Non-linear materials such as upconverting nanoparticles (UCNPs) are emerging technology with fast-growing applications in various fields. The power density dependence of the emission quantum yield (QY) of these non-linear materials makes them challenging to characterize using currently available commercial QY systems. We propose a multimodal system to measure QY over a wide dynamic range (1:104), which takes into account and compensates for various distorting parameters (scattering, beam profile, inner filter effect and bandwidth of emission lines). For this, a beam shaping approach enabling speckle free beam profiles of two different sizes (530 µm or 106 µm) was employed. This provides low noise high-resolution QY curves. In particular, at low power densities, a signal-to-noise ratio of >50 was found. A Tm-based core-shell UCNP with excitation at 976 nm and emission at 804 nm was investigated with the system.

Using density functional theory, corrected for on-site Coulomb interactions (DFT + U), we have investigated surface modification of TiO2 with metal chalcogenide nanoclusters for hydrogen evolution. The nanoclusters have composition M4X4 (M = Sn, Zn; X = S, Se) and are adsorbed at the rutile (110) surface. The nanoclusters adsorb exothermically, with adsorption energies in the range −2.8 eV to −2.5 eV. Computed density of states (DOS) plots show that cluster-derived states extend into the band-gap of the rutile support, which indicates that modification produces a redshift in light absorption. After modification, photoexcited electrons and holes are separated onto surface and cluster sites, respectively. The free energy of H adsorption is used to assess the performance of metal chalcogenide modified TiO2 as a catalyst for the hydrogen evolution reaction (HER). Adsorption of H at nanocluster (S, Se) and surface (O) sites is considered, together with the effect of H coverage. Adsorption free energies at cluster sites in the range −0.15 eV to 0.15 eV are considered to be favourable for HER. The results of this analysis indicate that the sulphide modifiers are more active towards HER than the selenide modifiers and exhibit hydrogen adsorption free energies in the active range, for most coverages. Conversely, the adsorption free energies at the selenide nanoclusters are only in the active range at low H coverages. Our results indicate that surface modification with small, dispersed nanoclusters of appropriately selected materials can enhance the photocatalytic activity of TiO2 for HER applications.

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Surgical guidance and diagnostics by diffuse optical imaging using micro camera technology at the tip endoscopic probes have the potential to act as intra-operative supportive tools for clinicians. Micro camera probes need to address undesirable specular reflections in order to be clinically relevant. In this work we overcome specular reflections caused by the glossy uneven tissue surface. We adapt and compare two techniques for miniaturised probes designed to view tissue. Two camera probes are developed using different modalities to remove these surface reflections, with line-of-sight to further miniaturisation. 1) The multi-flash technique illuminates the sample from four different positions, causing a shift in reflections which is filtered out in a post processing image reconstruction step. 2) The cross polarisation technique integrates orthogonal polarisers on to the tip of the illumination fibres and camera, respectively, to filter out the polarisation maintaining reflections. These form part of an imaging system that is capable of rapid image acquisition using different illumination wavelengths. The system is validated on tissue mimicking phantoms with high surface reflection, as well as excised human breast tissue. It is demonstrated that both methods effectively remove the specular reflections, revealing previously hidden underlying information. The methods demonstrate two effective options for improving image quality in miniaturised systems, for human and machine observers, in a surgical setting.

The hydrogen evolution reaction (HER) is a key reaction in water splitting and there is an intensive search for suitable HER catalysts that will promote this reaction and also show good stability, while not using precious metals. We have studied the surface modification of rutile TiO2 with metal chalcogenide nanoclusters for the promotion of the hydrogen evolution reaction (HER) using density functional theory corrected for on-site Coulomb interactions (DFT+U). Recently, metal chalcogenides have emerged as potential catalysts for the HER due to the favourable interaction of H at chalcogen sites, particularly those that are undercoordinated. In developing materials for HER the key descriptor has been the adsorption energy of hydrogen at the catalysts, with the target free energy being close to 0 eV. Analogous to noble metal loading, surface modification of TiO2 with nanoclusters of potential HER co-catalysts, based on earth-abundant materials, is an emerging strategy. This approach combines the desirable properties of a stable titania photocatalyst with active sites provided by the low-coordinated chalcogen ions of the supported clusters. Our models consist of M4X4 (M = Sn, Zn; X = S, Se) nanoclusters at the rutile (110) surface and we examine the Gibb’s free energy of H adsorption at the modified surface which is a useful material descriptor in assessing the performance of a HER catalyst. These calculations take into account changes in the entropy and the zero-point energies (ZPEs) of the reactants and products, which our results show are material specific. As expected, the interaction of H is more favourable at the titania surface and forms stable hydroxyls. However, after subsequent adsorption events the surface sites become saturated and H adsorption at chalcogen sites exhibit Gibb’s free energies in the active range, particularly for MS modifiers relative to MSe.