  Layered materials enable the assembly of a new class of heterostructures
where lattice-matching is no longer a requirement. Interfaces in these
heterostructures therefore become a fertile ground for unexplored physics as
dissimilar phenomena can be coupled via proximity effects. In this article we
identify an unexpected photoluminescence (PL) peak when MoSe$_2$ interacts with
TiSe$_2$. A series of temperature-dependent and spatially-resolved PL
measurements reveal this peak is unique to the TiSe$_2$-MoSe$_2$ interface,
higher in energy compared to the neutral exciton, and exhibits exciton-like
characteristics. The feature disappears at the TiSe$_2$ charge density wave
transition, suggesting that the density wave plays an important role in the
formation of this new exciton. We present several plausible scenarios regarding
the origin of this peak that individually capture some aspects of our
observations, but cannot fully explain this feature. These results therefore
represent a fresh challenge for the theoretical community and provide a
fascinating way to engineer excitons through interactions with charge density
waves.
