Highly Luminescent WS2 Quantum Dots/ZnO Heterojunctions for Light Emitting Devices

Sonication induced vertical fragmentation of two-dimensional (2D) WS2 nanosheets into highly luminescent, monodispered, zero-dimensional (OD) quantum dots (QDs) is reported. The formation of OD structures from 2D sheets and their surface/microstructure characterization are revealed from their microscopic and spectroscopic investigations. Size dependent optical properties of WS2 nanostructures have been explored by UV vis absorption and photoluminescence spectroscopy. Interestingly, it is observed that, below a critical dimension (similar to 2 nm), comparable to the Bohr exciton radius, the tiny nanocrystals exhibit strong emission. Finally, the electroluminescence characteristics are demonstrated for the first time, by forming a heterojunction of stabilizer free WS2 QDs and ZnO thin films. The signature of white light emission in the light emitting device is attributed to the adequate intermixing of emission characteristics of WS2 QDs and ZnO. The observation of white electroluminescence may pave the way to fabricate prototype futuristic efficient light emitting devices.