Luminescent Composition with Narrow Stokes Shift for Secure Inks
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Solution Overview
Problem
Current luminescent compositions often exhibit a significant shift in emission wavelength compared to the excitation wavelength, limiting their application in specific spectral regions, and there is a need for compositions that can be tailored for various absorption and emission frequencies, intensities, and persistence.
Innovation Solution
A luminescent composition comprising a host lattice and lanthanide element dopants, with controlled particle size and microstructure, that emits electromagnetic radiation within 1500 cm−1 of the excitation frequency, allowing for tailored absorption and emission characteristics for specific applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional luminescent compositions are used, then emission occurs at lower energy than excitation (Stokes Law), but this results in significant wavelength shift that limits application in specific spectral regions
Solution Approach 1:
The patent applies parameter changes by systematically varying dopant concentration, host lattice composition, and particle size to precisely control emission frequency. By changing these parameters, the emission can be tuned to occur within 1500 cm⁻¹ of the excitation frequency, resolving the contradiction between spectral adaptability and wavelength control precision.
Solution Approach 2:
The invention uses composite materials by combining specific host lattices (e.g., Y2O3, Lu2O3) with lanthanide dopants (e.g., Er, Tm, Ho) to create luminescent compositions with tailored optical properties. This composite approach enables precise control over emission characteristics while maintaining versatility across different spectral regions.
2Manufacturing precision
If Anti-Stokes materials are used to emit visible light from infrared excitation, then wavelength shift is achieved, but the emission is typically 200 nm or more shifted which limits narrow spectral range applications
Solution Approach 1:
The patent employs parameter changes by adjusting dopant types and concentrations to control the magnitude of frequency shift. This enables the emission to be precisely positioned within 1500 cm⁻¹ of excitation frequency, achieving both high frequency precision and broad application range by selecting appropriate parameter combinations.
3Manufacturing precision
If luminescent compositions are tailored for specific applications, then emission characteristics can be optimized, but this increases complexity in controlling host lattice, dopants, and preparation conditions
Solution Approach 1:
The patent manages complexity by systematically varying key parameters (dopant concentration, host lattice type, particle size) within defined ranges to achieve desired emission characteristics. This parameter-based approach provides a structured method for tailoring compositions without requiring complex multi-variable optimization.
Solution Approach 2:
The invention reduces complexity by using composite materials with specific host-lattice-and-dopant combinations that inherently provide desired optical properties. These pre-established composite systems simplify the tailoring process compared to optimizing individual components separately.
4Adaptability or versatility
If significant wavelength shift is accepted in conventional phosphors, then broad spectral coverage is achieved, but this prevents use in applications requiring emission near excitation frequency
Solution Approach 1:
The patent resolves this contradiction by enabling continuous adjustment of emission frequency through parameter changes in dopant concentration and host lattice composition. This allows the system to adapt to different spectral coverage requirements while maintaining the capability to match emission and excitation frequencies within 1500 cm⁻¹ when needed.
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 composition enables precise control over emission frequencies, intensities, and persistence, enhancing its suitability for diverse applications such as secure documents and luminescent inks by maintaining emission within a narrow spectral range of the excitation.
Implementation Method 1
Phosphors are compounds that are capable of emitting useful quantities of radiation in the visible, infrared and/or ultraviolet spectrums upon excitation of the phosphor compound by an external energy source
Implementation Method 2
Anti-Stokes or, as they are otherwise known, 'up-converting meterials', emit light (visible or ultraviolet) which has a shorter wavelength than the activating radiation
Data Source
AI summary
A particulate luminescent composition is disclosed that, when excited by electromagnetic radiation at a first frequency, emits electromagnetic radiation at a second frequency equal to or within 1500 cm−1 of the first frequency. The luminescent composition comprises substantially spherical particles having a weight average particle size of less than about 10 μm and a particle size distribution such that at least about 90 weight percent of the particles are not larger than twice the average particle size.