Wide-Gap Semiconductor Nanoparticle Taggants for Solar-Blind Security
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Solution Overview
Problem
Current taggant materials face limitations in high-security and covert applications due to visibility under standard lighting, environmental concerns, and inadequate absorption and emission properties, making them unsuitable for solar-blind and high-security uses.
Innovation Solution
A photoactive taggant material composed of wide-gap semiconductor nanoparticles and lanthanide ions, where energy transfer from non-visible light absorbed by the nanoparticles to the lanthanide ions enables solar-blind security inks with near-infrared emission, overcoming previous materials' absorption and emission limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If nanoparticle taggants (CdSe, CdS, PbSe, PbS) are used for high encryption, then encryption level is improved, but the materials absorb visible light and emit under standing lighting, making them conspicuous and unsuitable for covert applications
Solution Approach 1:
The patent changes the optical parameters of the nanoparticle taggants by selecting wide-bandgap materials (TiO2, ZnO, ZrO2, HfO2, Al2O3, SiO2, B2O3, P2O5) with bandgaps greater than 3.0 eV. These materials have absorption edges in the ultraviolet region and do not absorb visible light, fundamentally changing their optical response parameters to achieve solar-blind operation while maintaining high encryption capabilities
Solution Approach 2:
The patent converts the typically harmful effect of UV absorption into a beneficial feature for covert applications. By using wide-bandgap nanoparticles that absorb only UV radiation and emit in the NIR region, the taggants become invisible to the human eye under visible lighting conditions. The UV absorption, which could be considered a limitation, becomes the key mechanism for achieving solar-blind operation and covert security marking
2Use of energy by moving object
If luminescent dyes are used for wavelength conversion, then ultraviolet to visible or visible to near infrared conversion is achieved, but absorption and emission properties are inadequate and emission spectra are broad and asymmetric, making information retrieval difficult
Solution Approach 1:
The patent creates a composite luminescent system combining wide-bandgap semiconductor nanoparticles (TiO2, ZnO, ZrO2, HfO2, Al2O3, SiO2, B2O3, or P2O5) with lanthanide ions (Nd3+, Er3+, Ho3+, Tm3+, or Yb3+). This composite structure leverages the strong UV absorption and narrow bandgap of the semiconductor nanoparticle host and the sharp, characteristic emission lines of the lanthanide dopants, achieving both efficient wavelength conversion and precise spectral features for reliable information retrieval
Solution Approach 2:
The wide-bandgap semiconductor nanoparticle acts as an intermediary energy transfer mediator between UV excitation and lanthanide emission. The nanoparticle absorbs UV photons, generates excitons, and transfers energy to the lanthanide ions, which then emit at their characteristic narrow spectral lines. This intermediary mechanism enables efficient wavelength conversion while maintaining the sharp emission features needed for precise measurement and information retrieval
3Adaptability or versatility
If doped inks with magnetic particles are used for product identification, then product tracking is enabled, but the materials are absorptive in the visible spectrum and not ideal for high security applications
Solution Approach 1:
The patent changes the optical absorption parameters of the taggant materials by using wide-bandgap semiconductors with bandgaps greater than 3.0 eV. These materials have absorption edges in the ultraviolet region and are transparent to visible light, fundamentally changing their spectral response from visible absorption to UV-only absorption, thereby enabling covert security marking while maintaining product identification capabilities
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides solar-blind security inks that are environmentally friendly, cost-effective, and suitable for various applications, including covert and high-security uses, with controlled emission and encryption capabilities.
Implementation Method 1
The first material is composed of a wide-gap semiconductor nanoparticle that exhibits absorption of non-visible light
Implementation Method 2
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
Implementation Method 3
The second material is composed of a lanthanide ion that exhibits emission of light
Data Source
AI summary
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.