Spectroscopy of ytterbium-doped InP under high hydrostatic pressure

Abstract

The results of high-pressure low-temperature optical measurements in diamond-anvil cell of bulk indium phosphide crystals doped with Yb are reported. The observed initial increase in energy of $f\text{\ensuremath{-}}f$ intrashell transitions between the ${^{2}F}_{5/2}$ excited and ${^{2}F}_{7/2}$ ground levels at pressure up to 6 GPa is interpreted as a result of a linear increase in the spin-orbit parameter of ${\text{Yb}}^{3+}$ ions with pressure coefficient equal to $0.0059\text{ }{\text{cm}}^{\ensuremath{-}1}/\text{GPa}$ due to the covalency effects and mixing of the ${\text{Yb}}^{3+}$ and phosphorus wave functions. Above 6 GPa the pressure dependences of the peak positions of all the luminescence lines flatten out and the values of pressure coefficients strongly decrease. A tentative explanation is provided in terms of the $f$ levels of ${\text{Yb}}^{3+}$ approaching of the top of the valence band of InP crystal host, which limits further increase in $f\text{\ensuremath{-}}f$ intrashell transitions energies above 6 GPa pressure.