Professor Robert Taylor

Abstract:

Flexible optoelectronics have broad applications in healthcare and various industries. Unlike traditional (two-dimensional) 2D designs, flexible 3D optical sensors enable advanced functions like light directionality detection, intensity mapping, and velocity measurement. However, their integration with 2D circuit boards adds manufacturing complexity. Solving this could unlock untapped applications in navigation, agriculture, and remote sensing. In this study, selective buckling of flexible circuit boards is investigated to develop an all-in-one flexible (three-dimensional) 3D optical sensor for light detection with high sensitivity to periodic light pulses. By employing a buckling-based design, the developed flexible 3D phototransistor is found to be adjustable for measuring incident light angles between 0° and 87°, with an average error of less than 5°. Additionally, the sensor is able to measure object velocity with a maximum deviation of only 1.5% from the actual speed. In this design, the flexible circuit board is also integrated with Bluetooth Low Energy (BLE) technology to wirelessly transmit readings to a smartphone application to enable efficient data processing, transmission, visualization, and analysis. The platform's effectiveness is then demonstrated for unmanned aeraial vehicles (UAV) navigation and solar tracking, highlighting its strong potential for real-world use in autonomous systems and environmental monitoring.

Abstract:

The optical Aharonov-Bohm effect in a quantum ring was investigated in terms of magnetic field dependence of excitons and biexcitons. The fine exciton states of quantized orbital angular momentum in a quantum ring were considered theoretically, and the presence of quantum beats was predicted as evidence of the quantum coherence of the fine exciton states. In the case of GaAs/GaAlAs quantum rings grown by the droplet epitaxy, we found various disorder effects are associated such as structure anisotropy, localization, and internal electric field, resulting in a modulation of the oscillation periods. Additionally, we found that a strongly correlated exciton pair can be formed in a single quantum ring similar to the Wigner molecule. In this case, the biexciton emission energy changes abruptly at transition magnetic fields with a fractional oscillation period compared to that of the exciton, the so-called fractional optical Aharonov-Bohm oscillations.

Abstract:

The main challenges in the optical and morphological tuning of highly stable orange-emitting Mn-doped perovskite include achieving uniform dopant distribution, maintaining structural integrity under varying environmental conditions, and optimizing luminescent efficiency while minimizing non-radiative recombination pathways. This study presents a novel, one-step, water-induced ultrafast synthesis strategy for obtaining Mn-doped mixed-halide perovskites at room temperature. This technique offers morphological control by varying the amount of water-based precursor, allowing the tuning of resulting nanostructures to produce nanoplatelets, nanocubes, or nanowires. In the growth mechanism, Mn2+ dopants affect the crystal structure by promoting stable growth and uniform doping at higher concentrations, while water improves ion dispersion, reaction kinetics, and passivation, facilitating optimal crystal growth and the formation of desired nanostructure morphologies. The synthesized Mn:CsPbBr3−xClx NCs form a highly stable colloidal solution with approximately 100 % emission stability for up to one year under ambient conditions and retain 98.9 % of its photoluminescence after aging at 85 °C for 200 h. We also explore the PL mechanism in Mn:CsPbBr3-xClx NCs, where temperature-dependent PL analysis reveals energy transfer from CsPbBr3-xClx exciton states to Mn2+-doped levels, enhancing PL intensity, with both exciton and Mn2+ emissions exhibiting a blue shift as the temperature increased from 6 K to 300 K, attributed to lattice expansion and electron–phonon interactions. A warm white light emission is achieved with excellent stability and an exceptionally wide color gamut coverage. The proposed strategy has the potential to enable large-scale synthesis and fabrication of highly stable perovskite devices for high-quality display and lighting applications.

Abstract:

The optical properties of graphene (Gr)-covered CsPbBr₃ quantum dots (QDs) were investigated using micro-photoluminescence spectroscopy, revealing a remarkable three orders of magnitude enhancement in photoluminescence (PL) intensity compared to bare CsPbBr₃ QDs. To elucidate the underlying mechanisms, we combined experimental techniques with density functional theory (DFT) calculations. DFT simulations showed that the graphene layer generates interfacial electrostatic potential barriers when in contact with the CsPbBr₃ surface, impeding carrier leakage from perovskite to graphene and enhancing radiative recombination. Additionally, graphene passivates CsPbBr₃ surface defect states, suppressing nonradiative recombination of photo-generated carriers. Our study also revealed that graphene becomes n-doped upon contact with CsPbBr₃ QDs, activating its plasmon mode. This mode resonantly couples with photo-generated excitons in the perovskite. The momentum mismatch between graphene plasmons and free-space photons is resolved through plasmon scattering at Gr/CsPbBr₃ interface corrugations, facilitating the observed super-bright emission. These findings highlight the critical role of graphene as a top contact in dramatically enhancing CsPbBr₃ QDs’ PL. Our work advances the understanding of graphene-perovskite interfaces and opens new avenues for designing high-efficiency optoelectronic devices. The multifaceted enhancement mechanisms uncovered provide valuable insights for future research in nanophotonics and materials science, potentially leading to breakthroughs in light-emitting technologies.

Abstract:

The development of inexpensive and easily processable X-ray-sensitive materials is of great importance because a number of commercial scintillators, such as LaBr3(Ce), Gd3Al3Ga2O12(Ce), Cs2HfCl6, NaI:Tl, CsI:Tl, and LiI:Eu, are fabricated using highly toxic or rare-earth elements via high-temperature synthesis. This has spurred research into radioluminescence-enhancing mechanisms and solution-processable scintillating materials made from earth-abundant elements that have excellent optoelectronic properties, including high quantum yields and a low afterglow effect. In recent years, a range of metal halide perovskite (MHP) integrated with thermally activated delayed fluorescence (TADF) materials have been developed, exhibiting excellent scintillation properties and a high spatial resolution. Meanwhile, plasmonic technologies are reported to exploit light-energy confinement capabilities beyond the diffraction limit that produces local-field enhancement. This enhancement has subsequently improved the performance of small-sized optoelectronic devices such as solar cells and diagnostic optical sensors. This perspective summarizes the current development of innovative MHP, TADF, and plasmonic materials for use in scintillators and their integrated moieties while also identifying the relevant challenges. Following a thorough evaluation of the efforts made to improve the X-ray scintillation efficiency of these materials, we propose an outlook for future research in order to further enhance their scintillation properties and spatial resolution.