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The synthesis, structure, and optical properties are reported for a series of yttria-stabilized zirconia crystals in which some Y3+ was replaced by Eu3+. These crystals were grown by the optical floating zone (OFZ) method and were transparent without inclusions, cracks, or bubbles. They were all exclusively in the cubic phase, whereas the corresponding ceramic samples had a mixture of monoclinic and cubic phases. Absorption spectra showed a charge transfer band at 268 nm and a series of narrow peaks in the range 308–540 nm from Eu3+ f–f transitions. The crystals were efficiently excited at 393 nm, and exhibited excellent orange-red photoluminescence (PL) centred at 610 nm, from the 5D0 → 7F1 transition. The maximum PL intensity was observed with crystals prepared with 2.00 mol% Eu2O3, and compared with other rare earth ions; Eu3+-doped ZrO2–Y2O3 single crystals have a high concentration quenching threshold. The critical distance for Eu3+ ions was calculated as 11.8 Å, which indicates that multipole–multipole interactions dominate the non-radiative energy transfer between Eu3+ ions. Finally, the chromaticity coordinates (CIE) for all the samples were similar, and those for the (ZrO2)92(Y2O3)6(Eu2O3)2 crystal were (x = 0.6339, y = 0.3657) with a colour purity >98%. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]