Lithium fluoride (LiF) is a well-known dosimeter material in pure (McLaughlin et al. Nucl Instrum Methods 175:17–18, 1980) and doped (Lakshmanan et al. Phys Status Solidi (a) 153:265–273, 1996) form. Radiation detectors based on microcrystalline dispersion of LiF in a polymeric matrix have been introduced for gamma and electron high-dose dosimetry (Kovacs et al. Radiat Phys Chem 57:691–695, 2000). In recent years the area of growth and characterisation of LiF thin films has seen a considerable expansion. Polycrystalline LiF films grown by thermal evaporation were proposed and tested as nuclear sensors for neutrons (Cosset et al. Thin Solid Films 303:191–195, 1997) and for gamma dosimetry (Montecchi et al. Point defects in lithium fluoride films induced by gamma irradiation, ch. 116. In: Proceedings of the 7th international conference on advanced technology and particle physics, Como, pp 819–825, 2002). In the last years many efforts have been devoted to the development of novel imaging detectors for extreme-ultraviolet radiation and soft X-rays (Baldacchini et al. J Nanosci Nanotechnol 3:483–486, 2003), hard X-rays (Almaviva et al. Appl Phys Lett 89(5):054102, 2006), as well as low (Baldacchini et al. J Phys Condens Matter 10:857–867, 1998) and high energy electrons. Such solid-state detectors are based on the optical reading of photoluminescence (PL) from stable, visibleemitting colour centres (CCs), produced by irradiation with ionising radiations. These aggregate electronic defects are F2 and FC+ 3 CCs (two electrons bound to two and three close anion vacancies, respectively), which possess almost overlapping absorption bands, peaked at about 450 nm, called M band (Nahum, Phys Rev 157:817–830, 1967). By optical pumping in this spectral region, F2 and FC+ 3 CCs emit broad PL bands peaked at 678 and 541 nm, respectively. LiF films of different thickness were grown by thermal evaporation on different substrates, such as glass and silica, as well as plastic ones (Di Lazzaro et al. Extreme ultraviolet marking system for anti-counterfeiting tags with adjustable security level. In: Allakhverdiev KR (ed) XIX international symposium on high-power laser systems and applications, Istanbul. International Society for Optics and Photonics, p 86770T, 2013). Even in LiF thin films grown on transparent substrates, the direct use of optical absorption spectra to individuate the presence of different kinds of point defects is often precluded by the presence of interference fringes due to the refractive index difference between film and substrate (Nichelatti et al. J Non-Crystalline Solids 322:117–121, 2003). PL measurements are more sensitive and a very effective investigation method, called Combined Excitation-Emission Spectroscopy (Gill et al. Appl Phys Lett 64(19):2483, 1994), can be applied. In this work we present the basic characteristic of this technique and the first results of the investigation of polycrystalline LiF films grown by thermal evaporation on glass substrates and coloured by high-energy electrons in air. © Springer Science+Business Media Dordrecht 2015.

Photoluminescence of colour centres in Thermally-Evaporated LiF films for radiation imaging detectors

Nichelatti, E.;Rufoloni, A.;Montereali, R.M.;Messina, G.;Bonfigli, F.;Vincenti, M.A.
2015

Abstract

Lithium fluoride (LiF) is a well-known dosimeter material in pure (McLaughlin et al. Nucl Instrum Methods 175:17–18, 1980) and doped (Lakshmanan et al. Phys Status Solidi (a) 153:265–273, 1996) form. Radiation detectors based on microcrystalline dispersion of LiF in a polymeric matrix have been introduced for gamma and electron high-dose dosimetry (Kovacs et al. Radiat Phys Chem 57:691–695, 2000). In recent years the area of growth and characterisation of LiF thin films has seen a considerable expansion. Polycrystalline LiF films grown by thermal evaporation were proposed and tested as nuclear sensors for neutrons (Cosset et al. Thin Solid Films 303:191–195, 1997) and for gamma dosimetry (Montecchi et al. Point defects in lithium fluoride films induced by gamma irradiation, ch. 116. In: Proceedings of the 7th international conference on advanced technology and particle physics, Como, pp 819–825, 2002). In the last years many efforts have been devoted to the development of novel imaging detectors for extreme-ultraviolet radiation and soft X-rays (Baldacchini et al. J Nanosci Nanotechnol 3:483–486, 2003), hard X-rays (Almaviva et al. Appl Phys Lett 89(5):054102, 2006), as well as low (Baldacchini et al. J Phys Condens Matter 10:857–867, 1998) and high energy electrons. Such solid-state detectors are based on the optical reading of photoluminescence (PL) from stable, visibleemitting colour centres (CCs), produced by irradiation with ionising radiations. These aggregate electronic defects are F2 and FC+ 3 CCs (two electrons bound to two and three close anion vacancies, respectively), which possess almost overlapping absorption bands, peaked at about 450 nm, called M band (Nahum, Phys Rev 157:817–830, 1967). By optical pumping in this spectral region, F2 and FC+ 3 CCs emit broad PL bands peaked at 678 and 541 nm, respectively. LiF films of different thickness were grown by thermal evaporation on different substrates, such as glass and silica, as well as plastic ones (Di Lazzaro et al. Extreme ultraviolet marking system for anti-counterfeiting tags with adjustable security level. In: Allakhverdiev KR (ed) XIX international symposium on high-power laser systems and applications, Istanbul. International Society for Optics and Photonics, p 86770T, 2013). Even in LiF thin films grown on transparent substrates, the direct use of optical absorption spectra to individuate the presence of different kinds of point defects is often precluded by the presence of interference fringes due to the refractive index difference between film and substrate (Nichelatti et al. J Non-Crystalline Solids 322:117–121, 2003). PL measurements are more sensitive and a very effective investigation method, called Combined Excitation-Emission Spectroscopy (Gill et al. Appl Phys Lett 64(19):2483, 1994), can be applied. In this work we present the basic characteristic of this technique and the first results of the investigation of polycrystalline LiF films grown by thermal evaporation on glass substrates and coloured by high-energy electrons in air. © Springer Science+Business Media Dordrecht 2015.
Colour centres;Combined excitation-emission spectroscopy;Thin films;Lithium fluoride;Photoluminescence
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.12079/2700
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