Highlight
BL1B

Two-Photon Spectroscopy of Core Excitons with the Combinational Use of
Synchrotron Radiation and Laser Light

T. Tsujibayashi1, J. Azuma2, M. Watanabe3, O. Arimoto4, M. Itoh5, S. Nakanishi6,
H. Itoh6, M. Kamada2
1
Department of Physics, Osaka Dental Univ., Hirakata 573-1121, Japan
2
Synchrotron Light Application Center, Saga Univ., Saga 840-8502, Japan3
Department of Interdisciplinary Environment, Kyoto Univ., Kyoto 606-8501, Japan
4
Department of Physics, Okayama Univ., Okayama 700-8530, Japan
5
Department of Electrical & Electronic Engineering, Shinshu Univ., Nagano 380-8553, Japan
6
Department of Advanced Materials Science, Kagawa Univ., Takamatsu 761-0396, Japan
Synchrotron radiation facilities and lasers are themost valuable scientific inventions of the 20th century.
We have constructed a system for a combinational useof both the light sources at BL1B [1, 2] and applied it
to the study of valence excitons of wide bandgap
materials [3]. Furthermore, we performed two-photon
excitation of core excitons in BaF2, and the results ofthe experiments were published recently [4, 5]. In thispaper, we present the summary of those works.
The combinational use of synchrotron radiation(SR) and laser light dates back to 1980s. N2 andNd:YAG lasers with repetition rates lower than 100
Hz were used in the early stages of experiments [6, 7].
For the purpose of efficient measurements, it isdesirable that the laser pulses are synchronizedcompletely with SR pulses. The development of amode-locked laser enabled such experiments.
The aim of our two-photon absorption (TPA)
measurement is to investigate unoccupied states insolids. The TPA is a powerful technique as well as
inverse-photoemission measurement since its final
state of the transition is restricted by the selection
rules. In order to specify the final states, core electron
excitation are advantageous to valence electron
excitation, since core states are often flat in the
k-space and have well-defined symmetry. The TPA is
suitable for the measurement of high-angularmomentum states such as d and f orbitals because

these states cannot be reached by dipole transitions
from many core states, which consist of s and porbitals.
We show the experimental setup in Fig. 1. The
laser pulses are synchronized with SR pulses throughelectronic devices. The laser light propagates throughan optical fiber to the port of measurement. We
detected luminescence of the sample with use of aphotomultiplier of the microchannel plate-typethrough the time-correlated single photon counting
method. The laser light was turned on and off using
an optical shutter. The output of the detector isaccumulated in two MCAs: one works when the laser
light is on and the other when the light is off. The
difference is attributed to the signal due to TPA.
Figure 2 shows the TPA spectrum of BaF2. The
spin-orbit splittings of 4f and 6p states of Ba ions in
BaF2 were found to be 0.7 and 1.4 eV, respectively[4]. These values are well explained by the relativistic
quantum theory. It tells that the spin-orbit splittings ofhydrogen-like orbits specified (n, l) have thefollowing expression,' n,l v n 3l (l  1)

1

.

(1)

Expression (1) gives relative values of the splittings:' 5 p : ' 5 d : ' 4 f : ' 6 p | 3.0 : 1.0 : 1.0 : 1.7 . (2)Since the splitting of 5p levels was obtained
experimentally to be 2.2 eV [8], those of the otherstates are calculated with use of Eq. (2).
The calculated splitting of 5d states raises a query
about the so far proposed interpretations of thereflectivity spectrum of 5d-core excitons in BaF2. The

Fig. 1 The experimental setup of two-photon
excitation with use of SR and laser. Luminescencefrom the sample is detected as the signal.

Fig. 2 The TPA spectrum of 4f- and 6p-coreexcitons in BaF2. The energy diagram of 4f levels
is depicted on the left. See Ref. 4 for the details.

62

Highlight

Fig. 4 Time-response of the signal of TPA. The
output of the detector under excitation exclusively
with SR is subtracted from that with both the SR
and laser. The photon energy of SR is enough toexcite a core electron to a 5d level. The dip can beinterpreted that two-photon excited core excitons
have a finite lifetime, which should be comparedto the fast recombination of one-photon excitedcore electron. See Ref. 5 for the details.

Fig. 3 Which is the true diagram? Schematicenergy diagrams of 5d core excitons in BaF2
based on different models are shown. The upper
panel shows the reflectivity spectrum of theexcitons. The 5p and 5d levels split due tospin-orbit interaction. The p1/2-d3/2 and p3/2-d5/2transitions are allowed in electric dipole
transitions. The origin of the multi peaks is
attributed to the dispersion of the levels in (a)and (c), whereas to the crystal field effect in (b).
The exciton binding energy is assumed to beconstant and included in the diagrams above.

becomes weaker. In order to secure sufficient
intensity of the signal, the use of an undulator
beamline may be indispensable, though sample
damage should be carefully avoided.
In the present measuring system, TPA is detectedby luminescence. Unfortunately, TPA is not always
accompanied by characteristic luminescence, such as
Auger-free luminescence of BaF2 and other materials[12]. In order to study wide range of materials, a newtechnique that does not need such luminescenceshould be developed. Detecting reflectivity change
might be a powerful technique in the future.

first precise measurement of the spectrum of BaF2 inthe core excitation region was reported in 1972 [9],and the interpretation of the peaks is schematically
depicted in Fig. 3 (a). The splitting of 5d levels is
obtained to be 0.2 eV. An alternative interpretation of
the spectrum is possible [10]. Figure 3 (b) is based ona model where the crystal field splitting is assumed to
be as large as 0.8 eV and dispersion of the states are
not taken into consideration. The splitting of 5d levels
is deduced to be the same as the former case, which
value is inconsistent with Eq. (2).
The diagram of Fig. 3 (c) is based on a recent bandcalculation of energy levels [11]. It gives aninterpretation consistent with Eq. (2).
Spectroscopic study of core excitons revealed the
conduction band structure as described above.
Besides static properties, dynamical behavior of core
excitons was measured through the system depicted
in Fig. 1. An example of temporal behavior of thesignal luminescence is shown in Fig. 4. The lifetimeof the two-photon excited 6p-exciton was obtained tobe 0.2 ns [5].
The time resolution of the system is mainly
determined by excitation pulse widths. As depicted in
the upper panel of Fig. 4, the pulse width of SR was
about 0.6 ns (under the single bunch operation), andthat of the laser was 0.3 ns. The laser pulse expanded
during the propagation through the 50-m long fiber.
The laser pulse width can be shortened by shortening
the length of the fiber. However, it should be notedthat the shorter the pulse width is, the smaller theoverlap with the SR pulse is. Consequently, the signal[1] T. Tsujibayashi et al., UVSOR Activity Report
1996 (1997) 52.
[2] S. Asaka et al., Rev. Sci. Instrum. 69 (1998) 1931.
[3] T. Tsujibayashi et al., Phys. Rev. B 60 (1999)
R8442[4] T. Tsujibayashi et al., Phys. Rev. Lett. 94 (2005)
076401.
[5] T. Tsujibayashi et al., phys. stat. sol. (c) 2 (2005)
228.
[6] V. Saile et al., Phys. Lett. 79A (1980) 221.
[7] R. Pizzoferrato et al., Europhys. Lett. 2 (1986)
571.
[8] J. Reader and G.L. Epstein, J. Opt. Soc. Am. 65(1975) 638.
[9] G.W. Rubloff, Phys. Rev. B 5 (1972) 662.
[10] M. Yuri et al., J Phys. Soc. Jpn. 61 (1992) 2557.
[11] H. Jiang et al., J. Phys. Condens. Matter 15(2003) 709.
[12] M. Itoh, Recent Research Developments inPhysics Vol.4 (Transworld Research Network,
Trivanduram, 2003) Chap. 11.

63

BL1A, 5B, 7B&8B1Time Resolved Decay Curves of AlGaN and InAlGaN Measured in the
Wide Energy Range
S. Naoe1, S. Hamada2, K. Fukui2, H. Hirayama3, H. Miyake4, K. Hiramatsu4
1Faculty of Engineering, Kanazawa University, Ishikawa 920-1192, Japan
2
Research Center for Development of Far-Infrared Region,Fukui 910-8507, Japan
3
The Institute of Physical and Chemical Research, Wako 351-0198, Japan
4
Faculty of Engineering, Mie University, Mie 514-8507, Japan
AlGaN is the promising optical material having
variable band gap energy by selecting acompositional rate of the elements. However, theintensity of emission in AlGaN loses rapidly its
intensity with increasing temperature, though
InAlGaN gives effective luminescence intensity at RT.
The emission bands of those two alloy systems arebasically similar. Both of them consist of two
photoluminescence (PL) bands. One is B-band
emission which is ultraviolet (UV) emission band due
to exciton, and the other is visible (VIS) emission
band caused by some defects or impurities (Y-band).
Therefore, to investigate the precise emission processof III-V nitrides, the comparative studies of PL in
between AlGaN and InAlGaN become important.
All samples are made by MOCVD (MOVPE)
methods. The thickness of AlGaN thin films is about
1 Pm on 1 Pm AlN single crystal film with sapphire
substrates and that of InAlGaN thin films is about 80
nm on SiC substrates with Al0.2Ga0.8N buffer layers.
In our study, multi-bunch mode (15 full + 1 empty
bunchs, 11.1 ns period) of UVSOR is used as theusual stationary light source and single-bunch mode
(177.7 ns period, a 0.5 ns width) as the pulse lightsource for time resolved measurement by using timecorrelated single photon counting method (TCSPC).
Time resolved decay (TRD) measurements have been
performed at BL7B, BL5B, BL8B1 and BL1A. Same
conventional 30 cm monochromator via optical fiberis used to measure both PL spectra and TRD curvesof all samples.
In our previous work, TRD results in band-to-band
excitation (at BL7B) of both AlGaN and InAlGaN are
analyzed by using the same model of three single
exponential components linear combination model(decay time of the fast component is in less thansub-ns order, middle in ns, slow in 10 ns). The fast
one is the main PL component at RT. Both middle andslow ones rapidly decrease with increasing
temperature. Figs. 1 and 2 show B-band TRD curves
at 26 K of Al0.54Ga0.46N and In0.05Al0.20Ga0.75N,
respectively. Excitation energies are 4.7 eV (BL7B),
95 eV (BL5B), 405 eV (BL8B1) and 1.56 keV(BL1A). The fast component of InAlGaN TRD ismuch stronger than that of AlGaN even at low
temperature. This is one of the reasons that InAlGaN
is used as the active layer in UV-LED operated at RT.
In the inner shell excitation, many electron–hole pairs
are produced during the decay process of core holecoming up to valence band (photon multiplication),and make recombination as both B- and Y-band PL.
The behavior of three components of TRD in the
inner shell excitation becomes the interesting study toanalyze the emission mechanisms in AlGaN. A rate of
the fast component becomes to increase withincreasing the excitation photon energy and to takethe resembling curve to that of InAlGaN gradually.
This result suggests one possible model that the
optical transition corresponding to the fast component
in AlGaN may be caused by direct overlap of the
wave function between electron and hole states. The
overlap of wave functions will occur in the situationof many electron-hole pairs gathering at the bandedge. On the other hand, the fast component in
InAlGaN will be caused by the mixing of the allowed
part of wave function by the effect of incorporation of
In elements.
Normalized PL Intensity

26K

5.2eV
95eV
405eV
1.56keV
0

5

10

15

20

25

30

35

40

Time (ns)Fig. 1 Time resolved decay curves of Al0.54Ga0.46N
at various excitation energies. Each spectrum isshifted vertically for convenience.

Normalized PL Intensity

26K

㩷

4.7eV
95eV
405eV
1.56keV

0

5

10

15

20

25

30

35

40

Time (ns)Fig. 2Time resolved decay curves of
In0.05Al0.20Ga0.75N at various excitation energies. Eachspectrum is shifted vertically for convenience.

