Luminescence and Trapped-Charge Dating

Luminescence dating measures the radiation energy stored in minerals such as quartz and feldspar since they were last heated or exposed to light, dating events like firing pottery or burying sediment.

Definition

A family of chronometric dating methods that determine when minerals were last heated or exposed to sunlight by measuring the radiation-induced charge they have accumulated since that event.

Scope

This topic covers thermoluminescence (TL) and optically stimulated luminescence (OSL), together with related trapped-charge methods such as electron spin resonance. It addresses the trapping of charge by natural radiation, the zeroing of the signal by heat or light, the measurement of equivalent dose and dose rate, and the application of these methods to ceramics, burnt flint, and sediments beyond the radiocarbon range.

Core questions

• How do minerals accumulate and release trapped charge as luminescence?
• What event does a luminescence date actually measure?
• How are equivalent dose and environmental dose rate determined?
• When are luminescence methods preferable to radiocarbon?

Key theories

Trapped-charge accumulation and zeroing

The principle that ionizing radiation traps electrons in mineral lattice defects at a steady rate, and that heating or sunlight empties the traps, so the trapped signal measures time since that last zeroing event.

Dose and dose-rate determination

The method of dating by dividing the equivalent dose, the laboratory radiation needed to reproduce the natural signal, by the environmental dose rate from surrounding radioactivity.

History

Thermoluminescence dating of fired ceramics was developed in the 1960s and 1970s, notably at the Oxford laboratory under Martin Aitken. Optically stimulated luminescence, introduced in the 1980s, allowed dating of light-exposed sediments and became central to Quaternary and Paleolithic chronology, extending dating well beyond the radiocarbon limit.

Debates

Incomplete bleaching and signal stability

Reliable luminescence dating assumes the signal was fully reset before burial; partial bleaching and anomalous fading, especially in feldspar, drive debate over sample selection and correction methods.

Key figures

• Martin Aitken
• Ann Wintle
• Geoff Duller

Seminal works

• aitken1985
• aitken1998

Frequently asked questions

What does a luminescence date tell you?

It tells you how long ago a mineral was last strongly heated or exposed to sunlight, such as when a pot was fired or sediment was buried away from light.

When is luminescence used instead of radiocarbon?

It is used when there is no datable organic material, or when the age exceeds the roughly 50,000-year radiocarbon limit, since luminescence can reach back hundreds of thousands of years.