Spectroscopic properties of ebium doped tellurite glass

Abstract

Er3+ doped tellurite glasses of composition (75-x)TeO2-25ZnO-5Na2O-xEr2O3 with x = 0, 0.2, 0.4, 0.7, 0.9, 1.1 and 1.4 mol% were successfully prepared by melt quenching technique. No definite peaks were found from the X-ray diffraction pattern, thus verified the amorphous nature of glass. However, the X-ray diffraction pattern for heat treated glass showed a wide peak which indicated the occurrence of nanocrystallite particle in the sample. The crystallite size was determined by Scherrer equation and confirmed by the image obtained from transmission electron microscopy technique. The vibrational study was conducted using Fourier transform infrared (FTIR) spectroscopy in the range of 4000 cm-1 – 400 cm-1. It was observed that, four absorption peaks occur around 1600 cm-1 – 3400 cm-1, 666 cm-1 – 755 cm-1, 546 cm-1 – 684 cm-1 and 465 cm-1 which were due to the stretching mode vibration of OH bond, TeO4 trigonal bipyramids and TeO3 trigonal pyramids, Er-O bond and Zn-O tetrahedral bond, respectively. The FTIR spectra for heat treated samples generated a higher intensity absorption band located at 564 cm-1, 573 cm-1, 669 cm-1 and 688 cm-1. The thermal stability of the glass was investigated using differential thermal analyzer. The thermal parameters, such as the glass transition temperature (Tg), crystalline temperature (Tc), melting temperature (Tm) and thermal stability (Tc-Tg) were determined. It was found that, this glass system has glass formation range around 51.47oC - 99.35oC. The emission spectrum was recorded using photoluminescence spectrometer at room temperature. From the luminescence spectra, blue and green emission bands associated with Er3+ transition at (382 nm) 4G11/2?4I15/2, (465 nm) 4F5/2?4I15/2, (501 nm) 2H11/2?4I15/2 and (550 nm) 4S3/2?4I15/2 with an excitation wavelength ?exci = 786 nm were observed. Meanwhile, the luminescence intensity for heat treated samples was slightly higher. The absorption characteristic was determined using ultra violet-visible spectroscopy. It was observed that, the optical band gap (Eg) and the Urbach energy (?E) was in the range 2.89 eV - 2.18 eV and 0.59 eV - 0.15 eV, respectively depending on the Er2O3 concentration. For the heat treated samples, the optical band gap (Eg) and the Urbach energy (?E) was in the range of 2.72 eV - 2.68 eV and 0.54 eV - 0.21 eV, respectively.