Luminescence properties of Tb3Al5O12 garnet and related compounds synthesized by the metal organic decomposition method

The Tb-Al-O ternay compounds were prepared by the metal organic decompostion (MOD) method from mixted solutions of Al2O3 and Tb4O7 and subsequent calcination at Tc=1200 °C in air. The structural and optical properties of the synthesized compounds were examined using X-ray diffraction analysis, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, PL decay kinetics, and diffuse reflectance spetrosopy. The stoichiometric compounds of terbium aluminium garnet Tb3Al5O12 (TAG) and peroviskite-type TbAlO3 were synthesized at molar ratios of x=0.375 and 0.5 [x ≡Tb4O7/(Tb4O7+2Al2O3)], together with the end-point binary materials of rhombohedral Al2O3 (α-Al2O3; x=0) and cubic Tb4O7 (x=1.0). One can also expect synthesis of stoichiometric compounds Tb4Al2O9 and Tb3AlO12 at x=0.667 and 0.75, respectively; however, these compounds were found to be very difficult to synthesize by the MOD method or, probably by other methods. Temperature dependence of the PL spectra for TAG was measured from T=20-440 K in 10-K step and analyzed using a newly developed theoretical model. Raman scattering measurements were also performed on the Tb-Al-O material system with compositions widely varying from x=0 (α-Al2O3) to 1.0 (Tb4O7).