Volume 133, number 4 CHEMICAL PHYSICS LETTERS 23 January 1987 TRANSPARENT GLASS-CERAMICS DOPED WITH Cr ( III): LOW-TEMPERATURE TIME-RESOLVED SPECTRA AND CHARACTERIZATION OF GAHNITE AND VIRGILITE CRYSTALLINE PHASES Vincent PONCON ‘, Joshua KALISKY *, Georges BOULON zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO Physico-Chlmie des MatPriaux Luminescents, Unite Associk au CNRS No. 442, VniversitP Claude Bernard Lyon I, 69622 Vilkurbanne, France and Renata REISFELD 3 Department of Inorganic and Analytical Chemistry The Hebrew University of Jerusalem, Jerusalem, Israel Received 8 October 1986 Trivalent chromium in transparent glass-ceramics (73.6 SiOl: 11.8 Alz0,:4.2 Li,O:7.0 ZnO: 1.6 TiOz: 1.5 Zr02:0.3 AszOl: 0.024 Cr203 mole%) enters mainly the gahnite phase after an equilibrium has been reached. The intermediate phase during heat treatment is of virgilite-type Li,AlSi,_,O,. This glass-ceramic has been studied by X-ray diffraction and time-resolved spectros- copy at low temperatures under laser excitation 1. Introduction From our previous work on various Cr(III)-doped glass-ceramics [ l-61 we came to the conclusion that gahnite-type transparent glass-ceramics doped by Cr3+ show a distinct ZE+4A2 fluorescence character- ized by a quantum efficiency close to unity. In our recent papers we have reported room-temperature spectroscopy of Cr( III) in transparent glass-ceramics with a gahnite-type composition: 70.2 SiOz, 15.0 AlzO3, 4.4 ZnO, 7.1 Li20, 1.5 Ti02, 1.5 ZQ, 0.3 Asz03 doped by Cr3+ at a concentration of 1.1 x 1 019 ions/cm3 [ 71. The X-ray diffraction spec- tra of crystalline and glassy phases corresponding to various heat treatments were attributed to B-quartz, gahnite, Zr02, and petalite-like phases [ 81. While the crystallographic nature of the first three above-mentioned phases is well known the petalite- ’ Saint-Gobain Recherche. ’ Permanent address: Nuclear Research Centre, Negev, Beer- Sheva, Israel. 3 Enrique Berman Professor of Solar Energy. like phase warranted further investigation. In the present paper we have scanned a variety of crystal structures and compared their X-ray diffraction pat- terns with those of our glass-ceramics. The majority of the diffraction lines of NL3 glass-ceramics could be fitted to the recently described virgilite Lial,Si,_,O, structure [ 91 in addition to gahnite, Zr02 and B-quartz as previously described. The preparation of the glass and the glass-ceramics was carried out as described in ref. [ 8 1. The same assign- ments are used in this work. The optical measure- ments were made using the experimental apparatus described in ref. [ lo]. 2. Results zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK and discussion Fig. 1 presents the X-ray pattern of the parent glass N1, the glass-ceramics N, ,, Nr2 and N13 and petalite, virgilite, B-quartz, gahnite and tetragonal ZrO, crys- tals. The most intensive lines in the spectrum of the glass-ceramics correspond to the virgilite and B- quartz crystals. The gahnite lines are next in the 0 009-2614/87/$ 03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) 363