Structural and spectroscopic studies of Eu³⁺ doped Lu ₂O₃-Gd₂O₃ solid solutions

A series of europium doped (Lu_xGd_1-x) ₂O₃ (x = 1, 0.75, 0.5, 0.25 and 0) nanocrystalline powders were prepared using a polymer complex solution method based on a polyethylene glycol (PEG) as fuel. The samples were systematically characterized by powder X-ray diffraction, scanning and transmission electron microscopies and luminescence spectroscopy. The powders consisted of well-crystalline, cubic phase nanoparticles of 20-50 nm in size, which unit cell parameter increased with Gd content complying with Vegard's law. Upon blue light excitation all samples exhibited strong red luminescence typical of trivalent europium ion. The maximum splitting of the ⁷F₁ manifold changed linearly with the composition change and decreased with lowering of the crystal field strength. Relatively long lifetime values were obtained for ⁵D ₀ (∼1.4 ms) and ⁵D₁ (∼120 μs) levels. For all samples we estimated theoretical densities, refractive index coefficients, optical filling factors and Z_eff, in order to estimate the Judd-Ofelt intensity parameters and branching ratios. The calculated lifetime of ⁵D₀ level was in line with experimentally obtained luminescence lifetime values. Relative integrated emissions were measured on all samples and Gd₂O₃ sample proved to have a maximum amount of the characteristic Eu³⁺ luminescence.