The effects of energy transfer on the Er ³⁺ 1.54 μm luminescence in nanostructured Y ₂O ₃ thin films with heterogeneously distributed Yb ³⁺ and Er ³⁺ codopants

We report the effects of heterogeneous Yb ³⁺ and Er ³⁺ codoping in Y ₂O ₃ thin films on the 1535 nm luminescence. Yb ³⁺:Er ³⁺:Y ₂O ₃ thin films were deposited using sequential radical enhanced atomic layer deposition. The Yb ³⁺ energy transfer was investigated for indirect and direct excitation of the Yb ²⁺F _7/2 state using 488 nm and 976 nm sources, respectively, and the trends were described in terms of Forster and Dexters resonant energy transfer theory and a macroscopic rate equation formalism. The addition of 11 at. Yb resulted in an increase in the effective Er ³⁺ photoluminescence (PL) yield at 1535 nm by a factor of 14 and 42 under 488 nm and 976 nm excitations, respectively. As the Er ₂O ₃ local thickness was increased to greater than 1.1 Å, PL quenching occurred due to strong local Er ³⁺ ↔ Er ³⁺ excitation migration leading to impurity quenching centers. In contrast, an increase in the local Yb ₂O ₃ thickness generally resulted in an increase in the effective Er ³⁺ PL yield, except when the Er ₂O ₃ and Yb ₂O ₃ layers were separated by more than 2.3 Å or were adjacent, where weak Yb ³⁺ ↔Er ³⁺ coupling or strong Yb ³⁺ ↔ Yb ³⁺ interlayer migration occurred, respectively. Finally, it is suggested that enhanced luminescence at steady state was observed under 488 nm excitation as a result of Er ³⁺ → Yb ³⁺ energy back transfer coupled with strong Yb ³⁺ Yb ³⁺ energy migration.