Photostimulated Luminescence Intensity Research Articles

Scintillation and photostimulated-luminescence properties of Yb-doped SrCl2 transparent ceramics

We have investigated the photoluminescence (PL), scintillation, and photostimulated-luminescence (PSL) properties of Yb-doped SrCl2 transparent ceramics. The samples were prepared using the spark plasma sintering method. Emission peaks in the PL, scintillation, and PSL spectra were observed at 380 and 405 nm due to the spin-allowed and spin-forbidden 4f135d1–4f14 transitions of Yb2+, respectively. The PL quantum yield (QY) value elevated with increasing Yb concentration at 0.05%–1.0%, and the 1.0% Yb-doped SrCl2 transparent ceramic indicated the highest QY value. This concentration dependence was similar for the scintillation and PSL intensities.

Design and Characterization of Eu2+/Ln3+ Co-doped SrAl2Si2O8 Photostimulated Phosphors for Optical Information Storages

In this paper, a series of Sr0.96Al2Si2O8 phosphors doped with 0.02Eu2+ and 0.02Re3+ (where Re = Tm, Dy, Er, Nd, Sm, La, Ho) were synthesized using the high-temperature solid-phase method at 1350 °C for 4 hours. The samples underwent characterization for structural and phase analysis using XRD-6000. Fluorescence and photostimulated properties were evaluated with F-4600. The pyroluminescence curve indicates a trap depth of 0.6-0.8 eV for Sr0.96Al2Si2O8: 0.02Eu2+, 0.02Re3+ (where Re = Dy, Er, Sm, La, Ho), making it suitable for prolonged afterglow luminescence. In comparison with deep trap material Sr0.96Al2Si2O8: 0.02Eu2+, 0.02Nd3+, the generated traps approach or exceed 1 eV, suggesting its potential for use as a light excitation and optical storage material. Additionally, the correlation between sample TL and PSL was examined, confirming that the augmentation of initial photostimulated luminescence intensity is closely associated with the generation of new traps. Furthermore, considering the effect of different trivalent lanthanide rare earth ion doping on trap depth from a trap regulation perspective offers a potential avenue for elucidating the nuanced processes underlying photostimulated luminescence.

Long‐Lived UV‐Rewritable Luminescent Memory in a Fluoroperovskite Crystal

AbstractPhotostimulated luminescence phosphors are promising candidates for next‐generation optical data storage devices. Herein, optically‐reversible luminescence modulation is demonstrated using UV wavelengths in the fluoroperovskite RbCdF3:Mn, where the modulation is mediated by photostimulated luminescence processes. UV‐C stimulation enhances the luminescence from Mn2+ centers and simultaneously fills electron traps. This charging process occurs via electron transfer from Mn2+ ions to fluorine vacancies, yielding Mn3+ ions and F‐centers, and is mediated by conduction band transport. UV‐A stimulation restores the material to the initial state. This discharging process occurs via electron transfer from F‐centers to Mn3+ ions and is similarly mediated by conduction band transport. Moreover, the discharging process manifests Mn2+ photostimulated luminescence. The primary trap state has activation energies in the range 1.46 to 1.73 eV and has room temperature lifetimes exceeding 40 000 years. A kinetic model is presented and evaluated that accurately describes the charge transport and luminescence properties of the material. Thus, a material is presented via which ultra‐long term, multi‐level luminescent data storage can be realized, and a model via which precise control over the luminescence modulation and photostimulated luminescence intensities can be achieved.

Luminescence characteristics and X-ray-induced defects in BaFBr:Eu2+ storage phosphor.

