Structure and properties of the pure and Pr3+-doped Ge25Ga5Se70 and Ge30Ga5Se65 glasses

The Ge25Ga5Se70 and Ge30Ga5Se65 pure and Pr3+-doped glasses were prepared b y direct synthesis from elements and PrCl3. It was found that up to 1 mol% PrCl3 can be introduced in the Ge25Ga5Se70 and Ge30Ga5Se65 glasses. Both ty pes of glasses with overstoichiometric and substoichiometric content of Se were homogeneous and of black color. The optical energy gap is E-g(opt) = 2 .10 eV, and the glass transition temperature is T-g = 543 K for Ge25Ga5Se70 and T-g = 633 K for Ge30Ga5Se65. The long-wavelength absorption edge is ne ar 14 mu m and it corresponds to multiphonon processes. Doping by Pr3+ ions creates absorption bands in transmission spectra, which can be assigned to the electron transitions from the ground H-3(4) level to the higher energy levels of Pr3+ ions H-3(5), H-3(6), F-3(2), F-3(3) and F-3(4), respectivel y. By excitation with YAG:Nd laser line (1064 nm), two intense luminescence bands (1343 and 1601 nm) were excited. The first band can be ascribed to e lectron transitions between leg and H-3(5) energy levels of Pr3+ ions. Full width at half of maximum (FWHM) of the intensity of luminescence was found to be similar to 70 nm for (Ge25Ga5Se70)(1-x)(PrCl3)(x) and (Ge30Ga5Se65)( 1-x)(PrCl3)(x) glasses. The FWHM in selenide glasses is lower than in halid e and sulphide glasses. The second luminescence band (1601 nm) can be proba bly ascribed to the transitions between F-3(3) and H-3(4) energy levels of Pr3+ ions. The absorption and luminescence spectra of Pr3+ ions in studied glasses are slightly influenced by stoichiometry of glassy matrix. The Rama n spectra of studied glasses were deconvoluted and assignment of Raman band s to individual vibration modes of basic structural units was suggested. Th e structure of studied glasses is mainly formed by corner-sharing and edge- sharing GeSe4 tetrahedra. The vibration modes of Ga-containing structural u nits were not found, they are apparently overlapping with Ge-containing str uctural units due to small difference between atomic weights of Ge and Ga. In the glasses with substoichiometry of Se, the Ge-Ge bonds of Ge2Se6 struc tural units were found. In Se-rich glasses the Se-Se vibration modes were f ound. In all studied glasses also 'wrong' bonds between like atoms were fou nd in small amounts. Maximum phonon energy of studied glasses is similar to 320 cm(-1). (C) 2000 Elsevier Science B.V. All rights reserved.