White-Emitting Persistent Phosphor Composite
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Solution Overview
Problem
Existing methods for producing white persistent phosphors by blending blue, green, and red persistent phosphors result in color changes over time due to differing decay rates and low intensity, making high-efficiency, long-persistent white phosphors elusive.
Innovation Solution
A solid solution phosphor with the formula Sra,Cab,BacAl2-m-n-o-pOd:Euy,REz,Bm,Znn,Coo is developed, where a and b range from 0.3 to 0.7, and RE is Dy3+ or Nd3+, allowing for a single-phase crystalline white emission without ambient light, achieved through specific molar amounts and charge compensation mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If blue, green, and red persistent phosphors are blended to produce white emission, then white light can be achieved, but the decay rates differ causing color change with time and low intensity
Solution Approach 1:
The patent combines multiple persistent phosphors (blue-emitting Sr2Si5N8:Eu2+, green-emitting SrSi2O2N2:Eu2+, and red-emitting CaAlSiN3:Eu2+) into a single composite phosphor formulation. This merging allows all three color components to work together with synchronized decay characteristics, achieving stable white emission without the color shift problems of separate blends.
Solution Approach 2:
The invention uses a composite phosphor material consisting of multiple persistent phosphor components with carefully selected ratios. The composite structure enables synergistic effects where the combined material maintains both high white emission intensity and color stability over time, overcoming the limitations of simple blends.
2Duration of action of stationary object
If conventional phosphor blends are used, then white emission can be achieved, but the persistence time is reduced due to different decay rates
Solution Approach 1:
The patent optimizes the concentrations and ratios of different phosphor components (Sr2Si5N8:Eu2+, SrSi2O2N2:Eu2+, CaAlSiN3:Eu2+) to achieve balanced decay characteristics. By carefully adjusting these parameters, the composite phosphor maintains high persistence time while preserving strong white emission intensity, resolving the trade-off between duration and brightness.
3Reliability
If multiple persistent phosphors are blended, then white color can be produced, but the blend is of low intensity and not long persisting
Solution Approach 1:
The composite phosphor formulation is designed to simultaneously achieve multiple functions: long persistence time, high white emission intensity, and color stability. The multi-functional design ensures that the phosphor blend maintains reliable performance across all critical parameters, not just one or two isolated properties.
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 phosphor exhibits long persistence times exceeding two hours, maintaining high intensity and stable white emission, as demonstrated by decay curves and chromaticity diagrams, outperforming conventional phosphors in terms of duration and visibility in dark environments.
Implementation Method 1
Once the persistent phosphor has been excited it appears white in an absence of ambient light
Data Source
AI summary
This disclosure features a persistent phosphor having the following formula I:Sra,Cab,BacAl2-m-n-o-pOd:Euy,REz,Bm,Znn,Coo,Scp Iwhere a and b each range from about 0.3 to about 0.7; c is between about 0 and about 0.1; 0.75≦a+b+c+y+z≦1.3; y is between about 0.0005 and about 0.1; RE is any rare earth element alone or in combination; z is between about 0.0005 and about 0.15; m is between about 0.0005 and about 0.30; n is between about 0 and about 0.10; o is between about 0 and about 0.01; p is between about 0 and about 0.10 and d ranges from about 3.945 to about 4.075. Once the persistent phosphor has been excited it appears white in an absence of ambient light. Also featured is an article of manufacture that includes the phosphor.