  Strong light-matter interactions in layered transition metal dichalcogenides
(TMDs) open up vivid possibilities for novel exciton-based devices. The optical
properties of TMDs are dominated mostly by the tightly bound excitons and more
complex quasiparticles, the biexcitons. Instead of physically exfoliated
monolayers, the solvent-mediated chemical exfoliation of these 2D crystals is a
cost-effective, large-scale production method suitable for real device
applications. We explore the ultrafast excitonic processes in WS$_{2}$
dispersion using broadband femtosecond pump-probe spectroscopy at room
temperature. We detect the biexcitons experimentally and calculate their
binding energies, in excellent agreement with earlier theoretical predictions.
Using many-body physics, we show that the excitons act like Weiner-Mott
excitons and explain the origin of excitons via first-principles calculations.
Our detailed time-resolved investigation provides ultrafast radiative and
non-radiative lifetimes of excitons and biexcitons in WS$_{2}$. Indeed, our
results demonstrate the potential for excitonic quasiparticle-controlled
TMDs-based devices operating at room temperature.
