Zinc Sulfide Phosphor for Dual-Mode Security Verification
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Solution Overview
Problem
Existing electroluminescent security features in documents, such as banknotes and passports, require high-frequency electrical fields for authenticity verification, which can be impractical in decentralized settings or where equipment is not available, and lack alternative verification methods that do not reveal the functional principle.
Innovation Solution
A modified zinc sulfide phosphor with both electroluminescent and photoluminescent properties, exhibiting a characteristic color change under UV excitation, allowing for additional authenticity verification using conventional sensors and simpler detection methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ZnS electroluminophores are used in security documents, then high security level (Level 3) is achieved through electroluminescence, but verification requires complex high-frequency high-voltage equipment that is not available in decentralized settings
Solution Approach 1:
The patent applies multi-functionality by endowing the ZnS phosphor with both electroluminescent properties (for Level 3 security) and photoluminescent properties (for Level 2 security). This allows the same security feature to provide multiple verification methods: one requiring sophisticated equipment and another accessible with simple UV lamps and sensors, thereby resolving the contradiction between security reliability and verification equipment complexity
Solution Approach 2:
The patent changes the luminescence parameters of the ZnS phosphor by doping it with specific activators (Cu, Mn, Al, Ga, In, Bi) and coactivators (halides). This parameter modification enables the material to exhibit both electroluminescence and photoluminescence with characteristic color changes, allowing verification at different security levels without requiring different materials
2Measurement precision
If high-frequency electrical fields are used for authenticity verification, then reliable detection of electroluminescent features is achieved, but the method reveals the functional principle and requires specialized equipment not available in decentralized settings
Solution Approach 1:
The dual luminescence capability allows the security feature to be verified through multiple pathways: the sophisticated electroluminescence detection for high-precision verification and the simple photoluminescence detection using UV excitation. This resolves the contradiction by providing both high measurement precision through electroluminescence and ease of operation through photoluminescence
3Duration of action of stationary object
If ZnS phosphor particles are provided with water vapor barrier layers through microencapsulation, then service life of electroluminescent films is increased, but the coating process adds manufacturing complexity
Solution Approach 1:
The patent applies preliminary action by providing the water vapor barrier coating on the ZnS phosphor particles before they are incorporated into the electroluminescent film. This pre-coating approach protects the phosphor during storage and handling, extending the service life of the final product while simplifying the overall manufacturing process by eliminating the need for post-assembly coating operations
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
Enables reliable and easy authenticity verification independent of high-frequency electrical fields, enhancing the security features' usability and detectability with Level 2 status, complementing the Level 3 electroluminescent characteristics.
Implementation Method 1
ZnS phosphors capable of electroluminescence are usually doped with copper (Cu) and/or manganese (Mn)... emit light in the blue, green or orange range of the visible spectrum when an alternating electrical field of usually 110 V and 400 Hz is applied
Implementation Method 2
the invention relates to a zinc sulfide electroluminescent pigment... which has photoluminescence properties and a characteristic color change of the photoluminescence excited with shorter-wave or longer-wave UV radiation
Data Source
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AI summary
The present invention relates to a zinc sulphide phosphor and to a process for producing same. The invention further relates to a security document or document of value, to a security feature and to a method for detecting same. The phosphor according to the invention can act as electroluminescent phosphor and thus be excited by an electrical field, and this can result in emission of electroluminescent light in the blue and/or green colour region of the visible spectrum. The phosphor can moreover be excited by UV radiation in the wavelength range from 345 nm to 370 nm, and can thus emit photoluminescent light in the blue colour region of the visible spectrum. The phosphor can moreover be excited by UV radiation in the wavelength range from 310 nm to 335 nm, and can thus emit photoluminescent light in the green colour region of the visible spectrum.