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Abstract: Thermoluminescence emission spectra are presented for lithium doped variants of CaSO4:Dy or CaSO4:Tm dosimetry material. All three dopants (Li, Dy and Tm) variously introduce different changes in both the glow peak temperatures and the luminescence efficiency. In every case the emission signals display the line emission characteristic of the rare earth ions. At temperatures below ∼50K the relative peak intensities differ for Dy and Tm doped samples, and there are small temperature shifts between the Dy:Li and Tm:Li co-doped materials. Above room temperature the rare earth ions do not show peak temperature movements when co-doped with lithium. However they do influence the peak temperature by ∼5°C when they are the sole dopant. Inclusion of lithium dramatically moves the high temperature glow peak from ∼200°C down to 120°C. All these changes are consistent with a single defect model in which the trapping sites and luminescence occur within the complexes formed of the rare earth ion, an intrinsic sulphate defect and lithium. The evidence and rationale for such a model are presented. There is discussion which suggests that such defect complexes are the norm in thermoluminescence. [Copyright &y& Elsevier]

Abstract: The optical properties of alkaline earth aluminates doped with rare earth ions have received much attention in the last years and this is due to their chemical stability, long-afterglow (LAG) phosphorescence and high quantum efficiency. However, there is a lack of understanding about the nature of the rare earth ion trapping sites and the mechanisms which could activate and improve the emission centers in these materials. Therefore a new phosphor material composition, SrAl2O4:Mn2+, co-doped with Nd3+ was synthesized by a traditional solid-state reaction method. The influence of transition metal and rare earth doping on crystal structure and its luminescence properties have been investigated by using X-ray diffraction (XRD), Raman scattering, Photoluminescence (PL) and Radioluminescence (RL). Analysis of the related diffraction patterns has revealed a major phase characteristic of the monoclinic SrAl2O4 compound. Small amounts of the dopants MnCO3 and Nd2O3 have almost no effect on the crsytalline phase composition. Characteristic absorption bands from Nd3+ 4f–4f transitions in the spectra can be assigned to the transitions from the ground state 4I9/2 to the excited states. The luminescence of Mn2+ activated SrAl2O4 exhibits a broad green emission band from the synthesized phosphor particles under different excitation sources. This corresponds to the spin-forbidden transition of the d-orbital electron associated with the Mn2+ ion. In photo- and radio-luminescence spectra, Nd3+ 4f–4f transition peaks were observed. The emitted radiations for different luminescence techniques were dominated by 560, 870, 1057 and 1335nm peaks in the visible and NIR regions as a result of 4I9/2→4G7/2 and 4F3/2→4I J (J=9/2, 11/2 and 13/2) transitions of Nd3+ ions, respectively. Multiple emission lines observed at each of these techniques are due to the crystal field splitting of the ground state of the emitting ions. The nature of the emission lines is discussed. [Copyright &y& Elsevier]

Abstract: We report, for the first time on luminescence from a Er3+ doped SrAl2O4 phosphor. Effects of Eu3+ doping were also studied. The influence of rare-earth doping in crystal structure and its optical properties were analysed by means of X-ray diffraction (XRD), Raman scattering, optical absorption, excitation and emission (PL) spectroscopy, thermally stimulated luminescence (TSL) and scanning electron microscope (SEM). Luminescence spectra and luminescence decay curves for Er3+ transitions in the near infrared region were recorded. The PL maximum for Eu doped SrAl2O4 is obtained at 620nm and corresponds to the orange region of the spectrum. Diffraction patterns reveal a dominant phase, characteristic of the monoclinic SrAl2O4 compound and the presence of dopants has no effect on the basic crystal structure of SrAl2O4. The shapes of the glow curves are different for each dopant irradiated with either a 90Sr–90Y beta source, or UV light at 311nm, and in detail the TL signals differ somewhat between Er and Eu dopants. [Copyright &y& Elsevier]