Enhancing Silicon Nanocrystal Photoluminescence through Temperature and Microstructure

Routes to enhancing the photoluminescence (PL) of colloidal silicon nanocrystals (SiNCs) typically focus on changes in surface chemistry and the associated improvements in quantum yield. Here, we report a new more indirect approach that instead exploits the structure of the host matrix. Specifically, we demonstrate that changes in microstructure associated with a thermotropic phase transition in unbound ligand can increase the excitation fluence through scattering, yielding dramatic improvements in PL intensity without any discernible changes in fluorescence lifetime or quantum yield. Using size-purified plasma-synthesized SiNCs prepared as solid and liquid samples, we use experiment and computation to examine both intrinsic size-resolved differences in the temperature-dependent PL and an anomalous contribution linked to matrix microstructure. Beyond revealing a potential new route to improved PL intensity, our results further clarify the role of surface states and the challenges that they present.