ELSEVIER Spthdic Metals 86 (1997) 2171-2172 Optical and related properties of natural one-dimensional semiconductors based on PbI and SnI units I.B. Koutselas. D.B.Mitzi*, G.C. Papavassiliou, G.J. Papaioannoub. and H.KrautscheidC Theoretical and Physical Chemistry Institute, Nat. Hellenic Research Foundation, 48, Vassileos Constantinou Ave., 11635, Greece. aIBM T.J. Watson, Res. Center, Yorktown Heights, N.Y. 10598, USA bDept.of Physics, Athens University, Zographou, Athens 15771, Greece. CInst.Anorg.Chem., Universitiit Karlsruhe , D-76128 Karlsruhe, Germany. Abstract Optical absorption, reflectance, photoluminescence. photoluminescence excitation and photoconductivity spectra of [NH,C(I)=NH,],MI, (M=Pb, Sn), (Bu,N)Pb& and similar 1D semiconductors at room temperature are reported and compared with those of the corresponding 2D and OD analogues. Keyworck UV-vis absorption, reflection spectroscopy, photoluminescence, photoconductivity, semiconducting films. Introduction Lead-halide and tin-halide complexes have received much attention, recently, because of their interesting linear and non- linear optical properties (see [l, 21 and refs cited therein). (A),PbI,, for example, (where A= C,o%P3. C6H,CH,CH,NH3 , etc) are two-dimensional (2D) semiconduc- tors and the optical absorption spectra of these materials show sharp excitonic bands at ca 515 nm, which can be shifted to shorter wavelengths through the substitution of Br and/or Cl for I [2] and to longer wavelengths through the application of pres- sure [l]. Similar results have been observed in the photolumi- nescence spectra [3]. Also, devices based on these materials show highly- efficient electroluminescence (exciton emission) [4] as welI as non-linear optical properties (see [ 11 and refs [50- 551 cited therein), due to their self-organized quantum well structure. In this paper, the room temperature optical and related properties of some natural one-dimensional (1D) semiconduc- tors such 8s [H,NC(I)=NH,],MI, (M=Pb, Sn) [5] and (Bu,N)PbI, [6] are reported. The experimental and theoretical results are compared to those of the corresponding 2D and OD systems. Experimental The samples have been prepared in a single crystal form, as polycrystalline pellets or as thin deposits by methods re- ported ln [5-91 and their optical absorption (OA), reflectance, photoluminescence (PL), photoluminescence excitation (PLE) and photoconductivity (PC) spectra have been recorded by methods reported in [9]. Results and Discussion Compounds of the formula [NHZC(I)=NH,],MIS (M=Pb, Sn) are built up of infinite (1D) chains of opposite-comer-shar- ing MI, octahedra , which are separated by qC(I)=NH, mol- ecules [5]. Compounds (A) PbI, (A=Bu,N. Me,N) are built up of infinite (1D) chains of h-ans-face-sharing PbI, octahedra, which are separated by Bu,N, or Me,N molecules [6,71. An 0379-6779/97l$17.00 0 1997 Elsevier Science S.k All rights resend PII SO379-6779(96)04791-1 analogous compound, (Et,N)PbI, . DMF [6,9], was found to be isos-tructural with (Bu,N)Pb13. Also, (piperidinium) PbI, has a similar structure [8]. In all cases, the inorganic chains (wires of ca 3A radius) are the active part of the system, while the organ- ic part (ca 7A). which separates the chains, plays the role of barrier. Fig. la shows the OA spectrum of a thin deposit of [NH,C(I)=N$],PbI, on quartz plate . The absorption coeffi- cient obtained by Kramers-Kronig analysis of the reflectance spectrum of a polycrystalJine pellet has similar features as the OA spectrum. Fig. lb shows the PL spectrum of a single crystal of [NH,C(I)=NH,],PbI . I The peaks are due to excitons. There is a Stokes shift o the PL peak, perhaps, because of de- fects in the crystal. The excitonic bands of the SnIs- analogue occur at the same positions, but are broader than those of [NH,C(I)=NH,],PbI,. Fig. 2a and 2b show the PLE and PC - OD 459 468 350 400 4501 [w500 550 600 Flg.1. OA spectrum of a thin deposit (a) and PL spectrum of a single crystal (b) of [NH2C(I)=N~13PbIs. Arrows show the OA peak positions of the corresponding 2D and OD systems.