Two-Photon Lasing from Two-Dimensional Homologous Ruddlesden–Popper Perovskite with Giant Nonlinear Absorption and Natural Microcavities

Two-dimensional Ruddlesden–Popper perovskites (RPPs) with multiple quantum well-like structures, strong excitonic quantum confinement, and high stability are promising optical gain media. However, the lasing from such material with a small number of inorganic well layers is difficult to achieve. Herein, we demonstrate the low-threshold upconversion lasing from the homologous RPP (PEA)2(MA)n−1PbnI3n+1 (n = 2 and 3) microflakes with wavelength varies from 598 to 637 nm under 800 nm laser excitation at low temperature (≤153 K). Using the micro Z-scan technique, we discovered that the RPP flakes have a giant two-photon absorption coefficient β as high as 3.6 × 103 cm GW–1, resulting in the effective upconversion transition under two-photon excitation. Furthermore, the self-formation of Fabry–Pérot microcavities provides the support for lasing emission from the n ≥ 2 RPP flakes. Calculation results and microscopic transient absorption measurements reveal that low-threshold lasing is due to the high differential gain coefficient and the suppressed nonradiative Auger recombination rate inside the quantum confinement structures. These properties enable RPPs as potential gain media for developing upconversion microcavity lasers.