Abstract
Moiré heterostructures produced by twisted heterojunction of transition-metal dichalcogenides are recognized as novel platforms for unique and tunable means of controlling the optical phenomena including photoluminescence (PL). Despite some interesting results on the PL peak shifts by the heterojunction at twist angles (θ) far from 0 or 60°, all of them are redshifts. Here, we first report blue shift of energy and strong enhancement of intensity in the PL by twisted heterojunction of MoS2 and WS2 monolayers (MLs) in a particular range of θ. The PL peak energy of the heterobilayer steeply increases (about 120 meV) as θ gets closer to 15 or 52° from 3 or 57°, respectively and reaches a plateau at around 2.01 eV in the θ range from 15 to 52°, higher than that of the separate MoS2 or WS2 ML. The PL intensity shows a similar θ-dependent behavior with its magnitude in the plateau being ∼4 or 80 times larger than that of the WS2 or MoS2 ML, respectively. These novel light-emission behaviors are well explained with reference to theoretical predictions on the avoided crossing between the intralayer and interlayer excitons. Our findings highlight extendable tuning and remarkable enhancement of light emission from two-dimensional semiconductors by a simple approach of twisted heterojunction in a proper θ range, very useful for their optoelectronic device applications.
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