Thermally driven reversible photoluminescence modulation in WS2/VO2 heterostructure

We demonstrate reversible modulation of photoluminescence in chemical vapor deposition (CVD) grown WS2 monolayer transferred on VO2 thin films that undergo insulator-metal transition. Thermally driven phase transition in VO2 thin film involving structural change as well as thermal expansion mismatch at interfaces induce strain and able to reversibly tune photoluminescence (PL) of atomic thin WS2 layer. PL intensity is increased with enhancement factor of 1.83 which corresponds to similar to 250% enhancement when heated from 30 degrees C to 70 degrees C. With further increase of temperature, PL intensity is found to be decreasing due to thermal quenching. While interference effect arising from metallic VO2/WS2 interface may also contribute for luminescence enhancement in metallic state, the observed increase in photoluminescence intensity during heating within the insulating state reveals the role of thermal strain. Systematic in-situ Raman and PL measurements revealed role of phase transition in controlling the PL intensity of excitons in WS2 monolayer. Single crystalline VO2 microplates also have been used to confirm the PL intensity modulation across phase transition. The observed direct correlation between photoluminescence and phase change interaction of VO2 with atomic thin layer of WS2 provide novel platform to tune the optical properties for diverse smart photonic applications.