In contrast to the conventional powder phosphors consisting of particles with a uniform material composition, GaN-based nanostructure-embedded particles, which consist of GaN quantum dots or quantum wells in the AlN matrix, has been proposed. We can expect the novel phosphors to have higher luminescence efficiencies owing to the carrier confinement effect. To date, we have focused mainly on the synthesis and characterization of AlN core particles formed by the first process stage. In this study, we studied the conditions systematically, and found that the crystallinity of AlN core particle depends on the reaction temperature and atmosphere.