Collective Emission of Aggregates: From Amplified Spontaneous Emission to Superradiance/Superfluorescence

ABSTRACT

The collective emission from coupled emitters in aggregates is a frontier topic in condensed‐matter physics and optoelectronics. When isolated emitters form ordered aggregates, exciton delocalization fundamentally modifies the excited‐state dynamics, giving rise to amplified spontaneous emission (ASE), superradiance, and superfluorescence. These phenomena are driven by increasing quantum coherence. ASE, which is a weak coherence condition, is a propagative stimulated‐emission process in an inverted gain medium, whereas superradiance and superfluorescence arise from the many‐body strong coherent state. For an ideal multiexciton coherent state, the maximal collective emission rate can scale as N ² . These scalings occur in both superradiance and superfluorescence, which differ primarily in the preparation of coherence: superradiance starts from a coherently prepared state, whereas superfluorescence develops macroscopic coherence spontaneously from an initially phase‐disordered inversion and produces a delayed ultrashort pulse. This review summarizes the underlying exciton coupling and coherent state models and surveys ASE, superradiance, and superfluorescence in organic J‐, H‐, and X‐aggregates, AIE‐active crystals and cocrystals, inorganic crystals and perovskite nanocrystal superlattices. Particular attention is given to room‐temperature, polaron‐protected, and chiral superfluorescence. This review emphasizes diagnostic criteria and material‐design principles connecting molecular packing, coherence, and optical confinement.