Intercalated halogen molecules as radiative centers in transition metal dichalcogenides layered crystals

The radiative recombination in the layered transition metal dichalcogenide compounds 2H–WS2 : (Br2, I2), 2H–WSe2 : I2 and 2H–MoS2 : Cl2 has been investigated. It is shown that the strong photoluminescence (PL) of these indirect band gap semiconductors is caused by recombination of excitons bound to the neutral centres formed by halogen molecules intercalated in the well-defined sites of the van der Waals gap. These centres, located at energy ET ≈ 0.1 eV below the conduction band, display similar properties as the isoelectronic traps in GaP, providing the efficient radiative recombination. The observed broad band IR emission is attributed to the deep centres, caused by the intrinsic defects of the host lattices.