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Lowest 4 f → 5 d Transition of Trivalent Rare-Earth Ions in Ca F 2 Crystals

1966; American Institute of Physics; Volume: 147; Issue: 1 Linguagem: Inglês

10.1103/physrev.147.332

1536-6065

Eugene Loh,

Glass properties and applications

The lowest $4f\ensuremath{\rightarrow}5d$ ultraviolet absorption band of eleven (Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) of the fourteen trivalent rare-earth (RE) ions in host Ca${\mathrm{F}}_{2}$ crystals has been measured. The room temperature absorption cross section [${\mathrm{cm}}^{2}$] and half-width [${\mathrm{cm}}^{\ensuremath{-}1}$] of these bands for the first-half series of ${\mathrm{RE}}^{3+}$ are larger than that of the second-half series (from ${\mathrm{Tb}}^{3+}$ on), possibly because of some spin-forbiddenness in the transition of the latter. Typically, they are \ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ and \ensuremath{\sim}1700 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, for the former and \ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ and \ensuremath{\sim}1300 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, for the latter at typical concentration of \ensuremath{\sim}${10}^{\ensuremath{-}4}$. The oscillator strength is estimated to be \ensuremath{\sim}${10}^{\ensuremath{-}2}$ for the first half-series and \ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ for the second half-series ${\mathrm{RE}}^{3+}$. At liquid nitrogen temperature the band sharpens and shifts \ensuremath{\sim}200 ${\mathrm{cm}}^{\ensuremath{-}1}$ toward lower wave number, probably because of increasing crystal field in the contracted lattice; a zero-phonon line and some vibrational structure are also developed in ${\mathrm{Ce}}^{3+}$-and ${\mathrm{Pr}}^{3+}$-doped Ca${\mathrm{F}}_{2}$. The location of the band ranges from \ensuremath{\sim}33 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ (${\mathrm{Ce}}^{3+}$) to \ensuremath{\sim}71 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ (${\mathrm{Yb}}^{3+}$), with that of ${\mathrm{Gd}}^{3+}$ and ${\mathrm{Lu}}^{3+}$ outside (\ensuremath{\gtrsim}80 000 ${\mathrm{cm}}^{\ensuremath{-}1}$) of the transparent region of Ca${\mathrm{F}}_{2}$ crystal. Compared with the data available for the free ions ${\mathrm{Ce}}^{3+}$, ${\mathrm{Pr}}^{3+}$, and ${\mathrm{Yb}}^{3+}$, the location of the lowest $4f\ensuremath{\rightarrow}5d$ transition of ${(\mathrm{RE})}^{3+}$ ions in Ca${\mathrm{F}}_{2}$ is found to be lowered \ensuremath{\sim}18 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ in the crystal environment. The energy of the lowest $4f\ensuremath{\rightarrow}5d$ transition is described satisfactorily by a formula due to J\o{}rgensen for $4{f}^{n}\ensuremath{\rightarrow}4{f}^{n\ensuremath{-}1} 5d$ transitions in the free ion, decreased by 18 000 ${\mathrm{cm}}^{\ensuremath{-}1}$.