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 (0D) quantum dots (QDs) is reported. The formation of 0D 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 (∼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.