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

Experiment Report for Prefectural Beamline
Proposal no. : 1706046F

Beamline no.:Report date

BL15

: 01/25/2018

Local structures in Ga-Ge-Se glasses used for high-speedt e l e c o mmu n i c a t i o n s
J.R. Stellhorn and S. Hosokawa
Kumamoto University※１

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１ ． Summary（ Note: Please include conclusions）

We conducted a first experiment of anomalous x -ray scattering (AXS) at BL15.
The aim of our research project is the investigation of Er -doped(GeSe 2 ) 0. 8 (Ga 2 Se 3 ) 0. 2 chalcogenide glasses. For this first experiment, we limited
the sample choice to the undoped (GeSe 2 ) 0. 8 (Ga 2 Se 3 ) 0. 2 to establish the method
and to obtain reference data for future AXS experiments. The final information
gathered in this project are expected to elucidate the role of Er and Ga in t heamorphous structure and their impact on the photoluminescence properties.
Since AXS is sensitive to the short - and intermediate-range order, we expect toobtain information on the possible formation of Er clusters, which are expected
for higher concentrations of Er, and about the role of the Ga atoms, which are anecessary requirement to solve Er in the glass matrix [1, 2].

２．Purpose of experiment and background

Chalcogenide glasses are characterized by remarkable physical properties, such as highionic conductivity or large photosensitivity. In general, their properties can be fine-tuned byvarying the composition of the constituent elements. Specifically, the photoluminescence
properties in rare earth-doped Ga-Ge-Se glasses can be largely varied by the concentration

of Ga and the dopant. Er doped (GeSe2)0.8(Ga2Se3)0.2 glasses can be used for IR optical wave
guide applications and are thus important materials for high-speed telecommunications [1].
It was found that Ga is extremely important for the Er3+ activation, and secondly, that the IR
photoluminescence (PL) shows a complex dependence on the Er content [1,2]. The latter
results in a peak of the PL for an Er content of about 2%. The decrease of the PL above 2%
has been explained as being connected with the formation of Er clusters. However, suchclusters could so far not be confirmed by experiments.
Major problems to answer this question with usual x-ray techniques are- the low concentration of the rare earth element- the very similar atomic numbers (Z = 31, 32 and 34) of the elements of the base material- the proximity of several absorption edges (for extended XAFS investigations).
- even the application of neutron scattering is difficult, as the respective scattering lengths
are very similar (Ga: 7.288 fm, Ge: 8.185 fm, Se: 7.97 fm).
Anomalous

x-rayscattering(AXS),however,candistinguishelement-specificcontributions [3]. The AXS contrast is mainly given by the difference in the atomic form
factors at two energies near an absorption edge and the relative abundance of the element in
the material. However, this implies that even a dopant can be analyzed by AXS if the form
factor contrast is large enough. We therefore choose the LIII-absorption egde of Er, which
provides a much larger contrast than the K-edges that are usually used for AXS
experiments.
For this project, we already prepared samples with various dopant levels of Er. For the firstexperiment at Saga-LS, we used the undoped sample of (GeSe2)0.8(Ga2Se3)0.2 glass, whichshould serve as a reference for future experiments of the Er doping.

３．Experimental（Note: Description of sample，method of experiment and analysis, etc.）

The AXS experiment was carried out using a standard diffractometer installed at BL15. Anenergy-dispersive SDD detector was used to discriminate the elastic scattering signal fromspurious contributions of fluorescence lines and inelastic contributions. The energy
resolution of the detector was about 300 eV at 10 keV. We also used a second SDD detector tomonitor the fluorescence signals independently during the entire experiment, which greatly
facilitates the data analysis.

Fig. 1: Schematic setup for the AXS experiment. One SDD detector is used to collect the scatteredintensity in a 2θ range, the other detector is fixed in a backscattering position and mainly
monitors the fluorescence signals during the entire measurement.

The experiment itself was conducted at two incident x-rays energies of about 20 eV (nearedge) and 200 eV (far edge) below the K absorption edge of Ga (10.386 keV) and Ge (11.104keV). The scattering intensity was measured by a SDD detector in an angular range of about2θ = 3° ~ 130°, in steps of about 0.5°. Each scan took approximately 4 h, so that a pair ofincident energies could be measured during one day of beamtime.
The data were corrected for absorption effects and Compton scattering, and normalizedusing the Norman-Krogh-Moe method [4,5]. Further details on the theoretical andexperimental background of AXS can be found elsewhere [3, 6-9].

４．Results and Discussions

In this experiment, we investigated the chalcogenide glass (GeSe2)0.8(Ga2Se3)0.2 by AXS. We
have thereby established the AXS method at the Saga-LS, proved the possibility to gain
element-specific information and demonstrated the feasibility of the current AXS setup atBL15.
The differential structure factor of Ga, GaS(Q), is displayed in Fig. 2 along with theexperimental raw data. The results provide a basis for subsequent experiments (see also
section 5 below) aimed at gathering information about whether or not Er clusters areforming in the glassy network, and about the relationship between Ga and Er atoms. Theseresults are important to understand the role of each element and thus to develop optimized
wave guides for telecommunications.

Fig. 2: Experimental scattering data of the (Ga2Se3)0.25(GeSe2)0.75 chalcogenide glass collected at
the Ga edge (left) and the corresponding differential structure factor of Ga (right).

５．Future issues

Future experiments will investigate the Er dopant in Ga-Ge-Se glasses and its impact on thephotoluminescence properties. Since AXS is sensitive to the short- and intermediate-rangeorder, we expect to gain information on the possible formation of Er clusters, which areexpected for higher concentrations of Er, and about the role of the Ga atoms, which are anecessary requirement to solve Er in the glass matrix [1, 2]. Furthermore, we will acquirevital information on the feasibility of AXS for doped systems, and can thus expand theapplication of AXS to a whole new field of research.

６．References[1] J. Ikuta et at., J. Mater. Sci. Mater. Electron. 18, S231 (2007).
[2] K. Koughia et al., J. Lumin. 112, 92 (2005).
[3]Y.

Waseda,Anomalous

X-Ray

Scattering

forMaterials

Characterization,

Berlin-Heidelberg: Springer, 2002.
[4] J. Krogh-Moe, Acta Cryst. 9, 951 (1956).
[5] N. Norman, Acta Cryst. 10, 370 (1957).
[6] S. Hosokawa, I. Oh, M. Sakurai, W.-C. Pilgrim, N. Boudet, J.-F. Bérar, and S. Kohara,

Phys. Rev. B 84, 014201 (2011).
[7] J. R. Stellhorn, S. Hosokawa, and W.-C. Pilgrim, Z. Phys. Chem. 228, 1005 (2014).
[8] S. Hosokawa, Y. Wang, J.-F. Bérar, J. Greif, W.-C. Pilgrim, and K. Murase, Z. Phys. Chem.
216, 1219 (2002).
[9] S. Hosokawa, W.-C. Pilgrim, J.-F. Bérar, and S. Kohara, Eur. Phys. J. Special Topics 208,
291 (2012).

７．Publications, patents（Note: Typical deliverables related to this proposal．
）

８．Keywords（Note: 2-3 words about samples and experimental methods．）
Ga-Ge-Se, chalcogenide glass, anomalous x-ray scattering, photoluminescence
９．About the publication of research results
Please delete either item ① or item ② indicated below, according to a user’s choice of publications as
described in ※2. Also, please fill in an expected date of publication of a refereed journal article or an
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① Publication of a refereed journal article(the date of publication：January 2020）