Kyriacos Georgiou

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• PhD in Physics
• Research Fellow at University of Cyprus

Hybridization of two fluorescent BODIPY dyes in a microcavity is achieved by coupling different exciton transitions to the same cavity mode. We characterise the luminescence of such hybrid system following non-resonant laser excitation and show that the relative population along the different polariton branches can be controlled by changing cavity...

Strong coupling to the electronic or vibronic transitions of an organic semiconductor has been extensively studied in microcavity structures in which a molecular film is placed between two closely spaced mirrors. Recent experiments suggest that such strong coupling can be used to modify chemical reactions; however, the geometry of conventional micr...

Non‐radiative energy transfer between spatially‐separated molecules in a microcavity can occur when an excitonic state on both molecules are strongly‐coupled to the same optical mode, forming so‐called “hybrid” polaritons. Such energy transfer has previously been explored when thin‐films of different molecules are relatively closely spaced (≈100 nm...

Tin halide perovskite nanocrystals (NCs) are less prone to the environmental issues associated with the lead‐based NC analogs, however, they suffer from tin oxidation and structural polymorphism. NC durability deteriorates further in the solid state due to the greater exposure to humidity and oxygen, resulting in a very limited number of studies on...

Strong coupling between light and matter in a microcavity can produce quasi‐particle states termed cavity‐polaritons. In cavity architectures containing more than one excitonic species, the photon mode can simultaneously couple to the different excitons, generating new ʻhybrid‐polaritonʼ states. It is demonstrated that such hybrid polariton states...

Ultrafast all-optical logic devices based on nonlinear light-matter interactions hold the promise to overcome the speed limitations of conventional electronic devices. Strong coupling of excitons and photons inside an optical resonator enhances such interactions and generates new polariton states which give access to unique nonlinear phenomena, suc...

Strong light-matter interactions have attracted much attention as a means to control the physical/chemical properties of organic semiconducting materials with light-matter hybrids called polaritons. To unveil the processes under strong...

Strong coupling of a confined optical field to the excitonic or vibronic transitions of a molecular material results in the formation of new hybrid states called polaritons. Such effects have been extensively studied in Fabry–Pèrot microcavity structures where an organic material is placed between two highly reflective mirrors. Recently, theoretica...

The manipulation of exciton–polaritons and their condensates is of great interest due to their applications in polariton simulators and high‐speed, all‐optical logic devices. Until now, methods of trapping and manipulating such condensates are not dynamically reconfigurable or resulted in an undesirable reduction in the exciton–photon coupling stre...

The manipulation of exciton-polaritons and their condensates is of great interest due to their applications in polariton simulators and high-speed, all-optical logic devices. Until now, methods of trapping and manipulating such condensates are not dynamically reconfigurable or result in an undesirable reduction in the exciton-photon coupling streng...

Lead halide perovskite nanocrystals (NCs) are highly suitable active media for solution-processed lasers in the visible spectrum, owing to the wide tunability of their emission from blue to red via facile ion-exchange reactions. Their outstanding optical gain properties and the suppressed nonradiative recombination losses stem from their defect-tol...

While there have been numerous reports of long‐range polariton transport at room‐temperature in organic cavities, the spatiotemporal evolution of the propagation is scarcely reported, particularly in the initial coherent sub‐ps regime, where photon and exciton wavefunctions are inextricably mixed. Hence the detailed process of coherent organic exci...

We have fabricated dielectric microcavities containing the molecular dye 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (DPAVB) dispersed in a transparent polymer matrix. We show that despite the relatively broad absorption linewidth of the DPAVB, the cavities enter the strong coupling regime. We use <330 ps pulses at 355 nm from a Nd:YAG...

Two-Dimensional Electronic Spectroscopy reveals an ultrafast energy delocalization between 2μm distanced donor/acceptor molecules confined in a microcavity. This mechanism is promoted by the formation of hybrid-polariton states that induces a coupling in the entire system.

