III-V Core Quantum Dots with Alloyed II-VI Shell for Blue Light Absorbance
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Solution Overview
Problem
Quantum dots used for luminescent downconversion face challenges such as low absorbance in violet and blue wavelengths, toxicity issues due to heavy metals like Cd, and low photoluminescence quantum yield, which hinder their effectiveness in display and lighting applications.
Innovation Solution
A quantum dot design featuring a core of III-V material, a first layer of II-VI material, and an external shell of ternary or quaternary II-VI material with a controlled Cd content, optimized to enhance blue light absorbance and photoluminescence, while minimizing Cd usage to comply with regulatory limits, and incorporating a ligand shell for photostability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quantum dots with CdSe core and CdS shell are used for downconversion, then high photoluminescence quantum yield is achieved, but toxicity increases due to Cd content
Solution Approach 1:
The patent changes the compositional parameters by replacing CdSe/CdS with InP-based cores and ZnS/ZnSe shells, fundamentally altering the material system to eliminate toxic Cd while maintaining optical performance. This parameter change enables achieving high photoluminescence quantum yield without the harmful toxicity of cadmium
Solution Approach 2:
The patent employs composite material structures with InP cores and ZnS/ZnSe shells, creating a heterostructured quantum dot that combines the advantageous properties of different materials - InP provides the core optical properties while ZnS/ZnSe shells provide protection and enhance photoluminescence quantum yield, all without containing toxic cadmium
2Object-affected harmful factors
If quantum dots with InP core and ZnS/ZnSe shell are used for downconversion, then toxicity is reduced, but absorbance in violet and blue wavelengths becomes low
Solution Approach 1:
The patent modifies the shell composition parameters by introducing sulfur (S) into the ZnSe shell to create ZnSeS alloy shells. This compositional parameter change extends the absorbance range into the violet and blue wavelengths while maintaining the low-toxicity advantage of InP-based quantum dots
Solution Approach 2:
The patent applies local quality enhancement by creating a graded shell structure where ZnSeS alloy composition is optimized in specific regions. The shell contains ZnSeS with varying S content to specifically enhance blue light absorbance at the interface region while maintaining overall structural integrity and low toxicity
3Use of energy by moving object
If Cd content is increased to enhance blue light absorbance, then absorbance in violet and blue wavelengths improves, but Cd concentration exceeds legal restriction limits
Solution Approach 1:
The patent extracts and eliminates cadmium from the quantum dot structure, replacing it with non-toxic InP/ZnS/ZnSeS materials. This extraction of the harmful substance (Cd) achieves blue light absorbance enhancement through alternative material composition without exceeding any legal Cd concentration limits
Solution Approach 2:
The patent introduces ZnSeS shell as an intermediary material that mediates between the InP core and the external environment. The ZnSeS shell provides the necessary blue light absorbance enhancement and optical coupling while completely avoiding cadmium, serving as a safe intermediary that achieves the desired optical properties without toxic substances
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 quantum dots exhibit high absorbance in blue and violet wavelengths, high photoluminescent quantum yield, and reduced self-absorption, enabling efficient downconversion with minimal Cd content, suitable for opto-electronic applications and conversion of blue light to green or red for white color spectra.
Implementation Method 1
Quantum dots are an enabling material for applications relying on luminescent downconversion, i.e., conversion of light with a higher frequency to light with a lower frequency
Implementation Method 2
The obtained internal photoluminescent quantum yield is relatively high: it can be around 45%
Data Source
AI summary
The present disclosure relates to quantum dots with a core of III-V material, a first layer of II-VI material and an external shell of II-VI material to be used, for example, in downconverters. The external shell is preferably made of an alloy of Zn and Cd with Se or S. Introducing a small amount of Cd in the external shell provides excellent absorbance performance in blue, violet and UV wavelengths. The amount of Cd needed for this increase in absorbance can be very low. Further, the emitted light can be nearly monochromatic, which is especially interesting in electronic applications.