Judd−Ofelt Intensity Parameters and Spectral Properties of Gd2O3:Eu3+Nanocrystals

Abstract

Three nonequivalent centers of C_s (A, B, and C) in monoclinic phase and C₂ and S₆ centers in cubic phase were identified in the Gd₂O₃:Eu³⁺ nanocrystals with spectral techniques. Size dependence in the spectra indicated that the excitations from both host and charge-transfer band (CTB) for the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions were nearly equal for a larger size of 135 nm of the cubic phase; however, with decreasing the size to or less than 23 nm, the excitations by the CTB dominated. The variation of excitation leading to the symmetry and energy change in the C₂ and S₆ sites was also observed for larger particle sizes. The Judd−Ofelt intensity parameters Ω_λ (λ = 2, 4) for Gd₂O₃:Eu³⁺ nanoparticles were experimentally determined. The parameters Ω_λ were found to significantly change with the sizes of Gd₂O₃:Eu³⁺ from nanoparticles to bulk material. With decreasing the size from 135 to 15 nm, the quantum efficiencies for ⁵D₀ reduced from 23.6% to 4.6% due to the increasing ratio of surface to volume.