Rare earth doped optical fibres have found widespread use in a number of applications, most noticeably in erbium doped fibre amplifiers (EDFAs). These materials have also been used in optical fibre based temperature sensing applications, such as the fluorescence lifetime technique which utilises the temperature dependence of the lifetime of fluorescence emitted from such fibres, when illuminated by a modulated light source such as a laser diode. The annealing of a sample of rare earth doped fibre used in fluorescence based temperature sensing is illustrated.