64

BL1A

XAFS Study on Silica Glasses Irradiated in Nuclear Reactor

T. Yoshida1, T. Tanabe1, H. Yoshida2
1
Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8603, Japan2
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University,
Nagoya 464-8603, Japan
Irradiation effects by high-energy particles such as
neutron and ions on silica glasses are one of the mainconcerns for their application as optical windows,
insulators and optical fibers in nuclear environments.
The chemical states and density of defects in silica
glasses should be closely related to their optical andphysical properties such as the transparency andhardness. However, it is still difficult to observe thestructures of the defects at an atomic scale in a SiO2
glass, because the structural changes in its amorphousnature does not allow us to apply diffraction
techniques. In the present work, we have investigatedthe change of the local structure of the SiO2 glass
before and after in-reactor (i.e., neutron and J-ray)irradiation by Si K-edge X-ray absorption finestructure.
Samples used in this work were a synthesized silica
glass (T-4040) of 13 mm diameter and 2 mm thickness
with OH content of 800 ppm. The samples were
irradiated in the nuclear reactor YAYOI at the
University of Tokyo. YAYOI was operated with apower of 1.5 kW, where a neutron flux was about
6x1011 n/m2s with an average neutron energy of 1.3
MeV and J ray level was about 3.0 kGy/h.
Si K-edge X-ray absorption spectra were recorded
under vacuum (<10-6 Pa) at room temperature at BL7A
and 1A station of UVSOR, or at BL11B station of
Photon Factory, Institute of Materials Structure
Science, High Energy Accelerator Research
Organization (KEK-PF), using a two-crystal
InSb(111) monochromator. Two different recording
modes, i.e. a total electron yield (TEY) mode and afluorescent X-ray yield (FY) mode were employedwith detectors consisting of an electron multiplier anda gas-flow proportional counter, respectively.
Fig. 1 compares the radial structure functions(RSFs) obtained from Fourier transforms of the
k-weighted Si K-edge EXAFS spectra of a synthesized
silica glass before and after in-reactor irradiation
together with that of a SiO2 crystal (quartz) sample as areference. We also performed curve-fitting analysisof the Fourier-filtered EXAFS by the least-squares
method. In Fig. 1, the peaks in the region of 0.8-3.2 Å
were isolated with a Hanning window, and inversely
Fourier transformed. The curve-fitting analysis was
carried out with Si-O and Si-Si shells. The
curve-fitting results are summarized in Table 1.
The EXAFS spectra of the silica glasses irradiatedwith the low neutron fluence (less than ca. 1 x 1019
n/m2 ) were fundamentally the same as those of theirunirradiated ones (not shown here). The structuralchange was recognized in the EXAFS spectra of thesilica glasses irradiated with more than 2 x 1019 n/m2.
In the RSFs, it should be noted that the peak intensity
at 1.2 Å due to the Si-O bond increased to a level
similar to that of the quartz crystal. Moreover, thecoordination numbers of the first neighboring oxygen
atoms increased from ca. 3.7 to ca. 4.3 after in-reactor
irradiation (see Table 1). At the same time thecoordination number of the second neighboring Si
atoms decreased, i.e., the Fourier-filtered EXAFS
spectra of the irradiated silica glasses were not fitted
well using a Si-Si shell. However, the curve-fitting
using a Si-O shell instead of Si-Si shell was successful.
The distance 2.92 Å thus evaluated corresponds to thepath length of the multiple scattering for Si-O-O in theregular SiO4 tetrahedron. These results suggest somedecoupling of neighboring distorted SiO4 tetrahedrons
in a silica glass via the atomic displacement by neutron
irradiation. Accordingly, the decoupled distorted SiO4
tetrahedrons could be relaxed and return to regular or
isolated SiO4 tetrahedron and the O-Si-O angles would
be more uniform after the irradiation, as observed in
the growth of the peak assigned to Si-O in RSFs. This
does not mean the recovery of long range orders (orrecrystallization). The irradiation certainly gave moredisorder in long range as the appearance of Si
precipitates or each tetrahedron became more isolated.
a)synthesized silica glass
1.5b)quartz crystal
1.0

1.0

0.5

FT

FT

after irrad.

0.5

0.0

0.0

-0.5

before irrad.
-0.5

-1.0
0

1

2

3

4

5

6

0

1

2

R/Å

3

4

5

6

R/Å

Fig.1 Radial structural functions of k-weighted Si
K-edge EXAFS spectra of (a) the synthesized silica
glass before and after in-reactor irradiation, and (b) aquartz crystal. The neutron fluence of the irradiatedsynthesized silica glass is 2.7 x 1020 n/m2.
Table 1 Results of curve-fitting analyses

Table 1 Results of curve-fitting analyses
SampleQuartzSyn.silica (unirradiated)
Irrad. syn. silica (2.7x1020 n/m2)

65

Shell

coordination.
numberinteratomic
distance(Å)'V2 a) (Å2)

Si-O

4.0

1.61

0

Si-Si

4.0

3.02

0.00285

Si-O

3.7

1.61

0.00269

Si-Si

0.8

3.09

0.00332

Si-O

4.3

1.60

0.00114

Si-O

1.5

2.91

0.00150

Si-Sib)2.0

3.86-0.00358

BL1B

Two-Molecule Absorptions of Oxygen under High Pressure

Y. Akahama, T. Moriwaki, H. Kawamura
Department of Material Science, Graduate School of Material Science, 3-2-1 Kouto,
Kamigohri, Hyogo 678-1297 Japanenergy of excited states 16g+ and 1'g from the groundstate. As the results, the energy of 1'g rose withincreasing pressure. On the contrary, the energy of
1 +6g fell down. This pressure behavior of 16g+
supports recent results of molecular dynamic
simulations [3], in which an insulator to semi-metaltransition has been suggested by overlapping between
the excited state and the ground state indirectly in the
momentum space.

Introduction
The properties of condensed molecular oxygen havebeen of considerable interest for many years becauseof its simple and fundamental molecular magnetism.
In order to understand the properties on the base of
the electronic structure of the molecule, the study ofelectronic spectra is indispensable. Our recent studies
on UV absorption spectra of condensed oxygen up to
13 GPa have revealed that a relatively strong
absorption band was observed above 5 eV insuper-critical fluid, and further the new UV band
constructed the valence band of the E solid phase [1].
The results suggest that the intermolecular interaction
plays a main role in the optical properties. Therefore,
we concentrate our attention on the high-pressure
behavior of two molecule absorptions.

1

Absorbance (arb.)

solid

Experimental
Liquid oxygen was loaded in the sample chamber ofa sapphire or diamond-anvil pressure cell and thepressure was regulated at 300 K based on a rubypressure scale. The typical thickness and diameter ofthe sample chamber were about 150 Pm and 300 Pm,
respectively. UV absorption measurements werecarried out over a range from 0.2 to 8 GPa using an
UV source at the BL1B and 7B beam lines.

8.1
6.2
(GPa)

0.5

5.8
5.5
4.8
4.5
2.51
0.98
(GPa)

fluid

0
21'g

1

6g+ 1'g

400

500

600

700

Wavelength (Å)

Fig. 1 Two-molecule absorption spectra at variouspressure at 300 K.

Results and Discussion
Figure 1 shows the absorption spectra of condensed
oxygen at pressures up to 8 GPa and at 300 K. The
absorption bands are due to two-molecule transitionsof 236g- Æ16g+ + 1'g (0-0) and 21'g (0-0, 1-0, 2-0)
and the values of wavelength of these bands are
consistent with those in liquid phase at ambientpressure. The absorption intensity increases withpressure in the fluid phase. The behavior of theintensity is also consistent with the previous result ina pressure range up to 35 atoms [2]. Sudden increasein the intensity is observed above solidificationpressure of 5.9 GPa. The increase in the intensity,
which was correlated with the behavior of the UV
absorption band at 5 eV, is suggestive of theenhancement of intermolecular interaction. The
relatively weak absorption of the 236g- Æ16g+ + 1'g(0-0) transition could not be detected in the solid
phase due to a strong absorption of diamond anvils.
Figure 2 shows the pressure dependence of the
wavelengths of the two-molecule absorption bands.
The wavelength of the 16g+ + 1'g (0-0) band isindependent of pressure while those of 21'g (0-0, 1-0,
2-0) bands show a blue shift. From these spectra data,
we could estimate the pressure dependence of the

650
fluid

Wavelength (nm)

600

21'g

0-0

solid

E

G

H

1-0

550

2-0

500
1

6g+ 1'g
0-0

450
0

5

10

15

Pressure (GPa)Fig. 2 Pressure dependence of the wavelengths of
two-molecule absorption bands.
[1] Y. Akahama and H. Kawamura, Chem. Phys. Lett.
392 (2004) 467.
[2] V. I. Dianov-Klokov, Opt. Spectrosc. (USSR) 16(1964) 224.
[3] S. Serra et al., Phys. Rev. Lett. 80 (1998) 5160.

66

BL1B

VUV Reflectivity Spectra of CaMoO4 and CaWO4 Crystals
M. Fujita1, S. Takagi2, N. Fujita2, T. Shimizu2, M. Itoh2
1
Japan Coast Guard Academy, Wakaba, Kure 737-8512 Japan2
Department of Electrical and Electronic Engineering, Shinshu University,
Nagano 380-8553 Japan

Tungstate family such as CaWO4 and PbWO4 isknown as an intrinsic scintillation material. Recently,
molybdate crystals attract much attention in the fieldof astro-particle physics for the detection of weaklyinteracting massive particles. Although extensive
studies have been reported on the luminescence
properties, reliable optical constants have not been
established for most of tungstate and molybdate
compounds. In a recent study we measured opticalanisotropy of scheelite PbWO4 crystals in detail andconfirmed important contribution of Pb states to theelectronic structures at the band edge [1].
The present paper reports anisotropic opticalproperties of CaMoO4 and CaWO4 as typical crystalsof alkaline-earth metal molybdate and tungstate withscheelite-type structure.

splittings of the t1 state and the e state due to the
crystal-field potential of S4 symmetry.
The structures in the region 2 are assigned to thetransition from the top of the valence band to the next
higher conduction band of t2 symmetry, which ismainly made of the Mo4d (W5d) state with somehybridization of the Ca3d state.
The optical transition in the region 3 is supposed toinclude the excitation from the valence band to the
conduction band of Ca 3d state.
(a)1

CaMoO42
3

E//c

Experiment
Reflectivity spectra were measured for polishedsurfaces of CaMoO4 and CaWO4 single crystals, withuse of the polarized light parallel to the a-axis (E//a)and c-axis (E//c). The orientation of crystal axis wasdetermined by means of a pair of crossed polarizer.

REFLECTIVITY (arb. units)

E//a

Results and Discussion
Figure 1 shows reflectivity spectra of CaMoO4 andCaWO4 at 8 K. Close similarity is observed between
the spectra in Fig. 1(a) and (b). The structures in Fig.
1 are calssified into three groups according to the line
shape and polarization dependence. In contrast to theexciton band in PbWO4 [1], the lowest band 1 in
CaMoO4 and CaWO4 is broad. The width of the band
1 for E//a is larger than that for E//c for both materials.
In the region 2, the dichroism is seen distinctly.
The energy positions of the main structures in Fig.
1 agree, as a whole, with those of previous studies[2-4], but there exists serious disagreement among
their relative intensities. We confirmed the data
reproducibilty by measuring the reflectivity spectra
on a cleaved surface of CaWO4 crystal; the obtained
result was almost the same as Fig. 1(b).
According to a theoretical calculation of theelectronic structures of CaMoO4 and CaWO4 [5], thevalence band is mainly built up of the O2p state andthe conduction band is composed of the Mo4d (W5d)
state. The molecular orbitals at the top of the valenceband and the bottom of the conduction band are of t1
and e symmetry, respectively, in MoO4 (WO4)oxyanion complex of Td symmetry. Both the t1 and estates split into two sublevels in the S4 symmetry ofscheelite crystal. The polarization dependence of thewidth of the band 1 would be attributed to the

0

0

5
(b)

10
1

15
CaWO4

2

3

E//c

E//a

0
0

5

10
PHOTON ENERGY (eV)15

Fig. 1 Reflectivity spectra of (a) CaMoO4 and (b)CaWO4 at 8 K.
[1] M. Fujita et al., Phys. Rev. B 65 (2002) 195105.
[2] R. Grasser et al., Phys. Stat. Sol. (b) 69 (1975)
359.
[3] I. A. Kamenskikh et al., Nucl. Instrum. Methods
Phys. Res. A 470 (2001) 270.
[4] V. B. Mikhailik et al., Phys. Stat. Sol. (b) 242(2005) R17.
[5] Y. Zhang et al., Phys. Rev. B 57 (1998) 12738.

67

BL1B

Characterization of Partial Discharge Degradation of
Polyamide-6 Nanocomposites by a Photoluminescence Analysis
N. Fuse1, M. Kozako2,3, T. Tanaka2, Y. Ohki1
1
Department of EEBS, Waseda University, Shinjuku 169-8555, Japan
2
Graduate School of IPS, Waseda University, Kita-Kyushu 808-0135, Japan
3
Kagoshima National College of Technology, Aira 899-5193, Japan

Experimental
The samples investigated are polyamide-6 nanocomposite with 5 wt% mica nanofillers (NC-5) andpolyamide-6 without nanofillers (PA). They are of asheet shape 60 mm u 60 mm u 1 mm. Using the IEC(b) electrode system, which consists of a rod and aplane stainless steel electrode, ac 60-Hz high voltage
was applied to the sample for 48 hours.
Using synchrotron radiation (SR) under multibunch operation at the BL1B line of UVSOR Facility(Institute of Molecular Science, Okazaki, Japan, beamenergy: 750 MeV) as a photon source, photoluminescence (PL) spectra from the sample before andafter degradation by PDs were measured. The PL
decay characteristics were measured by a single
photon counting method using SR under single-bunch
operation (SR duration: 0.55 ns, interval: 177 ns).
Furthermore, the crystalline structure was observed by
X-ray diffraction spectroscopy (XRD).

indicates that Na+ ions are present in the inter-layerregions [3]. When NC-5 was degraded by PDs, a newpeak appears around 8.5qas shown in curve (b)This
result suggests that the nanofillers were rearranged andpiled up in parallel with their surfaces with a mutual
distance around 1.0 nm. Such layered structures seemto contribute to the high durability against PDs of
NC-5.
Normalized PL Intensity

Polymer nanocomposites have been attracting muchattention as new materials that have high potential forwide applications. Therefore, we have been examining
the dielectric properties of polyamide nanocomposites,
focusing especially on their resistance against partial
discharges (PDs).

1

4

0.8

3

0.6
1

0.4
0.2
0

2
2

3
4
Detected Photon Energy [eV]Fig. 1 PL spectra excited by SR photons at 5.2
eV. Curve 1: NC-5 before degradation, 2: PA
before degradation, 3: NC-5 after degradation byPDs, 4: PA after degradation by PDs.

