•Novel luminescent approach of the detection of radiation damage was demonstrated.•Cathodoluminescence is analysed within a thin proton-irradiated crystal layer.•Radiation defects are exhibited via ...typical emission and influence on the exciton one.•High radiation tolerance of MgO and Al2O3 crystals was confirmed.
Novel approach in the detection of radiation damage created by ion beams in optical materials was demonstrated. Protons of the energy of 100keV and fluence of 1017cm−2 create sufficient amount of crystal lattice defects in the thin surface layer for testing of optical materials needed for future fusion reactors. These structural defects can be detected and analysed using the spectra of cathodoluminescence excited in the irradiated layer by an electron beam with adjustable energy. The method was verified by the enhanced intensity of F-type luminescence that reflects the creation of radiation-induced oxygen vacancies in MgO and Al2O3 crystals. Low radiation resistance of nominally pure (Lu1-xGdx)2SiO5 crystals was demonstrated by almost total suppression of intrinsic luminescence after the same irradiation.
Optical absorption and photoluminescence of amorphous and crystalline HfO2 thin films grown by atomic layer deposition from HfCl4 and H2O were studied. Band-gap energy of (5.55#+0.03) eV was ...determined for monoclinic HfO2 with mean crystallite sizes of 30-40 nm as well as for amorphous HfO2. Excitation in the range of intrinsic absorption resulted in emission that had maximum intensity at 3.2 eV in the case of amorphous films and at 2.6 or 4.4 eV in the case of monoclinic films. The emission intensity of crystalline films exceeded that of amorphous films by an order of magnitude at all temperatures studied. The main luminescence band at 4.4 eV was tentatively assigned to the emission of self-trapped excitons while the emission at lower photon energies was attributed to defects and impurities. With the increase of temperature from 10 to 295 K, the low-energy edges of excitation spectra shifted towards lower energies by 0.1 eV in the case of amorphous films and by 0.15 eV in the case of crystalline films, indicating corresponding changes in the band-gap energies.
Characteristic dimensions and evolution times of regions of secondary electronic excitations created by the interaction of ionizing radiation with matter cannot be measured directly. At the same time ...these are essential parameters both for engineering of nanostructured composite materials defining optimal layer thickness and nanoparticles radii and for the development of optimized scintillators. The paper demonstrates how such spatial and temporal data can be extracted from luminescence decay kinetics excited by vacuum ultraviolet (VUV) and X-ray photons at modern sources of synchrotron radiation MAX IV and PETRA III. Specific features of energy-band structure of self-activated crystal CeF3 are discussed, and its potential for a super-fast detection of ionizing radiation evaluated. Diffusion-controlled dipole–dipole interaction of Frenkel excitons is demonstrated to account well for the luminescence non-exponential decay kinetics providing information on the scales of excited regions created by photons of different energy. For 20 eV photons the radius of excited regions is estimated to be 10 nm, and for 200 eV photons it increases to 18 nm. Effective radius of excited regions of complicated shape created by 19 keV is as large as 80 nm and the diffusion length of Frenkel excitons over radiative time is 14 nm.
Commonly used biological indicators for assessing the efficiency of decontamination procedures include the spores of Bacillus atrophaeus (BA) and Geobacillus stearothermophilus (GS). BA and GS spores ...emit tryptophan-like fluorescence around 320 nm when excited by 280 nm UV light. This fluorescence signal is highly dependent on vaporised hydrogen peroxide (VHP) concentration around the spores, since VHP quenches the fluorescence. In this study we investigated the precise influence of VHP concentration on the autofluorescence properties of BA and GS spores. For both types of spores, the fluorescence signal intensity was found to fall faster and to a relatively lower level when higher VHP concentration was applied. The shape of the signal fall-off as a function of time was found to be well approximated by biexponential decay functions with similar time-constants for BA and GS spores, finally resulting in the equilibrium (or plateau/residual) fluorescence intensity levels that were very different for these samples. The reasons for the fluorescence signal fall-off were investigated by spectral fluorescence signatures (SFS) of the spores. The SFS measurements of the spores during VHP decontamination revealed that the spectral maximum of tryptophan-like (Trp-like) fluorescence changes towards a smaller Stokes shift and has the intensity fall-off due to quenching and oxidation under VHP influence.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
5.
