Thorium-Doped Garnet Phosphor for High CRI White LEDs
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Solution Overview
Problem
Conventional garnet-based phosphors used in white LEDs have limited light emission in the red wavelength area, resulting in low color rendering index and high color temperature, and lack high-temperature stability.
Innovation Solution
A garnet-based phosphor doped with thorium as the main activator, represented by the formula (L1−x−yThxMy)3N5O12, which emits light in a more variable wavelength range and provides improved high-temperature stability and light emitting characteristics, is used in white LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional garnet-based phosphors are used, then high fluorescence efficiency is achieved, but red wavelength fluorescence is lacking resulting in low color rendering index
Solution Approach 1:
The patent changes the activator parameter from conventional cerium to thorium, and adjusts the compositional parameters (x, y ratios) to optimize the emission spectrum. This parameter change enables the phosphor to emit across blue-green-yellow-red wavelengths, achieving high color rendering index while maintaining fluorescence efficiency
Solution Approach 2:
The patent creates a composite phosphor material combining thorium-doped garnet structure with multiple activators (including Pr, Tb, Sm, Se, U, Li, Na) to achieve broad spectrum emission. This composite approach enables simultaneous high fluorescence efficiency and comprehensive color rendering by utilizing the complementary emission characteristics of different activators
2Illumination intensity
If conventional garnet-based phosphors are used, then high fluorescence efficiency is achieved, but high-temperature stability is insufficient
Solution Approach 1:
The patent modifies the compositional parameters by incorporating thorium at specific concentrations (0 < x ≤ 0.5) and adjusting the garnet structure composition. This parameter optimization enhances the thermal stability of the crystal structure while preserving the high fluorescence efficiency, enabling the phosphor to maintain performance at elevated temperatures
3Illumination intensity
If cerium is used as main activator, then light characteristics are improved, but light emitting wavelength range is limited
Solution Approach 1:
The patent fundamentally changes the activator parameter from cerium to thorium, which has different electronic structure and emission characteristics. This parameter change expands the emission wavelength range to include blue-green-yellow-red regions, achieving comprehensive spectral coverage while maintaining excellent light characteristics
Solution Approach 2:
The patent employs a composite activator system with multiple elements (Pr, Tb, Sm, Se, U, Li, Na) in addition to thorium, where each activator contributes to specific wavelength regions. This composite approach ensures broad wavelength coverage and excellent light characteristics that cannot be achieved with a single activator
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 thorium-doped garnet phosphor achieves superior light emission stability and high luminance, enabling white LEDs with higher luminance and color rendering index, suitable for general lighting and applications requiring high-quality white light.
Implementation Method 1
When the garnet-based phosphor uses ultraviolet or visible light having a wavelength of 100 nm to 600 nm as an excitation source, light may be emitted.
Data Source
AI summary
Provided is a garnet-based phosphor doped with thorium and a light emitting device using the same. In particular, a garnet-based phosphor having superior light characteristics and heat stability by using thorium as an activator, when compared to a conventional garnet phosphor using cerium as an activator, and a light emitting device using the same as a light source are provided.