The Experts below are selected from a list of 6171 Experts worldwide ranked by ideXlab platform
James Bullock - One of the best experts on this subject based on the ideXlab platform.
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Lithium Fluoride based electron contacts for high efficiency n type crystalline silicon solar cells
Advanced Energy Materials, 2016Co-Authors: James Bullock, Peiting Zheng, Quentin Jeangros, Mahmut Tosun, Mark Hettick, Carolin M SutterfellaAbstract:Low-resistance contact to lightly doped n-type crystalline silicon (c-Si) has long been recognized as technologically challenging due to the pervasive Fermi-level pinning effect. This has hindered the development of certain devices such as n-type c-Si solar cells made with partial rear contacts (PRC) directly to the lowly doped c-Si wafer. Here, a simple and robust process is demonstrated for achieving m Omega cm(2) scale contact resistivities on lightly doped n-type c-Si via a Lithium Fluoride/aluminum contact. The realization of this low-resistance contact enables the fabrication of a first-of-its-kind high-efficiency n-type PRC solar cell. The electron contact of this cell is made to less than 1% of the rear surface area, reducing the impact of contact recombination and optical losses, permitting a power conversion efficiency of greater than 20% in the initial proof-of-concept stage. The implementation of the LiFx/Al contact mitigates the need for the costly high-temperature phosphorus diffusion, typically implemented in such a cell design to nullify the issue of Fermi level pinning at the electron contact. The timing of this demonstration is significant, given the ongoing transition from p-type to n-type c-Si solar cell architectures, together with the increased adoption of advanced PRC device structures within the c-Si photovoltaic industry.
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Lithium Fluoride based electron contacts for high efficiency n type crystalline silicon solar cells
Advanced Energy Materials, 2016Co-Authors: James Bullock, Peiting Zheng, Quentin Jeangros, Mahmut Tosun, Mark Hettick, Carolin M SutterfellaAbstract:Low-resistance contact to lightly doped n-type crystalline silicon (c-Si) has long been recognized as technologically challenging due to the pervasive Fermi-level pinning effect. This has hindered the development of certain devices such as n-type c-Si solar cells made with partial rear contacts (PRC) directly to the lowly doped c-Si wafer. Here, a simple and robust process is demonstrated for achieving mΩ cm2 scale contact resistivities on lightly doped n-type c-Si via a Lithium Fluoride/aluminum contact. The realization of this low-resistance contact enables the fabrication of a first-of-its-kind high-efficiency n-type PRC solar cell. The electron contact of this cell is made to less than 1% of the rear surface area, reducing the impact of contact recombination and optical losses, permitting a power conversion efficiency of greater than 20% in the initial proof-of-concept stage. The implementation of the LiFx/Al contact mitigates the need for the costly high-temperature phosphorus diffusion, typically implemented in such a cell design to nullify the issue of Fermi level pinning at the electron contact. The timing of this demonstration is significant, given the ongoing transition from p-type to n-type c-Si solar cell architectures, together with the increased adoption of advanced PRC device structures within the c-Si photovoltaic industry.
R M Montereali - One of the best experts on this subject based on the ideXlab platform.
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visible photoluminescence of aggregate colour centres in Lithium Fluoride thin films for low energy proton beam radiation detectors at high doses
Journal of Luminescence, 2018Co-Authors: R M Montereali, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, M Piccinini, L Picardi, F Bonfigli, S Libera, M A VincentiAbstract:Abstract Colour centres (CCs) in Lithium Fluoride (LiF) are well known for application in tuneable lasers and dosimeters. The visible photoluminescence (PL) of radiation-induced, broad-band light-emitting aggregate CCs in LiF crystals and films has been proposed for high spatial resolution X-ray imaging; use of LiF-based detectors has been recently successfully extended to advanced diagnostics of low-energy proton beams. After exposure, transversal dose mapping was obtained on LiF films by acquiring the visible PL image of the irradiated spots in a fluorescence microscope under blue-light pumping. Irradiation of thermally evaporated LiF thin films with a proton beam of 3 MeV nominal energy, produced by a linear accelerator, in the fluence range of 1011–1015 protons/cm2, induces the formation of stable CCs, mainly the primary F centre and the aggregate F2 and F3+ defects. A comparison with irradiations performed at 7 MeV shows that the spectrally integrated PL as a function of the absorbed dose is independent on the selected beam energy, at least as far as typical LiF film thicknesses are concerned. The PL behaviour vs. dose can be described by a linear growth which covers up to three order of magnitude, followed by saturation at high values (> ≈105 Gy). The spectral contributions of F2 and F3+ CCs to the detected PL, in the red and in the green respectively, under laser pumping were carefully analysed in order to investigate behaviour differences of these defects at high doses.
