Layered transition metal dichalcogenides TX2 (T = Mo or W; X = S or Se) have been extensively investigated because of their interesting fundamental properties including the strong anisotropy of physical properties, the role of the d orbitals of the transition metal atom in the electronic band structure and the sharp excitonic structures in the visible region.1-3 Besides applications in such important areas as photovoltaic solar cells, catalysts, solid lubricants or intercalation batteries, the TX2 compounds could be of interest as efficient luminescent materials in the near IR spectral region.4 In addition to several papers about preparation and characterization of Mo1-xWxS2, only a few works concerning to the excitonic transitions have been reported.5FigureFig. 1. The experimental PzR spectra of Mo1−xWxS2 at RT K. The solid curves are least-squares fits to LLF. Fig. 2 The composition dependence of the excitonic transition energies for A and B features of Mo1−xWxS2 at RT. Fig. 3 PL spectra of 2H-MoS2 and 2H-WS2 crystals at 6 K: a broadband region and an excitonic region. The PzR spectra near the direct band edge for set of mixed crystals of Mo1−xWxS2 at RT are presented in Fig. 1. The values of excitonic energy obtained by Lorentzian lineshape function (LLF) fitting are indicated by arrows and denoted as A and B. The results show that the valence band maximum is located at the sixfold-degenerate K point of the Brillouin zone. It leads to conclusion that the A and B excitons correspond to the smallest direct gap at the K point and the A–B exciton splitting is due to interlayer interactions and spin–orbit splitting. The excitonic transition energies and the splitting between A and B transitions vary smoothly with W composition x (Fig. 2). As shown in PL spectra of 2H-MoS2 and 2H-WS2 synthetic crystals at 6 K (Fig. 3), the excitonic region is usually composed of zero-phonon lines followed by phonon replicas.