"Night Pearl" is a kind of natural gem, which can be seen clearly by human eyes in the dark and can glow by itself. From the point of view of solid state physics, the matrix materials of the mineral "night pearl" are all active crystalline phosphors in inorganic salts. The so-called active crystalline phosphor refers to the crystal that has the ability of "emitting light" due to the lattice distortion of the crystal lattice, and this distortion is mostly caused by some heavy metal impurities (activators) contained in the matrix. For example, a small amount of Cu in ZnS can emit yellow-green phosphorescence, which is called matrix and Cu is called activator.

At present, there are more than 100 kinds of commonly used phosphors, all of which are divalent metals (Ca. Sr？ Compounds-sulfide, selenide, telluride, silicate, aluminate, tungstate, phosphate and halophosphate.

Due to the different activators in active crystalline phosphors, active crystalline phosphors, namely "luminous pearls", can be divided into two categories:

(1) Permanent luminous luminous luminous luminous pearl: It does not need any external energy excitation, but contains an activator, such as 14C. ..

Radioisotopes such as 3h.147pm.226ra.232th. can emit light by self-excitation.

② Long-lasting luminous night pearl: The activator in the phosphor is not radioactive, and it can only emit light after being excited by external sunlight, ultraviolet rays and other light sources.

Its main component is fluorite with phosphorescence effect and contains some rare earth elements. If this fluorite is allowed to continuously absorb the energy of the sun during the day, or heated in hot water to give it enough energy, and then placed in a dark place, it can be seen that it shines in a natural state, and its luminous time is limited, which is related to the energy it absorbs. Different luminous pearls contain different rare earth elements, so their radioactivity is different. Some of them are very radioactive.