Picosecond quantum transients in halide perovskite nanodomain superlattices.

The high optoelectronic quality of halide perovskites makes them suitable for use in optoelectronic devices and, recently, in emerging quantum emission applications. Advancements in perovskite nanomaterials have led to the discovery of processes in which luminescence decay times are below 100 picoseconds, stimulating the exploration of even faster radiative rates for advanced quantum applications, which have only been realized in III-V materials grown using costly epitaxial growth methods. Here we discovered ultrafast quantum transients with timescales of around two picoseconds at low temperature in bulk formamidinium lead iodide films grown via scalable solution or vapour approaches. Using a multimodal strategy, combining ultrafast spectroscopy, optical and electron microscopy, we show that these transients originate from quantum tunnelling in nanodomain superlattices. The outcome of the transient decays, that is, photoluminescence, mirrors the photoabsorption of the states, with an ultranarrow linewidth at low temperature that can reach <2 nm (~4 meV). Localized correlation of the emission and structure reveals that the nanodomain superlattices are formed by alternating ordered layers of corner-sharing and face-sharing octahedra. This discovery opens new applications leveraging intrinsic quantum properties and demonstrates powerful multimodal approaches for quantum investigations.