Tip-induced strain, bandgap, and radiative decay engineering of a single metal halide perovskite quantum dot

Abstract: Strain engineering of perovskite quantum dots (pQDs) enables widely-tunable photonic device applications. However, manipulation at the single-emitter level has never been attempted. Here, we present a tip-induced control approach combined with tip-enhanced photoluminescence (TEPL) spectroscopy to engineer strain, bandgap, and emission quantum yield of a single pQD. Single CsPbBr${x}$I${3-x}$ pQDs are clearly resolved through hyperspectral TEPL imaging with $\sim$10 nm spatial resolution. The plasmonic tip then directly applies pressure to a single pQD to facilitate a bandgap shift up to $\sim$62 meV with Purcell-enhanced PL quantum yield as high as $\sim$10$^5$ for the strain-induced pQD. Furthermore, by systematically modulating the tip-induced compressive strain of a single pQD, we achieve dynamical bandgap engineering in a reversible manner. In addition, we facilitate the quantum dot coupling for a pQD ensemble with $\sim$0.8 GPa tip pressure at the nanoscale. Our approach presents a new strategy to tune the nano-opto-electro-mechanical properties of pQDs at the single-crystal level.