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photoluminescence of colour centres in Lithium Fluoride thin films from solid state miniaturised light sources to novel radiation imaging detectors
Journal of Luminescence, 2016Co-Authors: R M Montereali, Enrico Nichelatti, M Piccinini, F Bonfigli, M A VincentiAbstract:Abstract Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation detectors. Among them, colour centres in Lithium Fluoride, LiF, are well known for their application in tuneable lasers and dosimeters. Broad-band light-emitting F2 and F 3 + electronic defects, stable at room temperature, are produced in LiF crystals and films by different kinds of radiation. Under blue optical pumping in their overlapping absorption bands, the efficient photoluminescence spans over the green–red visible spectral range. Novel LiF thin-film radiation imaging detectors based on the exploitation of the peculiar spectral characteristics of F2 and F 3 + defects and of the optical properties and radiation sensitivity of the LiF material have been proposed and successfully tested for extreme ultraviolet radiation, soft and hard X-ray imaging, including micro-radiography of biological objects, even for in vivo samples. After exposure to X-rays, the latent images stored in the LiF thin layers by local formation of active defects are read with conventional and advanced optical fluorescence microscopes. Among the main advantages of the LiF thin-film imaging detectors, there are intrinsic very high spatial resolution, large field of view and wide dynamic range. Moreover, these solid state radiation detectors are easy to handle, as insensitive to ambient light, and no development process is needed. Recently their use has been extended to proton beam advanced diagnostics. In this paper, a short review of their properties, results and applications in X-ray biological imaging and proton dose-mapping is presented, underlying the great versatility and potentialities offered by LiF thin films, whose photoluminescence response can be improved through the choice of suitable substrates and growth conditions.
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photoluminescence of radiation induced color centers in Lithium Fluoride thin films for advanced diagnostics of proton beams
Applied Physics Letters, 2015Co-Authors: M Piccinini, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, F Ambrosini, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Systematic irradiation of thermally evaporated 0.8 μm thick polycrystalline Lithium Fluoride films on glass was performed by proton beams of 3 and 7 MeV energies, produced by a linear accelerator, in a fluence range from 1011 to 1015 protons/cm2. The visible photoluminescence spectra of radiation-induced F2 and F3+ laser active color centers, which possess almost overlapping absorption bands at about 450 nm, were measured under laser pumping at 458 nm. On the basis of simulations of the linear energy transfer with proton penetration depth in LiF, it was possible to obtain the behavior of the measured integrated photoluminescence intensity of proton irradiated LiF films as a function of the deposited dose. The photoluminescence signal is linearly dependent on the deposited dose in the interval from 103 to about 106 Gy, independently from the used proton energies. This behavior is very encouraging for the development of advanced solid state radiation detectors based on optically transparent LiF thin films f...
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solid state detectors based on point defects in Lithium Fluoride for advanced proton beam diagnostics
Journal of Luminescence, 2014Co-Authors: M Piccinini, A. Ampollini, C. Ronsivalle, F Ambrosini, M Carpanese, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Abstract Proton beams of 3 and 7 MeV energies, produced by a linear accelerator, were used to irradiate Lithium Fluoride crystals and thermally evaporated LiF thin films in the fluence range of 1011–1015 protons/cm2. The irradiation induces the formation of stable colour centres, mainly the primary F centre and the aggregate F2 and F3+ defects. By optical pumping in the blue spectral region, the F2 and F3+ centres emit broad photoluminescence bands in the visible spectral range. By conventional fluorescence microscopy, the integrated photoluminescence intensity was carefully measured in LiF crystals and thin films as a function of the irradiation fluence: a linear optical response was obtained in a large range of fluence, which is dependent on the used LiF samples and the selected beam energy. It was possible to record the transversal proton beam intensity profile by acquiring the photoluminescence image of the irradiated spots on LiF films by a standard optical microscope. Using LiF films grown on silicon substrates irradiated in a particular geometry, the same optical reading microscopy technique allowed one to measure the distribution of colour centres photoluminescence along the depth and direct imaging the Bragg peak position, which gives a rough estimation of the initial proton beam energy.
