The ${}^4{F}_{3/2}$ state of Nd${}^{3+}$ dopant ions is split due to the crystal field at orthorhombic $D_2$ symmetry sites in several members of the garnet family of crystals. In the gadolinium-gallium garnet crystal this splitting is found to almost disappear under hydrostatic pressures between 8 and 11 GPa created in the diamond-anvil cell. This pressure is much lower than that required for the phase transition to the so called high-pressure phase. This effect is explained with help of x-ray diffraction, optical spectroscopy, and ab initio calculations as an effect of accidental near-degeneracy arising from a particular lattice structure of garnets.

• Received 30 October 2010

DOI:https://doi.org/10.1103/PhysRevB.84.075483