Up-converted luminescence and excited-state excitation spectroscopy of Cr4+ ions in forsterite.

Abstract

The electronic structure of ${\mathrm{Cr}}^{4+}$-doped forsterite is studied using up-converted luminescence and excited-state excitation spectroscopy. Two metastable states with energies higher than the energy of the $^{3}$${\mathit{T}}_{2}$ lasing level are identified. The first, higher-lying state was identified as the $^{3}$${\mathit{T}}_{1}$(${\mathit{t}}_{2}$e) electronic state. Three lines were resolved at 26 424, 26 529, and 26 625 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, corresponding to the spin-orbit-split zero-phonon line of the $^{3}$${\mathit{T}}_{1}$(${\mathit{t}}_{2}$e) state. The lifetime of this state was measured to be 395 ps. The second, lower-lying state is located at 12 847\ifmmode\pm\else\textpm\fi{}90 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and is assigned to the $^{3}$${\mathit{T}}_{1}$(${\mathit{t}}_{2}^{2}$) state. Its lifetime is estimated to be of the order of a few hundred nanoseconds.