Extremal problems with rare events. I

Nakonechnyi, A. N.

doi:10.1007/bf01068550

Cited by 4 publications

(4 citation statements)

References 1 publication

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“…It has been shown that cadmium chalcogenides grow on CdSe at a higher rate than the corresponding zinc chalcogenides. [39][40] This difference in the reaction rates enabled us to obtain the desired composition gradient by combining CdSe NPLs with Cd(OA)2 and Zn(OA)2 in different ratios. The shell synthesis was performed at 300 °C by slowly injecting 1-octanethiol together with oleic acid.…”

Section: Cdse/cd X Zn 1-x S Core/shell Npls the Above Data Demonstramentioning

confidence: 99%

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Compositional Grading for Efficient and Narrowband Emission in CdSe-Based Core/Shell Nanoplatelets

et al. 2019

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Colloidal semiconductor nanoplatelets exhibit exceptionally narrow photoluminescence spectra. This occurs because samples can be synthesized in which all nanoplatelets share the same atomic-scale thickness. As this dimension sets the emission wavelength, inhomogeneous linewidth broadening due to size variation, which is always present in samples of quasi-spherical nanocrystals (quantum dots), is essentially eliminated. Nanoplatelets thus offer improved, spectrally pure emitters for various applications. Unfortunately, due to their non-equilibrium shape, nanoplatelets also suffer from low photo-, chemical, and thermal stability, which limits their use. Moreover, their poor stability hampers the development of efficient synthesis protocols for adding high-quality protective inorganic shells, a well-known strategy to improve the performance of quantum dots. Herein, we report a general synthesis approach to highly emissive and stable core/shell nanoplatelets with various shell compositions, including CdSe/ZnS, CdSe/CdS/ZnS, CdSe/CdxZn1-xS, and CdSe/ZnSe. Motivated by previous work on quantum dots, we find that slow, high-temperature growth of shells containing a compositional gradient reduces strain-induced crystal defects and minimizes the emission linewidth while maintaining good surface passivation and nanocrystal uniformity. Indeed, our best core/shell nanoplatelets (CdSe/CdxZn1-xS) show photoluminescence quantum yields of 90% with linewidths as low as 56 meV (19.5 nm at 655 nm). To confirm the high quality of our different core/shell nanoplatelets for a specific application, we demonstrate their use as gain media in low-threshold ring lasers. More generally, the ability of our synthesis protocol to engineer high-quality shells can help further improve nanoplatelets for optoelectronic devices.

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Section: Cdse/cd X Zn 1-x S Core/shell Npls the Above Data Demonstramentioning

confidence: 99%

“…We attribute this reduced homogeneous nucleation to a higher monomer solubility due to the injection of oleic acid and the lower reactivity of the Zn-precursor. 35,40 We discuss the optimization and characterization of CdSe/CdxZn1-xS core/shell NPLs further in a later section.…”

Section: Cdse/cd X Zn 1-x S Core/shell Npls the Above Data Demonstramentioning

confidence: 99%

Compositional Grading for Efficient and Narrowband Emission in CdSe-Based Core/Shell Nanoplatelets

et al. 2019

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show abstract

“…It has been shown that cadmium chalcogenides grow on CdSe at a higher rate than the corresponding zinc chalcogenides. [36][37] This difference in the reaction rates enabled us to obtain the desired composition gradient by combining CdSe NPLs with Cd(OA)2 and Zn(OA)2 in different ratios. The shell synthesis was performed at 300 °C by slowly injecting 1-octanethiol together with oleic acid.…”

Section: Resultsmentioning

confidence: 99%

“…We attribute this reduced homogeneous nucleation to a higher monomer solubility due to the injection of oleic acid and the lower reactivity of the Znprecursor . [37][38] We discuss the optimization and characterization of CdSe/CdxZn1-xS core/shell NPLs further in a later section.…”

Section: Resultsmentioning

confidence: 99%

High-Temperature Synthesis of CdSe-Based Core/Shell, Core/Shell/Shell, and Core/Graded-Shell Nanoplatelets for Stable and Efficient Narrowband Emitters

Rossinelli

Rojo²,

Mule³

et al. 2019

Preprint

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<div>Colloidal semiconductor nanoplatelets exhibit exceptionally narrow photoluminescence spectra. This occurs because samples can be synthesized in which all nanoplatelets share the same atomic-scale thickness. As this dimension sets the emission wavelength, inhomogeneous linewidth broadening due to size variation, which is always present in samples of quasi-spherical nanocrystals (quantum dots), is essentially eliminated. Nanoplatelets thus offer improved, spectrally pure emitters for various applications. Unfortunately, due to their non-equilibrium shape, nanoplatelets also suffer from low photo-, chemical, and thermal stability, which limits their use. Moreover, their poor stability hampers the development of efficient synthesis protocols for adding high-quality protective inorganic shells, which are well known to improve the performance of quantum dots. <br></div><div>Herein, we report a general synthesis approach to highly emissive and stable core/shell nanoplatelets with various shell compositions, including CdSe/ZnS, CdSe/CdS/ZnS, CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S, and CdSe/ZnSe. Motivated by previous work on quantum dots, we find that slow, high-temperature growth of shells containing a compositional gradient reduces strain-induced crystal defects and minimizes the emission linewidth while maintaining good surface passivation and nanocrystal uniformity. Indeed, our best core/shell nanoplatelets (CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S) show photoluminescence quantum yields of 90% with linewidths as low as 56 meV (19.5 nm at 655 nm). To confirm the high quality of our different core/shell nanoplatelets for a specific application, we demonstrate their use as gain media in low-threshold ring lasers. More generally, the ability of our synthesis protocol to engineer high-quality shells can help further improve nanoplatelets for optoelectronic devices.</div>

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Probability-theoretical analog of the vector lyapunov function method

Nakonechnyi¹

1994

Cybern Syst Anal

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The main ideas of the vector Lyapunov function (VLF) method were advanced in 1962 by Bellman [1] and Matrosov [2]. In this method [3], a Lyapunov function and a comparison equation are constructed for each subsystem. Then the dependences between the subsystems and the effect of external noise are allowed for by constructing a vector Lyapunov function (as a collection of the scalar Lyapunov functions of the subsystems) and an aggregate comparison function for the entire complex system. A probability-theoretical analog of this method for convergence analysis of stochastic approximation processes has been developed in [4].The abstract approach proposed in [5] eliminates all restrictions on the system phase space, the system trajectories, the class of Lyapunov functions, etc. The analysis focuses only on the conditions that relate sequences of Lyapunov function values with the derivative and ensure a particular type (mode, character) of stability. In our article, we extend this approach to the VLF method for discrete stochastic dynamic systems.

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Extremal problems with rare events. I

Cited by 4 publications

References 1 publication

Compositional Grading for Efficient and Narrowband Emission in CdSe-Based Core/Shell Nanoplatelets

Compositional Grading for Efficient and Narrowband Emission in CdSe-Based Core/Shell Nanoplatelets

High-Temperature Synthesis of CdSe-Based Core/Shell, Core/Shell/Shell, and Core/Graded-Shell Nanoplatelets for Stable and Efficient Narrowband Emitters

Probability-theoretical analog of the vector lyapunov function method

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