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BL6B

Infrared Reflection-Absorption Spectroscopy of Alq3 Thin Film on Silver
Surface Using Synchrotron Radiation

Y. Sakurai1, S. Kimura1,2, K. Seki3
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan2
Department of Structural Molecular Science, The Graduate University for Advanced Studies,
Okazaki 444-8585, Japan3
Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8602, Japan
study of the Alq3 isomers by Cölle et al. using thefacial isomer isolated in the pure form [5]. For thevibrational modes within the ligands observed in thewavenumber region above 700 cm-1, the differencesof the spectra between isomers appear only in thewidth of the absorption peaks. On the other hand,significant differences appear in the stretching modes
around the central Al atom, namely, Al-N and Al-O
stretching modes in the wavenumber region below
600 cm-1. Therefore these modes become goodprobes to distinguish the isomers. In this study, we
examined whether the facial isomer exists at theinterface between the Ag and the Alq3 film or not by
infrared reflection-absorption spectroscopy (IRAS)
using a synchrotron radiation (SR) light source. Useof highly brilliant infrared synchrotron radiation(IRSR) source enables us to obtain IRAS spectra in
the low wavenumber region, which cannot be coveredby conventional IRAS system using globar lightsource because of its low brilliance.
The SR-IRAS experiments were performed at an
infrared-to-terahertz beamline BL6B of UVSOR-II.
SR-IRAS system consists of an ultrahigh vacuum(UHV) chamber with evaporators (for Ag and Alq3),
focusing optics and a detector.
Horizontally
polarized parallel IRSR from a Michelsoninterferometer (Bruker IFS66v) is guided to an
off-axis parabolic mirror with the focal length f of
152.4 mm to be focused on the sample surface with
the incident angle of 80° relative to the surface
normal. The reflected light is collected by thesecond off-axis parabolic mirror (f =152.4 mm) andguided to the third off-axis parabolic mirror (f =101.6mm) to be focused on the detector. The UHVchamber is separated from the low vacuum of the
focusing and collecting optics chambers by KRS-5
windows. The base pressure of the UHV chamber
was below 5 x 10-7 Pa.
The Ag surface was prepared by vacuum
evaporation on Si substrates (20 x 7 mm2) using a
Knudsen cell.
Deposition of Alq3, which was
supplied by Nippon Steel Chemical Co., Ltd., wasperformed using a glass crucible coiled with atungsten wire heater. The Ag surface was kept atroom temperature during the deposition of Alq3.
The thickness of Alq3 film was monitored using a

Recently, organic semiconductors are attracting
attention because of possible applications toelectronic devices such as organic light emitting
diodes(OLEDs).
In
OLEDs,
tris(8-hydroxyquinoline) aluminum (Alq3) is mostwidely used as the electron transport/light emitting
material [1]. Alq3 has two possible geometricalisomers of meridional (C1 symmetry) and facial (C3symmetry) forms. In the meridional isomer, thethree ligands around the central Al atom are notequivalent (Fig. 1(a)), while they are equivalent in the
facial isomer (Fig. 1(b)). It has been reported thatthe meridional isomer is dominant in evaporated films[2]. However, in the case of Alq3 molecules
adsorbed directly on an Al surface, the facial isomeris predicted to be more stable than the meridional one
by a theoretical investigation [3]. Since the facialisomer generally acts as an electron trap in
amorphous film [4], this isomer may become an
obstacle for the charge transport in the device [3,4].
Thus it is important to find whether facial isomer
exists at the interface between the metal and the Alq3
film or not.
Vibrational spectroscopy such as infrared (IR)
spectroscopy is suitable technique for distinguishingthese isomers. There is already an IR spectroscopic

Fig. 1. The chemical structure and geometricalisomers of Alq3.

73

Highlight
facial isomer, on the other hand, the intensity of thepeak around 398 cm-1 is expected to be almost half ofthat of the peak at 423 cm-1 [5], and this peak should
be observed above the noise. In the spectrum of 1
nm thickness, however, no peak is observed at 398
cm-1, and we can conclude that the meridional isomer
is dominant even for the 1 nm thickness.
In the spectrum of the Alq3 film of 1 nm thickness,the observed frequency of the Al-N stretching mode
is slightly lower than that in the spectra of multilayer
Alq3. Similar “softening” of vibrational mode has
been observed in the CH stretching mode of n-alkane
adsorbed on metal surfaces, and it is ascribed to thesmall electron transfer from the metal to the molecule[6,7]. Moreover, DFT calculations by us show thatthe frequency of the Al-N stretching mode of Alq3
anion is lower than that of Alq3 molecule. Therefore
the softening in the Alq3/Ag system may originate
from the small electron transfer from Ag to Alq3
molecule. The observed much smaller frequency
shift of the Al-N stretching mode of Alq3 (3 cm-1)
than that of the CH stretching of n-alkanes (~100
cm-1) might be understood by the larger distance
between the central part of the Alq3 and the Ag
surface than that between the CH bond of flat-lying
n-alkane molecule and the metal surface.
To summarize, thin Alq3 films deposited on an Ag
surface were investigated by IRAS using a
synchrotron radiation light source. The observed
IRAS spectra indicate that the Alq3 film
predominantly consists of meridional isomerincluding the first monolayer adsorbed on the Ag
surface. In the spectrum of monolayer Alq3, Al-N
stretching mode slightly shifts to the lower
wavenumber side than that of multilayer Alq3,
possibly due to the charge transfer between the Alq3
and Ag surface.

Fig. 2. The thickness dependence of the IRAS spectraof an Alq3 film on Ag surface.
quartz microbalance.
SR-IRAS spectra wereaccumulated with a 6m-mylar beamsplitter in the
Bruker system and a liquid-helium-cooled Sibolometer. Five (for 1 nm thick sample) or three(others) spectra of 100 scans each with a resolution of
2 cm-1 were averaged.
Figure 2 indicates the thickness dependence of the
IRAS spectra of an Alq3 film deposited on an Ag
surface. In the spectrum of the film of 1 nm
thickness, corresponding to nearly one monolayer, apeak at 420 cm-1 with a shoulder at 423 cm-1 isobserved. With increasing thickness of Alq3, peaks
at 423 and 460 cm-1, which are assigned to the Al-N
stretching and pyramidalization modes of the nitrogenatoms [5], respectively, increase their intensity.
There are also other Al-N stretching andpyramidalization modes with different phase relation
among the ligands (for example, three Al-N bonds
stretch in-phase or out of phase) from thosementioned above, and they appear as weak peaks at
398 and 405 cm-1 (Al-N stretching) and 446 and 468
cm-1 (pyramidalization) modes, respectively [5].
Considering the central AlO3N3 fragment, themeridional isomer has three Al-N stretching modes
with different frequencies, while the frequencies of
the corresponding modes in the facial isomer are split
into two, with one of them doubly degenerated
because of the C3 symmetry [5]. All of them are
infrared active. The observed spectra of the Alq3
films, except for the one with 1 nm thickness, show
three Al-N stretching modes at 398, 405 and 423 cm-1.
This indicates that the evaporated Alq3 film
predominantly consists of the meridional isomer asreported before [2]. In the IRAS spectra of the filmof 1 nm thickness, two Al-N stretching modes at 397
and 405 cm-1 can not be observed. This can beunderstood if the molecules in the meridional form,
since the estimated intensities of these peaks is only
about 20% of that of the peak at 420 cm-1 [5], whichis the same level as the noise. In the case of the[1] C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett.
51 (1987) 913.
[2] M. Brinkmann et al., J. Am. Chem. Soc. 122(2000) 5147.
[3] S. Yanagisawa and Y. Morikawa, Chem. Phys.
Lett. 420 (2006) 523.
[4] A. Curioni, M. Boero, and W. Andreoni, Chem.
Phys. Lett. 294 (1998) 263.
[5] M. Cölle et al., Phys. Chem. Chem. Phys. 5(2003) 2958.
[6] M. Yamamoto et al., J. Phys. Chem. B 104 (2000)
7363.
[7] Y. Hosoi et al., Surf. Sci. 515 (2002) 157.

