Overcoming the Indirect Band Gap: Efficient Silicon Emission via Momentum-Engineered Photonic States

Silicon's indirect band gap severely suppresses radiative recombination, limiting its use as an efficient light-emitting material. Although nanoscale confinement of carriers, dielectric resonators, or plasmonic structures can partially mitigate this limitation, these approaches typically require complex fabrication. Here we report a fundamentally different and scalable mechanism that enables efficient light emission directly from bulk silicon. By decorating a silicon wafer with ultrasmall (<2 nm) gold or copper particles, we observe intense luminescence spanning the visible and near-infrared. Remarkably, the emission is indistinguishable for Au and Cu decorations in both spectral and temporal domains, demonstrating that the confinement extent, not the material composition, governs the effect. We attribute the emission to spatially confined photonic states with broadened momentum distributions, enabling phonon-independent optical transitions otherwise forbidden in silicon. This mechanism yields quantum efficiencies comparable to direct-band-gap semiconductors and produces ∼10⁵-fold enhancement in the integrated emission intensity, establishing a practical route toward silicon light-emitting devices.