Clusters of silver atoms captured in zeolites, a porous material with small channels and voids, have remarkable light-emitting properties. They can be used for more efficient lighting applications as a substitute for LED and TL lamps. Until recently, scientists did not know exactly how and why these small particles emit light. An interdisciplinary team of physicists and chemists led by KU Leuven has now demonstrated for the first time where these properties originate.