Photoluminescent amorphous silicon microspheres with intrinsic whispering-gallery-mode coupling and waveguide integration

Abstract On-chip silicon light sources are highly desirable for integrated photonics but remain challenging due to silicon’s indirect bandgap and low radiative efficiency. Amorphous silicon supports photoluminescence via band-tail states, yet lacks scalable cavity platforms for efficient light extraction and control. Here, we demonstrate solution-synthesized amorphous silicon microspheres that simultaneously serve as the luminescent medium and spherical optical cavity within a compact ~1 μm³ volume. The spheres exhibit whispering-gallery-mode-coupled photoluminescence, with resonances spanning 800–1100 nm and a maximum measured quality factor of 522, producing narrow and spectrally resolved emission peaks at room temperature. The emission exhibits active tunability through temperature, surrounding refractive index, and excitation power, reflecting the sensitivity of the WGM resonances to thermal and dielectric perturbations. Moreover, the microspheres are readily integrated with three-dimensionally printed waveguides, enabling on-chip routing of emitted light. These features position amorphous silicon microspheres as a versatile, room-temperature platform, offering cavity-enhanced emission and broad tunability for next-generation integrated photonic systems.