Cooperative and collective quantum light emission from perovskite superball superstructures.

Superfluorescence (SF), the coherent light burst from synchronized quantum emitters, has been demonstrated in perovskite quantum dot superlattices. However, limited control over self-assembly, heterogeneity and emitter properties has hindered systematic exploration of cooperative emission and its transition to collective emission regimes such as amplified spontaneous emission (ASE) and lasing. Here, we present emulsion-templated perovskite superballs (SBs) as a robust, tunable platform for investigating collective light-matter phenomena. This strategy enables versatile control over perovskite nanocrystal (PNC) size, packing density, ligand chemistry, optical cavity structure, etc. We identify a critical packing density (∼0.34) for triggering SF in PNC ensembles, in agreement with theoretical calculations. Larger SBs function as self-assembled microcavities, supporting low-threshold lasing with high quality factors. Tunable excitation fluence induces a crossover between the SF and lasing regimes, while high-density SB films also support ASE. These findings establish perovskite SBs as a versatile platform for studying cooperative and collective emission dynamics crucial for advancing scalable quantum photonic technologies.