PbS and PbS/CdS quantum dots: Synthesized by photochemical approach, structural, linear and nonlinear response propertie
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PbS and PbS/CdS quantum dots: Synthesized by photochemical approach, structural, linear and nonlinear response properties, and optical limiting Mehdi Molaeia)1, Masoud Karimipour1, Samaneh Abbasi1, Mohammad Khanzadeh1, Masoud Dehghanipour1 1
Department of the Physics, Faculty of Science, Vali-e-Asr University, Rafsanjan, Iran Address all correspondence to this author. e-mail: [email protected]
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Received: 22 June 2019; accepted: 6 January 2020
In this work, PbS and PbS/CdS core–shell quantum dots (QDs) were synthesized by a new photochemical approach. Prepared QDs were characterized by means of x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive x-ray analysis (EDAX), UV–Vis, and Z-scan analyses. Synthesized QDs were in a cubic phase with a spherical morphology, and the crystallite sizes are estimated using the strain–size method. A uniform shift of Bragg diffraction peaks and quenching (200) Bragg plane are interpreted as the growth of the CdS shell. Linear optical properties were investigated using Urbach analysis and Tauc formula. It was found that the density of states of QD conduction and valence bands are three dimensional. The estimated sizes of PbS QDs and PbS/CdS using exciton absorption peaks at room temperature are 1.8 and 2.7 nm, respectively, which are in good agreement with the strain–size plot analysis. The growth of the CdS shell resulted in a considerable decrease in the nonlinearity refractive index and a significant increase in the nonlinear absorption.
Introduction Lead sulfide (PbS) is an interesting direct and small–band gap (0.41 eV) semiconductor [1, 2]. Because of the quantum confinement effects, its band edge indicates a blue shift by decreasing the size lower than the Bohr radius [3, 4]. PbS nanoparticles are promising materials for different applications such as electroluminescence devices [1], solar cells [3], and sensors [4]. Mamiyev et al. reported preparing PbS QDs in a copolymer matrix at 80 °C temperature and investigated optical properties of prepared QDs [3]. Zhao et al. synthesized PbS QDs in different sizes and morphologies using a microwave-activated approach [5]. Other groups also reported different approaches for preparing PbS and PbS/CdS core– shell structures [6]. Moreover, Moreel et al. reported a quantitative analysis about the size dependence of the optical properties of PbS QDs using Maxwell-Garnett effective medium theory. They concluded that the estimated size from absorption spectra very well agreed with transmission electron microscopy (TEM) analysis and previously reported values [7].
ª Materials Research Society 2020
Nonlinear optical (NLO) properties are relevance for different applications such as nonlinear photonics, photovoltaic and photoconductivity [8], fast optical switching [9], and information processing [10]. The growth of an inorganic wider band gap semiconductor around QDs is a powerful approach for improving different optical properties of QDs, and also previous reports indicated NLO response enhanceme
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