Main Article Content
Abstract
Magnetite (Fe3O4) is a spinel-based material that has broad potential in various applications, one of which is for magneto-optics. However, the value of the energy gap obtained from magnetite is too small to be applied. Efforts to improve these characteristics are carried out through transition metal ion doping techniques, one of which is cobalt (Co2+) which is known to modify the electronic structure and stabilize the crystal lattice. This study aims to analyze the optical properties of magnetite nanoparticles that have been doped with Co2+ through energy gap and Urbach energy calculations. The synthesis of Co0.125Fe2.875O4 was carried out using the coprecipitation method. Furthermore, characterization was carried out using UV–Vis spectroscopy and analyzed the size of the energy gap and Urbach energy. The results showed that cobalt doping (Co0.125Fe2.875O4) produced two indirect energy gap values of 2.07 eV and 3.19 eV and one direct energy gap value of 3.63 eV. Urbach energy analysis revealed a very low Eu value of 0.0073 eV, indicating high crystal regularity and minimal structural defects in the material. This study demonstrated that cobalt doping not only increases the band gap energy of magnetite but also significantly lowers the Urbach energy, resulting in a material with more pronounced optical properties.
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Copyright (c) 2025 Kormil Saputra, Ika Umratul Asni Aminy, Rahmatun Inayah, Teguh Ardianto, Dian W. Kurniawidi

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References
I. D. Fajariman et al., “Comparative Behavior Of Magnetic Iron Oxide Nanoparticles (Mions) Via Mechanical And Chemical Routes,” Indones. Phys. Rev., vol. 8, no. 1, pp. 181–195, 2025, doi: 10.29303/ipr.v8i1.407.
S. A. A. Putri, S. Sunaryono, N. M. Chusna, N. Nasikhuddin, and K. Saputra, “Study of antioxidant of self nano emulsifying drug delivery system (SNEDDS)- Fe3O4/ginger extract ferrofluid,” AIP Conf. Proc., vol. 3197, no. 1, p. 020016, Feb. 2025, doi: 10.1063/5.0240583.
N. Kadian, R. Kumari, A. Panchal, J. Dalal, and D. Padalia, “Structural and optical properties of gadolinium doped-magnetite nano-crystal for photocatalytic application,” J. Alloys Compd., vol. 960, p. 170811, Oct. 2023, doi: 10.1016/j.jallcom.2023.170811.
B. M. Haque, D. B. Chandra, P. Jiban, I. Nurul, and Z. Abdullah, “Influence of Fe2+/Fe3+ ions in tuning the optical band gap of SnO2 nanoparticles synthesized by TSP method: Surface morphology, structural and optical studies,” Mater. Sci. Semicond. Process., vol. 89, pp. 223–233, Jan. 2019, doi: 10.1016/j.mssp.2018.09.023.
J. L. Verble, “Temperature-dependent light-scattering studies of the Verwey transition and electronic disorder in magnetite,” Phys. Rev. B, vol. 9, no. 12, pp. 5236–5248, 1974, doi: 10.1103/PhysRevB.9.5236.
M. Bayzidi and B. Zeynizadeh, “The Immobilized Zirconocene Chloride on Magnetite-reduced Graphene Oxide: A Highly Efficient and Reusable Heterogeneous Nanocatalyst for One-pot Three-component Synthesis of Tetrahydrobenzo[b]pyrans and Dihydropyrano[3,2-c]chromenes,” ChemistrySelect, vol. 7, no. 43, p. e202202708, 2022, doi: 10.1002/slct.202202708.
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A. G. Leonel et al., “Tunable magnetothermal properties of cobalt-doped magnetite–carboxymethylcellulose ferrofluids: smart nanoplatforms for potential magnetic hyperthermia applications in cancer therapy,” Feb. 2021, doi: 10.1039/D0NA00820F.
L. Sheng, H. Tan, L. Zhu, K. Liu, A. Meng, and Z. Li, “In situ anchored ternary hierarchical hybrid nickel@ cobaltous sulfide on poly (3, 4-ethylenedioxythiophene)-reduced graphene oxide for highly efficient non …,” Microchim. Acta, no. Query date: 2025-05-14 09:44:32, 2024, doi: 10.1007/s00604-024-06317-0.
M. Ledinsky et al., “Temperature Dependence of the Urbach Energy in Lead Iodide Perovskites,” J. Phys. Chem. Lett., vol. 10, no. 6, pp. 1368–1373, Mar. 2019, doi: 10.1021/acs.jpclett.9b00138.
L. Cerón-Urbano, C. J. Aguilar, J. E. Diosa, and E. Mosquera-Vargas, “Nanoparticles of the Perovskite-Structure CaTiO3 System: The Synthesis, Characterization, and Evaluation of Its Photocatalytic Capacity to Degrade Emerging Pollutants,” Nanomaterials, vol. 13, no. 22, Art. no. 22, Jan. 2023, doi: 10.3390/nano13222967.
