Synthesis and characterization of manganese-doped CdS nanoparticlesy Christine Barglik-Chory,* a Christian Remenyi, a Cristina Dem, b Michael Schmitt, b Wolfgang Kiefer, b Charles Gould, c Christian Ru ¨ster, c Georg Schmidt, c Detlev M. Hofmann, d Daniel Pfisterer d and Gerd Mu ¨ller a a Lehrstuhl fu ¨ r Silicatchemie, Bayerische Julius-Maximilians-Universita ¨t Wu ¨ rzburg, D-97070, Wu ¨ rzburg, Ro ¨ ntgenring 11, Germany. E-mail: barglik@silchem.uni-wuerzburg.de; Fax: +49 (0) 931/31-2109; Tel: +49 (0) 931/31-2633 b Institut fu ¨ r Physikalische Chemie, Lehrstuhl II, Bayerische Julius-Maximilians-Universita ¨t Wu ¨ rzburg, D-97074 Wu ¨ rzburg, Am Hubland, Germany c Physikalisches Institut, EP III, Bayerische Julius-Maximilians-Universita ¨t Wu ¨ rzburg, D-97074 Wu ¨ rzburg, Am Hubland, Germany d I. Physikalisches Institut, Justus-Liebig-Universita ¨ t, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany Received 13th January 2003, Accepted 14th February 2003 First published as an Advance Article on the web 6th March 2003 We present a novel colloidal route to photoluminescent CdS quantum dots and the doping of these nanoparticles with divalent manganese ions, resulting in emission caused by Mn 2+ in addition to the band gap related emission of CdS. The semimagnetic semiconductor was synthesized using dithiol 1,2- bis(mercaptomethyl)benzene as stabilizer. The purified and redispersed powder was characterized by UV/VIS absorption, photoluminescence, Raman, SQUID, and EPR spectroscopy. Introduction The synthesis and characterization of nanoparticles has become a major interdisciplinary field of research during the past decade. Semiconductor quantum dots of a few nan- ometers in diameter show unique chemical and electronic properties, which give rise to their potential use in the fields of nonlinear optics, luminescence, electronics, and optoelectro- nics, as well as other areas. Due to quantum confinement the nanoparticles have molecular-like discrete energy levels, and the semiconductor band gap exhibits strong size dependence. Furthermore, as particles become smaller the surface proper- ties become dominant since the surface/volume ratio is consid- erably increased. For the wet-chemical synthesis of II–VI semiconductor nano- crystallites the colloidal route is quite commonly applied. In solution the particle growth can be controlled by the use of sta- bilizers, the consequence of which is passivation of the particle surface and therefore inhibition of agglomeration and further growth. Among many other stabilizers aliphatic and aromatic mercaptans were used. 1–6 The doping of nanocrystalline semiconductors with divalent manganese ions results in new optical properties of these semi- magnetic semiconductor quantum dots. 7–20 In this paper we report on a novel aqueous colloidal route to photoluminescent CdS quantum dots and on the doping of these particles with divalent manganese ions, resulting in emis- sion caused by Mn 2+ in addition to the semiconductor band gap related emission. To the best of our knowledge, such an observation has not been described so far. In the literature either manganese-derived photoluminescence combined with trap emission is reported 8,12,15,19 or the emission from surface defects is suppressed by the occurrence of Mn 2+ luminescence. 9 Experimental For the stabilization of CdS nanoparticles we have used 1,2- bis(mercaptomethyl)benzene (1,2-BMMB) (Fig. 1a). For the synthesis 0.850 g (5 mmol) 1,2-BMMB were dissolved in 400 ml tetrahydrofuran and added to 0.570 g (2.5 mmol) CdCl 2 2.5H 2 O dissolved in 100 ml deionised water, then 3.25 ml tetramethylammonium hydroxide (25 wt.% in methanol) were added and stirred for 10 min. 1,1,1,3,3,3-Hexamethyl- disilathiane was used as a source of hydrogen sulfide, and in Fig. 1(b) its graphic formula as well as the hydrolysis reaction showing the generation of sulfide ions are given. The rapid y Electronic supplementary information (ESI) available: Optical prop- erties of Cd(Mn)S nanoparticles. See http://www.rsc.org/suppdata/ cp/b3/b300343d/ Fig. 1 Structural formula of (a) 1,2-bis(mercaptomethyl)benzene and (b) 1,1,1,3,3,3-hexamethyl-disilathiane with hydrolysis reaction show- ing the generation of hydrogen sulfide. DOI: 10.1039/b300343d Phys. Chem. Chem. Phys., 2003, 5, 1639–1643 1639 This journal is # The Owner Societies 2003 PCCP