Air Luminescence Research Articles

Effect of nitrogen/oxygen ratios on surface charge distributions generated by repetitive surface dielectric barrier discharges

Studies on the dielectric surface parameters and dielectric barrier discharges (DBD) characteristics considering the influence of gases in DBD on the surface charge distribution are scarce. Thus, to overcome this research gap, this study measured the potential distributions of AC-driven surface DBD in oxygen (O2), synthetic air and nitrogen (N2) as background gases using the Pockels effect. The results showed that the patterns of the filamentary discharges generated during the positive voltage polarity phase differed depending on the O2 ratio. In addition, the electrostatic repulsion forces between the residual charge and the newly created filament were analysed from the measured potential distribution and the greatest effect was observed in air, rather than in N2 and O2. The potential distribution was transformed into a charge density distribution and compared with the discharge luminescence in air and N2. The results showed that the shape of the filament tip differed between the charge density and discharge luminescence only in the case of air, which was attributed to the effect of attachment reactions on the formation of residual charge. The measurements showed that in a surface discharge, similar to the case in a volume discharge, the photoionisation and ionisation coefficients significantly affected the geometrical properties of the discharges.

Luminescent Porphyrinic Metal–Organic Frameworks for Oxygen Sensing: Correlation of Nanostructure and Sensitivity

Oxygen sensing capabilities of a series of luminescent zirconium-based porphyrinic metal–organic frameworks (MOFs) (PCN-222, PCN-223, and PCN-224) have been investigated. Design of experiments allowed identification of the most sensitive material, a PCN-224 MOF. In this material, luminescence in air is quenched by up to 7.3-fold with a bimolecular quenching constant kq of 56,000 Pa–1 s–1, which is significantly above the previously reported benchmark material of the same MOF type (kq of 34,000 Pa–1 s–1). The oxygen sensitivity increases in the order PCN-222 < PCN-223 < PCN-224 with effective Stern–Volmer (SV) constants in the range of 0.13 kPa–1 for PCN-222, 0.18 kPa–1 for PCN-223 and up to 0.45 kPa–1 for PCN-224-type materials. This effect is attributed to the increase in the porphyrin–porphyrin separation in these nanostructured materials that results in the increase in the fluorescence decay time and thus the probability of the quenching event. Defects in the nanostructure also are important and explain variations in the sensitivity within the MOFs of the same type. Among the investigated materials, those belonging to the PCN-223 type were found to be the most robust in terms of oxygen sensing capabilities with only little variation in the SV constants. The analogues of the PCN MOFs that utilize a Pt(II) porphyrin as a building block were also prepared. It is shown that the same synthetic protocols established for the metal-free systems can be used for the metal complex. Analogous to the MOFs based on the metal-free porphyrin, the oxygen sensitivity increases from Pt(II)PCN-222 (KSV 30 kPa–1) via Pt(II)PCN-223 (KSV 40 kPa–1) to Pt(II)PCN-224 (KSV up to 87 kPa–1).

Novel optical technologies for emergency preparedness and response: Mapping contaminations with alpha-emitting radionuclides

Radiological emergencies involving an accidental or deliberate dispersion of alpha-emitting radionuclides in the environment can cause significant damage to humans and societies in general. Currently, there is a metrology gap in managing such emergencies due to the lack of detectors that can measure alpha particles at distances greater than their range in air: most conventional alpha detectors are only effective when placed just a few centimeters above the contaminated area. This paper presents the development and testing of lens based optical detection systems that utilize alpha particle-induced ultraviolet (UV) luminescence of air, known as alpha radioluminescence. Telescopes based on fused silica and Poly(methyl 2-methylpropenoate) (PMMA) Fresnel lenses were investigated for their usability in facilitating emergency management related to alpha-emitting radionuclides. Careful matching of the diameter and focal length of the receiving optics, the response of the photocathode, and the passband of the filter allows detection sensitivities as high as 34s−1MBq−1 at 2m source-to-detector distance and background count rate of about 3s−1 in the UV-C spectral region, and suppression of daylight background count rate down to 16s−1. By flushing the source with nitrogen (N2) containing trace amounts of nitric oxide (NO), a groundbreaking sensitivity of 1.3×105s−1MBq−1 has been achieved, allowing detection limits as low as 100Bq with room lighting on, and 70Bq in a dark environment. In the UV-A spectral region, a detection limit of 4kBq could be achieved in a dark environment. These optical detection systems are aimed to facilitate a rapid, coordinated, and effective response in emergency situations involving the release of alpha-emitting radionuclides by mounting them on a tripod or an unmanned aerial device (UAV).

