  Single layers of transition metal dichalcogenides, such as WSe$_2$ have
gathered increasing attention due to their intense electron-hole interactions,
being considered promising candidates for developing novel optical
applications. Within the few-layer regime, these systems become highly
sensitive to the surrounding environment, enabling the possibility of using a
proper substrate to tune desired aspects of these atomically-thin
semiconductors. In this scenario, the dielectric environment provided by the
substrates exerts significant influence on electronic and optical properties of
these layered materials, affecting the electronic band-gap and the exciton
binding energy. However, the corresponding effect on the luminescence of
transition metal dichalcogenides is still under discussion. To elucidate these
impacts, we used a broad set of materials as substrates for single-layers of
WSe$_2$, enabling the observation of these effects over a wide range of
electrical permittivities. Our results demonstrate that an increasing
permittivity induces a systematic red-shift of the optical band-gap of WSe$_2$,
intrinsically related to a considerable reduction of the luminescence
intensity. Moreover, we annealed the samples to ensure a tight coupling between
WSe$_2$and its substrates, reducing the effect of undesired adsorbates trapped
in the interface. Ultimately, our findings reveal how critical the annealing
temperature can be, indicating that above a certain threshold, the heating
treatment can induce adverse impacts on the luminescence. Furthermore, our
conclusions highlight the influence the dielectric properties of the substrate
have on the luminescence of WSe$_2$, showing that a low electrical permittivity
favours preserving the native properties of the adjacent monolayer
