Inducing high-concentration Tb³⁺ with free oxygen via atomic layer deposition

Precise preparation and control of trivalent states in rare earth metal oxide films are crucial for their optical and magnetic applications. In this study, compact and continuous terbium-doped nanofilms were deposited on silica substrates using atomic layer deposition (ALD). The average nanoparticle size varied from 17.9 to 78.5 nm with increasing growth cycles. X-ray photoelectron spectroscopy showed that the Tb³⁺/Tb⁴⁺ ratio increased from 0.98 to 1.42. A valence reduction mechanism involving free oxygen was introduced to analyze the reasons for the enhanced Tb³⁺ concentration in the nanofilms. The enhanced photoluminescence of Tb³⁺ (⁵D₄→⁷F₅) ions and the increased magnetization in terbium oxide nanofilms both reveal that free oxygen ions are the effective active sites responsible for the transition from the tetravalent to the trivalent state, in excellent agreement with theoretical analysis. Size control and free oxygen induction are promising strategies for enhancing the optical and magnetic properties of multivalent rare earth oxides.