A model for the Universe is proposed where it is considered as a mixture of scalar and matter fields. The particle production is due to an irreversible transfer of energy from the gravitational field to the matter field and represented by a non-equilibrium pressure. This model can simulate three distinct periods of the Universe: (a) an accelerated epoch where the energy density of the scalar field prevails over that of the matter field, (b) a past decelerated period where the energy density of the matter field becomes larger than the scalar field energy density, and (c) a present acceleration phase where the scalar field energy density overcomes the energy density of the matter field.
