Systematic Analysis of the Crystal Chemistry and Eu3+ Spectroscopy along the Series of Double Perovskites Ca2LnSbO6 (Ln = La, Eu, Gd, Lu, and Y)

Eu3+ (1 mol %)-doped Ca(2)LnSbO(6) (replacing Ln(3+); Ln = Lu, Y, Gd, and La) and Ca2EuSbO6 were synthesized and structurally characterized by means of X-ray powder diffraction. The Eu' luminescence spectroscopy of the doped samples and of Ca2EuSbO6 has been carefully investigated upon collection of the excitation/emission spectra and luminescence decay curves of the I main excited states. Surprisingly, apart from the dominant red emission from D-5(0), all the doped samples show an uncommon blue and green emission contribution from D-5(J) (J = 1, 2, and 3). This is made possible thanks to both multiphonon and cross-relaxation mechanism inefficiencies. However, the emission from D-5(3) is more efficient and the decay kinetics of the D-5(J) (J = 0, 1, and 2) levels is slower in the case of Y- and Lu-based doped samples. This evidence can find a possible explanation in the crystal chemistry of this family of double perovskites: our structural investigation suggests an uneven distribution of the Eu3+ dopant ions in Ca2YSbO6 and Ca2LuSbO6 hosts of the general A(2)BB'O-6 formula. The luminescent center is mainly located in the A crystal site, and on average, the Eu-Eu distances are longer than in the case of the Gd- and La-based matrix. These longer distances can further reduce the efficiency of the cross-relaxation mechanism and, consequently, the radiative transitions are more efficient. The slower depopulation of Eu3+ D-5(2) and D-5(1) levels in Ca2YSbO6 and Ca2LuSbO6 hosts is reflected in the longer rise observed in the 'D, and s D o decay curves, respectively. Finally, in Ca2EuSbO6, the high Eu3+ concentration gives rise to an efficient cross-relaxation within the subset of the lanthanide ions so that no emission from D-5(J) = 1, 2, and 3) is possible and the D-5(0) decay kinetics is faster than for the doped samples.