While there have been numerous reports of long-range polariton transport at room-temperature in organic cavities, the spatio-temporal evolution of the propagation is scarcely reported, particularly in the initial coherent sub-ps regime, where photon and exciton wavefunctions are inextricably mixed. Hence the detailed process of coherent organic exc...

We have developed a simplified approach to fabricate high-reflectivity mirrors suitable for applications in a strongly-coupled organic-semiconductor microcavity. Such mirrors are based on a small number of quarter-wave dielectric pairs deposited on top of a thick silver film that combine high reflectivity and broad reflectivity bandwidth. Using thi...

Strong light–matter coupling to form exciton– and vibropolaritons is increasingly touted as a powerful tool to alter the fundamental properties of organic materials. It is proposed that these states and their facile tunability can be used to rewrite molecular potential energy landscapes and redirect photophysical pathways, with applications from ca...

Strong light-matter coupling to form exciton- and vibropolaritons is increasingly touted as a powerful tool to alter the fundamental properties of organic materials. It is proposed that these states and their facile tunability can be used to rewrite molecular potential energy landscapes and redirect photophysical pathways, with applications from ca...

Ultralong-range polariton-assisted energy transfer was achieved in a microcavity containing two J-aggregate cyanine dyes. The two dyes were separated by a distance of up to 2 μm using a polymeric spacer layer. Here, it was confirmed that hybrid middle polariton (MP) states, composed of a mixture between the cavity photon modes and the different exc...

We have fabricated organic semiconductor microcavities having an extended optical path-length (up to 2 µm) that contain J-aggregates of a cyanine dye. These structures are studied using optical-reflectivity and are found to be characterized by a series of polaritonic modes. By changing the effective oscillator strength of the dye within the cavity,...

Two-dimensional semiconducting transition metal dichalcogenides embedded in optical microcavities in the strong exciton-photon coupling regime may lead to promising applications in spin and valley addressable polaritonic logic gates and circuits. One significant obstacle for their realization is the inherent lack of scalability associated with the...

The addition of alkali metal halides to hybrid perovskite materials can significantly impact their crystallisation and hence their performance when used in solar cell devices. Previous work on the use of potassium iodide (KI) in active layers to passivate defects in triple-cation mixed-halide perovskites has been shown to enhance their luminescence...

Organic semiconductors are a promising platform for ambient polaritonics. Several applications, such as polariton routers, and many-body condensed matter phenomena are currently hindered due to the ultra-short polariton lifetimes in organics. Here, we employ a single-shot dispersion imaging technique, using 4 ns long non-resonant excitation pulses,...

Two-dimensional semiconducting transition metal dichalcogenides embedded in optical microcavities in the strong exciton-photon coupling regime may lead to promising applications in spin and valley addressable polaritonic logic gates and circuits. One significant obstacle for their realization is the inherent lack of scalability associated with the...

Exciton-polaritons in 2D lattice geometries now attract considerable attention as systems in which to explore new physics. However, such structures are relatively difficult to fabricate as this can involve sophisticated milling or etching of cavity layers to create arrays of defects. Here, a straightforward technique is reported that allows rapid f...

Organic semiconductors are a promising platform for ambient polaritonics. Several applications, such as polariton routers, and many-body condensed matter phenomena are currently hindered due to the ultra-short polariton lifetimes in organics. Here, we employ a single-shot dispersion imaging technique, using 4 nanosecond long non-resonant excitation...

Researchers from the University of Sheffield use focused‐ion beam lithography to etch micropillars into a planar microcavity formed from two dielectric mirrors placed on either side of a fluorescent conjugated‐polymer (see article number 1900067 by David G. Lidzey and co‐workers). The photoluminescence from the micropillars is explored using a seri...

Bose-Einstein condensates of exciton-polaritons in inorganic semiconductor microcavities are known to possess strong interparticle interactions attributed to their excitonic component. The interactions play a crucial role in the nonlinear dynamics of such systems and can be witnessed as the energy blueshifts of polariton states. However, the locali...

