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857 KiB

Open AccessArticle

Electric Field Effects on Photoluminescence of CdSe Nanoparticles in a PMMA Film

by Takakazu Nakabayashi, Ruriko Ohshima and Nobuhiro Ohta

Crystals 2014, 4(2), 152-167; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst4020152 - 23 Jun 2014

Cited by 13 | Viewed by 6136

External electric field effects on spectra and decay of photoluminescence (PL) as well as on absorption spectra were measured for CdSe nanoparticles in a poly(methyl methacrylate) (PMMA) film. Electrophotoluminescence (E-PL) spectra as well as electroabsorption spectra show a remarkable Stark shift which depends [...] Read more.

External electric field effects on spectra and decay of photoluminescence (PL) as well as on absorption spectra were measured for CdSe nanoparticles in a poly(methyl methacrylate) (PMMA) film. Electrophotoluminescence (E-PL) spectra as well as electroabsorption spectra show a remarkable Stark shift which depends on the particle size, indicating a large electric dipole moment in the first exciton state. The E-PL spectra also show that PL of CdSe is quenched by application of electric fields, and the magnitude of the field-induced quenching becomes larger with increasing size. The PL decay profiles observed in the absence and presence of electric field show that the field-induced quenching of PL mainly originates from the field-induced decrease in population of the emitting state prepared through the relaxation from the photoexcited state. Full article

(This article belongs to the Special Issue Semiconductor Nanocrystals)

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789 KiB

Open AccessArticle

Growth Mechanisms of CdS Nanocrystals in Aqueous Media

by Loredana Latterini and Alessandro Iagatti

Crystals 2012, 2(2), 618-626; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst2020618 - 06 Jun 2012

Cited by 2 | Viewed by 5674

Abstract

CdS nanocrystals were prepared in water-in-oil microemulsions. The nanocrystal properties, absorption and luminescence spectra and size distributions, were monitored at different times after mixing the microemulsions of the two precursors to obtain information on their growth mechanism. In particular, CdS nanocrystals were prepared [...] Read more.

CdS nanocrystals were prepared in water-in-oil microemulsions. The nanocrystal properties, absorption and luminescence spectra and size distributions, were monitored at different times after mixing the microemulsions of the two precursors to obtain information on their growth mechanism. In particular, CdS nanocrystals were prepared using water-in-heptane or water-in-nonane microemulsions. The results obtained from the investigation of nanocrystals prepared using heptane as the organic phase, confirmed that nanocrystal nucleation is fast while their growth is determined by droplet exchange content rate. Size distribution histograms obtained from the sample at early time points after mixing presented a bimodal population having average sizes of 3.0 ± 0.1 and 5.8 ± 0.1 nm, thus indicating that surface process controls the nanocrystal growth. With longer reaction times the occurrence of water droplet coalescence is likely responsible for the formation of nanocrystal agglomerates. Using a water-in-nonane microemulsion, the droplet exchange rate can be modified, thus leading to smaller CdS nanocrystals. However, the development of structural defects cannot be excluded, as evidenced by the luminescence spectra of the suspension. In general, aging of the nanocrystal in the pristine microemulsion resulted in the development of cubic semiconductor nanostructures. Full article

(This article belongs to the Special Issue Semiconductor Nanocrystals)

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575 KiB

Open AccessArticle

Influence of Semiconductor Nanocrystal Concentration on Polymer Hole Transport in Hybrid Nanocomposites

by Ryan Pate and Adrienne D. Stiff-Roberts

Crystals 2012, 2(1), 78-89; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst2010078 - 16 Jan 2012

Cited by 4 | Viewed by 5735

Abstract

This article investigates hole transport in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)/CdSe colloidal quantum dot (CQD) nanocomposites using a modified time-of-flight photoconductivity technique. The measured hole drift mobilities are analyzed in the context of Bässler’s Gaussian disorder model and the correlated disorder model in order to [...] Read more.

This article investigates hole transport in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)/CdSe colloidal quantum dot (CQD) nanocomposites using a modified time-of-flight photoconductivity technique. The measured hole drift mobilities are analyzed in the context of Bässler’s Gaussian disorder model and the correlated disorder model in order to determine the polymer internal morphology of hybrid nanocomposite thin films. This work shows that increasing the CdSe CQD concentration decreases the polymer hole mobility from ~5.9 × 10⁻⁶ cm²/Vs in an MEH-PPV film to ~8.1 × 10⁻⁸ cm²/Vs in a 20:80 (wt%) MEH-PPV:CdSe CQD nanocomposite film (measured at 25 °C and ~2 × 10⁵ V/cm). The corresponding disorder parameters indicate increasing disruption of interchain interaction with increasing CQD concentration. This work quantifies polymer chain morphology in hybrid nanocomposite thin films and provides useful information regarding the optimal use of semiconductor nanocrystals in conjugated polymer-based optoelectronics. Full article

(This article belongs to the Special Issue Semiconductor Nanocrystals)

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