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

Abstract

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 D-5(0) - GT :F-7(2) and markedly visible D-5(0)- GT F-7(0) 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)3 D-5(0)- GT F-7(0) transition is barely visible while D-5(0)- GT F-7(2) is not prominent, and with temperature drop three D-5(0)- GT F-7(j) (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 C-3v and C-3h 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. (C) 2013 Elsevier Ltd. All rights reserved.