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Faculty of Biology, Chemistry & Earth Sciences

Research Group Luminescence

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Basic Principles

The luminescence dating technique exploits the ability of mineral grains (mainly quartz and feldspar) to store energy that is transmitted to them by ionising radiation. This radiation derives from the radioactive decay of naturally occurring radioisotopes of the elements potassium, thorium and uranium and from the cosmic particles. Irradiation results in the generation of free electrons which can get trapped in defects in the crystal lattice over geological periods. Supply of external energy (stimulation by heat or light) leads to the release of trapped electrons, the amount of which relates to the number of measured photons (luminescence signal).

In this way, heat and light are capable of emptying all electron traps in the mineral and to set the clock to zero. After exposure to heat and light ceased, the buried minerals start again to accumulate energy transferred by the radiation of surrounding sediment. This means, the longer minerals are buried, the more energy they accumulate and the more photons are produced and measured during laboratory stimulation. Therefore, the luminescence signal is a function of the stored energy. Provided the strength of irradiation (rate of energy supply per unit time) was constant during the dating period, the following formula gives the age of a luminescence sample:

Age = Equivalent dose [Gy]/Dose rate [Gy/a]

    - Age: Time of last exposure to heat or light
    - Equivalent dose: Amount of absorbed energy per unit mass, given in Gy = J/kg
    - Dose rate: Dose transferred per unit time, given in Gy/a

Depending on the mode of stimulation, we distinguish between:

  • Thermoluminescence (TL; stimulation by heat)
  • Optically stimulated luminescence (OSL; stimulation by light)
  • Radiofluoreszenz (RF: stimulation by ionizing radiation)

Luminescence dating can be applied to a range of archaeological materials (ceramics, heated silex artefacts, hearths) as well as to aeolian, fluvial, glacial and lacustrine sediments. From these, quartz and feldspar grains are extracted for luminescence measurements. Recently, the luminescence signal of quartz and feldspar was shown to allow reconstructing the temperature history of crustal rocks.

Dating techniques

  • Thermoluminescence (TL)
    Stimulation by heat supply
    Application range: ceramics, heated rocks, sediments
  • Optical stimulated luminescence (OSL)
    Stimulation by visible wavelength light, e.g. blue, green, yellow
    Application range: Sediments / quartz
  • Infrared-stimulated luminescence (IRSL)
    Stimulation by infrared light
    Application range: Sediments / feldspar
  • Radiofluorescence (RF)
    Stimulation by ionizing radiation
    Application range: Sediments / feldspar

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