Optically Stimulated Luminescence (OSL) Dating is a Quaternary geologic age-dating technique used to determine the depositional age of sediments based on solid state properties of mineral grains rather than isotopic decay of constituent elements.

The minerals that compose the vast majority of sediments on earth, Quartz and Feldspars, exhibit solid state physical properties that allow them to record and erase their expose to ionizing radiation.

The interaction of ionizing radiation with the mineral grains creates charge pairs (e- and holes+) [a].  These charge carriers can subsequently become localized or trapped at crystal defects [b].  The amount of stored charges increases with dose which is proportional to exposure time and age.  Visible light provides the mineral grains with the appropriate energy to liberate trapped charge carriers and initiate recombination which can results in luminescence emission (OSL) [c].
 

The natural combination of these effects - through the sedimentary processes of erosion, transportation, and deposition - produce a geologic clock that we can read in the laboratory.

A hypothetical luminescence history of a sediment sample demonstrating the basic concepts of OSL dating.  The accumulation or build-up of stored charge after deposition due to exposure to ionizing radiation (a, b, g) from naturally occurring U, Th, K and cosmic rays and depletion or resetting of stored charge by exposure to solar energy.

Why OSL?  The unique advantages of OSL dating:

Sediments ranging in age from tens (10E1) to hundreds of thousands (10E5) of years old can be dated using luminescence techniques.  OSL dating provides absolute (numeric) ages as opposed to relative chronologies and the ages are determined directly from the sediment grains themselves.  The method is not limited to deposits containing organic matter or pristine volcanic materials.  Because OSL is not an isotopic technique, confounding issues such as variability in cosmogenic isotope production rates and incomplete geochemical system closure are not germane.

The effective age range and the unique properties of the technique make it particularly suited for paleoenvironmental and paleoclimatic research as well as archaeological investigations.  The method has also been proposed for use on Mars.