Part 1: VK or G&T?

Fact: A Gin and Tonic glows bright blue under UV light.

Or more accurately, tonic water glows blue (gin optional).

Tonic water contains the molecule Quinine, which is found in the bark of willow trees and is the ingredient that gives tonic water its characteristic bitter taste. Quinine has plenty of tricks up its sleeve – it’s been used for centuries to cure malaria – but perhaps less usefully it also glows fluorescent blue.

When UV light (which we can’t see) hits quinine, it gives some electrons in the molecule more energy (called ‘excitation’). These excited electrons then hang about for a while, and after a few nanoseconds they release all that absorbed energy again as light and go back to an ‘unexcited’ state. However, while ‘hanging about’ in their excited state, the electrons lose a little bit of energy to the environment. This means that when they release light, it is of lower energy than the UV light they absorbed – i.e. they convert invisible UV light into blue light that we can see, and so the tonic water glows blue.

Part 2: Ice cream. Next week.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license, by Sam-Cat, unedited.


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