Single crystal growth of BaFBr:Eu storage phosphor with alkali impurities (original) (raw)
Related papers
Physical Review B, 1991
Photostimulable x-ray-storage phosphors in the form of image plates are one of the most important applications of defect centers in ionic crystals. Understanding the underlying mechanism, apart from its practical relevance, creates additional insights into the generation and kinematics of radiation defects in this class of materials. In this paper the commercial storage phosphor BaFBr:Eu is investigated. It is shown that x-ray irradiation produces both fluorine and bromine F centers, and aggregates thereof. Only the bromine F centers were found to contribute to the photostimulability, part of which are spatially correlated with an Eu-hole complex, whereas others are uncorrelated. Apart from the photostimulable centers, the nonphotostimulable centers could be identified via their characteristic infrared emission. Numbers can be deduced on the fraction of photostimulable and nonphotostimulable, correlated and uncorrelated centers. These numbers depend on the sample preparation as well as radiation history. The spectroscopic data and methods presented below should help to control better and improve the properties of storage phosphors.
On the role of nonstoichiometry on the photostimulated luminescence in Ba(1−)Sr FBr:Eu
Radiation Measurements, 1998
ÐThe in¯uence of Sr-doping and changing the F/Br-ratio on the properties of the widely used X-ray storage phosphor BaFBr:Eu is investigated. It is con®rmed that Sr-doping considerably increases sensitivity and it is shown that Sr gives rise to new stimulation bands at 1.92 and 2.28 eV. In order to increase the phosphor performance for stimulation at 633 nm a Sr concentration between 15±20% is most favorable. Further results indicate that for storage phosphors synthesized from BaBr 2 , SrBr 2 , BaF 2 and SrF 2 an F/Br-ratio of 107/93 seems to be most favorable for practical application.
X-Ray Storage Luminescence of BaFCl:Eu 2+ Single Crystals
The Journal of Physical Chemistry B, 2005
Temperature behaviors of X-ray luminescence (XL), photoluminescence (PL), photostimulated luminescence, and thermoluminescence (TL) were studied in BaFCl:Eu 2+ single crystals from room temperature to liquid nitrogen temperature. Six emissions at 275, 315, 365, 385, 435, and 500 nm were observed in the XL spectra and are attributed to Cl excitons, V k (Cl 2 -), the 4f 6 5d 1 ( 2 e g ) f 4f 7 ( 8 S 7/2 ) transition of Eu 2+ , and oxygen vacancies, respectively. Three emission peaks at 315, 365, and 390 nm were observed in the PL and TL measurements. These three emissions are from the transitions of 4f 7 ( 6 I 7/2 ) f 4f 7 ( 8 S 7/2 ), 4f 7 ( 6 P 7/2 ) f 4f 7 ( 8 S 7/2 ), and 4f 6 5d 1 ( 2 e g ) f 4f 7 ( 8 S 7/2 ) of Eu 2+ , respectively. In our measurements, we observed that the emission of Eu 2+ increases in intensity upon -irradiation and did not see any signals related to Eu 3+ ions, which indicates that Eu 2+ ions might not be oxidized to Eu 3+ upon X-ray or -irradiation. Instead, the color centers, Cl excitons, and oxygen defects are created and are stable at room temperature, and they might play a key role in the storage luminescence.
New developments in X-ray storage phosphors
Radiation Measurements, 2004
We found a signiÿcant PSL e ect in Eu 2+-doped uorozirconate glasses (ZBLAN) which were additionally doped with Br − or Cl − ions. The PSL is attributed to the characteristic emission of Eu 2+ present in nano-crystallites of BaBr2 or BaCl2, which form in the glass upon annealing. The metastable hexagonal form of BaX2 (X = Br; Cl) is always formed ÿrst before it is converted into the stable orthorhombic form. The particle size increases upon annealing and so does the PSL e ciency of the glass ceramic. However, there is a saturation of the PSL e ciency, which is for Br − doping about 9% and for Cl −-doping about 80% of the Eu-doped BaFBr standard. The particle size was determined by transmission electron microscopy (TEM). The TEM results show a clear tendency for bigger particles for longer annealing at the expense of its number. The particle size for the most e cient phosphor is about 100 nm.
Mechanism of charge storage and luminescence stimulation in BaFBr: RE phosphors
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1991
ABSTRACT We have prepared polycrystalline samples of BaFBr doped with 0.1 mol% of the rare earths Ce, Eu, Tb, Dy and Yb in order to study the mechanism of photostimulated luminescence (PSL) in these materials. Thermoluminescence, PSL and electron spin resonance measurements were used to monitor the formation of defect centres after exposure to β and γ radiation, and the fading of these centres with and without thermal or optical stimulation. We examine accepted mechanisms for the stimulated processes in the light of our results.
Tape casting of storage phosphor BaFBr:Eu2+ for X-ray imaging
Materials Science and Engineering: B, 2002
Tape casting of BaFBr:Eu 2' , an important storage phosphor material for X-ray detection was investigated. Rheological measurement, thickness evaluation and scanning electron microscopy were used to monitor the processes. Measurements of the physical imaging performance in terms of modulation transfer function, noise power spectrum and noise equivalent quanta were used to characterize the storage phosphor plates (SPPs). It was found that careful control of the processes, especially the optimization of the dispersants, resulted in superior SPPs with excellent packing structure and lowest structure noise. Measurements with a commercial Guinier Camera were also presented.
Photostimulation redshift for nonstoichiometric Ba1−xSrxFBr:Eu2+
Journal of Applied Physics, 1996
The oxygen-free x-ray storage phosphor BaFBr, doped with Sr 2ϩ and having Br Ϫ vacancies due to fluorine excess, is shown to have a high photostimulability shifted appreciably to lower photon energy compared to nondoped BaFBr because of the predominant generation of F A ͑Sr 2ϩ ͒ centers on the Br Ϫ sublattice upon room-temperature x irradiation. The F A ͑Br Ϫ ,Sr 2ϩ ͒ centers are less stable than unperturbed F͑Br Ϫ ͒ centers. Therefore, the redshift of the photostimulability disappears upon thermal activation above room temperature. From the failure to observe an F center infrared emission, it is concluded that F and F A centers are spatially correlated to hole centers of yet unknown nature.
New synthesis of high-quality storage phosphors
Radiation Measurements, 2010
We present a single step synthesis method for the photostimulable X-ray storage phosphor BaFBr:Eu 2þ which results in a highly sensitive powder with a relatively small average grain size of 5.4 mm. The starting chemical reagents are BaCO 3 , NH 4 F, NH 4 Br and EuF 3 . The reaction initiated by the decomposition of the ammonium materials leads to highly volatile hydrogen halide gases which react with the BaCO 3 to form BaFBr at temperatures up to 300 C. Further heating results in the incorporation of Eu 2þ and the formation of halide vacancies at temperatures in between 390 and 580 C. The resulting photostimulated luminescence (PSL) efficiency is optimized after sintering at 800 C. The reaction process is monitored by differential thermal analysis (DTA) and the reaction products are detected by mass-spectroscopy which confirms the proposed chemical reactions. Intermediate and final products are identified using X-ray diffraction. Photoluminescence (PL) and PSL spectra show the incorporation of Eu 2þ into the lattice, as well as a PL peak at 470 nm which is not present in the PSL spectrum. This peak is shown to originate from O 2À in the lattice and directly affects the PSL sensitivity.