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This PhD project will demonstrate the outstanding potential of novel organic light-emitting materials for high-efficiency thermally-activated delayed fluorescent (TADF) OLEDs and low threshold organic semiconductor lasers emitting in the near infrared (NIR) spectral region.

OLEDs emitting in the visible spectral range are now widely commercially used in the displays of smartphones and televisions. While strong efforts are still devoted to the improvement of blue organic electroluminescence (EL), recent research has also focused on the development of high-performance NIR OLEDs due to their potential for various applications in the biological/medical field and for new technologies in the areas of facial recognition, eye tracking and sensing.[1] An important breakthrough was reported in 2018 by Dr Ribierre and Dr D'Aleo with the first demonstration of NIR TADF OLEDs based on a borondifluoride curcuminoid derivative.[2] Their other collaborative studies provided important information on the influence of the molecular structure on the photophysical properties of this family of dyes.[3,4] 

This PhD project aims to develop novel NIR emitters for high-efficiency OLEDs and organic lasers. The light-emitting molecules will be synthesized by the group of Dr D'Aleo (in Strasbourg, France) and the recruited PhD student at St Andrews will focus on the photophysical studies, fabrication of novel organic EL device architectures and their characterization. The measurements will be carried out using the world-class research facilities of the Organic Semiconductor Centre (OSC) at St Andrews. The successful outcome of this project will tackle some key challenges currently met by NIR OLED materials and will lead to a next generation of near infrared organic EL technologies with improved performance. The student will learn and apply a broad range of organic light-emitting device fabrication and characterization techniques as well as various optical spectroscopic tools to investigate TADF properties and excitonic processes. Overall, the student will gain strong scientific expertise in the active and interdisciplinary field of organic electronics that will allow him/her to follow a successful scientific career in either academia or industry.   

Informal enquiries are very welcome and should be made by email to Dr Jean-Charles Ribierre (jr43@st-andrews.ac.uk). 

[1] A. Minotto et al., Light Sci. Appl. 10, 18 (2021).
[2] D. H. Kim, A. D?Aleo, X. K. Chen, A. S. D. Sandanayaka, D. Yao, L. Zhao, T. Komino, E. Zaborova, G. Canard, Y. Tsuchiya, E. Y. Choi, J. W. Wu, F. Fages, J. L. Bredas, J. C. Ribierre, C. Adachi, Nature Photon. 12, 98 (2018).
[3] H. Ye, D. H. Kim, X. K. Chen, A. S. D. Sandanayaka, J. U. Kim, E. Zaborova, G. Canard, Y. Tsuchiya, E. Y. Choi, J. W. Wu, F. Fages, J. L. Bredas, A. D?Aleo, J. C. Ribierre, C. Adachi, Chem. Mater. 30, 6702 (2018).
[4] A. D'Aleo, M. H. Sazzad, D. H. Kim, E. Y. Choi, J. W. Wu, G. Canard, F. Fages, J. C. Ribierre, C. Adachi, Chem. Comm. 53, 7003 (2017).

• The Organic Semiconductor Centre

Water is one of the most miraculous gifts to humankind. Our present-day lifestyle, industrialization, farming practices, medical care and warfare activities have given rise to a wide range of contaminants of emerging concerns (CECs). They enter our environment through various pathways, accumulate leading to hazardous effects on ecological and human health.  Optical chemical sensors have a huge potential in sensitive, convenient, cost-effective and real-time environmental monitoring of pollutants. They make use of optical parameters like absorbance; Raman spectrum; and fluorescence intensity, wavelength, lifetime and quantum yield for detection of contaminants. Variation in any of these parameters in presence of specific contaminants gives detectable optical signals for detection.

This project, will develop trace optical sensors for industrial contaminants, and pharmaceuticals in water bodies. Experimental work will include clean-room fabrication of thin-film sensors, optical characterisation of their response to different contaminants, and testing the sensors in real-world environments.

EPSRC DTP (Must be within EPSRC remit.)

• Organic Semiconductor Centre

Light-emitting polymers are promising materials for lasers because they combine novel optoelectronic properties with simple fabrication. In addition to being flexible, they have high gain and broad emission spectra. So far, the broad emission spectra have been used to make lasers that can be tuned over a range of wavelengths.
However, broad emission spectra open up another very interesting possibility, namely the possibility of generating short light pulses. This follows from the uncertainty principle DEDt>h/4p. A very short light pulse (small Dt) must contain a range of energies (wavelengths) of light (large DE). Light-emitting polymers can lase over a large range of wavelengths, and so have the potential to generate femtosecond light pulses. This project will explore generating short light pulses from these materials by a range of techniques, and particularly by the process of modelocking in which the phase of different modes is locked together such that their interference gives a train of short light pulses. This new type of laser would be compact, lightweight and generate short light pulses at a range of wavelengths in the visible region of the spectrum.