Results and Discussion
Intensity

In our previous work, surface observation using an
atomic force microscope shows superiority in PD
resistance of NC-5 to PA [1]. Fig. 1 shows PL spectra
excited by SR photons at 5.2 eV, before and after
degradation by PDs. Note that the PL intensities arenormalized by the height of the PL peak around 4.3 eV.
The spectral shape of the rather broad PL peak around
3.0 eV differs between the samples before and after thePDs, and the difference is much clearer in PA. The
decay profiles of the 3.0eV PLs observed in NC-5 andPA before and after the PD degradation agree with theprofile of an apparently similar PL peak at 3.0 eV
observed in polyethylene irradiated by an ArF excimer
laser. Since the PL in polyethylene originates frompolyenes induced in the degradation process [2], thePLs observed in NC-5 and PA should similarly
originate from polyenes. The result shown in Fig. 1
indicates that the number of polyenes induced by the
PD degradation is suppressed by the effect ofnanofillers. Fig. 2 shows XRD spectra obtained forNC-5 before and after the degradation by PDs. Curve(a) shows a diffraction peak around 9.5q, which

(a)
(b)
(c)
(d)

6

8

10
2T [deg]1214Fig. 2 XRD spectra of NC-5 before degradation(a), degraded by PDs (b), degraded by an active
plasma (c), and degraded by a weak plasma (d).
Since the volume of the sample differed among thesamples, the intensity cannot be directly compared.
[1] M. Kozako et al., IEEE Trans. Dielectr. Electr.
Insul., Vol. 11, No. 5 (2004) 833.
[2] T. Ito et al., IEEJ Trans. FM, Vol. 124, No. 7 (2004)
624.
[3] K. Yasue et al., Japan Plastics, Vol. 47, No. 6(1996) 100 (in Japanese).

68

BL1B

Luminescence Properties of Tl+ Centers Doped in KH2PO4
T. Fuyuki, N. Ohno
Division of Electronics and Applied Physics, Graduate School of Engineering
Osaka Electro-Communication University, Neyagawa, Osaka 572-8530, Japan.
1.0
INTENSITY (arb. units)

KDP:Tl+12 K

Cxyemissionexc. 5.66 eVCz

excitation
emi. 4.50 eV
Bxy

Axy

0.5
Az

E㼠c
E//c
0

4

Bz

5

6

7

8

PHOTON ENERGY (eV)Fig. 1 Luminescence (green), excitation of the
4.50 eV band (blue and red) and absorption(broken) spectra of KDP:Tl+ measured at 12 K.
350
KDP:Tl+exc. 5.66 eV

250

200

150
Tc

TEMPERATURE (K)300
INTENSITY (arb. units)

Ferroelectric material potassium dihydrogen
phosphate KH2PO4 (KDP) single crystals containinga small amount of thallium ions Tl+ exhibit fivecharacteristic polarized absorption bands Az, Axy, Bxy,and Cz in the ultraviolet region [1,2]. Symmetry of
the local crystal field at Tl+ ion which replaces thepotassium ion is approximately S4 in the ferroelectricphase. The observed experimental results have been
qualitatively explained by taking into account the
spin-orbit, crystal-field and electronic-vibrational
interactions [3].
In the present study, photoluminescence and photoexcitation spectra of KDP:Tl+ have been investigatedat the BL1B station at the UVSOR facility. The
optical measurements of CDP:Tl+ have been also
carried out. Single crystals of KDP and CDP
containing ~ 0.02 mol% Tl+ ions were grown by
slowly cooling a saturated aqueous solution at about
60°C after several times of recrystallization.
Figure 1 shows the luminescence (green solid
curve) and the excitation spectra (blue and red solid
curves) of KDP:Tl+ measured at 12 K. The broken
curve in the figure is the absorption-edge spectrum ofan undoped KDP for comparison [4]. A broad
luminescence band excited with 5.66 eV photons isobserved at 4.50 eV, showing a Gaussian lineshapeand a large Stokes shift. The excitation spectra for the
4.50 eV band for polarization E//c and E ӆc are
depicted by blue and ed solid curves, respectively. It
is found that the 4.50 eV band is induced under theexcitation of the A, B and C absorption bands
associated with impurity Tl+ ions [2,3]. The present
excitation spectra of the 4.50 eV band indicate thatthe 4.50 eV is originated from the relaxed excitedstates of the Tl+ ion.
Figure 2 shows the 4.50 eV luminescence spectra
at temperatures between 12 and 300 K. The excitation
was made with 5.66 eV photons (A band excitation).
The luminescence spectra exhibit a drastic change at
the ferroelectric transition temperature TC = 123 K;
the peak energy shows a high-energy shift withincreasing temperature at T  TC, and then an abrupt
low-energy shift above TC. The bandwidth has also
been changed drastically at TC. These results indicate
clearly that the relaxed excited electronic states of the
Tl+ ions are strongly influenced by the ferroelectric
local field due to surrounding ligand ions.

100

50
0
4.0

4.5

5.0

0

PHOTON ENERGY (eV)Fig. 2 Temperature dependence of the 4.50 eV
luminescence spectra of KDP:Tl+ at 12 to 300 K.
[1] I. Fujita, J. Phys. Soc. Jpn. 44 (1078) 275.
[2] I. Fujita, J. Phys. Soc. Jpn. 46 (1079) 1889.
[3] I. Fujita, Phys. Rev. B 49 (1994) 6462.
[4] T. Fuyuki and N. Ohno, UVSOR Activity Report
2003 (2004) 51.

69

BL1B

Luminescence of Bi3+ Ions Doped in NaYF4

T. Hirai1, K. Chong1, N. Ohno1, T. Kawai2, S. Hashimoto2
1
Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa
572-8530 Japan
2
Faculty of Science, Osaka Women’s University, Sakai 590-0035 JapanXe dimer (Xe2) discharge fluorescent lamps haverecently attracted much attention as alternative
lighting devices to conventional Hg discharge
fluorescent lamps. The Xe2 discharge generates
vacuum ultraviolet (VUV) light peaking at around
172 nm. For the practical use of Xe2 discharge
fluorescent lamps, it is necessary to develop new
phosphors that convert the VUV light efficiently into
blue, green and red light.
Oxide phosphors have been used in the Hg
discharge fluorescent lamps. In most of the oxide
phosphors, the VUV light below 200 nm is little
absorbed by the activators because of the absorptionof the oxide hosts, so that the conversion of the VUVlight is unlikely to be efficient. Most fluoride hosts,
by contrast, are transparent down to ~150 nm. Thus,
we expect that the fluoride phosphors are suitable foruse in the Xe2 discharge fluorescent lamps, because
the VUV light generated by Xe2 discharge (~172 nm)
can directly excite the activators.
Several groups have extensively studied electronictransitions in rare earth ions doped into fluorides [1].
Some of the rare earth ions such as Eu3+ show
absorption due to f n ĺ f n ( f - f ) transitions in the
VUV spectral region (150í200 nm). Since theabsorption due to the parity-forbidden f - f transitions
is weak, the conversion of the VUV light by thoserare earth ions is probably inefficient.
Metal ions with s2 electronic configurations ininsulating hosts, called Tl+-type impurity ions, exhibit
strong absorption due to parity-allowed s2 ĺ sptransitions at the longer wavelength side of the hostabsorption. The strong absorption by Tl+-type ions
may lead to efficient conversion of the VUV light.
However, Tl+-type ions in fluoride hosts have beenless investigated so far.
In the present study, we have investigatedluminescence and excitation spectra of Bi3+ ions
doped in NaYF4 by using synchrotron radiation at theBL1B of the UVSOR facility. The Bi3+ ions aretrivalent Tl+-type ions that easily substitute for Y3+
ions in NaYF4.
The right-hand side of Fig. 1 (350í600 nm) shows
the luminescence spectrum of NaYF4:Bi3+ excited at
172 nm at room temperature. One can see a broad
luminescence band peaking at ~430 nm. Thisluminescence band is attributed to the radiativetransitions from the relaxed excited states (3P1) to theground state (1S0) in Bi3+ ions. On the left-hand sideof Fig. 1 (100í350 nm), the excitation spectrum forthe luminescence band at 430 nm is shown. Several
excitation bands are observed at around 300, 250 and

Luminescence Intensity (arb. units)

200 nm. These excitation bands should arise from thetransition from the ground state to some excited states
given by the sp electronic configuration.
It is well known that Tl+-type ions doped in alkali
halide crystals with NaCl-type structure show threeabsorption bands originating from the intra-ionictransitions: A, B and C bands, named in sequence of
decreasing wavelength. The A, B and C bands havebeen assigned to the transition to 3P1, 3P0 and 1P1states, respectively. In Bi3+ ions doped in Cs2NaYCl6,
A and C bands have been observed at ~320 and 220
nm [2]. In Bi3+ ions in fluoride hosts, those absorption
bands would shift toward the shorter wavelength side,
as compared to those in chloride hosts. Accordingly,
we can attribute the excitation bands at 300 and 200
nm to A and C bands. However, the origin of thestrongest excitation band at 250 nm is unclear atpresent. Further experiments are needed to clarify theorigin. Finally, it should be noted that NaYF4:Bi3+
absorbs the VUV light generated by Xe2 discharge(~172 nm) due to the electric dipole allowed 1S0
ĺ1P1 transition (C absorption), and yields the blue
luminescence (~430 nm).

3+

NaYF :BiRT

4

detected
at 430 nm
0
100

200

300

excitedat 172 nm
400

500

600

Wavelength (nm)Fig. 1 Excitation (left) and luminescence (right)
spectra of NaYF4:Bi3+ at room temperature.
[1] R. T. Wegh, A. Meijerink, R-J. Lamminmäki, J.
Hölsä, J. Lumin. 87-89 (2000) 1002.
[2] A. C. van der Steen, phys. stat. sol. (b) 100 (1980)
603.

70

BL1B

Detection of Host-Guest Complexation at the Water Surface
by Photoionization Measurements

T. Ishioka, A. Harata
Department of Molecular and Material Sciences, Kyushu University, Kasugakoen 6-1,
Kasuga-shi, Fukuoka 816-8680, Japan
constant is estimated to be 14,000 M-1 by UV-VIS
absorption measurements while the ionophore does
not show any complexation in aqueous solutions. The
difference by solvents can be explained by inhibitionof host-guest complexation by hydrogen bonds withwater molecules.
Photoionization threshold of the ionophore at thewater surface depends which anion species is present
in the bulk solution (Table 1). Compared toperchlorate and sulfate, lower shift of photoionizationthreshold was observed when chloride and phosphatein the solution. The trend conincides with the generalaffinity of anions by hydrogen bondings that isevaluated to ClO4-<NO3-<Cl-<H2PO4-. These results
suggest that hydrogen-bonded complex is formed at
the water surface.
Photoionization threshold is known to relate withstandard electrochemical potential of the molecule. If
we assume that the state of molecular polarization bysurrounding molecules does not largely change bycomplexation and the difference is regarded as
constant value at the water surface, the complexation
constant can be evaluated by the shift ofphotoionization threshold. The shift of thresholdenergy for the complex with dihydrogenphosphate is
0.13 eV lower than the value of perchlorate and thebinding constant for the ionophore in radical cation
form is estimated 160 times larger than its neutral
form. The enhancement factor coincides with thevalue in acetonitrile and the molecular environment at
the water surface resembles in acetonirile.

Photocurrent has been measured at an
ionophore-modified water surface by synchrotron
radiation. Lower shift of photoionization threshold
was observed when guest anion (phosphoric acid) waspresent in the aqueous solution. It is suggested that
host-guest complex is formed at the water surface byhydrogen bondings.

Introduction
Threshold energy measurements of photoionization
at the water surface give useful information on electricstates and structures of adsorbed species [1].
Photoionization by SR light is convenient formeasuring precise threshold energy by its inherent
tunability in photon energy. However, it has not been
fully applied to the analysis of surface reactions suchas host-guest complexation at the water surface.
Host-guest complexation by hydrogen bonding isessential for molecular recognition in biologicalsystems and it is known that interfaces plays importantroles in enhancing such interactions. Air/waterinterface is one of such interfaces and specifichydrophobic nature has been reported by various
spectroscopic measurements such as sum-frequency
generation.
In
thisreport,neutralionophorefordihydrogen-phosphateionisspreadonanion-containing water surface and measure thresholdenergies for analyzing host-guest interaction that is too
weak to be measured in bulk aqueous solutions.

Experimental
The monochromated synchrotron light (4-8 eV) was
obtained from BL1B at the UVSOR facility andemitted from the chamber to a He-purged cell throughan MgF2 window. The emitted light was reflected onan Al mirror and vertically irradiated on the aqueous
solution surface through a Cu-mesh electrode. The
electrode was set at 5 mm high above the liquidsurface and high voltage (500 V) was applied. The
photocurrent (a 100 fA) was measured by apicoammeter.
An ionophore optimized for dihydrogenphosphate
recognition (Fig. 1) was synthesized from
2-aminoanthraquinone and dissolved in benzene at 0.2
mM. The benzene solution was spread by 10 µL on thesurface of aqueous solutions containing 0.1 M anion
species as acid solutions.

O

H
N

H
N

C8H17

S
O

Fig. 1
Structure of synthesized inophore fordihydrogenphophate recognition.
Table 1 Measured threshold energy of the ionophoreat the water surface with 0.1 M anion species insolution.
SoluteThreshold enegy / eV

None
HClO4
H2SO4
HNO3
HCl
H3PO4

6.03
6.12
6.13
6.08
6.04
5.99

Results and Discussion[1] T. Ishioka, A. Harata, UVSOR Activity Report
2003 (2004) 62.

Used ionophore shows 1:1 complexation withdihydrogenphosphate in acetonitrile and its binding

71

BL1B

Surface-Sensitive Variation of Reflection Spectra of ZnWO4
in the Exciton Band Region
M. Itoh1, N. Fujita1, S. Takagi1, T. Shimizu1, M. Fujita2, S. Oishi1
Faculty of Engineering, Shinshu University, Wakasato, Nagano 380-8553
2Japan Coast Guard Academy, Wakaba, Kure 737-8512
narrowness. This fact indicates that the Zn 3d andZn 4p states contribute, to some extent, to the topof the valence band and the bottom of the
conduction
band,
respectively.
Similarhybridization of the electronic states between
metal and WO42 ions has been confirmed
experimentally for PbWO4 [5]. The broad band(s)at around 6.0 eV is commonly observed in thetungstates and is assigned to the O 2poW 5dtransition.

