Structure and properties of the pure and Pr 3+-doped Ge 25Ga 5Se 70 and Ge 30Ga 5Se 65 glasses

Abstract

The Ge 25Ga 5Se 70 and Ge 30Ga 5Se 65 pure and Pr 3+-doped glasses were prepared by direct synthesis from elements and PrCl 3. It was found that up to 1 mol% PrCl 3 can be introduced in the Ge 25Ga 5Se 70 and Ge 30Ga 5Se 65 glasses. Both types of glasses with overstoichiometric and substoichiometric content of Se were homogeneous and of black color. The optical energy gap is E opt g =2.10 eV , and the glass transition temperature is T g =543 K for Ge 25Ga 5Se 70 and T g =633 K for Ge 30Ga 5Se 65. The long-wavelength absorption edge is near 14 μm and it corresponds to multiphonon processes. Doping by Pr 3+ ions creates absorption bands in transmission spectra, which can be assigned to the electron transitions from the ground 3H 4 level to the higher energy levels of Pr 3+ ions 3H 5, 3H 6, 3F 2, 3F 3 and 3F 4, respectively. 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 electron transitions between 1G 4 and 3H 5 energy levels of Pr 3+ ions. Full width at half of maximum (FWHM) of the intensity of luminescence was found to be ∼70 nm for (Ge 25Ga 5Se 70) 1 − x (PrCl 3) x and (Ge 30Ga 5Se 65) 1 − x (PrCl 3) x glasses. The FWHM in selenide glasses is lower than in halide and sulphide glasses. The second luminescence band (1601 nm) can be probably ascribed to the transitions between 3F 3 and 3H 4 energy levels of Pr 3+ ions. The absorption and luminescence spectra of Pr 3+ ions in studied glasses are slightly influenced by stoichiometry of glassy matrix. The Raman spectra of studied glasses were deconvoluted and assignment of Raman bands to individual vibration modes of basic structural units was suggested. The structure of studied glasses is mainly formed by corner-sharing and edge-sharing GeSe 4 tetrahedra. The vibration modes of Ga-containing structural units were not found, they are apparently overlapping with Ge-containing structural units due to small difference between atomic weights of Ge and Ga. In the glasses with substoichiometry of Se, the Ge–Ge bonds of Ge 2Se 6 structural units were found. In Se-rich glasses the Se–Se vibration modes were found. In all studied glasses also `wrong' bonds between like atoms were found in small amounts. Maximum phonon energy of studied glasses is ∼320 cm −1.