Up-conversion luminescence and Judd–Ofelt analysis of Nd2O3-doped yttria stabilized zirconia single crystals

Abstract

Transparent single crystals of (ZrO₂)₉₂(Y₂O₃)_8−x(Nd₂O₃)_x (x = 0.30, 0.50, 0.75, 1.00, 1.25, 1.50) were prepared by the optical floating zone method, and shown by XRD to have a cubic phase structure. Nd³⁺ entered into the crystal structure during crystal growth, and the lattice parameters and cell volume increased with increasing Nd₂O₃ concentration as Nd³⁺ replaced the smaller Y³⁺. A series of absorption peaks involving transitions from the Nd³⁺ ground state (⁴I_9/2) were observed in the UV-vis-NIR absorption spectra. Under excitation with yellow light at 589 nm, up-conversion luminescence spectra showed three distinct emission peaks, corresponding to the ⁴D_5/2 → ⁴I_9/2 (334 nm), ⁴D_3/2 → ⁴I_9/2 (363 nm) and ²P_1/2 → ⁴I_9/2 (442 nm) transitions. The maximum intensity of the emission spectra was with 0.75 mol% Nd₂O₃, and higher concentrations resulted in quenching through electric dipole–quadrupole interactions. From analysis of the absorption and emission spectra using the Judd–Ofelt theory, values for the strength parameters Ω_t (t = 2, 4, 6) and radiative transition properties were obtained for the (ZrO₂)₉₂(Y₂O₃)_7.25(Nd₂O₃)_0.75 single crystal. These showed Ω₄> Ω₂> Ω₆, with the large Ω₂ value indicating a highly covalent interaction and asymmetric local environment for Nd³⁺. The spectroscopic quality factor (χ) and radiative properties, such as the transition probability, radiation lifetime and branching ratio, indicate that this sample is a potential material for near-UV up-conversion luminescence and laser output.