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

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 (I-4(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 D-4(5/2) -> I-4(9/2) (334 nm), D-4(3/2) -> I-4(9/2) (363 nm) and P-2(1/2) -> I-4(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 omega(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 omega(4)> omega(2)> omega(6), with the large omega(2) value indicating a highly covalent interaction and asymmetric local environment for Nd3+. The spectroscopic quality factor (chi) 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.