74

BL1B

Vacuum Ultraviolet Spectroscopy of Heavily Boron-Doped Diamonds
O. Arimoto1, D. Gotoh2, T. Katagiri3, T. Aoki3, D. Iri3, M. Itoh3
1
Department of Physics, Kyoto Pharmaceutical University, Kyoto 607-8412, Japan
2
Graduate School of Natural Science and Technology, Okayama University,
Okayama 700-8530, Japan3
Department of Electrical and Electronic Engineering, Shinshu University,
Nagano 380-8553, Japan

Diamond is known as a band insulator of indirecttype with a wide band gap of 5.5 eV [1,2]. By theslight doping of boron, it becomes a p-type semiconductor, making a shallow acceptor level above the
top of the valence band with an activation energy of~0.37 eV. With increasing boron concentration
beyond the critical value nc~21020 cm-3 for the
metal-insulator (MI) transition, the boron-doped
diamond shows metallic character. Recently, Ekimov
and coworkers have found superconductivity in theheavily boron-doped diamond synthesized byhigh-pressure high-temperature (HPHT) method [3].
Subsequently, studies on the superconductivity usingfilms made by a microwave plasma-assisted chemical
vapor deposition (MPCVD) method confirmed reproducibility of the superconductivity [4]. The MPCVD
method is a useful technique to control the boron
density in a wide range. In order to understand theelectronic structure and the mechanism of thesuperconductivity in heavily boron-doped diamond,various theoretical proposals and experiments such as
angle-resolved photoemission spectroscopy [5] havebeen performed. However, systematic measurementof the fundamental optical spectra has not been done
so far.
In the present study, we have performed measurements of vacuum ultraviolet reflection spectra of pureand heavily boron-doped diamonds. The top ofvalence band and the bottom of conduction band ofpure diamond locates at the  point and the X point in
the Brillouin zone, respectively [1,2]. The reflection
spectrum is characterized by the reflection peaks at
7.4 eV and 12.6 eV. The former corresponds to thedirect transition at the  point, while the latter to thedirect transition at the X point [1,2] .
All the samples used in the present study were
supplied from the Kawarada’s laboratory, Waseda
University. Heavily boron-doped epitaxial diamondfilms were grown on the type Ib diamond substrates
by using the MPCVD method. Figure 1 showsreflection spectra of pure and heavily boron-doped
diamonds around the direct transition at the X point.
Measurements were done at room temperature. The
spectra (a) and (b) are for the single crystals of purediamond (type IIa) and type Ib diamond, respectively,
grown by HTPT synthesis. The spectra (c) to (e) arefor the heavily doped samples. Boron concentrationsof the samples B65, B67, B63 and B69 are 6.21019cm-3, 2.81020cm-3, 1.81021cm-3, and 8.11021cm-3,

Fig. 1. Reflection spectra of pure and heavily
boron-doped diamonds in the energy region of thedirect transition at the X point. See text for details.
respectively. The sample B65 is insulating(semiconducting) and the sample B67 is metallic,while the samples B63 and B69 are superconductingwith Tc of 2.5 K and 7.2 K, respectively. Vertical bars
in the figure show the reflection peak originatingfrom the direct transition at the X point, which locatesat 12.6 eV for the pure diamond. As seen in the figure,the reflection peak shows low energy shift withincrease of the boron concentration. This factindicates that an optical energy gap at the X point
becomes narrow with increase of the boron
concentration. It is noteworthy that any evident
energy shift was not confirmed for the reflection peakat 7.4 eV due to the direct transition at the  point.
[1] W. C. Walker et al., Phys. Rev. 134 (1964) A153.
[2] W. Saslow et al., Phys. Rev. Lett. 16 (1966) 354.
[3] E. A. Ekimov et al., Nature 428 (2004) 542.
[4] Y. Takano et al., Appl. Phys. Lett. 85 (2004)
2851.
[5] T. Yokoya et al., Nature 438 (2005) 647.

75

BL1B

Photoionization of Perylene on Ionic Liquid Surfaces

N. Inoue, T. Ishioka, A. Harata
Department of Molecular and Material Sciences, Kyushu University, Kasugakoen 6-1,
Kasuga-shi, Fukuoka 816-8680, Japan
Ionic liquids are rapidly expanding topics ofresearch because of their favorable properties such as
high
ionic
conductivity
andcontrollablehydrophobicity. Much effort has focused on thephysical properties of ionic liquids. The dielectric
environment is a key factor for modeling solvent
behavior because many approaches rely on dielectric
continuum models for the solvent. Interfacialdielectric properties can be different from those ofbulk liquids, which may distort analysis of interfacial
behavior such as calculation of solvation energies ofmolecules across the interface. Photoionization is asuitable technique studying for interfacial process,and ionization threshold measured by this method
directly reflects dielectric environment. In this reportionization threshold energies of perylene on ionicliquid were measured, and interfacial dielectric
properties of ionic liquids were studied.
Ionic liquids : 1-butyl-3-methylimidazolium tetra
fluoroborate,
hexafluorophosphate,bistrifluoro
methane sulfonylimide ([bmim][BF4], [bmim][PF6],
and[bmim][Tf2N]),
ethylammonium
nitrate([EtA][NO3]), and protonated betaine bistrifluoro
methane sulfonylimide ([Hbet][Tf2N]) were prepared
as described elsewhere. In a typical experiment, thelight was emitted from the chamber to a He-purged
cell through an MgF2 window. Light energy is in
4-8eV. The emitted light was reflected with an Al
mirror and vertically irradiated on the sample surface.
Applied voltage was 400V (interval length of meshelectrode and solution is 5mm). Hexane solution ofperylene at 110-4 M was added dropwise by 250lonto each ionic liquid in a Pt cell of 2.5cm indiameter. After evaporation of hexane thephotoinduced current (1pA) was measured by apicoammeter (Keithly model 428).
Measured photoionization spectra were analyzed andthreshold values were determined by fitting thespectra to the empirical formula of I = (E-Eth)2.5.
Table1 shows the measured photoionization thresholdof perylene on ionic liquids. In the case of[bmim][Tf2N], current signal was below the detection
limit in a vacuum. The threshold energy lies higher ina vacuum than in any other solvent because
polarization energy is always exothermic and current
by photoionization should have been detected within
the measured range of wavelength if the perylene
molecule is present at the surface of ionic liquids. It isconsidered that perylene molecule lies enough deep tokeep photoinduced electron within [bmim][Tf2N].
The energy required to photoionize a solute in a solu-

Table 1. Measured photoionization thresholds ofperylene on ionic liquids and the relative dielectric
constant of ionic liquids.

-tion satisfy E = Ip + Vo + P+, where Ip stands forionization potential of solute in vacuum, Vo
conduction band energy of solvent, and P+
polarization energy of solvent. In this experiment, Vo
equals zero because electron is emitted from surface.
Photoionization threshold of imidazolium based ionicliquids is lower than that in a vacuum (6.960eV). This
result is consistent with that of water surface.
However, P+ is much smaller than water. It issuggested that solvation by imidazolium based ionicliquid is weak. With respect to dielectric constant,[bmim][BF4] is larger than [bmim][PF6], but inpolarization energy, the order is in inverse. This may
relate to the character that [bmim][BF4] is morehydrophilic than [bmim][PF6].
Some kind of
attractive interaction between [bmim][BF4] and polar
species formed by photoionization or trace impurityof water may explain the results. Photoionizationthreshold of [EtA][NO3] is close with that of water. It
is reasonable because the dielectric constant of[EtA][NO3] is higher than that of imidazolium basedionic liquids. Photoionization threshold of [Hbet][Tf2N] was quite lowered. [Hbet][Tf2N] is an ionicliquid with the ability to coordinate metal ion. This
property may cause that anomalous behavior.
Dielectric environment of perylene on ionic liquids
are largely influenced by the composition of ionicliquids. It is not clear that which property of ionicliquid contributes the solvation energy of perylene.
Further research is in pregress to clarify interfacialdielectric property of ionic liquids.
[1] Inoue et al., Chem. Lett. (1998) 609.
[2] Wakai et al., J. Phys. Chem. B 109 (2005) 17028.
[3] Krossing et al., J. Am. Chem. Soc. 128 (2006)
13427.
[4] N.Inoue, unpublished results[5] Weingartner et al., J. Phys. Chem. A 105 (2001)
8646.