Luminescent studies of bisphenol A solutions under the action of the electron beam

The results of measuring the luminescence of ambient air and solutions of an organic compound during their irradiation with a high-current pulsed electron beam with an average energy of Ee=170 keV and a duration of 2 ns, generated by the RADAN-303 accelerator, are presented. It is shown that, under such exposure, the transformation of dissolved bisphenol A occurs, which is accompanied by an increase in the absorption coefficient of the solution in the wavelength range of more than 300 nm and, as a consequence, a decrease in the intensity of air luminescence bands with an increase in the number of irradiation pulses. The results showed the degradation of the BPA solution to complete decomposition under the action of an electron beam treatment. Keywords: electron beam, air, solutions of organic compounds, luminescence, absorption, decomposition.

Люминесценцентные исследования растворов бисфенола A под действием электронного пучка

The results of measuring the luminescence of ambient air and solutions of an organic compound during their irradiation with a high-current pulsed electron beam with an average energy of Ee=170 keV and a duration of 2 ns, generated by the RADAN-303 accelerator, are presented. It is shown that, under such exposure, the transformation of dissolved bisphenol A occurs, which is accompanied by an increase in the absorption coefficient of the solution in the wavelength range of more than 300 nm and, as a consequence, a decrease in the intensity of air luminescence bands with an increase in the number of irradiation pulses. The results showed the degradation of the BPA solution to complete decomposition under the action of an electron beam treatment.

Organic long-persistent luminescence stimulated by visible light in p-type systems based on organic photoredox catalyst dopants.

Organic long-persistent-luminescent (OLPL) materials demonstrating hour-long photoluminescence have practical advantages in applications owing to their flexible design and easy processability. However, the energy absorbed in these materials is typically stored in an intermediate charge-separated state that is unstable when exposed to oxygen, thus preventing persistent luminescence in air unless oxygen penetration is suppressed through crystallization. Moreover, OLPL materials usually require ultraviolet excitation. Here we overcome such limitations and demonstrate amorphous OLPL systems that can be excited by radiation up to 600 nm and exhibit persistent luminescence in air. By adding cationic photoredox catalysts as electron-accepting dopants in a neutral electron-donor host, stable charge-separated states are generated by hole diffusion in these blends. Furthermore, the addition of hole-trapping molecules extends the photoluminescence lifetime. By using a p-type host less reactive to oxygen and tuning the donor-acceptor energy gap, our amorphous blends exhibit persistent luminescence stimulated by visible light even in air, expanding the applicability of OLPL materials.

Small molecule-doped organic crystals towards long-persistent luminescence in water and air

A doped-crystalline material based on two organic small molecules exhibits visible long-persistent luminescence performance in aqueous solution or in air.

Standoff UV-C imaging of alpha particle emitters

Alpha particles are proven to be very useful in many areas of medicine, technology and science. Yet, they represent the biggest risk to soft biological tissues compared to all nuclear decay products when ingested or inhaled, implying thus stringent radiation protection measures in the management and monitoring of samples that emit them. In this paper we present a standoff optical imaging approach that enables sensing of a radiological threat items at facilities where alpha-emitting material is manufactured, handled, used and stored, at safe distances without putting personnel at risk or contaminating equipment. The optical imaging of alpha-emitting samples is based on the radiation induced air luminescence (radioluminescence) in the UV-C (solar-blind) spectral region which enables detection of alpha particles even under bright light conditions. We show that by adding trace amounts of nitric oxide into the nitrogen atmosphere surrounding the sample, alpha sources with specific activities as low as 1.5 Bq/cm2 can be remotely imaged. This work provides a proof-of-concept implementation of a novel imaging approach that not only enhances capabilities of a state to take actions which effectively mitigate consequences of an radiological emergency for the society, health, environment and economy, but also benefits nuclear industry in decommissioning efforts.

Highly Efficient Organic Afterglow from a 2D Layered Lead-Free Metal Halide in Both Crystals and Thin Films under an Air Atmosphere.

