Structural and spectroscopic properties of Eu3+ doped Y4Al2O9 compounds through a soft chemical process

Abstract

The present work reports on the synthesis, structural and optical properties of (Y1-xEux)4Al2O9 powders, with x ranging from 0.001 to 0.030. We prepared the materials using a modified polymeric precursors method, and the effect of annealing temperature and Eu3+ concentrations were evaluated. Structural and microstructural parameters, such as cell parameters, crystallite size and grain size were determined and evaluated by using the results from X-ray diffraction and high-resolution transmission electron microscopy techniques. An annealing temperature of 800 °C was enough to obtain single Y4Al2O9 crystalline phase with good distribution of Eu3+ ions. Diffuse reflectance spectra and optical bandgap of 4.52 eV for (Y0.995Eu0.005)4Al2O9 – determined by Kubelka-Munk model – showed good optical quality of the samples, which were considered non-conducting. All doped samples possessed visible photoluminescence emission from Eu3+ ions under excitation at 393 nm, with higher emissions occurring in the red region from 5D0 → 7F2 transition, with R/O relation of 1.69 for the sample with x = 0.010. Analyzing photoluminescence emission spectra, the lifetime values and Judd-Ofelt parameters, we determined that Eu3+ occupied three different sites of the Y4Al2O9 (YAM) structure, replacing Y3+ ions, with the quenching concentration occurring between x = 0.020 and x = 0.030. We noted that Eu3+ ions are in a chemical environment with low polarization, and their degree of covalence is low. Finally, samples with x = 0.020 (Y0.980Eu0.020)4Al2O9 seems to be useful as red phosphors.