Ultraviolet Absorption Spectra of $\Pr^{3 +}$ Ion in Alkaline-Earth Fluorides

The ultraviolet absorption spectra of

\Pr^{3 +}

in Ca

F_{2}

, Sr

F_{2}

, and Ba

F_{2}

have been measured at room and liquid-nitrogen temperatures. These spectra are similar to those of

{Ce}^{3 +}

reported previously except that

\Pr^{3 +}

absorptions generally occur at higher photon energies. This general similarity between the uv absorption spectra of

{Ce}^{3 +}

and

\Pr^{3 +}

in solids indicates that the crystal field is dominant in the higher configurations,

5 d

and

6 s

, of rare-earth ions in solids. For

\Pr^{3 +}

in Ca

F_{2}

the three interconfigurational transitions are: (1)

4 f \to 5 d

between 44 000 and 69 000

{cm}^{- 1}

; (2) a possible

4 f \to 6 s

at ∼76 000

{cm}^{- 1}

; (3) a charge transfer

F^{-} (2 p^{6}) \to \Pr^{3 +} (6 s)

near ∼80 000

{cm}^{- 1}

. Other effects, such as vibronics in the lowest

4 f \to 5 d

band and their concentration dependence, the effect of cluster formation on

4 f \to 5 d

bands, and the crystal effect on the free-ion data, are all similar to the previously reported data on

{Ce}^{3 +}

in alkaline-earth fluorides. The cross section of

{}^{1}S_{0}

absorption of

\Pr^{3 +}

in Ca

F_{2}

is estimated to be concentration-independent, which is consistent with the shielded character of

4 f \to 4 f

transitions. Absorption to the

{}^{1}S_{0}

state and the vibronics are also observed in Ba

F_{2}

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Ultraviolet Absorption Spectra ofPr3+Ion in Alkaline-Earth Fluorides