Cadmium-Free Quantum Dots with Halogen Shell for Thermal Stability
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Solution Overview
Problem
Existing quantum dots face challenges in maintaining high photoluminescence efficiency at elevated temperatures due to thermal quenching, and most efficient ones contain cadmium, which is environmentally harmful.
Innovation Solution
Development of cadmium-free quantum dots with a core-shell structure, where the shell comprises crystalline or amorphous material and at least two halogens, such as fluorine, chlorine, or iodine, to enhance thermal stability and photoluminescence efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If quantum dots contain cadmium to achieve high photoluminescence efficiency, then luminous efficiency is improved, but environmental harm increases
Solution Approach 1:
The patent changes the chemical composition parameters of the quantum dot shell by incorporating halogen elements (fluorine, chlorine, bromine, or iodine) at specific concentrations (0.1-50 atomic percent). This compositional modification enables cadmium-free quantum dots to achieve high photoluminescence efficiency (exceeding 90% quantum efficiency) while eliminating the environmental harm associated with cadmium.
Solution Approach 2:
The patent creates a composite shell structure combining semiconductor materials (such as ZnS, CdS, ZnSe, CdSe, ZnTe, or CdTe) with halogen elements. This composite material approach allows the shell to simultaneously provide structural integrity, surface passivation, and enhanced photoluminescence properties without requiring cadmium in the core, thereby resolving the contradiction between efficiency and environmental safety.
2Temperature
If quantum dots operate in high temperature environment, then device operational range is improved, but photoluminescence efficiency deteriorates due to thermal quenching
Solution Approach 1:
The patent applies beforehand cushioning by incorporating halogen elements into the shell structure prior to high-temperature operation. The halogen-containing shell (with 0.1-50 atomic percent halogen) pre-establishes thermal stability and reduces thermal quenching effects, allowing the quantum dot to maintain high photoluminescence efficiency (exceeding 90% quantum efficiency) even when operated at elevated temperatures up to 150°C or higher.
Solution Approach 2:
The patent modifies the shell's physical and chemical parameters by adding halogen elements, which changes the shell's thermal properties and energy band structure. This parameter change creates a more thermally stable shell that prevents non-radiative recombination pathways at high temperatures, thereby cushioning against thermal quenching and maintaining high luminous efficiency across a broader temperature range.
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 dots exhibit solid state photoluminescence quantum efficiency greater than 95% at 90°C and 80% at 150°C, compared to 25°C, while being environmentally friendly.
Implementation Method 1
Quantum dots may absorb light from an excitation source and may emit light energy corresponding to an energy bandgap of the quantum dot
Implementation Method 2
A quantum dot having a core-shell structure may have a slightly increased luminous efficiency due to surface passivation by the shell
Data Source
AI summary
A quantum dot includes a core-shell structure including a core including a first semiconductor nanocrystal and a shell disposed on the core, and including a material at least two different halogens, and the quantum dot does not include cadmium.