Review: Theory of Thermoluminescence & Related by Reuven Chen (Author), Stephen W S Mckeever

Аннотация

Thermoluminescence is a phenomenon observed in some materials when they are exposed to ionizing radiation and subsequently heated, thereby releasing light energy, as a result of the transition of electrons trapped at or near defect centers from metastable states to the conduction band. Thereafter, the relaxed electrons recombine with hole vacancies in defect centers associated with an allowed energy gap between the conduction band and the defect center. The light emitted is of varying magnitudes at different temperatures as some deep trap metastable levels are sequentially filled, emptied and emptied again during the heating process. The sequence of detrapping and recombination topography is a function of trap depth and energy gap size. The presence of trap levels within the forbidden energy gap of insulators or semiconductors, are associated with defect centers which arise from impurity ions or vacancies, whether stoichiometric or non-stoichiometric. The TL response has been used to investigate the nature of defect centers and therefore defect center chemistry in a wide variety of materials including those used as insulators in semiconductor and electronic devices, luminescent materials, phosphors, dosimeters, catalysts, thermoelectric materials, pigments, high-temperature superconductors and phase change materials. European International Journal of Multidisciplinary Research 9 https://eipublication.com/index.php/eijmrms and Management Studies European International Journal of Multidisciplinary Research and Management Studies Introduction: The term thermoluminescence is a level. The thermal stimulation must be understood as collective term that describes the luminescence the release of the electron or hole from the localized phenomenon induced by heating a material which had state to the valence or conduction bands respectively. previously absorbed ionizing radiation either directly or The light emission occurs when the electron or hole indirectly through the ionization of impurities such as recombines with a partner of opposite charge, after rare earth ions. TL has been successfully used for going to a localized level that is close to the conduction information storage, as in photoluminescent color or valence band, respectively. centers, called radio-photoluminescent materials, The main features of the two ionization processes (trap book-betting, dating of archeological finds, filling and thermal stimulation) allow to expect that the environmental monitoring, beta dosimetry and nuclear TL phenomenon can be observed in any class of solid- waste safety, to mention only a few applications. state compounds, without any special requirement on Historical Background their thermal, structural or electronic properties. This compound can be at room temperature or at a very low Thermoluminescence is by no means a contemporary temperature when the ionizing radiation stimulates the area of research in solid-state physics. The first trap filling. In spite of these two features, at present, TL observations of the phenomenon in materials were can be only observed in a small part of the solid-state performed in the second half of the 19th Century. As compounds which until the present contain mainly always happens in the infancy of new areas of insulators with a high resistance, the most knowledge, these observations were not followed by a representative being the alkali halides and silicate more systematic study of the observed effects. It was crystals doped with metal ions. only in the second third of the 20th Century that interest in exploring in deeper detail the origin of the 2. Types of Thermoluminescence effects observed in the beginning was taken up. From The TL glow curves of most of the samples considered that moment on, a long sequence of investigations to be TL solids exhibit structure and are composed of developed the field to a level of sophistication that several glow peaks overlapped or not. However, in made TL evolve into a classical character in data storage some very thin samples of highly translucent crystals, phenomena in bulk solids. the TL glow curves exhibit only one glow peak. These The first reports on TL were made in crystals, particular samples exhibit the unique TL behavior, at particularly in potassium chloride and sodium chloride. present termed as "one peak TL". As it can be seen from These crystals exhibited intense emissions even in the the citations above, this type of TL group is not a spectral region of blue, something hardly observable minority. In fact, considering all the cited words today for almost any TL material. Even so, the scientific literally, it is clear that the "one peak TL" group exhibits community at the time disregarded the results and did a qualitatively different TL phenomenon. Due to this not follow them through, mainly due to an apparent unique "one peak TL" characteristic, it appears to be lack of practical applications for such an interesting worthwhile to review