Title

THERMALLY STIMULATED LUMINESCENCE OF UV‐AND X‐IRRADIATED CAFFEINE

Abstract

Abstract— Thermally stimulated luminescence studies of UV‐ and X‐irradiated caffeine have been conducted in the interval77–300 K. The X‐ray‐induced glow curve exhibits peaks at 102, 128, 158, and 198 K, whereas the UV‐induced curve is characterized by peaks with maxima at 120 and 208 K. Analysis of the X‐ray‐induced glow peaks revealed that the 102 and 128 K peaks obeyed first‐order kinetics, while the 158 and 198 K ones followed orders of 1.3 and 1.8, respectively. Trapping parameters associated with the peaks were also elucidated. Concomitant emission spectra of each glow peak (both UV and X‐ray induced) were identical and consisted of a band with well‐defined maxima at 405 and 480 nm which are attributed to singlet (S1→ S0+ hv) and triplet (T1→ S0+ hv) transitions, respectively. At elevated temperatures the triplet transition is not observed due to quenching of the triplet state or to triplet‐triplet interactions. An energy‐level diagram depicting the thermally stimulated processes in irradiated caffeine is presented. Copyright © 1985, Wiley Blackwell. All rights reserved

Publication Title

Photochemistry and Photobiology

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