Kyushu Synchrotron Light Research Center（ Form: No.5）

Experiment Report for Prefectural Beamline
Proposal no. : 1605028P
Beamline no.: BL11
Report date: 10/11/2016

The rare earth and transition metal codoped gallium garnet:
experimental and the density functional theory study
1Liping Tong 1 and T.X. Fan 1
Shanghai Jiao Tong University, China
Katsuhiko Saito 2 and Qixin Guo 22
Saga University, Japan※１Long term users of Advanced Research User Proposal s are requested to submit thisreport corresponding to each research term (I), (II), or (III), specifying each researchterm at the end of the Report Title.

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１ ． Summary
Yb 3 + , Er 3 + , Bi 3 + co-doped Gd 3 Ga 5 O 1 2 has been prepared by sol-gel method, which isactivated by the visible light at 522.5nm and exhibits strong emission at 1533nm. By using
EXAFS technique, our experiment provides strong evidence of atomic sites of Bi, Yb, and Er in
Gd 3 Ga 5 O 1 2 crystal for constructing the structure model of GGG: Yb 3 + , Bi 3 + , Er 3 + with firstprinciples calculation. Moreover, the EXAFS of GGG: Yb 3 + , Bi 3 + , Er 3 + at different preparedtemperatures enable us to gain the variation of atomic sites as the change of preparedtemperatures, and then to discuss the crystal of GGG: Yb 3 + , Bi 3 + , Er 3 + at different preparedtemperatures.
２．Purpose of experiment and background
Inorganic luminescent materials have been rapidly developed in the past decade because they havearoused great interest in their versatility in devices, such as fiber-optic amplifiers, waveguide lasers, anddisplays [1-3], but also in photovoltaic and biomedical applications [4,5]. The rare-earth doped near-infrared
luminescent materials have been developed for the well applications in solid state lasers [6-7] due to theirunique optical property resulted from their electronic configuration [8]. The Er-doped light-emitting materials
with great promise in telecom technology [9-10] have gradually attracted attention, because Er3+ has a 4I13/2→ 4I15/2 transition around 1540 nm which is corresponding to the third standard wavelength of communication
window, largely stimulated by 980nm or 880nm laser [11,12]. Up to now, only a few visible excited NIR

(1550nm) materials have been reported in very recent years, with the strong intensity. However, the low
solubility of erbium ions is always a problem, which would directly influence the emission intensity andlifetime. That limits its application in the field of miniature integrated optics.
Luckily, Er and other cations co-doped in host materials could improve the solubility and then enhanceemission intensity and lifetime. The host material is another way to improve the solubility. The synthetic
inorganic compounds with a garnet structure have many
interestingproperties.

However,

therearefew

researches on gadolinium gallium garnet [Gd3Ga5O12(GGG)] glass, which has better solubility and lower
phonon energy than other oxide glass. The crystal
structure of Gd3Ga5O12 is shown in Fig. 1. It is an
important lasing host material for various dopants,especially, for several kinds of rare-earth ions. Thechange of crystal structure would induce its structure
defects (the vacancies and change of round environment
Fig. 1. The crystal structure of GGG. The smallof dopant), and then influence its optical behavior, such

red ball is O atom, middle reseda ball is Ga atom

as the wavelength blueshift or redshift, and the variation

and big purple ball is Gd atom.

of emission intensity.
Also, the impacts of intensity and lifetime ofemission wavelength caused by the defects due to dopant, are immensely important. Therefore, it is very
important to study the location of different concentration dopants and their neighbors which are prepared invarious temperatures for luminescence materials. In our research, as a perfect technique for our polybasicsystem, the novel setup of XAFS would determine the exact locations of dopant in GGG and its neighbors,then analyzing the performance of luminescence.
３．Experimental
The Bi, Yb, and Er atom positions of Gd3-x-y-zGa5O12: xYb3+, yBi3+, zEr3+ (x=0.042, y=0.042, z=0.042)
were determined at room temperature by X-ray absorption fine structure (XAFS), which is performed on abeamline BL11 with fluorescence mode XAFS (SAGA Light Source, Japan). The samples for XAFS wereobtained by putting the powder into wafer with tablet press for diameter of 1cm at room temperature. Dateanalyses were carried out using Athena soft with theoretical treatment provided by the FEFF8 code.

(a)Fig. 2. EXAFS measurement for Bi in GGG: Yb3+, Bi3+, Er3+
at different prepared temperature. (a) EXAFS functions(b)xμ(E) for Bi in GGG: Yb3+, Bi3+, Er3+. (b) EXAFS functionskχ(k) for Bi in GGG: Yb3+, Bi3+, Er3+. (c) Magnitudes ofFourier transforms of kχ(k) for Bi in GGG: Yb3+, Bi3+, Er3+.
The k region to be transformed is 0-6 Å-1.

