Quadrupole coupling and crystal-field shielding in ${CaF}_{2}$ : ${Eu}^{3 +}$ : $O^{2 -}$ under hydrostatic pressure

The nuclear quadrupole interactions in the

{}^{7}F_{0}

ground electronic state and the

{}^{5}D_{0}

excited state of the

{}^{151}{Eu}^{3 +}

and

{}^{153}{Eu}^{3 +}

ions have been investigated by optical means. The optically detected nuclear quadrupole resonance, excitation, and luminescence of the

{Eu}^{3 +}

O^{2 -}

C_{3 v}

symmetry center have been studied at 4.2 K in single crystals of

{CaF}_{2}

:Eu:O under hydrostatic pressure up to 7.5 kbar. An energy-level diagram of the lower

{}^{7}F_{J}

electronic states has been established. The two dominating components of the hyperfine quadrupole energy for

{}^{151}{Eu}

have been determined:

P_{lat = - 22}

MHz,

P_{4 f}^{(2)}

(^{7}

F_{0}

)=+29 MHz. Their pressure derivatives are -20±2 and +16±2 kHz/kbar, respectively. The value of the crystal-field parameter

A_{2}^{0}

〈

r^{2}

〉=615

{cm}^{- 1}

has been found. From the experimentally determined sum of the electronic shielding factors (

R_{Q}

σ_{2}

)apeq20 it has been concluded that shielding of the crystal field at the 4

f^{6}

electronic shell is very small. The pressure derivatives of the...

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Quadrupole coupling and crystal-field shielding in CaF2:Eu3+:O2− under hydrostatic pressure