Three different approaches used to synthesize a sensitive BaFBr:Eu2+ X-ray storage photostimulated luminescence (PSL) phosphor at 850°C for 1 h in a reducing atmosphere are reported. The effects of F/Br and Eu concentration on photoluminescence (PL) and PSL sensitivities synthesized by the three approaches were compared. In the first recipe, BaFBr:Eu2+ prepared using a BaF2 , BaBr2 and EuF3 mixture using solid-state diffusion (Recipe I), even in a reducing atmosphere, yielded a low PL and PSL intensity due to oxygen contamination that acted as competing hole traps. When BaFBr:Eu2+ was prepared using ammonium bromide and ammonium fluoride by two different recipes (Recipes II and III), oxygen contamination was eliminated, resulting in enhanced PSL efficiency. The proposed PSL process in BaFBr:Eu2+ was consistent with the experimental results. Increased F/Br molar ratios would incorporate fluorine ion interstitials that act as hole traps accompanied by bromine ion vacancies that act as electron traps. Although two types of F centres, F(Br- ) and F(F- ) are possible, F(Br- ) centres formed during X-irradiation are only vital for the PSL process. Structural, morphology, and thermoluminescence (TL) properties of the samples were also examined using XRD, field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDAX), and TL studies.

Radionuclide distribution in irradiated BWR tie plate

The contents and distribution of radionuclides in activated metallic wastes are major concerns while designing a leaching model in a safety case. This study investigated 60Co as a typical activation product in the lower tie plate (i.e., stainless steel endpiece of BWR fuel assembly) irradiated for 35.0 GWd/tHM burnup, using the imaging plate (IP) method. The activation calculations coupled with the Monte Carlo burnup and neutron transport calculation code (MCNP-BURN2) were also performed based on the burnup and operation conditions. The Co impurity content in the irradiated tie plate was obtained and used as an input to MCNP-BURN2. The IP method results showed that the intensity of photostimulated luminescence decreased with increasing distance from the top (near fuels) to bottom. This trend was consistent with that exhibited by MCNP-BURN2.Therefore, the simulations allowed us to model the three-dimensional radionuclide distribution within the tie plate.Graphical abstractDistribution of 60Co in the irradiated lower tie plate. Left shows the vertical distribution comparing the measurements and the MCNP-BURN2 results. Right represents the 3D model of 60Co distribution in the lower tie plate.

The role of boric acid in optical information storage properties in Eu doped BaSi2O5

Optical information storage technology is emerging, therefore materials suitable for optical write-in and read-out are in demand. In this study the influence of boric acid addition during synthesis on the optical information storage properties of BaSi2O5:Eu material, that has been recently offered as a perspective material for this application. A thorough investigation is carried out to establish the relationship between boric acid addition, phase composition and photostimulated luminescence performance of the samples. The present work demonstrates the influence of the boric acid addition on the trapping center distribution in the material, thus leading to the improvement of photostimulated luminescence intensity. This can lead to the optimization of BaSi2O5:Eu material for optical information storage.

Photostimulated luminescence in Tl-doped NH4Br translucent ceramics synthesized by SPS

We have prepared Tl-doped NH4Br translucent ceramics by spark-plasma sintering and evaluated their photoluminescence (PL) and photostimulated luminescence (PSL) properties. In PL, two luminescence peaks appeared due to 3P1 → 1S0 transitions of Tl+ and off-center self-trapped excitons (STEs) localized around Tl+ in all the samples. In PSL, the 0.1%–3% Tl-doped samples showed luminescence related to the off-center STEs around 500 nm by stimulation light at 630 nm. When correlations between exposure dose and PSL intensity were examined, we confirmed that the 0.1%–1% and 3% Tl-doped samples showed linear responses over ranges of 10–10 000 and 1–10 000 mGy, respectively.

Using a Tritium Imaging Plate Technique to Measure the Hydrogen Solubility and Diffusivity of Zr-Doped BaInO2.5

A tritium imaging plate technique (TIPT) was used to measure the hydrogen solubility and diffusivity of a proton-conducting material, Zr-doped BaInO2.5. After being exposured to tritiated water vapor, the specimen was cut into halves and photo-stimulated luminescence (PSL) images of the cross-section of the cut specimen were obtained. Based on the PSL distribution profiles and intensities, hydrogen diffusivity and solubility in the specimens were determined. The hydrogen solubility and diffusivity in Zr-doped BaInO2.5 clearly depended on the content of Zr. This characteristic of the Zr content is in agreement with the Zr-content dependency of its proton conductivity, which was measured by an alternating current (AC) impedance method.

