X-ray Storage Phosphor Research Articles

X-ray storage phosphors in the system Y 2SiO 5:Ce,Tb,Zr

Coactivation of Y 2SiO 5 (oxyorthosilicate of X 2 type) with Ce, Tb and Zr introduces storage properties by the formation of suitable carrier trapping defect centres. Upon irradiation by x-rays or cathode rays energy is stored and released by photostimulation or thermal stimulation, giving activator luminescence. A model for the storage mechanism is discussed.

On the recombination mechanism in x-ray storage phosphors based on lanthanum fluoride

LaF 3 doped with trivalent rare earths can act as an X-ray storage phosphor. Trivalent luminescent rare earth ions are used as a probe to elucidate the recombination mechanism. The photoluminescence emission spectra of LaF 3:RE 3+ (RE = Ce, Pr, Gd, Tb, Dy, Ho, Tm) are compared to those of the thermally stimulated luminescence (TSL) after X-ray irradiation. In the TSL spectra of LaF 3: Pr 3+, LaF 3: Tb 3+, LaF 3: Ho 3+ and LaF 3: Tm 3+ the emissions from the higher excited states are weaker or absent. LaF 3: Ce 3+ and LaF 3: Gd 3+ do not exhibit thermally stimulated emission. It is proposed that upon recombination an exciton is formed, which is able to transfer its energy to Pr 3+, Tb 3+, Dy 3+, Ho 3+ and Tm 3+ at about 22000 cm -1. The lowest excited levels of Ce 3+ and Gd 3+ in this lattice are at too high energy to allow this transfer.

Method for the determination of photostimulable defect center concentrations, production rates, and effective formation energies

A new method is proposed to determine radiation-induced defect center concentrations in solids which exhibit photostimulable luminescence. The technique relies on the determination of the number of photons released by spontaneous and photostimulated luminescence. A comparison with the x-ray-absorbed energy yields the effective formation energy of spontaneous luminescence photons and photostimulable centers. The method is applied representatively to BaFBr:Eu2+, which is utilized commercially as photostimulable x-ray storage phosphor in image plates for x-ray, γ-ray, electron, and neutron radiography. It is shown that in the utilized material on average 8 photostimulable F(Br−) centers (color centers based on bromine vacancies) and about 5 spontaneously emitted photons are generated by the absorption of 1 keV x-ray energy. Taking recent investigations into account which show that the x-ray generation of spontaneous luminescence and photostimulated luminescence centers is accompanied by the creation of approximately 36 nonphotostimulable defect centers, an average formation energy of about 20 eV per defect center can be calculated.

The X-ray storage properties of barium phosphate doped with trivalent rare earth ions

Barium orthophosphate doped with Ce3+, Pr3+, Gd3+, or Tb3+ acts as an efficient X-ray storage phosphor. The four compositions have different thermal stimulation properties; the thermally stimulated luminescence (TSL) occurs at higher temperatures than in Ba3(PO4)2:La3+. Similar to this latter compound, atomic hydrogen is present after irradiation in Ba3(PO4)2:Ce3+ and Ba3(PO4)2:Gd3+, but its electron paramagnetic resonance (EPR) signal disappears before the TSL takes place. In Ba3(PO4)2:Pr3+ and Ba3(PO4)2:Tb3+, no H0 is found. In the four cases studied, codoping with Eu2+ changes the TSL properties. In view of these results it is concluded that the storage mechanism is different for barium phosphate doped with luminescent trivalent rare earth ions on the one hand, and barium phosphate with La3+ or Y3+ on the other.

The luminescence and X-ray storage properties of Pr 3+ and Ce 3+ in YNbO 4 and M′-YTaO 4

The luminescence of Pr 3+ in YNbO 4 and YTaO 4 is described. Emissions from both the 3P 0 and the 1D 2 levels are observed, the latter of which is dominant. The Ce 3+ ion does not luminesce in these hosts; its presence quenches the host lattice emission as well. This is ascribed to a metal-to-metal charge transfer state at low energy. A comparison to other cases of quenched Ce 3+ luminescence is made. YTaO 4:Pr acts as a photostimulable X-ray storage phosphor, which may also be filled by UV irradiation.

