Amplified Spontaneous Emission Enhancement in FAPbI ₃ Nanocrystal Films via PMMA and Mechanical Tunability on Flexible PET

Lead halide perovskites (LHPs), such as FAPbI3 nanocrystals (NCs), exhibit suitable bandgap energy and superior thermal and chemical stability, making them ideal for photovoltaic and near-infrared (NIR) laser applications. However, recent studies on NIR amplified spontaneous emission (ASE) from FAPbI3 NCs under nanosecond pulsed laser excitation still face the challenge of high lasing thresholds. In this work, FAPbI3 NCs were synthesized via the hot-injection method and deposited on a PMMA passivation layer (S-II). Owing to the passivation effect, S-II exhibits enhanced photoluminescence (PL) intensity, a longer carrier lifetime, and higher two-photon absorption (2PA) performance compared to those directly deposited on the glass substrate (S-I). Besides, the improved thermal stability of S-II has been demonstrated based on temperature-dependent ASE measurements, showing a higher characteristic temperature (TC ∼176 K). Under both backward- and sideward-scattering configurations, S-II exhibits a lower ASE threshold, higher optical gain, and a higher degree of polarization (DOP), which is attributable to the gain-guiding effect. The flexible ASE of an FAPbI3 NC film was produced using PET as the substrate, exhibiting a redshift in the emission peak and an increase in intensity under mechanical-stress-induced bending. The high-performance NIR ASE produced from FAPbI3 NCs using PMMA as a passivation layer, combined with mechanical flexibility, demonstrates high potential as a promising gain medium for NIR laser applications.