Silica-coating of nano-Y$_3$Al$_5$O$_{12}$:Ce$^{3+}$ synthesized by self-combustion

[摘要] Y$_{2.91}$Ce$_{0.09}$Al$_5$O$_{12}$ is obtained by self-combustion, grinding and sol–gel coating. X-ray diffraction, transmission electron microscopy, photoluminescence and absorption measurements were used to identify the structural and optical properties of each step of the process. The process is composed of a combination of chemical and physico-chemical processesincluding combustion and thermal steps, followed by grinding, powder dispersion by acidic passivation, stabilization of particle dispersions with citrate ligands and embedding of yttrium aluminium garnet (YAG) particles into SiO$_2$ shells usinga seeded growth process before drying. The initial state of the obtained powder is composed of 35 nm crystallites, sintered and agglomerated. The grinding step breaks the sintered bridge, while the passivation and citrate adsorption steps separate the particles by electrostatic repulsion before the silica coating. The optical characterizations are performed and compared separately for the powdered samples that represent the initial and final states of our process, and the dispersion sample represents the intermediate state of our process. The optical measurement revealed an important amount of optical defectsat the surface of the particles, compared with micrometric commercial particles. The grinding, nitric acid and citrate steps remove some of these defects. The final state of the sample still possesses lower quantum efficiency than that of a micrometric sample, but the SiO$_2$ coating allows for a perfect separation of the particle, suitable for implementation in small devices.

[学科分类] 材料工程

[关键词] Self-combustion;YAG;core–shell;SiO$_2$ coating.