arXiv subjects

Sebastian Mackowski

Publications and source records attributed to Sebastian Mackowski.

5 recordsLinked to original sources

arXiv2026

Quench, Glow, or Stay Silent: Distance-Controlled Up-Conversion Emission near Metallic Nanowires

We demonstrate controlled transitions between competing radiative and nonradiative decay channels in the up-conversion luminescence of NaYF4:Er3+/Yb3+ nanocrystals placed in proximity to metallic nanowires. The nanocrystal-nanowire separation is used as a key control parameter governing the optical response. An essential aspect of our approach is the removal of inhomogeneous residual polymer layers from the nanowires, eliminating any compromise on distance control and reproducibility in emitter-metal hybrid nanostructures. Replacing them with a well-defined polymer spacer yields controlled access to three qualitatively distinct interaction regimes: luminescence quenching, plasmonic enhancement, and effective decoupling. Transitions between these regimes are shown to reflect changes in the dominant energy relaxation pathways: from nonradiative losses in direct contact with the metal, through modification of the local photonic density of states and coupling to plasmon-mediated modes, to behavior characteristic of quasi-isolated emitters. The plasmonic origin of the emission enhancement in the intermediate regime is evidenced by an increase in luminescence intensity accompanied by shortened decay times, as revealed by fluorescence lifetime imaging microscopy of up-conversion nanocrystals. All experiments were performed on single nanostructures, thereby excluding artefacts arising from aggregation effects and strengthening the interpretation of the observed phenomena. The presented approach provides controlled access to plasmon-modified decay channels and offers a basis for the rational design of functional nanophotonic and sensing structures with tailored optical properties.

physics.optics↗

arXiv2020

Identifying and reducing interfacial losses to enhance color-pure electroluminescence in blue-emitting perovskite nanoplatelet light-emitting diodes

Perovskite nanoplatelets (NPls) hold great promise for light-emitting applications, having achieved high photoluminescence quantum efficiencies (PLQEs) approaching unity in the blue wavelength range, where other metal-halide perovskites have typically been ineffective. However, the external quantum efficiency (EQE) of blue-emitting NPl light-emitting diodes (LEDs) have only reached 0.12%, with typical values well below 0.1%. In this work, we show that the performance of NPl LEDs is primarily hindered by a poor electronic interface between the emitter and hole-injector. Through Kelvin Probe and X-ray photoemission spectroscopy measurements, we reveal that the NPls have remarkably deep ionization potentials (>=6.5 eV), leading to large barriers for hole injection, as well as substantial non-radiative decay at the interface between the emitter and hole-injector. We find that an effective way to reduce these non-radiative losses is by using poly(triarylamine) interlayers. This results in an increase in the EQE of our blue LEDs emitting at 464 nm wavelength to 0.3%. We find that our results can be generalized to thicker sky-blue-emitting NPls, where we increase the EQE to 0.55% using the poly(triarylamine) interlayer. Our work also identifies the key challenges for further efficiency increases.

physics.optics↗

arXiv2019

Giant Fine Structure Splitting of the Bright Exciton in a Bulk MAPbBr$_3$ Single Crystal

Exciton fine structure splitting in semiconductors reflects the underlying symmetry of the crystal and quantum confinement. Since the latter factor strongly enhances the exchange interaction, most work has focused on nanostructures. Here, we report on the first observation of the bright exciton fine structure splitting in a bulk semiconductor crystal, where the impact of quantum confinement can be specifically excluded, giving access to the intrinsic properties of the material. Detailed investigation of the exciton photoluminescence and reflection spectra of a bulk methylammonium lead tribromide single crystal reveals a zero magnetic field splitting as large as $\sim 200\mu$eV. This result provides an important starting point for the discussion of the origin of the large bright exciton fine structure observed in perovskite nanocrystals.

cond-mat.mes-hall↗

arXiv2015

Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene

The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated {\pi}-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale.

cond-mat.mes-hall↗

arXiv2015

Dependence of the Energy Transfer to Graphene on the Excitation Energy

Fluorescence studies of natural photosynthetic complexes on a graphene layer demonstrate pronounced influence of the excitation wavelength on the energy transfer efficiency to graphene. Ultraviolet light yields much faster decay of fluorescence, with average efficiencies of the energy transfer equal to 87% and 65% for excitation at 405 nm and 640 nm, respectively. This implies that focused light changes locally the properties of graphene affecting the energy transfer dynamics, in an analogous way as in the case of metallic nanostructures. Demonstrating optical control of the energy transfer is important for exploiting unique properties of graphene in photonic and sensing architectures.

cond-mat.mes-hall↗