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near field optical spectroscopy of colored centers stripes written in Lithium Fluoride by electron beam lithography
Radiation Effects and Defects in Solids, 2002Co-Authors: Sorin Tascu, M Piccinini, R M Montereali, R J Reeves, B Jacquier, P Moretti, Fabrizia Somma, C SeassalAbstract:Electron-beam lithography has been used to define color center stripes of about one hundred micrometers length and variable width (100 v nm to 5 v m) in Lithium Fluoride. These structures have for the first time been illustrated and spectrally characterized in near field optical microscopy (SNOM) operating in local illumination mode with an optical fiber probe and far field fluorescence detection.
M A Vincenti - One of the best experts on this subject based on the ideXlab platform.
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visible photoluminescence of aggregate colour centres in Lithium Fluoride thin films for low energy proton beam radiation detectors at high doses
Journal of Luminescence, 2018Co-Authors: R M Montereali, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, M Piccinini, L Picardi, F Bonfigli, S Libera, M A VincentiAbstract:Abstract Colour centres (CCs) in Lithium Fluoride (LiF) are well known for application in tuneable lasers and dosimeters. The visible photoluminescence (PL) of radiation-induced, broad-band light-emitting aggregate CCs in LiF crystals and films has been proposed for high spatial resolution X-ray imaging; use of LiF-based detectors has been recently successfully extended to advanced diagnostics of low-energy proton beams. After exposure, transversal dose mapping was obtained on LiF films by acquiring the visible PL image of the irradiated spots in a fluorescence microscope under blue-light pumping. Irradiation of thermally evaporated LiF thin films with a proton beam of 3 MeV nominal energy, produced by a linear accelerator, in the fluence range of 1011–1015 protons/cm2, induces the formation of stable CCs, mainly the primary F centre and the aggregate F2 and F3+ defects. A comparison with irradiations performed at 7 MeV shows that the spectrally integrated PL as a function of the absorbed dose is independent on the selected beam energy, at least as far as typical LiF film thicknesses are concerned. The PL behaviour vs. dose can be described by a linear growth which covers up to three order of magnitude, followed by saturation at high values (> ≈105 Gy). The spectral contributions of F2 and F3+ CCs to the detected PL, in the red and in the green respectively, under laser pumping were carefully analysed in order to investigate behaviour differences of these defects at high doses.
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photoluminescence of colour centres in Lithium Fluoride thin films from solid state miniaturised light sources to novel radiation imaging detectors
Journal of Luminescence, 2016Co-Authors: R M Montereali, Enrico Nichelatti, M Piccinini, F Bonfigli, M A VincentiAbstract:Abstract Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation detectors. Among them, colour centres in Lithium Fluoride, LiF, are well known for their application in tuneable lasers and dosimeters. Broad-band light-emitting F2 and F 3 + electronic defects, stable at room temperature, are produced in LiF crystals and films by different kinds of radiation. Under blue optical pumping in their overlapping absorption bands, the efficient photoluminescence spans over the green–red visible spectral range. Novel LiF thin-film radiation imaging detectors based on the exploitation of the peculiar spectral characteristics of F2 and F 3 + defects and of the optical properties and radiation sensitivity of the LiF material have been proposed and successfully tested for extreme ultraviolet radiation, soft and hard X-ray imaging, including micro-radiography of biological objects, even for in vivo samples. After exposure to X-rays, the latent images stored in the LiF thin layers by local formation of active defects are read with conventional and advanced optical fluorescence microscopes. Among the main advantages of the LiF thin-film imaging detectors, there are intrinsic very high spatial resolution, large field of view and wide dynamic range. Moreover, these solid state radiation detectors are easy to handle, as insensitive to ambient light, and no development process is needed. Recently their use has been extended to proton beam advanced diagnostics. In this paper, a short review of their properties, results and applications in X-ray biological imaging and proton dose-mapping is presented, underlying the great versatility and potentialities offered by LiF thin films, whose photoluminescence response can be improved through the choice of suitable substrates and growth conditions.
