Zero-phonon structures in the optical spectra of some transition-metal ions in CdSe crystals

TLDR: In this paper, a zero-phonon line was detected at the 14 175-degree line at the center of the Jahn-Teller interaction, which may be related to an antiresonance of the spin-orbit coupling.

Abstract: Zero-phonon structures of the ${\mathrm{Fe}}^{2+}$ $3{d}^{6}^{5}E(D)\ensuremath{\leftrightarrow}^{5}T_{2}(D)$ transition in absorption and emission include a coinciding line at 2376 ${\mathrm{cm}}^{\ensuremath{-}1}$. Polarized transmission spectra of the ${\mathrm{Co}}^{2+}$ $3{d}^{7}$ transition $^{4}A_{2}(F)\ensuremath{\rightarrow}^{4}T_{1}(P)$ display components split by second-order spin-orbit coupling and indicate an autoionization effect at the 14 175-${\mathrm{cm}}^{\ensuremath{-}1}$ line. Symmetry arguments support the interpretation of this antiresonance by a ${\mathrm{Co}}^{2+}\ensuremath{\rightarrow}{\mathrm{Co}}^{3+}$ charge-transfer process with a threshold at about 13 800 ${\mathrm{cm}}^{\ensuremath{-}1}$. The $^{4}T_{2}(F)\ensuremath{\rightarrow}^{4}A_{2}(F)$ luminescence transition of ${\mathrm{Co}}^{2+}$ gives rise to a zero-phonon line at 2867 ${\mathrm{cm}}^{\ensuremath{-}1}$. The fine structure of the $^{3}T_{1}(F)\ensuremath{\rightarrow}^{3}T_{1}(P)$ absorption of ${\mathrm{Ni}}^{2+}$ $3{d}^{8}$ suggests a strong reduction of spin-orbit coupling by the Jahn-Teller interaction. With ${\mathrm{Ni}}^{2+}$ ions, radiative recombination from the $^{3}T_{1}(P)$, $^{3}A_{2}(F)$, and $^{3}T_{2}(F)$ levels to the $^{3}T_{1}$ ground state is detected, and the first and the last transitions exhibit zero-phonon lines at 10 926 and 3607 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively. An abundant novel emission band characterized by a zero-phonon transition at 10 170 ${\mathrm{cm}}^{\ensuremath{-}1}$ may be related to an $M$ center, i.e., a ${({V}_{\mathrm{Se}}^{\ensuremath{-}}{V}_{\mathrm{Se}}^{\ensuremath{-}})}^{2+}$ associated defect.