Author name: Thomas Hainschwang

Luminescence imaging and spectroscopy have become essential in gem testing, as most gem minerals and materials exhibit specific luminescence when properly excited. With a range of techniques introduced in gem testing laboratories in the past quarter century, such as luminescence imaging and photoluminescence (PL) emission and excitation spectroscopies, there are many applications to gem materials for establishing their identity, separating natural from synthetic gems, and detecting potential treatments. Further, these techniques often give clues towards the identity of emitting defects. Luminescence-based testing has recently gained attention even outside the gemmological laboratory as many simple luminescence-based instruments are offered to the gem and jewellery trade to separate natural from synthetic diamonds or from their imitations.

Luminescence is the eye-catching phenomenon of light emission by a mineral after some input of energy (the excitation). Although commonly used in Earth sciences only to produce images, much more can be extracted from this phenomenon. Luminescence is extremely sensitive to low levels of emitters (activators), which helps to reveal the geochemistry or the creation of defects. We give an overview of the great variety of techniques (cathodoluminescence, photoluminescence, and more), discuss vocabulary issues (such as excitation versus stimulation, or the different types of persistent luminescence phenomena), and propose wording we feel best reflects today’s knowledge. We explain the basics of luminescence spectroscopy with emission, excitation, and time-resolved spectra to obtain useful data for Earth scientists.