Refractive Index Matched Phosphors for Infrared Security
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Solution Overview
Problem
Current security features in plastic substrates lack effective methods for authentication that are both visually clear and detectable using infrared sources, which is essential for preventing counterfeiting and verifying the authenticity of value documents.
Innovation Solution
Incorporating a phosphor composition with active ions and a fluoride-containing crystalline host lattice material into transparent plastic substrates, allowing for detection using an infrared emitting source without compromising the transparency of the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphor composition is incorporated into transparent plastic substrate for security features, then detectability by infrared excitation is improved, but visual clarity and transparency are worsened
Solution Approach 1:
The refractive index of the phosphor composition is specifically adjusted to match that of the plastic substrate within 2%, preventing light scattering and maintaining visual clarity. This parameter optimization allows the phosphor to provide infrared detectability while remaining optically invisible in the visible spectrum.
Solution Approach 2:
A composite phosphor composition is created combining active ions (such as rare earth ions like Er³⁺, Tm³⁺, Ho³⁺) with a fluoride-containing crystalline host lattice material. This composite structure provides both the infrared absorption/emission properties needed for security detection and the refractive index matching required for visual transparency.
2Adaptability or versatility
If phosphor composition with infrared absorption is incorporated into plastic substrate, then security detection capability is improved, but refractive index mismatch causes light scattering and reduces transparency
Solution Approach 1:
The refractive index of the phosphor composition is precisely controlled to be within 2% of the plastic substrate's refractive index. This parameter matching eliminates optical scattering at the phosphor-substrate interface, allowing the phosphor to provide infrared detection functionality while maintaining the substrate's visual transparency.
Solution Approach 2:
The phosphor composition is designed to optically blend with the surrounding plastic matrix by matching its refractive index, effectively making the phosphor particles 'disappear' from the visible spectrum while retaining their infrared absorption and emission properties for security detection.
3Reliability
If visible security features are used in plastic substrates, then authentication is improved, but counterfeiting using photocopiers or scanners becomes easier
Solution Approach 1:
Instead of using visible security features that can be copied, the invention inverts the approach by using invisible phosphor compositions that absorb infrared radiation and emit visible light. This inverted visibility approach creates security features that are undetectable by conventional photocopiers and scanners but can be authenticated using infrared excitation sources.
Solution Approach 2:
The phosphor composition acts as an intermediary that converts infrared energy to visible light emission. This energy conversion mechanism provides a hidden authentication layer that requires specialized infrared detection equipment, thereby preventing counterfeiting by standard copying devices while maintaining reliable authentication capability.
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 phosphor-based security features enable the authentication of value documents by maintaining visual clarity while being detectable through infrared excitation, providing a secure and effective means to verify authenticity without affecting the transparency of the plastic substrate.
Implementation Method 1
The phosphor composition includes at least one active ion and a fluoride containing crystalline host lattice material. The phosphor composition has absorption in the infrared, and has a refractive index which is within 2% of the refractive index of the plastic material.
Implementation Method 2
directing an infrared emitting source at the plastic substrate to excite the phosphor composition. The phosphor composition has absorption in the infrared
Data Source
AI summary
Phosphor compositions are provided that can be incorporated into or onto plastic substrates as covert security features. The plastic substrates can be transparent and the phosphor compositions have a refractive index that effectively matches the refractive index of the plastic substrate to maintain the transparency. The phosphor compositions have absorption in the infrared, thus enabling excitation and detection of the compositions with an infrared emitting source.