Optically stimulated luminescence (OSL) thermochronometry is a dating method used to determine the time since quartz and/or feldspar began to store charge as it cools through the effective closure temperature. The closure temperature for quartz and Na-rich K-feldspar is 30-35 °C and 25 °C respectively. When quartz and feldspar are beneath the earth, they are hot. They cool when any geological process e.g. focused erosion causes their exhumation to the earth surface. As they cool, they trap electron charges originating from within the crystal lattice. These charges are accommodated within crystallographic defects or vacancies in their crystal lattices as the mineral cools below the closure temperature.

During detrapping of these electrons, luminescence is produced. The luminescence or light emission from the mineral is assumed to be proportional to the trapped electron charge population. The age recorded in standard OSL method is determined by counting the number of these trapped charges in an OSL detection system. The OSL age is the cooling age of the quartz and/or feldspar. This cooling history is a record of the mineral's thermal history, which is used to reconstruct the geological event.

The sub-Quaternary period (10⁴ to 10⁵ years) is the geological age where OSL is a favourable dating technique because of low closure temperature of quartz and feldspar used in this technique. The Quaternary period is marked by intense crustal erosion particularly within active mountain ranges, leading to high exhumation rate of crustal rocks and formation of sub-Quaternary sediments. Previous techniques (e.g. Apatite Fission Track, Zircon Fission Track, and (Uranium-Thorium)/ Helium dating) could not adequately track the geological age records particularly in the last ~300 thousand years. OSL dating is currently the only dating method that has been successfully applied to understand the cooling ages of the geological events.

In natural environment, crystal lattices of quartz and/or feldspar are bombarded with radiation released from radiogenic source such as in -situ radioactive decay. As the crystals are irradiated, charges are stored up in their crystallographic defects. The charge trapping process involves atomic-scale ionic substitution of both electron and hole within the crystal lattices of quartz and feldspar. The electron diffusion happens in response to ionizing radiation as the minerals cools below their closure temperature.

If quartz or feldspar gains are exposed to natural light source such as the sun, the trapped charges will be evicted in form of luminescence. This natural process is called bleaching. Any other process that could heat up the sample will also cause the trapped electrons to escape from the crystal lattice known as thermal bleaching. Optical bleaching of the mineral leads to eviction of trapped charges in the minerals, hence, careful sampling and handling must be followed to avoid using bleached sample for OSL thermochronometry. To artificially produce luminescence in the laboratory for luminescence study of the mineral, these two processes are adopted.

A wide range of kinetic models have been developed to explain trapping and detrapping processes in quartz and feldspar crystals. Two of these models are particularly useful in determining the cooling histories of quartz or feldspar These models are known as the general order kinetic model and band tail model. The two models consider three major processes to characterize the mineral luminescence, which are: trapping process, thermal detrapping process and athermal detrapping process. Each of the processes are guided by different equations discussed below. These models are useful for the determining of cooling history of the mineral, which involves subtracting the differential sum of thermal detrapping and athermal detrapping from the trapping process (i.e. Trapping – (Thermal detrapping + Athermal detrapping).

By combining the four equations above, a single differential equation is developed to convert the luminescence into cooling rate. We have:

${\displaystyle {\frac {d{\tilde {n}}}{dt}}={\frac {D_{R}}{D_{o}}}(1-{\tilde {n}})^{\alpha }-s{\tilde {n}}^{\beta }\exp \left({\frac {-E}{kT}}\right)-s{\tilde {n}}^{\beta }\exp \left(-p'^{-{\tfrac {1}{3}}}r'\right)}$ for the general order kinetic model; and