Thermoluminescence may be defined as the emission of light from solid state materials caused by thermal recombination of previously trapped electrons and holes. In solids, electrons and holes formed by exposure to light or radiation may become separated and trapped in energy wells at defect or impurity sites such that the probability of recombination by either radiative or nonradiative processes is very low. If the temperature is raised thermal energy may become sufficient to allow the electrons and holes to escape from the traps and recombine. When this occurs by a radiative process then, as the temperature is increased, the sample will begin to emit light and continue to emit until all of the traps are emptied. Glow curves of emission intensity as a function of temperature give information on trap energies. Natural and synthetic thermoluminescent materials are described by Vij (1993). Doped inorganic crystals and glasses are most common, however, many organic polymers and some biological and biochemical materials also show thermoluminescence following irradiation at low temperature.
Applications of thermoluminescence measurements are discussed by Mahesh et al. (1989) and include radiation dosimetry and the dating of archaeological and geological samples. Both applications rely on the principle that the intensity of emission is related to the total radiation dose. In thermoluminescence dating the high temperature firing of pottery or casting of metals around a "core", depletes any thermoluminescent minerals present, such as quartz, of trapped electrons and hole. The intensity of any subsequent thermoluminescence is therefore an indication of the radiation dose received since firing. If the radiation dose at the site can be estimated using thermoluminescent standards, and the sensitivity of the material determined using laboratory irradiation conditions then dating is possible. (See also Photoluminescence.)
Vij, D. R. (1993) Thermoluminescent Materials, PTR Prentice Hall, Englewood Cliffs NJ.
Mahesh, K., Weng, P. S. and Furetta, C. (1989) Thermoluminescence in Solids and its Applications, Nuclear Technology Publishing, Ashford UK.