  The large family of layered transition-metal dichalcogenides is widely
believed to constitute a second family of two-dimensional (2D) semiconducting
materials that can be used to create novel devices that complement those based
on graphene. In many cases these materials have shown a transition from an
indirect bandgap in the bulk to a direct bandgap in monolayer systems. In this
work we experimentally show that folding a 1H molybdenum disulphide (MoS2)
layer results in a turbostratic stack with enhanced photoluminescence quantum
yield and a significant shift to the blue by 90 meV. This is in contrast to the
expected 2H-MoS2 band structure characteristics, which include an indirect gap
and quenched photoluminescence. We present a theoretical explanation to the
origin of this behavior in terms of exciton screening.
