Excited-state absorption spectra for optically forbidden f-f transitions in an Eu3+: Y2SiO5 crystal and Eu3+ aqueous solution

摘要

Extremely small transmission change spectra due to 4f-4f transitions in a rare-earth ion Eu3+ in a crystal and in an aqueous solution were measured, to the best of our knowledge, for the first time. By multichannel double-lock-in pump-probe spectroscopy, photoluminescence (PL) and difference transmission spectra were simultaneously recorded for an Eu3+:Y2SiO5 crystal with broadband lamp light sources for both the pump and the probe. A very weak transmission change signal hidden behind a 1-2 orders of magnitude more intense PL background signal was readily extracted. By comparing the transmission decrease due to the excited-state absorption (ESA) and the transmission increase due to the ground-state depletion it was found in the crystal that the oscillator strengths for the f-f transitions to the same final states are of the same order of magnitude for both the spin-allowed transitions from D-5(0) in the ESA and the spin-forbidden transitions from F-7(0) in the ground-state absorption (GSA). In addition, crystal-field split f-f transitions that have been hidden by the intense charge-transfer band in the GSA were revealed. (C) 2008 Optical Society of America.