The effect of the size of raw Gd(OH)₃ precipitation on the crystal structure and PL properties of Gd₂O₃:Eu

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 Gd₂O ₃:Eu nanoparticles, leading to the reduction of Eu-O CTS absorption.