S. Bazsefidpar, M. Freitas, C. Pereira, G. Gutiérrez, and ..., “Fe3O4@Au Core–Shell Magnetic Nanoparticles for the Rapid Analysis of E. coli O157:H7 in an Electrochemical Immunoassay,” Biosensors, no. Query date: 2025-05-14 09:44:32, 2023, [Online]. Available: https://www.mdpi.com/2079-6374/13/5/567
P. Makuła, M. Pacia, and W. Macyk, “How To Correctly Determine the Band Gap Energy of Modified Semiconductor Photocatalysts Based on UV–Vis Spectra,” J. Phys. Chem. Lett., vol. 9, no. 23, pp. 6814–6817, Dec. 2018, doi: 10.1021/acs.jpclett.8b02892.
S. Benramache, Y. Aoun, S. Lakel, B. Benhaoua, and C. Torchi, “The calculate of optical gap energy and urbach energy of Ni1−xCoxO thin films,” Sādhanā, vol. 44, no. 1, p. 26, Jan. 2019, doi: 10.1007/s12046-018-1003-y.
T. Pham, T. Huy, and A. Le, “Spinel ferrite (AFe 2 O 4)-based heterostructured designs for lithium-ion battery, environmental monitoring, and biomedical applications,” RSC Adv., no. Query date: 2025-05-14 09:44:32, 2020, [Online]. Available: https://pubs.rsc.org/en/content/articlehtml/2020/ra/d0ra05133k
Y. Zheng, R. Gao, Y. Qiu, L. Zheng, Z. Hu, and X. Liu, “Tuning Co2+ Coordination in Cobalt Layered Double Hydroxide Nanosheets via Fe3+ Doping for Efficient Oxygen Evolution,” Inorg. Chem., vol. 60, no. 7, pp. 5252–5263, Apr. 2021, doi: 10.1021/acs.inorgchem.1c00248.
P. N. Anantharamaiah and P. A. Joy, “Effect of co-substitution of Co2+ and V5+ for Fe3+ on the magnetic properties of CoFe2O4,” Phys. B Condens. Matter, vol. 554, pp. 107–113, Feb. 2019, doi: 10.1016/j.physb.2018.11.031.
V. Naresh and S. Buddhudu, “Studies on Optical, Dielectric and Magnetic Properties of Mn2+, Fe3+ & Co2+ Ions Doped LFBCd Glasses,” Ferroelectrics, vol. 437, no. 1, pp. 110–125, Jan. 2012, doi: 10.1080/00150193.2012.741987.
D. Mishra, J. Nanda, S. Parida, K. J. Sankaran, and S. Ghadei, “Effect of Y3+ and Co2+ co-doping on the structural, optical, magnetic and dielectric properties of LaFeO3 nanoparticles,” J. Sol-Gel Sci. Technol., vol. 111, no. 2, pp. 381–394, Aug. 2024, doi: 10.1007/s10971-024-06452-3.
N. T. T. Mai, N. K. Nga, D. T. M. Hue, T. N. Dung, H. D. Chinh, and T. Q. Huy, “Characterization of Co2+- and Fe3+-Codoped TiO2 Nanomaterials for Photocatalytic Degradation of Organic Pollutants under Visible Light Irradiation,” Adsorpt. Sci. Technol., vol. 2021, p. 9193052, Jan. 2021, doi: 10.1155/2021/9193052.
L. C. Sonia and S. Phanjoubam, “Study on structural, optical and magnetic properties of cobalt substituted magnetite nanoparticles for ferrofluid applications,” Mater. Today Proc., vol. 65, pp. 2883–2888, Jan. 2022, doi: 10.1016/j.matpr.2022.06.434.
S. Anjum, R. Tufail, K. Rashid, R. Zia, and S. Riaz, “Effect of cobalt doping on crystallinity, stability, magnetic and optical properties of magnetic iron oxide nano-particles,” J. Magn. Magn. Mater., vol. 432, pp. 198–207, June 2017, doi: 10.1016/j.jmmm.2017.02.006.
S. Anjum, R. Tufail, H. Saleem, R. Zia, and S. Riaz, “Investigation of Stability and Magnetic Properties of Ni- and Co-Doped Iron Oxide Nano-particles,” J. Supercond. Nov. Magn., vol. 30, no. 8, pp. 2291–2301, Aug. 2017, doi: 10.1007/s10948-017-4044-2.
M. Subash, M. Chandrasekar, S. Panimalar, C. Inmozhi, and R. Uthrakumar, “Synthesis, characterizations of pure and Co2+ doped iron oxide nanoparticles for magnetic applications,” Mater. Today Proc., vol. 56, pp. 3413–3417, Jan. 2022, doi: 10.1016/j.matpr.2021.10.340.
S. Muruganandam, K. Parivathini, and G. Murugadoss, “Effect of co-doped (Ni2+:Co2+) in CdS nanoparticles: investigation on structural and magnetic properties,” Appl. Phys. A, vol. 127, no. 6, p. 400, May 2021, doi: 10.1007/s00339-021-04555-0.