Wet chemical synthesis and luminescence properties of erbium-doped nanocrystalline yttrium oxide

The luminescence properties of nanocrystalline Y₂O₃:Er³⁺ prepared via wet chemical synthesis were investigated. A broadening of both the reflectance spectrum and 77 K luminescence spectrum (λ_exc = 488 nm) was observed in the nanocrystalline material compared to bulk Y₂O₃:Er³⁺. The spectral broadening was attributed to the presence of Er³⁺ ions on the surface of the particle, which experienced different crystal fields than the ions buried in the core of the particle. Upconversion was observed in both the bulk and nanocrystal material following excitation with 650-nm or 800-nm radiation. Following excitation with 800-nm radiation, an enhancement of the red (⁴F_9/2 → ⁴I_15/2) upconverted emission was observed and occurred as a result of the (⁴I_9/2, ⁴I_11/2) → (⁴I_13/2, ⁴F_9/2) ion-pair process that directly populated the ⁴F_9/2 state. The magnitude of the red enhancement in the nanocrystalline material prepared via wet chemical synthesis was less than that of the identically doped bulk sample and less still than Y₂O₃:Er³⁺ nanocrystals prepared via a combustion synthesis technique. An explanation is proposed to account for the drastic difference in the red upconverted luminescence intensity.