In a Physics lesson today our teacher performed a demonstration to show how quinine in tonic water glows blue when under UV light. He showed us the same demonstration using water in a Pyrex beaker, and with just the Pyrex beaker itself in order to compare the effects.

Under UV light the Pyrex beaker glowed orange. Why did this happen?

And more generally, what determines the colour of visible light emitted by the object under UV light?

If you were able to shed some light (:D) on this it would be appreciated.