High-pressure laser spectroscopy of Cr3+:Gd3Sc2Ga3O12 and Cr3+:Gd3Ga5O12.

Abstract

We report on the effect of high pressure on the room-temperature emission spectra and lifetimes of ${\mathrm{Cr}}^{3+}$:GSGG (${\mathrm{Gd}}_{3}$${\mathrm{Sc}}_{2}$${\mathrm{Ga}}_{3}$${\mathrm{O}}_{12}$) and ${\mathrm{Cr}}^{3+}$:GGG (${\mathrm{Gd}}_{3}$${\mathrm{Ga}}_{5}$${\mathrm{O}}_{12}$). In both systems we observed a dramatic change of the overall emission band shape upon increasing pressure, from a nearly structureless broadband ${(}^{4}$${\mathit{T}}_{2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{A}}_{2}$) to a highly structured narrow band ${(}^{2}$E${\ensuremath{\rightarrow}}^{4}$${\mathit{A}}_{2}$). From the peak energy of the broadband emission, we estimated the pressure-induced blueshift of the $^{4}$${\mathit{T}}_{2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{A}}_{2}$ transition to be 10 (\ifmmode\pm\else\textpm\fi{}2) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/kbar. High-resolution measurements in the R-line region (\ensuremath{\sim}700 nm) revealed that the $^{2}$E${\ensuremath{\rightarrow}}^{4}$${\mathit{A}}_{2}$ transition hardly shifts at low pressures (40 kbar), whereas at higher pressures (>60 kbar) a nearly linear redshift of 0.65 (\ifmmode\pm\else\textpm\fi{}0.05) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/kbar is observed. Besides pressure-induced spectral changes, an enormous increase in the emission lifetime with increasing pressure was found for both systems. In the case of ${\mathrm{Cr}}^{3+}$:GSGG, the lifetime changed from 110 \ensuremath{\mu}s at ambient pressure to 4.4 ms at 125 kbar. For ${\mathrm{Cr}}^{3+}$:GGG, the lifetime increased from 168 \ensuremath{\mu}s to 7.3 ms for the same pressure range. The pressure-induced spectral and lifetime changes are described by a single configurational coordinate model that considers the effect of pressure on the thermal and spin-orbit coupling of the $^{2}$E and $^{4}$${\mathit{T}}_{2}$ states. A previously reported pressure-induced R-line-shift reversal in ${\mathrm{Cr}}^{3+}$:GSGG and the effect of high pressure on the lifetime in ${\mathrm{Cr}}^{3+}$:YAG are also discussed within the same framework.