Organic afterglow materials (OAMs) with a lifetime longer than 0.1 s have recently received much attention for their fascinating properties meeting the critical requirements of applications in newly emerged technologies. However, the development of OAMs lags behind for their low luminescence efficiency. Usually, enhancing the phosphorescence efficiency of organic materials causes a short lifetime. Here, we report two kinds of OAMs, two-dimensional (2D) layered organic-inorganic hybrid zinc bromides (PEZB-NTA and PEZB-BPA), obtained in an environmentally friendly ethanol solvent by a low-temperature solution method. They display highly efficient and persistent luminescence in air in both crystals and thin films with phosphorescence quantum yields up to 42% in crystals and 27% in films. For OAMs, the two quantum yields are the highest values ever reported for crystals and films. Due to the excellent crystalline and film-forming ability, PEZB-NTA and PEZB-BPA in ethanol can be used as inks to construct patterns on various rigid and flexible substrates, including paper, iron, plastic, marble, tin foil, and cloth. Consequently, the novel OAMs show great application prospects in the fields of anti-counterfeiting and information storage because of their economic synthesis, solution processing, and easy operation.

Intense radioluminescence of NO/N2-mixture in solar blind spectral region.

Luminescence in air induced by alpha particle emitters can be used to optically detect radioactive contamination from distances that surpass the range of the alpha radiation itself. Alpha particles excite nitrogen molecules in air and the relaxation creates a faint light emission. When the composition of the gases surrounding the alpha particle emitter is altered then the luminescence spectrum changes. In this work, we report the creation of an intense light emission in the wavelength regime below 300 nm originating from alpha particle excited nitric oxide (NO). The light yield has been investigated as a function of the NO concentration in an N2 atmosphere. Unlike the emission from molecular nitrogen, NO emits at wavelengths shorter than 300 nm, where solar background and artificial lighting are negligible, thus enabling optical detection of alpha radiation even under bright lighting conditions. We show that the radioactively induced NO emission reaches its maximum intensity at a concentration of 50 ppm of NO diluted in N2. At this concentration, the strongest emission line of NO is about 25 times more intense than the most intense line of N2 radioluminescence. Lastly, we discuss potential applications and limitations of the technique.

Imaging of Ra-223 solution using an optical method

Ra-223 has recently been introduced in alpha-targeting radionuclide therapy. According to the decay scheme of Ra-223, beta particles with higher energy than the Cerenkov-light threshold are emitted. In addition, there are reports that the alpha particles themselves emit luminescence in water and air. However, measured optical imaging results from Ra-223 have not yet been reported. Therefore, we conducted optical imaging of an Ra-223 solution and compared it with that of an F-18 solution. Ra-223 and F-18 solutions contained in transparent glass vials were imaged using a high-sensitivity CCD camera. We could obtain an image of the Ra-223 solution with radioactivity of 0.72 MBq in an acquisition time of less than 10 s. At the same level of radioactivity, the intensity of the optical signal in the solution part of the vial of Ra-223 was 21 times higher than that of F-18. Furthermore, in the air part of the vials, Ra-223 had higher luminescence than that of F-18. The light spectra for Ra-223 and F-18 solutions were similar, but those in the vials' air parts were different. The optical signals in the solution part of both Ra-223 and F-18 are attributed to Cerenkov light, while that in the air part of Ra-223 is attributed to the scintillation of N2 gas in air. No obvious luminescence of water by the alpha particles was observed. We concluded that optical imaging of the Ra-223 solution was possible, and this solution's light intensity was much higher than that of the F-18 solution and thus easier to detect. Therefore, Ra-223 is a promising radionuclide for optical imaging in distribution measurements.

Luminescence imaging of biological subjects during X-ray irradiations lower energy than Cerenkov-light threshold

It is commonly thought that UV or visible-light luminescence imaging of biological subjects during X-ray irradiation at the energy below 120 keV is impossible because the secondary electrons produced in this energy range do not emit Cerenkov light. Contrary to this consensus, we found UV or visible-light luminescence imaging of the subjects were possible with X-ray irradiations of this energy range. We placed one of the biological subjects in a black box; visible-light luminescence images were measured with a high-sensitivity, cooled charge coupled device (CCD) camera during X-ray irradiation at energy below 120 keV. We also conducted the imaging of air without subjects during irradiation of the same X-ray. The biological subjects emitted visible-light luminescence, and the imaging was possible with the irradiation of the X-ray below 120 keV. The luminescence images were observed in only the X-ray irradiated areas. Also air luminescence images could be obtained and the intensity of the luminescence measured from the images was proportionally increased with the exposure dose. UV or visible-light luminescence imaging of biological subjects was possible during X-ray irradiations lower energy than the Cerenkov-light threshold. The phenomenon was different from general X-ray fluorescence because wavelength of the luminescence is UV or visible-light. The luminescence imaging method is promising for estimating the irradiated area with X-ray, which could be used for interventional radiology (IVR). Also air luminescence imaging would be applied to the exposure dose distribution measurements for X-ray of diagnostic X-ray systems.

