Benefit of Pr^3+ ions to the spectral properties of Pr^3+/Er^3+:CaGdAlO_4crystal for a 27 μm laser

Abstract

The spectra of ${\mathrm{Er}}^{3+}\text{:}{\mathrm{CaGdAlO}}_4$ and ${\mathrm{Pr}}^{3+}/{\mathrm{Er}}^{3+}\text{:}{\mathrm{CaGdAlO}}_4$ crystals were measured under the same conditions. With the presence of ${\mathrm{Pr}}^{3+}$ ions, the intensities of the green, red upconversion and near-infrared emissions are dramatically reduced to $1/20$, $1/150$, and $1/8.5$ of those for ${\mathrm{Er}}^{3+}\text{:}{\mathrm{CaGdAlO}}_4$. Furthermore, the lifetimes of ${}^4{\mathrm{I}}_{11/2}$ upper and ${}^4{\mathrm{I}}_{13/2}$ lower laser levels fall from 450 and 982 μs to 84.8 and 74.3 μs. It is obvious that the self-saturation for ${\mathrm{Er}}^{3+}$ 2.7 μm laser is effectively suppressed. The energy transfer efficiencies and coefficients of ${\mathrm{Er}}^{3+}\to {\mathrm{Pr}}^{3+}$ are also calculated. These results indicate that ${\mathrm{Pr}}^{3+}$ codoping is beneficial in achieving 2.7 μm laser in ${\mathrm{Pr}}^{3+}/{\mathrm{Er}}^{3+}\text{:}{\mathrm{CaGdAlO}}_4$ crystal.