It is now exactly 20 years since we started to study diamond by photoluminescence microscopy after irradiation in a transmission electron microscope. I will explain the motivation for this approach, how it has developed, some of the lessons we have learned, draw attention to its particular strengths and highlight some of its achievements.

John is an Emeritus Professor of Physics at the University of Bristol. He is well known for his investigations of the microstructure of materials using electron microscopy/diffraction. Early in his career, he produced seminal work on dislocation arrangements in deformed copper crystals, which is a basis for the more recent theories of work hardening. More recently he has turned his attention to defects in wide-bandgap semiconductors. He was elected a Fellow of the Royal Society in 1988. In 1996, he received the Holweck Prize, awarded jointly by the Institute of Physics and Société Française de Physique.