Effect of Thermal Fluctuations on the Radiative Rate in Core/Shell Quantum Dots

Balan, Arunima D.; Eshet, Hagai; Olshansky, Jacob H.; Lee, Youjin V.; Rabani, Eran; Alivisatos, A. Paul

doi:10.1021/acs.nanolett.6b04816

Cited by 31 publications

(50 citation statements)

References 81 publications

(145 reference statements)

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“…To acquire more intrinsic characteristics of the photogenerated excitons in the high color-purity NBE-T-CQDs, temperature-dependent PL spectra were also recorded, and the resulting emission narrowing was analyzed, as has long been used to assess mechanisms of electron–phonon coupling in a wide range of bandgap emitting inorganic QDs 44 , 45 . As the temperature is decreased from 295 to 85 K, all the PL peaks of the NBE-T-CQDs show continuous narrowing and blue-shift (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…2g , the FWHM reduces from 164.7 (30 nm) to 95.4 meV (16 nm) and the emission peak energy of the B-NBE-T-CQDs shifts toward higher energy from 2.627 to 2.725 eV with decreasing temperature from 295 to 85 K. The narrowed FWHM and blue-shifted emission peaks of the NBE-T-CQDs with decreasing temperature are well described by traditional empirical Varshni models, which can be explained by the reduced electron–phonon coupling due to the restricted structural vibrations and distortions at the lower temperatures 44 – 46 . It has been demonstrated that the electron–phonon coupling resulting from structural vibrations and distortions plays a dominating role in determining the FWHM of the PL spectra of inorganic QDs 44 , 45 . Therefore, it is reasonable to conclude that the dramatically reduced electron–phonon coupling demonstrated by the temperature-dependent PL spectra leads to the high color-purity, free-excitonic emission of the NBE-T-CQDs.…”

Section: Resultsmentioning

confidence: 99%

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Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs

et al. 2018

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Carbon quantum dots (CQDs) have emerged as promising materials for optoelectronic applications on account of carbon’s intrinsic merits of high stability, low cost, and environment-friendliness. However, the CQDs usually give broad emission with full width at half maximum exceeding 80 nm, which fundamentally limit their display applications. Here we demonstrate multicolored narrow bandwidth emission (full width at half maximum of 30 nm) from triangular CQDs with a quantum yield up to 54–72%. Detailed structural and optical characterizations together with theoretical calculations reveal that the molecular purity and crystalline perfection of the triangular CQDs are key to the high color-purity. Moreover, multicolored light-emitting diodes based on these CQDs display good stability, high color-purity, and high-performance with maximum luminance of 1882–4762 cd m−2 and current efficiency of 1.22–5.11 cd A−1. This work will set the stage for developing next-generation high-performance CQDs-based light-emitting diodes.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs

et al. 2018

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“…This strategy relies on the fact that the QD emission peak energy is temperature dependent and furthermore is approximately linear in temperature over the 80−300 K range. 41 We could therefore place a 78 K sample into an integrating sphere and record PLQYs while the sample warmed to RT and then use the emission peak energy to determine the corresponding temperature. This process was repeated 5−7 times for each sample to obtain accurate PLQY vs temperature data.…”

Section: Resultsmentioning

confidence: 99%

Temperature-Dependent Hole Transfer from Photoexcited Quantum Dots to Molecular Species: Evidence for Trap-Mediated Transfer

et al. 2017

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The effect of temperature on the rate of hole transfer from photoexcited quantum dots (QDs) is investigated by measuring the driving force dependence of the charge transfer rate for different sized QDs across a range of temperatures from 78 to 300 K. Spherical CdSe/CdS core/shell QDs were used with a series of ferrocene-derived molecular hole acceptors with an 800 meV range in electrochemical potential. Time-resolved photoluminescence measurements and photoluminescence quantum yield measurements in an integrating sphere were both performed from 78 to 300 K to obtain temperature-dependent rates for a series of driving forces as dictated by the nature of the molecular acceptor. For both QD sizes studied and all ligands, the Arrhenius plot of hole transfer exhibited an activated (linear) regime at higher temperatures and a temperature-independent regime at low temperatures. The extracted activation energies in the high-temperature regime were consistent across all ligands for a given QD size. This observation is not consistent with direct charge transfer from the QD valence band to the ferrocene acceptor. Instead, a model in which charge transfer is mediated by a shallow and reversible trap more accurately fits the experimental results. Implications for this observed trap-mediated transfer are discussed including as a strategy to more efficiently extract charge from QDs.

