An optical spectral-hole burning technique has been used to study the nuclear quadrupole splitting in the ground state of ${}_{}{}^{243}{}_{}{}^{}\mathrm{Am}_{}^{3+}{}_{}{}^{}$ in ${\mathrm{LaCl}}_3$. The observed splitting is consistent with ${\mathrm{Am}}^{3+}$ ions on an axially symmetric site. The nuclear quadrupole coupling constant P=-75±1 MHz for the ${}_{}{}^7{}_{}{}^{}$${\mathit{F}}_0$ ground state is obtained based on an effective operator Hamiltonian. The crystal-field antishielding effect dominates whereas contributions from the 5f electrons and from the pseudoquadrupole interaction are negligible (${\mathit{P}}_{5\mathit{f}}$/${\mathit{P}}_{\mathrm{latt}}$=0.03). The Sternheimer antishielding factor, ${\gamma }_{\mathrm{\infty }}$=-154, is determined and comparison is made between the actinide ion ${\mathrm{Am}}^{3+}$ and its rare-earth analogy ${\mathrm{Eu}}^{3+}$. © 1996 The American Physical Society.

• Received 30 October 1995

DOI:https://doi.org/10.1103/PhysRevB.53.2385