Optical absorption of Dy 3 + in yttria stabilized zirconia (YSZ) single crystals has been measured at temperatures between 10 and 300 K in the 200-2000 nm range in three samples with different Dy 3 + concentration. The emission spectrum from the F 4 9 / 2 excited level in the visible and near infra-red spectra region has been measured at temperatures between 10 and 600 K. Determination of the Dy 3 + content of the samples allow us, by using the Judd-Ofelt (J-O) theory, to calculate from the 300 K spectrum the intensity parameters, transition probabilities and emission branching ratios, which are compared with experiment. Lifetime measurements have been performed as a function of the temperature and Dy 3 + concentration. Strong emission concentration quenching has been observed. Electron paramagnetic resonance of Dy 3 + measured at 10 K has been interpreted by an axial spin Hamiltonian with Z 111 , g 17.5 and g 8. Hyperfne structure due to the interaction with the two y 1 6 1 Dy and y 1 6 3 Dy isotopes has also been resolved. Narrow band excited luminescence allow to distinguish between two different sites for this ion, which correspond to a statistical distribution of strongly perturbed octo and heptacoordinated Dy 3 + ions.