Restored thermoluminescence in oxide crystals

• Published in: Journal of luminescence 2010-11, Vol.130 (11), p.2004-2012
• Main Authors: Rakov, A.F., Salikhbaev, U.S., Islamov, A.K., Bartram, R.H., Melcher, C.L.
• Format: Article
• Language: English
• Subjects: Byproducts; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Crystals; Exact sciences and technology; Heating; Lattice vacancies; Luminescence; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other luminescence and radiative recombination; Oxide crystals; Oxides; Physics; Restored thermoluminescence; Shallow and deep traps; Thermoluminescence; Tunneling
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2010.05.018

In this paper, we present the results of a thermoluminescence study on several oxide crystals, including Y 3Al 5O 12 (YAG), Y 3Al 5O 12:Nd (YAG:Nd), Lu 2SiO 5:Ce (LSO:Ce), Y 2SiO 5:Ce (YSO:Ce), Gd 2SiO 5:Ce (GSO:Ce), PbWO (PWO), and PbWO:La (PWO:La). A phenomenon involving restoration of thermoluminescence (TL) glow peaks is found to occur in some of the crystals investigated; crystals γ-irradiated at room temperature and subsequently stored for some time in the dark at 77 K exhibit TL glow peaks in the range below room temperature. This phenomenon is caused not by a thermally or optically stimulated process, but rather as a by-product of a tunneling process. The intensity of the restored TL glow peaks measured in LSO:Ce crystals is found to be proportional both to the radiation dose and to the storage-time at low temperature. A phenomenological theoretical model is proposed, in which tunneling recombination occurs between deep electron and hole traps accompanied by the simultaneous ejection of an electron to the conduction band; some of these conduction electrons then repopulate shallow traps. An oxygen vacancy with two trapped electrons is assumed to be the deep electron trap in this model. The role of oxygen vacancies is confirmed by heating in air at 1000 °C. This model is applied specifically to LSO:Ce, and several possible candidates are suggested for shallow traps in that material.