The Effects of Heat Treatment on the Crystallinity and Luminescence Properties of YInGe₂O₇ Doped with Eu³⁺ Ions

Yttrium indium germanate, YInGe₂O₇, doped with Eu³⁺ ions was synthesized by a solid-state reaction using a vibrating mill with metal oxides. The compound was characterized and its optical properties were investigated. The yielded powders were heated at various temperatures from 1100°C to 1400°C in air for 10 h. The X-ray diffraction profiles showed that all peaks could be attributed to the monoclinic YInGe₂O₇ phase at the various calcination temperatures for YInGe₂O₇ doped with 5 mol.% Eu³⁺ ions. A second phase of In₂O₃ was observed in the X-ray powder diffractometry pattern when the calcination temperature was over 1200°C. Scanning electron microscopy showed that the particle sizes increased significantly with increasing calcination temperature. The calcined powders emitted a reddish luminescence centered at 611 nm under excitation of 393 nm due to the electric dipole transition ⁵D₀ → ⁷F₂. Powders fired at 1200°C were found to have the maximum photoluminescent intensity for YInGe₂O₇ doped with 5 mol.% Eu³⁺ ions. Furthermore, the existence of the second phase caused the decay time to decrease with increasing calcination temperature.