XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
35
I–17
Multisite luminescence of rare earth ions doped Y
4
Al
2
O
9
crystals
Michał Malinowski
1
, Marcin Kaczkan
1
, Sebastian Turczyński
2
1
Institute of Microelectronics and Optoelectronics, Technical University of Warsaw, Koszykowa 75,
00-662 Warsaw, Poland, e-mail: m.malinowski@elka.pw.edu.pl
2
Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland
Over the past several years there has been an ongoing research for trivalent rare-earth (RE
3+
)
activated materials for optical amplifiers, lasers, phosphors and scintillators. Oxide crystals and
nanocrystals from the Y
2
O
3
-Al
2
O
3
binary system are one of the most studied groups of optical
materials, owing to their various applications. The monoclinic Y
4
Al
2
O
9
(YAM) phase is the least
studied one and only limited information is available on the spectroscopic properties of this
system so far. YAM is more complicated than YAG and YAP crystals due to the existence of
four distinct Y
3+
sites which could be substituted by RE
3+
ions [1]. Limited spectroscopic studies
of RE
3+
ions in YAM have confirmed multisite features of this host lattice [2–4].
In this study, we have considered RE
3+
dopant ions as structural probes to investigate
changes of the local environment and to resolve the multisites of rare earth ions in YAM host.
This was based on high resolution absorption, excitation and emission spectra measurements
and selectively excited fluorescence decays performed at low temperatures.
YAM samples, with Pr
3+
, Sm
3+
, Eu
3+
and Yb
3+
activator concentrations of 0.1, 1, 5 and 10 at.%,
used in this study were grown by micro-pulling down (-PD) method in the Institute of
Electronic Materials Technology (ITME) in Warsaw. Polycrystals in the form of rods 2–3 mm
in diameter and several cm long were obtained.
Sm
3+
and Eu
3+
have been employed as a structural probe because of its hypersensitive
transitions;
4
G
5/2
→
6
H
9/2
and
5
D
0
→
7
F
2
respectively, which intensity can vary by orders of
magnitude depending on the local environment. Also, important and unique feature of Eu
3+
ions
is the existence of
7
F
0
↔
5
D
0
transitions connecting two non-degenerate levels that cannot be
split by crystal-field effects. Thus, the number of lines related to this transition reflects the
number of sites occupied by Eu
3+
ions in the matrix. Anti-Stokes, up-conversion fluorescence
originating from the
3
P
0
state while exiting the
3
H
4
→
1
D
2
transition was observed in Pr
3+
:YAM.
The participation of distinct sites to up-conversion emission was revealed for the first time. The
dynamical behavior of the upconverted emission arising from four sites was studied and
modeled via energy transfer process.
New results on the site preferences for impurity ions, number of ion sites, their relaxation
dynamics and energy transfer between RE
3+
ions in different sites are presented and discussed in
a function of temperature and activator concentration.
Keywords: rare earth ions; photoluminescence; site-selective spectroscopy; energy transfer
Acknowledgment
This work was supported by the Polish National Science Center NCN 2012/07/B/ST5/02406 project.
References
[1] C. D. Brandle, H. Steinfink, Inorg. Chem. 8 (1969) 1320.
[2] Y. Rabinovitch, O.K. Moune, D. Tetard, M.D. Faucher, J. Phys. Chem. A 108 (2004) 8244.
[3] M. Kaczkan, Z. Boruc, S. Turczyński, D. Pawlak, M. Malinowski, J. Lumin. 170 (2016) 330.
[4] M. Kaczkan, S. Turczynski, D.A. Pawlak, M. Wencka, M. Malinowski, Opt. Mater. 58 (2016) 412.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
36
I–18
Terahertz-band spectroscopy investigation of boson peak
in glassy glucose
Tatsuya Mori
1
, Mikitoshi Kabeya
1
, Yasuhiro Fujii
2
, Suguru Kitani
3
,
Hitoshi Kawaji
3
, Akitoshi Koreeda
2
, Jae-Hyeon Ko
4
, and Seiji Kojima
1
1
Division of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan,
2
Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan,
3
Laboratory for Materials and Structures, Tokyo Institute of Technology, Yokohama 226-8503, Japan
4
Department of Physics, Hallym University, Chuncheon, Gangwondo 24252, South Korea,
e-mail: mori@ims.tsukuba.ac.jp
Glassy materials show the boson peak (BP) at terahertz frequency region, which is a
universal feature observed in specific heats, Raman scattering, and inelastic neutron scattering.
Recently, we have pointed out that terahertz time-domain spectroscopy (THz-TDS) is suitable to
detect the BP [1], although many recent researchers had been not aware that or forgotten the past
far-infrared studies[1].
In the vibrational density of states spectrum g, the BP appears as a peak in the representation
of g/ν
2
(ν: frequency) not in the g spectrum directly. Considering the relation of α = CIR∙g (α:
absorption coefficient, CIR: infrared light-vibration coupling coefficient) [2], the BP appear in
the α/ν
2
representation in infrared spectrum, i.e. the BP is not a peak of the absorption spectrum,
although it is a universal dynamic feature of glassy materials.
In this study, we demonstrate the THz-TDS on vitreous glucose which is hydrogen-bonded
organic glass material. Fig. 1 shows boson peak representation α/ν
2
of vitreous glucose. The BP
appears at around 1 THz clearly. Due to the relaxation process existing in low frequency region,
the low frequency part of the each THz spectrum increases as temperature increases. We will
compare the results with the low-frequency Raman scattering and low-temperature specific heat
results.
0
1
2
0
10
20
30
40
50
300 K
300 K
150 K
250 K
100 K
200 K
50 K
14 K
α
/
ν
2
(
cm
-1
T
H
z
-2
)
ν
(THz)
Glassy glucose
Boson peak
14 K
Fig. 1. Boson peak representation α/ν
2
of glassy glucose detected by THz-TDS.
Keywords: Boson peak, terahertz time-domain spectroscopy, specific heat, glass, glucose
Acknowledgments
This work was partially supported by JSPS KAKENHI Grant No. 17K14318 and No. 26287067, the
Nippon Sheet Glass Foundation for Materials Science and Engineering, and the Asahi Glass Foundation.
References
[1] C. D. Brandle, H. Steinfink, Inorg. Chem. 8 (1969) 1320M. Kabeya, T. Mori, Y. Fujii, A. Koreeda, B.
W. Lee, J. H. Ko, S. Kojima, Physical Rev. B 94 (2016) 224204.
[2] F. L. Galeener and P. N. Sen, Physical Rev. B 17 (1978) 1928.
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