Phase-Purity Engineering in Quasi-2D Perovskites for Amplified Spontaneous Emission
Solution-processable quasi-2D perovskites are promising laser gain media due to their high exciton binding energy and improved stability relative to 3D counterparts. However, conventional synthesis yields mixed n-value phases, introducing interfacial defects and energetic disorder that impede charge injection into desired emission centers. Here, we report the first demonstration of stimulated emission from a phase-pure quasi-2D perovskite (n=8) achieved via a solvent-sieving method for selective phase removal. This dynamic purification yields near-unity phase purity (99.85%) with no detectable low-n phases, as confirmed by X-ray diffraction and ultraviolet-visible spectroscopy. The phase-pure film exhibits a narrower and more intense (001) diffraction peak (FWHM 0.16 nm, intensity 16,129) compared to pristine films (FWHM 0.22 nm, intensity 3,304), indicating enhanced crystallinity and increased grain size. Time-resolved photoluminescence reveals a prolonged carrier lifetime of 6.98 ns, suggesting reduced trap density. Atomic force microscopy shows a nearly pinhole-free surface with root mean square roughness of 1.18 nm. Consequently, the amplified spontaneous emission threshold is reduced to 13.82 μJ cm−2, a 12.5% improvement over conventional mixed-phase films (15.8 μJ cm−2). This work provides an efficient route to pure-phase quasi-2D perovskites for low-threshold lasers.