76

BL1B

Photoluminescence in LaAlO3 Single Crystals

K. Kanai, E. Hirata, Y. Ohki
Dept. Electrical Engineering and Bioscience, Waseda University, Shinjuku 169-8555 Japan
Lanthanum aluminate (LaAlO3) has been attracting
much attention as a promising candidate for a gateinsulator in advanced metal-oxide-semiconductor
devices. By analyzing photoluminescence (PL)properties of LaAlO3, we have been examining the
localized states present in the band gap that are
assumed to cause leakage current.

Experimental
The samples examined are Czochralski-grown
LaAlO3 (100) single crystals, about 0.5 mm thickwith both sides polished. Using synchrotron radiation
under multibunch operation at the BL1B line of
UVSOR Facility as a photon source, PL, PL
excitation (PLE), and absorption spectra were
measured at 10 K.

Results and Discussion
Figure 1 shows PL spectra of LaAlO3 excited at 5.1
eV. Three sharp PL peaks are observed at around 1.60,
1.64, and 1.675 eV, while a broad PL peak isobserved at around 2.8 eV. Figure 2 shows the PLE
spectra of LaAlO3 for each PL. Note that the PLE
spectra are normalized to respective maximum
intensities. The PLE spectrum detected at 2.8 eV
begins to rise at around 4.5 eV, and decreases sharply
at around 5.7 eV. On the other hand, the PLE spectraof the other three PLs show an abrupt rise at around
5.7 eV.
The absorption spectrum shown in Fig. 3 shows asteep rise at around 5.7 eV, namely at the energy ingood agreement with the band gap energy of 5.6 eV[1]. Furthermore, the energy of 5.7 eV corresponds tothe energy at which the PLE spectrum detected at 2.8
eV shows a steep decrease and to the energy at which
the PLE spectra detected at 1.60, 1.64, and 1.675 eVshow an abrupt increase in Fig. 2. In addition, it
seems that the gradual absorption increase in therange from 4.7 to 5.7 eV corresponds to the broad
peak appearing in the PLE spectrum detected at 2.8
eV. From these results, the 2.8-eV PL is assumed tobe caused by electrons excited to localized states inthe band gap. In contrast, the other three PLs ataround 1.60, 1.64, and 1.675 eV are assumed to becaused by de-excitation of electrons excited to the
conduction band.

Fig. 2. PLE spectra of LaAlO3 detected at 1.60, 1.64,
1.675, and 2.8 eV.

Fig. 3. Absorption spectrum of LaAlO3.
[1] S. G. Lim et al., J. Appl. Phys. 91 (2002) 4500.

Fig. 1. PL spectra of LaAlO3 excited at 5.1 eV.

77

BL1B

Luminescence Properties of Bi12GeO20 (BGO) Crystals

T. Katagiri1, D. Iri1, T. Aoki1, M. Itoh1, M. Fujita2, Y. Usuki3
1
Department of Electrical and Electronic Engineering, Shinshu University, Nagano 380-8553
2Japan Coast Guard Academy, Kure 737-8512
3
Furukawa Co. Kannondai, Tsukuba 305-0856
emission intensity in Fig. 1.
The present work is the first observation of the
intrinsic luminescence of Bi12GeO20.

Introduction
Bismuth germanium oxide, Bi12GeO20 (BGO), is avery efficient photoconductor and has both highsensitivity and quick response as a photorefractive
crystal. However, little is known about its opticalproperties, as compared to another BGO (Bi4Ge3O12)
that is widely used as a scintillation material. In thepresent study, we have investigated reflection spectra,
emission-excitation spectra, and luminescence decay
kinetics of Bi12GeO20 crystals.

Experiment
Crystals of Bi12GeO20 were obtained from
Furukawa Co. Reflection spectra were measured on
the cleaved surfaces. Emission spectra were examinedusing a grating monochromator equipped with a
LN/CCD camera in the temperature range T = 5300
K. Luminescence decay kinetics was detected by an
MCP with use of a time-correlated single-photon
counting technique under the single-bunch operationof the storage ring (time duration: 1.3 ns; pulseinterval: 177.6 ns).

Fig. 1. Emission spectra of Bi12GeO20 excited at 150
nm in the temperature range T = 545 K.

Results and Discussion



The reflection spectra measured at T = 5 K showed asharp peak at the fundamental absorption edge. This
peak locating at 3.65 eV (340 nm) is naturally
assigned to the excitonic transition of Bi12GeO20.
Figure 1 shows the emission spectra measured
under the excitation with 150-nm photons at verious
temperatures in the range of T = 545 K. A strong
band peaking at 452 nm is observed together with avery weak band around 650 nm. The intensity of the
452 nm band decreases rapidly with increasing T.
The excitation threshold of the 452 nm emission
was around 3.44 eV (360 nm), which coincides withthe low-energy tail region of the exciton band. This
fact suggests that the 452 nm luminescence isintrinsic to Bi12GeO20, and arises from the radiativeannihilation of the excitons that have self-trapped byinducing lattice deformation around themselves. The
self-trap site could be either Bi3+ or O2.
In Fig. 2 are shown the decay behaviors of the 452
nm luminescence measured in the range of T = 545
K. One may see two decay components: a fast one
with a lifetime of nanoseconds and a slow one with alifetime of more than 1 s. The latter is seen as apiled-up component. As T is increased, the lifetime ofthe slow component becomes shorter, resulting in
reduction of the piled-up component. This result is
consistent with the temperature dependence of the

INTENSITY (arb. units)









0

50
100
TIME (ns)Fig. 2. Decay behaviors of the 452 nm luminescenceof Bi12GeO20 excited at 150 nm at T = 545 K.

78

BL1B

1

Optical Studies of Hydrogen-Bonded Dielectrics TlH2PO4

T. Kawai1, N. Ohno2
Graduate School of Science, Osaka Prefecture University, Sakai 599-8531, Japan
2
Graduate School of Engineering, Osaka Electro-Communication University,
Neyagawa 572-8530, Japan
peak with dispersive structure at 5.70 eV in TDP
would be the first exciton transition. It is well-known
that the Tl+ impurity centers doped in the KDP-type
crystals exhibit the absorption band due to theintra-cationic transition in the Tl+ ion at 5.8 eV [7,8].
Therefore, the sharp dispersion-like structure of TDP
at 5.8 eV should be attributed to the exciton transition
based on cationic excitation in the Tl+ ions.


