Energy Transfer from ${\mathrm{Er}}^{3+}$ to ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ Ions in Crystals

Energy transfer from ${\mathrm{Er}}^{3+}$ to ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ ions in crystals has been found to occur. Transfer proceeds from the ${}_{}{}^4{}_{}{}^{}I_{\frac{13}{2}}^{}{}_{}{}^{}$ state of ${\mathrm{Er}}^{3+}$ to the ${}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ and ${}_{}{}^5{}_{}{}^{}I_7^{}{}_{}{}^{}$ emitted states of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$, respectively. Phonon emission is required to conserve energy. The enhancement of infrared emission from ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ ions due to energy transfer from ${\mathrm{Er}}^{3+}$ results in a lowering of the threshold for maser oscillation of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ ions in CaMo${\mathrm{O}}_4$. However, results indicate that greater benefit from energy transfer can be obtained in the garnets where ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ emission is strengthened by two orders of magnitude.