Optically Stimulated Luminescence in Fluoroperovskites for Dosimetric Applications

Abstract

Radiation dosimetry using the optically stimulated luminescence (OSL) effect is a promising alternative to conventional means of dosimetry based on film or thermoluminescence (TL) dosimetry, electronic dosimetry or ionization chambers. It involves an easy to perform optical readout of radiation induced defect states in insulating materials. This thesis describes a systematic experimental study of ternary fluorides of the composition ABF3 (A: monovalent cation, B: divalent cation), also referred to as fluoroperovskites, doped with the luminescence activators manganese and europium, with regards to their OSL properties. Besides the direct measurements of radiation induced OSL, the study involves spectroscopic, optical and TL mesurements in order to get a deeper understanding of the processes leading to the observed OSL. A high sensitivity to UV radiation was observed in RbCdF3:Mn2+, and a detailed model of the luminescent properties of this compound was developed. It was found that the europium activator is particularly suitable for OSL in fluoroperovskites of the form AMgF3, as the corresponding luminescence emission occurs in the wavelength region between 350 and 400 nm, where common optical detectors show a high sensitivity. Stimulation of this luminescence in the fluoroperovskites RbMgF3, KMgF3 and NaMgF3 can be performed in the visible part of the optical spectrum, and the main defects involved in the process are tentatively identified as F-centres, i.e. electrons trapped at fluorine vacancies after irradiation. The most promising results for use in OSL dosimetry were obtained with NaMgF3:Eu2+. NaMgF3 offers the advantage of being easy to produce, not hygroscopic, highly sensitive to ionizing radiation and having a close to tissue-equivalent photon energy dependence. Efficient TL phosphors, characterized by a relatively simple glow curve structure, are obtained when doping the fluoroperovskites with manganese.