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<p>Zn<sub>1−<i>x</i></sub>Sm<sub><i>x</i></sub>O (x = 0, 2, 5, and 10&#xa0;atom%) thin films were successfully deposited by spray pyrolysis at 450&#xa0;°C and systematically investigated. XRD analysis confirmed the preservation of the wurtzite structure, with lattice parameters slightly varying around a ≈ 0.3252–0.3256&#xa0;nm and c ≈ 0.5207–0.5213&#xa0;nm, while crystallite size ranged from 44 to 55&#xa0;nm and lattice strain increased up to 0.159%. The incorporation of Sm<sup>3+</sup> ions into the ZnO lattice induces structural distortion and defect formation, which play a key role in modifying the electronic structure and, consequently, the multifunctional behavior of the films. Optical studies revealed band gap tuning from 3.30&#xa0;eV (pure ZnO) to 3.22&#xa0;eV (5% Sm) and 3.26&#xa0;eV (10% Sm), which is attributed to the combined effects of sp–d exchange interactions and defect-related states introduced by Sm doping. The refractive index decreased from 2.08 to 1.64 (at 599&#xa0;nm), indicating a reduction in film density and polarizability linked to dopant-induced disorder. Importantly, Sm incorporation significantly enhances the carrier concentration (from 5.73 × 10<sup>17</sup> to 5.34 × 10<sup>18</sup>&#xa0;cm<sup>−3</sup>), which increases the Fermi level position toward the conduction band. This shift explains the observed decrease in the Seebeck coefficient and demonstrates the transition toward degenerate semiconductor behavior. Photocatalytic degradation of methylene blue reached a maximum efficiency of 87% for 2% Sm–ZnO (<i>k</i> = 0.00917&#xa0;min<sup>−1</sup>), which can be correlated to an optimal balance between charge carrier generation and recombination rates at moderate doping levels. Similarly, gas sensing and photodetection performances showed optimal response at 2–5% Sm, highlighting that excessive doping may introduce recombination centers that limit performance. Overall, these results demonstrate that controlled Sm incorporation governs the interplay between structural defects, charge transport, and optical properties, thereby enabling the tuning of ZnO thin films for multifunctional applications.</p>

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Structure–property correlations in Sm-doped ZnO thin films: impact on optical, thermoelectric, photocatalytic, scavengers test, and gas sensing performance

  • 期刊论文

  • 发表日期：

    2026年5月28日

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  • Sabrina Roguai

摘要

Zn1−xSmxO (x = 0, 2, 5, and 10 atom%) thin films were successfully deposited by spray pyrolysis at 450 °C and systematically investigated. XRD analysis confirmed the preservation of the wurtzite structure, with lattice parameters slightly varying around a ≈ 0.3252–0.3256 nm and c ≈ 0.5207–0.5213 nm, while crystallite size ranged from 44 to 55 nm and lattice strain increased up to 0.159%. The incorporation of Sm3+ ions into the ZnO lattice induces structural distortion and defect formation, which play a key role in modifying the electronic structure and, consequently, the multifunctional behavior of the films. Optical studies revealed band gap tuning from 3.30 eV (pure ZnO) to 3.22 eV (5% Sm) and 3.26 eV (10% Sm), which is attributed to the combined effects of sp–d exchange interactions and defect-related states introduced by Sm doping. The refractive index decreased from 2.08 to 1.64 (at 599 nm), indicating a reduction in film density and polarizability linked to dopant-induced disorder. Importantly, Sm incorporation significantly enhances the carrier concentration (from 5.73 × 1017 to 5.34 × 1018 cm−3), which increases the Fermi level position toward the conduction band. This shift explains the observed decrease in the Seebeck coefficient and demonstrates the transition toward degenerate semiconductor behavior. Photocatalytic degradation of methylene blue reached a maximum efficiency of 87% for 2% Sm–ZnO (k = 0.00917 min−1), which can be correlated to an optimal balance between charge carrier generation and recombination rates at moderate doping levels. Similarly, gas sensing and photodetection performances showed optimal response at 2–5% Sm, highlighting that excessive doping may introduce recombination centers that limit performance. Overall, these results demonstrate that controlled Sm incorporation governs the interplay between structural defects, charge transport, and optical properties, thereby enabling the tuning of ZnO thin films for multifunctional applications.