Optically Stimulated Luminescence (OSL- also known as Photo Stimulated Luminescence-PSL) is the emission of luminescence from an irradiated sample upon stimulation with light. The methods make use of electrons and holes generated by ionizing radiation which are trapped at metastable defect sites located in the forbidden gap of the solid. Depending on the lifetime, trapped charges might stay there therefore storage of radiation information is possible. Later, when stimulated with a light of proper energy these trapped charges can be released from the traps and subsequently recombine with charges of the opposite charge. In such a process a faint light whose intensity is dependent on the trapped charge population is emitted and this luminescence emission is called Optically Stimulated Luminescence. Since the number of trapped charges is dependent on the radiation dose absorbed by the sample the luminescence intensity can be calibrated to measure the radiation dose.
Two very common excitation profiles are the continuous wave-OSL (CW-OSL) and the Linearly Modulated OSL (LM-OSL). In CW-OSL the stimulation power kept constant and the luminescence decay is recorded as a function of time as the trapped charges deplete. In LM-OSL the stimulation light intensity increased linearly from zero to a maximum in a predetermined measurement time.
In some cases the pulsed stimulation is also employed. The luminescence emission can be detected during or after the light pulse thus enabling the discrimination of short and long lifetime emissions.
Thermoluminescence
Thermoluminescence is the elder sister of the OSL. The two technique differs in the way of detrapping of trapped charges. Instead of light, heat is used to free the trapped charges. Generally, the temperature is linearly increased and the luminescence emission is recorded as a function of temperature.
by Assoc.Dr. Enver BULUR