Thallium dihydrogen phosphate TlH2PO4 (TDP) is
closely related to the KH2PO4(KDP) -type crystals,
which are interesting hydrogen- bonded materials
undergoing structural phase transitions accompanied
by ferroelectricity and antiferroelectricity. In thesecompounds, short hydrogen bonds link PO4 groups inthree-dimensional (KDP) or two-dimensional (TDP)
networks. The TDP crystal undergoes theantiferroelectric phase transition from the monoclinic
P21/a symmetry to the triclinic C1 symmetry at 230 K[1]. Though a number of studies on crystal structureand dielectric properties of TDP have been madeabove and below the phase transition temperature[1-4], optical properties and the electronic states arecomparatively less studied.
In the present study, we have investigated theoptical properties of TDP for the first time in UV andVUV regions at the BL-1B beam line of UVSOR.
The TDP compound was synthesized by mixing
stoichiometric amounts of Tl2 CO3 and H3PO4. Afterseveral times of recrystallization, crystals of TDP
were grown by an ordinary evaporation method fromthe saturated aqueous solution.
Figure 1 shows the reflection (red curve) andabsorption (blue) spectra of TDP measured at 10 K.
The dip structure at 5.26 eV in the reflection
spectrum is due to the reflection from the backsurface of the crystal, because the energy position
corresponds to that where the absorption spectrum
exhibits a sharp increase. A sharp peak withdispersive structure is observed at 5.70 eV above therise of the absorption spectrum. In the higher-energy
region, several broad structures are also observed.
Most of the KDP-type crystals exhibits no obvious
dispersion-like structure due to the exciton transitionin the reflection spectra and broad structures areobserved in the energy region from 7.0 to 8.2 eV [5,6].
The broad structures of KDP have been ascribed tothe transition related with the energy levels in
H2PO4  complex anions. The distinguished sharp

Fig. 1. Reflection spectrum (red) and absorption
spectrum (blue) of TlH2PO4 at 10 K.

[1] I. H. Oh et al., Acta Cryst. B 62 (2006) 719.
[2] N. Yasuda, S. Fujimoto, T. Asano, Physics Lett.
76A (1980) 174.
[3] H. Yoshida et al., J. Phys. Soc. Jpn. 53 (1984)
910.
[4] E. Alvarez-Otero et al., Acta Cryst. B 58 (2002)
750.
[5] S. Saito, R. Onaka, Ferroelectrics 21 (1978) 553.
[6] S. Matsumoto, M. Fujisawa, S. Suga, J. Electron.
Spectrosc. Relat. Phenom. 79 (1996) 51.
[7] I. Fujita, J. Phys. Soc. Jpn. 66 (1997) 2893.
[8] K. Ichimura et al., Phys. Status Solidi (c) 3 (2006)
3607.

79

BL1B

Vacuum-Ultra Violet Reflectance Spectroscopy of Orbital-Ordered Bilayer
Manganites
Y. S. Lee1, Y. Tokunaga2, T. Arima3, Y. Tokura2,4,5

Department of Physics, Soongsil University, Seoul 156-743, Korea
2
ERATO ( Multi-Ferroics), Japan Science and Technology Agency (JST) Tsukuba 305-8562
3
Tohoku University
4
Correlated Electron Research Center (CERC) National Institute of Advance Industrial
Science and Technology (AIST), Tsukuba 305-8562Japan
5
Department of Applied Physics, University of Tokyo, Tokyo 113-8656 Japan
Figure 1 shows the optical conductivity spectra forthe x = 0.2 and 0.9 PSCMO. The dominant structures
observed in optical conductivity spectra are labeled as
A, B, C, and D, from the lowest energy sequence. The
lowest energy of the A structure, mainly responsible
for the transport, is associated with the electron
hopping from Mn3+ to Mn4+ eg bands. This structure
is located at much lower energy for the x = 0.2
compound with the 2D metallic character than thatfor the x = 0.9 compound with the insulating
charge-orbital ordering. The B structure is assigned as
the charge transfer energy from O 2p to Mn eg bands.
On the other hand, it is difficult to assign structures
above 5 eV as transitions with a single character,because the valence bands of four elements (Pr, Sr,
Ca, and Mn) should be involved in a complicatedmanner. While the C structure is associated with thetransitions from O 2p to Pr 3d, Ca 4s, and Sr 5s bands,
the occupied Pr 5p, Ca 3p, and Sr 4p may be involvedin the formation of the D structure. In this case, thestrong difference in the intensity of the D structure
between x = 0.2 and x = 0.9 compounds implies that
the Ca 3p band should be located in much deeper thanthe Sr 4p band.

Recent studies on strongly correlated electronicsystems have revealed many unexpected phenomena
due to the interplay among the spin, charge, and orbital
degrees of freedom. Especially, the nanoscale
self-organization and the associated complexity ofelectronic systems are issues of current interest. One of
the representative phenomena is the concomitantcharge and orbital orderings in manganites, which is
involved in the metal-insulator transition withmagnetic field and other various control parameters. At
the lowest temperatures, the charges are ordered in acheckerboard type, forming alternating Mn3 +/Mn4 +sites, and simultaneously, the eg orbitals in Mn3+ sites
are aligned in zigzag chain type. The direction of eg
orbital lobes defines the orbital chain and stripe. This
well-organized charge, spin, or orbital ordering occurs
in the ab plane for a variety of manganites including
layered compounds.
In this beamtime, we have measured thereflectivity spectra of the bilayer manganites,
Pr(Sr1-xCax)2Mn2O7 (PSCMO), for 0  x  1 in aphoton energy range of 4 – 30 eV at room
temperature using the beam line BL1B. We
connected the measured spectra to the low energy
ones below 5 eV, and calculated the opticalconductivity spectra through the Kramers-Kronigtransformation.
The bilayer PSCMO compounds exhibit anpeculiar phase diagram spanning from the A-type 2D
metallic phase to the charge-orbital ordered phase with
the increasing x from x = 0. The boundary between twophases is located around x = 0.4. Notably, the PSCMO
compounds with the ground state of the charge-orbital
ordering experiences the spontaneous rotation oforbital stripe by 90° with the variation of temperature.
Two successive charge-orbital ordering transitions
were studied in details at a particular concentration x =0.9 by performing a combination of various
experimental measurements such as Dc resistivity,
magnetization, optics, x-ray scattering measurements,and so on. It is noted that the ground charge-orbital
ordering states turn out to be a charge polarized state
due to the coincidence in the stacking patterns of the
distorted bilayer Mn-O network and the charge ordering
along the c axis.

Fig. 1. Optical conductivity spectra of the x=0.2 (red line)
and x = 0.9 (black line) Pr(Sr1-xCax)2Mn2O7 compounds.

[1] Y. Tokura, Rep. Prog. Phys. 69 (2006) 797.
[2] Y. Tokunaga et al., Nature Materials 5 (2006)
937.

80

BL1B

Optical Properties of Sm2+ in KY3F10

T. Nakamura, T. Ishikawa, M. Satoh, N. Kashiwagura, M. Yamaga
Department of Mathematical and Design Engineering, Faculty of Engineering, Gifu
University, Gifu 501-1193 Japan
Introduction
Rare earth ion-doped materials have been
extensively studied for use in important applications
such as laser, scintillator [1], and optical memory.
Persistent spectral hole burning (PSHB) is applied tofrequency domain optical memories. The holeburning of Sm2+ in disordered crystals and glasses
was reported. Temperature dependence of the Sm2+
emission in KY3F10 crystals excited by vacuum
ultraviolet (VUV) and ultraviolet (UV) lights wasmeasured, in order to examine dynamic processes of
the 4f6 and 4f55d1 excited states of Sm2+ in the crystal.

Experimental

Sm2+ doped KY3F10 crystals were grown using theBridgeman method.
The optical absorption,
emission and excitation spectra of Sm2+ in the crystal
were measured using the BL1B beam line in the
UVSOR. The measurement temperatures were in
the range of 17-300 K.

