Sol-gel synthesis and characterization of praseodymium-doped and calcium-, titanium-substituted yttrium aluminium garnets Pr:Y3-xCaxAl5-yTiyO12

Abstract

Mixed-metal garnets with novel chemical compositions (Pr:Y3-xCaxAl5-yTiyO12) have been synthesized by a simple aqueous sol–gel method. The praseodymium-doping and calcium- and titanium-substitution effects in these mixed-metal garnets have been investigated. The sol–gel derived garnet samples were characterized by powder X-ray diffraction analysis (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The positive effect of co-substitution with calcium and titanium ions in Y3-xCaxAl5-yTiyO12 samples in comparison with single aliovalent substitution of calcium in Y3-xCaxAl5O12 and titanium in Y3Al5-yTiyO12 samples was determined from the results of XRD analysis. The XRD patterns of these samples clearly showed that about 30 % of yttrium and aluminium could be substituted by calcium and titanium without destroying garnet crystal structure. On the other hand, the single-phase garnets Y3-xCaxAl5O12 and Y3Al5-yTiyO12 were obtained at lower substitutional level (∼20 % Ca2+ for Y3+ and ∼ 11 % Ti4+ for Al3+). Such different substitutional effects were explained by formation of different point defects in the crystal structures. The luminescent properties of Pr3+-doped Y3-xCaxAl5-yTiyO12 garnets were also investigated.