Tritium distributions on tungsten and carbon tiles used in the JET divertor

Tritium distributions on the W-coated divertor tiles used with Be wall in JET 2011–2012 ITER-like wall (JET-ILW) campaign were measured using an imaging plate (IP) technique. The high intensity of photo-stimulated luminescence (PSL) from IP was observed at the regions covered by deposited Be layers. However, the PSL intensity was not simply proportional to the thickness of the deposited Be layers; the shadowed region of Tile 4 showed the highest PSL intensity though the thickness of deposited Be layer on this region was smaller than that on Tile 0 and the apron of Tile 1 by an order of magnitude. These observations indicated the influence of impurities such as oxygen on tritium retention in the deposited Be layers. The C tiles used in the 2007–2009 JET carbon wall (JET-C) campaign were also examined. The high PSL intensity was observed for the regions covered with deposited C layers in this case. The area of tile surfaces covered by the deposited tritium-rich layers on the W-coated-tiles used in the JET-ILW campaign was significantly smaller than that on the C tiles used in the JET-C campaign.

Long persistent and photostimulated luminescence properties of Sr2Al2SiO7:Eu2+/Tm3+ phosphors

AbstractA series of Sr2Al2SiO7 phosphors with fixed Eu2+ concentration and various Tm3+ concentrations were synthesized via a high temperature solid state reaction. The structure and luminescence properties of the samples were characterized by X-ray powder diffraction (XRD), photoluminescence (PL) spectra, decay curves, thermoluminescence (TL) glow curves as well as the photostimulated luminescence (PSL) spectra. Sr2Al2SiO7:Eu2+, Tm3+ phosphors exhibited strong green phosphorescence and photostimulated luminescence originating from 4f65d1–4f7 transition of Eu2+ after ultraviolet light stimulation. Deep traps were found by analyses on the phosphorescence decays and thermoluminescence spectra. It was also found that with increasing the time interval between UV excitation turn-off and stimulation turn-on, the photostimulated luminescence became stronger. This phenomenon resulted from the fact that the captured electron was retrapped by the deep traps. Compared with the Tm3+-free sample, it was found that the PSL intensity was strongly enhanced in Tm3+ codoping samples.

A new strontium-aluminate-based long-persistence photostimulated phosphor

We have identified general aspects of the composition dependences of the photostimulated luminescence intensity and decay time in the range 475–525 nm for Sr3.91–x Eu0.04Tm0.05Er x Al13.36B0.64O25 solid solutions. The results have been used to develop a new blue-green photostimulated phosphor. After laser stimulation at 0.810 and 0.940 µm, it offers a longer afterglow duration in comparison with the FV-490M and FV-490DM industrial phosphors.

Thermal neutron imaging with CsBr storage phosphors

The storage phosphor material CsBr:Eu2+ has been investigated for use in thermal neutron imaging. CsBr:Eu2+ imaging plates were prepared in a polycrystalline form by cold pressing starting powders. These as-prepared materials show only small photostimulated luminescence intensity under thermal neutron irradiation, but the luminescence intensity can be increased by incorporating separate neutron converters, in the form of lithium, boron or gadolinium containing compounds. An imaging plate containing 5% 10B2O3 as a neutron converter has 50% the photostimulated luminescence intensity of a commercial Fuji neutron imaging plate. Thermal neutron imaging was shown to be possible with the CsBr:Eu2+-based imaging plates, and the differences in thermal neutron and X-ray images were clearly observed.

Photostimulated luminescence properties of BaFBr:Eu under ion irradiation

The photostimulated luminescence (PSL) properties of the phosphor BaFBr:Eu after ion beam irradiation was analyzed; in particular, the PSL intensity dependent on ion fluence. The PSL intensity increased linearly with the ion fluence up to 1012 ions/cm2, and subsequently decreased gradually. The ion fluence dependence was observed to be similar among samples containing different F centers or different Eu concentrations. The fluence dependence was quantitatively analyzed based on a trapping model, in which competition between the trapping processes to storage centers and radiation defects is assumed; the model explained the experimental data quantitatively. The results indicate that radiation defects influence the PSL properties via the trapping of photostimulated electrons.

