Is thermoluminescence dating
There are two different methods of OSL dating: multiple-aliquot-dose and single-aliquot-regenerative-dose (SAR).
A sample in which the mineral grains have all been exposed to sufficient daylight (seconds for quartz; hundreds of seconds for potassium feldspar) can be said to be of zero age; when excited it will not emit any such photons.
The older the sample is, the more light it emits, up to a saturation limit.
Single Quartz OSL ages can be determined typically from 100 to 350,000 years BP, and can be reliable when suitable methods are used and proper checks are done.
Feldspar IRSL techniques have the potential to extend the datable range out to a million years as feldspars typically have significantly higher dose saturation levels than quartz, though issues regarding anomalous fading will need to be dealt with first.
The minerals that are measured are usually either quartz or potassium feldspar sand-sized grains, or unseparated silt-sized grains.