The origin of luminescence centres in ZrO2 crystals was studied using Raman scattering, luminescence spectroscopy and quantum-chemical calculations. The 2.7 eV luminescence band and 5.2 eV absorption/luminescence excitation band are associated with an oxygen vacancy. It was shown, that a half of the Stokes shift in blue photoluminescence spectra is equal to the trap thermal activation energy 1.25 eV. Within quantum-chemical simulations it was demonstrated that both electrons and holes can be trapped on oxygen vacancies in ZrO2. Hence, oxygen vacancies are supposed to operate as traps responsible for the blue luminescence band in ZrO2.