Alaric Taylor

A bioinspired solution for spectrally selective thermochromic VO 2 coated intelligent glazing

We present a novel approach towards achieving high visible transmittance for vanadium dioxide (VO(2)) coated surfaces whilst maintaining the solar energy transmittance modulation required for smart-window applications. Our method deviates from conventional approaches and utilizes subwavelength surface structures, based upon those present on the eyeballs of moths, that are engineered to exhibit broadband, polarization insensitive and wide-angle antireflection properties. The moth-eye functionalised surface is expected to benefit from simultaneous super-hydrophobic properties that enable the window to self-clean. We develop a set of design rules for the moth-eye surface nanostructures and, following this, numerically optimize their dimensions using parameter search algorithms implemented through a series of Finite Difference Time Domain (FDTD) simulations. We select six high-performing cases for presentation, all of which have a periodicity of 130 nm and aspect ratios between 1.9 and 8.8. Based upon our calculations the selected cases modulate the solar energy transmittance by as much as 23.1% whilst maintaining high visible transmittance of up to 70.3%. The performance metrics of the windows presented in this paper are the highest calculated for VO(2) based smart-windows.

Homeotropic alignment and Förster resonance energy transfer: The way to a brighter luminescent solar concentrator

We investigate homeotropically aligned fluorophores and Forster resonance energy transfer (FRET) for luminescent solar concentrators using Monte-Carlo ray tracing. The homeotropic alignment strongly improves the trapping efficiency, while FRET circumvents the low absorption at homeotropic alignment by separating the absorption and emission processes. We predict that this design doped with two organic dye molecules can yield a 82.9% optical efficiency improvement compared to a single, arbitrarily oriented dye molecule. We also show that quantum dots are prime candidates for absorption/donor fluorophores due to their wide absorption band. The potentially strong re-absorption and low quantum yield of quantum dots is not a hindrance for this design.

Efficiency and loss mechanisms of plasmonic Luminescent Solar Concentrators

Using a hybrid nanoscale/macroscale model, we simulate the efficiency of a luminescent solar concentrator (LSC) which employs silver nanoparticles to enhance the dye absorption and scatter the incoming light. We show that the normalized optical efficiency can be increased from 10.4% for a single dye LSC to 32.6% for a plasmonic LSC with silver spheres immersed inside a thin dye layer. Most of the efficiency enhancement is due to scattering of the particles and not due to dye absorption/re-emission.

Flexible and fluorophore-doped luminescent solar concentrators based on polydimethylsiloxane.

We demonstrate a simple and inexpensive method to fabricate flexible and fluorophore-doped luminescent solar concentrators (LSCs). Polydimethylsiloxane (PDMS) serves as a host material which additionally offers the potential to cast LSCs in arbitrary shapes. The laser dye Pyrromethene 567 is used as a prototype fluorophore, and it is shown that it has a high quantum yield of 93% over the concentration range investigated. The optical efficiency and loss channels of the flexible LSCs are investigated; it is also demonstrated that the efficiency remains high while bending the LSC which is essential for flexible LSCs to make an impact on solar energy.

Highly sensitive optical microresonator sensors for photoacoustic imaging

We present novel concave Fabry Perot (FP) sensor arrays for photoacoustic imaging which were fabricated using a high-precision inkjet printing approach to produce the cavity and employed physical vapor deposition to form the dielectric mirrors. Our concave FP cavity design provides excellent beam confinement within the cavity enabling high finesse and thus high sensitivity to be achieved. Two such concave sensors are evaluated in terms of their sensitivity and acoustic bandwidth. A 66 μm thick concave sensor is shown to provide a noise equivalent pressure (NEP) of 85 Pa and an acoustic bandwidth of 16 MHz, and can potentially be used as a sensitive broadband sensor for superficial imaging. A 250 μm thick sensor with an NEP of 12 Pa and acoustic bandwidth of 4 MHz was also developed for deep tissue imaging applications.

Large Scale Production of Photonic Crystals on Scintillators

Heavy inorganic scintillator based detectors are used in various applications. You can find them in high energy physics as well as in nuclear medical imaging systems but also in homeland security radiation monitoring devices. In all these different detectors, light is produced in the scintillator and has to be transported towards a photodetector. The standard optical coupling of such a detector suffers from an inefficient light extraction towards the photodetector due to the high index of refraction of the scintillator and the accompanying total internal reflections. With the means of photonic nanostructuring of the different surfaces of the scintillator, the light transport can be optimized, which has a direct impact on the timing and light yield performance of the detector. Previous work from our group has already shown that photonic crystals (PhCs) can be used as diffraction gratings to improve the light coupling between a photodetector and a scintillator. Moreover, nanoscale surface structuring techniques could also be extended to the sidewalls, the wrapping, or the detector itself, which would open up a number of new possibilities for optimization of the light transport of scintillation based detectors. To show that PhCs can also be produced on a large industrial scale, we started to investigate different methods for cheap and large area PhC structuring. In this work, the current results on our efforts on PhC scintillator production will be described. The different projects include nanoimprint technologies, interference lithography and colloidal lithography. To conclude, we will summarize the different efforts of our group and collaborators and show up-to-date results of PhC improved scintillators.

Influence of Depth of Interaction upon the Performance of Scintillator Detectors

The uncertainty in time of particle detection within a scintillator detector, characterised by the coinci- dence time resolution (CTR), is explored with respect to the interaction position within the scintillator crystal itself. Electronic collimation between two scintillator detectors is utilised to determine the CTR with depth of interaction (DOI) for different materials, geometries and wrappings. Significantly, no rela- tionship between the CTR and DOI is observed within experimental error. Confinement of the interaction position is seen to degrade the CTR in long scintillator crystals by 10%.

Robust Operation of Mesoporous Antireflective Coatings under Variable Ambient Conditions

Generating mesoporous films with adequate film thickness and refractive index is a common method to achieve amplitude and phase matching in low-cost interference-based antireflective coatings (ARCs). For high-surface-energy materials, pores on the 2-50 nm (i.e., on the subwavelength scale) are subject to capillary condensation by surrounding gas phase water molecules, which hampers their functioning. In this work, we examine the effect of relative humidity on mesoporous ARCs and present a simple method for the preparation of ARCs with robust operation under variable conditions. The materials route is based on the generation of well-defined porous aluminosilicate networks by block copolymer co-assembly with poly(isobutylene)- block-poly(ethylene oxide) and postsynthesis grafting of trichloro(octyl)silane molecules to the pore walls. The functionalized films exhibited a maximum transmittance value of 99.8%, with an average transmittance of 99.1% in the visible wavelength range from 400 to 700 nm. Crucially, the antireflection performance was maintained at high humidity values, with an average transmittance decrease of only 0.2% and maximum values maintained at 99.7%. This compared to maximum and average losses of 3.6 and 2.7%, respectively, for nonfunctionalized reference samples. The ARCs were shown to retain their optical properties within 50 humidity cycles, indicating long-term stability against fluctuating environmental conditions.