Thermoluminescence

Thermoluminescence is a form of luminescence in which a material emits light when heated. The light arises from the release of stored energy from charge carriers trapped in the lattice after prior exposure to ionizing radiation. When heated, trapped electrons recombine with holes at luminescent centers, producing photons that can be measured.

Mechanistically, irradiation creates electron–hole pairs, with electrons often captured in traps and holes remaining at recombination centers. Heating provides energy to release trapped electrons, which migrate and recombine, emitting light. The emitted intensity as a function of temperature, shown as a glow curve, reflects the distribution of trap depths; different traps release charge at characteristic temperatures. The total light yield is related to the absorbed dose of radiation, though the response can depend on material, dose rate, and thermal history. Fading and changes in sensitivity can occur due to environmental conditions and subsequent heating.

Measurement typically uses a thermoluminescence reader that heats a sample with a controlled ramp while detecting emitted light with a photomultiplier. The integrated glow signal relates to the radiation dose the material received since its last heating event, or since it was last exposed to light in the case of optically stimulated luminescence. After readout, samples are annealed to reset the traps.

Applications include dosimetry for radiation exposure (personal, medical, and industrial), and luminescence dating, notably thermoluminescence dating of ceramics, minerals, and burnt stones. Common TL materials are natural quartz and feldspars, with calcite and glasses also used. Feldspars can exhibit anomalous fading, complicating age estimates. Thermoluminescence is related to, but distinct from, optically stimulated luminescence, which uses light stimulation rather than heating to release trapped charge.