Tuning photoluminescence spectra of MoS ₂ with liquid crystals

The photoluminescence (PL) and Raman spectra of molybdenum disulfide (MoS₂) can be tuned with liquid crystals. A nematic liquid crystal, 5CB, was aligned in a zigzag direction on an MoS₂ monolayer flake. The PL and A_1g Raman mode peaks of the MoS₂ monolayer were shifted by 46 meV and 2 cm^-1, respectively, owing to the interaction between MoS₂ and the liquid crystal. Based on Lorentzian fitting analysis, it was confirmed that the peak positions and intensity ratios of the trion PL and exciton PL varied with the phase transition of the liquid crystal. This phenomenon was possibly caused by the transfer of electrons from MoS₂ to the liquid crystal. This electron transfer varies with the temperature-dependent change in the liquid crystal phase. Therefore, the PL spectra of MoS₂ can be tuned simply by controlling the phase, without changing the type of added material.