Low‐Threshold Amplified Spontaneous Emission in Thermally Imprinted Phase‐Stabilized MAPb 0.25 Sn 0.75 I 3 Thin Films for Near‐Infrared Distributed Feedback Lasers

Tin–lead mixed perovskites have emerged as promising candidates for amplified spontaneous emission (ASE) and lasing applications, owing to their exceptional optoelectronic properties and facile solution‐processability. Here, morphology‐smooth MAPb 0.25 Sn 0.75 I 3 polycrystalline thin films are synthesized by combing spin‐coating with thermal imprinting. Upon cooling from 300 to 100 K, the ASE threshold decreases by a factor 15 (from 93.1 µJ cm −2 to 5.9 µJ cm −2 ), accompanied by an increase of a factor of 2.5 in the net modal gain coefficient (from 374 cm −1 to 948 cm −1 ). Notably, the films maintained robust phase stability throughout the cooling process. Using these high‐quality films as gain media, distributed feedback (DFB) lasers are fabricated, for the first time operating in single‐mode infrared lasing at both 300 and 100 K with pronounced linear polarization characteristics. At 300 K, the lasing threshold is 52.7 µJ cm −2 with stable operation over 6.6 × 10 7 excitation pulses. While at 100 K, the threshold is further reduced to 2.6 µJ cm −2 (of about 20‐fold reduction), with operational stability exceeding 9.6 × 10 7 pulses. These results demonstrate a lead‐reduced gain medium with superior lasing performance and operational robustness, positioning as pivotal building blocks for next‐generation photonic technologies.