This PhD project will explore the development of a novel hybrid metamaterials/solar cell-based optical neural network (ONN) for real-time, energy-efficient environmental monitoring and object recognition. The concept harnesses solar cells not only as energy harvesters, but also as both sensors and computational nodes, removing the need for conventional cameras or external power supplies. This radically reduces energy demands and system complexity.

The research will investigate the integration of metasurfaces to enhance optical sensitivity and spectral selectivity, enabling the ONN to detect and classify objects based on subtle light patterns and colours. Such a system holds the potential to deliver scalable, self-powered sensor networks capable of continuous operation in remote or inaccessible environments.

The PhD candidate will combine expertise in nanophotonics, materials science, and machine learning to design, fabricate, and test prototypes of this new class of devices. Beyond addressing challenges of energy consumption, scalability, and real-time processing, the project offers the opportunity to contribute to a transformative platform for sustainable monitoring technologies with clear pathways toward commercialization and global deployment.

This project would be eligible for funding including: NextGenTech CDT (Requires 50% matched funding).

• Synthetic Optics group

Metamaterials (MMs) are man made materials with engineered optical properties. They are made assembling their artificial atoms at a scales much smaller than that of light, so as to appear homogenous. They are at the basis of very thought provoking proposals, including super imaging and cloaking applications. In the group of Synthetic Optics we have developed a large portfolio of fabrication techniques for one- and two-dimensional MMs.

The aim of this project is to develop the fabrication protocol and applications of three-dimensional MMs obtained with a bottom up approach. The student will combine the extraordinary physical and optical properties of silica based aerogels with the flexibility of the design of nanoplasmonics to realise effective materials with bespoke optical behaviour. The aerogel is an ultra light material with refractive index close to unity and thermally more insulating than air. Combining these features with the field enhancement offered by infiltrated metallic nano particles is specially suited to address nonlinear effects at ultra-low powers.

This challenging but rewarding project requires a thorough understanding of the physics involved and the experimental rigour to fabricate and test the MMs, but offers the student the chance to learn a broad range of design, fabrication and experimental techniques.

• Synthetic Optics group

Black holes can be understood in a simple picture: Imagine a river flowing towards a waterfall with ever increasing flow speed. Also imagine fishes in the river swimming upstream. At some position in the river the maximum speed of the fish will equal the flow speed and all fish beyond that "point of no return" will be flushed into the waterfall. Here the flow speed corresponds to the gravity of a black hole and the point of no return to the event horizon.
Arguably the most facinating aspects of astronomical black holes is the emission of Hawking radiation from the event horizon, an intriguing quantum effect combining gravity, thermodynamics and quantum mechanics.

Unfortunately, the astrophysical Hawking radiation is far too weak to ever being detected directly. Recently, however, we have invented a method to create moving artificial event horizons with short pulses in optical fibers. Moreover, the expected Hawking radiation is strong enough to be detectable with single photon coincindence counting.

The idea of the PhD programme is the calculation, detection, and characterization of this elusive Hawking radiation for the first time. The work has already gained momentum in our group and a setup is built using optical pulses of just a few cycles pulse length. In addition we will explore further quantum field theory effects in curved spacetime.

• Experimental quantum optics
• Quantum optics and information

Visible light communication is an emerging field that aims to deliver high-bandwidth wireless data through solid-state (LED) lighting. A key challenge in developing this optical version of WiFi is to make optical detectors that have very fast response, are very sensitive, and can receive data signals from any angle. This project aims to develop the next generation of receiver technologies for wireless optical communications.

The project will develop optical data receivers based on luminescent polymer films. Photonic nanostructures embedded within the fluorescent film will modify the radiative lifetime and direction of the light emission to collect and concentrate incoming optical signals onto a fast silicon detector. The student will design novel optical antennas, and fabricate these using thin film deposition and nanoimprint lithography. Working with collaborators at the University of Oxford, these components will be combined with silicon photomultiplier detectors to assess their performance in optical data links.

1. "Optical antennas for wavelength division multiplexing in visible light communications beyond the étendue limit", Manousiadis, P., Chun, H., Rajbhandari, S., Vithanage, D., Malyawan, R., Faulkner, G., Haas, H., O'Brien, D. C., Collins, S., Turnbull, G. A. & Samuel, I. D. W., Advanced Optical Materials 1901139 (2019).
2. "Wide field-of-view fluorescent antenna for visible light communications beyond the étendue limit”, Manousiadis, P., Rajbhandari, S., Mulyawan, R., Vithanage, C. D. A., Chun, H., Faulkner, G., O'Brien, D. C., Turnbull, G. A., Collins, S. & Samuel, I. D. W., Optica 3, 702 (2016).

