The luminescent properties of hexagonal NaY,,.,~_.,.Gd.rCe,,.,~,Tbo.0,F4 have been investigated. For x > 0.45 and at room temperature, excitation into the Ce 3+ ion (k~.• = 254 nm) results mainly in Tb :~+ emission. We also observed two different Ce :~+ emissions. This is related to the crystal structure of NaGdF4:Ce,Tb. It is shown that the excitation energy migrates from the Ce 3+ ion over the Gd ~ sublattice to the Tb :~+ traps. Energy transfer probabilities for this process are derived and compared with the probabilities derived for the system LiGdF~:Ce,Tb, which leads to some recommendations for the use of the Ce ' ~+ ion as a sensitizer of the Gd :~+ ion.

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For x > 0.45 in NaY0.98‐xGdxCe0.01Tb0.01F4 and at room temp., excitation of the Ce3+ ion (254 nm) results mainly in Tb3+ emission and also in two different Ce3+ emissions.