Spectral hole burning and energy level structure of Tb3+:LiYF4

To investigate the potential for photon-gated hole burning through two-step photoionization in Tb3+:LiYF4, energies of the 4f8 and 4f75d levels relative to the host band states were determined. From X-ray photoemission spectroscopy, the 4f8 ground-state binding energy was found to be in the band gap at 2.9 eV above the valence band maximum. The effects of electron–lattice coupling on ionization processes were considered, and it was determined that the level at 54950 cm−1 is the lowest 4f75d state that will produce ionization. Those results were extended to other rare-earth ions in LiYF4. High-resolution spectral hole burning on the 7F6–5D4 transition displayed hole/anti-hole structure attributed to population redistribution among the Tb3+ hyperfine levels with additional sidebands due to 7Li and 19F nuclear spin flips.