Er ³⁺ interlayer energy migration as the limiting photoluminescence quenching factor in nanostructured Er ³⁺:Y ₂O ₃ thin films

We report the effects of Er ³⁺ nanostructuring on optical properties of heterogeneously doped Er ³⁺:Y ₂O ₃ thin films synthesized by radical enhanced atomic layer deposition. By alternating the cycle sequences of Y ₂O ₃ and Er ₂O ₃, rare earth (RE) ion concentrations were controlled from 4.8 to 11.8 at. Er and the local Er ₂O ₃ thicknesses were varied between 0.7 to 7.6 Å. Photoluminescence (PL) was used to examine the 1535 nm (Er ⁴I _13/2→ ⁴I _15/2) emission at two excitation wavelengths, 488 nm and 976 nm. The normalized PL increased with increasing Er ³⁺ concentrations up to 11.8 and 9.6 at. under 488 and 976 nm excitations, respectively. The introduction of a local Er ₂O ₃ layer greater than 2.4 Å resulted in significant PL quenching, over an order of magnitude, under both excitation wavelengths. The quenching was attributed to enhanced local Er ³⁺Er ³⁺ interlayer energy migration. Compared to homogeneously doped RE systems where the RE concentration is directly related to the average RERE spatial distance, increased luminescence was observed at high Er ³⁺ concentrations in heterogeneously doped systems. These results suggest that controlling the RE proximity is key to engineering the optical properties of RE doped heterogeneous materials.