Silver aggregates in photoluminescent phosphate glasses of the `Ag 2 O±ZnO±P 2 O 5 ' system I. Belharouak a , C. Parent a , B. Tanguy a , G. Le Flem a, * , M. Couzi b a I.C.M.C.B, Ch^ ateau Brivazac, Avenue du Docteur Schweitzer, UPR CNRS 9048, 33608 Pessac, cedex, France b L.P.C.M, UMR 5803 CNRS, Universit e de Bordeaux I, 351 cours de la liberation, 33405 Talence, France Received 27 May 1998; received in revised form 26 October 1998 Abstract Photoluminescent properties of glasses of the Ag 2 O±ZnO±P 2 O 5 system are reported. The compositions of the glasses are limited by the polyphosphate and diphosphate domain of this system. The phosphate structural units of the network former are deduced from Raman spectra. A comparison with the luminescent properties of crystallized silver phos- phates of similar composition allows identi®cation of two dierent emitting centers: isolated Ag  , Ag  ±Ag  pairs, and a third center resulting from an Ag  ±Zn 2 interaction. The introduction of 1 mol% SiO 2 or Al 2 O 3 in these glasses leads to precipitation of silver particles, whose dimensions range from nanometers to micrometers, and to the appearance of luminescent centers (Ag 2 )  detected around the micrometer particles by optical microscopy. We assume that these centers are an intermediate stage during the process of silver precipitation. Ó 1999 Elsevier Science B.V. All rights reserved. 1. Introduction The investigation of silver (I) luminescence in glasses was the subject of extensive research in relation to the use of these materials as c-radiation and X-ray dosimeters [1±3]. More recently the possibility of white light generation was investi- gated in phosphate and borate glasses [4,5]. The eect of the conditions of Na  /Ag  exchange on the luminescent properties of soda lime glasses have been reported [6]. In addition silver particles embedded in glass matrices induce non-linear op- tical properties depending on the size, density and distribution of these particles [7]. The ¯uorescence of Ag  is due to the transition 4d 9 5s ® 4d 10 , strictly forbidden for the free ion but partially allowed in crystals or glasses by coupling with lattice vibrations of odd parity. In glasses the active center can occupy a variety of sites which thereby results in an increase in the width of the ¯uorescent bands [5]. Moreover the identi®cation of the silver species involved in the luminescence process is complicated by the tendency of Ag  to aggregate and/or to be pho- toreduced [6]. The aggregation and photoreduc- tion can occur simultaneously which creates the conditions for silver particles precipitation. This tendency of Ag  to aggregate was discus- sed in Ref. [8]. In most cases cationic and anionic components of the structures can be distinguished, this description giving evidence of extended silver aggregates. The Ag  ±Ag  distance can be less than Journal of Non-Crystalline Solids 244 (1999) 238±249 * Corresponding author: Tel.: +33-5 56 84 62 94; fax: +33-5 56 84 27 61; e-mail: le¯em@chimsol.icmcb.u-bordeaux. 0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 0 1 4 - 9