Gallium Sulfide Quantum Dots with Zinc Sulfide and Alumina Shells Showing Efficient Deep Blue Emission.

Solution-processed quantum dot (QD) based blue emitters are of paramount importance in the field of optoelectronics. Despite large research efforts, examples of efficient deep blue/near UV-emitting QDs remain rare due to lack of luminescent wide bandgap materials and high defect densities in the existing ones. Here, we introduce a novel type of QDs based on heavy metal free gallium sulfide (Ga2S3) nanocrystals and their core/shell heterostructures Ga2S3/ZnS as well as Ga2S3-ZnS-Al2O3. The PL properties of core Ga2S3 QDs exhibit various decay pathways due to intrinsic defects, resulting in a broad overall PL spectrum. We show that the overgrowth of the Ga2S3 core QDs with a ZnS shell results in the suppression of the intrinsic defect mediated states leading to efficient narrow deep blue emission at 400 nm. Passivation of the core/shell structure with amorphous alumina yields a further enhancement of the photoluminescence quantum yield approaching 50% and leads to an excellent optical and colloidal stability. Finally, we develop a strategy for the aqueous phase transfer of the obtained QDs retainining 80% of the initial fluorescence intensity.