Low-Alkali Glass Phosphor Composition for LED Luminance Stability
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Solution Overview
Problem
Wavelength conversion members with inorganic phosphors dispersed in a glass matrix face degradation due to heat and high-energy light from LEDs or LDs, leading to decreased luminescence intensity over time, especially with increasing output power of light sources.
Innovation Solution
A wavelength conversion member is developed with a glass matrix composition that minimizes alkali metal components to suppress the formation of color centers, using alkaline-earth oxides to lower the softening point without affecting luminescence intensity, and incorporating specific inorganic phosphors for high thermal resistance and efficient light conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If inorganic phosphors with low thermal resistance are used to achieve high color rendition, then color rendering is improved, but the inorganic phosphors are easily degraded by firing during production, causing luminance deterioration
Solution Approach 1:
The patent changes the thermal parameters of the glass matrix by adjusting its composition (adding specific oxides like B2O3, SiO2, Al2O3) to increase the softening point and thermal resistance. This allows the use of low thermal resistance phosphors for high color rendition while the improved thermal matrix prevents degradation during firing, resolving the contradiction between color rendering and production stability.
Solution Approach 2:
The patent creates a composite material system consisting of inorganic phosphors dispersed in a specially formulated glass matrix. The composite structure combines the high color rendition properties of low thermal resistance phosphors with the thermal stability of a high softening point glass matrix, allowing both requirements to be satisfied simultaneously.
2Ease of manufacture
If the softening point of glass powder is decreased by incorporating alkali metal oxide to suppress phosphor degradation during firing, then ease of manufacture is improved, but luminescence intensity decreases with time due to temperature quenching
Solution Approach 1:
The patent changes the chemical composition parameters of the glass matrix by replacing alkali metal oxides with alkaline earth metal oxides and adjusting the ratios of B2O3, SiO2, and Al2O3. This composition optimization achieves the right balance: low enough softening point for easy firing (maintaining ease of manufacture) while high enough thermal resistance to prevent temperature quenching and maintain luminescence intensity stability over time.
3Ease of manufacture
If inorganic phosphors are dispersed in resin matrix to form wavelength conversion member, then ease of manufacture is improved, but the resin degrades under heat and high-energy light causing discoloration and deformation
Solution Approach 1:
The patent replaces the degradable resin matrix with an inorganic glass matrix that has superior thermal and light resistance. While glass requires different processing methods, it eliminates the degradation issues entirely, providing long-term reliability for high-power LED applications where resin would fail under continuous heat and high-energy light exposure.
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 significantly reduces the decrease in luminescence intensity over time, enhancing the long-term reliability of light emitting devices, particularly suitable for on-vehicle lighting applications like headlamps.
Implementation Method 1
the glass serving as the matrix is less likely to be degraded by heat and irradiation light from an LED
Implementation Method 2
absorbs part of the light from the LED to convert it to a yellow light
Implementation Method 3
a wavelength conversion member is disposed on an LED for emitting a blue light and absorbs part of the light from the LED to convert it to a yellow light
Data Source
AI summary
Provided is a wavelength conversion member that is less decreased in luminescence intensity with time by irradiation with light of an LED or LD and a light emitting device using the wavelength conversion member. A wavelength conversion member is formed of an inorganic phosphor dispersed in a glass matrix, wherein the glass matrix contains, in % by mole, 30 to 85% SiO2, 0 to 20% B2O3, 0 to 25% Al2O3, 0 to 3% Li2O, 0 to 3% Na2O, 0 to 3% K2O, 0 to 3% Li2O+Na2O+K2O, 0 to 35% MgO, 0 to 35% CaO, 0 to 35% SrO, 0 to 35% BaO, 0.1 to 45% MgO+CaO+SrO+BaO, and 0 to 4% ZnO, and the inorganic phosphor is at least one selected from the group consisting of an oxide phosphor, a nitride phosphor, an oxynitride phosphor, a chloride phosphor, an oxychloride phosphor, a halide phosphor, an aluminate phosphor, and a halophosphate phosphor.