Cadmium-Free Core-Shell Quantum Dot for Red Light Emission
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Solution Overview
Problem
Current semiconductor nanocrystal quantum dots, particularly those emitting red light, face challenges in achieving high luminous efficiency and narrow emission spectra without using cadmium, which is environmentally hazardous, and struggle with forming uniform shells of sufficient thickness for increased emission wavelengths.
Innovation Solution
A cadmium-free quantum dot with a core/shell structure composed of zinc, tellurium, selenium, and sulfur, where the shell has varying compositions in a radial direction, including a first layer of zinc and selenium and a second layer of zinc and sulfur, achieving an emission peak wavelength of greater than 600 nm and high luminous efficiency of over 50% with a full width at half maximum (FWHM) of less than 60 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If cadmium-free quantum dots are used to avoid environmental hazards, then environmental safety is improved, but luminous efficiency and emission wavelength control deteriorate
Solution Approach 1:
The patent employs composite material structures (core/shell quantum dots with specific element combinations like CdSe/ZnS or InP/ZnS) to achieve both cadmium-free composition and high luminous efficiency. The composite structure allows optimization of each layer's properties to overcome the limitations of individual materials.
Solution Approach 2:
The patent applies local quality by creating non-uniform element distribution within the quantum dot structure, such as gradient shells or segmented layers with different compositions. This allows different regions to perform different functions: the core provides the emission wavelength, while the shell enhances efficiency and stability without requiring cadmium throughout the entire structure.
2Length of moving object
If shell thickness is increased to achieve longer emission wavelengths, then emission wavelength is improved, but manufacturing uniformity deteriorates
Solution Approach 1:
The patent divides the shell into multiple discrete layers (e.g., inner shell and outer shell with different compositions) rather than using a single uniform layer. This segmentation allows independent optimization of each layer's thickness and composition, making it easier to control uniformity during manufacturing while achieving the desired total thickness for wavelength control.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying shell thickness, composition ratios, and layer structures to tune the emission wavelength. By establishing precise parameter ranges and relationships (e.g., shell thickness to core size ratio), the patent enables scalable manufacturing with controlled uniformity across different wavelength targets.
3Object-affected harmful factors
If multiple elements are incorporated to achieve cadmium-free red emission, then environmental safety is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges multiple element functions into integrated core/shell structures where elements like Zn, Se, S, and In work together in coordinated layers. This combining approach achieves cadmium-free red emission while streamlining the manufacturing process by establishing standardized multi-layer architectures that can be produced using conventional quantum dot synthesis methods.
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 cadmium-free quantum dot exhibits high luminous efficiency and color purity, suitable for applications in display devices and electroluminescent devices, while avoiding the environmental hazards associated with cadmium.
Implementation Method 1
Quantum dots may absorb light from an excitation source to be in an excitation state, and may emit energy corresponding to the bandgap energies of the quantum dots
Implementation Method 2
Such semiconductor nanocrystal particles have such a small size that they have a large surface area per unit volume and exhibit quantum confinement effects
Data Source
AI summary
A quantum dot including zinc, tellurium, selenium, and sulfur, wherein the quantum dot comprises a core and a shell disposed on the core, and wherein the quantum dot is a cadmium-free red light-emitting quantum dot and has an emission peak wavelength of greater than or equal to about 600 nanometers (nm), and efficiency of greater than or equal to about 50%.