As is well known, reflection spectra are very
sensitive to the surface condition of samples. Zinc
tungstate (ZnWO4) is not exceptional. To ourknowledge, its reflection spectrum was firstmeasured in 1999 [1]. Since then, two researchgroups have reported the reflection spectra ofZnWO4 [2-4]. However, there are some serious
discrepancies among their results.
We have continued reflection measurements ofZnWO4 at every opportunity for the past five
years. The results obtained during this period arereported in the present paper.
ZnWO4 has the wolframite structure (P2/c).
All the measurements were carried out fororiented crystals at 6 K. The SR light was incident
on the (010) face with the electric vector parallelto the crystal c-axis.

㩷

(a)

(b)

Figure 1 shows three reflection spectra ofZnWO4 in the 3-10 eV range. The spectrum (a)was measured for an as-grown surface of thecrystal obtained from Dr. Alov (Russia). This
specrum resembles those of Refs. [1,2]. The
spectrum (b) was measured for an as-grownsurface of the crystal grown by the flux method.
The curve (c) was recorded from the same surface
as that of (b) two years later, in substantial
agreement with the result of Ref. [3]. One may
see clear discrepany and change among thespectra (a), (b) and (c).
The crystal used for the measurement of (c) in
Fig. 1 was fleshly cleaved in the air. The
reflection spectrum of the cleaved surface isshown by the solid curve in Fig. 2, along with thetransmission spectrum (broken curve). This
reflection spectrum is similar to that of Ref. [4],although fine structures are more clearly seen
here. We believe that the result of Fig. 2 is themost reliable one.
In the tungstates, the valence band is mainly
built of the O 2p state and the conduction band iscomposed of the W 5d state. In Fig. 2, a clear
peak at 4.37 eV is reasonably attributed to thelowest exciton band originating in the cationictransition, because of the sharpness and

㩷

0

(c)
0

0
2

Results and Discussion㩷Experiment㩷

REFLECTIVITY (arb. units)

㩷

㩷

3

4
5
6
7
8
PHOTON ENERGY (eV)910Fig. 1 Reflection spectra of ZnWO4 crystals
with different surface condition.
REFLECTIVITY (arb. units)

㩷

0
2

3

4
5
6
7
8
PHOTON ENERGY (eV)

9

0
10

㩷
TRANSMITTANCE(arb. units)

1Fig. 2
Reflection (solid) and transmission(broken) spectra of a fleshly cleaved surface ofZnWO4 crystal.
[1] M. Itoh et al., UVSOR Activity Report 1999
(2000) 72.
[2] V. N. Kolobanov et al., SCINT99, Moscow
State Univ. (2000) 648.
[3] V. N. Kolobanov et al., Nucl. Instrum.
Methods Phys. Res. A 486 (2002) 495.
[4] V. Nagirnyi et al., Nucl. Instrum. Methods
Phys. Res. A 486 (2002) 395.
[5] M. Fujita et al., Phys. Rev. B 65 (2002)
195105.

72

BL1B

Photoluminescence of Hydroxyapatite Irradiated by Ultraviolet
Synchrotron Orbital Radiation Light

M. Ohta
Department of Material Science and Technology, Faculty of Engineering, Niigata University,
8050 Ikarashi 2-no-cho, Niigata 950-2181, Japan
Rare earth is used in various materials around us
until now, for example phosphors, magnetic materials,
catalyst, optical glass, and so on. Recently, rareearth is also useful as a contrast medium for magnetic
resonance imaging, restriction enzyme, biocatalyst,
and so on in fields of biochemistry, physiology,
medicine, etc. However, the behavior of rare earth in
the living body system remains an open question until
now. It was known that rare earth ions dosed for oral
administration to mouse and rat are transferred toblood vessel through the ileum and deposited its teeth
and bone, which mainly consists of hydroxyapatite(Ca10(PO4)6(OH) 2) [1-2]. We have found that Eu ion
substituted Ba ion in Eu doped Ba10(PO4)6Cl2
phosphor, which matrix is apatite structure [3]. In thisstudy, rare earth ion-doped hydroxyapatite samples
were prepared in order to make clear the segregation
mechanism of rare earth ion on teeth and bone. Theircharacteristics were investigated by photoluminescent
property of rare earth ion-doped hydoxyapatite
samples excited by ultraviolet synchrotron orbitalradiation light.
Gd-dopedhydroxyapatite
andYb-dopedhydroxyapatite samples were prepared as follows:hydroxyapatite was soaked in GdCl3 or YbCl3
aqueous solution. After 72 hr, Gd-doped or Yb-dopedhydroxyapatite was separated from GdCl3 or YbCl3
aqueous solution by filtation and then dried by usingwith infrared ray.The photoluminescent property ofeach sample exited by ultraviolet synchrotron orbitalradiation light (BL1B) was detected by using with amulti-channel analyzer.
Figure 1 shows photoluminescence spectra of rareearth ion-doped hydroxyapatite samples excited by
BL1B. The photoluminescent spectra of rare earth
ion-doped hydroxyapatite exited by 100 nm or 150
nm had many peaks which were not ascribed to rareearth ion. These facts indicates the traps of electron
and/or hole due to the defects of crystal structure exits
in rare earth ion-doped hydroxyapatite, since thephotoluminescent property is similar to that of self
doped phosphors.
The photoluminescent spectra of Yb-dopedhydroxyapatite exited by 200 nm or 250 nm had abroad peak due to charge transfer state (CTS) ĺ 2F2/5
of Yb3+ [4] or due to 4f135d1 ĺ 4f14 of Yb2+ [5]. On
the other hand, that of Gd-doped one are thought tohave not a peak due to Gd3+. These facts indicate theexistence of Yb3+ or Yb2+ as a lattice ion.
When hydroxyapatite particles were soaked in
GdCl3 or YbCl3 aqueous solution, the amount of Gd
ion deposited on the surface of hydroxyapatite

particles was less than that of Yb ion. Therefore, theexistence of Gd3+ as a lattice ion cannot be confirmed
from this experiment.

Emission intensity / Relative value

Gd-doped

300

400

500

600

700

800

500
600
700
Wave length / nm

800

Yb-doped

300

400

amplitude;: x 1,: x10

Fig. 1 Photoluminescent spectra of rare earth
ion-doped hydroxyapatite samples excited byultraviolet synchrotron orbital radiation light.

[1] S. Hirano, K. T. Suzuki, Environ. Health Perspect.
104 (Supplement 1) (1996) 85.
[2] K. Kostial, B. Kargacin, M. Lendeka, Int. J.
Radiat. Biol. Relat. Stud. Phys. Chem. Med. 51(1987) 139.
[3] M. Sato, T. Tanaka, M. Ohta, J. Electrochem. Soc.
141 (1994) 1851.
[4] F. C. Palilla, B. E. O’Reilly, V. J. Abbbruscato, J.
Electrochem. Soc. 117 (1970) 87.
[5] E. Nakazawa, J. Lumin. 18/19 (1979).

73

BL1B

Band-Structure Design of Fluoride Complex Materials
for Deep Ultraviolet Light Emitting DiodeR. E. Ouenzerfi1, A. Quema1, H. Murakami1, S. Ono1, N. Sarukura1, T. Nishimatsu2,
N. Terakubo2, H. Mizuseki2, Y. Kawazoe2, A. Yoshikawa2, T. Fukuda2
1

Institute for Molecular Science, Okazaki 444-8585 Japan
2
Tohoku University, Aoba-ku, Sendai 980-8577, Japan
ones. Compositions with equal lattice constants are
represented by straight dotted lines called equi-latticelines. From this chart, we can propose then-LiBaF3/Li0.875K0.125Ba0.876Mg0.124F3/p-LiBaF3 andn-KMgF3/Li0.870K0.130Ba0.847Mg0.153F3/p-KMgF3
double-hetero structure LD emitting in around 198
nm (6.25 eV). This structure will be sufficient forLED. With appropriate cavity design, LD will be also
feasible.
The LDA generally underestimates the width ofband gaps. The transmission edges of LiBaF3 andKMgF3 single crystals are estimated down to 126.3
nm and 121.5 nm from Fig. 2. For KMgF3 single
crystals, an absorption dip around 130 nm might be
attributable to defects of crystals. The transmission
edges are defined as absorption coefficient of 20 cm-1.
The transmission edges of LiBaF3 and KMgF3
correspond to energy band gaps of 9.8 eV and 10.2
eV, respectively. The measured band gaps of LiBaF3
and KMgF3 are 51% and 40% higher than calculated
values of 6.51 eV and 7.29 eV. From these results,
there is a possibility that complex fluoride opticaldevises operate with shorter wavelength than thatpredicted by ab initio calculation within the LDA.

There had been continuous efforts for thedevelopment of wide-gap solid-state optical devices
in the short wavelength region over these two decades.
The operating wavelength is basically limited by theband gap of materials and is controlled by selecting
the composition of complex materials. From thisviewpoint, the most prominent candidates arefluorides. The main advantage of fluorides is theirwide band gaps. Additionally, fluorides havewide-selection of complex materials, and are possible
to select the band structure, band gap and lattice
constant as predicted by Nishimatsu et al.
To determine the Li(1-x)KxBa(1-y)MgyF3 composition
suitable for the design of either a light emitting diodeor a laser diode; the energy gap, band structure andthe lattice constants of perovskite LiBaF3, LiMgF3,
KBaF3 and KMgF3 are needed. Band gap energy andband structure are determined by ab initio calculation
within the local density approximation (LDA) as
reported by Nishimatsu et al. [1]. The variation ofboth band gap energy and lattice constant as afunction of the composition is investigated in analogy
with a previous work on semiconductor compound
lasers reported by Sasaki et al. This study is
performed as in the case of Thompson and Woolley’s
work
for
mixed
semiconductors.
For
Li(1-x)KxBa(1-y)MgyF3 Perovskite fluoride, the band
gap energy can be written as follows :LiMgF3E = 5.97 eV
a = 3.807 A

6.25

6.75

6.50

7.00

R

'
E ī,LiR,(1- x)'K x MgF3  E ī,LiR,(1- x) K x BaF3

3.
98
9

ī, R, 'E Li
y  E ī,LiR,(1- x)'K x BaF3 (1 - y) (1- x) K x MgF3

*

5.25

4.75

where

6.50

R, '
R, '
E ī,KBaF
x  E ī,LiBaF
x 1- x 33

Į Li(1- x) K x BaF3
E

ī, R, '
KBaF3

E

ī, R, '
LiBaF3

LiBaF3E = 6.51 eV
a = 3.994 A

x 1- xR, 'R, 'E ī,KMgF
x  E ī,LiMgF
x 1- x 33

Į Li (1-x) K x MgF3
R, '
R, '
E ī,KMgF E ī,LiMgF
3
3

6.00

5.50

5.00
x
Li(1-x)KxBaF3

4.50

KBaF3
E = 4.24 eV
a = 5.002 A

Fig. 1 Variations of band gap energy structure andlattice constants of Li(1-x)KxBa(1-y)MgyF3 with respect
to composition.

2'
E ī,LiR,(1-x) K x MgF3

5.75

y 1- y2

E ī,LiR,(1- x)'K x BaF3

KBa(1-y)MgyF3

3.
99
4

E ī,LiR,(1- x)'K x Ba (1 y ) Mg yF3

y

6.25

6.25

Į Li(1- x) K x Ba (1 y ) Mg y F3

KMgF3
E = 7.29 eV
a = 3.989 A

x 1- x2andĮ Li (1-x) K x Ba (1-y) Mg y F3

Į KBa (1-y) Mg y F3  Į LiBa (1-y) Mg y F3 (1  x )Here, the energy gap sag ҏD is assumed here to be 0.3
as proposed by Thompson and Woolley. For thelattice constant of Li(1-x)KxBa(1-y)MgyF3, weconsidered that the variation follows the Vegard’s law.
Thus,
a Li (1-x) K x Ba (1-y) Mg y F3

Fig. 2 Absorption coefficient of LiBaF3 and KMgF3
compounds in ultraviolet region

a LiBaF3 (1 - x)(1 - y)  a KBaF3 x(1 - y)  a LiMgF3 (1 - x)y  a KMgF3 xy

The plot in Fig. 1 illustrates the quaternary chart
representing the variations of R, 'ᴾand *ᴾband gap
valleys. The thick solid lines on the plot representborders between either 'ᴾand *ᴾdomains or *ᴾand R[1] T. Nishimatsu et al., Jpn. J. Appl. Phys. 41 (2002)
L365.
[2] R. El Ouenzerfi et al., J. Appl. Phys. 96 (2004)
7655.

