GCN-Seminar: Photoluminescence

The topic of this Greater-Copenhagen Nanoscience Seminar is "Photoluminescence".

The will be three speakers, one from each hub (Copenhagen University, DTU and NanoLund).

Speakers and titles:

• Tom Vosch (KU): Lanthanide up-conversion nanoparticles
• Donatas Zigmantas (NanoLund): Excitation dynamics in DNA-templated silver nanoclusters
• Nicolas Stenger (DTU): Photoluminescence of defects in 2D materials

Talk Abstracts

Tom Vosch (KU): Lanthanide up-conversion nanoparticles

Lanthanide-doped upconversion nanoparticles have the unique ability to absorb multiple photons in a consecutive manner, leading to emission that is anti-Stokes in nature with respect to the excitation wavelength. In this presentation I will discuss some recent results how this can be used for the development of background-free assays and imaging applications.^1,2
 

1. Frequency Encoding of Upconversion Nanoparticle Emission for Multiplexed Imaging of Spectrally and Spatially Overlapping Lanthanide Ions. Mikkel Baldtzer Liisberg, Satu Lahtinen, Ane Beth Sloth, Tero Soukka, and Tom Vosch. J. Am. Chem. Soc. 2021, Accepted
2. Thulium- and Erbium-Doped Nanoparticles with Poly(acrylic acid) Coating for Upconversion Cross-Correlation Spectroscopy-based Sandwich Immunoassays in Plasma. Satu Lahtinen, Mikkel Baldtzer Liisberg, Kirsti Raiko, Stefan Krause, Tero Soukka, and Tom Vosch
   ACS Appl. Nano Mater. 2021, 4, 1, 432–440.

Donatas Zigmantas (NanoLund): Excitation dynamics in DNA-templated silver nanoclusters

DNA-templated silver nanoclusters have fascinating properties, including high absorption cross section and high fluorescence quantum yield. Importantly, these and other features can be readily tuned by changing DNA sequence. The combination of desirable properties and tunability makes them suitable for a wide range of applications from biosensing to nanophotonics. We applied two-dimensional electronic spectroscopy to investigate photo-induced dynamics in a couple of DNA-templated silver nanoclusters¹. Rather surprisingly, we see diverse behaviour, albeit both clusters feature sub-100 fs energy relaxation between absorbing and emitting states. We discuss electronic structure, nature of observed transitions and relaxation dynamics in these systems.

1. Erling Thyrhaug, ..., Tom Vosch and Donatas Zigmantas. Ultrafast coherence transfer in DNA-templated silver nanoclusters. Nat Commun 8, 15577 (2017).

Nicolas Stenger (DTU): Photoluminescence of defects in 2D materials

The recent discovery of quantum emitters at room temperature in the two-dimensional material hexagonal Boron Nitride¹ has triggered a large number of research work. However, the generation of these ultrabright quantum emitters is mostly uncontrolled and their microscopic origin remains elusive. Here, we present a novel generation process to create luminescent centres in hBN by irradiation engineering². We systematically study the density of luminescent centres at different irradiation energies and irradiation fluences (defined as the number of oxygen atoms per area). Increasing the irradiation fluence by ten results in a five-fold enhancement of the density. In combination with molecular dynamics simulations we clarify the generation mechanism, for the first time to the best of our knowledge. Furthermore, we infer that two defects are most likely generated, namely VNCB and VB-. Ab initio calculations of these defects show excellent agreement with experimental photoluminescence line shapes. The generation of quantum emitters by irradiation engineering is a step towards the controlled generation of quantum emitters in hBN. Furthermore, the presented irradiation engineering is wafer-scalable and could be adapted to other irradiating atoms or ions as well as other gapped 2D materials.

1. T. T. Tran et al. Quantum emission from hexagonal boron nitride monolayers, Nature Nanotechnology 11, 37 (2016).
2. M. Fischer et al. Controlled generation of luminescent centres in hexagonal boron nitride by irradiation engineering, Science Advances 7, eabe7138 (2021).

Short Bio of the Speakers

Tom Vosch (KU)

Tom Vosch has a background in single molecule fluorescence microscopy and spectroscopy. During his PhD, he studied the fluorescent properties of rylene labeled dendrimers at the single molecule level, resulting in the demonstration of several Förster type energy transfer processes like energy hopping, singlet-singlet annihilation and singlet-triplet annihilation at the single molecule level. As a postdoctoral fellow, he got interested in the unique fluorescence properties of small noble metal clusters and their applications in life and material sciences. He also initiated research leading to the discovery of bright photo stable fluorescent silver clusters in zeolites. His research group at the University of Copenhagen is mainly focused on the development of new emissive materials and imaging applications.

Donatas Zigmantas (NanoLund)

Donatas Zigmantas has been using advanced time-resolved spectroscopy techniques to study light triggered dynamics in a wide range of systems and materials at the intersection of physics, chemistry and biology. In the course of PhD studies at Lund University he investigated photophysical properties of biomolecules carotenoids, as well as their light-triggered functions in photosynthetic systems. During postdoctoral stay at the University of California, Berkeley Donatas explored regulation of excitation energy in photosynthetic systems of plants. In late 2006 he started his independent carrier at Lund University using multidimensional electronic spectroscopy as the main tool to disentangle complex coherence as well as excitation and charge transfer dynamics in various photosynthetic complexes, which are precise molecular machines, with a typical size of 10 nm. Most recently he established the lab of time-resolved photoemission electron spectroscopy, where excited charge carrier dynamics are studied in semiconductor and metallic nanostructures with femtosecond time and nanometer spatial resolution.

Nicolas Stenger (DTU)

Nicolas Stenger obtained his PhD in 2008 from the University of Strasbourg in condensed matter physics. He did his postdoc at the Karlsruhe Institute of Technology on optical and mechanical metamaterials. He moved to DTU in 2012 to work on quantum related effects in the optical response of small metallic nanoparticles. He became Associate Professor at DTU in 2017 and works currently on the design and fabrications and optical characterization of functional photonic devices for future information processing technologies. His main focus is on strong light-matter interactions between nanophotonics cavities and two-dimensional materials as well as the characterization of these effects in the near-field.