Thermoluminescence is exhibited by certain crystalline materials, such as some minerals, when energy absorbed from electromagnetic radiation or other ionizing radiation is re-emitted as light when the material is heated. The amount of luminescence is proportional to the dose of radiation received. In thermoluminescence dating, this phenomenon is used to date buried objects that have been heated in the past, such as pottery, because heating resets the thermo-luminescent signature of the material. Web resource here.

Illustration by Z. Keizars.