Comparative structural and photoluminescent study of Eu3+-doped La2O3 and La(OH)3 nanocrystalline powders Original Research Article

Eu3+-doped La2O3 nanocrystalline powder was prepared by polymer complex solution method and further used for preparation of Eu3+-doped La(OH)3. Structural and optical characterization was carried out by powder X-ray diffraction and photoluminescent spectroscopy. XRD measurements confirmed the formation of hexagonal La2O3 and its recrystallization into La(OH)3 in a humid atmosphere. Excitation spectra show redshift of host lattice and charge transfer emission bands in La(OH)3 while bands that correspond to Eu3+f–f transitions are placed at same wavelengths in both samples. Photoluminescence spectra recorded over the temperature range from 10 K to 300 K show that intensities of emission lines in Eu3+-doped La2O3 do not depend on temperature as much as in La(OH)3 sample. Observed dominant 5D0→7F2 and markedly visible 5D0→7F0 emissions in doped La2O3 indicate that Eu3+ ion is located in a structural site without an inversion center. On the other hand, in Eu3+-doped La(OH)35D0→7F0 transition is barely visible while 5D0→7F2 is not prominent, and with temperature drop three 5D0→7FJ (J=1, 2, 4) transitions become almost of the same intensity. In both La2O3 and La(OH)3 structures Eu3+ ion replaces La3+ in non-centrosymmetric C3v and C3h crystallographic sites, respectively, and difference in symmetry of the crystal field around europium ion is explained by comparing shape and volume of these sites. Decay times of the 5D0- level recorded over the temperature range 10−300 K revealed that emission lifetime values in La2O3 (~0.7 ms) are almost two times higher than in La(OH)3 (~0.4 ms), and unlike in La2O3, lifetime in La(OH)3 is temperature dependent.