Alkali metal and alkaline earth metal niobates and tantalates as security feature substances
The invention relates to a security feature having a luminescent substance with the general formula AXO 3 : Z (I) or B 0.5 XO 3 : Z (II) or A 1-2y B y XO 3 : Z (III), where A is an alkali metal, B is an alkaline earth metal, X stands for Nb or Ta, Z is the luminescence activator, and y lies between 0 and 0.5. The invention also relates to a security element, a security paper and a value document which is equipped with the security feature according to the invention, and to the use of the luminescent substance with the general formula (I), (II) or (III) as a feature substance for authentication. The luminescent substance is obtained by annealing solid starting materials.
1. A security feature, comprising at least one luminescent substance for authentication of a security element, a security paper, a value document or another object, the at least one luminescent substance having a host lattice doped with at least one luminescence activator, wherein the at least one luminescent substance has the general formula AXO 3 :Z (I)
wherein:
A is at least one element selected from the group consisting of alkali metals;
X is either or both Nb and Ta;
Z is the luminescence activator, and is at least one element selected from the group consisting of the rare earth metals and transition metals in the oxidation states in which the relevant transition metals are activatable to luminesce; and
wherein the host lattice is additionally doped with at least one element E which serves for charge equilibration.
2. The security feature according to claim 1 , wherein the host lattice is additionally doped with a luminescence sensitizer which absorbs energy and transfers it to the luminescence activator and is selected from the transition metal cations.
3. The security feature according to claim 1 , wherein the element serving for charge equilibration is selected from the group consisting of transition metal cations, rare earth cations and cations of the elements of the third and fourth main groups.
4. The security feature according to claim 1 , wherein the luminescent substance is present in the form of a powder with a grain size between 1 μm and 6 μm.
5. The security feature according to claim 1 , wherein the luminescent substance comprises 0.05 to 5 wt % of the luminescence activator Z.
6. The security feature according to claim 1 , wherein the luminescent substance has an emission spectrum outside the visible spectral region.