beyond which the point-to-point mapping can only be obtained by changing either the location of the lens, object or the imaging sensor. In this study, the depth of focus of a refractive lens in static mode has been expanded using a recently developed computational reconstruction method, Lucy-Richardson-Rosen algorithm (LRRA). The imaging process consists of three steps. In the first step, point spread functions (PSFs) were recorded along different depths and stored in the computer as PSF library. In the next step, the object intensity distribution was recorded. The LRRA was then applied to deconvolve the object information from the recorded intensity distributions during the final step. The results of LRRA were compared with two well-known reconstruction methods, namely the Lucy-Richardson algorithm and non-linear reconstruction

Deep Deconvolution of Object Information Modulated by a Refractive Lens Using Lucy-Richardson-Rosen Algorithm

A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances satisfy the imaging conditions. However, static imaging is limited to the depth of focus, beyond which the point-to-point mapping can only be obtained by changing either the location of the lens, object or the imaging sensor. In this study, the depth of focus of a refractive lens in static mode has been expanded using a recently developed computational reconstruction method, Lucy-Richardson-Rosen algorithm (LRRA). The imaging process consists of three steps. In the first step, point spread functions (PSFs) were recorded along different depths and stored in the computer as PSF library. In the next step, the object intensity distribution was recorded. The LRRA was then applied to deconvolve the object information from the recorded intensity distributions during the final step. The results of LRRA were compared with two well-known reconstruction methods, namely the Lucy-Richardson algorithm and non-linear reconstruction