Editing Phosphorescence (section)

==Persistent phosphorescence==
{{Main|Persistent luminescence}}
[[File:Fused silica phosphorescence from a 24 million watt flash.jpg|thumb|An extremely intense pulse of short-wave UV light in a [[flashtube]] produced this blue persistent-phosphorescence in the amorphous, [[fused silica]] envelope, lasting as long as 20 minutes after the 3.5 microsecond flash.]]
[[File:MoS2 vacancies.jpg|thumb|An [[electron microscope]] reveals vacancy defects in a crystalline lattice of [[molybdenum disulfide]]. The missing sulfur atoms leave [[dangling bonds]] between the molybdenum atoms, creating traps in the empty spaces.]]
Solid materials typically come in two main types: crystalline and amorphous. In either case, a lattice or network of [[atom]]s and [[molecule]]s form. In crystals, the lattice is a very neat, uniform assembly. However, nearly all crystals have defects in the stacking sequence of these molecules and atoms. A [[vacancy defect]], where an atom is simply missing from its place, leaving an empty "hole", is one type of defect. Sometimes atoms can move from place to place within the lattice, creating [[Schottky defect]]s or [[Frenkel defect]]s. Other defects can occur from impurities in the lattice. For example, when a normal atom is substituted by a different atom of much larger or smaller size, a [[substitutional defect]] occurs, while an [[interstitial defect]] occurs when a much smaller atom gets trapped in the "interstices", or the spaces between atoms. In contrast, amorphous materials have no "long-range order" (beyond the space of a few atoms in any direction), thus by definition are filled with defects.

When a defect occurs, depending on the type and material, it can create a hole, or a "trap". For example, a missing [[oxygen]] atom from a [[zinc oxide]] compound creates a hole in the lattice, surrounded by unbound zinc-atoms. This creates a net [[force]] or attraction that can be measured in [[electron-volt]]s.{{explain|reason=eV is a unit of energy, not force.|date=May 2024}} When a high-energy [[photon]] strikes one of the zinc atoms, its electron absorbs the photon and is thrown out into a higher orbit. The electron may then enter the trap and be held in place (out of its normal orbit) by the attraction. To trigger the release of the energy, a random spike in thermal energy of sufficient magnitude is needed to boost the electron out of the trap and back into its normal orbit. Once in orbit, the electron's energy can drop back to normal (ground state) resulting in the release of a photon.<ref>''Practical Applications of Phosphors'' by William M. Yen, Shigeo Shionoya, Hajime Yamamoto -- CRC Press 2018 Page 453--474</ref>

The release of energy in this way is a completely random process, governed mostly by the average temperature of the material versus the "depth" of the trap, or how many electron-volts it exerts.{{cn|reason=If the process depends on some variables, such as temperature of the material or nature of the trap, then it cannot be "completely random".|date=May 2024}} A trap that has a depth of 2.0 electron-volts would require a great amount of thermal energy (very high temperature) to overcome the attraction, while at a depth of 0.1 electron-volts very little heat (very cold temperature) is needed for the trap to even hold an electron. Generally, higher temperatures cause a faster release of energy, resulting in a brighter yet short-lived emission, while lower temperatures produce a dimmer but longer-lasting glow. Temperatures that are too hot or cold, depending on the substance, may not allow the accumulation or release of energy at all. The ideal depth of trap for persistent phosphorescence at room temperature is typically between 0.6 and 0.7 electron-volts.<ref>''Persistent Phosphors: From Fundamentals to Applications'' by Jianrong Qiu, Yang Li, Yongchao Jia -- Elsevier 2020 Page 1--25</ref> If the phosphorescent [[quantum yield]] is high, that is, if the substance has a large number of traps of the correct depth, this substance will release a significant amount of light over a long period of time, creating a so-called "glow in the dark" material.