Semiconductor Nanocrystals High-Temperature Photoluminescence Stability
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Solution Overview
Problem
Semiconductor nanocrystals experience a significant decrease in solid state photoluminescence external quantum efficiency with increasing temperature, affecting their performance in various applications.
Innovation Solution
Developing semiconductor nanocrystals with a multiple LO phonon assisted charge thermal escape activation energy of at least 0.5 eV and maintaining a solid state photoluminescence external quantum efficiency of at least 95% at temperatures up to 90°C, achieved through a method involving the introduction of chalcogenide and metal precursors in specific molar ratios and reaction temperatures to form shells around the nanocrystal cores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If semiconductor nanocrystals are used in solid state photoluminescence applications, then light emission is achieved, but the external quantum efficiency decreases significantly with increasing temperature
Solution Approach 1:
The patent modifies the electronic structure parameters of the nanocrystals by introducing deep trap states within the bandgap through specific shell compositions and growth conditions. This changes the thermal activation energy parameter from typical values to at least 0.5 eV, fundamentally altering the temperature dependence of carrier escape and maintaining high photoluminescence efficiency across a broad temperature range from 25°C to 90°C and beyond.
2Reliability
If the nanocrystal structure is modified to improve temperature stability, then radiative lifetime and efficiency are enhanced, but the manufacturing process complexity increases
Solution Approach 1:
The patent employs a segmented core-shell structure where the shell is composed of multiple materials with different bandgaps and compositional gradients. This segmentation creates distinct functional regions: the core provides quantum confinement, the intermediate shell layers create deep trap states at specific energy levels, and the outer shell provides passivation. This segmented approach systematically achieves temperature stability while maintaining manufacturing feasibility through sequential shell growth.
3Reliability
If deep trap states are introduced to prevent thermal escape, then charge carrier confinement is improved, but the absorption characteristics may be affected
Solution Approach 1:
The patent applies local quality by creating spatially and energetically localized deep trap states within the shell structure. These trap states are positioned at specific energy levels within the bandgap through controlled compositional gradients and thickness variations in different shell regions. The local modification of electronic structure at specific locations and energy levels enables selective carrier confinement without significantly affecting the overall optical absorption properties of the nanocrystal.
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 nanocrystals retain high photoluminescence efficiency across a broad temperature range, ensuring consistent performance in applications from 25°C to 90°C, with enhanced radiative lifetime and absorption characteristics.
Implementation Method 1
The solid state photoluminescence external quantum efficiency of semiconductor nanocrystals have been observed to be adversely affected during use by at least the temperature of the environment in which the nanocrystals are used
Implementation Method 2
a multiple LO phonon assisted charge thermal escape activation energy of at least 0.5 eV
Data Source
AI summary
A semiconductor nanocrystal characterized by having a solid state photoluminescence external quantum efficiency at a temperature of 90° C. or above that is at least 95% of the solid state photoluminescence external quantum efficiency of the semiconductor nanocrystal at 25° C. is disclosed. A semiconductor nanocrystal having a multiple LO phonon assisted charge thermal escape activation energy of at least 0.5 eV is also disclosed. A semiconductor nanocrystal capable of emitting light with a maximum peak emission at a wavelength in a range from 590 nm to 650 nm characterized by an absorption spectrum, wherein the absorption ratio of OD at 325 nm to OD at 450 nm is greater than 5.5. A semiconductor nanocrystal capable of emitting light with a maximum peak emission at a wavelength in a range from 545 nm to 590 nm characterized by an absorption spectrum, wherein the absorption ratio of OD at 325 nm to OD at 450 nm is greater than 7. A semiconductor nanocrystal capable of emitting light with a maximum peak emission at a wavelength in a range from 495 nm to 545 nm characterized by an absorption spectrum, wherein the absorption ratio of OD at 325 nm to OD at 450 nm is greater than 10. A composition comprising a plurality of semiconductor nanocrystals wherein the solid state photoluminescence efficiency of the composition at a temperature of 90° C. or above is at least 95% of the solid state photoluminescence efficiency of the composition 25° C. is further disclosed. A method for preparing semiconductor nanocrystals comprises introducing one or more first shell chalcogenide precursors and one or more first shell metal precursors to a reaction mixture including semiconductor nanocrystal cores, wherein the first shell chalcogenide precursors are added in an amount greater than the first shell metal precursors by a factor of at least about 2 molar equivalents and reacting the first shell precursors at a first reaction temperature of at least 300° C. to form a first shell on the semiconductor nanocrystal cores. Populations, compositions, components and other products including semiconductor nanocrystals of the invention are disclosed. Populations, compositions, components and other products including semiconductor nanocrystals made in accordance with any method of the invention is also disclosed.