Two-photon pumped amplified spontaneous emission in flexible paper-based perovskites.

This study characterizes the optoelectronic properties of perovskite polycrystals grown on paper-based substrates, comparing them with quartz-based films and bulk crystals. The paper-based samples demonstrated amplified spontaneous emission (ASE) under both visible (430 nm) and near-infrared (800 nm, 950 nm) excitation, with the latter attributed to efficient two-photon absorption (TPA). Notably, photoluminescence (PL) could still be detected under excitation wavelengths extending to 1500 nm, indicating the possible contribution of three-photon absorption (3PA) processes. This pronounced multiphoton response-spanning both TPA and potential 3PA regimes-underscores the material's strong nonlinear optical properties and its promise for applications in long-wavelength-pumped photonic devices.