Luminescence properties of Eu3+ doped CaMoO4nanoparticles

Abstract

When Eu³⁺ ions occupy Ca²⁺ sites of CaMoO₄, which has a body centered tetragonal structure with inversion symmetry, only the magnetic dipole transition (⁵D₀→⁷F₁) should be allowed according to Judd–Ofelt theory. Even if there are a few distortions in the Eu³⁺ environment, its intensity should be more than that of the electric dipole transition (⁵D₀→⁷F₂). We report here the opposite effect experimentally and ascribe this to the polarizability effect of the MoO₄ tetrahedron, which is neighboring to EuO₈ (symmetric environment). The contribution of the energy transfer process from the Mo–O charge transfer band to Eu³⁺ and the role of Eu³⁺ over the surface of the particle could be distinguished when luminescence decay processes were measured at two different excitations (250 and 398 nm). Further, the luminescence intensities and lifetimes increase significantly with increasing heat-treatment temperature of the doped samples. This is attributed to the reduction of H₂O from the surface of the particles and a non-radiative process after heat treatment.