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Title: X-ray Excitation Triggers Ytterbium Anomalous Emission in CaF 2 :Yb but Not in SrF 2 :Yb

Abstract

Materials that luminesce after excitation with ionizing radiation are extensively applied in physics, medicine, security, and industry. Lanthanide dopants are known to trigger crystal scintillation through their fast d–f emissions; the same is true for other important applications as lasers or phosphors for lighting. However, this ability can be seriously compromised by unwanted anomalous emissions often found with the most common lanthanide activators. We report high-resolution X-ray-excited optical (IR to UV) luminescence spectra of CaF2:Yb and SrF2:Yb samples excited at 8949 eV and 80 K. Ionizing radiation excites the known anomalous emission of ytterbium in the CaF2 host but not in the SrF2 host. Wave function-based ab initio calculations of host-to-dopant electron transfer and Yb2+/Yb3+ intervalence charge transfer explain the difference. The model also explains the lack of anomalous emission in Yb-doped SrF2 excited by VUV radiation.

Authors:
; ; ; ; ; ; ORCiD logo
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
FOREIGN
OSTI Identifier:
1372921
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry Letters; Journal Volume: 8; Journal Issue: 6
Country of Publication:
United States
Language:
ENGLISH
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Hughes-Currie, Rosa B., Ivanovskikh, Konstantin V., Wells, Jon-Paul R., Reid, Michael F., Gordon, Robert A., Seijo, Luis, and Barandiarán, Zoila. X-ray Excitation Triggers Ytterbium Anomalous Emission in CaF 2 :Yb but Not in SrF 2 :Yb. United States: N. p., 2017. Web. doi:10.1021/acs.jpclett.7b00262.
Hughes-Currie, Rosa B., Ivanovskikh, Konstantin V., Wells, Jon-Paul R., Reid, Michael F., Gordon, Robert A., Seijo, Luis, & Barandiarán, Zoila. X-ray Excitation Triggers Ytterbium Anomalous Emission in CaF 2 :Yb but Not in SrF 2 :Yb. United States. doi:10.1021/acs.jpclett.7b00262.
Hughes-Currie, Rosa B., Ivanovskikh, Konstantin V., Wells, Jon-Paul R., Reid, Michael F., Gordon, Robert A., Seijo, Luis, and Barandiarán, Zoila. Mon . "X-ray Excitation Triggers Ytterbium Anomalous Emission in CaF 2 :Yb but Not in SrF 2 :Yb". United States. doi:10.1021/acs.jpclett.7b00262.
@article{osti_1372921,
title = {X-ray Excitation Triggers Ytterbium Anomalous Emission in CaF 2 :Yb but Not in SrF 2 :Yb},
author = {Hughes-Currie, Rosa B. and Ivanovskikh, Konstantin V. and Wells, Jon-Paul R. and Reid, Michael F. and Gordon, Robert A. and Seijo, Luis and Barandiarán, Zoila},
abstractNote = {Materials that luminesce after excitation with ionizing radiation are extensively applied in physics, medicine, security, and industry. Lanthanide dopants are known to trigger crystal scintillation through their fast d–f emissions; the same is true for other important applications as lasers or phosphors for lighting. However, this ability can be seriously compromised by unwanted anomalous emissions often found with the most common lanthanide activators. We report high-resolution X-ray-excited optical (IR to UV) luminescence spectra of CaF2:Yb and SrF2:Yb samples excited at 8949 eV and 80 K. Ionizing radiation excites the known anomalous emission of ytterbium in the CaF2 host but not in the SrF2 host. Wave function-based ab initio calculations of host-to-dopant electron transfer and Yb2+/Yb3+ intervalence charge transfer explain the difference. The model also explains the lack of anomalous emission in Yb-doped SrF2 excited by VUV radiation.},
doi = {10.1021/acs.jpclett.7b00262},
journal = {Journal of Physical Chemistry Letters},
number = 6,
volume = 8,
place = {United States},
year = {Mon Feb 27 00:00:00 EST 2017},
month = {Mon Feb 27 00:00:00 EST 2017}
}
