Applications of ZnS:Mn 2+ nanocrystals
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Applications of ZnS:Mn2+ nanocrystals J. F. Suyver1 , A. Meijerink and J. J. Kelly Debye Institute, Physics and Chemistry of Condensed Matter, Utrecht University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands. ABSTRACT Nonstoichiometric precursor-ratios for the synthesis of ZnS:Mn2+ are discussed and the significant influence on the luminescence features and crystal size is explained. From the temperature quenching of the ZnS photoluminescence a luminescence excitation model is proposed. Measurements of the photoelectrochemical properties of nanocrystalline ZnS electrodes doped with Mn2+ are also presented and discussed. The observation of both anodic and cathodic photocurrent is direct evidence for the nanocrystalline nature of the system. In-situ photoluminescence measurements showed stable Mn2+ related photoluminescence over a large potential range. INTRODUCTION Research on electroluminescent devices has started to focus on nanocrystalline composite materials [1–3]. The main reasons for the increasing interest in these materials are, on the one hand, the simple fabrication of (doped) semiconductor nanocrystals (NC) [4, 5] and, on the other hand, the fact that in combination with a suitable semiconducting polymer and conducting substrate electrons and holes can be injected directly into the conduction- and valence bands of the nanocrystals [2, 6]. This might allow for an electroluminescent device based on doped semiconductor nanocrystals. In this paper both the preparation of ZnS:Mn2+ nanocrystal powders and electrodes based on layers of these nanocrystals is described. Photoluminescence (PL), X-ray powder diffraction, and photoelectrochemical methods are used to characterize the powders and the electrodes. In particular photocurrent-potential and in-situ photoluminescence measurements can be used to show that the electrodes have properties typical of nanoparticulate layers. EXPERIMENTAL The inorganic synthesis used to prepare ZnS:Mn2+ nanocrystals is similar to that described in the literature [7]. All steps of the synthesis were performed at room temperature and under conditions of ambient pressure and atmosphere. A capping polymer was used to prevent particle agglomeration. For this purpose, 10.2 g of Na(PO3 )n was dissolved in (80 − x) ml of ultrapure water (R ∼ 16 MΩ). While the solution was stirred, 10 ml of a 1 M Zn(CH3 COO)2 ·2H2 O solution was added and allowed to mix, followed by 10 ml of a 0.1 M MnCl2 ·4H2 O solution and, after a few minutes stirring, x ml of a 1 M Na2 S·9H2 O solution. A white opaque solution resulted. Corresponding author. Tel.: +31 − 30 − 253 2214; Fax: +31 − 30 − 253 2403; E-mail: [email protected] 1
Y3.8.1
6 2-
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[S ] / [Zn ] = 0.4
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Figure 1: (A) Emission spectra for ZnS:Mn2+ nanocrystals dependent on the precursor
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