74

BL1B

Vacuum-Ultraviolet Reflectance Spectroscopy of Strongly CorrelatedElectron System

S. Miyasaka1, J. Fujioka1, Y. Tokura1,2,3
1
Department of Applied Physics, University of Tokyo, Tokyo 113-8656 Japan
2
Correleted Electron Research Center (CERC), National Institute of Advanced Industrial
Science and Technology (AIST), Tsukuba 305-8562 Japan
3
Spin Superstructure Project (SSS), ERATO, Japan Science and Technology Agency (JST),
Tsukuba 305-8562 JapanOne of the most important characteristics for thecorrelated electron systems is the drastic
re-construction of electronic structure over an energy
scale of eV with changes of temperature, doping
concentration, and/or external field. Therefore,
optical reflectivity measurement over a wide energy
range and the optical conductivity spectra derived
from the reflectivity spectra provide us with very
useful information about the strongly correlated
electron systems.
In this beam time, we measured the reflectivity
spectra of several transition-metal oxides, including V,
Cr, Mn, Fe and Mo, for an energy range of 4 eV < E <35 eV at room temperature using the beam line BL1B.
The measured reflectivity data, together with thelower-energy data below 4 eV, were used to derive
the optical conductivity spectra or dielectric function
via the Kramers-Kronig analysis. As an example, theimaginary part of the dielectric function of single
crystals of La1-xSrxVO3 with the several Srconcentration x, which are grown by a floating zone
method, is shown in Fig. 1.
La1-xSrxVO3 is one of the classic Mott transition
systems, although the single-crystal specimens
necessary for detailed optics measurements have beenlacking so far. The parent compound LaVO3 is a
Mott-Hubbard-type insulator with the V electron
configuration of 3d2, and undergoes a magnetictransition
fromaparamagnetictoanantiferromagnetic state, and also a structural phasetransition from orthorhombic to monoclinic follows
right below the magnetic transition temperature.
Sawada and co-workers have theoreticallydemonstrated that this compound in the monoclinic
structural phase and related compound, YVO3, havedifferent types of orbital ordering, the alternate
G-type dxy1dyz1/dxy1dzx1 electron configuration for
LaVO3 and C-type for YVO3. The carrier doping bysubstitution of La with Sr causes a transition from acorrelated insulator to a metal around x = 0.176. The
metal-insulator transition accompanies the structuralphase transition related to the orbital order-disordertransition. To clarify the change of the electronic
structure caused by the orbital-ordered Mott
insulator-metal transition, we have revisited
La1-xSrxVO3.
We present the spectra of the imaginary part of thedielectric function (İ2) for La1-xSrxVO3 samples withseveral Sr concentrations in Fig. 1. In the spectrum of
LaVO3 (x = 0), the lowest optical transition A around
2 eV can be assigned to the optical transition acrossthe Mott-type gap. Above the Mott gap, a much more
intense optical transition B is clearly discerned. The
position and intensity suggest that the transition be
assigned to the charge transfer excitation from O 2p
to V 3d upper Hubbard state. The transition isaccompanied by another spectral structure C, which is
1 eV above the transition B. Above 7 eV, three peakstructures, D, E, and F are observed. These absorption
bands are assigned to the transition from O 2p to La
5d or V 4s/4p state, that from O 2s to V 3d, and thatfrom La 5p to La 5d, respectively.
With the increase of Sr concentration x, theMott-Hubbard gap disappears. In addition, thesubstitution of La with Sr changes the peak shapearound 6 eV. The spectra for the insulating samples
with x = 0 and 0.10 show double structure around 5-6
eV. This feature is caused by the ligand field splittingof 3d orbitals, which tends to stabilize the orbital
ordering at low temperatures. In contrast, the double
peak-structure is not observed in the spectra for the
metallic sample with Sr concentration x = 0.18 and0.26. The present results indicate that even in thehigh-energy region above 5 eV, the Sr doping causes
the change of the spectral feature, which is related tothe metal-insulator transition and perhaps to theorbital ordering.
10

O 2p
ω
V 3d
C

8

O 2p
ω
D La 5dV 4s/4p

La 1-x Sr x VO 3
E//c-axis
x=0
0.10
0.18
0.26

ǭ2

6
B

4
2

0

O 2s
ω
V 3d EA

10
20Photon Energy (eV)

La 5p
‫ޓ‬ω
La 5d F

30

Fig. 1 The spectra of the imaginary part of thedielectric function (İ2) for insulating samples (black
curves, x = 0 and 0.10) and those for metallic ones
(red curves, x = 0.18 and 0.26) in La1-xSrxVO3.

75

BL1B

Vacuum Ultraviolet Spectroscopy of BaMgF4:Ce3+ Crystals

E. Hayashi1, K. Itoh1, M. Yamaga1, S. Ono2, N. Sarukura2
1
Department of Electric and Electronic Engineering, Gifu University, Gifu 501-1193, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan
Successful laser operation based on the 5d ĺ 4f
transitions of Ce3+ has been reported for LiYF4,
LiLuF4, and LiCaAlF6[1]. Recently, laser materials
operating below 200 nm is required. In order to satisfy
this requirement, a frequency doubling method using anonlinear effect is useful. Ce3+-doped BaMgF4(BMF)
crystals attract attention as laser materials with anonlinear effect. Recently, the BMF crystal growthand optical properties in the ultraviolet and visible
range were reported[2]. In this report, we discuss theenergy level of Ce3+ in BMF estimated from theoptical spectra extended to the vacuum ultraviolet(VUV) range[3].
Figure 1 shows a unit cell of the crystal structure of
BaMgF4. Each octahedron consists of a central Mg2+
ion and six nearest-neighbour F- ligand ions. Ba2+ ionsare located at centers of trigonal prisms, eachcomposed of six nearest-neighbour F- ligand ions. Ce3+
ions substitute for Ba2+ ions. In such a configuration,
the excited state of Ce3+ is split into Eg and T2g states
as shown in a lower part of Fig.1.
Figure 2 shows absorption, excitation, and emission
spectra of Ce3+ in BMF crystals measured at 17K inthe VUV, UV and visible ranges. There are threedifferent luminescence bands denoted by A, B, and C.
Each of these luminescence bands has double peaks.
The energy difference of the peak to peak is equal to
the ground-state slipping between 2F5/2 and 2F7/2 ofCe3+.
The excitation spectrum of the A-band
luminescence consists of five broadbands at 178, 197,
233, 245, 257 nm. These bands are coincident toabsorption bands. The peaks at 178/197 nm and
233/245/257 nm correspond Eg and T2g, respectively
as shown in Fig. 1. Similarly, the excitation spectrumof the B-band luminescence has five broadbands at
159, 228, 256, 294, 300nm. In order to identify peaksof the C-band excitation spectrum, we refer to optical
spectra of Ce3+:SrMgF4, of which crystal structure issimilar to Ce3+:BaMgF4. The peak of the C-band
excitation spectrum are 225, 259, 298, 325, 377 nm.
These results suggest the A-band luminescence isestimated to Ce3+ ions which substitute for Ba2+ ions.
The B-band luminescence is estimated to Ce3+ ionsperturbed by Na+ ions as charge compensators. The
C-band luminescence is assigned to a complex centerof Ce3+ and lattice defects which are different fromNa+.

Fig.1 A unit cell of the crystal structure of BaMgF4.
17K
Absorption

A

Excitation

Emission

Oem=300nm

Oex=258nm

B

Oem=350nm

Oex=299nm

C
Oem=420nm

100

200

Oex=160nm

300
400
500
Wavelength [nm]600

Fig.2 Optical spectra of Ce3+:BaMgF4.
[1] N. Sarukura, M. A. Dubinskii, Z. Liu, V. V.
Semashko, A. N. Naumov, S.L. Korableva, R. Y.
Abdulsabirov, K. Edamatsu, Y. Suzuki, T. Itoh, Y.
Segawa, IEEE J. Selected Topics Quantum Electron. 1(1995) 792.
[2] M. Yamaga, K. Hattori, N. Kodama, N. Ishizawa,
M. Honda, K. Shimamura, T. Fukuda, J. Phys.:
Condens. Matter 13 (2001) 10818.
[3] E. Hayashi, K. Itoh, S. Yabashi, M. Yamaga, N.
Kodama, S. Ono, N. Sarukura, J. Alloys andCompounds (2005) in press.

76

BL1B

Temperature Dependence of Reflectivity C60F18 Single Crystals

V. G. Stankevich1,2, A. M. Lebedev2, N. Yu. Svechnikov2, K. A. Menshikov2,
O. V. Boltalina3, L. N. Sidorov3,S.Kimura1, M. Hasumoto1
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan.
2
Russian Research Centre Kurchatov Institute,Kurchatov Sq.1,123182, Moscow, Russia.
3
Chemistry Department, Moscow State University,119899, Moscow, Russia.
ensemble of these polar molecules caused bydipole-dipole interaction. We have estimated the TC
value at first approximation. The interaction energy oftwo parallel identical dipoles is defined by [4]:Introduction
At present one of the most promising directions isthe developing and use of new carbon nanostructureswith sp2 hybridization – fullerenes, nana tubes and thinfilms based on these compounds. Special interest
represents investigations of fullerenes doped withdifferent atoms leading to considerable changing ofproperties. Doping with halogens, in particular withfluorine, is leading to strong changes of chemical andphysical properties. Additional interest for thesecompounds is connected with theoretical prediction[1] of significant decrease of penetration barrier forsome ions and atoms through the walls of carbon nanatubes due to fluorination. Therefore, within the last
few years we investigated fluorinated fullerenes
C60F2X with different amount of fluorine’s.
In Ref. [2], we have investigated optical propertiesof different thin films based on C60F48, C60F36, C60F24
and C60F18 molecules. It was established that opticalabsorption edge is shifting to the higher energy region(from 1.9 eV for pure C60 to 4.2 eV for C60F48) due todestruction of initial S-electron subsystem of pure C60
and creation of new V-orbital with C-F bonds. Besides
for these compounds we have observed unusualphotoluminescence temperature dependence.
All fluorofullerenes molecules are very large, withatomic masses exceeding 1000 amu and with sizes
about 1 nm. These nana objects manifested very
interesting molecular structures, having a spherical C60
skeleton, surrounded by appropriate amount of
attached fluorine atoms different symmetries.
Among these, special attention should be paid to a
C60F18 molecule due to a high asymmetry (Fig. 1) [3].

E

d2
(1)
R3

Where d – a dipole moment of molecule [D], R – a
distance between two dipoles [Å], E – energy [eV]. If
d = 10 D and R = 19 Å [3], the disorder temperature isfound to be TC = 112 K.

Results and discussion
Here we report first reflectivity spectra of the highquality C60F18 single crystals prepared via vacuum
sublimation. Figure 2 shows the reflectivity spectra
one of the rectangular plane size 100*60 microns2 withroom temperature and 50 K.
0.00350.0030C60F18 SC T(S)

Refl.Arb.Un.

0.00250.002050K

0.00150.0010300K
0.0005
2

4

6

8

10

12

14

E (eV)

Fig. 2

Reflection spectra C60F18 single crystal.

The main changes in reflectivity are observed forthe energy about 4 eV (typical for S-S* transitions)with shifting of reflection minimum to a low energyside, and for E > 8 eV for deeper electronic levels.
As a result, the observable changes of reflection
spectra are demonstrating the existence of theferroelectric phase transition; however the detailanalysis and calculations are in progress now.
[1] P. V. Avramov, B. I. Yakobson, G. E. Scuceria, T. A.
Romanova, IWFAC-2003 works (St. Peterburg,
Russia) (2003) 22.
[2] P. V. Dudin, S. V. Amarantov, V. G. Stankevich etal., Surf. Rev. Lett. 9 (2002) 1339.
[3] I. V. Goldt, O. V. Boltalina, L. N. Sidorov et al.,Sol. St. Sci. 4 (2002) 1395.
[4] F. Jona, D. Shirane, Ferroelectric crystals (Mir,
Moscow) (1965) 41.

Fig. 1 Molecule C60F18 structure.
As seen, 18 fluorine atoms occupy only one half of a
C60 deformed skeleton. This is leading to a high dipole
moment, and theoretical estimation [3] gives the value
about 10D. In principle it is possible to arrange aferroelectric ordering at the Curie temperature TC for77

BL5B, 7B&8B1

Excitation Spectra of VIS-UV Emission in AlGaN and InAlGaN
K. Fukui1, S. Hamada1, S. Naoe2, H. Hirayama3, H. Miyake4, K. Hiramatsu4
1
Research Center for Development of Far-Infrared Region,Fukui 910-8507, Japan
2
Faculty of Engineering, Kanazawa University, Ishikawa 920-1192, Japan
3
The Institute of Physical and Chemical Research, Wako 351-0198, Japan
4
Faculty of Engineering, Mie University, Mie 514-8507, Japan
AlGaN becomes a promising semiconductor opticalmaterial because of variable band gap energy from 0.8
to 6.28 eV according to composition ratio of elements.
However, the photoluminescence (PL) intensity at low
temperature is not sustained in increasing temperature
to RT. By contrast with this, InAlGaN gives theeffective rate of PL intensity at RT. Both studies of
AlGaN and InAlGaN PLs are necessary to explain themechanism of PL process in AlGaN.
All samples are made by MOCVD (MOVPE)
methods. The thickness of AlGaN thin films are about
1 Pm on 1 Pm AlN single crystal film with sapphire
substrates and those of InAlGaN thin films are about
80 nm on SiC substrates with Al0.2Ga0.8N buffer layers.
The measurements were carried out at BL7B, BL5B
and BL8B1, under multi-bunches operation in theenergy range from 2 to 500 eV. Same conventional 30
cm monochromator with liquid N2 cooled CCD
detector via optical fiber is used for PL measurementsof all samples.
In both AlGaN and InAlGaN, PL spectra arecomposed of two bands. One is UV band PL(B-emission) corresponding to exciton, the other isvisible (VIS) band (Y-emission) caused by latticedefects or impurities. Figs. 1 (a) and (b) show both Band Y-emission excitation spectra of Al0.34Ga0.66N and
In0.04Al0.35Ga0.61N, respectively. Intensity (verticalaxis) represents the integrated intensity per excitation
photon of B- or Y-emission calculated from PL
spectrum at each excitation photon energy. Eachspectrum is normalized for convenience. Arrows infigures represent of the peak position of B-emission
and almost correspond to the band-gap energies.
Since Y-emission is caused by the recombination
luminescence of electron and hole at trapping centersof defects or impurities, the excitation spectra of Yemission are expected to give the absorption spectra of
the samples originating from band-to-band transition.
In fact, the excitation spectra of both AlGaN and
InAlGaN Y-emission seem to be proportional to therate of absorption of the sample. Peak-like spectralfeature is only observed near band edge of AlGaN
B-emission. This result suggests that the initial state of
B-emission of AlGaN constructs some bound exciton
states. The tail-like structures at the lower excitationenergy side of InAlGaN relative to those of AlGaN
probably reflects the inhomogeneous special
dispersion of In element in InAlGaN alloy.
Fig. 2 shows the both excitation spectra of AlGaN
and InAlGaN in the starting area of inner shell
excitation. Since vertical axis (intensity) represents

the integrated intensity per excitation photon,
intensity increasing with increasing exciting photon
energy suggests that more than one electron-hole pairs
are produced during the relaxation process of an innershell hole from core to valence band, which is known
as photon multiplication.

