While these compounds do exist, analogous chemicals that contain lanthanum, praseodymium, gadolinium, holmium, terbium, or ytterbium have not been discovered, as of 2008.
The fluorescence of fluorite may be due to mineral impurities such as yttrium, ytterbium, or organic matter such as volatile hydrocarbons in the crystal lattice.
The researchers also want to add traces of further elements to the ytterbium rhodium silicide, which would probably change its electronic properties considerably.
