While there already are organic materials that change color in response to ultraviolet radiation exposure, those color-changes involve reorganization of the material's molecular structure, so it can only be used a limited number of times. A new material known as SensoGlow, however, can be used to detect and measure UVs over and over.

Developed at Finland's University of Turku, SensoGlow is composed largely of a synthetic version of hackmanite, an inexpensive photochromic mineral. Depending on how the composite material is "tuned," it can be made to respond to either UVA, UVB or UBC radiation, with the extent of its color-change indicating the radiation's intensity.

That color-shift occurs not because of changes to SensoGlow's molecular structure, but is instead based on how many excited electrons are stored within it. When the material is removed from a source of UV radiation, the electrons return to their inactive ground state, and the material returns to its neutral color.

It is now hoped that SensoGlow could be used to make affordable and long-lasting UV detectors, that could possibly take the form of a sticker applied to a watch. A smartphone app could be used to image that sticker, and then analyze its color in order to let the user know the current UV index.

A paper on the research was recently published in the journal Materials Horizons.