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It includes techniques such as optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), and thermoluminescence dating (TL)."Optical dating" typically refers to OSL and IRSL, but not TL.Luminescence dating (including thermoluminescence and optically stimulated luminescence) is a type of dating methodology that measures the amount of light emitted from energy stored in certain rock types and derived soils to obtain an absolute date for a specific event that occurred in the past.The method is a direct dating technique, meaning that the amount of energy emitted is a direct result of the event being measured.The radiation causes charge to remain within the grains in structurally unstable "electron traps".The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.It is useful to geologists and archaeologists who want to know when such an event occurred.
Crystalline rock types and soils collect energy from the radioactive decay of cosmic uranium, thorium, and potassium-40.
The energy released by stimulating the crystals is expressed in light (luminescence).
The intensity of blue, green or infrared light that is created when an object is stimulated is proportional to the number of electrons stored in the mineral's structure and, in turn, those light units are converted to dose units.
For example, in quartz a short daylight exposure in the range of 1–100 seconds before burial is sufficient to effectively “reset” the OSL dating clock.
This is usually, but not always, the case with aeolian deposits, such as sand dunes and loess, and some water-laid deposits.