Radiative recombination of excitons in the transition-metal dichalcogenides MoS2:Cl2 and WS2:Br2

The comparative study of the excitonic radiative recombination in 2H-MoS2:Cl2 and 2H-WS2:Br2 layered crystals is presented. The steady-state emission spectra of both the investigated materials include two distinct regions. The short-wavelength region consisting of sharp lines is produced by bound excitons, related to the halogen molecules intercalated in the layered semiconductors during the growth process. The second spectral region-a vibronic broad band identical for both types of crystals, is attributed to the deep radiative centres, caused by the intrinsic defects of the host lattices. The atypical temperature increase of the excitonic radiative decay time observed for 2H-WS2:Br2 in the range T=2-7K is related to the presence of a long lifetime sublevel, placed 0.3 meV above the lowest excitonic state.