Photoluminescence of europium(III)-doped (Y_xSc_1-x)₂O₃ nanoparticles: Linear relationship between structural and emission properties

Europium (III)-doped (Y_xSc_1-x)₂O₃ nanocrystalline powders of different compositions (x=0, 0.25, 0.5, 0.75 and 1) are synthesized using a polymer complex solution method. Comparative structural and optical characterization is carried out with powder X-ray diffraction and photoluminescence excitation, emission and emission decay measurements. Detailed information about unit cell parameter and energy levels of europium (III) ions are presented for all powder compositions. The second rank crystal field parameters (B02) and (B22) and crystal field strength (N_v) are calculated from the energies of Stark components of the ⁷F₁ manifold of the europium (III) emissions. It has been shown that the crystal field parameter changes with the powder composition and shows a linear relationship with the average ionic radii of cations in the solid solutions. A similar dependence is also found for the magnitude of splitting of ⁷F₁ manifold vs. unit cell parameter values. Moreover, this linear relationship is demonstrated for the whole family of europium (III)-doped mixed rare-earth sesquioxide hosts (RR'O₃; R, R′=rare earth ions) by taking into consideration results published in the literature so far. A simple, semi-empirical equation which relates structural properties (unit cell parameters, ionic radii) of the sesquioxide host material and the emission properties of europium (III) ions (energy splitting of the ⁷F₁ manifold, crystal field parameters and crystal field strength) are presented.