Systematics of 4f electron energies relative to host bands by resonant photoemission of rare-earth ions in aluminum garnets - art. no. 085107

energies of trivalent rare-earth ions relative to the host valence band wer e measured for a series of rare-earth-doped yttrium aluminum garnets RxY3-x Al5O12 (R=Gd, Tb, Dy, He, Er, Tm, Yb, and Lu and 0 less than or equal tox l ess than or equal to3), using ultraviolet photoemission spectroscopy. The 4 f photoemission spectra were acquired using synchrotron radiation, exploiti ng the 4d to 4f "giant resonance" in the 4f electron photoemission cross se ction to separate the 4f contribution. Theoretical valence band and 4f phot oemission spectra were fit to experimental results to accurately determine electron energies. The measured 4f(n) ground-state energies of these ions r ange from 700 meV above the valence band maximum for Tb3+ to 4.7 eV below t he valence band maximum for Lu3+, and all ground-state energies, except for Tb3+, are degenerate with valence band states. An empirical model is succe ssful in describing the relative energies of the 4f(n) ground states for ra re-earth ions in these materials. This model is used to estimate the positi ons of the lighter rare-earth ions, giving good agreement with published ex cited-state absorption and photoconductivity measurements on Ce3+ in yttriu m aluminum garnet. It is shown that the energies of the 4f electrons relati ve 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 stud ies of additional host compounds will rapidly lead to a broader picture of the effect of the host lattice on the 4f electron binding energies.