Temperature behavior of optical absorption bands in colored LiF crystals

We measured the optical absorption spectra of thermally treated, gamma irradiated LiF crystals, as a function of temperature in the range 16–300 K. The temperature dependence of intensity, peak position and bandwidth of F and M absorption bands were obtained. Keywords: Lithium fluoride, Optical absorption, Low temperature, Color center

Confocal fluorescence microscopy and confocal raman microspectroscopy of X-ray irradiated LIF crystals

Radiation-induced color centers locally produced in lithium fluoride (LiF) are successfully used for radiation detectors. LiF detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging applications with laboratory radiation sources, as well as large-scale facilities. Among the peculiarities of LiF-based detectors, noteworthy ones are their very high intrinsic spatial resolution across a large field of view, wide dynamic range, and versatility. LiF crystals irradiated with a monochromatic 8 keV X-ray beam at KIT synchrotron light source (Karlsruhe, Germany) and with the broadband white beam spectrum of the synchrotron bending magnet have been investigated by optical spectroscopy, laser scanning confocal microscopy in fluorescence mode, and confocal Raman micro-spectroscopy. The 3D reconstruction of the distributions of the color centers induced by the X-rays has been performed with both confocal techniques. The combination of the LiF crystal capability to register volumetric X-ray mapping with the optical sectioning operations of the confocal techniques has allowed performing 3D reconstructions of the X-ray colored volumes and it could provide advanced tools for 3D X-ray detection

Confocal Fluorescence Microscopy and Confocal Raman Microspectroscopy of X-ray Irradiated LiF Crystals

Radiation-induced color centers locally produced in lithium fluoride (LiF) are successfully used for radiation detectors. LiF detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging applications with laboratory radiation sources, as well as large-scale facilities. Among the peculiarities of LiF-based detectors, noteworthy ones are their very high intrinsic spatial resolution across a large field of view, wide dynamic range, and versatility. LiF crystals irradiated with a monochromatic 8 keV X-ray beam at KIT synchrotron light source (Karlsruhe, Germany) and with the broadband white beam spectrum of the synchrotron bending magnet have been investigated by optical spectroscopy, laser scanning confocal microscopy in fluorescence mode, and confocal Raman micro-spectroscopy. The 3D reconstruction of the distributions of the color centers induced by the X-rays has been performed with both confocal techniques. The combination of the LiF crystal capability to register volumetric X-ray mapping with the optical sectioning operations of the confocal techniques has allowed performing 3D reconstructions of the X-ray colored volumes and it could provide advanced tools for 3D X-ray detection

Proton beam dose-mapping via color centers in LiF thin-film detectors by fluorescence microscopy

With the purpose of studying the behavior of novel solid-state lithium fluoride (LiF) films detectors based on the photoluminescence (PL) of radiation-induced defects for proton beam diagnostics and dosimetry, polycrystalline LiF thin films thermally evaporated on glass were irradiated at room temperature in a linear proton accelerator under development at ENEA. The irradiations were performed in air by proton beams of 3 and 7 MeV energy, in a fluence range from 1011 to 1015 protons/cm2. In the LiF films, proton irradiation induces the formation of F2 and $\text{F}_{3}^{+}$ aggregate color centers, which simultaneously emit broad PL bands in the visible spectral range under excitation in the blue one. The integrated PL signal, acquired by a fluorescence microscope equipped with a s-CMOS camera, shows a linear dependence on the dose deposited in LiF films, extending from 103 to 106 Gy, independently of the proton energy. A simple theoretical model is put forward for the formation of color centers in LiF and is utilized to obtain a proton beam dose-map by processing the PL image stored in the LiF film detectors

Spin-coating deposition of thermoresponsive microgel thin films

Smart surfaces and surface coatings have been attracting increasing interest in the last decades. In particular, thin films assembled from microgels offer good control of morphology, elasticity and hydrophobicity thanks to the high tunability of microgel mechanical properties and chemical composition. Among smart microgels, Poly(N-isopropylacrylamide) (PNIPAM) based microgels are the most used systems for theoretical and experimental studies and for nanotechnological applications. When used as building blocks to fabricate 2D assemblies, they exhibit new properties offering many advantages for additional applications in different fields. Here we report a systematic investigation of aqueous suspensions of soft PNIPAM microgels through Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS) and rheometry. Starting from these suspensions, optical and morphological properties of PNIPAM microgel thin films deposited by spin-coating on a glass substrate at different weight concentrations and deposition conditions are investigated through UV-Vis-NIR spectroscopy and Atomic Force Microscopy (AFM). Homogeneous and smooth thin films of soft PNIPAM microgels were obtained with high transparency in the whole wavelength range from the visible to the near-infrared region. Moreover, their optical properties were correlated to microgel arrangement at the solid surface that can be opportunely tuned by changing the spin-coating deposition parameters

High-temperature long-lasting stability assessment of a single-crystal diamond detector under high-flux neutron irradiation

An innovative diamond detector layout is presented that is designed to operate at high temperature under intense neutron and gamma fluxes. It is made of a 500 μm "electronic grade" diamond film with 100 nm thick Ag metal contacts deposited onto each surface of the film by means of thermal evaporation. A thick layer of 6LiF has been deposited on top of one of the two Ag contacts to make the detector sensitive to thermal neutrons. The device was tested at the ISIS spallation neutron source (Rutherford Appleton Laboratory, UK) using the INES beam line. The detector was continuously irradiated for 100 hours in vacuum , exposed to a neutron flux of about 106 n cm−2 s−1 at a temperature . The aim of this experiment was to study the time dependence of the diamond detector performance while operating at high temperature under irradiation, providing a first experimental proof of reliable continuous operation for 100 hours at high temperature in a harsh environment

Visible radiophotoluminescence of color centers in lithium fluoride thin films for high spatial resolution imaging detectors for hard X-rays

International audiencePassive solid-state detectors based on the visible radiophotoluminescence (RPL) of stable aggregate F$_2$ and F$_3$$^+$ color centers in lithium fluoride (LiF) are successfully used for X-ray imaging and advanced diagnostics of intense X-rays sources. Among their advantages, these detectors offer a wide dynamic range and simplicity of use. They can be read non-destructively using a fluorescence microscope, enabling high spatial resolution over a large field of view. Optically transparent LiF films, of three different increasing thicknesses, were grown by thermal evaporation on glass and silicon substrates and subsequently irradiated with monochromatic 7 keV X-rays at several doses from 1.3 × 10$^1$ to 4.5 × 10$^3$ Gy at the SOLEIL synchrotron facility. For all the LiF films, the RPL response was found to depend linearly on the irradiation dose, with films grown on Si(100) substrates exhibiting up to a 50% higher response compared to those grown on glass. A minimum dose of 13 Gy was detected, despite the low thickness of the irradiated films. The limited thickness of the homogeneously colored LiF film allowed to obtain a spatial resolution of (0.44 ± 0.04) μm in edge-enhancement imaging experiments conducted by placing an Au mesh in front of the samples