Dual-function ZnO–Bi–carbon dot heterojunction thin films for X-ray shielding and UV photoresponse

The increasing demand for lightweight, environmentally sustainable, and nontoxic radiation shielding materials has stimulated research into alternatives to traditional systems, highlighting dual functional designs that combine shielding with additional photoactive performance. This work examines the fabrication of zinc oxide nanorods thin films (ZnONRs-TFs) as a potential candidate for X-ray radiation protection with additional photoactive functionality. The films were synthesised using the chemical bath deposition (CBD) technique and were designed as pure ZnONRs-TF and modified with a specified amount of bismuth nitrate (BN) and carbon dots (CDs) applied through 3× and 6× spin-coating cycles. TOPAS Monte Carlo simulations were performed to benchmark the experimental setup and replicate photon attenuation by scoring intensities across the thin film layers. Their shielding properties were evaluated through experimental measurements across an X-ray photon energy range of 50–120 kVp. while I–V, I–t, and UV–Vis analyses were conducted to characterize their electrical and optical behavior. The results revealed that the highest linear attenuation coefficient (μ) was achieved by the ZnONRs-TF doped with 1 g of BN, corresponding to an improvement of approximately 39% compared to the undoped sample at 50 kVp. This superior shielding is attributed to the synergistic effect of bismuth's high atomic number (Z = 83) and the structural densitification induced by Bi doping, which led to a thinner film with improved packing density that effectively fills interstitial voids. Conversely, the Bi-doped film with 3× spin coated CDs exhibited the largest mass attenuation coefficient (μ m ), resulting from enhanced electron interaction and increased photon interaction routes provided by the CDs, representing an increase of about 26% compared to the Bi-doped sample. At higher energy levels, a gradual decrease in shielding performance was observed for all samples due to increased photon penetration and the prevalence of Compton scattering. The simulations demonstrated high fidelity to the experimental results, with a relative deviation of approximately 2.6%, effectively benchmarking the normalized attenuation trends across the examined voltages. The ZnONRs-TF doped with 1 g of BN configuration enhanced shielding across all energy ranges, highlighting its potential as a sustainable and lightweight alternative for ionizing radiation protection. This research advances the development of thinner, eco-friendly radiation shielding materials via nanotechnology.