Synthesis and Luminescence Properties of Core/Shell ZnS:Mn/ZnO Nanoparticles

Nanoscale Research Letters, Jan 2009

In this paper the influence of ZnO shell thickness on the luminescence properties of Mn-doped ZnS nanoparticles is studied. Transmission electron microscopy (TEM) images showed that the average diameter of ZnS:Mn nanoparticles is around 14 nm. The formation of ZnO shells on the surface of ZnS:Mn nanoparticles was confirmed by X-ray diffraction (XRD) patterns, high-resolution TEM (HRTEM) images, and X-ray photoelectron spectroscopy (XPS) measurements. A strong increase followed by a gradual decline was observed in the room temperature photoluminescence (PL) spectra with the thickening of the ZnO shell. The photoluminescence excitation (PLE) spectra exhibited a blue shift in ZnO-coated ZnS:Mn nanoparticles compared with the uncoated ones. It is shown that the PL enhancement and the blue shift of optimum excitation wavelength are led by the ZnO-induced surface passivation and compressive stress on the ZnS:Mn cores.

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Synthesis and Luminescence Properties of Core/Shell ZnS:Mn/ZnO Nanoparticles

Daixun Jiang 0 Lixin Cao 0 Wei Liu 0 Ge Su 0 Hua Qu 0 Yuanguang Sun 0 Bohua Dong 0 0 D. Jiang L. Cao (&) W. Liu G. Su H. Qu Y. Sun B. Dong Institute of Materials Science and Engineering, Ocean University of China , Qingdao 266100, People's Republic of China In this paper the influence of ZnO shell thickness on the luminescence properties of Mn-doped ZnS nanoparticles is studied. Transmission electron microscopy (TEM) images showed that the average diameter of ZnS:Mn nanoparticles is around 14 nm. The formation of ZnO shells on the surface of ZnS:Mn nanoparticles was confirmed by X-ray diffraction (XRD) patterns, high-resolution TEM (HRTEM) images, and X-ray photoelectron spectroscopy (XPS) measurements. A strong increase followed by a gradual decline was observed in the room temperature photoluminescence (PL) spectra with the thickening of the ZnO shell. The photoluminescence excitation (PLE) spectra exhibited a blue shift in ZnO-coated ZnS:Mn nanoparticles compared with the uncoated ones. It is shown that the PL enhancement and the blue shift of optimum excitation wavelength are led by the ZnO-induced surface passivation and compressive stress on the ZnS:Mn cores. - In recent years, a great deal of attention has been devoted to doped semiconductor nanomaterials mainly due to their unique luminescence properties arising from quantum confinement effects. The doping ions act as recombination centers for the excited electronhole pairs and play an influential role in determining optical properties, resulting in strong luminescence. Among the semiconductor nanomaterials, zinc sulfide is particularly suitable for use as luminescent host materials for a variety of dopants because of its wide band gap energy at room temperature. There have been numerous reports about the structural and luminescence properties of doped ZnS nanocrystals, such as ZnS nanocrystals doped with manganese [14], copper [57], silver [8], samarium [9], europium [10, 11], and terbium [12]. It has been extensively studied for a variety of commercial devices, such as electro-optic modulators, photoconductors, optical coatings, field effect transistors, infrared windows, electroluminescent display [1317]. Unfortunately, serious drawbacks exist in these nanomaterials, such as their instability under high temperature treatment [18], degradation during the operation and dispersal into vacuum, which will contaminate the field emitter and thus hinder the electron emission [19], and high surface-to-volume ratio because of small particle size, which will result in low luminescence efficiency. In order to conquer such serious shortcomings, accordingly, core/ shell structural nanomaterials have been developed and have shown dramatically enhanced properties. Enhanced luminescence and/or stability has been observed in ZnS:Mn/SiO2 nanoparticles [20], ZnS:Mn/ZnS nanocrystals [21], ZnS:Mn/Zn(OH)2 nanoparticles [22], ZnS:Mn/ ZnO nanocrystals [23], and CdSe/ZnO nanoparticles [24]. In addition, the ZnO particles on the ZnS:Ag particulates have demonstrated a high effectiveness to prevent the degradation of ZnS:Ag particulates from electron bombardment [25]. Compared with the uncoated nanocrystals, the photoluminescence of the nanocrystals with a core/shell structure is enhanced. This is usually interpreted as being due to the surface passivation that inhibits the nonradiative recombination, thus improving the photoluminescence properties. At the same time, a higher stability will be obtained, coming from the protection effect of the surrounding matrix [26]. ZnO-coated ZnS:Mn nanoparticles have been prepared by different groups [23, 27]; however, the ZnO shells reported in these literatures are of rather poor crystallinity, which is indicated by their X-ray diffraction (XRD) results. Usually, the ZnO shell with higher crystallinity will produce stress on the ZnS:Mn because of the lattice mismatch, and bring efficient luminescent transitions inducing enhanced luminescence [28]. In this paper, a convenient route to prepare higher crystallinity core/shell structural ZnS:Mn/ZnO nanoparticles is reported, with the emphasis on the improved luminescence properties brought by the ZnO capping on the ZnS:Mn nanoparticles. The shell material, ZnO, is a wide band gap semiconductor with excellent chemical and thermal stability. Therefore, surface modification of ZnS:Mn nanoparticles by ZnO shell is expected to have a passivating effect on the surface states of ZnS:Mn, which would result in enhanced luminescence. All the reactants and solvents used in this work were of analytical grade and used without any further purification. Synthesis of ZnS:Mn Cores Typically, 0.01 mol zinc acetate [Zn(CH3COO)2 2H2O], 0.005 mol thioacetamide [CH3CSNH2], and 5 9 10-5 mol manganese acetate [Mn(CH3COO)2 4H2O] were put into a Teflon-lined stainless steel autoclave of 72 mL capacity, and then the autoclave was filled with a mixture solvent of ethylenediamine and deionized water (in 1:1 volu (...truncated)


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Daixun Jiang, Lixin Cao, Wei Liu, Ge Su, Hua Qu, Yuanguang Sun, Bohua Dong. Synthesis and Luminescence Properties of Core/Shell ZnS:Mn/ZnO Nanoparticles, Nanoscale Research Letters, 2009, pp. 78-83, Volume 4, Issue 1, DOI: 10.1007/s11671-008-9205-6