Effect of the dopant selection (Er, Eu, Nd or Ce) and its quantity on the formation of yttrium aluminum garnet nanopowders

Hydroxide precursors, synthesized using the co-precipitation method, were calcined for 1 h at the temperatures of 900, 1000 and 1100 °C, respectively, and heated directly to 1500 °C to produce various Y3Al5O12 (YAG) nanopowders with different doping quantities of erbium, europium, neodymium and cerium. All samples were investigated using thermo-gravimetry (TG) and differential thermal analysis (DTA), field emission gun-scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).TG and DTA experiments were performed from room temperature up to 1500 °C; the weight loss curves combined with the presence of exo- and endo-thermal events were related to phase transformation phenomena. FEG-SEM and TEM micrographs showed aggregated particles with a rounded morphology with an average size of around 50 nm.Analysis of XRD patterns confirmed the formation of YAG phase with lattice parameter dependent on the specific dopant, its amount and temperature treatment. In some cases, the YAH (YAlO3 hexagonal) and YAP (YAlO3 perovskite) crystalline phases’ formation was observed at intermediate stages of heating. A reduction of YAG cell parameter was observed after high temperature treatment, probably due to defect release in the garnet structure.The large solubility of neodymium ions that substitute for yttrium ions in the dodecahedral sites of the garnet structure was confirmed. From phase’s analysis and lattice parameter variation of YAG as a function of doping and annealing temperature, it appeared that also europium and erbium ions were soluble in the YAG nanocrystalline matrix. This behaviour was opposite to the case of cerium ions where the cubic CeO2 (cerianite) phase was observed together with YAG even for very low amount of doping.