Fig. 1. Absoprtion, emission and excitation spectra of
Sm2+ in KY3F10 at 14 K

Results and Discussion
Figure 1 shows the optical absorption, emission
and excitation spectra observed in Sm2+-doped
KY3F10 at 10 K.
The absorption spectrum iscomposed of many bands in the wavelength range of100-400 nm. The 160-nm excitation produces abroadband with a peak of 450 nm and three intenseline groups around 560, 600, and 650 nm due toresidual Sm3+ ions in the crystal. The 195-nm
excitation produces only the 450-nm broadband.
On the other hand, the emission spectrum excited at
300 nm is different from that excited at 160 nm.
The emission lines around 550 and 700 nm are due tothe transition from the higher energy levels of 5D3 and5
D0 to the lower energy levels of 7FJ (J=0-3) of Sm2+.
The excitation spectra for the emission wavelengths
at 500, 510, and 690 nm have the band structure in
the range of 180-420 nm, being almost similar to theabsorption spectrum.
Figure 2 shows the temperature dependence of theemission spectra excited at 280 nm. The 450-nm
broadband and sharp lines in the range of 500-660 nm
are drastically decreased above 150 K, while the
sharp lines in the range 690-800 nm are almost
constant up to 300 K.
This result suggests that theexcited states of 5DJ (J=3,2,1) deexcite nonradiatively
to the ground state with the increase of temperatures.
The temperatures corresponding to the decrease of theintensities of the emission from the 5DJ (J=3,2,1,0)
excited states increase with the decrease of thenumber of J, that is, the emission from the the 5D0
excited state is stable up to 300 K.

Fig. 2. Temperature dependence of the emission
spectra of Sm2+ in KY3F10excited at 280 nm.
[1] M. Yamaga et al., J. Materials Science: Materials
in Electronics (2008) in press.

81

BL1B

Luminescence Properties of YBO3:Bi3+ and YBO3:Sb3+
N. Ohno, K. Kohmoto
Division of Electronics and Applied Physics, Graduate School of Engineering,Osaka Electro-Communication University, Neyagawa, Osaka 572-8530, Japan
assigned as the A band nature due to 1S0  3P1
transition in Bi3+ and Sb3+ impurity ions. The
excitation bands at 6 –8 eV show composite structures,
which is a common feature of the C band of Tl+-typeions. Therefore, these structures in the VUV region
are ascribed to the C band originated from 1S0  1P1
transitions in Bi3+ and Sb3+ ions.

Xe dimer (Xe2) discharge fluorescent lamp is oneof the candidates for alternative lighting sources to aconventional Hg discharge fluorescent lamp. New
phosphors suitable for the conversion of vacuum
ultraviolet (VUV) light into visible light are quitedesired at present. In the Xe2 discharge florescentlamps, phosphors are excited by VUV light of 7.2
and 8.4 eV. Most phosphate and borate hosts aretransparent up to ~ 10 eV, so that the VUV light candirectly excite impurity activators in these hosts. The
strong absorption due to the impurity ions would giveefficient conversion of the VUV light.
In the present study, luminescence properties oftrivalent Tl+-type centers in yttrium borate have beenstudied in the UV and VUV region. The YBO3:Bi3+
and YBO3:Sb3+ phosphors were prepared by amountsof the appropriate starting compound powders of
YBO3 adding Bi2O3 or Sb2O3 (1 mol %), mixing andfiring in a carbon crucible at 1100ºC in air or nitrogen
atmosphere [1]. Impurity Bi3+ and Sb3+ ions would be
expected to be substituted for Y3+ ions in the hostlattices.
Figure 1 shows luminescence (blue curve) andphoto-excitation (red curve) spectra of YBO3:Bi3+
measured at room temperature. Luminescence peaks
located at 3.8 eV and a small hump at 2.8 eV are
observed for the excitation of VUV light. The 3.8 eV
luminescence is excited with photons of 4.7 eV and
6-8 eV of Xe discharge energies. These excitation
peaks are located at lower energies than theabsorption edge of the host YBO4 (~ 10 eV). Therefore, the observed luminescence bands of YBO3:Bi3+
would be responsible for intra-ionic transitions in
impurity Bi3+ ions.
Figure 2 shows luminescence (blue curve) andphoto-excitation (red curve) spectra of YBO3:Sb3+ atroom temperature. There appear luminescence peaks
at 3.6 eV and 2.9 eV for the excitation of VUV light.
The 3.6 eV luminescence band is stimulated withphotons of 4.7 eV and 6-8 eV. These luminescenceand excitation peak energies are found to be quite
similar to those of YBO3 :Bi3+.
Tl+-type ions doped in alkali-halide crystals with ahigh symmetry crystal structure exhibit threecharacteristic absorption bands arising from the s2 
sp transitions, namely, A, B and C bands [2]. Theseabsorption bands have been attributed to the opticaltransition from the 1S0 ground state to 3P1, 3P2, and1P1 excited states, respectively. The present study has
shown that the excitation band at 4.7 eV in
YBO3:Bi3+ and YBO3:Sb3+ could be tentatively

Fig. 1. Luminescence (blue curve) and excitation (redcurve) spectra of YBO3:Bi3+ at room temperature.

Fig. 2. Luminescence (blue curve) and excitation (redcurve) spectra of YBO3:Sb3+ at room temperature.
[1] X. Z. Zeng et al., J. Lumin. 121 (2006) 1.
[2] W. B. Fowler, Physics of Color Centers,
Academic Press Inc., New York, 1968.

82

BL1B

Photoluminescence of Hydroxyapatite Irradiated by Ultraviolet
Synchrotron Orbital Radiation Light (4)M. Ohta
Department of Material Science and Technology, Faculty of Engineering, Niigata University,
8050 Ikarashi 2-no-cho, Niigata 950-2181, Japan
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]. Recently, rare earth isalso 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. We have found that Eu ion substituted
Ba ion in Eu doped Ba10(PO4)6Cl2 phosphor, which
matrix is apatite structure [3]. The Eu ions or Gd
ions are also found to substitute easily for calcium
ions in hydroxyapatite which is soaked in EuCl3 or
GdCl3 aqueous solution, and to play on emission
center.
In this study, hydroxyapatite samples doped with
YbCl3 aqueous solution were prepared in order toapply to phosphor. Their characteristics were
investigated by photoluminescent property of Yb
ion-doped hydoxyapatite samples excited byultraviolet synchrotron orbital radiation light.
Yb-doped hydroxyapatite samples were prepared
as follows: hydroxyapatite was soaked in YbCl3
aqueous solution. After 72 hr, Yb-dopedhydroxyapatite was separated from YbCl3 aqueous
solution by filtation and then dried by using with
infrared ray.
The photoluminescent property of each sample
exited by ultraviolet synchrotron orbital radiation
light (BL-1B) was observed by using with amulti-channel analyzer.
Figure 1 shows photoluminescence spectra of Yb
ion-doped hydroxyapatite samples excited by BL-1B.
The photoluminescence spectra have the peak due to5
D5/25F7/2 (about 980 nm), regardless of excitation
wave length from120 to 420 nm. The peak intensity ishigher at 150 and 210 nm of excitation wave length.
The peak intensity increases with the concentration of
YbCl3 aqueous solution and is held constant at from 1
to 10 mM. This fact is different from the results of
Eu-doped and Gd-doped samples, reported previously
[4].

1mM

10mM

Fig. 1. Photoluminescent spectra of Yb ion-dopedhydroxyapatite samples excited by ultraviolet
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] M. Ohta, UVSOR Activity Report 2006 (2007)
75.

