Plasma-synthesized Al₂O₃:Eu²⁺ Nanorods for highly sensitive pressure sensing

Accurate pressure probing in extreme environments demands robust sensors capable of withstanding harsh conditions. Herein, we report the synthesis of Eu²⁺-doped Al₂O₃ (Al₂O₃:Eu²⁺) nanorods via a plasma-assisted direct current arc method and demonstrate their utility as ultrasensitive optical pressure sensors. Comprehensive characterization-spanning XRD, EDS, and XPS-confirmed the phase purity and chemical composition, while TEM, HRTEM, and SAED analyses elucidated a uniform one-dimensional morphology (∼30 nm in length, ∼7 nm in diameter) coupled with high crystallinity. Optically, the nanorods exhibit intense blue emission centered at 460 nm under UV excitation, attributed to the 4f⁶5d¹→ 4f⁷ transition of Eu²⁺ ions. Crucially, in situ high-pressure photoluminescence spectroscopy revealed a pronounced pressure-dependent response up to 20 GPa. The emission maxima undergo a monotonic red shift with distinct pressure coefficients (1.01 and 2.30 nm/GPa for different fitting regimes), concomitant with a systematic broadening of the full width at half maximum (2.50 and 4.15 nm/GPa). This predictable evolution of spectral features facilitates a stable, linear calibration against pressure, enabling high-fidelity sensing. The resultant sensor combines high sensitivity, an extended dynamic range (>20 GPa), and remarkable thermal stability, positioning it as a powerful candidate for monitoring geodynamic processes, deep-sea exploration, and structural health in heavy-load engineering.