Structural and upconversion emission properties of $\mathrm{Zr}{\mathrm{O}}_2:{\mathrm{Yb}}^{3+}\text{–}{\mathrm{Ho}}^{3+}$ nanocrystals were analyzed as function of ${\mathrm{Yb}}^{3+}$ concentration. Structural characterization shows a crystallite size up to 80 nm and tetragonal and cubic phase as the main crystalline structures. Strong green (540 nm) and weak red (670 nm) and near infrared (760 nm) emission bands were observed with 968 nm excitation. The upconversion is based on two photons absorption either by the energy transfers from ${\mathrm{Yb}}^{3+}$ ion or by the excited state absorption. The energy transfer efficiency was calculated to be 50% for 2 mol % of ${\mathrm{Yb}}^{3+}$ diminishing to less than 20% for higher concentration. The ${\mathrm{Yb}}^{3+}$ concentration also affects the decay time of the green emission of ${\mathrm{Ho}}^{3+}$ ion diminishing from $140\mu \mathrm{s}$ for 2 mol % of Yb to $76\mu \mathrm{s}$ for higher concentration.

The structural and luminescence properties of erbium doped zirconium oxide prepared by the sol-gel processes were analyzed. The annealed powders presented a concentration dependent crystallite sizes and crystalline phase, ranging from 28 to 46 nm and from 40 to 96% for the monoclinic phase, respectively. Green (545 nm) and red (680 nm) emissions bands were observed with 489 and 962 nm excitation. Experimental results showed that the emission bands can be tuned by controlling the ${\mathrm{Er}}^{\text{3+}}$ concentration and that the red band is almost quenched with 489 nm whereas it is enhanced with 962 nm excitation. The nature of this behavior is discussed taking into account the nonradiative energy transfer and cross-relaxation process.