Photon Recycling Triggered Amplified Spontaneous Emission in MAPbBr 3 ‐Ni(AcO) 2 Nanocomposite Waveguides

Abstract Metal halide perovskites’ optoelectronic properties are particularly interesting for lasers, yet obtaining efficiently the required charge carrier density can be challenging. Photon recycling, a critical process in optoelectronic devices, is harnessed here to enable lasing under a low threshold in a system based on MAPbBr 3 nanocrystals (NCs). This is achieved in a waveguide structure where the NCs are grown in‐situ within a Ni(AcO) 2 matrix, offering a cost‐effective and straightforward approach for producing a high‐quality active material with exceptional optical properties and outstanding photoluminescence quantum yield. The film contains two distinct NCs populations, sized 5 and 50 nm, enabling emitted light from smaller NCs to be reabsorbed by larger ones. The concentration of NCs is optimized to enhance photons recycling across 2–3 mm long waveguide structures. The propagating flux of emitted light plays an important role in facilitating waveguided stimulated emission, controlling the emission wavelength, and significantly lowering the amplified stimulated emission threshold to P th ≈1 µJ cm −2 , which is three times smaller than a similar device without photon recycling. The device also exhibits narrow and stable emission lines with an exceptionally high‐quality factor (≈10⁴), a result of random lasing modes caused by the formation of scattering loops through the large NCs.