• Organic Semiconductor Optoelectronics research group

Halide perovskite semiconductors possess many excellent optoelectronic properties making them suitable for a variety of devices such as solar cells, light-emitting diodes and photodetectors. Recently it has been shown that some family of these materials shows ferroelectricity and piezoelectric properties. Ferroelectric materials possess spontaneous polarization even in the absence of an external electric field and find applications in memory devices, energy harvesting, and radiofrequency and microwave devices. The piezoelectric properties would enable the development of ambient mechanical energy harvesters to self-power the small electronic components in the Internet of Things (IoT) and wearable electronics (WE). Even though halide perovskite semiconductors have been thoroughly explored for solar cell applications, their other energy harvesting applications are little explored.
In the proposed project, hybrid perovskite-based thin films will be investigated for their ferroelectric and piezoelectric properties. The ferroelectric properties will be explored using the P-E loop (polarisation-electric field) and piezo-force microscopy (PFM) method. Piezoelectric charge coefficient will be optimized as a function of different halide perovskite compositions to maximise the output power. The project would mainly involve the optimisation of ferroelectric and piezoelectric properties and develop the composition with the optimized properties towards a thin-film based ambient mechanical energy harvester to generate useful electricity to power small electronic components such as temperature sensors applicable to the IoT systems.
References:
1.    Kim et al Energy Environ. Sci., 2020, 13, 2077—2086
2.    Wilson et al APL Mater. 2019, 7, 010901

This project would be eligible for funding including: University Scholarship.

• Energy Harvesting Research Group

Organic semiconductors based on light-emitting conjugated polymers are attracting considerable interest in semiconductor physics and are emerging as exceptional 'plastic-like' materials for optoelectronic applications including displays, lasers and solar cells. We have recently reported the first single-molecule studies regarding the conformation of individual polymer chains in organic solvents commonly used for device fabrication [1-3]. Now, in this project, we aim to combine single-molecule super-resolution spectroscopy with magnetic tweezers to apply force to the polymer chain. By merging these techniques, we will be able to stretch the polymer chain at will and understand in more detail how the conformation of the polymer chain impacts its light-emission properties. Importantly, we will apply for the first-time super-resolution imaging methods to resolve, beyond the diffraction limit, the structure of the polymer chain as a function of applied force. The results will help to develop new solution-processing methods that improve device performance. The project is a collaboration between the groups of Prof Ifor Samuel and Dr Carlos Penedo.

[1] Dalgarno, Paul A., Christopher A. Traina, J. Carlos Penedo, Guillermo C. Bazan, and Ifor D. W. Samuel. (2013) Solution-Based Single Molecule Imaging of Surface-Immobilized Conjugated Polymers. J. Am. Chem. Soc. 135 (19): 7187–93.
[2] Tenopala-Carmona, F.,  Fronk, S., Bazan, G., Samuel, I. D. W., Penedo, J.C. (2018) Real-time observation of conformational switching in single conjugated polymer chains. Sci. Advances, 4: eaao5786.
[3] Brenlla, A., Tenopala-Carmona, F., Kanibolotsky, A. L., Skabara, P., Samuel, I. D. W., Penedo, J.C. (2019) Single-Molecule Spectroscopy of Polyfluorene Chains Reveals β-Phase Content and Phase Reversibility in Organic Solvents. Matter, 1, 1399–1410.

When light is confined on the nanoscale it is possible to observe light-matter interactions that are not normally observed in bulk materials. One example is the strong coupling of photons and excitons in wavelength-scale microcavities, in which the modes of the cavity couple with the exciton to make a hybrid light-matter state called a polariton [1,2]. Polaritons can form a Bose-Einstein condensate [3], and we have demonstrated low threshold polariton lasers [4].
Organic semiconductors are particularly interesting for the study of polaritons because their excitons have binding energies much greater than the thermal energy at room temperature. This means that polaritonic phenomena that are restricted to low temperature in other materials are readily observed at room temperature in organic semiconductors. The purpose of this project is to explore aspects of room temperature polaritons in organic semiconductors. First, the possibility of using strong light-matter coupling to tune the energy levels of organic semiconductors will be explored. Then the effects of polaritons being delocalised will be studied.  Normally excitons in organic semiconductors are localised and can only travel a few nanometers. However polaritons are delocalised and so may access a much larger volume. Finally these two strands of work will be combined to make sensors that are both selective and sensitive. The selectivity will arise from the tuning of energy levels, and the sensitivity from polaritons being delocalised.

[1] C. Weisbuch et al., Phys. Rev. Lett. 69, 3314 (1992)
[2] D.G. Lidzey et al., Nature 395, 53 (1998)
[3] J D Plumhof, T Stöferle, L Mai, U Scherf & R F Mahrt, Nature Materials 13, 247–252 (2014)
[4] Rajendran, S. K., Wei, M., Ohadi, H., Ruseckas, A., Turnbull, G. A. & Samuel, I. D. W.  Advanced Optical Materials. 7, 1801791 (2019)

• Organic Semiconductor Optoelectronics research group