Intensity (arb.units)(a)Al0.34Ga0.66N

Y
B

15K

(b)

In0.04Al0.35Ga0.61N

B

Y
15K
4.0

4.5

5.0

5.5

Photon Energy (eV)

6.0

6.5

Fig. 1 Photoluminescence excitation spectra of
Al0.34Ga0.66N (a) and In0.04Al0.35Ga0.61N (b) at BL7B.

(a) Al

Ga0.66N

15K

㩷(b) In0.04Al0.35Ga0.61N
㩷Intensity (arb.units)

0.34

15K
20

40

60

80

100

120

140

160

Photon Energy (eV)Fig. 2 Photoluminescence excitation spectra of
Al0.34Ga0.66N (a) and In0.04Al0.35Ga0.61N (b) at BL5B.

78

BL5B

Transmission Spectra of Amorphous Semiconductor Thin Films
in the Vacuum Ultra-Violet Region

K. Hayashi
Department of Electrical and Electronic Engineering, Gifu University, Gifu 501-1193, Japan
Amorphous chalcogenide semiconductor materials,
such as amorphous As2S3 (a-As2S3), amorphous
As2Se3 (a-As2Se3), and amorphous Se (a-Se) etc.,
exhibit a variety of photoinduced phenomena. The
application of these amorphous semiconductormaterials to the optoelectronic devices is very much
expected, because these materials are very sensitive
to the light. Although a large number of studies [1-3]have been done on the photoinduced phenomena ofthese amorphous semiconductor materials, little is
known about the details of these mechanisms. Thesephenomena were studied by exciting outer coreelectrons with the irradiation of light with the energy
corresponding to the optical bandgap or sub-bandgap.
The interest has been attracted for the change of the
optical properties in the energy region of the visible
light. Little attention has been given to photoinduced
effects by exciting inner core electrons with theirradiation of higher energy photon. We areinteresting for the change of the optical properties in
the higher energy region. To obtain a wide knowledgeof the photoinduced phenomena, it is necessary toinvestigate to the photoinduced effects on wide
energy region. In previous reports, we reported thephotoinduced change at the VUV reflection spectra of
the amorphous chalcogenide semiconductor films
induced by bandgap light. In present report, we report
the examination on the more exact measuring methodof the photoinduced change at the spectrum in the
VUV region. In this report, we measured the VUVtransmission spectra in amorphous chalcogenide
films.
Samples used for the measurement of transmission
spectrum were amorphous chalcogenide (a-As2S3 anda-As2Se3) semiconductor films. Thin films ofamorphous chalcogenide semiconductor wereprepared onto ultrathin collodion films by
conventional evaporation technique. A typical
thickness of an amorphous film was around 160 nm.
The ultrathin collodion films were prepared onto
stainless steel metal plates with a pinhole of the 1 mm
diameter. The transmission spectrum was measured
through the pinhole by a silicon photodiode. The
transmission spectra in the VUV region were
performed at room temperature at the BL5B beamline of the UVSOR facility of the Institute of
Molecular Science. In present experiment, toeliminate the higher order light from themonochromator, an aluminum thin film was inserted
between the monochromator and sample. We also
monitored the spectrum of the light source bymeasuring the photoyield of the gold mesh. The
transmission spectra were obtained by normalizing

the spectra by the spectrometer system response.
Figure 1 shows the VUV transmission spectrum of
a-As2Se3/collodion at room temperature in the
wavelength region between 15 nm and 35 nm. The
transmission spectrum of an aluminum filter with 100
nm film thickness supported by the metal mesh isalso shown in Fig. 1. In the figure, every transmission
spectrum has not been normalized by thespectroscopic system response, and that has beennormalized at the maximum value of the transmitted
light intensity. Two main absorption peaks of
a-As2Se3 were observed in this region. One
absorption peak around 22 nm corresponds to the 3dcore level of Se atom. Another absorption peakaround 28 nm corresponds to the 3d core level of As
atom. These peak positions agree well with the resultof the reflection spectrum [4]. In addition, it waspossible to also confirm the two peaks that
correspond to the core level of Se atom of 3d3/2 and3d5/2 in present measurement. At present, it is notpossible to obtain the accurate transmission spectrum,
because there is a problem on effect of higher order
light and reproducibility of the wavelength. It is
examined in respect of these at present. The detailed
experiments and analysis will be done in the next
step.

Inte nsity [a.u]G2M 4Al/mesh

a-As 2 Se 3 /collodion

15

20

25

30

35

Wave le ngth [nm]Fig. 1
Normalized transmission
a-As2Se3/collodion and Al/mesh.

spectraof[1] Ke. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] K. Shimakawa, A. Kolobov, and S. R. Elliot, Adv.
Phys. 44 (1995) 475.
[3] Ke. Tanaka, Encyclopedia of Nanoscience andNanotechnology 7 (2004) 629.
[4] K. Hayashi, UVSOR Activity Report 2002 (2003)
130.

79

BL6B(IR)&7B

Optical Response of CuIr2Se4

L. Chen1, T. Nanba1, T. Matsumoto2, S. Nagata3
1
Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan
2
National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305-0047, Japan3
Department of Materials Science and Engineering, Muroran Institute of Technology,
Muroran, Hokkaido 050-8585, JapanThe spinel compound CuIr2Se4 at atmosphericpressure is a metal at wide temperature range, but
undergoes a stabilization of the insulating phase athigh pressures above 3 GPa.[1,2] To study its
electronic state close to the Fermi level ambientpressure, we measured the temperature dependence of
optical reflectivity spectra R(Z) of polycrystalline
CuIr2Se4.

strengthen the hybridization between the 5d states of Ir
atoms belonging to the neighboring sites ,and the Ir 5d
and Se 4p states in CuIr2Se4 so as to form a clear
energy gap state at around EF. Thus, we consider thatin CuIr2Se4 the weak hybridization due to the larger
lattice constant might be the main reason that themetal-insulator transition does not occur atatmospheric pressure. The application of the highpressure to this compound will induce the clear
opening of the energy gap state because of the increasein the hybridization by the decrease in the lattice
constant.Such experiment is now on progress.

Experimental
The optical reflectivity spectra R(Z) at ambientpressure was measured in the wide photon energy
range from 7 meV to 30 eV in the temperature range of
8-300 K. The measurements were performed using a
Fourier-transform interferometer combined with athermal light source and synchrotron radiation sourceat the beam line BL6B & 7B of UVSOR. The opticalconductivity V1(Z)and complex dielectric function
H1(Z) were obtained from a standard Kramers-Kronigtransformation of the measured reflectivity spectrum.

-1

Wave Number (cm )
100
1.0

1000

10000

a

R

0.8

Results and discussions

0.6
0.4

Figure 1 shows the temperature dependences of the
R-spectra (upper panel) and V -spectra (lower panel)of CuIr2Se4 below 25 eV. The arrow in the V -spectra
shows the direction of cooling from 300 K to 8 K. In
the V -spectra, several distinct peaks corresponding
to electronic interband transitions were resolved ataround 0.2, 0.8, 2.0, 4.0, 6.5 and 13 eV, together with
the Drude component given by conduction electrons
below 0.2 eV. The Drude component still survived
even at 8 K but became narrower with cooling. The
peak intensity at around 0.2 eV increased instead of
the suppression of the Drude component with cooling
so as to compensate the spectral weight. The peaks
above 0.8 eV were almost insensitive to temperature.
We fitted the V -spectra below 3 eV with a
Drude-Lorentz model and estimated the carrier
densities ,for example, as 1.02 x 1021 cm-3 (300 K),
6.5 x 1020 cm-3 (80 K) and 4.6 x 1020 cm-3 (8 K). The
carrier density decreases gradually with cooling but isstill measurable even at 8 K.
CuIr2Se4 exhibits a broad peak structure at around
0.2 eV, which becomes distinct instead of the Drude
component with cooling. The development of a low
energy peak at around 0.2 eV accompanying the
suppression of the Drude component suggests the
precursor for the formation of the pseudo-gap state ataround EF with cooling at atmospheric pressure. Since
the lattice constant of CuIr2Se4 is larger than that of
CuIr2S4, temperature cooling is not sufficient to

0.2

300 K
180 K
120 K
80 K
8K

3

b

300 K

2

3

-1

-1

V(10 : cm )100000

1
8K

0
0.01

0.1

1

10 30

Photon Energy (eV)Fig. 1 Temperature dependences of (a) R (Z ) and (b)V (Z ) -spectra from 300 K to 8 K.
[1] J. Tang, T. Furubayashhi, T. Kosaka, S. Nagata,Y.
Kato and T. Matsumoto: Rev. High Pressure Sci.
Technol. 6 (1997) 496.
[2] J. Tang, T. Furubayashhi, T. Kosaka, S. Nagata, Y.
Kato and T. Matsumoto: Rev. High Pressure Sci.
Technol. 7 (1998) 362.

80

BL6B(IR)Metal-Nonmetal Transition of Bismuth Clusters

H. Ikemoto, S. Yoshida, A. Asai
Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
Raman-scattering measurements of clusters ofbismuth exhibit a phase transition from rhombohedral
Bi nanocrystalline to amorphouslike clusters
depending on cluster size [1]. They also suggest that
amorphous clusters are semiconducting and covalentinteractions increase with decreasing size.
The Raman studies are good tools but indirect
evidences for the transition. So it is very important toinvestigate the optical property directly to reveal themechanism of the phase transition. In the present
study we report results of optical absorption
coefficients for Bi clusters.

following mechanism of the phase transition fromsemi-metallic nanocrystalline to semiconducting
amorphous clusters. Even if the clusters are small, thethree-folded covalent bonds are similar with that of
the crystalline and the layer structures are reserved.
But the amorphousization of the thin films results inthe disappearance of the interlayer correlation. The
loss of the overlap between the orbitals in adjacentlayers gives rise to the bond shrinkage and thesemiconducting nature.


Experimental

PO
PO
PO
PO
PO
ET[UVCNNKPGD EO

Bismuth of 99.999% purity was slowly deposited
onto the substrates from a tungsten boat. The Bi film
was discontinuous with isolated island formation.
Then, KBr of 99.99% purity was deposited to cover
the Bi islands. By repeating these procedures, asample of Bi clusters isolated in an alkali-halidematrix was obtained. The size of the islands was
adjusted by controlling the thickness deposited on thesubstrates, which was monitored with a quartz
oscillator. The thickness ratio of the Bi and the matrix
is about 1:20. As mentioned above the Bi clusters areformed in thin films, and samples are represented bytheir average thickness of the Bi thin films in thispaper.
Measurements of optical absorption coefficientswere performed in the energy range of 0.05 a 0.95 eVwith the rapid-scan Michelson interferometer (Bruker,
IFS-66V) at the IR beam line (BL6B) by using a KBr
beam splitter. A HgCdTe detector was used.

















Photon Energy (eV)Fig. 1 Variations in optical absorption coefficientsof the as-deposited Bi clusters for different thickness.
Triangles denote those of polycrystalline [3].

[1] M. G. Mitch, S. J. Chase, J. Fortner, R. Q. Yu, andJ. S. Lannin, Phys. Rev. Lett. 67 (1991) 875-878.
[2] N. F. Mott and E.A. Davis, Electronic Progress in
Non-Crystalline
Materials,
SecondEdition(Clarendon Press, Oxford, 1979) p. 413.
[3] E.V. Potapov, Soviet Phys.-JETP 20 (1965) 307.