83

BL1B

Effects of Curing and Filler Dispersion Methods
on Dielectric Properties of Epoxy Nanocomposites
M. Okada1, N. Hirai1, T. Tanaka2, Y. Ohki1, T. Imai3, M. Harada4, M. Ochi4
1
Department of EEBS, Waseda University, Shinjuku 169-8555, Japan
2
Graduate School of IPS, Waseda University, Kita-Kyushu 808-0135, Japan
3
Power and Industrial Systems R&D Center, Toshiba Corp., Kawasaki 212-8582, Japan
4
Department of Applied Chemistry, Kansai University, Suita 564-8680, JapanThe effects of the differences in the curing andfiller dispersion methods on the dielectric properties
were examined for epoxy/clay nanocomposites.
The base epoxy resin is diglycidyl either ofbisphenol A cured with acid anhydride or with amine,while the clay added is montmorillonite modified byeither a solubilization method or an organo method.
The clay content was constant at 5 wt% throughout all
the samples [1]. Table 1 shows the sample codes.
The electric conductivity was calculated bymeasuring the absorption current for 1000 s after theapplication of electric field of 10 kV/mm, while thepermittivity was measured in the range of 10-1-107 Hz.
All the above measurements were carried out at room
temperature.
Using synchrotron radiation (SR) undermulti-bunch operation at the BL1B line of UVSOR
Facility (beam energy: 750 MeV) as a photon source,theultraviolet(UV)photonabsorbance,
photoluminescence (PL) and PL excitation (PLE)
spectra from the samples were measured at 10 K.
Irrespective of the filler dispersion method, boththe electric conductivity and permittivity are higher in
the amine-cured samples than in the acid anhydride-cured samples as shown in Figs. 1 and 2.
Furthermore, UV photon absorption becomessignificantly larger at photon energies higher than 3.4
eV in the amine-cured samples and at energies higher
than 4.0 eV in the acid anhydride-cured samples,irrespective of the filler dispersion method, as shownin Fig. 3. A PL band, which shows an emission
peak at the energy where the UV absorption begins toincrease, was found to appear in all the samples asshown in Fig. 4. From these results, the PL is due toelectronic transition across the band gap, which issmaller in the amine-cured samples than in the acidanhydride-cured samples.
In most materials, the permittivity and conductivity
become higher if the band gap is smaller. The
present results agree with this general tendency.
Table 1.

Fig. 1. Electrical conductivity (1000 [s] after voltage
application).

Fig. 2 Dielectric constant (a) and dielectric loss
factor (b) of each sample

Fig. 3. Ultraviolet absorption spectra.

Sample codes.

Unmodified epoxy

Solubilization
MethodOrgano Method

Acid anhydride
curing agent

E(U)AH

C(S)AHC(O)AH

Amine curing agent

E(U)AM

C(S)AM

C(O)AM

Fig. 4. PL peak, PLE onset, and absorbance onset
energies.
[1] M. Harada et al., Network Polymer Symposium
Japan (2006) 105 (in Japanese).

84

BL1B

The Temperature Dependence of Absorption Spectra for Heavy
Lanthanides in LiYF4 and its First-Principles Analysis

S. Watanabe1, H.Yoshida1, K. Ogasawara1, M. Yoshino2
1
Department of Chemistry, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337 Japan2
Department of Materials, Physics and Engineering, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya, 464-8603, Japan
reproduced fairly
parameters.

The divalent or trivalent lanthanide ions in wideband gap host crystals or glasses have drawn
attentions due to their application for luminescentmaterials in UV and VUV regions such as solid-statelasers or phosphors. In those materials, the trivalentlanthanide ions (Ln3+) in LiYF4 crystal have been wellknown as exquisite luminescence centers.
In this work, we have investigated the temperaturedependence of 4f n-4f n-15d1 absorption spectra forheavy lanthanides in LiYF4 host crystal. As theluminescence centers, we adopted the three heavy
lanthanide ions, which are Terbium (Tb3+),
Dysprosium (Dy3+) and Erbium (Er3+). And we also
analyzed the spectra based on the first-principles
calculation for multiplet energy and absorption
spectrum using the 4-component relativistic
configuration interaction (CI) method [1]. This
calculation method has been successfully applied to
calculation of the multiplet energy levels and opticalabsorption spectrum between multiples for impurity
ions in host crystals [2]. By measurements of theabsorption spectrum at low temperature, we could
directly compare the theoretical absorption spectrum
to that obtained by the first-principles calculation.
Therefore, the combination of measurements of theabsorption spectrum at low temperature andfirst-principles calculations is very effective
procedure for analysis of optical properties.
The LiYF4 single crystal doped with Ln3+
(Ln3+=Tb3+, Dy3+, Er3+) were grown by
Bridgman-Stockbarger method. The concentration of
Ln3+ in the sample was 0.3 mol%.
Fig. 1 shows the temperature dependence ofexperimental absorption spectra and the theoreticalabsorption spectrum for Dy3+ in LiYF4.
The 4f 9-4f 85d1 absorption spectrum for Dy3+ in
LiYF4 is observed by using the SR source for the firsttime. The experimental absorption spectra were very
complicated and did not strongly depend on
temperature except for the peak D, E. These results
indicate that the configuration interaction of each
multiplet is very strong. In addition to Dy3+ impurity
absorption, the absorption of LiYF4 host crystal wasobserved above about 10.8 eV.
The theoretical spectrum is in good agreement withexperimental one. Though the absolute mutiplet
energy levels are not reproduced exactly, the relative
peak position and shapes of absorption spectrum are

wellwithoutanyempirical

Fig. 1. The theoretical absorption spectrum and thetemperature dependence of experimental absorption
spectra for Dy3+ in LiYF4.
[1] K. Ogasawara et al., Phys. Rev. B 64 (2001) 143.
[2] K. Ogasawara et al., J. Solid Statate Chem. 178(2005) 412.

85

BL1B

Excitation Spectra for Lanthanides in YAG
and its First-Principles Analysis

M. Yoshino1, S. Watanabe2, H. Yoshida2, K. Ogasawara2
1
Department of Materials, Physics and Energy Engineering, Nagoya University, Nagoya
464-8603, Japan2
Department of Chemistry, Kwansei Gakuin University, Sanda 669-1337, JapanThe trivalent lanthanide ions (e.g. Nd3+, Er3+, Yb3+) in
Y3Al5O12 (YAG) crystals have drawn attentions due totheir application for luminescent materials in NIR to UV
regions such as solid-state lasers or phosphors. And, Pr3+
and Tb3+ have also attracted attentions as luminescencecenters. In this work, the 4f n-4f n-15d 1 excitation spectra
and emission spectra for lanthanides in YAG crystal
have been measured. As the luminescence centers, Pr3+
and Tb3+ are used. The lanthanides ion doped YAG
samples are produced by solid state reactions. The
concentration of Ln3+ in the samples are 3 mol%. And
the spectra are analyzed based on the first-principles
calculation for multiplet energy and absorption spectrum
using the relativistic configuration interaction (CI)method [1]. This calculation method has beensuccessfully applied to calculation of the multiplet
energy levels and optical absorption spectrum for
impurity ions in hosts [2]. Fig. 1 shows the experimental
excitation spectrum for Pr3+ in YAG. The two peaks
exist around 4-6 eV correspond to the 4f 2-4f 15d 1
absorption. And the spectrum above about 6.5 eV relates
to absorption of YAG host. And this sample shows
strong emission in VIS region as shown in Fig. 2. Fig. 3
shows the theoretical absorption spectrum for Pr3+ in
YAG. Though the absolute multiplet energy levels are
not reproduced, the shapes and distribution of peak
position in excitation spectrum are roughly reproduced
without any empirical parameters. The experiments andcalculation are also examined about Tb3+ in YAG (Fig. 4).

3+

Fig. 1. Experimental excitation spectrum for Pr
YAG.

Fig. 2. Experimental emission spectrum for Pr3+ in
YAG.

Fig. 3. Theoretical absorption spectrum for Pr3+ in
YAG.

Fig. 4. Experimental excitation spectrum for Tb3+ in
YAG.

in

[1] K. Ogasawara et al., Phys. Rev. B 64 (2001) 143.
[2] K. Ogasawara et al., J. Solid State Chem. 178 (2005)
412.

