Apparently there are companies out there who engineer otherwise inert particles, or mixes of particles, that fluoresce under specific wavelengths, for example Mobil might add the particles to their premium Mobile 1 synthetic motor oil product to find counterfeit products in certain markets. By opening a bottle of oil purchased off the shelf they can hit it with ~620nm && ~580nm and if it does not respond correctly, it is relatively easy to demonstrate that it is counterfeit and quickly get it removed from shelves. This can also be applied to crude oil and quietly tested at the refinery to verify it hasn't been diluted with similar product.