Spectral study of radioluminescence in carbon-doped aluminium oxide
- Authors: Nyirenda, Angel N , Chithambo, Makaiko L
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/110067 , vital:33220 , https://doi.org/10.1016/j.radmeas.2018.06.026
- Description: The spectral emission study of the radioluminescence (RL) measured from carbon-doped aluminium oxide (α-Al2O3:C) at various temperatures between 30 and 300∘C is reported. The energy-resolved RL emission spectra measured at room temperature show seven gaussian emission bands centred at 1.75, 1.79, 1.85, 2.22, 2.96, 3.72 and 4.44 eV. The 2.96-eV emission, associated with F-centres, is the primary RL emission whereas the narrow (R-line) emission centred at 1.79 eV, associated with Cr3+ impurity ions, is the most intense secondary emission. However, the intensity of 1.79-eV emission decreases with repeated RL measurements. The central emission energy for F-centres is constant throughout the temperature range of investigation. The full width at half maximum (FWHM) for the F-centre emission band increases with temperature whereas the F-centre peak intensity exhibits thermal quenching behaviour at temperatures above 160∘C. On the other hand, the emission energy for the R-line emission of Cr3+ is constant for temperatures between 30 and 160∘C, whereas its peak intensity generally decreases with temperature. F-centres experience strong-coupling in their crystallographic sites with estimated electron-lattice coupling parameters of S = 5.0 ± 0.9, Ep = 0.079 ± 0.008 eV and ν = 1.91 × 1013 Hz where S, Ep and ν are the Huang-Rhys factor, the phonon energy and the phonon frequency, respectively. The RL spectra recorded while ramping the temperature of a sample at a constant rate have been compared against conventional TL spectra.
- Full Text: false
- Date Issued: 2018
Factors influencing the shape of CW-OSL signal obtained by stimulation of very deep traps in carbon-doped aluminium oxide: an experimental study
- Authors: Nyirenda, Angel N , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115493 , vital:34149 , https://doi.org/10.1016/j.jlumin.2017.07.016
- Description: The optically stimulated luminescence from carbon-doped aluminium oxide (α-Al2O3:C) displays a peak with time under certain measurement conditions. In this paper, we present factors that influence the peak-like shape of continuous-wave optically stimulated luminescence (CW-OSL) signal. The report is based on the experimental study of OSL signals obtained by stimulation of very deep traps in α-Al2O3:C. Methods exploiting post-irradiation annealing, variable dose and temperature dependent OSL measurements were used in the investigation. It is found that the rising part of the CW-OSL peak is obtained when the rate of retrapping at the most optically active trap (main trap) exceeds the rate of direct radiative recombination following optical release of charges from all optically active traps. This is possible if, during optical stimulation, the primary trap responsible for OSL i.e. the main trap, is substantially unoccupied and the very deep, donor traps are substantially filled up. The rate of charge retrapping itself is deduced to depend on the occupancy of the acceptor traps i.e. shallow, main and secondary traps; concentration of charge carriers in the very deep, donor traps; the post-irradiation annealing temperature and the temperature at which the OSL is measured.
- Full Text: false
- Date Issued: 2017
The influence of radiation-induced defects on thermoluminescence and optically stimulated luminescence of α-Al2O3: C
- Authors: Nyirenda, Angel N , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/119818 , vital:34786 , https://doi.org/10.1016/j.nimb.2017.02.077
- Description: It is known that when α-Al2O3:C is exposed to excessive amounts of ionising radiation, defects are induced within its matrix. We report the influence of radiation-induced defects on the thermoluminescence (TL) and optically stimulated luminescence (OSL) measured from α-Al2O3:C after irradiation to 1000 Gy. These radiation-induced defects are thermally unstable in the region 450–650 °C and result in TL peaks in this range when the TL is measured at 1 °C/s. Heating a sample to 700 °C obliterates the radiation-induced defects, that is, the TL peaks corresponding to the radiation induced defects are no longer observed in the subsequent TL measurements when moderate irradiation doses below 10 Gy are used. The charge traps associated with these radiation-induced defects are more stable than the dosimetric trap when the sample is exposed to either sunlight or 470-nm blue light from LEDs. TL glow curves measured following the defect-inducing irradiation produce a dosimetric peak that is broader and positioned at a higher temperature than observed in glow curves obtained before the heavy irradiation. In addition, sample sensitization/desensitization occurs due to the presence of these radiation-induced defects. Furthermore, both the activation energy and the kinetic order of the dosimetric peak evaluated when the radiation-induced defects are present in the sample are significantly lower in value than those obtained when these defects are absent. The radiation-induced defects also affect the shape and total light sum of the OSL signal as well as the position and width of the resultant residual phototransferred thermoluminescence main peak.
- Full Text: false
- Date Issued: 2017
On luminescence stimulated from deep traps using thermally-assisted time-resolved optical stimulation in α-Al2O3: C
- Authors: Nyirenda, Angel N , Chithambo, Makaiko L , Polymeris, G S
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124627 , vital:35639 , https://doi.org/10.1016/j.radmeas.2016.01.016
- Description: We report a study of charge transfer mechanisms of electrons stimulated optically from very deep traps, also known as donor traps, in α-Al2O3:C. The investigations were carried out using thermally-assisted time-resolved optical stimulation, thermoluminescence and by way of residual thermoluminescence from the main electron trap. When the charges are optically stimulated from the deep traps, they are redistributed via the conduction band to the main electron trap and the shallow trap from where they are optically or thermally released for recombination at luminescence centres. The luminescence is strongly quenched at high measurement temperature as evident by very short luminescence lifetimes at these temperatures. The main peak due to residual thermoluminescence is located at a higher temperature than the conventional main peak.
- Full Text: false
- Date Issued: 2016