Energy levels, fluorescence lifetime and Judd-Ofelt parameters of Eu3+ in Gd2O3 nanocrystals

Crystal-field (CF) levels below 36 000 cm(-1) of Eu3+ at the C-2 site of Gd2O3 nanorods are experimentally determined from the excitation and emission spectra at 10 K. The levels are analysed in terms of 20 freely varied free-ion and CF parameters, and energy-level fit yields a final standard deviation of 12.9 cm(-1), showing very good agreement between the observed and the calculated values. The Judd - Ofelt (JO) intensity parameters Omega(2,4,6) are determined to be 12.39, 2.02 and 0.19 ( in 10(-20) cm(2)) which takes J-mixing into account. For the first time the absolute value of the Omega(6) parameter is reliably determined. The calculated radiative transition rates and branching ratios for the transitions from D-5(0) agree well with the experiments. The size dependence of the JO intensity parameters of Eu3+ in RE2O3 (RE = Y, Gd, Lu) nanocrystals is clarified. The fluorescence lifetime of D-5(0) of Eu3+ in Gd2O3 nanorods is observed to be significantly affected by the surrounding media, giving rise to a filling factor of 0.58 for the nanoparticles.