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“…Indium phosphide QDs have garnered significant interest as a cadmium-free option that is tunable throughout the visible wavelength regime (Micic et al, 1994 ; Guzelian et al, 1996 ; Battaglia and Peng, 2002 ; Xie et al, 2007 ; Li and Reiss, 2008 ; Xu et al, 2008 ; Tamang et al, 2016 ). As-synthesized InP QDs, however, are non-emissive due to non-radiative relaxation of excitation generated charge carriers facilitated by trapping at surface defects (Dennis et al, 2012a ; Omogo et al, 2013 ; Balan et al, 2017 ; Reid et al, 2018 ). Fabrication of emissive cores can be performed through two main synthetic routes: etching the surface of the nanoparticle using a fluoride, or overcoating with a larger bandgap semiconductor to create a core/shell heterostructure (Danek et al, 1996 ; Dabbousi et al, 1997 ; Talapin et al, 2002 ; Adam et al, 2005 ; Chen et al, 2013 ; Mordvinova et al, 2014 , 2017 ).…”

Section: Introductionmentioning

confidence: 99%

Bandgap Engineering of Indium Phosphide-Based Core/Shell Heterostructures Through Shell Composition and Thickness

et al. 2018

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The large bulk bandgap (1.35 eV) and Bohr radius (~10 nm) of InP semiconductor nanocrystals provides bandgap tunability over a wide spectral range, providing superior color tuning compared to that of CdSe quantum dots. In this paper, the dependence of the bandgap, photoluminescence emission, and exciton radiative lifetime of core/shell quantum dot heterostructures has been investigated using colloidal InP core nanocrystals with multiple diameters (1.5, 2.5, and 3.7 nm). The shell thickness and composition dependence of the bandgap for type-I and type-II heterostructures was observed by coating the InP core with ZnS, ZnSe, CdS, or CdSe through one to ten iterations of a successive ion layer adsorption and reaction (SILAR)-based shell deposition. The empirical results are compared to bandgap energy predictions made with effective mass modeling. Photoluminescence emission colors have been successfully tuned throughout the visible and into the near infrared (NIR) wavelength ranges for type-I and type-II heterostructures, respectively. Based on sizing data from transmission electron microscopy (TEM), it is observed that at the same particle diameter, average radiative lifetimes can differ as much as 20-fold across different shell compositions due to the relative positions of valence and conduction bands. In this direct comparison of InP/ZnS, InP/ZnSe, InP/CdS, and InP/CdSe core/shell heterostructures, we clearly delineate the impact of core size, shell composition, and shell thickness on the resulting optical properties. Specifically, Zn-based shells yield type-I structures that are color tuned through core size, while the Cd-based shells yield type-II particles that emit in the NIR regardless of the starting core size if several layers of CdS(e) have been successfully deposited. Particles with thicker CdS(e) shells exhibit longer photoluminescence lifetimes, while little shell-thickness dependence is observed for the Zn-based shells. Taken together, these InP-based heterostructures demonstrate the extent to which we are able to precisely tailor the material properties of core/shell particles using core/shell dimensions and composition as variables.

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Effect of Thermal Fluctuations on the Radiative Rate in Core/Shell Quantum Dots

Cited by 31 publications

References 81 publications

Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs

Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs

Temperature-Dependent Hole Transfer from Photoexcited Quantum Dots to Molecular Species: Evidence for Trap-Mediated Transfer

Bandgap Engineering of Indium Phosphide-Based Core/Shell Heterostructures Through Shell Composition and Thickness

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