Temperature dependence of the photostimulated luminescence in KCl:Eu2+

The goal of this work is to understand the physical mechanism behind the signal stabilization process in KCl:Eu2+, a storage phosphor material that has generated renewed interest due to its potential in radiation therapy dosimetry application. The temperature dependency of the photostimulated luminescence (PSL) spectra and intensity vs. time post X-ray irradiation was measured. Commercial BaFBr:Eu2+ materials were included in this study for comparison. Unlike BaFBr:Eu2+, broadening of the F(Cl−) stimulation band and red-shift of the peak were observed for KCl:Eu2+ with increasing temperature. For irradiations at temperatures lower than 200K, PSL intensity of KCl:Eu2+ showed recuperation behavior in the first 2h post-irradiation and stayed almost constant with time thereafter. Moreover, spatially-correlated storage centers increased from 24% for irradiation at 50K to 31% at 195K and almost 100% at room temperature. The data suggest that certain types of charge storage-centers were mobile and contribute to the fast fading in PSL.

The role of activator concentration and precipitate formation on optical and dosimetric properties of KCl:Eu2+ storage phosphor detectors

The activator ion (Eu(2+) in KCl:Eu(2+)) plays an important role in the photostimulated luminescence (PSL) mechanism of storage phosphor radiation detectors. In order to design an accurate, effective, and robust detector, it is important to understand how the activator ion concentration affects the structure and, consequently, radiation detection properties of KCl:Eu(2+). Potassium chloride pellets were fabricated with various amounts of europium dopant (0.01-5.0 mol.% Eu(2+)). Clinical radiation doses were given with a 6 MV linear accelerator. Radiation doses larger than 100 Gy were given with a (137)Cs irradiator. Dose response curves, radiation hardness, and temporal signal stability were measured using a laboratory PSL readout system. The crystal structure of the material was studied using x ray diffraction and luminescence spectroscopy. The most intense PSL signal was from samples with 1.0 mol.% Eu. However, samples with concentrations higher than 0.05 mol.% Eu exhibited significant degradation in PSL intensity for cumulated doses larger than 3000 Gy. Structural and luminescence spectroscopy showed clear evidence of precipitate phases within the KCl lattice, especially for high activator concentrations. Analysis of PL emission spectra showed that interactions between Eu-Vc dipoles and Eu-Vc trimers could explain trends in PSL sensitivity and radiation hardness observations. The concentration of the activator ion (Eu(2+)) significantly affects radiation detection properties of the storage phosphor KCl:Eu(2+). An activator concentration between 0.01 and 0.05 mol.% Eu in KCl:Eu(2+) storage phosphor detectors is recommended for linear dose response, good PSL sensitivity, predictable temporal stability, and high reusability for megavoltage radiation detection.

Photostimulated luminescence of Sr3Al2O5Cl2:Eu2+, Tm3+ with a large energy storage capacity

Strong and long-lasting photostimulated luminescence (PSL) is observed and studied in Eu2+ and Tm3+ codoped Sr3Al2O5Cl2 under 980nm continuous stimulation after UV and blue light pre-irradiation. Compared to the Eu2+ singly doped one, the PSL intensity and energy storage capacity in the doubly doped material are enhanced by a factor of 400 and 91, respectively. The study indicates that codoping Tm3+ leads to a large increase of traps that enlarge energy storage capacity as three times as the commercial phosphor SrS:Eu2+, Sm3+.

