  The excellent electronic and mechanical properties of graphene allow it to
sustain very large currents, enabling its incandescence through Joule heating
in suspended devices. Although interesting scientifically and promising
technologically, this process is unattainable in ambient environment, because
graphene quickly oxidises at high temperatures. Here, we take the performance
of graphene-based incandescent devices to the next level by encapsulating
graphene with hexagonal boron nitride (hBN). Remarkably, we found that the hBN
encapsulation provides an excellent protection for hot graphene filaments even
at temperatures well above 2000 K. Unrivalled oxidation resistance of hBN
combined with atomically clean graphene/hBN interface allows for a stable light
emission from our devices in atmosphere for many hours of continuous operation.
Furthermore, when confined in a simple photonic cavity, the thermal emission
spectrum is modified by a cavity mode, shifting the emission to the visible
range spectrum. We believe our results demonstrate that hBN/graphene
heterostructures can be used to conveniently explore the technologically
important high-temperature regime and to pave the way for future optoelectronic
applications of graphene-based systems.
