Tuning Laser Threshold within the Large Optical Gain Bandwidth of Halide Perovskite Thin Films

Metal halide perovskite semiconductors show considerable promise as an efficient coherent light source, but the extent of their spectral tunability and optical gain bandwidth have not been established. Here, we demonstrate continuously tunable single-mode lasing from halide perovskite thin films over a wide spectral range (758-804 nm for CH3NH3PbI3, 653-684 nm for Cs0.4(CH3NH3)0.6Pb(Br0.4I0.6)3, and 520-542 nm for CsPbBr3) at room temperature for the first time. The large optical gain bandwidth (∼90 meV) and high modal gain coefficient (533 cm-1) are key enabling factors for this achievement. Period-varying chirped Bragg gratings utilized for optical feedback allow fine-tuning of the lasing output, with a minimum spectral tuning spacing, Δλlasing ∼1.4 nm. This precise tuning control allows us to obtain the lowest possible lasing threshold throughout the gain bandwidth, useful for designing highly efficient electrically pumped lasers.