luminescence and ultraviolet radiation
There are two types of luminescence in gemstones under the influence of UV rays: fluorescence and phosphorescence . The former is characterized by the fact that the electrons leave their higher energy level immediately and the glow only lasts as long as the effect of the radiation is maintained. This is different with luminescence, as can be seen in phosphor, for example (phosphorescence). In this case, the energy is not released immediately, but only slowly. This means that the luminescence continues even when no radiation is affecting the gemstone.
While fluorescence occurs in a wide range of gemstones, phosphorescence is more of a special case. This form of luminescence can be very impressive, for example in rare blue diamonds, which glow deep red after exposure to UV radiation.
Luminescence to determine the authenticity of pearls
X-rays cause freshwater pearls to glow brightly, whereas seawater pearls do not react at all to the radiation. Man-made pearls are usually made from the nacre of freshwater pearls, which is why the luminescence properties can be used to determine whether a pearl is real or not.
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