  • The crystal structure of (Yb/ONC(CN)/sub 2///sub 2//OP(N(CH/sub 3/)/sub 2/)/sub 3///sub 4/)ONC(CN)/sub 2/ has been determined by x-ray diffraction analysis (diffractomter, Mo K..cap alpha.. radiation, 4396 reflections, isotropic-anisotropic least-squares method in the full-matrix variant to R = 0.081). The parameters of the monoclinic cell are: a = 11.440(3), b = 14.728(3), c = 34.912(9) A, ..beta.. = 97.53(2)/sup 0/, V = 5832(3) A/sup 3/, d(pycn) = 1.30(1), d(x-ray) = 1.335 g/cm/sup 3/, Z = 4, space group P2/sub 1//c. The structural elements of the crystals are the (Yb/ONC(CN)/sub 2///sub 2//OP(N(CH/sub 3/)/sub 2/)/sub 3///sub 4/)/sup +/ complex cation and the outer-sphere ONC(CN)/submore » 2/ group, which randomly occupies two positions. The coordination number of ytterbium is 6 (all the ligands are coordinated as monodentate ligands by means of an oxygen atom), and the coordination polyhedron is an asymmetrically elongated tetragonal bipyramid, whose axial vertices are occupied by the oxygen atoms of the ..pi..-acid ligands. The mean length of the Yb-O(OP(N(CH/sub 3/)/sub 2/)/sub 3/) bonds is 2.197(11) A. The distances from the Yb atom to the oxygen atoms of the ONC(CN)/sub 2/ groups are equal to 2.233(15) and 2.315(18) A. A special feature of the complex cation is the presence of a fourth-order inversion pseudoaxis. A discussion of the structure of the coordination polyhedron and of the phosphoryl and nitrosodicyanomethanide ligands has been conducted with the aid of literature data.« less
  • CaF/sub 2/ and SrF/sub 2/ crystals were doped with trivalent yttrium ions, and x-irradiated, which resulted in similar coloration spectra for both substances. The bands seemed to satisfy Mollwo's relation nu a/sup 2/ = const, since the SrF/sub 2/ hands were shifted to longer wavelengths compared with fhe corresponding CaF/sub 2/ bands. The absorption spectra were interpreted in terms of the 4d electrons of the bivalent yttrium ions, whose formation was explained by spectra of the CaF/sub 2//Y crystals were identical with the fourabsorption- band spectra of natural crystals or synthetic p crystals grown from natural material. This supports stronglymore » the assumption that the four-absorption- band spectra in natural CaF/sub 2/ is produced by yttrium impurities; this however invalidates hypotheses according to which the four-absorption-band spectrum of CaF/sub 2/, obtained after irradiation, is typical of intrinsic lattice imperfections in alkaline earth fluorides. (auth)« less
  • Single crystals of solid solutions of a high optical quality are grown in the concentration vicinity of the saddle point of the ternary CaF{sub 2}-SrF{sub 2}-YbF{sub 3} system. Efficient lasing with a small Stokes shift (at 1025 nm) was obtained in 980-nm diode-pumped single crystals. The total lasing efficiency (with respect to the absorbed average pump power) was 59% and the slope efficiency was 83%. (special issue devoted to the 25th anniversary of the a.m. prokhorov general physics institute)
  • Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF{sub 2} and Yb/Sr pairs in SrF{sub 2} crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4f{sup N−1}5d excited states of Y b{sup 2+}: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b{sup 2+} + Ca{sup 2+} (Sr{sup 2+}) → Y b{sup 3+} + Ca{sup +} (Sr{sup +}) electron phototransfer. This mechanism applies to all the observed Ymore » b{sup 2+} 4f–5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF{sub 2}:Y b{sup 2+} because the Y b{sup 3+}–Ca{sup +} states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF{sub 2}:Y b{sup 2+} at the wavelengths of the first 4f–5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b{sup 2+} active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF{sub 2} host, associated with the lowest 4f–5d band.« less