The study, published in the journal Light: Science and Applications, reveals the quantum-mechanical effects in the luminescence emanating from thin monocrystalline gold flakes. The researchers used a thin film of monocrystalline gold produced with a novel synthesis technique to study the photoluminescence process as they made the metal thinner and thinner. They observed certain quantum mechanical effects emerging in films of up to about 40 nanometers, which was unexpected, because normally for a metal, you don’t see such effects until you go well below 10 nm.