Structural, thermal, and optical absorption studies of Er3 +, Tm3 +, and Pr3 +-doped borotellurite glasses

Abstract

Borotellurite glasses containing different rare-earth (RE) ions (Er, Tm, and Pr) with the nominal composition (50–x) B2O3–10 TeO2–10 MoO3–10 ZnO–10 Na2O–10 SrO–(x) Er2O3/(x) Tm2O3/(x) Pr2O3 (x=0, and 1.0mol%) were prepared by the melt quenching technique. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements confirm the amorphous nature for the prepared glasses and energy dispersive X-ray analysis (EDAX) confirms that all the elements present in the respective glasses. The presence of various functional groups such as OBO bond bending vibrations and specific vibrations of Na+, and Sr2+ bonds, vibrations of metal cations such as Zn2+, BO stretching vibrations of the BO4 tetrahedral units, stretching vibrations of BO bonds of pyroborate groups, vibrations due to BO2O− triangles linked with BO units, stretching vibrations of BO bonds involving nonbridging oxygen (NBO) and being part of a boron-oxygen network, alkali or alkaline tetra borate groups, isolated diborate groups, pentaborate, tetraborate and diborate units, symmetric bending vibrations of TeO4 tbps and symmetric stretching of the TeeqOaxTe bond, stretching and bending vibrations of TeOTe linkages in TeO4 (tbps), TeO3+1 polyhedra and TeO3 (tps), and stretching vibrations of MoOMo linkages or vibrational modes of MoO42− tetrahedral units including stretching vibrations of ZnO4− structural units, and non-hygroscopic nature of the glasses are confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectra, respectively. The thermal properties of the glasses were studied by simultaneous thermal analysis (STA) technique and from the differential scanning calorimetry (DSC) profiles the glass transition temperature (Tg), onset crystallization temperature (Tx), and crystallization temperature (Tc) are identified and from these values, the calculated thermal stability values are varied in the temperature range 88–103°C with different rare earth ions incorporation. From the measured optical absorption spectrum of the host glass, direct and indirect optical band gap energies were evaluated and the values of indirect optical band gap energies calculated from the absorption spectrum (Eopt) matches well with the values of optical band gap energies (Eoptasf) calculated from absorption spectrum fitting (ASF) method, and the glass has Urbach energy value 0.627eV. The fundamental absorption edge wavelength (λedge) shows red-shift with RE ions doping into the host glass due to the formation of non-bridging oxygens.