86

BL5B

Absorption Spectra of Dilute Magnetic Semiconductor GaCrN in VUV Region
S. Emura, S. Kimura, Y. Hiromura, H. Asahi
ISIR, Osaka University, Mihoga-oka 8-1, Ibaraki, Osaka 567-0047
GaN:Cr layer surfaces.
In consideration of the electronic state of Cr in
GaN matrix to survey the origin of theferromagnetism of GaCrN, the molecular orbital
schema of CrN4 is important. The molecular orbitalsof (CrN4)-9 are resolved in tetrahedral symmetry bygroup theory as follows,In
presentsociety,
infrastructuresofcommunication are demanded to expand in the speed
and the quantity. One of future devices in this field isa spin-related device. Several candidates are
considered and a part of those starts in fundamental
research. Theoretical study also reveals thepossibility of dilute magnetic semiconductor thatexhibits ferromagnetism at room temperature andpredicted
that
GaN-based
dilutemagnetic
semiconductors, especially Cr-doped GaN, are highly
potential candidates for those materials. This material,
Cr doped wide gap semiconductor, shows
ferromagnetic
properties
even
at
400K
experimentally. This is one of highest Curie
temperatures at present in dilute magnetic
semiconductors. Furthermore, GaCrN substanceemits luminescence at the energy of near the band
gap of Ga. We have, thus, three independent
characters for GaCrN, semiconductor nature,
ferromagnetism, and optical feature.
The origin of the magnetic behaviors of dilute
magnetic semiconductors based on nitride is still
open in discussion, though several first-principles
calculations, as described above, appeal to the public.
It seems that their predictions do not clearly explain
magnetic characteristics such as the dependence ofthe magnetic strength on the magnetic dopant
concentration, peculiar form of M – H curve, and theweak hysteresis.
The growth of cubic-GaN:Cr layers was performedon MgO (001) substrates by radio frequency (RF)plasma-assisted molecular beam epitaxy techniques.
Sources used here were elemental Ga and Cr andplasma-excited nitrogen. After thermally cleaning of
MgO substrate surfaces, several monolayer of GaN
were grown at low substrate temperature (540AC) andthen 50 nm of cubic-GaN buffer layer was grown at
700AC. On the cubic-GaN buffer layer, cubic-GaCrN
layer with approximately 100 - 200 nm in the
thickness was grown as a function of Cr celltemperature (TCr = 810 - 1030AC). The fixed nitrogenflow rate (1.5 SCCM) with the fixed plasma power(180 W) was supplied during growth for all of the
cubic-GaN:Cr layers. Growth rate and slightly N-richcondition of V-III ratio were kept constant for all thesamples grown at different substrate temperatures.
Therefore, the Ga flux of 1.9, 1.6 and 1.3x10-7 Torr
was used for the substrate temperature of 700, 540
and 350AC respectively because evaporation of Ga
atoms is suppressed on the grown surface at lower
temperature. Finally, GaN layer with 10 nm in the
thickness was deposited to avoid the oxidation of

N-2p: a1 + e + t1 + 2t2 (a1 and t2 are  orbitals) (1)N-2s: a1 + t2
(2)
Cr-3d: e + t2
(3)
The schematic semi-quantitative diagram is shownin Fig.1. The quantitative parts in the figure arededuced from the combination of 1s core absorption
spectra and VUV absorption spectra observed. The
three electrons belonging to the magnetic dopant Cr
atom occupy with a manner of two kinds, so-called,
low spin state and high spin state. The present
problem is which state is preferable. It strongly
affects the ferromagnetism of this system GaCrN.
The VUV dichronic and ESR measurements arenecessary to confirm whether the Cr state takes low
or high spin state.

Fig. 1. Schematic energy diagram of the (CrN4)-9molecular.

87

BL5B

Photostructural Changes in Amorphous Chalcogenide Materials

K. Hayashi
Department of Electrical and Electronic Engineering, Gifu University, Gifu 501-1193, Japan
Results and Discussion
Figure 1 shows the VUV transmission spectrum ofan as-deposited a-As2Se3 film at room temperature in
the photon energy region between 40 and 65eV. Twomain absorption peaks were observed in this energy
region. One absorption peak around 44eVcorresponds to the 3d core level of As atom. Anotherabsorption peak around 57eV corresponds to the 3dcore level of Se atom. As shown in the Fig. 1, thespectral line width of that absorption is very broad
and multiple shoulders are observed. A similar
spectrum is observed in the as-deposited a-As2S3
film. It can be attributed to the spin-orbit splitting of
the 3d core level of each atom as observed by XPS.
As for the origins of the shoulders, it is not clear. I
think that these shoulders are related to the local
structures of the amorphous network. The detailed
experiments and analysis will be done in the next
step.
0.6

a-As2Se3

0.5

Transmission[a.u.]

Introduction
It is well-known that amorphous chalcogenide
materials exhibit a variety of photoinduced
phenomena by irradiation of light with energy
corresponding to the optical band gap [1].
Photoinduced changes observed in amorphouschalcogenide materials are classified into two types,
irreversible and reversible changes. Reversible
changes can be induced optically in amorphous bulk
materials and well-annealed evaporated thin films, inwhich the changes can be removed by annealing to
the glass-transition temperature. The reversible
photodarkening arising from the red-shift of the
optical absorption edge is a typical reversible
photoinduced phenomenon. Irreversible changes are
induced in as-deposited evaporated thin films. The
irreversible
photodarkeninginas-deposited
amorphous films is an irreversible change, it isbelieved that it occurred by photo-polymerization.
The irreversible changes observed in EXAFS [2-3]and IR [4] are interpreted by rearrangement ofbonding configurations of molecular species within
as-deposited evaporated films.
To our knowledge, little attention has been given to
photoinduced changes at the vacuum ultra-violet(VUV) absorption spectrum. In this report, weinvestigate photoinduced changes at the VUVtransmission spectra on as-deposited evaporated films
and well-annealed evaporated films.

0.4
0.3
0.2
0.1

Experimental
Thin
films
of
amorphouschalcogenide
semiconductor (a-As2S3 and a-As2Se3) were preparedonto ultrathin collodion films by conventional
evaporation technique. A typical thickness of anamorphous film was around 200nm. The ultrathin
collodion films were prepared onto stainless steel
metal plates in which two pinholes of the 1.0mm
diameter opened. A xenon arc lamp with IR-cut-off
filter was used as a light source. Before themeasurement of the VUV transmission spectrum, theunilateral of the sample was irradiated with the lightin a vacuum to the degree in which the sample
sufficiently produced the photodarkening. The
measurement of the VUV transmission spectra werecarried out at room temperature at the BL5B beamline of the UVSOR facility of the Institute for
Molecular Science. And the spectrum was measured
by using the silicon photodiode as a detector. To
eliminate 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 total photoyield of a gold mesh.

As 3d

Se 3d

0
40

45

50

55

60

65

Photon Energy [eV]Fig. 1. The VUV transmission spectrum of anas-deposited a-As2Se3 film.
Acknowledgements
This work was partly supported by Research
Foundation for the Electrotechnology of Chubu.
[1] Ke. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] J.P. De Neuvile, S.C. Moss, and S.R. Ovsinsky, J.
Non-Cryst. Solids, 13 (1973/1974) 191.
[3] A.J. Lowe, S.R. Elliot, and G.N. Greaves, Philos.
Mag. B 54 (1986) 483.
[4] S. Onari, K. Asai, and T.Arai, J. Non-Cryst.
Solids 77&78 (1985) 1215.

