Site-selective spectroscopy of Er³⁺ ions in the Bi₁₂SiO₂₀ piezoelectric crystal

Site-selective spectroscopy fluorescence experiments (emission and excitation) in the near-infrared region associated with the ⁴I_15/2↔⁴I_11/2 transitions of Er³⁺ ions have been successfully used to show the presence of two different Er³⁺ centres in the Bi₁₂SiO₂₀ piezoelectric crystal. Green (545-570 nm), red (650-690 nm) and near-infrared (850-890 nm) up-converted emissions have been observed and resolved for each type of centre under excitation up to the ⁴I_11/2 state. The Stark energy level schemes of the three lower energy states of Er³⁺ ions have been determined and compared for both centres, showing two quite different crystalline field environments. The mechanisms responsible for the up-conversion process (excited state absorption and/or energy transfer up-conversion) are also analysed.