Results and Discussion
Figure 1 presents a representative set of curves forthe optical absorption coefficients of various
thickness films. Several of the characteristics can beseen by examining the absorption data by itself. The
absorption coefficients of the 300 nm and 10 nm thickfilms are close to those of bulk Bi, suggesting thatthese films are semimetallic. There is a noticeablechange in the optical behavior between the 10 nm
thick film and the 5 nm thick film. The absorption
coefficients of the 5, 2 and 0.5 nm thick films arerather small compared to those of bulk Bi, indicatingthat those films are semiconductors.
The optical absorption coefficients for Bi thin films
exhibit a phase transition from semi-metallic
nanocrystalline to semiconducting amorphousclusters with decreasing the size. The semimetallic
nature of rhombohedral Bi is attributed to the overlap
between the back lobes of orbitals in adjacent layers,
and the semiconducting nature of amorphous Bi is
attributed to the loss of this overlap [2]. We suppose

81

BL6B(IR)Terahertz Spectroscopy of a Kondo Semiconductor SmB6

S. Kimura1,2, S. Kunii3
1
UVSOR Facility, Institute for Molecular Scinece, Okazaki 444-8585, Japan2
Deparment of Molecular Structural Science, The Graduate University for Advanced Studies,
Okazaki 444-8585, Japan3
Department of Physics, Tohoku University, Sendai 980-8577, Japan
SmB6, which is a typical Kondo semiconductor,
has been studied over two decades. In the previous
studies, two different energy gap size were proposed,
one is about 5 meV and the other about 15 meV [1].
However, a recent study using higher purity samples
reveals that the lower energy absorption band
originates from impurities because the lower energy
absorption becomes small [2]. The higher energy gap
is concluded to be intrinsic and to originate from thehybridization between the localized Sm 4f state andthe Sm 5d conduction band, so-called cf hybridization[3]. In the case of the cf hybridization, the electronic
structure including the energy gap is rigid. However,the specific heat curve cannot be explained by therigid band model [4]. This means that there is thetemperature dependent part in the electronic structure.
On the other hand, the magnetic excitation at 14
meV grows up with decreasing temperature below 20
K observed by a neutron inelastic scattering [5]. Theenergy of 14 meV is similar to the energy gap
observed in optical spectra. Therefore if the cf
hybridization bands exist at the energy gap edge, thecharacter of carriers should have the same
temperaturedependence.
Opticalreflection
spectroscopy is one of good probe to investigate thecharacter of carriers. In SmB6 case, the signal fromthe thermally excited carriers appears in the terahertz
region. Then we measured the temperaturedependence of the reflectivity spectrum in theterahertz region.
Figure 1 (a) indicates the temperature dependenceof reflectivity spectrum of SmB6 by red marked lines.
At T = 5 K, the reflectivity at hQ = 1 meV is almost
constant less than unity. This indicates that thecharacter is insulating. With increasing temperature,
the spectral weight grows up from the lower energy
side. The spectral weight originates from the Drude
part due to thermally excited carriers. The Drude part
indicates the electronic structure thermally excitedarea near the energy gap edge.
The fitted function using one Drude and two
Lorentz functions are indicated by blue solid lines inFig. 1 (a). The fitting functions (the parameters are
not shown.) can reproduce the experimental curves
well. The obtained effective electron number (Neff)and relaxation time (W) derived from the fitting
parameters are shown as the function of temperaturein Fig. 1 (b). Neff cannot be explained by an activation
type behavior [ N eff v exp( 2 E g / k BT ) , where Eg is

Two-state model might be assumed to explain the
behavior [6]. On the other hand, W drastically changes
at 20 K. The temperature is coincident with that of thegrowth of the magnetic excitation at 14 meV. Thismeans that the thermally excited carriers relates to themagnetic excitation at 14 meV.
(a)(b)

Fig. 1 (a) Temperature dependence of reflectivity
spectrum of SmB6 in the THz region (red marks) andfitting functions by the combination of a Drude andtwo Lorentz functions (blue lines). (b) Obtained
parameters of the effective electron number (Neff) andthe relaxation time (W) of the Drude function as afunction of temperature.
[1] G. Travaglini and P. Wachter, Phys. Rev. B 29
(1984) 893.
[2] S. Kimura et al., Phys. Rev. B 50 (1994) 1406.
[3] G. Aeppli and Z. Fisk, Comments Condens.
Matter Phys. 16 (1992) 155.
[4] T. Kasuya et al., Valence Fluctuation in Solids,(North-Holland, 1981) p. 215.
[5] P.A. Alekseev et al., J. Phys.: Condens. Matter 7(1995) 289.
[6] B. Gorchunov et al., Phys. Rev. B 59 (1999) 1808.

the energy gap and kB the Boltzmann constant].

82

BL6B(IR)Millimeter Wave Reflection Measurements ofSecondary Battery Substance LixMn2O4

H. Ohta1, A. Taketani2, H. Ishikawa2, T. Hirano2, T. Nanba2, A. Hirano3, R. Kanno4
Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai, Nada, Kobe
657-8501, Japan
2
The Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada,
Kobe 657-8501, Japan
3
Faculty of Engineering, Mie University, 1515 Kamihama-cho, Tsu 514-8507, Japan
4
Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of technology,
4259 Nagatsuda, Midori, Yokohama 226-8502,Japan
1

The Li ion secondary battery substances LiCoO2and LiNiO2, are in the commercial use. LiMn2O4 is
also a promising material for the Li ion secondary
battery and it has attracted much attention recently.
We have been studying the millimeter wave reflection
measurements of LiCoO2 and LiNiO2 and related
substances using UVSOR to investigate thedynamical properties of Li ions [1-9]. The increase ofreflection is observed in the low energy region above
300 K for LiNiO2 and Li1-xCoO2. We proposed that
this increase of reflection is related to the motion of
Li ion in the system but it turned out to be flat in theobserved region for LiCoO2 [8]. LiMn2O4 is
considered as a new promising material for the
positive electrode of the Li ion secondary battery
from the economical point of view. Especially, areflection measurements of LixMn2O4 because itcorresponds to the recharge or discharge processes inthe Li ion secondary battery. Therefore, we performed
the millimeter wave reflection measurements of
LixMn2O4.
The reflection measurements of LixMn2O4 sinteredsample, in which the Li ion is extracted chemically,
with a diameter of 10 mm have been performed in the
spectra region from 5 to 60 cm-1 using the beam line
BL6B of UVSOR. As Li1-xMn2O4 is very fragile, thesurrounding of the sample is molded by the stycast.
The low pass filter was used in order to achieve themeasurement below 22 cm-1. The temperature waschanged from 77 to 380 K. The gold plate was used
as a reference and InSb detector was used as adetector.
Figure 1 shows the reflectivity results of LixMn2O4.
The data below 8 cm-1 is not reliable due to the low
reflection from the reference. We can see the increaseof the reflection in all temperature region from 77 to
380 K but the difference among the temperature is notclear. As Li1-xMn2O4 is very fragile, the surface
condition may not be so good as other samples like
LiCoO2 and LiNiO2. Therefore, observed increase of
the reflection is intrinsic or not remains as a future
problem.

0.40
LixMn2O4

Reflectivity

0.30

77K
197K
300K
340K
380K

0.20

0.10

0.00

0

5
10
15
Wavenumber (cm -1)

Fig. 1

Reflection spectra of LixMn2O4.

20[1] H. Ohta et al., UVSOR Activity Report 1996
(1997) 182.
[2] H. Ohta et al., UVSOR Activity Report 1997
(1998) 128.
[3] H. Ohta et al., UVSOR Activity Report 1998
(1999) 158.
[4] H. Ohta et al., UVSOR Activity Report 1999
(2000) 93.
[5] H. Ohta et al., UVSOR Activity Report 2000
(2001) 121.
[6] H. Ohta et al., Jpn. J. Applied Phys. 39, Suppl.
39-1 (2000) 409-410.
[7] H. Ohta et al., UVSOR Activity Report 2001
(2002) 138.
[8] H. Ohta et al., UVSOR Activity Report 2002
(2003) 142.
[9] Y. Nagasaka et al., J. Phys. Chem. Solids 64(2003) 1949-1951.

83

BL6B(IR)Far-Infrared Reflectivity Measurement of YbB12

H. Okamura1, S. Kimura2, T. Nanba1, F. Iga3, T. Takabatake3
1
Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan.
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan.
3
ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan.
YbB12 has been well known [1-3] as an example ofthe Kondo semiconductors [3-5]. It develops a smallenergy gap at the Fermi level below 80 K. The gap
width in YbB12 has been estimated to be 12.7 meV(136 K) from electrical resistivity [2], 15 meV (180K) from Hall effect [2], and approximately 15 meVfrom electronic specific heat and photoemission
experiments. The gap formation mechanism in the
Kondo semiconductor has been discussed extensively.
In the so-called band model, the gap is regarded as aband gap resulting from the hybridization between awide conduction (c) band and a flat f-electron band
[3-5]. Previously, we reported an optical study of
YbB12 single crystals [6]. The optical conductivity
spectrum, V Z of YbB12 clearly showed an energy
gap formation below 80 K. The gap development
involved a progressive depletion of V Z below ashoulder at a 40 meV. In addition, we observed astrong mid-infrared (mIR) absorption in V Z peaked
at a 0.25 eV, which was also strongly T-dependent.
However, the minimum photon energy of theprevious work was limited to about 8 meV (60 cm-1),
and the lowest temperature was 20 K.
In this work, we have measured V Z of YbB12
down to 1.3 meV (10 cm-1) at 8 K. Owing to therecent upgrade of the BL6B front-end optics, both thetotal photon flux and the photon flux density at the
sample position in the terahertz and far-infrared range(10 – 500 cm-1) have become much higher [8]. In
addition, a rapid-scan type Martin-Pupplet
interferometer has been newly introduced at BL6B.
Using this interferometer, the signal-to-noise ratio of
the obtained spectra has become much higher.
Figure 1 shows the measured optical reflectivity
spectra R(Z) and the optical conductivity spectra
V Z . V Z was obtained from R(Z) using the
Kramers-Kronig relations. As the gap develops in
V Z with decreasing temperature below 80 K, a
sharp minimum in R(Z) is observed to shift to lower
energy. This minimum is the plasma edge due to theDrude response of residual free carriers. Since thecarrier density decreases with gap development, theplasma edge shifts to lower energy. Previously, thisshift was observed only to 40 K [6]. However, here
we can observe it down to 20 K owing to theextended energy range of this work. In V Z , a clear
onset of conductivity (indicated by the red arrow in
Fig. 1) is observed at 15 meV at 20 and 8 K. This
onset of V Z is a direct result of the hump in R(Z),indicated by the blue arrow in Fig. 1. This onset
energy of 15 meV is identified as the gap width of

YbB12 manifested in V Z . The width of 15 meVagrees very well with those obtained by otherexperiments cited above. In the band model of Kondo
semiconductor, there are both indirect and direct gaps
in the c-f hybridization states near the Fermi level[4,5]. These results suggest that the gap in V Z is dueto the indirect gap. Since indirect transitions are
forbidden within the first-order optical processes, it islikely that phonon-assisted transitions give rise to theappearance of indirect gap in V Z of YbB12.

1.00
50 K
60 K
70 K

R(Z)

0.95

80 K
100 K
120 K

0.90
0.85

8K

V(Z) [00100 K

40 K
30 K

20
120 K

40

60

40

60

80 K

4

3

:-1cm-1]

20 K

6

YbB12

70 K
60 K
50 K

2 40 K
30 K
20 K

0

8K

0

20

Photon Energy (meV)Fig. 1 (a) Reflectivity spectra R(Z) and (b) opticalconductivity V Z of YbB12 at various temperatures.
[1] M. Kasaya, F. Iga, K. Negishi, S. Nakai and T.
Kasuya, J. Magn. Magn. Mater. 31-34 (1983) 437.
[2] F. Iga, N. Shimizu and T. Takabatake, J. Magn.
Magn. Mater. 177-181 (1998) 337.
[3] T. Takabatake et al., J. Magn. Magn. Mater.
177-181 (1998) 277.
[4] G. Aeppli and Z. Fisk, Comments Condens.
Matter Phys. 16 (1992) 155.
[5] P. S. Riseborough, Adv. Phys. 49 (2000) 257.
[6] H. Okamura et al., Phys. Rev. B 58 (1998) R7496.
[7] S. Kimura et al., AIP Conf. Proc. 705 (2004) 416.

84

BL6B(IR)Infrared Reflection Absorption Spectroscopy on Li-doped Alq3
Y. Sakurai1, S. Kimura1, T. Yokoyama2, K. Seki3
1
Institute for Molecular Science, Okazaki 444-8585 Japan
2
Faculty of Engineering, Chiba University, Chiba 263-8522 Japan
3
Research Center for Materials Science, Nagoya University 464-8602 Japan

Tris-(8-hydroxyquinoline) aluminum (Alq3) is mostwidely used as the electron transport/light emitting
layer in organic light emitting diodes (OLEDs). The
chemical structure of Alq3 and its two possible
geometrical isomers, meridional (C1 symmetry) andfacial (C3 symmetry) forms are shown in Figure 1. It
has been reported that the meridional isomer is thedominant species in most cases, including amorphousevaporated films.
A typical OLED consists of indium tin oxide (ITO)
as the anode, on which organic thin films aresequentially deposited, with low work function metals
such as Al finally deposited as the cathode. Recently, it
was reported that insertion of a thin layer of an
insulator such as LiF at the Al/Alq3 interface
significantly enhances electron injection. Various
mechanisms for this enhancement, including thecomplexation between Alq3 and Li released by thereaction between LiF and Al, have been proposed andinvestigated using various techniques [1,2].
Infrared Reflection Absorption Spectroscopy(IRAS) is a powerful probe for the structure andchemistry of the surface and interface. Though IR
spectrum below 1000 cm-1 is expected to besignificantly change by interaction between metal and
Alq3, it is difficult to obtain IRAS spectrum of thisregion using a globar source. In this paper, we report
the IRAS spectra of pristine and Li-doped Alq3
measured using synchrotron radiation (SR) source.

window and at an angle of incidence of 80° relative tosurface normal. The reflected light was detected withan MCT detector.
Figure 2 shows the IRAS spectra of Alq3 film of 20
nm thickness before and after lithium evaporation.
After Li evaporation, the observed spectra show thefollowing changes. Intensity of IR bands at 1500 and
1389 cm-1 becomes weak, new band appears at 520
cm-1, broad bands appear around 1535-1570 and
1250-1300 cm-1, band at 1471 cm-1 becomes broader.
These changes in the region between 1000 and
1800cm-1 are similar to those in the case of K
deposition on Alq3 [3]. The appearance of new bandat 520 cm-1 was newly detected by using SR source.
Figure 2 also indicates theoretically simulated
spectrum of Li-Alq3 complex in the meridional
isomer by DFT calculation with B3LYP functionaland 6-31G(d) basis set. The geometry optimization
was carried out starting from a geometry similar tothat reported by Curioni and Andreoni [4]. In themeridional isomer, the Li atom lies between ligands A
and B. The simulated spectrum agrees well with theobserved IRAS spectrum. The spectrum of Li-Alq3
complex in the facial isomer is expected to be more
simple and very different from that of meridional
isomer because of its symmetry (Li atom is on thethreefold symmetry axis) [4].
Since significant changes of IRAS spectrum are
expected in the region between 300 and 500 cm-1 by
the DFT calculation, more information will beobtained by IRAS measurement in the far-IR region.

