Purcell enhanced emission and saturable absorption of cavity-coupled CsPbBr3 quantum dots*

Colloidal perovskite quantum dots are promising quantum emitters because of their bright emission, color tunable optical properties, low-cost chemical synthesis, scalability and ease of nano-photonics integration. Their coherence time is a considerable fraction of their short radiative lifetime suggesting that moderately Purcell-enhanced nanophotonic cavity integration has the potential to achieve transform-limited photon coherence. In addition, cavities enhance the light-matter interaction , and the interplay between the system's absorption characteristics and the confinement of photon modes within the cavity can lead to pronounced nonlinear effects. We integrate zwitterionic CsPbBr3 quantum dots to a polarization degenerate Bullseye cavity mode exhibiting higher Q than reported before. We achieve an average of around 10 times improvement in the brightness of the cavity coupled dots compared to the bulk. From time-resolved lifetime measurement, we calculate a factor of 8 times Purcell enhancement for the cavity coupled dots. We also observe saturable absorption behavior of the perovskites inside the cavity where the cavity quality factor increases by around 20% with quantum dot saturation. These findings are an important step towards utilizing cavity coupled perovskites as efficient light sources and for strong optical nonlinearity.