We report the effects of synthesis pressure and sodium content in reactants on the lattice structure and photoluminescence properties of Eu-doped CaAlSiN3, a red phosphor, synthesized by a low-temperature process (up to 800 degrees C) from ammonometallates. The lattice parameters and average and anisotropic values of crystallite size and lattice strains were calculated by refining against X-ray diffraction data. These values are correlated with synthesis pressure and sodium content. The light emission was shown to be a result of a compromise between the effects of the lattice cell dimensions and the strains. The sample obtained at Na/Ca=2.0 under 100 MPa showed the best photoluminescence emission among all the produced samples. On the other hand, our analysis suggests the optimum pressure and Na/Ca ratio for a maximum light emission could be around 60 MPa and 2, respectively.