Excitonic luminescence of the tungsten disulfide crystals intercalated with halogen molecules

Abstract

The radiative recombination in the layered disulfide transition metal dichalcogenide compounds 2H-WS2:I2 and 2H-WS2:Br2 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 neutral centres formed due to the intercalation of halogen molecules Br2 and I2 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 the same properties as the isoelectronic traps in GaP, providing the efficient radiative recombination. The temperature dependences of the quenching zero-phonon spectral line intensities are described by a simple expression for both types of crystals.