Luminescent mechanism of Eu³⁺-doped epitaxial Gd ₂O₃ films grown on a Si (111) substrate using an effusion cell

Eu³⁺-doped epitaxial Gd₂O₃ (111) films with well-ordered crystalline structures were grown on oxidized Si (111) using the physical vapor deposition method. The mole fraction (x) of Eu³⁺ in Gd_2-xO₃:Eu³⁺_x ranged from 0.02 to 0.22. The photoluminescence characteristics, measured at an excitation wavelength of 254 nm, showed that even at the very low Eu³⁺ concentration, x = 0.18, the ⁵D₀ → ⁷F ₂ transition occurred at the maximum 612-nm emission. Based on the critical distance calculated using the decay curves at 612 nm, we proved that the ⁵D₀ → ⁷F₂ transition of the Gd₂O₃:Eu³⁺ originated from an electric dipole-dipole transition. In addition, the critical distance (R_c) was greater than that reported previously due to the perfectly crystalline film. This significantly decreases the mole fraction which maximize the photoluminescence intensity because the non-radiative transition is much lower than that of the chemically synthesized Gd₂O₃:Eu ³⁺.