18 June 1999 Ž . Chemical Physics Letters 306 1999 280–284 Photoluminescence of Cs PbBr crystals and thin films 4 6 M. Nikl a,) , E. Mihokova a , K. Nitsch a , F. Somma b , C. Giampaolo c , G.P. Pazzi d , P. Fabeni d , S. Zazubovich e a Institute of Physics, AS CR, CukroÕarnicka 10, 162 53 Prague, Czech Republic b Department of Physics and UdR INFM, Uni Õersita Roma Tre, Via della Vasca NaÕale 84, I-00146 Rome, Italy c Department of Geology, UniÕersita Roma Tre, Largo S.L. Murialdo 1, I-00146 Rome, Italy d IROE del CNR, Via Panciatichi 64, I-50127 Florence, Italy e Institute of Physics, UniÕersity of Tartu, Riia 142, EE-2400, Tartu, Estonia Received 27 July 1998; in final form 23 April 1999 Abstract Absorption, emission and decay kinetics characteristics of Cs PbBr bulk and thin film samples were measured in the 4 6 UV–visible spectral range over 4.2–250 K. An emission band at 375 nm was ascribed to the Cs PbBr structure itself with 4 6 two excitation maxima round 310 and 240 nm coinciding with absorption peaks in the thin film absorption spectrum. The coexistence of Cs PbBr and CsPbBrphases was evidenced in both the bulk and thin film systems. q 1999 Elsevier 4 6 3 Science B.V. All rights reserved. 1.Introduction Photoluminescence studies of several alkalilead w x halides have been reported 1–4 . Lead-rich phases Ž .w x as, for example, RbPb X XsCl, Br 1,4 show 2 5 the emission properties and namely the decay kinet- w x Ž ics close to that of PbX 5,6 dominant component 2 . in the microsecond time scale . Particular properties Ž . were reported for CsPbX crystals X s Cl, Br , 3 which are actually wide-gap semiconductors show- ing free-exciton lines at ;420 and ;535 nm, w x respectively4,7,8 .Theseemissionsare charac- Ž terised by very small Stokes shiftsa few tens of . wx meV and very fast sub-nanosecond decay times 8 . The opposite‘ionic’ limit was found for the Cs PbCl crystal, the emission of which was found 4 6 ) Corresponding author. E-mail: nikl@fzu.cz to be similar to, for example, KCl:Pb.Both systems Ž . show two typical fastand slow decay components wx in the ns and ms time scales, respectively 9 in the main emission band. Such a similarity is induced by almostthe same first coordination sphere of Pb 2q ions in both Cs PbCl and KCl matrices, which is a 4 6 regularoctahedron created by six Cl y ions.In the Cs PbCl structure, these octahedra are well sepa- 4 6 wx Ž rated by Cs bridges 3 , which despite the high Pb . concentrationpreventinteractionbetweenPb cations.Moreover, the lack ofneed fora charge compensating cationicvacancyin the Cs PbCl 4 6 structure results in a higher local symmetry of Pb 2q centres with respect to KCl:Pb 2q , which is reflected in the perfect single-exponential decay course of the fast component in the Cs PbCl system. 4 6 To complete the study of luminescence properties of these heavy alkali metal–lead halides, the crystals 0009-2614r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 0 9 - 2 6 1 4 9 9 0 0 4 7 7 - 7