Thin films of HfO2 and ZrO2 as potential scintillators Kirm, Marco; Aarik, Jaan; Jürgens, Meelis ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2005, Letnik:
537, Številka:
1-2
Journal Article
Recenzirano
Emission, excitation and absorption spectra of HfO2 and ZrO2 thin films grown by atomic layer deposition were investigated in the temperature range of 10-300K. Time-resolved luminescence spectra were ...excited with a pulsed ArF laser and tuneable synchrotron radiation in UV–VUV. The strong emission with the peak position at 4.2–4.4eV and with the decay time in μs range was revealed at 10K in both materials. The emission was ascribed to the radiative decay of self-trapped excitons (STE). the features observed in the absorption and excitation spectra at 5.8 and 5.4eV were most probably due to the formation of excitons; While the interband transitions started to dominate at 6.15 and 5.85ev in HfO2 and ZrO2, respectively.
This study is devoted to the development of a UV fluorimetry sensor capable of real-time monitoring of the decontamination process of microbiological pathogens by hydrogen peroxide vapour (HPV) ...treatment. The sensor is operating on the autofluorescence signal of tryptophan. The Bacillus atrophaeus (B. atrophaeus) and Geobacillus stearothermophilus (G. stearothermophilus) spores were exposed to HPV and the resulting dynamic change in tryptophan fluorescence intensity as a function of time was recorded and analysed. It was revealed that the introduced HPV atmosphere caused a 4-time decrease in the fluorescence intensity of the tryptophan emission due to the interaction of HPV with the spores. It was shown that achieving a persistent minimal level of the autofluorescence signal due to the microorganism-bound tryptophan during the defined time period is well correlated with the efficiency of the ongoing decontamination process in the HPV treatment course. Therefore, the progress of the HPV decontamination procedure can be firmly evaluated, using fluorescence data obtained in real time and the validity of the method was demonstrated by comparing the fluorescence data with the reference information obtained by implementing classical microbiology viability tests (incl. time behaviour) for various microorganisms in the HPV atmosphere.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We report on the luminescence properties of hydrothermally synthesized BaLuF5:Pr3+(1%) nanoparticles having a cubic crystal structure. The properties were investigated at low temperatures using ...time-integrated and time-resolved luminescence spectroscopy under VUV photon excitation in the energy range of 5–45 eV. This spectral region covers both the Pr3+ 4f2→4f15d1 transitions and the intrinsic absorption of the host material. Due to the weak crystal field, only the intra-configurational Pr3+ 4f2→4f2 transitions were observed, resulting in photon cascade emissions. According to structural and morphological studies, the nanoparticles, with an average size of 21 ± 4 nm, were found to possess large amounts of defects, which are further confirmed through luminescence spectroscopy. The influence of non-radiative decay at the surface and energy transfer to the defects are responsible for the shortening of luminescence decay detected for the 1S0 transitions of Pr3+ ions and intrinsic UV cross-luminescence of host materials. We have discussed the specific energy transfer processes that populate various luminescence centers and evaluated BaLuF5:Pr3+(1%) nanoparticles for potential optical applications.
•“Investigated luminescence properties of hydrothermally synthesized BaLuF5+:Pr3+(1 %) nanoparticles under VUV excitation”.•“Photon cascade emission observed due to the 4f21S0 level being below the 4f15d1 states”.•“Structural and morphological studies reveal a significant amount of defects in nanoparticles”.•“Non-radiative decay at surfaces and energy transfer to defects shorten luminescence decay times”.•“Potential optical applications in fast timing due to ultrafast cross-luminescence and 1S0 transitions of Pr3+ ions”.
Cathodoluminescence yield of hot intraband luminescence (IBL) under ∼100 keV pulsed electron excitation was evaluated in several halide and oxide compounds. Its values lie in the range of ...5–35 ph/MeV, which is in accordance with the general assumptions on the mechanism of IBL. The expected inverse correlation between the IBL yield and highest phonon energies was found for binary compounds, therefore the IBL yield dependence on charge carrier thermalisation rate was experimentally confirmed. Consequently, CsI was found to have the highest IBL yield (33 ph/MeV) compared to other studied crystals due to its lowest phonon energy among them. The studied sample of pure CsI shows both cathodoluminescence and scintillation yields significantly higher than the value frequently cited earlier (2000 ph/MeV), pointing out that its intrinsic scintillation properties might be currently underestimated. CsI shows good coincidence time resolution (CTR) up to 110 ps FWHM in a TOF-PET-like geometry, which surpasses all the materials studied so far except the much more expensive scintillators from the lutetium-yttrium silicates family (CTR values up to 73 ps). Therefore, CsI can be considered as a promising material for low-cost TOF-PET machines. For complex (ternary) compounds the phonon energies and IBL yield are not noticeably correlated, and the highest spectral yield (at 2.5 eV) among the studied compounds is shown by Na2Mo2O7.
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