Semiconductor Quantum Dot Lifetime Near an Atomically Smooth Ag Film Exhibits a Narrow Distribution

We investigate photoluminescence from individual "giant" CdSe/CdS core/thick-shell quantum dots (gQDs) placed near an epitaxial Ag film with an atomically smooth surface. The key observation is that the lifetimes of the gQDs are drastically reduced and exhibit a remarkably narrow distribution compared to the gQDs deposited on a thermally deposited Ag film. The larger variations in gQDs' lifetimes on the thermally deposited Ag film arise from excitonic coupling to localized surface plasmons associated with nanoscale surface corrugations of different heights. A calculation is performed based on a simple model system of a QD coupled to a metallic nanosphere. The calculation shows that the QD lifetime initially shortens and reaches a saturated value with increasing radius of the metal nanoparticle (MNP). Because the epitaxial film can be treated as a sphere with an infinitely large radius, the calculation confirms and explains the different QD dynamics near the two types of Ag films as observed experimentally. Our studies demonstrate that epitaxial Ag films serve as an ideal material platform for reliable control over the QD lifetime and may lead to improved photodetectors and light emitting devices requiring fast response or modulation.