Abstract
We have measured the room temperature (RT) and 20 K luminescence lifetime of ${\mathrm{Cr}}^{3+}$ in yttrium aluminum garnet as a function of pressure up to 240 kbar. The RT lifetime changed from 1.7(1) ms at ambient pressure to 42(2) ms at 220 kbar and the 20 K lifetime from 8.8(1) ms at ambient pressure to 67(2) ms at 240 kbar, the largest value ever observed for a ${\mathrm{Cr}}^{3+}$-doped material. The distinct pressure dependences of the RT and 20 K lifetimes allowed us to clearly distinguish the contributions of electronic radiative decay, ${}^{2}E{\ensuremath{\rightarrow}}^{4}{A}_{2}$ vibronic transitions, and the thermal population of the ${}^{4}{T}_{2}$ state to the ${}^{2}E{\ensuremath{\rightarrow}}^{4}{A}_{2}$ transition of ${\mathrm{Cr}}^{3+}.$ Analysis of the temperature dependence of the ambient-pressure lifetime showed that both the ${}^{2}E{\ensuremath{\rightarrow}}^{4}{A}_{2}$ and ${}^{4}{T}_{2}{\ensuremath{\rightarrow}}^{4}{A}_{2}$ vibronic transitions have a significant effect on the ${}^{2}E{\ensuremath{\rightarrow}}^{4}{A}_{2}$ luminescence lifetime. Within the context of the single configurational coordinate model, the coupling of the ${}^{2}E$ and ${}^{4}{T}_{2}$ states via the spin-orbit coupling $({\mathcal{H}}_{\mathrm{SO}})$ and the electron-phonon coupling $({\mathcal{H}}_{\mathrm{EP}})$ mechanisms was considered in describing the observed lifetime as a function of pressure. Models formulated in either the ${\mathcal{H}}_{\mathrm{EP}}>{\mathcal{H}}_{\mathrm{SO}}$ or ${\mathcal{H}}_{\mathrm{SO}}>{\mathcal{H}}_{\mathrm{EP}}$ perturbation schemes agreed well with the lifetime data.
Published Version
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