Europium Activator Research Articles

Evaluation of structural and spectroscopic results of tetragonal tungsten bronze MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors and comparison on the basis of Judd-Ofelt parameters

The crystal structure with different cationic sites and the superiority of allowing doping make TTB (tetragonal tungsten bronze) structures very interesting in terms of exhibiting different physical properties. The new spectroscopic and structural results of MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors were presented in the study. The incorporation of europium activator into the different cationic (Sr, Ba, Pb) tunnel structures of TTB crystal with TaO6 octahedral exhibited interesting structural and optical properties. The relationship between coordination number and CTB showed that the highly coordinated A and B sites of TTB crystal caused the CTB to shift to low energy or over 300 nm. The spectral properties of TTB-MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors were compared by determining the Judd-Ofelt (JO) intensity parameters from PL emission spectrum. The (decreasing trend of the Ω2 parameter and asymmetry ratio is SrTa2O6:Eu3+>BaTa2O6:Eu3+>PbTa2O6:Eu3+, and the Eu–O bonds of PbTa2O6:Eu3+ compared to other matrices indicated a more ionic character and a relatively high symmetry environment around Eu3+. The deviation of the experimental (βexp) and Judd-Ofelt (βcal) branching ratios for transition 5D0→7F2 are well below 10%, indicating good consistency. All the 5D0 decay profiles of the phosphors are exponential, and slightly reductions occurred in the luminescence lifetimes for SrTa2O6:Eu3+ and BaTa2O6:Eu3+. XRD results of Eu3+ doped SrTa2O6 series of the high-temperature TTB polymorph reported in this study confirmed the single-phase up to 10 mol%. SEM examinations revealed the change of size and shape of SrTa2O6 samples depending on Eu3+ concentration.

Role of pressure in stabilization of oxynitride phosphor synthesis

The possibilities of improving the crystallization and optical properties of strontium europium oxonitridosilicate phosphor powders were discussed. Two different routes of synthesis were presented: traditional solid-state reaction method and gas pressure synthesis. It was proven that altering the partial pressure during the process of synthesis enhances crystallization of a desired single, triclinic SrSi2O2N2 phase. XANES measurements confirmed complete reduction of the trivalent europium activator ions in all of the tested materials. The photoluminescent properties were determined by emission, excitation and decay times measurements. CIE1931 colour points and luminous efficacy were calculated as well. Thermal quenching studies in the range of 0–225 °C confirmed good thermal stability of the investigated powders combined with excellent quantum efficiency at room temperature.

Direct-white-emitting phosphor SrAl2O4: Eu2+/3+ with colour-tunable photoluminescence by variation of europium activator valence

Eu2+ and Eu3+ co-doped phosphors SrAl2O4: Eu were synthesized in air via conventional solid-state reaction. The composition and valance state of doped ions were examined and verified by x-ray photoelectron spectra (XPS), diffuse reflection spectra and photoluminescence (PL)/photoluminescence excitation (PLE) spectra. Under ultraviolet (UV) excitation, the broad emission peaking at 519 nm was assigned to the 4f65d–4f7 transition of Eu2+, and the series of narrow bands peaking at 619 nm originated from the 4f–4f transition of Eu3+ ions. The self-reduction processing of Eu3+ could be controlled by the variation of the Eu3+ doping concentration, annealing temperature and holding time, and the emission colour of synthesized phosphors could be regulated from yellowish green to white. The optimized doping concentration of Eu3+ was 1 mol%, and the annealing temperature and holding time were 1350 °C and 3 h, respectively. Accordingly, the phosphor emitted white light under the excitation of 365 nm with the CIE coordinates (0.3312, 0.3578) and colour temperature 5562 K.

Optical and luminescence spectroscopy of zinc gallate phosphors codoped with manganese and europium ions

ABSTRACTZinc gallate compounds codoped with manganese and europium ions were synthesized using the high-temperature solid-state reaction method. All samples were “characterized” by X-ray diffraction measurements, ultraviolet reflection spectroscopy, and photoluminescence spectroscopy. Structural investigations confirmed that incorporation of europium ions in zinc gallate host leads to distortion of the spinel unit cell and increase in lattice parameter. Manganese ions show the intense excitation in the region of band-to-band transitions. Zinc gallate spinel compounds codoped with manganese and europium ions exhibit emission in the whole spectral region. Among the manganese and europium activator emissions in the “green” and “red” spectral regions, the “blue” emission of spinel matrix was observed. Photoluminescence excitation spectra of europium ions and reflection spectra show similar results in the near-ultraviolet region of the spectra. The optimal concentration of europium activator was determined. Europium doping level leads to redistribution of excitation and emission intensities of zinc gallate codoped samples. The possible energy transfer mechanisms between matrix, manganese, and europium ions are discussed. Overlapping of excitation bands of all types of luminescence gives a possibility to obtain emission in the whole visible spectral range. The Commission Internationale de l’Eclairage chromaticity diagrams confirmed a possible application of the studied zinc gallate spinel compounds codoped with manganese and europium ions for the development of ultraviolet and near-ultraviolet phosphors with flexible emission color in the visible spectral range.

