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Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

Masai H, Yanagida T, Mizoguchi T, Ina T, Miyazaki T, Kawaguti N, Fukuda K - Sci Rep (2015)

Bottom Line: In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution.However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection.The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.

ABSTRACT
Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

No MeSH data available.


Related in: MedlinePlus

STEM images of 80LiF-15CaF2-5EuF2+δ eutectics.STEM image (a) and the EDS mappings of F (b), Ca (c), and Eu (d). The elemental mappings of each cation show that Eu cations are homogenously dispersed in the CaF2 region without remarkable aggregation at the interface. Bright spots in the HAADF image (e) indicate existence of Eu cation in the CaF2 at the Ca site. The processed image (f) clearly shows that they are regularly dispersed in the crystal lattice of the eutectics.
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f5: STEM images of 80LiF-15CaF2-5EuF2+δ eutectics.STEM image (a) and the EDS mappings of F (b), Ca (c), and Eu (d). The elemental mappings of each cation show that Eu cations are homogenously dispersed in the CaF2 region without remarkable aggregation at the interface. Bright spots in the HAADF image (e) indicate existence of Eu cation in the CaF2 at the Ca site. The processed image (f) clearly shows that they are regularly dispersed in the crystal lattice of the eutectics.

Mentions: As shown in Supplementary Fig. 3(c), it is suggested that an aggregation of Eu species induces concentration quenching. It is often expected that dopant cations segregate at the interface or defect of the sample. Since there is no information about the location of the Eu cations, we have examined the direct observation of the sample using electron beam microscopy. Since segregation of Eu cations possessing high refractive indices will be a source of opacity, it is expected that the dispersion may be a key factor for the fabrication of transparent materials. Figure 5 shows (a) the STEM image of a 5mol% Eu-doped LiF/CaF2 eutectics. Energy Dispersive x-ray Spectroscopy (EDS) mapping of (b) F, (c) Ca, and (d) Eu are also shown. Because Li cannot be detected by means of EDS, dispersion of F ions, as shown with dashed lines, indicates the sample shape. As shown in the elemental mapping of the cross-section (dotted lines), the obtained EDS mappings suggest that the Eu cations are incorporated into Ca2+ sites. Additionally, apparent aggregation at the interface is not observed, although Eu concentration varies to some extent depending on the observed spot. In the high-resolution high-angle annular dark-field (HAADF) image (e), the Eu cations are observed as a bright spot because of their high atomic number, and the processed image (f) clearly shows that they are regularly dispersed in the crystal lattice of the eutectics. Owing to the lack of aggregation at the edge of the CaF2 region, the decrease of emission intensity is explained by concentration quenching, i.e. the homogeneous dispersion of Eu cation that induces decrease of the inter-cation distance in the CaF2 crystal. The obtained results ensure that the Eu cation located at the CaF2 site generates visible photons effectively through energy transfer from the LiF region that absorbs neutron energy.


Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

Masai H, Yanagida T, Mizoguchi T, Ina T, Miyazaki T, Kawaguti N, Fukuda K - Sci Rep (2015)

STEM images of 80LiF-15CaF2-5EuF2+δ eutectics.STEM image (a) and the EDS mappings of F (b), Ca (c), and Eu (d). The elemental mappings of each cation show that Eu cations are homogenously dispersed in the CaF2 region without remarkable aggregation at the interface. Bright spots in the HAADF image (e) indicate existence of Eu cation in the CaF2 at the Ca site. The processed image (f) clearly shows that they are regularly dispersed in the crystal lattice of the eutectics.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4544017&req=5

f5: STEM images of 80LiF-15CaF2-5EuF2+δ eutectics.STEM image (a) and the EDS mappings of F (b), Ca (c), and Eu (d). The elemental mappings of each cation show that Eu cations are homogenously dispersed in the CaF2 region without remarkable aggregation at the interface. Bright spots in the HAADF image (e) indicate existence of Eu cation in the CaF2 at the Ca site. The processed image (f) clearly shows that they are regularly dispersed in the crystal lattice of the eutectics.
Mentions: As shown in Supplementary Fig. 3(c), it is suggested that an aggregation of Eu species induces concentration quenching. It is often expected that dopant cations segregate at the interface or defect of the sample. Since there is no information about the location of the Eu cations, we have examined the direct observation of the sample using electron beam microscopy. Since segregation of Eu cations possessing high refractive indices will be a source of opacity, it is expected that the dispersion may be a key factor for the fabrication of transparent materials. Figure 5 shows (a) the STEM image of a 5mol% Eu-doped LiF/CaF2 eutectics. Energy Dispersive x-ray Spectroscopy (EDS) mapping of (b) F, (c) Ca, and (d) Eu are also shown. Because Li cannot be detected by means of EDS, dispersion of F ions, as shown with dashed lines, indicates the sample shape. As shown in the elemental mapping of the cross-section (dotted lines), the obtained EDS mappings suggest that the Eu cations are incorporated into Ca2+ sites. Additionally, apparent aggregation at the interface is not observed, although Eu concentration varies to some extent depending on the observed spot. In the high-resolution high-angle annular dark-field (HAADF) image (e), the Eu cations are observed as a bright spot because of their high atomic number, and the processed image (f) clearly shows that they are regularly dispersed in the crystal lattice of the eutectics. Owing to the lack of aggregation at the edge of the CaF2 region, the decrease of emission intensity is explained by concentration quenching, i.e. the homogeneous dispersion of Eu cation that induces decrease of the inter-cation distance in the CaF2 crystal. The obtained results ensure that the Eu cation located at the CaF2 site generates visible photons effectively through energy transfer from the LiF region that absorbs neutron energy.

Bottom Line: In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution.However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection.The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.

ABSTRACT
Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

No MeSH data available.


Related in: MedlinePlus