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photoluminescence of radiation induced color centers in Lithium Fluoride thin films for advanced diagnostics of proton beams
Applied Physics Letters, 2015Co-Authors: M Piccinini, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, F Ambrosini, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Systematic irradiation of thermally evaporated 0.8 μm thick polycrystalline Lithium Fluoride films on glass was performed by proton beams of 3 and 7 MeV energies, produced by a linear accelerator, in a fluence range from 1011 to 1015 protons/cm2. The visible photoluminescence spectra of radiation-induced F2 and F3+ laser active color centers, which possess almost overlapping absorption bands at about 450 nm, were measured under laser pumping at 458 nm. On the basis of simulations of the linear energy transfer with proton penetration depth in LiF, it was possible to obtain the behavior of the measured integrated photoluminescence intensity of proton irradiated LiF films as a function of the deposited dose. The photoluminescence signal is linearly dependent on the deposited dose in the interval from 103 to about 106 Gy, independently from the used proton energies. This behavior is very encouraging for the development of advanced solid state radiation detectors based on optically transparent LiF thin films f...
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solid state detectors based on point defects in Lithium Fluoride for advanced proton beam diagnostics
Journal of Luminescence, 2014Co-Authors: M Piccinini, A. Ampollini, C. Ronsivalle, F Ambrosini, M Carpanese, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Abstract Proton beams of 3 and 7 MeV energies, produced by a linear accelerator, were used to irradiate Lithium Fluoride crystals and thermally evaporated LiF thin films in the fluence range of 1011–1015 protons/cm2. The irradiation induces the formation of stable colour centres, mainly the primary F centre and the aggregate F2 and F3+ defects. By optical pumping in the blue spectral region, the F2 and F3+ centres emit broad photoluminescence bands in the visible spectral range. By conventional fluorescence microscopy, the integrated photoluminescence intensity was carefully measured in LiF crystals and thin films as a function of the irradiation fluence: a linear optical response was obtained in a large range of fluence, which is dependent on the used LiF samples and the selected beam energy. It was possible to record the transversal proton beam intensity profile by acquiring the photoluminescence image of the irradiated spots on LiF films by a standard optical microscope. Using LiF films grown on silicon substrates irradiated in a particular geometry, the same optical reading microscopy technique allowed one to measure the distribution of colour centres photoluminescence along the depth and direct imaging the Bragg peak position, which gives a rough estimation of the initial proton beam energy.
M Piccinini - One of the best experts on this subject based on the ideXlab platform.
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visible photoluminescence of aggregate colour centres in Lithium Fluoride thin films for low energy proton beam radiation detectors at high doses
Journal of Luminescence, 2018Co-Authors: R M Montereali, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, M Piccinini, L Picardi, F Bonfigli, S Libera, M A VincentiAbstract:Abstract Colour centres (CCs) in Lithium Fluoride (LiF) are well known for application in tuneable lasers and dosimeters. The visible photoluminescence (PL) of radiation-induced, broad-band light-emitting aggregate CCs in LiF crystals and films has been proposed for high spatial resolution X-ray imaging; use of LiF-based detectors has been recently successfully extended to advanced diagnostics of low-energy proton beams. After exposure, transversal dose mapping was obtained on LiF films by acquiring the visible PL image of the irradiated spots in a fluorescence microscope under blue-light pumping. Irradiation of thermally evaporated LiF thin films with a proton beam of 3 MeV nominal energy, produced by a linear accelerator, in the fluence range of 1011–1015 protons/cm2, induces the formation of stable CCs, mainly the primary F centre and the aggregate F2 and F3+ defects. A comparison with irradiations performed at 7 MeV shows that the spectrally integrated PL as a function of the absorbed dose is independent on the selected beam energy, at least as far as typical LiF film thicknesses are concerned. The PL behaviour vs. dose can be described by a linear growth which covers up to three order of magnitude, followed by saturation at high values (> ≈105 Gy). The spectral contributions of F2 and F3+ CCs to the detected PL, in the red and in the green respectively, under laser pumping were carefully analysed in order to investigate behaviour differences of these defects at high doses.
