Phosphor Composition for Blue-Violet Excitation Efficiency
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Solution Overview
Problem
Yttrium aluminum garnet (YAG:Ce) phosphors face challenges in enhancing external quantum efficiency when excited by blue-violet light, as increasing gallium (Ga) addition improves absorptance but shifts the peak wavelength, compromising luminescent chromaticity and internal quantum efficiency.
Innovation Solution
A phosphor composition represented by the formula (3-a)YO3/2.aCeO3/2.(5-b)AlO3/2.bGaO3/2.cKO1/2.dPO5/2, where a, b, c, and d are within specific ranges, is developed, allowing for enhanced absorptance and chromaticity by adjusting the addition amounts of Ce, Ga, K, and P, and optimizing the firing atmosphere with increased oxygen partial pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If gallium (Ga) addition is increased to improve absorptance of blue-violet light, then absorptance is improved, but peak wavelength shifts and luminescent chromaticity deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters by introducing potassium (K) and phosphorus (P) elements in addition to gallium (Ga), creating a multi-element doped system. This allows independent optimization of absorptance (through Ga) and chromaticity (through K and P) without the trade-off that exists in simple Ga-doped systems.
Solution Approach 2:
The patent creates a composite phosphor material with the general formula Y3-a-b-cAl5-b-dGa b+dB1-c-dO12-a-b-c, where multiple dopant elements (Ga, K, P) work synergistically. The composite structure enables simultaneous improvement of light absorption and emission characteristics that cannot be achieved with single-element doping.
2Power
If cerium (Ce) concentration is increased to improve yellow light emission, then internal quantum efficiency is improved, but external quantum efficiency deteriorates due to concentration quenching
Solution Approach 1:
The patent introduces potassium (K) and phosphorus (P) as intermediary elements that mediate between Ce ions. These intermediaries facilitate energy transfer and reduce concentration quenching effects, allowing higher Ce concentrations to be used while maintaining high external quantum efficiency. The B element (O, F, or Cl) also serves as an intermediary in the crystal structure.
Solution Approach 2:
The patent optimizes the Ce concentration parameter (a) within a specific range (0.05 ≤ a ≤ 0.20) and combines it with controlled additions of Ga, K, and P. This multi-parameter optimization approach allows achieving high internal quantum efficiency while avoiding the concentration quenching that limits external quantum efficiency in conventional phosphors.
3Power
If oxygen partial pressure in firing atmosphere is increased to improve luminescent properties, then internal quantum efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent employs high oxygen partial pressure (10^-3 to 10^0 atm) during firing to create an oxidizing atmosphere that promotes proper oxidation states of dopant elements (particularly Ce3+ and Ga3+). This strong oxidation condition improves luminescent properties by ensuring correct valence states and reducing defects, while the use of conventional oxygen atmosphere simplifies the manufacturing process.
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 solution achieves high external quantum efficiency while maintaining desirable luminescent chromaticity and internal quantum efficiency, enabling effective yellow light emission under blue-violet excitation.
Implementation Method 1
phosphors (YAG:Ce) in which cerium (Ce) ions serving as luminescent centers are added to yttrium aluminum garnet are known. It is known that YAG:Ce phosphors are excited by irradiation with corpuscular beams, such as electron beams, or electromagnetic waves, such as ultraviolet rays and blue light, and emit yellow to green visible light.
Data Source
AI summary
A phosphor includes, as a main component, a compound represented by a general formula (3-a)YO3/2.aCeO3/2.(5-b)AlO3/2.bGaO3/2.cKO1/2.dPO5/2, where a, b, c and d satisfy 0.12≤a≤0.18, 1.50≤b≤3.00, 0.01≤c≤0.08, and 0.01≤d≤0.08.