Pressure-Induced Polyhedral Reorganization Causes Indirect-to-Direct Band-Gap Transition in Spinel Structure

Spinel oxides (${\mathrm{AB}}_{2}{\mathrm{O}}_{4}$) are promising optoelectronic materials due to their structural stability and tunable electronic properties. However, conventional strategies like doping, element substitution, and thermal treatment have achieved limited success in optimizing their performance. Here, we demonstrate that pressure-induced polyhedral reorganization triggers an indirect-to-direct band-gap transition driven by the enhanced hybridization of $\mathrm{O}\text{\ensuremath{-}}{p}_{y}$ orbitals in ${\mathrm{AB}}_{2}{\mathrm{O}}_{4}$ systems. The pressure-induced polyhedral reorganization also causes a connectivity shift from corner-sharing tetrahedra (${\mathrm{GaO}}_{4}$) to edge-sharing octahedra (${\mathrm{GaO}}_{6}$) in single-phase ${\mathrm{CaGa}}_{2}{\mathrm{O}}_{4}:{\mathrm{Bi}}^{3+}$ crystals, which tailors the electronic redistribution from isolated to quasi-1D ladderlike configurations. The optimized electronic structure leads to a concurrent enhancement in the photoresponsivity by $\ensuremath{\sim}200%$ and the emergence of an exotic white-light emission, which can be quenched to ambient conditions. These findings reveal how ${\mathrm{GaO}}_{\mathrm{x}}$ polyhedral reorganization directly governs electronic evolution in ${\mathrm{CaGa}}_{2}{\mathrm{O}}_{4}:{\mathrm{Bi}}^{3+}$, providing a new pathway to tailor electronic structures and optoelectronic properties through pressure-driven design that bypasses the limitations of traditional approaches.