Realizing a SnO2-based ultraviolet light-emitting diode via breaking the dipole-forbidden rule

It is commonly believed that bulk SnO2 is not a suitable ultraviolet (UV) light emitter due to the dipole-forbidden nature of its band-edge states, which has hindered its potential use in optical applications. Here, we demonstrate both theoretically and experimentally an effective method to break the dipole-forbidden rule in SnO2 via nano-engineering its crystalline structure. Furthermore, we designed and fabricated a prototypical UV-light-emitting diode (LED) based on SnO2 thin films. Our methodology is transferable to other semiconductors with ‘forbidden’ energy gaps, offering a promising route toward adding new members to the family of light-emitting materials.