Studies of Er 3+ doped germanate–oxyfluoride and tellurium–germanate–oxyfluoride transparent glass–ceramics Z. Pan * , A. Ueda, M. Hays, R. Mu, S.H. Morgan Physics Department, Fisk University, 1000, 17th Avenue North, Nashville, TN 37208, USA Received 22 August 2005; received in revised form 4 January 2006 Available online 10 March 2006 Abstract An erbium doped germanate–oxyfluoride glass 60GeO 2 Æ 20PbO Æ 10PbF 2 Æ 10CdF 2 (GPOF) and a tellurium–germanate–oxyfluoride glass 30TeO 2 Æ 30GeO 2 Æ 20PbO Æ 10PbF 2 Æ 10CdF 2 (TGPOF) were prepared in the bulk form. By appropriate heat treatment of the as- prepared glasses above, transparent glass–ceramics were obtained with the formation of b-PbF 2 nanocrystals in the glass matrix con- firmed by X-ray diffraction. Optical absorption and photoluminescence measurements were performed on as-prepared glass and glass–ceramics. The luminescence of Er 3+ ions in transparent glass–ceramics revealed sub-band splitting generally seen in a crystal host. The intensity of red and near infrared luminescence significantly increased in transparent glass–ceramic compared to that in as-prepared glass. Two luminescence bands at 758 nm from 4 F 7/2 ! 4 I 13/2 and at 817 nm from 2 H 11/2 ! 4 I 13/2 transitions were observed from trans- parent glass–ceramic but cannot be seen from the corresponding as-prepared glass. These results are attributed to the change of ligand field of Er 3+ ions and the decrease of effective phonon energy when Er 3+ ions were incorporated into the precipitated b-PbF 2 nanocrystals. Ó 2006 Elsevier B.V. All rights reserved. PACS: 42.70.Àa; 61.43.Fs; 61.46.+w; 78.55.Hx Keywords: Glass–ceramics; Fluorides; Optical properties; Luminescence; Germanates; Rare-earths in glasses 1. Introduction Transparent glass–ceramics are a two-phase system, containing nanocrystals that are controllably grown within the host glass by appropriate heat treatment. Rare-earth doped transparent glass–ceramics have been the subject of several recent investigations [1–8]. It is our intension to combine the advantages of oxide glasses and heavy- metal fluorides. The oxide glasses generally possess a good mechanical strength, chemical durability, and thermal sta- bility while the heavy-metal fluorides possess a low vibra- tional energy, resulting in an increased radiative emission rate of the incorporated rare-earth ions. Rare-earth doped germanate–oxyfluoride transparent glass–ceramics have been reported in 50GeO 2 – (50 À x)PbO–xPbF 2 [9] and PbGeO 3 –PbF 2 –CdF 2 systems [3,10]. These authors presented evidence that b-PbF 2 nano- crystals were formed in a germanate–oxyfluoride glass matrix by a proper heat treatment on as-formed glasses. They observed an increased emission cross-section from transparent glass–ceramics, indicating the incorporation of rare-earth ions in the crystalline phase. Tellurite glass has the lowest maximum phonon energy among common oxide glasses, a larger rare-earth solubility, and a low melting point. Tellurite glass has a larger refrac- tive index compared to germanate, silicate, and fluoride glasses. These properties suggest their potential for optical device applications [11–14]. Tellurite based transpar- ent glass–ceramics have been less studied so far. Ribeiro et al. reported a transparent glass–ceramic system with 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.01.023 * Corresponding author. Tel.: +1 615 329 8622; fax: +1 615 329 8634. E-mail address: zpan@fisk.edu (Z. Pan). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 801–806