MnS clusters in natural zeolites Felicia Iacomi a, *, Aurelia Vasile b , E.K. Polychroniadis c a Faculty of Physics, ‘‘Al.Cuza’’ University, Ro-6600 Iasi, Romania b Faculty of Chemistry, ‘‘Al.Cuza’’ University, Ro-6600 Iasi, Romania c Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece Abstract FTIR, ESR, optical absorption, photoconductivity, and luminescence measurements are used to evidence the nature of MnS clusters, synthesized by treating the Mn 2 forms of natural zeolites with Na 2 S. # 2003 Published by Elsevier Science B.V. Keywords: FTIR; ESR; Zeolites; Clusters; Ultraviolet absorption spectroscopy; Photoluminescence 1. Introduction Low-dimensional chalcogenides represent an active area of research due to their interesting optical or magneto-optical properties. Manganese sulfide is a compound member of the family of magnetic semicon- ductors whose crystalline structure may be of type rock salt (a-MnS) or zinc blende (b-MnS) or wurtzite (g- MnS) [1 /3]. In this work, we report for the first time, the appropriate conditions to isolate MnS clusters inside two natural zeolite frameworks: microcrystalline clin- optilolite and laumontite single crystal, and the optical properties of clusters. MnS clusters, isolated into zeolite channels, exhibit ESR spectra that reflect the interaction of clusters with the lattice. The zeolite structures permit one to vary the cluster concentration and the intercluster geometry in a con- trolled manner over the periodicity defined by the host zeolite lattice [4,5]. Host matrices like zeolites reduce the interchain and interlayer perturbations often encoun- tered in other low-dimensional solids. Clinoptilolite is one of the most abundant natural zeolites and has a broad spectrum of industrial applica- tions. The clinoptilolite structure exhibits three types of structural channels confined by tetrahedral ring systems. A and B channels run parallel to c -axis and are confined by 10- and 8-membered rings of tetrahedra with a highly disordered Si and Al distribution (7.05 /4.25 A ˚ 2 respectively 4.60 /3.95 A ˚ 2 ). C channels, which are determined by another set of eight-membered rings, run parallel to a- axis and the [1 0 2]-direction. The channel system is two-dimensional parallel to (0 1 0). Exchange cations (Na, K, Ca, and Mg) exhibit coordi- nation to framework oxygen and water molecules in the channels [6,7]. Laumontite, a less common zeolite, is a monoclinic mineral characterized by single four-ring tetrahedral chains as secondary building units and large channels of 10-membered tetrahedral rings (4.6 /6.4 A ˚ 2 ) which are parallel to c -axis. The channels are occupied by Ca and H 2 O and minor Na and K [8,9]. 2. Experimental The semiconductor clusters were prepared in water media according to the published procedure of Barbna- kov et al. [10], who noted that the stability of the samples obtained by this method is very high. In order to remove the impurities, the powdered clinoptilolite, from Ma ˆrsid-Romania, was first submitted to an acid treatment, using 1 N HCl solutions [11]. The zeolites in their sodium cation form were first thermal treated at 673 K during 4 h and then ion-exchanged by treating with 0.1 N aqueous manganese nitrate solutions at 296 K (pH 5.8), using a solid/liquid ratio of 1/50. The ion- loaded zeolites were washed and dried at 378 K and then submitted to a sulfidation process with 1 M Na 2 S * Corresponding author. E-mail address: iacomi@uaic.ro (F. Iacomi). Materials Science and Engineering B101 (2003) 275  /278 www.elsevier.com/locate/mseb 0921-5107/03/$ - see front matter # 2003 Published by Elsevier Science B.V. doi:10.1016/S0921-5107(02)00697-9