Formation of semiconductor clusters in zeolites Felicia Iacomi * Faculty of Physics, Al.I. Cuza University, Blvd. Carol I, 11, RO-6600 Iasi, Romania Abstract CdS and ZnS particles were synthesised inside some synthetic and natural zeolite frameworks by treating the calcined Cd 2þ or Zn 2þ ion exchanged forms with 1 molar aqueous solution of Na 2 S. The absorption and photoluminescence emission spectra suggest that clusters interconnect to form well-defined aggregates with a behaviour intermediate be- tween that of discrete clusters and the bulk semiconductor. The dynamics and the optical absorption are strongly influenced by the interface and host. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Zeolites; Clusters; Visible/ultraviolet absorption spectroscopy; Photoluminescence; Semiconducting surfaces 1. Introduction Many of the advanced materials applications of zeolites involve the synthesis and stabilisation of isolated intrazeolite semiconductor aggregates of sub-colloidal dimension [1–7]. Most studied nanocrystalline semiconductors belong to the II– VI group as they are relatively easy to synthesise. Among II–VI compounds, CdS and ZnS are the most studied (semiconductors with direct band gaps of E g ¼ 2:40 and 3.67 eV, respectively). The techniques utilised in synthesis of zeolite-encap- sulated semiconductor nanoclusters have included aqueous ion exchange, melt ion exchange, vapour phase impregnation, intrazeolitic chemical vapour deposition of organometallics, and chemical va- pour deposition [7–12]. In this work we explore the use of some zeolite host matrices, high siliceous once (mordenite, clinoptilolite), in which the CdS and ZnS clusters are created in situ to impose crystalline order and physical constraint upon the included semicon- ductor guests. Mordenites (Na 8 [(AlO 2 ) 8 (SiO 2 ) 40 ]24H 2 O) pre- sent a pore structure consisting of main straight channels in the c-direction having a slightly ellip- tical cross-section of 6.7  7.0  A 2 (12-membered rings) and secondary channels in the b-direction with a 2.6  5.7  A 2 aperture (8-membered rings). The diameter of these secondary channels presents a restriction of 2.8  A preventing the intercon- nection of the main channels. The clinoptilolite (Na 6 [(AlO 2 ) 4 (SiO 2 ) 20 ]24H 2 O) 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 (with 7.05  4.25  A 2 and 4.60  3.95  A 2 , respectively) of tetrahedra with a highly disordered Si, Al distribution. C channels, which are determined by another set of 8-mem- bered rings, run parallel to a-axis and the [102] direction [13,14]. * Tel.: +40-232-201-169; fax: +40-232-201-150/201. E-mail address: iacomi@uaic.ro (F. Iacomi). 0039-6028/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0039-6028(03)00446-1 Surface Science 532–535 (2003) 816–821 www.elsevier.com/locate/susc