B
N

N

Al
O

O

Li-Alq3 (mer)calculationNC(a) meridionalA

AbsorbanceO(b) facial

Fig. 1 The chemical structure and geometricalisomers of Alq3.

0.05

Li-doped
Alq3

pristine
Alq3

Experiments including the sample preparation andmeasurement were performed in an ultrahigh vacuum
chamber. Alq3 was supplied by Nippon Steel Chemical.
Ag film was deposited on Si (100) substrate from a
Knudsen cell. Alq3 film was prepared by vacuum
evaporation onto this Ag film kept at room
temperature. The thickness of Alq3 film was monitored
using a quartz microbalance. Lithium was depositedon the Alq3 films from a SAES getter source. IRAS
spectra were measured at BL6B of UVSOR. The
spectra were obtained with SR light through a KRS-5

600

800

1000 1200 1400
-1
Wavenumber (cm )

1600

1800

Fig. 2 IRAS spectra of pristine and Li-doped Alq3
and theoretically simulated IR spectrum of themeridional Li-Alq3 complex.
[1] M. G. Mason et al., J. Appl. Phys. 89 (2001) 2756.
[2] P. He et al., Appl. Phys. Lett. 82 (2003) 3218.
[3] Y. Sakurai et al., J. Appl. Phys. 96 (2004) 5534.
[4] A. Curioni and W. Andreoni, J. Am. Chem. Soc.
121 (1999) 8216.

85

BL7B

Optical Spectra and Electronic Structure of Calcium Fluorapatite

M. Kitaura1, S. Oishi2, M. Oda3, Y. Chikama3, H. Nakagawa3
1
Fukui National College of Technology, Sabae 916-8507 Japan
2
Dept. of Environmental Science and Technology, Shinshu University, Nagano 380-8553 Japan
3
Dept. of Electrical and Electronics Engineering, Fukui University, Fukui 910-8507 Japan
Calcium hydroxyapatite Ca5(PO4)3OH is of great
potential for applications in medical science, becauseof its biocompatibility. One of the peculiar propertiesof this material is the ability that incorporates various
cations and anions as constituents [1]. This property
comes from its crystal structure, in which calcium ion
and hydroxide ions are easily replaced by foreign
cations and anions, respectively. Actually, it is wellknown that the replacement of hydroxide ions byfluorine ions causes a preventive action in theoccurrence of dental cavities. The purpose of thisstudy is to understand the fluorination effect of
calcium hydroxyapatite in the viewpoint of electronic
structure. In this work, the spectra of absorption andreflectivity in calcium fluorapatite Ca5(PO4)3F grownfrom KF flux [2] have been measured at 9 K using a
3-m normal incidence monochromator at BL7B.

regarded as an indication of the band gap position.
Our experimental results can be almost explainedby the electronic structure of the model cluster
mentioned here. We further continue several
investigations for a detailed understanding of theelectronic structure of calcium fluorapatite andcalcium hydoxyapatite. On this basis, the changes in
the charge density and bond overlap population by
the fluorination effect will be cleared.

Results and Discussion
The spectra are shown in Fig. 1. As indicated by abroken curve, the absorption edge is located around6.01 eV. The lowest energy reflectivity peak appears
at 9.51 eV. This peak accompanies a shoulder
structure in the low energy side. They could not beclearly separated by varying the polarization of
excitation light. Several peaks are observed in theenergy range of 10-20 eV.
The electronic structure of calcium flourapatite wascalculated by the DV-XĮ method. The method has
successfully applied for understanding of theelectronic structure in organic and inorganic crystals.
The detail of this method has been described in ref.
[3]. Figure 2 shows the energy level diagram of aCa21(PO4)18F30 cluster embedded in the crystal lattice.
The valence band is primarily composed of the 2p
orbitals of oxygen. The 2p orbitals of fluorine also
includes in the upper valence band. The shallow corestates are made of the 2s orbitals of oxygen. On theother hand, the conduction band is complicated ascompared to the valence band. The bottom of the
conduction band is dominated by the 4s orbitals of
calcium. The band gap energy is estimated to be 9.47
eV.
From the calculated results, the electronictransition from the valence state of O 2p to the
conduction state of Ca 4s is expected in the region
near the fundamental gap, because this type of thetransition is of allowed type. Therefore, we assign the9.51 eV peak to the O 2p ĺ Ca 4s transition. A dip is
located at 10.04 eV in the high-energy side of the9.51 eV peak. The energy is in good agreement withthe calculated band gap energy, so the dip is probably

㩷

REFLECTIVITY (arb. units)

Ca5(PO4)3F
9K

5

10

15

20

25

30

PHOTON ENERGY (eV)Fig. 1 Reflectivitiy (solid curve) and absorption(broken curve) spectra of calcium fluorapatite at 9 K.

20

0

㩷

ENERGY (eV)

10

-10
-20
TOTAL

4s 4p
Ca

3s

3p 3d
P

2s

2p
O

2s

2p
F

Fig. 2 Energy level diagram of a Ca21(PO4)18F30
model cluster embedded in the crystal lattice of
calcium fluorapatite.
[1] For example, J. C. Rendon-Angeles, K.
Yanagisawa, N. Ishizawa and S. Oishi, J. Solid State
Chem. 151 (2000) 65.
[2] S. Oishi and T. Kamiya, J. Chem. Soc. Jpn. (1994)
800 (in Japanese).
[3] H. Adachi, M. Tsukada and C. Satoko, J. Phys.
Soc. Jpn. 45 (1978) 875.

86

BL7B

Vacuum UV Reflectivity Spectroscopy of PZT and LNO

J. Mistrik1, T. Yamaguchi1, N. Dai2, M. Shimizu3
1
Research Institute of Electronics, Shizuoka University, Hamamatsu 432-8013 Japan
2
National Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese
Academy of Sciences, Shanghai 200083 China
3
Division of Electronic Materials and Devices, Department of Electrical Engineering andComputer Sciences, Graduate School of Engineering, University of Hyogo, Himeji 671-2201
Japan
Perovskite-type oxides Pb(ZrTi)O3 (PZT) and
LaNiO3 (LNO) are interesting materials for both
applied and fundamental research. In spite of this,
there are only a few papers devoted to its opticalproperties. Recently we have reported spectroscopic
ellipsomety studies on LNO and PZT thin films
performed in visible and near UV spectral regions[1,2]. Our further effort is focused on thedevelopment of a new dispersion model for thesematerials based on parameterization of the joint
density of the electronic states in the vicinity of thevalence and conduction bands [3,4]. Therefore, ourbeam time was used to record the UV and vacuum
UV reflectivity spectra of PZT and LNO samples.
Polycrystalline PZT films were deposited bysol-gel and MOCVD on LNO/Pt/Ti/SiO2/Si seedstructure and platinized Si substrates Pt/SiO2/Si
respectively. Thin monocrystalline PZT film wasgrown by MOCVD on SRO/STO substrate. For the
study of LNO reflectivity the seed structure for PZT
films, LNO/Pt/Ti/SiO2/Si, was used.
Selected spectral range (6 - 25eV) from UVSOR
synchrotron radiation was scanned by the 3-m normal
incidence monochromator (beam line 7B). Two
monochromator gratings G2 (600 l/mm) and G1(1200 l/mm) and LiF filter were used to cover thestudied spectral range. Incident and reflected lightintensity was measured in room temperature by a Si
photodiode. Angle of incidence was less then 15 deg.
Fig. 1 presents selected reflectivity spectra of
sol-gel deposited polycrystalline PZT and LNO films.
Reflectivity in the visible and near UV spectral
ranges was carried out by spectrophotometer
PerkinElmer Lambda 45 and these data were used asa reference to adjust the absolute reflectivity values of
UV and vacuum UV ranges. The spectral features up
to about 5 eV come from the light interference in PZTand LNO films which thickness is 217 nm and 96 nm,
respectively. Obtained reflectivity spectra are typicalfor transition metal oxide compounds withperovskite-type structure [5]. Detailed discussion of
PZT and LNO electronic structure demand theknowledge of their electronic permittivity spectra andtheir parameterization by joint density of electronic
states. This will be done in forthcoming paper.

[1,2] G2+LiF G2

G1

0.5

PZT

Reflectivity

0.4
0.3
0.2
0.1
0
0.4

Reflectivity

0.3
0.2
0.1

LNO
0
0

5
10 15 20
Photon Energy [eV]25

Fig. 1 Reflectivity spectra of PZT and LNO films[1] D. Franta, I. Ohlidal, J. Mistrik, T. Yamaguchi, G.
J. Hu, and N. Dai, App. Surf. Sci. 244 (2005)
338-342.
[2] J. Mistrik, T. Yamaguchi, D. Franta, I. Ohlidal, G.
J. Hu, N. Dai, App. Surf. Sci. 244 (2005) 431-434.
[3] D. Franta, B. Negulescu, L. Thomas, P. R. Dahoo,
M. Guyot, I. Ohlidal, J. Mistrik, and T. Yamaguchi,
App. Surf. Sci. 244 (2005) 426-430.
[4] D. Franta, I. Ohlidal, M. Frumar, J. Jedelsky, App.
Surf. Sci. 212-213 (2003) 116-121.
[5] T. Arima, and Y. Tokura, J. Phys. Soc. Jap. 64(1995) 2488-2501.

87

BL7B

VUV Absorption Spectroscopy of SiO2 Thin Film
K. Nakagawa, H. Mikami, T. Ishikawa, Y. Shiraishi,
A. Ejiri, H. Matsumoto, S. Matsumoto
School of Science & Technology, Meiji University, Kawasaki 214-8571 Japan
We calculate energy levels of SiO2 by the DV-X D
molecular orbital method. From the results ofcalculation, the valence band (VB) is almost
composed of the O 2p orbital, which consists of twoparts, lower part and higher part. And the lowest
conduction band (CB) is composed of mixed orbitalof Si 3s, Si 3p and Si 3d. It is found that the higher
VB is very tight structure. Therefore, the sharp peaksin the region of near the fundamental absorption gap
may be the transition from O 2p to mixed orbital of
3s, 3p and 3d in Si.

-1

Absorption Coefficient (cm )Absorption spectrum of silicon dioxide (SiO2) thinfilm was studied in the VUV region with synchrotron
radiation. Refractive index and extinction coefficientwere carried out from Kramers-Kronig transformation
using absolute values of absorption coefficientsobtained from the experiment. It is necessary for
accurate simulation to know absorption coefficientsin higher photon energy region. On the basis of
optical property of SiO2, absorption spectrum in UV–VUV region is particularly important because of highband gap energy. Reflection spectrum of SiO2 hadbeen report by Philipp et al. [1], but the absorption
spectrum of SiO2 has not been studied. We report theabsorption spectrum and optical constants n and N
of SiO2 thin film up to 30 eV.

5

10

20

Experimental

㪛

15

The SiO2 thin film was prepared by RF magnetron
sputtering method. The SiO2 plate with 99.99% purity
was used as a target and the sputtering was carriedout in argon gas under a total pressure of 0.8 Pa. The
film was sputtered onto thin substrate of collodion atroom temperature and the incident RF power of 100
W. The film thickness was about 15 nm.
The absorption spectrum of SiO2 thin film wasmeasured in the vacuum ultraviolet region up to 30
eV with the 3-m normal incident monochromator(grating: G1 and G2) at BL7B of UVSOR-II. And
silicon photodiode sensor was used as a detector forthe transmission light.

㪜
㪙 㪚
㪘

10
5
0

0

5

10

15

20

25

30

Photon Energy (eV)Fig. 1 Absorption spectrum of SiO2 thin film in theregion from 3 to 30 eV at room temperature.
2.5

3.0

Figure 1 shows absorption coefficient of SiO2 thinfilm at room temperature. The peaks are named asindicated in the figures for convenience. Five peaks
named as A, B, C, D and E were observed at about
10.5 eV, 11.9 eV, 14.1 eV, 17.6 eV and 21.0 eV,
respectively. One can see that peaks A, B, and C(below 15 eV) were characteristic sharp structure.
Similar peaks have been found at the near position in
the reflectance spectra of crystalline SiO2 and fused
SiO2 reported by Philipp [1].
The optical constants were evaluated by the
Kramers-Kronig analysis. Figure 2 shows therefractive index n and the extinction coefficient N
of SiO2 thin film obtained by the Kramers-Kronig
analysis from the absorption spectrum withexperimental data. Refractive index and extinction
coefficient obtained from experiment were measured
with ellipsometer in the range from 1.5 eV to 5.0 eV.
Comparing theoretical value and experimental valueof optical constants, both values were good agreed
with each other.

2.5

2.0
Expt.

2.0

1.5

1.5

1.0

N

1.0

0.5

0.5
Expt.

0.0

0

5

10

15

20

25

㩷

Refractive indexnExtinction coefficient

Results and Discussion

0.030

Photon energy (eV)Fig. 2 Refractive index n and extinction coefficient
N spectra of SiO2 thin film obtained by
Kramers-Kronig analysis from the absorption
spectrum.
[1] H. R. Philipp, Solid. State. Commun. 4 (1966) 73.

88