Dissertation defence (Chemistry): MChem Hannah Byron


16.6.2023 at 12.00 - 16.00
MChem Hannah Byron defends her dissertation in Chemistry entitled “Tuning Photochromic Sodalites across the Visible Spectrum” at the University of Turku on 16 June 2023 at 12.00pm (University of Turku, Main Building, Säästöpankki lecture hall, Turku).

The audience can participate in the defence also through remote connection: https://echo360.org.uk/section/e7b160df-5f06-41d9-8e48-d50e97790f27/public (copy the link to the browser).

Opponent: Professor Mark Weller (Cardiff University, United Kingdom)
Custos: Professor Mika Lastusaari (University of Turku)

Digital copy of the dissertation at UTUPub: https://urn.fi/URN:ISBN:978-951-29-9307-9.


Summary of the Doctoral Dissertation:

The average person may be exposed to invisible but highly damaging forms of radiation, such as ultraviolet (UV) or X-rays, at some time in their life. UV radiation from the sun is the most common of these, and can cause serious harm to the human body. It is therefore important to monitor exposure to such radiation possible.

The photochromic sulfur-doped form of the natural mineral sodalite has been proposed for use in UV indexing and dosimetry since research into its possible applications reignited in the last decade. This material, when synthetically prepared, changes from white to pink upon exposure to high-energy radiation; the colour change is fully reversible, so the material can be reused indefinitely. Photochromic sodalite is non-toxic, low-cost, robust, and recyclable. Nevertheless, its properties still require optimisation before commercialisation.

In this dissertation, four different methods were used to prepare photochromic sodalite with the aim of improving its optical properties. The most successful of these was a solid-state synthesis starting from zeolite A. The effect of composition on the colour change was explored: simple changes to the stoichiometry resulted in a tuneable material that changed from white to almost any desired colour. Partial replacement of sodium with calcium produced one of the most surprising yet positive results: yellow photochromism.

Whilst the colour change usually occurs only on exposure to high-energy UVC radiation, introduction of selenium in place of sulfur proved an effective way to lower the threshold at which colouration occurs. Selenium also has no effect on the colour, meaning the colour and the type of radiation to which the material is most sensitive can be tuned independently. Highly tuned sodalites are demonstrated to show improved suitability to applications already present in the literature, such as in UV indexing and X-ray imaging, as well as for new ones, including blue light detection.
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