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Abstract: Our experiments show that cetyltrimethylammonium bromide (CTAB) has an obvious effect on the particle size of the precipitation of Gd(OH)3. Without CTAB, the particle size of the Gd(OH)3 precipitation is about 50 nm, whereas with CTAB, the particle size is less than 5 nm. We propose a mechanism where CTAB micelles work as a catalyst for the nucleation process and result in the precipitation of 5 nm particles. These small particles, after heat treatment at 1073 K, did not result in small Gd2O3 nanoparticles of the same size, but instead, forming crystals of 30–80 nm size in both cubic and monoclinic phases. When monitoring the photoluminescence (PL) peak at 610 nm, we found that the charge transfer state (CTS) absorption amplitude of Eu–O is reduced in the mixed structures. We speculate that the mixed structures modify the surface properties of the Gd2O3:Eu nanoparticles, leading to the reduction of Eu–O CTS absorption. [Copyright &y& Elsevier]