Electrons from these substances get trapped in the mineral's crystalline structure, and continuing exposure of the rocks to these elements over time leads to predictable increases in the number of electrons caught in the matrices.
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.Better still, unlike radiocarbon dating, the effect luminescence dating measures increases with time.As a result, there is no upper date limit set by the sensitivity of the method itself, although other factors may limit the method's feasibility.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.TL dating is a matter of comparing the energy stored in a crystal to what "ought" to be there, thereby coming up with a date-of-last-heated.
In the same way, more or less, OSL (optically stimulated luminescence) dating measures the last time an object was exposed to sunlight.
Using conventional (multiple-grain) optical dating methods, we estimate that the base of the deposit is 22 kyr.
However, dating of individual grains shows that some have been buried more recently.
The exposure to radioactive elements continues, and the minerals begin again storing free electrons in their structures.
If you can measure the rate of acquisition of the stored energy, you can figure out how long it has been since the exposure happened.
Luminescence dating is good for between a few hundred to (at least) several hundred thousand years, making it much more useful than carbon dating.