Luminescent mechanism of Eu3+-doped epitaxial Gd2O3 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 Gd2−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 → 7F2 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 (Rc) 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:Eu3+.