Single Photons from Silver Dopant Cations in CdSe Nanoplatelets

Quasi-two-dimensional cadmium selenide (CdSe) nanoplatelets (NPLs) have garnered significant research attention in recent years due to their extremely narrow band-edge exciton photoluminescence (PL) linewidths, well-defined absorbance features, and short PL lifetimes. Adding small amounts of aliovalent dopant ions to the NPLs, such as silver, gives rise to a broad and red-shifted dopant-related emission. However, the origin and photophysical properties of the dopant-related emission are not well understood for NPLs. We will discuss NPL photophysical measurements of Ag-doped 4.5 monolayer CdSe NPLs as a function of their lateral size and relative dopant concentrations. We have found that that NPLs with the same concentration of incorporated silver ions but varying lateral areas show large differences in the PL efficiency (relative to the excitonic PL) from the dopant. Furthermore, PL from individual NPLs show dual emission from both the band edge exciton and the dopant state, indicating a homogeneous doping process across the ensemble. Dopant PL intensity and spectral fluctuations across individual NPLs indicate a dynamic hole trapping process which may reflect a heterogeneous distribution of Ag atoms substitutionally placed across the lattice, which is supported by high-resolution electron microscopy images. Under ambient conditions, the dopant emission state also exhibited pronounced photon antibunching with a g2(0) = 0.24, potentially providing a bright, efficient single photon source, which would have potentially important implications for the transmission of quantum information using light. Overall, our findings illustrate the importance of NPL morphology as it relates to the unique single particle photophysics of doped CdSe NPLs.