Microwave synthesis of YAG:Eu by sol-gel methodology

Yttrium-aluminum oxides are interesting compounds and they have been extensively used as host for lasers and phosphors, due to their stable physical and chemical properties. The fabrication of yttrium-aluminum garnet (YAG) has been investigated thoroughly. Single-crystal YAG is expensive and to produce it a new way has been investigated. This process consists of modifying the methodology of reagents mixture and the process of heating them. The microwave irradiation is used to heat-treat the oxide mixture. The traditional synthesis of YAG powders occurs through the reaction of aluminum and yttrium powders at high temperatures. With this work we investigated the preparation of YAG by non-hydrolytic sol-gel route as an alternative methodology to obtain yttrium-aluminum matrix from inorganic precursors (yttrium and aluminum chloride). The preparation of the gel was carried out in an oven-dried glassware. The AlCl₃, YCl₃ and ethanol were reacted in reflux under argon atmosphere. Europium III chloride was added as a structural probe. The powder was dried and heat-treated in modified microwaves. The samples were pre-treated at 50 and 800^oC during 1 h and then heated in microwaves for 30 s, 2 and 4 min. The formation process and structure of the powders were studied by means of X-ray diffraction (XRD), photoluminescence (PL) and transmission electronic microscopy (TEM). XRD presents only picks corresponding to the YAG phase and confirmed by TEM. PL date showed that the YAG phase was formed in 2 min with the samples pre-treated at 50 °C. For the samples pre-treated at 800 °C, the YAG phase appears in 30 s. The excitation spectra present a maximum of 394 nm corresponding to the ⁵L₆ level and emission spectra of Eu III ion present bands characteristic transitions arising from the ⁵D₀→⁷F_J (J=1, 2, 3, 4) monifolds excited at their maximum. The magnetic dipole ⁵D₀→⁷F₁ transition presents more intensity than the electric dipole ⁵D₀→⁷F₂ transition. This methodology showed efficiency in obtaining YAG phase.