Thermoluminescence (Tl) From Photosynthetic Materials

Introduction When a thermoluminescent material is supplied energy by electromagnetic radiations, some of this energy is stored in the form of electrons trapped into so called forbidden levels, metastable or traps. During the de-excitation process, this energy is released in the form of luminescence. In case of thermoluminescence thi s de-exc itation is thermally stimulated. The usefulness of the thermoluminescence (TL) technique as a sensitive monitor of defect concentrations in material s and for applications in areas like geological dating and radiation dosimetry is well known l-4• TL studies provide vital information about the mechanism of generation and modification of traps and nature of traps 5,6. TL systems used for studies on phosphors, alkali halides etc_ record high temperature TLI. Because of the simplicity in des ign, such systems are commercially availab le. However, these are not suitable for the study of biological spec imens like photosynthetic materials, proteins, enzymes and nucleic acids, where sample degradation may occur at high temperatures 7.8. Low temperature TL studies have unique advantages over high temperature studies. They form one of the sensitive techniques to study post irradiation events where the excited states are investigated by lowering the temperature to appropriate levels. Their interactions can then be explored further by allowing the temperature to ri se at controlled rates,IO. TL can be observed in photosynthetic bacteria, algae and various higher plant preparations, ranging from intact leaves to purified PS II RC complexes . TL curves have been investigated in the temperature region -1 96DC to 100°C and about 13 TL bands have been shown to ex ist in th is temperature region ll. The mai n peaks are denoted as A(peak f) (-30°C -20°C) ,