Ersan Özelci
Humboldt Universität zu Berlin
Ersan Özelci was born in Kastamonu, Turkey. He received his B. Sc.degree in Physics Engineering from Istanbul Technical University, Istanbul, Turkey, in 2012. He later joined the M.Sc. program in Optoelectronics and Photonics Engineering at Koç University, Istanbul. His M. Sc. degree thesis is Optofluidic Microlasers Based on Non-Radiative Energy Transfer in Surface-supported Liquid Microdroplet. Since 2015, he is PhD student at HU Berlin Physics Department.
A key parameter for fluorescence applications presents the photoluminescence quantum yield (QY), the number of emitted per number of absorbed photons, which can determined by optical methods either relative to a standard with... [ view full abstract ]
A key parameter for fluorescence applications presents the photoluminescence quantum yield (QY), the number of emitted per number of absorbed photons, which can determined by optical methods either relative to a standard with known QY or absolutely with integrating sphere spectroscopy [1]. An interesting alternative, expandable to single emitters, utilizes the modification of the spontaneous emission of a fluorophore in the neighborhood of a metallic surface according to the pioneering experiment by Drexhage [2]. This quantum electrodynamic approach enables the direct measurement of QY by changing the local density of states (LDOS) [3]. Our goal is to quantitatively compare both approaches to establish reliable QY measurements over a vast concentration range from macroscopic ensembles down to single emitters.
In our experimental approach, we use a spherical ball coated with silver as in [3] instead of a mirror. These balls in tripod configuration are placed on a PMMA-coated glass substrate (Fig. 1). Then, fluorescence lifetime imaging (FLIM) studies are performed, here with a dye exemplary chosen from the class of perylene bisimides (PBIs), used in organic electronics, photovoltaics, and as sensor materials [4], employing a scanning piezo stage and a confocal microscope. This yields FLIM map (inset of Fig.2). The concentric rings, centered with respect to the contact point of the sphere and the PMMA surface, reflect the increasing distance between the PBI molecules and the silver surface, which can be regarded as locally flat. The variation of the fluorescence lifetime as a function of the molecule-to-sphere distance can then be extracted from the FLIM map. Also, we fitted these data to theoretical curves considering a semi-infinite glass substrate, vacuum, the silver sphere’s SiO2 coating, and the semi-infinite silver layer [5] (Fig.2) and derived the QY of our PBI dye. In the future, we will combine this experimental concept with a microfluidics setup for solution studies.
[1] C. Würth et al., Nat Protocols 2013.
[2] K.Drexhage et al, J.Lumin, 1-2, 693 (1970).
[3] Lunnemann et al, ACS Nano 2013, 5984-5992.
[4] Würthner et al. Chem.Commun. 2004,1564-1579.
[5] Paulus et al., Phys. Rev. E 2000, 62, 5797–5807.
Photonic & plasmonic nanomaterials , Strong light-matter interactions at the nanoscale , Enhanced spectroscopy and sensing
