Luminescence of Cadmium Fluoride Doped with Rare-earth Ions

Absorption, excitation and emission spectra of cadmium fluoride crystals doped with rare-earth ions were investigated. In contrast to alkaline-earth fluorides the absorption spectra due to 4f-5d transitions of Ce³⁺, Pr³⁺ and Tb³⁺ ions are broadened. No 5d-4f emissions were observed. These prove that 5d( eg) levels of rare earth ions lie in conduction band of CdF2 crystal. Emission spectra of Tb³⁺ show the group of 4f-4f ⁵D4-⁷Fj lines in contrast to other alkaline-earth fluorides where emission due to ⁵D3-⁷Fj transitions is also observed. The absence of the emission is due to position of ⁵D₃ level within condution band. Among the all measured crystals doped with impurity ions (Pr, Nd, Eu, Ho, Tb, Tm, Yb, Ga, In or Mn), the CdF₂ doped with Pr³⁺, Tb³⁺, or Mn²⁺ ions have the highest light outputs under X-ray excitation.