SU-E-T-46: Optimization of Activator Concentration in KCl:Eu2+ Storage Phosphors for Megavoltage Dosimetry

Purpose: Recent work has shown that the storage phosphor, KCl:Eu2+, has great potential to become the physical foundation of a reusable, highresolution planar dosimeter. The activator ion (Eu2+) plays an important role in storage phosphor performance. The effects of activator concentration on dosimetric properties must be understood to design a robust dosimeter with a linear dose response, high sensitivity, and is easily integrated into clinical application. In this work, we investigate the effects of adjusting the activator concentration in KCl:Eu2+ on dose response, sensitivity, and temporal stability. Methods: Six mm diameter, 1mm thick KCl:Eu2+ pellets were fabricated using a hydraulic press. Europium concentration was varied between 0.01–5.0 mole percent. Pellets were irradiated with a 6MV photon beam. Signal stability and dose response linearity were studied using a laboratory photostimulated luminescence (PSL) readout system. PSL emission and stimulation measurements were obtained at room temperature to determine if concentration‐induced effects occurred in the electronic structure. Results: The highest PSL intensity was achieved for samples with approximately 1 mole % europium. Significant degradation of PSL intensity was observed for samples with europium concentration greater than 1 mole %. PSL stimulation data showed that no additional storage centers were created with increased europium concentrations. Fading curve measurements showed a thermal treatment at 70 °C for 15 minutes was able to eliminate the fast fading component, regardless of concentration. Conclusions: Concentration quenching of CsBr:Eu2+ (commercially available computed radiography storage phosphor panel) occurs at much lower activator concentrations (∼0.05 mole % Eu2+), compared to KCl:Eu2+. The higher quenching concentration of KCl:Eu2+ may indicate that precipitate formation has an insignificant effect on PSL properties. Further, KCl:Eu2+ dosimeters can be manufactured with an activator concentration as low as 0.01 mole percent while maintaining a linear dose response and reasonable PSL sensitivity. This work was supported in part by NIH Grant No. R01CA148853.

A new photostimulated strontium-aluminate-based blue-green phosphor

We have proposed, experimentally demonstrated, and implemented a technique for producing a new photostimulated blue-green phosphor with increased photostimulated luminescence intensity via additional doping of the Sr4Al14O25:Eu,Tm phosphor with La3+. The photostimulated phosphor (FV-490M) has been commercialized and is used most widely in security and authentication applications, both as an individual phosphor and in combination with the photostimulated red phosphor SrS:Eu,Sm. When IR-stimulated, the combination phosphor exhibits a dynamic visual kinetic effect.

Damage and recovery processes for the luminescence of irradiated PEN films

The degradation and recovery of the optical emission characteristics of polyethylene naphthalate (PEN) films were studied during irradiation with MeV protons and UV photons. The photo-stimulated luminescence (PL) consisting of two major peaks decreased with the incident energy fluence, particularly for ion irradiation. At the beginning of irradiation, the rate of reduction of the PL intensity in the UV-irradiated film was comparable to that for ion irradiation, but the residual PL intensity in the UV-irradiated film was considerably larger at higher fluences. In addition, no change in the PL characteristics of the UV-irradiated film was observed after stopping the UV irradiation, indicating that the damage caused by the UV photons was permanent. However, the PL intensity from the ion irradiated film increased immediately when the film was exposed to air. The recovery of the luminescence centers in the ion-irradiated PEN film is attributed to ion-induced surface modification, which plays a role in the enhancement of the dissociation of water molecules and the diffusion process for constituent atoms.

Strongly enhancing photostimulated luminescence by doping Tm^3+ in Sr_3SiO_5: Eu^2+

We report a large enhancement of yellow photostimulated luminescence (PSL) by codoping Tm3+ in Sr3SiO5:Eu2+ upon infrared stimulation at 980 nm after pre-exposure in Ultraviolet light. The initial PSL intensity and light storage capacity are enhanced by a factor of 33 and 2, respectively, for Tm3+ concentration at 0.0004. The thermoluminescence spectra indicate that codoping Tm3+ generates a trap peaking at 385 K. The trap is much more sensitive to infrared light than the original one, so that the light storage period of the material is beyond tens of days with the minimum detectable infrared power density only 54 μW/cm2.