https://www.sciencedaily.com/releases/2020/02/200218182152.htm

Semi-conductor materials capable of emitting light are used in sectors as diverse as telecommunications, light emitting devices (LEDs) and medical diagnostics. Light emission occurs when an electron jumps inside the semi-conductor from a higher energy level to a lower level. It is the difference in energy that determines the colour of the emitted light. For light to be produced, the velocity of the electron before and after the jump must be exactly the same, a condition that depends on the specific semiconducting material considered. Only some semi-conductors can be used for light emission: for example, silicon -- used to make our computers -- cannot be employed for manufacturing LEDs.

"We asked ourselves whether two-dimensional materials could be used to make structures that emit light with the desired colour," explains Alberto Morpurgo, a professor in the Department of Quantum Matter Physics, at the UNIGE Faculty of Science. Two-dimensional materials are perfect crystals which, like graphene, are one or a few atoms thick. Thanks to recent technical advances, different two-dimensional materials can be stacked on top of each other to form artificial structures that behave like semi-conductors. The advantage of these "artificial semi-conductors" is that the energy levels can be controlled by selecting the chemical composition and thickness of the materials that make up the structure.