Single crystals of Ho2O3-doped Y2O3 stabilized ZrO2 (YSZ) with different Y2O3 and Ho2O3 contents were grown by the optical floating zone method. XRD and Raman spectra were measured and showed that crystal samples all had tetragonal structures. Measurements of positron annihilation lifetime spectra indicated that the increase in Y2O3 concentration led to the increases of defects and mean positron lifetime, which enhanced the scattering of light and reduced the luminous intensity and the quantum yield (QY) of the crystal. Under the excitation at 446 nm, photoluminescence (PL) spectra of Ho2O3-doped YSZ crystals showed emission peaks at 540, 551, 670, and 757 nm corresponding to Ho3+ transitions from 5S2, 5F4, 5F5, and 5I4 excited states to the 5I8 ground state, respectively. At low Ho2O3-doped concentrations (0.10–0.50 mol%), the overall emission intensity increased with Ho2O3 contents, reached the maximum value at 0.50 mol%, then decreased with higher Ho2O3 contents, probably as a result of increased non-radiative relaxation caused by increased interactions between Ho3+ ions. Quenching of the PL occurred at Ho2O3 concentrations > 0.5 mol% and due to the electric dipole–dipole interaction. The calculated chromaticity coordinates (CIE) were approximately (0.307, 0.683) and the color purity achieved 99.6%. The results showed that Ho2O3: YSZ crystals were suitable for green light-emitting devices.

Blue, green, and red emissions through upconversion and energy transfer processes are investigated as a function of the Tm3+ concentration in Tm/Er/Yb triply doped yttria stabilized zirconia (YSZ) crystals upon excitation at 980 nm. YSZ doped with 0.075–0.250 mol% Tm2O3, 1.50 mol% Er2O3, and 2.00 mol% Yb2O3 are prepared by the optical floating zone method, and confirmed to be in the cubic phase by X‐ray diffraction. The blue emission corresponds to the Tm3+ 1G4→3H6 transition, and is produced through a three‐photon process, whereas the green and red light are emitted through two‐photon processes from the Er3+ 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions for green and the Er3+ 4F9/2→4I15/2 transition for red. However, interactions between the different lanthanide ions is a factor in determining the overall color of these triply doped crystals, and this is not simply a summation of the results from the singly doped systems, so this mechanism of energy transfer is discussed in detail. The CIE color chromaticity coordinates for the present samples under excitation at 980 nm approach (0.39, 0.55), which is in the yellow‐green region.

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