Effects of increasing size and changing europium activator concentration in KCaI3 scintillator crystals

KCaI3:Eu crystals have been identified as very promising for use in spectroscopic detector applications related to nuclear nonproliferation and domestic security efforts. Initial studies have shown for small crystals a few mm3 in size with 3% europium dopant concentration, a high light yield of >70,000ph/MeV and energy resolution of ≈3% at 662keV is attainable which is comparable with the highest performance scintillators discovered. In this work, single crystals of KCaI3 with a range of Eu2+ doping between 0 and 5at% substituting for Ca2+ were grown at 22mm diameter and their performance for gamma-ray spectroscopy studied. Comparisons among crystals approximately Ø22mm×22mm (8.4cm3 or ≈0.5in3) provide a more accurate understanding of how scintillation performance changes with Eu doping and increased crystal size. KCaI3 in the undoped form is shown to be a highly efficient intrinsic scintillator with a defect-related emission at 404nm which coexists with the Eu2+ 5d–4f emission in low dopant concentrations and is completely re-absorbed in more heavily doped crystals. For larger crystals, effects from self-absorption due to Eu activation become more evident by a near doubling of decay time for 0.5in3 crystals as the activator is increased from 0.5 to 5.0at% Eu. Comparisons of pulse-height spectra obtained for Ø22mm×22mm cylinders with varying Eu concentration suggests best performance is achieved using lower Eu additions closer to 0.5–1.0at%. Using a modified crystal packaging featuring an offset reflector geometry, 0.5in3 crystals of KCaI3:Eu can attain under 4% energy resolution at 662keV.

In situ diagnostics of the crystal-growth process through neutron imaging: application to scintillators.

Neutrons are known to be unique probes in situations where other types of radiation fail to penetrate samples and their surrounding structures. In this paper it is demonstrated how thermal and cold neutron radiography can provide time-resolved imaging of materials while they are being processed (e.g. while growing single crystals). The processing equipment, in this case furnaces, and the scintillator materials are opaque to conventional X-ray interrogation techniques. The distribution of the europium activator within a BaBrCl:Eu scintillator (0.1 and 0.5% nominal doping concentrations per mole) is studied in situ during the melting and solidification processes with a temporal resolution of 5-7 s. The strong tendency of the Eu dopant to segregate during the solidification process is observed in repeated cycles, with Eu forming clusters on multiple length scales (only for clusters larger than ∼50 µm, as limited by the resolution of the present experiments). It is also demonstrated that the dopant concentration can be quantified even for very low concentration levels (∼0.1%) in 10 mm thick samples. The interface between the solid and liquid phases can also be imaged, provided there is a sufficient change in concentration of one of the elements with a sufficient neutron attenuation cross section. Tomographic imaging of the BaBrCl:0.1%Eu sample reveals a strong correlation between crystal fractures and Eu-deficient clusters. The results of these experiments demonstrate the unique capabilities of neutron imaging for in situ diagnostics and the optimization of crystal-growth procedures.

SU‐E‐T‐476: Improving KCl:Eu2+ Dosimeter Sensitivity: The Role of Oxygen

Purpose:Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. The purpose of this work is to determine if increased signal could be realized in KCl:Eu2+ by incorporating oxygen in the material fabrication process.Methods:The prototype KCl:Eu2+ dosimeters have a physical makeup similar to thermoluminescent dosimeter chips. The photostimulation light source consists of either a He‐Ne laser or a UV enhanced Xe arc lamp with wavelength selection provided by a motorized monochromator. X‐ray diffraction is used to determine the phase composition of the dosimeters. Photoluminescence (PL) and photostimulated luminescence (PSL) emission spectra are obtained using a Nanolog Spectrofluoremeter.Results:Europium activator is completely incorporated into the KCl parent‐matrix without the formation of a noticeable secondary phase. Regardless of synthesis atmosphere, air or pure nitrogen, PSL amplitude shows a maximum at 1.0 mol % Eu. Depending on europium concentration, dosimeters fabricated in air exhibit stronger PSL by a factor of 2 to 4 compared to those made in N2. There is no change in PSL stimulation spectrum while noticeable shifts in both PL and PSL emission spectra are observed for air versus nitrogen. Almost all charge‐storage centers are spatially correlated, suggesting oxygen's stabilization role in the PSL process. KCl:Eu2+ made in oxygen‐rich air is capable of measuring a dose‐to‐water as low as 0.01 cGy from a 6MV photon beam with a signal‐to‐noise ratio greater than 6.Conclusions:Synthesis in a reduction atmosphere, for example, nitrogen, was thought to be mandatory in order to retain europium activator's divalent status to be PSL active. Fortunately, divalent europium can be well preserved in an oxygen‐rich atmosphere. More importantly, oxygen can enhance PSL by a factor of 2 to 4.HL is the founder of DoseImaging, LLC that is exclusively dedicated to commercializing this technology.