(c)

４．Results and Discussions
Fig. 3. XAFS measurement for Bi in GGG:Yb3+, Bi3+, Er3+. (a) EXAFS functions xμ(E)for Bi in GGG: Yb3+, Bi3+, Er3+. (b) EXAFSfunctions k2χ(k) for Bi in GGG: Yb3+, Bi3+,Er3+. (c) Magnitudes of Fourier transforms ofkχ(k) for Bi in GGG: Yb3+, Bi3+, Er3+. The kregion to be transformed is 0-6 Å-1. (d)APCFT of Bi in GGG: Yb3+, Bi3+, Er3+
measured at room temperature. Black line,magnitude; red line, imaginary part.

The EXAFS functions xμ(E) and k2χ(k) for Bi in GGG: Yb3+, Bi3+, Er3+ are shown in Fig. 3 (a) and Fig.
3 (b), respectively. A fast Fourier transform of r space is described in Fig. 3 (c). According to thecrystallographic data [13], GGG has four O neighbors to each Gd at 2.36Å and four other ones to Gd at 2.47 Å
to form the dodecahedral coordination around Gd, which occupies the (c) site. The neighboring coordination
around Ga consists of six O neighbors at 2.01 Å to form the octahedral coordination about the (a) site on whichfraction of Ga atoms located is 0.4, and four O neighbors at 1.85 Å to form the tetrahedral coordination aboutthe (d) site on which the fraction of Ga is 0.6. Bi atoms in Bi2WO are also around oxygen neighbors at 2.54 Å[14]. So, in Fig.3 (c), it can be distinguished that the strongest peak at about 2.76 Å, is corresponding to Bi-O
atomic pairs. This peak has about 0.22 Å shift to the high r region in comparison with the neighboring Bi-O ofprevious studies [15] due to the phase-shift function.
In order to detect a possible atom from the imperfect cubic structure, we applied kχ(k) for Bi in GGG: Yb3+,Bi3+, Er3+, as shown in Fig. 3(d). The main peak of Bi in the magnitude of Fourier transform is at about 2.76 Å.
This distance is close to the distance of neighboring coordination about Bi (2.54 Å). This is confirmed by thefact that imaginary part is also peaked at 2.53 Å. The small distance mismatch of the peaks between themagnitude and imaginary part mainly comes from the multi-distance subshell in neighboring coordination.
There is one smaller peak in the imaginary part at about 2.47 Å as shown in Fig. 3(d). This distance for Bi(2.47 Å) is the same as the one of the Gd-O (2.47 Å) pair in which Gd is located at the (c) site. Therefore, Bi islocated at the (c) site. According to the radii substitution principle, the difference of radii of Gd and Bi is larger
than the difference of radii of Gd and Er (Yb), so Er (Yb) is more easily substitution for Gd than Bi dose.
Therefore, for Yb3+, Bi3+, Er3+ co-doped GGG, because Gd is replaced by Bi, Gd is also replaced by Er and Yb.
This EXAFS measurement has confirmed the hypothesis, with which we built the structure model of GGG:
Yb3+, Bi3+, Er3+ for first principles calculation.
５．Future issues
The refined crystal structure will be obtained by using IFEFFIT software to analyze the EXAFS data, andthen could determine the coordination number (N), interatomic distance (R), the difference of Debye-Wallerfactors.
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[4] A. Kaminska, R. Buczko, W. Paszkowicz, et al., “Merging of the 4F3/2 level states of Nd3+ ions in thephotoluminescence spectra of gadolinium-gallium garnets under high pressure” Physical Review B, 2011,84(7): 075483.
[5] A. Abdukayum, J. T. Chen, Q. Zhao, et al., “Functional near infrared-emitting Cr3+/Pr3+ co-doped zinc
gallogermanate persistent luminescent nanoparticles with superlong afterglow for in vivo targeted bioimaging”,
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[7] S. Schmitt-Rink, C. M.Varma, A. F. J. Levi, “Excitation mechanisms and optical properties of rare-earth
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doped Zinc Alumino Bismuth Borate glasses”, Optical Materials, 2013, 36(2): 362-371.
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Nd3+/Yb3+ codoped CaWO4”, Optics letters, 2014, 39(16): 4635-4638.
[14] F. S. Galasso, “Structure and Properties of Inorganic Solids”, International Series of Monographs in Solid
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[15] M. S. Islam, S. Lazure, R. Vannier, et al., “Structural and computational studies of Bi2WO6 based oxygenion conductors”, J. Mater. Chem., 1998, 8(3): 655–660.

７．Publications, patents（Note: Typical deliverables related to this proposal．
）
The experimental data obtained in this work will be submitted to an international scientific journal.
８．Keywords（Note: 2-3 words about samples and experimental methods．）
Gd3Ga5O12, EXAFS, atomic sites, refined crystal structure
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