Security feature for securing a valuable document based on a
transition metal-containing ESR active substance, which has an
alkaline earth metal-containing or
zinc-containing host lattice with garnet or
perovskite structure and the following general formula E a R b T c X d Q e Z f O 12has, where E is at least one
alkaline earth metal or Zn chosen from the elements Mg, Ca, Sr, Ba and a satisfies the condition 0 < a ≤ 4; R is at least one
rare earth metal chosen from the elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and b satisfies the condition 0 ≤ b ≤ 4; T is at least one
transition metal chosen from the elements Cr, Mn, Fe, Cu and c satisfies the condition 1 ≤ c ≤ 5; X is at least one trivalent codotand chosen from the elements B, Al, Ga, Bi and d satisfies the condition 0 ≤ d ≤ 4; Q is at least one four-valued codotand chosen from the elements Si, Ge, Sn, Ti, Zr, Hf and e satisfies the condition 0 ≤ e ≤ 4; Z is at least one five-valued codotand chosen from the elements P, As, Sb, V, Nb, Ta and f satisfies the condition 0 ≤ f ≤ 4.