Methods dating sediments
The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.Stimulating these mineral grains using either light (blue or green for OSL; infrared for IRSL) or heat (for TL) causes a luminescence signal to be emitted as the stored unstable electron energy is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.In multiple-aliquot testing, a number of grains of sand are stimulated at the same time and the resulting luminescence signature is averaged .The problem with this technique is that the operator does not know the individual figures that are being averaged, and so if there are partially prebleached grains in the sample it can give an exaggerated age .Most luminescence dating methods rely on the assumption that the mineral grains were sufficiently "bleached" at the time of the event being dated.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.
Ioannis Liritzis, the initiator of ancient buildings luminescence dating, has shown this in several cases of various monuments.
The concept of using luminescence dating in archaeological contexts was first suggested in 1953 by Farrington Daniels, Charles A. Saunders, who thought the thermoluminescence response of pottery shards could date the last incidence of heating.
The traditional OSL method relies on optical stimulation and transfer of electrons from one trap, to holes located elsewhere in the lattice – necessarily requiring two defects to be in nearby proximity, and hence it is a destructive technique.
Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating.
It is useful to geologists and archaeologists who want to know when such an event occurred."Optical dating" typically refers to OSL and IRSL, but not TL.