Trapping of electrons by H+ in the X-ray storage phosphor Ba3(PO4)2:Eu2+, La3+

When co-doped with La3+, Ba3(PO4)2:Eu2+ shows an intense thermally stimulated luminescence after X-ray irradiation. The phosphor is also optically stimulable. The stimulated emission is due to the Eu2+ ion. In the absence of Eu2+ a broad emission band is observed which is tentatively ascribed to a phosphate group close to the La3+ ion. EPR reveals the presence of H0 after irradiation. It is concluded that the substitution of La3+ on a Ba2+ site is accompanied by the introduction of H+ into the lattice. The latter ion acts as an electron trap; detrapping yields the stimulated luminescence.

Color Centers in the Near Infrared Region in Crystals MFX (M = Ba, Sr; X = Cl, Br)

Color centers with absorption bands in the near infrared region (peaking near 900 nm) in X-rayed MFX crystals have been found. They might be attributed to the aggregates of F(X-) centers which are similar to M centers in MX crystals. The interconversion among F(F-), F(Br-), and M centers in BaFBr crystals has been found. These aggregated color centers are stable and exhibit stimulable absorption bands in the region from 700 to 1000 nm. Therefore some solid state lasers can be used as stimulating light sources instead of He-Ne lasers for reading the information stored in PSL image plates made of these X-ray storage phosphors.

Study of spatial correlations between radiation-induced defects and the activator Eu2+ in the X-ray storage phosphor BaFBr:Eu2+ with optical detection of electron paramagnetic resonance

For the understanding of the photostimulated emission process of the storage phosphor BaFBr it was assumed that a spatial correlation exists between the F centres and hole centres generated by X-rays and the activator ion Eu2+. The authors present direct experimental evidence for such a correlation with the detection of cross-relaxation effects in the optically detected electron paramagnetic resonance. A quantitative analysis of the intensity and spectral shape of the Eu2+ cross-relaxation spectra is presented. It follows that a substantial fracture of F centres and O- centres (in oxygen-containing BaFBr) are generated with a distance of about 20 AA from the Eu2+ activators.

X-ray imaging with photostimulable phosphors

Abstract Image plates based on photostimulable X-ray storage phosphors establish a promissing alternative to conventionally utilized two-dimensional X-ray detectors. These image plates consist of a layer of powdered X-ray storage phosphor, usually the alkaline-earth halide BaFBr:Eu 2+ , mixed with an organic binder and mounted on a polymeric film. Upon absorption of ionizing radiation, electrons and holes are produced efficiently. Both species are trapped in the immediate surrounding of their creation thereby forming a latent image. The readout of this image occurs by photostimulation whereby the trapped electrons are liberated and recombine radiatively with the trapped holes under emission of Eu 2+ light. In the present paper the principle of the imaging system is introduced followed by a brief review of the underlying physics explaining the nature of the involved traps and the mechanism of photostimulation. Advantages and disadvantages of image plate detectors and their physical nature are discussed and possible improvements suggested. Present and future fields of application are presented.

The crystal structure of Ba5SiO4Br6

Abstract The crystal structure of the x-ray storage phosphor Ba5SiO4Br6 is described. Ba5SiO4Br6, Mr=1258.16, monoclinic, C2/c, a =9.783(4) A , b =15.232(16) A , c =12.028(16) A , β=104.99(7)°, V =1731(8) A 3 , Z=4, Dx=4.827Mg m−3, λ( Mo K α)=0.71069 A , μ=25.0 mm−1, F(000)=2144, room temperature, final R=0.051 for 3244 observed reflections.

Photostimulated luminescence and thermally stimulated luminescence of Y2SiO5-Ce, Sm

The photostimulated luminescence (PSL) and thermally stimulated luminescence (TSL) of Y2SiO5-Ce3+ and Y2SiO5-Ce3+, Sm3+ is reported and discussed. The PSL measurements show that these compositions are rather efficient X-ray storage phosphors with a short response and decay time (35+or-10ns). A model for the recombination mechanism is suggested on the basis of PSL and TSL measurements.

Photostimulated luminescence and thermally stimulated luminescence of some new X-ray storage phosphors

The photostimulated luminescence (PSL) and thermally stimulated luminescence (TSL) properties of two new X-ray storage phosphors, Ba2B5O9Br-Eu2+ and Ba5GeO4Br6-Eu2+, are reported and discussed. The PSL measurements show that bromine vacancies act as electron traps and that Eu2+ is involved in the hole trapping. A direct recombination mechanism, suggested by PSL results, is confirmed by TSL measurements. Analysis of the glow curves shows first-order kinetics in combination with low-frequency factors which is characteristic for centre-to-centre recombination.