  Light-emitting electronic devices are ubiquitous in key areas of current
technology, such as data communications, solid-state lighting, displays, and
optical interconnects. Controlling the spectrum of the emitted light
electrically, by simply acting on the device bias conditions, is an important
goal with potential technological repercussions. However, identifying a
material platform enabling broad electrical tuning of the spectrum of
electroluminescent devices remains challenging. Here, we propose light-emitting
field-effect transistors based on van der Waals interfaces of atomically thin
semiconductors as a promising class of devices to achieve this goal. We
demonstrate that large spectral changes in room-temperature electroluminescence
can be controlled both at the device assembly stage -- by suitably selecting
the material forming the interfaces -- and on-chip, by changing the bias to
modify the device operation point. Even though the precise relation between
device bias and kinetics of the radiative transitions remains to be understood,
our experiments show that the physical mechanism responsible for light emission
is robust, making these devices compatible with simple large areas device
production methods.
