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Nanostructural origin of blue fluorescence in the mineral karpatite

The schematic shows the non-layered crystal structure of synthetic coronene (left) and the layered structure of natural karpatite (right). Both structures were determined through X-Ray crystallography (centre) and electron microscopy.

31 August 2017

Research from the School of Chemistry solves a decades-old mystery as to why a naturally-occurring organic crystal known as karpatite fluoresces blue under ultra-violet light, yet when grown under laboratory conditions fluoresces with an intense green colour.

The Research, led by Simon Hall's group, is explored further in a recent publication. 

The colour of crystals is a function of their atomic structure. In the case of organic crystals, it is the spatial relationships between molecules that determine the colour, so the same molecules in the same arrangement should produce crystals of the same colour, regardless of whether they arise geologically or synthetically. There is a naturally-occurring organic crystal known as karpatite which is prized for its beautiful blue fluorescence under ultra-violet illumination. When grown under laboratory conditions however, the crystals fluoresce with an intense green colour. For 20 years, this difference has been thought to be due to chemical impurities in the laboratory-grown material. Using electron microscopy coupled with fluorescence spectroscopy and X-Ray diffraction, we report here that this disparity is instead due to differences in the structure of the crystals at the nanoscale. The results show that in nature, karpatite has a nanotexture that is not present in the synthetic crystals, which enables different photonic pathways and therefore a blue, rather than green colour whilst undergoing fluorescence.

Further information

Paper: Nanostructural origin of blue fluorescence in the mineral karpatite 

Nature: Scientific Reports 7, Article number: 9867(2017)

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