Sm^2+ → Nd^3+ energy transfer in CaF_2

We measured the energy-transfer efficiency of Sm2+ → Nd3+ in CaF2 and found that the transfer occurs through the dipole–dipole interaction. Our calculations of the efficiency from the emission and absorption properties of the Sm2+ and Nd3+ ions are in good agreement with those obtained from the Foerster–Dexter analysis of the emission transients. In addition, the comparison of the excitation and absorption spectra of codoped samples quantitatively confirms that energy initially absorbed by Sm2+ is actually being converted into Nd3+ luminescence. Although efficiencies of 0.9 can be achieved with reasonable levels of Nd3+ doping, the Sm2+ luminescence begins to quench at temperatures >220 K. The selection of an optimal host for application to solid-state laser systems is discussed in the light of the Sm2+ spectral characteristics and the need for good efficiency at room temperature.