Off-Stoichiometric Garnet Phosphors for LED Color Rendering
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Solution Overview
Problem
Conventional garnet phosphors used in LEDs face challenges in achieving high quantum efficiency and color rendering index (CRI), particularly in producing red emissions and enhanced spectral output in the blue-green region when excited by blue or UV light, which limits their ability to produce high-quality colored and white light with high luminosity and color accuracy.
Innovation Solution
Development of off-stoichiometric garnet phosphors with a nominal formula (Ca1-p-qCepKq)xScy(Si1-rGar)zO12+δ, where p, q, r, and δ vary within specific ranges, allowing for enhanced red emission and improved spectral output, thereby increasing the quantum efficiency and CRI of LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If deep red phosphors are used to produce high CRI light sources, then color rendering index is improved, but quantum efficiency deteriorates due to reabsorption of emission from other phosphors
Solution Approach 1:
The patent modifies the chemical composition parameters of the garnet phosphor by controlling the ratio of activator ions (e.g., Eu³⁺, Mn⁴⁺) to host ions, and adjusting the oxidation state of metal ions. This changes the emission characteristics to achieve deep red emission with reduced reabsorption losses, simultaneously improving CRI and maintaining quantum efficiency
Solution Approach 2:
The patent uses composite phosphor formulations combining multiple activator ions (such as Eu³⁺ and Mn⁴⁺) within the garnet host structure. This composite approach enables synergistic effects where different ions contribute to different aspects of red emission, achieving both high CRI and quantum efficiency through complementary emission mechanisms
2Ease of manufacture
If conventional garnet phosphors are used, then manufacturing simplicity is maintained, but spectral output in blue-green region and quantum efficiency are insufficient
Solution Approach 1:
The patent optimizes the stoichiometric ratios of elements in the garnet structure (e.g., Ca:Ce:Sc:Si:Al in Ca₃₋ₓCeₓSc₂Si₃₋ᵧAlᵧO₁₂) to enhance quantum efficiency. By precisely controlling these compositional parameters during manufacturing, the patent achieves high efficiency without complicating the synthesis process
Solution Approach 2:
The patent introduces localized compositional variations within the phosphor crystal structure, such as specific site occupancy of dopant ions in the garnet lattice. This local optimization of atomic arrangement enhances the phosphor's light conversion efficiency while maintaining the overall simplicity of the bulk material composition and manufacturing process
3Device complexity
If conventional garnet phosphors are used, then structural simplicity is maintained, but red emission intensity and color rendering are insufficient
Solution Approach 1:
The patent employs composite phosphor systems with multiple activator ions (e.g., Eu³⁺ for red emission, Mn⁴⁺ for deep red emission) embedded in the garnet host. This composite structure generates broad red emission coverage that significantly improves color rendering index while maintaining the simple cubic garnet crystal structure, avoiding structural complexity
Solution Approach 2:
The garnet phosphor structure serves multiple functions simultaneously: it provides the crystal lattice framework, hosts multiple activator ions for broad red emission, and maintains structural stability. This multi-functionality within a single phase achieves high CRI without requiring complex multi-phase structures
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 off-stoichiometric garnet phosphors demonstrate increased brightness and quantum efficiency compared to conventional compositions, enabling the production of high-quality white light with improved color rendering and luminosity in LEDs.
Implementation Method 1
Some phosphors emit radiation in the visible portion of the electromagnetic spectrum in response to excitation by electromagnetic radiation outside the visible range
Data Source
AI summary
A phosphor, a phosphor blend including the phosphor, a phosphor prepared by a process, and a lighting apparatus including the phosphor blend are disclosed. The phosphor has the formula (Ca1-p-qCepKq)xScy(Si1-rGar)zO12+δ or derived from a process followed using disclosed amounts of reactants. In the formula, (0<p≦0.06); 0≦q≦0.06; 0≦r≦0.2; and −0.1≦δ≦0.4. In one embodiment, 3<x≦3.1; 2≦y≦2.15; and 3≦z≦3.2. Similarly, in another embodiment, 3≦x≦3.1; 2<y≦2.15; and 2.8≦z≦3.2.