Controlling Spontaneous Emission of CdSe Nanoparticles Dispersed in Electrospun Fibers of Polycarbonate Urethane

Abstract

Luminescent fibrous composite films consisting of submicrometer diameter fibers were prepared by electrospinning of segmented polycarbonate urethane (PCU) in dimethyl formamide and tri-n-octylphosphine oxide (TOPO)-capped CdSe nanocrystals (5 nm in diameter) in toluene. Using a pair of conductive electrodes separated with an air gap, we successfully produced randomly deposited and uniaxially aligned electrospun fibers. The surface structure of the electrospun fibers was studied using atomic force microscopy (AFM) and was compared to the corresponding film prepared by casting. In cast film, tapping mode AFM imaging suggests that hard urethane segments organize into rodlike morphology dispersed in soft polycarbonate. When PCU/CdSe dispersions were subjected to electrospinning, copolymer domains were forced to arrange into lamella along the fiber axis due to elongational flow and high stretching. Molecular orientation in the domains of the composite fibers was confirmed by polarized infrared spectroscopy. We demonstrated that formation of the oriented domains by electrospinning develops a hierarchical structure, which consequently modifies spectral properties because new multiple sharp lines appeared in the photoluminescence (PL) spectra of the fibers. In contrast to randomly deposited fibers, the PL intensity of uniaxially aligned fibers was found to be angle dependent. We propose that the elongated internal structure within the fibers controls the spontaneous emission of CdSe nanoparticles dispersed throughout the electrospun mat. A discussion on the nature of the controlled spontaneous emission is provided.

Fabrication and Characterization of Electrospun Semiconductor Nanoparticle—Polyelectrolyte Ultra-Fine Fiber Composites for Sensing Applications

“…This change in the PL lineshape is expected if the SNPs are confined within the fiber [30]. Additionally, there are new higher energy peaks in the PL of the fiber mats that have been also shown by Demir et al when quantum dots are confined in fibers that are smaller than the emission wavelength [27] (Figure 4(c). The excited lifetimes of the SNPs in water and the aqueous PAA-SNP solution are the same, 20 ns ± 2 ns and 19 ns ± 4 ns respectively but are reduced to 14 ns ± 2 ns in the fiber mat suggesting there is an a new relaxation pathway introduced by the fiber geometry (Figure 4(d).…”

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“…We furthermore showed control of spontaneous emission originating from nanocrystals embedded in electrospun nanobers. 35 …”

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