What is the substance that released stored radiation energy in thermoluminescent dosimeters (TLD)?

Thermoluminescent dosimeters (TLD) function by utilizing certain materials, commonly lithium fluoride, that store energy when they are exposed to radiation. When these materials are heated, they release the stored energy in the form of visible light. This process occurs because the heat excites the trapped electrons, allowing them to return to their normal state and emit light as they do so. This emitted light is then measured to quantify the amount of radiation exposure.

In the context of the question, heat is the catalyst that causes the released stored radiation energy in TLDs. The other options, while related to concepts of energy and light, do not describe the mechanism by which TLDs operate in releasing stored energy.