Photoactive taggant materials comprising semiconductor nanoparticles and lanthanide ions
This invention provides, in one aspect, a procedure to use optically transparent nanocrystalline quantum dots to absorb UV light. This absorption process leads to an energy transfer to a chemically bound and chelated lanthanide ion that may emit light in either the visible spectrum (400-700 nm) or in the near infrared (700-1600 nm). This invention also provides methods for the use of these taggant materials in inks and aerosols used to disperse the taggant.
1. A photoactive material comprising:
a first material comprising a wide-gap semiconductor nanoparticle, wherein the first material exhibits absorption of non-visible light and no appreciable absorption of visible light;
a second material comprising a lanthanide ion, wherein the second material exhibits emission of light;
a linker compound bonded to the first material;
a chelator compound covalently bonded to the linker and bonded to the second material; and
a functional group bonded to the chelator compound providing chemical functionality to the photoactive material;
wherein the linker compound and chelator compound each exhibits no absorption of UV, NIR or visible light and participates in a transfer of energy from the first material to the second material, wherein the energy is derived from the non-visible light absorbed by the first material;
wherein the functional group exhibits no absorption of UV, NIR, or visible light, and does not inhibit the emission of light exhibited by the second material.
2. The photoactive material of claim 1 wherein the first material exhibits absorption of ultraviolet light.
3. The photoactive material of claim 1 wherein the wide-gap semiconductor nanoparticles comprise metal oxide nanoparticles.
4. The photoactive material of claim 1 wherein the second material exhibits emission of non-visible light.
5. The photoactive material of claim 1 wherein the second material exhibits emission of near-infrared light.
6. The photoactive material of claim 1 wherein the linker compound is an organic molecule selected from the group consisting of a hydrocarbon and an oxyhydrocarbon.