Localization and Migration of Energy amongSm3+Ions in CaWO4Crystals

We investigate energy transfer between ${\mathrm{Sm}}^{3+}$ ions in different crystal-field sites in CaW${\mathrm{O}}_4$ crystals by use of laser time-resolved spectroscopy techniques. The dependence of the results on time and temperature show the interaction to be electric quadrupole-quadrupole and the interaction strength to be much less than the inhomogeneous line-width of the transition. This leads to the localization of the energy at low temperatures, confirming the predictions of Anderson.