Extrinsic Light Emission of 2D Semiconductor for Multi-Index Optical Sensing

Two-dimensional transition metal dichalcogenides (2D TMDs) possess a tunable excitonic emission that varies with extrinsic electrostatic or chemical doping, which is beneficial to 2D material based optical sensing applications. Here we revealed the interaction between DNA nucleobases and monolayer WS₂ by investigating the change of the photoluminescence (PL) emission of WS₂ with the coatings of nucleobases solutions. The p-type doping of WS₂ by introducing adenine is clearly evidenced by both evolutions of the PL spectra and the electrical transport behaviors. Besides the tunability of PL spectra shapes, we also demonstrated the tailoring of valley degree of freedom by electrostatic and optical doping. We performed the circular polarized PL measurement on monolayer WS₂ with various carrier densities at 80 k. The doping induced 5-fold increase of polarization degree of charged exciton emission is achieved even under off-resonance laser excitation, without the requirement of cryogenic temperature or magnetic field. Our findings fill the gaps in previously reported optical biosensing methods and indicate rich possibilities for developing optical sensing platform with both excitonic and valleytronic indices.