Bi-Assisted Double-Sided ZnO Nanorod Architectures for Fast and Geometry-Enhanced X-Ray Scintillation

Abstract Bi-assisted ZnO nanorod (NR) arrays are investigated as thin, transparent, and fast nanostructured scintillator architectures for X-ray detection. Vertically aligned ZnO:Bi NR arrays were grown hydrothermally on fused-silica substrates in single-sided, refresh-grown, and double-sided configurations to investigate the effects of Bi-assisted growth, effective scintillating volume, and collection geometry on the measured luminescence response. Structural and morphological analyses show that moderate Bi-assisted growth preserves the preferential c-axis-oriented wurtzite ZnO structure while producing dense, high-aspect-ratio NR arrays. Optical spectroscopy reveals a visible-emission-dominant response, with broad yellow–orange photoluminescence centered at ∼580–600 nm and weak near-band-edge emission. Cathodoluminescence imaging and spectral mapping further show that the visible emission is spatially enhanced at NR edge/sidewall regions, supporting a surface/defect-mediated recombination mechanism. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy analyses of representative ZnO:Bi samples support the presence of Bi species and surface/defect-related oxygen contributions. Time-resolved PL measurements yield a fast amplitude-weighted average lifetime of ∼5.3 ns, indicating rapid defect-mediated visible recombination. Under 45 kV X-ray tube voltage, double-sided ZnO:Bi NR arrays exhibit broad radioluminescence centered at ∼600 nm in both reflection and transmission geometries. Under the investigated measurement conditions, the integrated detected RL intensity in transmission geometry is approximately 6–8 times that measured in reflection geometry. Among the double-sided samples, ZnO:Bi (5%) provides the highest measured transmission-mode RL intensity, whereas higher nominal Bi loading reduces the response, consistent with increased disorder and nonradiative loss pathways. The spectral separation between strong near-band-edge absorption and yellow–orange RL emission may reduce reabsorption losses and facilitate visible-light transport through the NR architecture. These results demonstrate that Bi-assisted double-sided ZnO NR architectures provide a promising platform for fast, transparent, and geometry-enhanced X-ray scintillators.