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 (4I9/2) 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 4D5/2 → 4I9/2 (334 nm), 4D3/2 → 4I9/2 (363 nm) and 2P1/2 → 4I9/2 (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 Ωt (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.