  Quasi-two-dimensional (2D) films of layered metal-chalcogenides have
attractive optoelectronic properties. However, photonic applications of thin
films may be limited owing to weak light absorption and surface effects leading
to reduced quantum yield. Integration of 2D films in optical microcavities will
permit these limitations to be overcome owing to modified light coupling with
the films. Here we present tunable microcavities with embedded monolayer MoS2
or few monolayer GaSe films. We observe significant modification of spectral
and temporal properties of photoluminescence (PL): PL is emitted in spectrally
narrow and wavelength-tunable cavity modes with quality factors up to 7400; PL
life-time shortening by a factor of 10 is achieved, a consequence of Purcell
enhancement of the spontaneous emission rate. This work has potential to pave
the way to microcavity-enhanced light-emitting devices based on layered 2D
materials and their heterostructures, and also opens possibilities for cavity
QED in a new material system of van der Waals crystals.
