Abstract
Recently efficient blue‐white luminescence from 
was reported. The emission was assigned to a ligand‐to‐metal charge‐ transfer transition of 
. Charge transfer (CT) emission from 
, or any other tetravalent lanthanide, had not been reported previously. Here, further research on the luminescence of 
is reported. Three topics are discussed. First the nature of the luminescence is investigated. The results provide evidence that the efficient blue‐white emission is not related to a lattice defect and support the assignment of the emission to a 
CT transition. Second, lifetime measurements are discussed. The life‐ time, 65 ± 5 μs at 6 K, is long for a parity allowed CT transition. The spin‐forbidden nature of the emission can explain the observed lifetime. Finally, the temperature dependence of the emission intensity and luminescence lifetime is investigated. At 300 K both the emission intensity and the lifetime are reduced to about 50% of the values at 6 K. This shows that the quantum efficiency measured to be about 40% at room temperature is close to the maximum efficiency at room temperature. The low quenching temperature is a serious drawback for application of 
as a phosphor in lighting. © 2000 The Electrochemical Society. All rights reserved.