Complex Functional Materials Group, School of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom.
Bristol Centre for Functional Nanomaterials, HH Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom.
Sci Rep. 2017 Aug 29;7(1):9867. doi: 10.1038/s41598-017-10261-w.
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.
晶体的颜色是其原子结构的一个函数。在有机晶体的情况下，决定颜色的是分子之间的空间关系，因此相同的分子以相同的排列方式应该产生相同颜色的晶体，无论它们是地质形成的还是合成的。有一种天然存在的有机晶体，称为萤石，因其在紫外线照射下发出美丽的蓝色荧光而备受珍视。然而，在实验室条件下生长时，晶体发出强烈的绿色荧光。20 年来，人们一直认为这种差异是由于实验室生长材料中的化学杂质造成的。我们在这里使用电子显微镜结合荧光光谱和 X 射线衍射报告说，这种差异是由于纳米尺度上晶体结构的差异造成的。结果表明，在自然界中，萤石具有一种纳米结构，而在合成晶体中则不存在这种结构，这使得在进行荧光时可以有不同的光子路径，从而呈现出蓝色而不是绿色。
