Linear polarized photoluminescence properties of few-layer ReS$_{\mathrm{\mathbf{2}}}$\textbf{ and ReSe}$_{\mathrm{\mathbf{2}}}$

Here, we present layer-, temperature- and polarization-dependent photoluminescence (PL) measurements on ReS$_{\mathrm{2}}$ and ReSe$_{\mathrm{2}}$ thin crystals. The few-layer samples were prepared by mechanical exfoliation of bulk crystals on SiO$_{\mathrm{2}}$/Si substrates and characterized by AFM and low frequency Raman spectroscopy. At 300K, the PL spectra of both ReS$_{\mathrm{2}}$ and ReSe$_{\mathrm{2}}$ show a weak broad peak. A multicomponent PL structure becomes clearly resolved in the low temperature spectra featuring well-separated peaks, and being dominated by two linearly polarized excitonic peaks observed on all samples from bulk to bilayer. Both ReS$_{\mathrm{2}}$ and ReSe$_{\mathrm{2\thinspace }}$exhibit a very similar near-IR anisotropic PL response, although the polarization angle and the relative intensities of these PL peaks depend on the material and vary with the thickness of the layer.