Energy levels and optical spectroscopy of Er3+ in Gd2O3 nanocrystals

Based on the high-resolution excitation and emission spectra at 10 and 297 K, we have determined 107 crystal-field (CF) levels below 43 000 cm(-1) of Er3+ at the C-2 site of Gd2O3 nanocrystals. The levels were analyzed in terms of 16 free-ion and 14 CF parameters. The CF modeling of the experimental energy levels yielded physically reasonable Hamiltonian parameters with a final root-mean-square deviation of 12.5 cm(-1). A modified Judd-Ofelt (JO) intensity analysis was proposed in evaluating the spectroscopic parameters such as JO parameters, radiative lifetime, and branching ratios for rare-earth ions doped in nanocrystals. Three JO parameters were obtained (Omega(2,4,6) = 4.96, 2.23, and 0.49, in units of 10(-20) cm(2)). The effect of J-mixing was taken into account in the energy-level-fitting and in the J-J' transition intensity calculation, which is observed to be responsible for the significant increase of the radiative transition rate of S-4(3/2). Furthermore, the luminescence lifetimes of several excited multiplets of Er3+ were measured, and vibronic side bands and self-absorption were observed in the 10 K emission spectrum.