The remote methods for radwaste and SNF control

With the examples of developments carried out in the Kurchatov Institute and by the world leaders in the field the presentation considers the devices and methods to obtain remotely information on the distribution of radioactivity in radwaste and SNF. It describes the different types of light portable gamma cameras. The application of scanning spectrometric systems is considers also. The methods of recording UV radiation for detection of alpha contamination with the luminescence of air are presented. We discuss the scope and tasks that can be solved using remote and non-destructive methods.

Synthesis of cytocompatible luminescent titania/fluorescein hybrid nanoparticles.

Luminescent titania-fluorescein (FS) hybrid nanoparticles (NPs) were successfully synthesized by a sol-gel reaction of titanium alkoxide in the presence of octadecylamine using a fluidic reactor with a Y-type channel. The molar ratio of FS/Ti ratio was varied in the range from 1/1000 to 1/100 in order to obtain the hybrid NPs with the different luminescent behavior. The shape of the NPs is spherical and their sizes are 400 nm which is almost the same irrespective of the FS content, suggesting the different FS molecular states in one NP. We also demonstrated that the hybrid NPs exhibited a characteristic luminescence; the NPs with the higher and lower FS contents exhibited an enhanced luminescence in PBS and air, respectively, indicating that the FS states responded to the molecular environment. Through cytocompatible experiments using the NPs, it turned out that they had a high compatibility for fibroblasts. Therefore, the preparation of a series of the luminescent NPs with a tunable luminescence property was achieved. The results will lead to a guideline to determine a proper combination between material composition and an environment where they are used, being useful for biomedical applications.

Possibilities of optical imaging of the (99m)Tc-based radiopharmaceuticals.

In vivo optical imaging is widely used in preclinical studies. Recently, the application of optical imaging systems for preclinical visualization of gamma-emitting isotopes has become of interest since the evaluation of various organs relies on (99m)Tc-based radiopharmaceuticals (RPs). In vitro radioluminescence of (99m)Tc-based RPs, including pertechnetate, albumin macroaggregates, dimercaptosuccinic acid, phytate colloid, and ethylenediamine tetramethylene phosphonic acid, was studied with IVIS Spectrum CT™ optical imaging system. The distribution of phytate colloid was also studied in vivo with and without scintillating materials and the results were compared with those obtained with a conventional scintigraphy. The visible light emission appeared to be due to the radioluminescence of water and luminophores contained in RPs rather than from Cherenkov radiation. Weak air luminescence affected the background. The radioluminescence of fluids induced by (99m)Tc-based tracers could be detected using charge-coupled device optical imaging systems. The radioluminescence intensity and its spectral distribution depend on the surrounding fluid and known luminophores present. Thus, in some cases the in vivo optical imaging is possible but the use of scintillator, e.g., borosilicate glass or bismuth germanate, is preferred.

Surface photochemistry: p-Hydroxystilbazol within nanochannels of Na + and H + ZSM-5 zeolites

This work reports the surface photochemistry study of p-hydroxystilbazol adsorbed within nanochannels of MFI zeolites, namely in a series of NaZSM-5 and HZSM-5 zeolites where the surface acidity of the host was varied systematically. Laser-induced room temperature luminescence of air equilibrated solid powdered samples of p-hydroxystilbazol adsorbed onto the two sets of zeolites, revealed the existence of multiple emissions of p-hydroxystilbazol, namely as a broad band centered at about 470 nm all cases where the host surface was highly acidic, while in other cases emissions with maxima at about 410, 530 and 660 nm were also detected. The decay times of the p-hydroxystilbazol emission vary greatly going from solution to entrapment within the nanochannels of the ZSM-5 zeolites and roughly increase by an order of magnitude upon inclusion. A lifetime distribution analysis has shown that the longest lifetime for the p-hydroxystilbazol fluorescence emission exists in the case where the 530 nm type emission was detected, i.e. whenever the hydrophobic character of the host increases. p-Hydroxystilbazol entrapped in the more acidic zeolites emits mainly in the protonated form. However, p-hydroxystilbazol may emit from neutral, protonated and zwitterionic forms in the case of the more hydrophobic zeolites. High energy (266 nm excitation and high fluences of the excitation laser (30 mJ per pulse) enabled us to evidence a 660 nm emissive form assigned to the quinoid derived from the zwitterionic form of p-hydroxystilbazol. Delayed fluorescence of p-hydroxystilbazol was also detected for the HZSM-5 and NaZSM-5 entrapment both at room temperature.