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proton beam spatial distribution and bragg peak imaging by photoluminescence of color centers in Lithium Fluoride crystals at the top implart linear accelerator
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2017Co-Authors: M Piccinini, A. Ampollini, C. Ronsivalle, G. Bazzano, Paolo Nenzi, L Picardi, F Bonfigli, E Trinca, Monia Vadrucci, Enrico NichelattiAbstract:Abstract Solid-state radiation detectors based on the photoluminescence of stable point defects in Lithium Fluoride crystals have been used for advanced diagnostics during the commissioning of the segment up to 27 MeV of the TOP-IMPLART proton linear accelerator for proton therapy applications, under development at ENEA C.R. Frascati, Italy. The LiF detectors high intrinsic spatial resolution and wide dynamic range allow obtaining two-dimensional images of the beam transverse intensity distribution and also identifying the Bragg peak position with micrometric precision by using a conventional optical fluorescence microscope. Results of the proton beam characterization, among which, the estimation of beam energy components and dynamics, are reported and discussed for different operating conditions of the accelerator.
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photoluminescence of colour centres in Lithium Fluoride thin films from solid state miniaturised light sources to novel radiation imaging detectors
Journal of Luminescence, 2016Co-Authors: R M Montereali, Enrico Nichelatti, M Piccinini, F Bonfigli, M A VincentiAbstract:Abstract Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation detectors. Among them, colour centres in Lithium Fluoride, LiF, are well known for their application in tuneable lasers and dosimeters. Broad-band light-emitting F2 and F 3 + electronic defects, stable at room temperature, are produced in LiF crystals and films by different kinds of radiation. Under blue optical pumping in their overlapping absorption bands, the efficient photoluminescence spans over the green–red visible spectral range. Novel LiF thin-film radiation imaging detectors based on the exploitation of the peculiar spectral characteristics of F2 and F 3 + defects and of the optical properties and radiation sensitivity of the LiF material have been proposed and successfully tested for extreme ultraviolet radiation, soft and hard X-ray imaging, including micro-radiography of biological objects, even for in vivo samples. After exposure to X-rays, the latent images stored in the LiF thin layers by local formation of active defects are read with conventional and advanced optical fluorescence microscopes. Among the main advantages of the LiF thin-film imaging detectors, there are intrinsic very high spatial resolution, large field of view and wide dynamic range. Moreover, these solid state radiation detectors are easy to handle, as insensitive to ambient light, and no development process is needed. Recently their use has been extended to proton beam advanced diagnostics. In this paper, a short review of their properties, results and applications in X-ray biological imaging and proton dose-mapping is presented, underlying the great versatility and potentialities offered by LiF thin films, whose photoluminescence response can be improved through the choice of suitable substrates and growth conditions.
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photoluminescence of radiation induced color centers in Lithium Fluoride thin films for advanced diagnostics of proton beams
Applied Physics Letters, 2015Co-Authors: M Piccinini, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, F Ambrosini, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Systematic irradiation of thermally evaporated 0.8 μm thick polycrystalline Lithium Fluoride films on glass was performed by proton beams of 3 and 7 MeV energies, produced by a linear accelerator, in a fluence range from 1011 to 1015 protons/cm2. The visible photoluminescence spectra of radiation-induced F2 and F3+ laser active color centers, which possess almost overlapping absorption bands at about 450 nm, were measured under laser pumping at 458 nm. On the basis of simulations of the linear energy transfer with proton penetration depth in LiF, it was possible to obtain the behavior of the measured integrated photoluminescence intensity of proton irradiated LiF films as a function of the deposited dose. The photoluminescence signal is linearly dependent on the deposited dose in the interval from 103 to about 106 Gy, independently from the used proton energies. This behavior is very encouraging for the development of advanced solid state radiation detectors based on optically transparent LiF thin films f...
