Anti-Stokes Phosphor Concentration Control for Luminescence Kinetics
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Solution Overview
Problem
Existing anti-Stokes phosphors used in security documents face challenges in adjusting build-up and decay times of luminescence due to concentration quenching, making it difficult to optimize their use for secure authentication and identification.
Innovation Solution
An anti-Stokes phosphor with a gadolinium oxysulfide base doped with ytterbium and thulium, where the concentrations of these ions are carefully controlled to achieve specific build-up and decay times, allowing for adjustable attack and cooldown times, suitable for high-speed reading and detection in security documents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the concentration of activator ions (ytterbium and thulium) is increased to enhance luminescence intensity, then the brightness and detectability improve, but concentration quenching occurs which reduces quantum yield and shortens luminescence lifetime
Solution Approach 1:
The patent optimizes the concentration parameters of activator ions (ytterbium and thulium) within specific ranges (ytterbium: 4-50 wt%, thulium: 0.01-5 wt%) to achieve the desired balance between luminescence intensity and quantum yield. By carefully controlling these compositional parameters, the patent resolves the contradiction between enhancing brightness and maintaining efficiency.
2Speed
If the concentration of activator ions is increased to reduce build-up time, then the response speed improves, but the decay time becomes too short reducing authentication reliability
Solution Approach 1:
The patent adjusts the concentrations of ytterbium and thulium ions within optimized ranges to control both build-up and decay times. The specific concentration ranges enable the phosphor to achieve appropriate luminescence kinetics for security applications, where both rapid response and sustained emission are required.
Solution Approach 2:
The patent uses a composite phosphor system combining multiple rare earth ions (ytterbium as sensitizer and thulium as activator) in a host matrix. This composite approach allows independent optimization of different kinetic parameters through the synergistic interaction of the dopant ions, enabling control over both build-up and decay characteristics.
3Quantity of substance
If higher concentrations of rare earth ions are used to enhance luminescence properties, then the authentication signal strength improves, but manufacturing precision becomes more difficult to control
Solution Approach 1:
The patent defines specific concentration ranges for ytterbium (4-50 wt%) and thulium (0.01-5 wt%) that balance signal strength with manufacturability. These optimized parameter ranges ensure that the phosphor can be produced with acceptable precision while maintaining strong luminescence properties for authentication.
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 controlled concentrations of ytterbium and thulium in the anti-Stokes phosphor enable adjustable build-up and decay times, enabling secure authentication and identification at reading speeds between 3 m/s to 10 m/s, enhancing the security features of documents like banknotes and passports.
Implementation Method 1
the wavelength of an emitted electromagnetic radiation of the anti-Stokes phosphor according to the invention is shorter than the wavelength of an electromagnetic radiation absorbed by the anti-Stokes phosphor according to the invention
Implementation Method 2
The phosphor used is e.g. (Gd 0.87 Yb 0.13 Tm 0.001 ) 2 O 2 S given. Ytterbium acts as an absorber ion while thulium acts as an emitter ion
Implementation Method 3
Ytterbium acts as an absorber ion to absorb electromagnetic radiation while thulium acts as an emitter ion to emit electromagnetic radiation
Implementation Method 4
the concentrations of the absorber ions and the emitter ions are selected to vary the rise times and/or the decay times of the anti-Stokes phosphor in such a way that a proportionate quenching of the anti-Stokes luminescence occurs
Data Source
AI summary
Anti-stokes-luminescent material for applying on security documents, in which wavelength of emitted electromagnetic radiation is shorter than the wavelength of an absorbed electromagnetic radiation, comprises a gadolinium basic lattice material made of gadolinium oxide sulfide, in which ytterbium (7.5-35 wt.%) and thulium (0.05-0.75 wt.%) are doped, where ytterbium acts as an absorber ion for absorbing the electromagnetic radiation, and thulium acts as an emitter ion for emitting the electromagnetic radiation. A proportional deletion of the anti-stokes-luminescence takes place. Anti-stokes-luminescent material for applying on security documents, in which wavelength of emitted electromagnetic radiation is shorter than the wavelength of an absorbed electromagnetic radiation, comprises a gadolinium basic lattice material made of gadolinium oxide sulfide, in which ytterbium (7.5-35 wt.%) and thulium (0.05-0.75 wt.%) are doped, where ytterbium acts as an absorber ion for absorbing the electromagnetic radiation, and thulium acts as an emitter ion for emitting the electromagnetic radiation. A proportional deletion of the anti-stokes-luminescence takes place. The anti-stokes-luminescent material exhibits specific reminiscent- and decay time. Independent claims are also included for: (1) a security feature on the security document, comprising the above mentioned anti-stokes-luminescent material; and (2) the security document comprising the safety feature.