Energy transfer between Tb³⁺ and Eu³⁺ in co-doped Y₂O₃ nanocrystals prepared by Pechini method

Tb³⁺ and Eu³⁺ co-doped Y₂O₃ nanoparticles with a volume-weighted average size of about 30 nm were synthesized via simple Pechini-type sol–gel process. The growth of monocrystalline nanoparticles is investigated via XRD and TEM analysis. The study of energy transfer between Tb³⁺ and Eu³⁺ ions was carried out by means of PL, PLE, and photoluminescence decay analyses. The energy transfer from Tb³⁺ to Eu³⁺ is efficient and we show how a resonant type via a dipole–dipole interaction is the most probable mechanism. We compared the energy-transfer efficiencies calculated from the intensities and from the lifetimes of \({}^5\hbox{D}_4 \longrightarrow ^7\hbox{F}_5\) transition of Tb, showing the presence of two populations of Tb, with different local surroundings, in the matrix. Furthermore, the critical distance between Tb³⁺ and Eu³⁺ ions has been calculated by means of different theories, from a new probabilistic approach based on the discretization of the theory of Chandrasekhar about the distribution of the nearest neighbors in a random distribution of particles, and from the PL data, suggesting a value of about 7 Å.