Luminescence of Eu$^{3+}$ ions in ultradisperse diamond powders

The luminescence of Eu$^{3+}$ ions implanted in ultradisperse diamond powders, activated by impregnating with a solution of Eu(NO$_{3})_3\cdot6$H$_2$O and heat-treated at various temperatures, is studied. A multiple increase in the efficiency of excitation in the charge-transfer band is observed for the $^5!D_0$ state of Eu$^{3+}$ ions as compared to europium nitrate heat-treated similarly. This effect is explained by an increase in the degree of Eu–O bond covalency and a change in the activator coordination polyhedron due to the formation of chemical bonds Eu–O–C.