What is luminescence dating?

A Brief History

Luminescence dating is not a new Science. Back in the 1663s, R. Boyle started doing experiments and observations on the optical properties of minerals when exposed to heat. But, then, we have to wait until the invention of the photomultiplier (PMT) tube to be able to record a light signal. In the 1960s, we were able to detect a light signal from pottery because this light signal is obtained by heating the grains of sand contained in the pottery; we call it a Thermoluminescence signal. After the demonstration of the method’s feasibility, TL was widely used during the seventies and had a particularly powerful impact, creating the “TL revolution” in respect of some museum exhibits (TL was used to identify fake artifacts). Then the application of the method was extended to calcite and burnt flint from Paleolithic sites and sediment, which allowed the possibility of reaching beyond the ten thousand-year limit of pottery availability and eventually beyond the fifty thousand-year limit of radiocarbon. In 1985, D. Huntley discovered that instead of using heat to get a luminescence signal out of the grains, we could use light; this is the invention of Optically Stimulated Luminescence (OSL). Over the last 20 years, the field has grown exponentially in terms of methodological innovations and applications. Luminescence is a leading dating method because it’s applied to quartz and feldspar that exist all over the surface of the Earth and beyond.

Today there are 19 luminescence laboratories in North America and about 500 in total around the world.

General principle

Luminescence dating relies on the capacity of certain minerals to record the amount of natural radiation to which they have been exposed during burial. In the laboratory, the total amount of energy stored in the mineral is measured as a dose (Gy). The rate of absorption of energy (dose rate, Gy/year) is derived from a knowledge of the natural radioactivity in the sediment. The quotient of these two values (dose/dose rate) gives the burial time.

Luminescence techniques

Luminescence is a highly versatile dating method. The choice of the technique (i.e., the kind of signal we are going to exploit) depends on i) the kind of event we want to date, ii) the material we have, and iii) the age range we are interested in.