Researchers have optically connected organic semiconductors and inorganic thin films to produce a light-emitting diode powered by quasi-particles that are part light and part matter. Polaritons, which form when electron–hole pairs in a semiconductor interact with photons, can be energy efficient sources of coherent light. Rahul Jayaprakash from the...

Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic materials are of current interest as active materials for their ability to sustain exciton-polaritons even at room temperature. Howe...

The light emission from a series of micropillar microcavities containing a fluorescent, red‐emitting conjugated polymer, is explored. Cavities are fabricated by defining two dielectric mirrors either side of a polymer active region. Focused ion‐beam (FIB) lithography is then used to etch pillar structures into the planar cavity having diameters bet...

We report on the origin of energy-shifts in organic polariton condensates. The localised nature of Frenkel excitons in molecular semiconductors precludes interparticle Coulomb exchange interactions -the latter being the dominant mechanism for blueshifts in inorganic semiconductor microcavities that bear Wannier-Mott excitons. We examine the contrib...

We report on the origin of energy-shifts in organic polariton condensates. The localised nature of Frenkel excitons in molecular semiconductors precludes interparticle Coulomb exchange interactions -the latter being the dominant mechanism for blueshifts in inorganic semiconductor microcavities that bear Wannier-Mott excitons. We examine the contrib...

A material system is proposed to generate polariton lasing at room temperature over a broad spectral range. The system developed is based on a boron‐dipyrromethene fluorescent dye (BODIPY‐G1) that is dispersed into a polystyrene matrix and used as the active layer of a strongly coupled microcavity. It is shown that the BODIPY‐G1 exciton polaritons...

We explore the generation of anti-Stokes fluorescence from strongly coupled organic dye microcavities following resonant ground-state excitation. We observe polariton emission along the lower polariton branch, with our results indicating that this process involves a return to the exciton reservoir and the absorption of thermal energy from molecules...

We explore the generation of anti-Stokes fluorescence from strongly coupled organic dye microcavities following resonant ground-state excitation. We observe polariton emission along the lower polariton branch, with our results indicating that this process involves a return to the exciton reservoir and the absorption of thermal energy from molecules...

David G. Lidzey, Paclos G. Lagoudakis, and co-workers demonstrate room temperature polariton condensation in the yellow part of the visible spectrum from a planar organic semiconductor microcavity containing the molecular dye BODIPY-Br in article number 1700203. Single-shot polariton dispersion imaging is exploited to observe the collapse of the en...

Rapid excited-state quenching in the solid state is a widespread limitation for organic chromophores. Even when molecules are dispersed in neutral host matrices, photoluminescence quantum yields decrease sharply with increased concentration, pointing to efficient intermolecular non-radiative decay pathways that remain poorly understood. Here we stu...

Polariton condensation in the yellow part of the visible spectrum from a planar organic semiconductor microcavity containing the molecular dye bromine-substituted boron-dipyrromethene is observed. This study provides experimental fingerprint of polariton condensation under nonresonant optical excitation, including the nonlinear dependence of the em...

Polariton condensation in the yellow part of the visible spectrum from a planar organic semiconductor microcavity containing the molecular dye bromine-substituted boron-dipyrromethene is observed. This study provides experimental fingerprint of polariton condensation under nonresonant optical excitation, including the nonlinear dependence of the em...

On page 1615, D. G. Lidzey and co-workers explore changes in polariton population distribution in strongly coupled microcavities containing a fluorescent molecular dye. Radiative pumping of polariton states from weakly coupled species within the cavity is identified as the dominant population mechanism. A phenomenological fitting model is developed...

The optical properties of a series of strongly coupled microcavities containing the fluorescent molecular dye BODIPY-Br (bromine-substituted boron-dipyrromethene) dispersed into a transparent dielectric matrix are explored, with each cavity having a different exciton–photon detuning. Using temperature dependent emission, time-resolved spectroscopy,...