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solid state detectors based on point defects in Lithium Fluoride for advanced proton beam diagnostics
Journal of Luminescence, 2014Co-Authors: M Piccinini, A. Ampollini, C. Ronsivalle, F Ambrosini, M Carpanese, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Abstract Proton beams of 3 and 7 MeV energies, produced by a linear accelerator, were used to irradiate Lithium Fluoride crystals and thermally evaporated LiF thin films in the fluence range of 1011–1015 protons/cm2. The irradiation induces the formation of stable colour centres, mainly the primary F centre and the aggregate F2 and F3+ defects. By optical pumping in the blue spectral region, the F2 and F3+ centres emit broad photoluminescence bands in the visible spectral range. By conventional fluorescence microscopy, the integrated photoluminescence intensity was carefully measured in LiF crystals and thin films as a function of the irradiation fluence: a linear optical response was obtained in a large range of fluence, which is dependent on the used LiF samples and the selected beam energy. It was possible to record the transversal proton beam intensity profile by acquiring the photoluminescence image of the irradiated spots on LiF films by a standard optical microscope. Using LiF films grown on silicon substrates irradiated in a particular geometry, the same optical reading microscopy technique allowed one to measure the distribution of colour centres photoluminescence along the depth and direct imaging the Bragg peak position, which gives a rough estimation of the initial proton beam energy.
F Bonfigli - One of the best experts on this subject based on the ideXlab platform.
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visible photoluminescence of aggregate colour centres in Lithium Fluoride thin films for low energy proton beam radiation detectors at high doses
Journal of Luminescence, 2018Co-Authors: R M Montereali, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, M Piccinini, L Picardi, F Bonfigli, S Libera, M A VincentiAbstract:Abstract Colour centres (CCs) in Lithium Fluoride (LiF) are well known for application in tuneable lasers and dosimeters. The visible photoluminescence (PL) of radiation-induced, broad-band light-emitting aggregate CCs in LiF crystals and films has been proposed for high spatial resolution X-ray imaging; use of LiF-based detectors has been recently successfully extended to advanced diagnostics of low-energy proton beams. After exposure, transversal dose mapping was obtained on LiF films by acquiring the visible PL image of the irradiated spots in a fluorescence microscope under blue-light pumping. Irradiation of thermally evaporated LiF thin films with a proton beam of 3 MeV nominal energy, produced by a linear accelerator, in the fluence range of 1011–1015 protons/cm2, induces the formation of stable CCs, mainly the primary F centre and the aggregate F2 and F3+ defects. A comparison with irradiations performed at 7 MeV shows that the spectrally integrated PL as a function of the absorbed dose is independent on the selected beam energy, at least as far as typical LiF film thicknesses are concerned. The PL behaviour vs. dose can be described by a linear growth which covers up to three order of magnitude, followed by saturation at high values (> ≈105 Gy). The spectral contributions of F2 and F3+ CCs to the detected PL, in the red and in the green respectively, under laser pumping were carefully analysed in order to investigate behaviour differences of these defects at high doses.
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proton beam spatial distribution and bragg peak imaging by photoluminescence of color centers in Lithium Fluoride crystals at the top implart linear accelerator
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2017Co-Authors: M Piccinini, A. Ampollini, C. Ronsivalle, G. Bazzano, Paolo Nenzi, L Picardi, F Bonfigli, E Trinca, Monia Vadrucci, Enrico NichelattiAbstract:Abstract Solid-state radiation detectors based on the photoluminescence of stable point defects in Lithium Fluoride crystals have been used for advanced diagnostics during the commissioning of the segment up to 27 MeV of the TOP-IMPLART proton linear accelerator for proton therapy applications, under development at ENEA C.R. Frascati, Italy. The LiF detectors high intrinsic spatial resolution and wide dynamic range allow obtaining two-dimensional images of the beam transverse intensity distribution and also identifying the Bragg peak position with micrometric precision by using a conventional optical fluorescence microscope. Results of the proton beam characterization, among which, the estimation of beam energy components and dynamics, are reported and discussed for different operating conditions of the accelerator.
