Axially Composition‐Gradient Perovskite for Continuously Tuning Visible Lasing

Abstract Broadband‐tunable microlasers are critical light sources for advanced photonic integration, microdisplays, etc. Changing the optical gain medium composition is a common approach to adjust lasing wavelengths. However, continuous modulation of the composition within an on‐chip device to achieve broadband and continuously tunable gain spectrum remains technically challenging. Here, a uniform perovskite CsPbBr ₃ shell is evaporated onto a microcapillary template serving as a high‐quality microcavity with whispering‐gallery‐mode (WGM) resonance. Subsequently, axially composition‐gradient perovskite microwires are fabricated via solid‐phase anion exchange. Energy Dispersive X‐ray Spectroscopy (EDS) line scanning reveals a gradient distribution of halide elements (Cl, Br, and I), and X‐ray diffraction (XRD) demonstrates systematic shifts in diffraction peaks. Furthermore, micro‐region absorption spectra show a progressive redshift of the absorption edge from ≈440 to 650 nm, corresponding to continuously tunable photoluminescence (PL) from ≈450 to 680 nm. Crucially, continuous halide modulation enables broadband‐tunable lasing covering nearly the entire visible range (480–620 nm) under 400 nm femtosecond laser excitation. This integrated strategy enables direct red‐green‐blue (RGB) laser emission from a single chip, providing a compact solution for full‐color displays, white‐light laser sources, and visible‐light communication without external optical mixing.