TH-C-19A-12: Two-Dimensional High Spatial-Resolution Dosimeter Using Europium Doped Potassium Chloride

Purpose: Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. This work reports our attempts to fabricate 2D KCl:Eu2+ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. Methods: A thin layer of KCl:Eu2+ was deposited on a substrate of borosilicate glass (e.g., laboratory slides) with a PVD system. For tape casting, a homogenous suspension containing storage phosphor particles, liquid vehicle and polymer binder was formed and subsequently cast by doctor-blade onto a polyethylene terephthalate substrate to form a 150 μm thick SPF. Results: X ray diffraction analysis showed that a 10 μm thick PVD sample was composed of highly crystalline KCl. No additional phases were observed, suggesting that the europium activator had completed been incorporated into the KCl matrix. Photostimulated luminescence and photoluminescence spectra suggested that F (Cl−) centers were the electron storage centers post x ray irradiation and that Eu2+ cations acted as luminescence centers in the photostimulation process. The 150 μm thick casted KCl:Eu2+ SPF showed sub-millimeter spatial resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu2+ and 80% low Z polymer binder exhibited almost no energy dependence in a 6 MV beam. KCl:Eu2+ pellet samples showed a large dynamic range from 0.01 cGy to 60 Gy dose-to-water, and saturated at approximately 500 Gy as a Result of its intrinsic high radiation hardness. Conclusions: This discovery research provides strong evidence that KCl:Eu2+ based SPF with associated readout apparatus could Result in a novel electronic film system that has all the desirable features associated with classic radiographic film and, importantly, water equivalence and the capability of permanent identification of each detector. This work was supported in part by NIH Grant No. R01CA148853. The authors would like to thank Paul Leblans (AGFA Healthcare, Belgium) for many helpful discussions on this topic.

Two-dimensional high spatial-resolution dosimeter using europium doped potassium chloride: a feasibility study

Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. This work reports the authors’ attempts to fabricate 2D KCl:Eu2+ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. X-ray diffraction analysis showed that a 10 µm thick PVD sample was composed of highly crystalline KCl. No additional phases were observed, suggesting that the europium activator had been completely incorporated into the KCl matrix. Photostimulated luminescence and photoluminescence spectra suggested that F (Cl−) centers were the electron storage centers post x-ray irradiation and that Eu2+ cations acted as luminescence centers in the photostimulation process. The 150 µm thick casted KCl:Eu2+ SPF showed sub-millimeter spatial-resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu2+ and 80% low Z polymer binder exhibited almost no energy-dependence in a 6 MV beam. KCl:Eu2+ pellet samples showed a large dynamic range from 0.01 cGy to 60 Gy dose-to-water, and saturated at approximately 500 Gy as a result of KCl's intrinsic high radiation hardness. Taken together, this work provides strong evidence that KCl:Eu2+-based SPF with associated readout apparatus could result in a novel electronic film system that has all the desirable features associated with classic radiographic film and, importantly, water equivalence and the capability of permanent identification of each detector.

Self-flux sodium based charge compensation in crystals of trivalent europium activated alkaline earth metal tungstate phosphors

Alkaline earth metal tungstate compounds activated by trivalent europium (Eu3+) are promising candidates for narrow spectral emission red phosphors suitable for high efficacy white light emitting diodes (LEDs). By growing crystals of these compounds from high temperature flux containing Na+ as the charge compensation element, enhancement in the emission intensity of A1 − xWO4: (A = Mg, Ca, Sr) has been demonstrated compared to phosphor powders synthesized using traditional solid state reaction. An optimum flux to solute ratio of 1.5:1 resulted in the largest size crystals using the sodium tungstate flux at growth temperature around 1300 °C. Amongst the three compounds studied, calcium tungstate exhibited the highest luminescence and magnesium tungstate the lowest. These results have been explained by the differences in the ionic radii of the cations compared to the europium activator and the energy bandgap of the host lattice. CaWO4:Eu3+/Na+ flux grown phosphor crystals exhibit almost five times higher emission intensity as compared to phosphor powders synthesized by solid-state reaction.