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photoluminescence of colour centres in Lithium Fluoride thin films from solid state miniaturised light sources to novel radiation imaging detectors
Journal of Luminescence, 2016Co-Authors: R M Montereali, Enrico Nichelatti, M Piccinini, F Bonfigli, M A VincentiAbstract:Abstract Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation detectors. Among them, colour centres in Lithium Fluoride, LiF, are well known for their application in tuneable lasers and dosimeters. Broad-band light-emitting F2 and F 3 + electronic defects, stable at room temperature, are produced in LiF crystals and films by different kinds of radiation. Under blue optical pumping in their overlapping absorption bands, the efficient photoluminescence spans over the green–red visible spectral range. Novel LiF thin-film radiation imaging detectors based on the exploitation of the peculiar spectral characteristics of F2 and F 3 + defects and of the optical properties and radiation sensitivity of the LiF material have been proposed and successfully tested for extreme ultraviolet radiation, soft and hard X-ray imaging, including micro-radiography of biological objects, even for in vivo samples. After exposure to X-rays, the latent images stored in the LiF thin layers by local formation of active defects are read with conventional and advanced optical fluorescence microscopes. Among the main advantages of the LiF thin-film imaging detectors, there are intrinsic very high spatial resolution, large field of view and wide dynamic range. Moreover, these solid state radiation detectors are easy to handle, as insensitive to ambient light, and no development process is needed. Recently their use has been extended to proton beam advanced diagnostics. In this paper, a short review of their properties, results and applications in X-ray biological imaging and proton dose-mapping is presented, underlying the great versatility and potentialities offered by LiF thin films, whose photoluminescence response can be improved through the choice of suitable substrates and growth conditions.
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photoluminescence of radiation induced color centers in Lithium Fluoride thin films for advanced diagnostics of proton beams
Applied Physics Letters, 2015Co-Authors: M Piccinini, Enrico Nichelatti, A. Ampollini, C. Ronsivalle, F Ambrosini, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Systematic irradiation of thermally evaporated 0.8 μm thick polycrystalline Lithium Fluoride films on glass was performed by proton beams of 3 and 7 MeV energies, produced by a linear accelerator, in a fluence range from 1011 to 1015 protons/cm2. The visible photoluminescence spectra of radiation-induced F2 and F3+ laser active color centers, which possess almost overlapping absorption bands at about 450 nm, were measured under laser pumping at 458 nm. On the basis of simulations of the linear energy transfer with proton penetration depth in LiF, it was possible to obtain the behavior of the measured integrated photoluminescence intensity of proton irradiated LiF films as a function of the deposited dose. The photoluminescence signal is linearly dependent on the deposited dose in the interval from 103 to about 106 Gy, independently from the used proton energies. This behavior is very encouraging for the development of advanced solid state radiation detectors based on optically transparent LiF thin films f...
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solid state detectors based on point defects in Lithium Fluoride for advanced proton beam diagnostics
Journal of Luminescence, 2014Co-Authors: M Piccinini, A. Ampollini, C. Ronsivalle, F Ambrosini, M Carpanese, L Picardi, F Bonfigli, S Libera, M A Vincenti, R M MonterealiAbstract:Abstract Proton beams of 3 and 7 MeV energies, produced by a linear accelerator, were used to irradiate Lithium Fluoride crystals and thermally evaporated LiF thin films in the fluence range of 1011–1015 protons/cm2. The irradiation induces the formation of stable colour centres, mainly the primary F centre and the aggregate F2 and F3+ defects. By optical pumping in the blue spectral region, the F2 and F3+ centres emit broad photoluminescence bands in the visible spectral range. By conventional fluorescence microscopy, the integrated photoluminescence intensity was carefully measured in LiF crystals and thin films as a function of the irradiation fluence: a linear optical response was obtained in a large range of fluence, which is dependent on the used LiF samples and the selected beam energy. It was possible to record the transversal proton beam intensity profile by acquiring the photoluminescence image of the irradiated spots on LiF films by a standard optical microscope. Using LiF films grown on silicon substrates irradiated in a particular geometry, the same optical reading microscopy technique allowed one to measure the distribution of colour centres photoluminescence along the depth and direct imaging the Bragg peak position, which gives a rough estimation of the initial proton beam energy.