GAGG

Gadolinium Aluminum Gallium Garnet, the yellow lumogarnet that can glow in the dark! 

A cousin to the GGG traditionally used in gemstones, GAGG gets the 'A' in its name from added aluminum that increases its hardness.  Currently, GAGG is used to detect high energy radiation in medical devices. When radiation (like an X-ray or gamma ray) hits it, it glows! And since it's so sensitive, blue and UV light will also bring out its yellow fluorescence.