Effect of pressure and temperature on the lifetime ofCr3+in yttrium aluminum garnet

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, ${}^{2}E{\to }^4{A}_2$ vibronic transitions, and the thermal population of the ${}^4{T}_2$ state to the ${}^{2}E{\to }^4{A}_2$ transition of ${\mathrm{Cr}}^{3+}.$ Analysis of the temperature dependence of the ambient-pressure lifetime showed that both the ${}^{2}E{\to }^4{A}_2$ and ${}^4{T}_2{\to }^4{A}_2$ vibronic transitions have a significant effect on the ${}^{2}E{\to }^4{A}_2$ 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 $\left({\mathcal{H}}_{\mathrm{SO}}\right)$ and the electron-phonon coupling $\left({\mathcal{H}}_{\mathrm{EP}}\right)$ 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.