One of the most appealing aspects of 2D perovskites for polaritonics is their narrow, single-peak absorption and emission at room temperature (Figure ). However, as shown in Figure , the low-temperature absorption spectrum reveals three excitonic features, while the emission spectrum exhibits two distinct emission peaks: a high-energy emission, referred to as PL1, and a low-energy emission, referred to as PL2. The origin of these spectral features remains debated, with explanations ranging from multiple distinct exciton polarons to vibronic progressions .