Phosphorescent Phosphor Composition for Extended Afterglow Luminance
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Solution Overview
Problem
Conventional phosphorescent phosphors exhibit short afterglow times and poor light resistance, limiting their application in luminous devices such as watches and safety signs, where longer afterglow luminance is desired.
Innovation Solution
A phosphorescent phosphor composition comprising strontium, magnesium, and barium as the matrix, with europium and dysprosium as activators and co-activators, and small amounts of alkali metal elements like sodium, optimized to achieve high afterglow luminance, produced through a high-temperature firing process in a reducing atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional phosphorescent phosphors (sulfide or simple aluminate) are used, then the phosphor can be manufactured with simpler composition, but the afterglow luminance and duration are insufficient
Solution Approach 1:
The patent employs a composite phosphor system combining SrAl2O4 matrix with multiple dopants (Mg, Ba, Eu, Dy, and alkali metals) to achieve synergistic effects. The Mg and Ba elements substitute into the SrAl2O4 lattice to create optimized defect structures, while Eu serves as the primary luminescent center and Dy as a co-activator to extend afterglow duration. The alkali metal elements (Na, K, Li, or Rb) further modify the crystal field to enhance electron trap density and depth, collectively producing superior afterglow performance that cannot be achieved with single-element dopants alone.
2Reliability
If sulfide phosphors are used to achieve phosphorescence, then the phosphor can be synthesized with simpler materials, but the light resistance and chemical stability are poor
Solution Approach 1:
The patent utilizes high-temperature firing (1200-1800°C) in a reducing atmosphere to transform the crystal structure and chemical properties of the phosphor. This thermal parameter change enables the formation of a stable SrAl2O4:Eu,Dy matrix with enhanced light resistance, while the reducing atmosphere prevents oxidation of the Eu2+ activator. The prolonged heating time (2-24 hours) ensures complete reaction and optimal dopant distribution within the crystal lattice, achieving both reliability and manufacturability.
3Illumination intensity
If the activator concentration is increased to enhance afterglow luminance, then the emission intensity improves, but the afterglow duration may be reduced due to concentration quenching
Solution Approach 1:
The patent employs spatially differentiated dopant distribution where Eu activators are localized at specific crystal lattice sites within the SrAl2O4 structure, while Mg and Ba elements occupy distinct substitutional positions to create localized electron trap regions. This local quality differentiation allows Eu centers to maintain high luminescence efficiency without excessive concentration quenching, as the Mg/Ba-modified lattice provides distributed trap sites that extend electron release times. The alkali metal elements further refine the local crystal field around Eu, optimizing both intensity and duration independently.
4Duration of action of moving object
If multiple dopants are added to improve afterglow characteristics, then the phosphorescence performance is enhanced, but the manufacturing precision and composition control become more difficult
Solution Approach 1:
The patent employs a pre-mixing step where all raw materials (SrCO3, Al2O3, MgO, BaCO3, Eu2O3, Dy2O3, and alkali metal carbonates) are thoroughly blended before firing. This preliminary homogeneous distribution ensures consistent dopant placement throughout the batch, reducing variation in final phosphor performance. The use of carbonate precursors for most elements provides uniform reactivity during high-temperature synthesis, facilitating precise composition control despite the multi-component system.
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 phosphorescent phosphor exhibits significantly improved afterglow luminance, maintaining visibility for extended periods, enhancing its suitability for applications in luminous watches and safety signs.
Implementation Method 1
the afterglow time of a phosphor is extremely short, and the emission of a phosphor rapidly decays when external excitation is ceased. However, in rare cases, even after the cessation of external excitation, some phosphors maintain afterglow of a level perceivable with the naked eye for a considerably long period of time
Data Source
AI summary
A phosphorescent phosphor having a high afterglow luminance is provided. The phosphorescent phosphor comprises, as a matrix, a compound represented by MAl2O4, the metal element represented by M comprising Sr, Mg and Ba, and the phosphorescent phosphor containing, Eu as an activator, and Dy as a co-activator, wherein the content of Eu, in terms of molar ratio, is 0.001≤Eu/(M+Eu+Dy)≤0.05; the content of Dy, in terms of molar ratio, is 0.004≤Dy/(M+Eu+Dy)≤0.06; the content of Mg, in terms of molar ratio, is 0.02≤Mg/(M+Eu+Dy)≤0.1; the content of Ba, in terms of molar ratio, is 0.03≤Ba/(M+Eu+Dy)≤0.15; and the phosphorescent phosphor contains at least one alkali metal element of the group consisting of Li, Na, K and rubidium (Rb). Mg and Ba as well as the alkali metal element(s) contained in the phosphorescent phosphor provide an excellent phosphorescent phosphor having a high afterglow luminance.