Lanthanide Upconverting Microrods for High-Resolution Security Tags
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Solution Overview
Problem
There is a need for lanthanide-based upconverting microrods with improved physical characteristics and optical properties for security tags and sensing applications, as existing technologies do not provide sufficient resolution and efficiency in infrared-to-visible photon conversion.
Innovation Solution
The development of monodispersed lanthanide-based upconverting microrods, specifically β-NaYF4:Yb3+, Er3+ and β-NaYF4:Yb3+, Tm3+, capped with oleic acid and embedded in polymer matrices, which are synthesized through a process involving refluxing and hydrothermal treatment, allowing for high aspect ratio microrods that respond to different excitation wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional synthesis methods (co-precipitation, hydrothermal, solvothermal) are used to produce upconverting nanoparticles, then production scalability is improved, but manufacturing precision and uniformity of particle size and shape deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-forming microrod structures with controlled dimensions before the upconversion synthesis. The microrods are prepared with specific aspect ratios (length 100-350 nm, width 10-15 nm) through controlled nucleation and growth conditions, then used as templates for subsequent lanthanide doping. This preliminary structuring ensures uniform particle size and shape while maintaining production scalability.
Solution Approach 2:
The patent employs parameter changes by systematically optimizing synthesis conditions including temperature (160-195°C), pH (8.0-9.0), and reactant ratios to achieve monodisperse microrod formation. The aspect ratio is controlled by adjusting the ratio of sodium hydroxide to lanthanide salts and the concentration of oleic acid, enabling precise control over particle morphology while maintaining high yield.
2Manufacturing precision
If high aspect ratio microrods are synthesized through extended hydrothermal treatment, then manufacturing precision and monodispersity are improved, but production time and energy consumption increase
Solution Approach 1:
The patent applies periodic action through a two-stage synthesis process: (1) initial nucleation phase at 160-180°C for 4-6 hours to form seed microrods, and (2) growth phase at 180-195°C for 50-60 hours to achieve final monodisperse structure. This periodic temperature and reaction condition control enables precise monodispersity while reducing total processing time compared to continuous extended hydrothermal treatment.
Solution Approach 2:
The patent utilizes phase transitions by controlling the crystallization process from amorphous precursors to crystalline β-NaYF4 structure during hydrothermal treatment. The phase transition occurs at specific temperature thresholds (160°C onset, 195°C completion), allowing controlled microrod formation with high monodispersity in reduced time by exploiting the thermodynamic driving force of phase change.
3Reliability
If oleic acid capping is applied to microrods, then stability and optical properties are improved, but ease of manufacture and process complexity increase
Solution Approach 1:
The patent uses oleic acid as an intermediary molecule that caps the microrod surfaces, providing steric stabilization and preventing aggregation. The oleic acid molecules coordinate with surface lanthanide ions, creating a stable hydrophobic layer that enhances colloidal stability without requiring complex post-synthesis functionalization. This intermediary approach simplifies the overall manufacturing process while achieving high stability.
Solution Approach 2:
The patent controls the oleic acid concentration (5-10 mM) and pH (8.0-9.0) to optimize capping efficiency. By adjusting these parameters, the microrods achieve maximum stability with minimal oleic acid usage, simplifying the manufacturing process. The pH control ensures deprotonation of oleic acid for effective surface coordination, while the optimized concentration prevents excessive complexity in the synthesis protocol.
4Power
If lanthanide doping is optimized for maximum upconversion efficiency, then optical performance is improved, but manufacturing precision and control over emission wavelength become more difficult
Solution Approach 1:
The patent applies local quality by selectively doping specific crystallographic sites within the β-NaYF4 structure with different lanthanide ions. Yb3+ ions are positioned at specific lattice sites for efficient NIR absorption, while Er3+ or Tm3+ ions occupy other sites for desired visible emission. This spatial arrangement of different dopants at optimal locations achieves high upconversion efficiency while maintaining precise control over emission wavelength through site-specific optical properties.
Solution Approach 2:
The patent creates composite doped structures by combining multiple lanthanide ions (Yb3+, Er3+, or Tm3+) within the single β-NaYF4 crystal lattice. This composite doping approach enables energy transfer from Yb3+ (NIR absorber) to Er3+ or Tm3+ (visible emitters), achieving high upconversion efficiency. The emission wavelength is precisely controlled by the specific lanthanide composition and their relative concentrations, maintaining manufacturing precision through defined molar ratios.
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 resulting microrods exhibit enhanced optical properties and physical characteristics, enabling efficient upconversion processes for security tags and sensing applications, with the ability to create high-resolution patterns and respond to various excitation wavelengths, thus improving upon existing technologies.
Implementation Method 1
Upconversion was first recognized and formulated by Auzel in the mid-1960s, which is a process where low energy light, usually near-infrared (NIR) or infrared (IR) is converted to higher energies, ultraviolet (UV) or visible, via multiple absorptions or energy transfers.
Implementation Method 2
Rare-earth ions doped luminescence upconversion nano-particles have attracted much attention in recent years owing to their superior spectroscopic properties
Implementation Method 3
it utilizes NIR light for the excitation and UV or VIS light will be emitted
Data Source
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AI summary
The present invention provides a monodispersed lanthanum based upconverting microrods comprising β -NaYF4:Yb3+, Er3+ and β -NaYF4:Yb3+, Tm3+, capped with oleic acid. The upconverting microrods, embedded in polymer matrices is used for making security tags and for sensing application. The process of preparation of the oleic acid capped upconverting microrods is also disclosed.