Optically stimulated luminescence

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In physics Optically stimulated luminescence or (OSL) is a method for measuring doses from ionizing radiation (commonly known as radioactive radiation).

The method makes use of electrons trapped between the valence and electron band in the crystaline structure of matter. Aluminum oxide is one such type of matter. The trapping sites are imperfections of the lattice - impurities or defects. The ionizing radiation produces electron-hole pairs - electrons are in the conduction band and holes in the valence band. The electrons which have been excited to the conduction band may become trapped in traps present. Under stimulation of light the electrons may free themselves from the trap and get into the conduction band. From the conduction band they may recombine with holes trapped in hole traps. If the centre with the hole is a luminescence centre emission of light will occur. The photons are detected using a photomultiplier tube. The signal from the tube is then used to calculate the dose that the material had absorbed.

OSL is used in at least two different applications: optical dating of ancient materials (identical in purpose to the better known technique of radiocarbon dating), and as a method of radiation dosimetry which is the measurement of accumulated radiation dose in the tissues of health care, nuclear, research and other workers, as well as in building materials in regions of nuclear disaster.

The difference between radiocarbon dating and luminescence dating is that the former is used to date organic materials and luminescence dating to date minerals, like quartz and feldspars. Events that can be dated using [optical dating|OSL dating]] are for example last exposure to sunlight - for example the deposition of geological sediments after being transported by air (eolian sediments) or rivers (fluvial sediments). In archaeology, OSL dating finds application to dating of ceramics - the dated event is the time of last heating to high (in excess of 400 °C)

The most popular OSL method is called Single-aliquot regeneration (or SAR) - see optical dating.