A Tale of Seemingly “Identical” Silicon Quantum Dot Families: Structural Insight into Silicon Quantum Dot Photoluminescence

Two quantum dots, both alike in composition, but differing in structure, where we lay our scene. From broader classes, to bring deeper understanding, to the crystalline core that drives the quantum dot's sheen. In this contribution we examine two families of silicon quantum dots (SiQDs) that bring to mind the Capulets and the Montagues in Shakespeare’s Romeo and Juliet because of their stark similarities and differences. SiQDs are highly luminescent, heavy-metal-free and based upon earth-abundant elements. As such, they have attracted attention for far reaching applications ranging from biological imaging to luminescent solar concentrators to light-emitting diodes that rely on their size-dependent optical response. Unfortunately, correlating SiQD “size” to their photoluminescence maximum is often challenging. Herein, we provide essential structural insight into the correlation of SiQD dimension and PL maximum through a direct comparison of samples that exhibit statistically identical physical dimensions (d_TEM) and chemical compositions, but different crystallite size (d_XRD) and PL maxima. We then expand the scope of this investigation and systematically compare groupings of SiQDs: one in which the d_XRD and d_TEM agree and one where d_XRD < d_TEM. This latter comparison clearly shows d_XRD better predicts SiQD optical response when using the well-established effective mass approximation.