Resonant energy transfer in heterostructures of direct-indirect band gap transition-metal dichalcogenides

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have shown great promise in the next generation optoelectronic, electronic, and photonic applications. Heterostructures (HSs) made of stacking atomically thin layers allow us to manipulate the optical and electronic properties. We have fabricated the TMDC HSs of monolayers of direct-indirect band gap having the resonance between dark excitonic states. Here, we propose the energy transfer (ET) process enhancing photoluminescence (PL) and valley polarization in these TMD HSs, which is beyond conventional understanding of ET process. We utilize a series of optical and electron spectroscopy techniques complemented by the density functional theory calculations, to describe a massive photoluminescence enhancement from the HS area due to an efficient dark excitonic energy transfer (ET) process.