Luminescence studies of Eu3+ doped BaGd2O4 phosphor

The spectroscopic properties of BaGd2-xO4:Eux (x = 0.0 - 0.1) phosphors were investigated. The phosphors were synthesized by conventional solid state reaction method. The samples were characterized by powder-XRD and energy dispersive spectroscopy (EDS) techniques. The photoluminescence (PL) and thermally stimulated luminescence (TSL) studies of these materials were investigated. For PL studies the samples were excited with 258 nm UV light. All the samples showed strong red emission at 611 nm due to 5D0→ 7 F2 electric dipole transition of Eu3+ ions. PL peak intensity was found to increase with increase in the dopant concentration. For TSL studies, samples were γ-irradiated with different dose rates using 60Co source. TSL of these phosphors showed a sharp glow peak with maxima at 394 K. Incorporation of europium activator in BaGd2O4 phosphor resulted in the increase of peak intensity. The trap parameters viz., order of kinetics (b), activation energy (E) and frequency factor (S) associated with the most intensive glow peak of BaGd2O4:Eu3+ phosphor were determined using glow curve shape (Chen’s) method. These phosphors can be useful in TL dosimetry Keywords: Phosphors, Photoluminescence, U.V Excitation, Thermoluminescence, Dosimetry

Luminescence Studies of Eu 3+ Doped BaGd 2 O 4 Phosphor

The spectroscopic properties of BaGd 2-x O 4 :Eu x (x = 0.0 - 0.1) phosphors were investigated. The phosphors were synthesized by conventional solid state reaction method. The samples were characterized by powder-XRD and energy dispersive spectroscopy (EDS) techniques. The photoluminescence (PL) and thermally stimulated luminescence (TSL) studies of these materials were investigated. For PL studies the samples were excited with 258 nm UV light. All the samples showed strong red emission at 611 nm due to 5 D 0 → 7 F 2 electric dipole transition of Eu 3+ ions. PL peak intensity was found to increase with increase in the dopant concentration. For TSL studies, samples were γ-irradiated with different dose rates using 60 Co source. TSL of these phosphors showed a sharp glow peak with maxima at 394 K. Incorporation of europium activator in BaGd 2 O 4 phosphor resulted in the increase of peak intensity. The trap parameters viz., order of kinetics (b), activation energy (E) and frequency factor (S) associated with the most intensive glow peak of BaGd 2 O 4 :Eu 3+ phosphor were determined using glow curve shape (Chen's) method. These phosphors can be useful in TL dosimetry.

Synthesis and luminescence characteristics of K2Bi(PO4)(MO4):Eu3+(M = Mo,W) red-emitting phosphor for white LEDs

Abstract K2Bi(PO4)(MO4):Eu3+(M = Mo,W) red-emitting phosphors were synthesized by solid state reaction and characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectrum. XRD and FT-IR analysis confirmed the formation of K2Bi(PO4)(MO4):Eu3+(M = Mo,W) pure phase. Photoluminescence results showed that the series phosphors can be excited efficiently by either UV light range from 200 to 300 nm or near-UV between 375 and 410 nm, and then exhibited bright pure red emission. The concentration quenching occurs at a relatively higher concentration of europium activator, which resulted from the special structure of host lattice and efficient energy transfer within the nearest-neighbor Eu3+ ions. An enhancement of Eu3+ luminescence is observed when W6+ replaces into Mo6+ in this phosphor, which might be attributed to the changing of crystal field environment of Eu3+ resulting from the forming solid solution of host by introducing WO4. The composition-optimized phosphor, K2Bi(PO4)(WO4):0.80Eu3+ presents the best luminescence performance, which can be used as a potential candidate for the phosphor-converted white LEDs.

Effect of Local Structures on the Luminescence of Li2 ( Sr , Ca , Ba ) SiO4 : Eu2 +

The baricenter and crystal field splitting of the 5d transition of the activator were approximated from the experimental spectrum data for , , and hosts and examined in conjunction with the ionic radii of neighboring alkali earth ions and the local structure around the divalent europium activator. In addition, ternary phosphors were screened in terms of photoluminescence (PL) intensity and color chromaticity at an excitation of to determine their suitability for use in white-light-emitting diodes. As a result, several intermediate compounds (mixtures or solid solutions) were pinpointed in a specific composition range in the ternary composition library. In particular, showed the best performance in terms of both PL intensity and color chromaticity.

Searching for the dopant ion in Eu 2+-activated BaMgAl 10O 17 phosphor with synchrotron diffraction

Searching for the multiple sites predicted in the literature for the europium activator in the BaMgAl 10O 17:Eu 2+ phosphor, we undertook a detailed structural study using synchrotron powder diffraction. Three different positions were found for Eu 2+ in the Beevers–Ross site, near the mid-oxygen position and in substitution for the interblocks Al–O–Al bridge. By favoring the migration of the activator ion, the resulting vacancies in the Beevers–Ross sites may be a major cause of the degradation of the phosphor.