The effect of charge density in tropospheric thunderclouds on production of sprites and terrestrial gamma ray flashes

[1] We demonstrate that positive cloud-to-ground lightning flash (most often responsible for sprites) from stratiform tropospheric thundercloud leading to charge moment change iΔMq high above the sprite “threshold” 500 C km really triggers the high-altitude discharge exciting the air luminescence at sprite altitudes with brightness close to the observed brightness. Specifically, we present results for three configurations with the same charges Qcl = 200 C located at altitudes 6 and 8 km (iΔMq = 1200 C km for +Qcl at 6 km and iΔMq = 1600 C km for +Qcl at 8 km) differing by a magnitude of charge density, namely, σ = 1.86, 2.88, and 4.41 C km−2. All three configurations produce luminescence at sprite altitudes with brightness close to the observed one. In addition, the configuration with σ = 2.88 C km−2 produces observable γ emission, which can be detected in near space as terrestrial gamma-ray flashes (TGFs). The configuration with σ = 4.41 C km−2, provided it really could develop, would produce a blue fluorescence directly near the cloud top and extremely intensive γ emission not observed till now. The results obtained for smaller σ prove that too small-charge density in stratiform thunderclouds and consequently too weak electric field above them could account for the lack of Reuven Ramaty High Energy Solar Spectroscopic Imager TGFs correlated with large-charge moment change.

An air scintillator

A method for bremsstrahlung dosimetry by air luminescence at high-power pulsed electron accelerators is considered. Light emitted in an air scintillator is focused by the lens at the tip of a quartz optical fiber and transmitted to the photocathode of a photomultiplier tube. The sensitivity of the measuring channel is determined using a standard ribbon lamp. Bremsstrahlung pulses producing an exposure of 0.18 C/kg at the bremsstrahlung beam axis in a ∼20-ns time interval are detected at the ЛИУ-30 electron accelerator with a high accuracy. This exposure corresponds to an absorbed dose rate, integrated over the beam diameter, of 7.5 × 107 Gy m/s.

Surface photochemistry: Benzophenone within nanochannels of H + and Na + ZSM-5 zeolites

This work reports a surface photochemistry study of benzophenone within nanochannels of MFI zeolites, in this case a series of H + and Na + ZSM-5 zeolites where the acidity of the host is varied systematically. Laser-induced room temperature luminescence of air equilibrated or argon purged solid powdered samples of benzophenone adsorbed onto the two sets of zeolites, which we will name HZSM-5 and NaZSM-5 zeolites, revealed the existence of three different benzophenone emissions. In the nanosecond time range a broad band centred at about 430 nm was detected and its origin was hydrogen bonded benzophenone. A second broad band peaking at about 470 nm and in the millisecond time range was also detected, which was the emission of the protonated benzophenone. Finally a vibrationally structured emission existed (448 nm), the normal room temperature phosphorescence emission of benzophenone. Triplet–triplet transient absorption of benzophenone was obtained for all zeolites under study, and clear evidence for the formation of hydroxybenzophenone radicals was obtained for the NaZSM-5 series (only Lewis acid sites). The more acidic the internal surface the more radical was detected. Other products resulting from α-cleavage of benzophenone were also identified. When the host was HZSM-5 (Brönsted and Lewis acid sites) benzophenone seemed to be less reactive, and no ketyl radicals from benzophenone were detected. All these findings clearly show that benzophenone is an excellent probe which is able to provide important information regarding the internal surfaces of MFI zeolites, namely the different photocatalytic activity of the different active sites of these zeolites. The present study is paradigmatic in what regards the host influence on the photochemistry of the guest.

Dosimetry based on air luminescence

A method for detecting the absorbed dose rate by measuring the glow of air excited by ionizing radiations is described. Light is transmitted through optical fibers to a photomultiplier tube. The threshold absorbed dose rate is calculated as a function of the aperture of the detection system and the size of the light-emitting air region. The results of calculations and experiments with a nanosecond-duration beam of electrons with an energy of up to 300 keV have shown that air luminescence with the transmission of light through an optical fiber can be used for diagnostics of ionizing radiations with a resolution of no worse than 2 ns at an absorbed dose rate of >1 GGy/s.