Post-synthesis annealing is commonly required to achieve intense luminescence from nanoparticles synthesized by means of the solution combustion synthesis (SCS) method. We carried out investigation to gain insight on the underpinning mechanisms related to this enhancement. Gd 2 O 3 :Eu nanoparticles were prepared by SCS and characterized in their structure, crystallinity, crystallite size, photoluminescence (PL) and PL lifetime. After synthesis, samples were calcined at 500°C for 4h to eliminate organic residues, and annealed in air at 1000°C for up to 180min. The fast increase of PL intensity in the first ∼15min of annealing is understood by the decrease of the probability of non-radiative recombination through the elimination of quenching defects. This is in agreement with increasing crystallinity, as determined by the absolute intensity of the (222) and (440) diffraction peaks as a function of annealing time. The systematic measurements of crystallinity, crystallite size, PL intensity and lifetime as a function of annealing time carried out in this work supports the assignment of a major role to crystallization and the elimination of structural disorder on PL yield of SCS-prepared materials.