Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS2 MLs the photoluminescence (PL) spectra even at low temperature consists typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here we show that in superacid treated MoS2 MLs the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T = 4 K, with linewidth for the neutral exciton of 15 meV, but with similar intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emission. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for both complexes and valley coherence for only the neutral exciton.Introduction.-Transition metal dichalcogenide (TMD) monolayers (ML) such as MoS 2 , MoSe 2 , WS 2 and WSe 2 are a new class of two-dimensional semiconductors with a direct bandgap in the visible region of the spectrum [1-3] and very unique properties. Strong spin orbit coupling combined with a crystal lattice that has no inversion symmetry allows for optical manipulation of the spin and valley degree of freedom in these materials [4]. In addition to their potential for unconventional, atomically thin and flexible electronics or valleytronics, they also are ideal candidates for optoelectronic and spin-optronic applications. For example, solar cells

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