Systematics of (formula presented) electron energies relative to host bands by resonant photoemission of rare-earth ions in aluminum garnets

Abstract

The energies of trivalent rare-earth ions relative to the host valence band were measured for a series of rare-earth-doped yttrium aluminum garnets (formula presented) Tb, Dy, Ho, Er, Tm, Yb, and Lu and (formula presented) using ultraviolet photoemission spectroscopy. The (formula presented) photoemission spectra were acquired using synchrotron radiation, exploiting the (formula presented) to (formula presented) “giant resonance” in the (formula presented) electron photoemission cross section to separate the (formula presented) contribution. Theoretical valence band and (formula presented) photoemission spectra were fit to experimental results to accurately determine electron energies. The measured (formula presented) ground-state energies of these ions range from 700 meV above the valence band maximum for (formula presented) to 4.7 eV below the valence band maximum for (formula presented) and all ground-state energies, except for (formula presented) are degenerate with valence band states. An empirical model is successful in describing the relative energies of the (formula presented) ground states for rare-earth ions in these materials. This model is used to estimate the positions of the lighter rare-earth ions, giving good agreement with published excited-state absorption and photoconductivity measurements on (formula presented) in yttrium aluminum garnet. It is shown that the energies of the (formula presented) electrons relative to the valence band can be estimated from the photoemission spectrum of the undoped host, providing a simple method for extending these results to related host crystals. The success of this model suggests that further studies of additional host compounds will rapidly lead to a broader picture of the effect of the host lattice on the (formula presented) electron binding energies. © 2001 The American Physical Society.