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.