A technique used to date crystalline material, most commonly ceramics, and sediments. Crystalline materials absorb radiation from the decay of radioactive elements in the soil around them and from cosmic radiation. When these materials are heated, as in firing ceramics, their absorbed radiation is released as thermoluminescence. Once cooled, they resume their absorption of ionizing radiation. This releases electrons, a proportion of which become trapped in defects and impurities in the crystal lattice. Crystals in sediments begin absorbing radiation from the time they are buried. Subsequent heating or exposure to light releases thermoluminescence that can be measured and the age of the sample can be calculated from the amount of radiation emitted. Thermoluminescence dating is used widely in archaeology and has an age range of 1000–500 000 years.

http://geology.cr.usgs.gov/capabilities/gronemtrac/geochron/thermo/tech.html Explains and describes the thermoluminescence technique.