Identification of electronic Stark levels in Yb/sup 3+/-doped sesquioxides by pair spectroscopy

Summary form only given. Ytterbium doped insulators have been subject of intensive research for their unique spectroscopic properties as well as for their laser properties. A central problem is the exact assignment of the electronic Stark levels of the Yb/sup 3+/-ions. Due to strong electron phonon coupling the unambiguous identification of the Yb Stark levels is not possible for many materials, including the well known Y/sub 3/Al/sub 5/O/sub 12/. Yb/sup 3+/ has only one excited 4f state separated by about 10,000 cm/sup -1/ from the ground state. This allows the study of extremely weak pair transitions within the bandgap of the host material which in most rare earth ions are covered by other 4f states. Pair effects in Yb-systems have been first observed by Nakazawa in 1970. Pair transitions show a much lower electron phonon coupling than single ion transitions, which allows to assign the electronic levels with much more clarity.