Charge Transfer Luminescence of YB3+

In this century, luminescence of rare earth ions has been well studied. Since the application of luminescence from rare earth ions in fluorescent tubes, colour television and X-ray phosphors, numerous papers have appeared on 4fⁿ-4fⁿ and 4f^n-15d-4fⁿ emissions. One kind of rare earth luminescence is still relatively unknown: charge transfer luminescence. This transition is the reverse of the well-known charge transfer absorption. Until now only three papers have reported on luminescence from the charge transfer state (CTS) of a rare earth ion [2, 3, 4] although the CTS is important for applications. For example in the red phosphor used in fluorescent tubes (Y₂O₃:Eu³⁺), UV radiation from the Hg-discharge is efficiently absorbed in the CTS of the Eu³⁺ - ion. After nonradiative decay to the lower ⁵D_J states, luminescence occurs. In Eu³⁺ luminescence from the CTS can not be observed, because there will always be fast relaxation to the lower 4f levels...