88

BL5B, BL7B

Optical Oscillator Strength Distribution of Amino Acids from 3 to 250 eV
and Examination of the Thomas-Reiche-Kuhn Sum Rule[1]M. Kamohara, Y. Izumi, M. Tanaka, K. Okamoto, K. Nakagawa*
Graduate school of Human Development and Environment, Kobe University,
Tsurukabuto, Nada-ku,Kobe 657-8501, Japan

Absorption spectra of amino acid films were
measured in the photon energy range of vacuum
ultraviolet (VUV) and soft X-ray region in an attempt
to examine the validity of the Thomas-Reiche-Kuhn
oscillator strength sum rule.
Thin films of glycine (Gly), alanine (Ala),
phenylalanine (Phe), and methionine (Met) wereprepared by the vacuum sublimation technique on thecollodion substrates.
Absorption spectra were measured at the beamline
5B and 7B of the synchrotron radiation facility
UVSOR in the Institute of Molecular Science,
Okazaki, Japan. Values of optical absorption crosssection (E) at photon energy E were translated
into the optical oscillator strength distribution df /dE .
An example of obtained results for Met films isshown in Fig. 1, in which large peak from 10 eV to
70eV is due to transitions between valence levels andsmall peak from 170 eV to 250 eV was due totransitions from 2s and 2p levels of sulfur atom ofMet.
According to the Thomas-Reiche-Kuhn oscillator
strength sum rule, integrated value ftotal of df /dEshould be equal to the number of electrons Ne
associated to the optical transition within the energy
range of integration. After careful examinations, we
obtained values of ftotal and Ne to be 27.3 and 30 for
Gly, 31.0 and 36 for Ala, 63.2 and 64 for Phe, and60.1 and 62 for Met, respectively. We concluded that
the T-R-K sum rule meets in a good manner foramino acid molecules.
This work was done thorough the joint programs of
the Institute for Molecular Science, 18-515 and18-534.

Fig. 1. Optical oscillator strength distribution of
methionine thin film.
*Corresponding author: nakagawa@kobe-u.ac.jp[1] M. Kamohara et al., J. Rad. Phys Chem. (2008) inpress.

89

BL6B

Far-Infrared and Millimeter Wave Spectroscopyof Superionic Copper Conductors

T. Awano
Department of Electronic Engineering, Tohoku Gakuin University, Tagajo 985-8537, Japanmode, i.e. below 35cm-1, at 298 K. The plasma
frequency, 45 cm-1, in the fitting parameters is
proportional to the inverse of square root of mass
ratio of silver and copper ion, comparing with thosein MAg4I5[1] i.e. 26-27cm-1. The plasmon fitting was
impossible for the spectra at low temperatures. Thismeans that such a movement in phase needs kinetic
energy of the conduction ion much larger than theactivation energy of the ionic conduction.

Superionic conductors have high ionic conductivity
as liquid or electrolyte solution. Far-infrared andmillimeter wave region corresponds to the frequency
boundary between translation and vibration
movement of conduction ion. Spectroscopic study ofthis frequency region, therefore, seems to makecharacteristic dynamics of mobile ions in superionic
conductors, such as correlative collective movementof mobile ions clear.
RbCu4 Cl3+xI2-x crystals have the highest ionic
conductivity at room temperature and have the samestructure as RbAg4I5. Therefore this is a suitablesystem to compare dynamics of mobile ions.
Fig. 1 shows absorption spectra of RbCu4Cl3.25I1.75
crystalobtained by K-K analysis from reflectivity
spectra. Broad absorption peak was observed around40, 80 and 110-200cm-1 at room temperature. Thesebands have doublet structure at low temperature. This
seems to be due to difference of local structure bychlorine and iodine ion. The number of couples ofcations and chlorine or iodine ions is comparable andabsorption intensity seems to be almost equal.
The 110-200 cm-1 bands seems to be symmetricbreathing modes of CuX4 (X= Cl or I) tetrahedron. In
CuI, TO phonon frequency is 130 cm-1 and 170 cm-1
in CuCl. These bands were observed around 100-120
cm-1 in RbAg4I5. This frequency shift coincides with
the inverse of square root of the mass ratio ofconduction ions.
The 80 cm-1 band seems to be Rb-X vibration in
RbX6 octahedron. In RbI, the frequency of TO
phonon is 80cm-1.
The 40 cm-1 band seems to be the attempt mode
which is an outward motion of the mobile ion in
halogen cage. In silver conductors, the attempt mode
is observed around 20 cm-1[1]. This frequency shiftcoincides with the inverse of square root of the mass
ratio of conduction ions.
Reflectivity at low energy side increased at room
temperature. This is due to translational movement ofconduction ion. Correlation of ionic movement by
coulomb repulsion seems to occur because thenumber of available site for conduction ion is not somany and the distance between them is not so large.
Such a collective movement in phase is able to be
regarded as “ionic plasmon”. Plasmon fitting by
Drude model in energy loss function spectra of
RbCu4 Cl3.125I1.875 is shown in fig. 2. Energy loss
function, Im(1/), is proportional to absorption
intensity by transverse wave. The dotted line shows
calculated one from the Drude model. The fitting
curve well coincides with the energy loss function
spectrum of the spectral region below the attempt

Fig. 1. Absorption spectra of RbCu4Cl3.25I1.75.

Fig. 2. Energy
RbCu4 Cl3.125I1.875.

loss

function

spectraof[1] T. Awano, T. Nanba, M. Ikezawa, Solid State
Ionics 53-56 (1992) 1269.

90

BL6B

1

Infrared Spectroscopy on CeIn3 under Pressure

T. Iizuka1, T. Mizuno1, K. E. Lee2, H. J. Im2, 3, Y. S. Kwon2, S. Kimura3, 1
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan2
Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Introduction

Okamura et. al. [3], previously. In their interpretation,
the reflectivity peak in the middle infrared region
originates from the optical transition in between thebonding and antibonding states of the hybridization
band of the conduction and local 4f electrons
predicted with PAM. Due to the PAM, the R( ,P)
peak must shift to the higher energy side. However, in
this study, the R(,P) peak does not shift withincreasing pressure. The result is not consistent withthe prediction of PAM. This result suggests that theinterpretation by usual PAM is insufficient. Recent
theoretical study on YbAl3 indicates that the infrared
peak originates from the band structure including the
hybridization between the conduction and 4f electrons[4]. Our result is consistent with the theoretical work.

In recent years, some compounds called “heavy
fermion” (HF) attract attention because of theirvarious physical properties. The physical properties
originate from the hybridization between itinerant
conduction electrons and local 4f electrons.
One ofthecharacteristic
physicalproperties
issuperconductivity due to the HF, which appears neara quantum critical point (QCP) located in between thelocal and itinerant characters of 4f electrons. There
are many experimental and theoretical studies toclarify the origin of the various physical properties at
QCP. The various physical properties originate fromelectronic structure near the Fermi level. To
investigate the electronic state at QCP and thetranslation process from local to itinerant character of
4f electrons, we measured reflectivity spectra of
CeIn3 that is an AuCu3-type cubic intermetallic HF
compound with a magnetic ground state resulting
from the competition between long ranged
antiferromagnetism(TN=11K), which is produced by
RKKY interaction, and the Kondo effect. With
applying pressure, the ground state changes from
antiferromagnetic to nonmagnetic HF state via the
QCP [1]. Therefore this material is suitable toinvestigate the electronic structure around the QCP.

Experimental
The single crystalline CeIn3 sample wassynthesized by an arc melting under argon
atmosphere, and then annealed at 600  for three
weeks inside an evacuated quartz tube. The THz
reflection spectroscopy under pressure was performedat the THz micro-spectroscopy end station of
UVSOR-II BL6B. A diamond anvil cell was
employed to produce high pressure. KBr was used asa pressure medium and a gold film as a reference. The
pressure was calibrated by a ruby fluorescencemethod.

Fig. 1. Reflectivity spectra [R(,P)] of CeIn3 with
AuCu3-type cubic crystal structure (inset) underpressure at 300K divided by that at 0.7 GPa. The
hatched area is that R( ,P) cannot be measured
because of an absorption of the diamond.
[1] S. Kawasaki et al., J. Phys. Soc. Jpn. 73 (2004)
1647.
[2] J. N. Hancock et al., Phys. Rev. Lett. 92 (2004)
186405.
[3] H. Okamura et al., J. Phys. Soc. Jpn. 76 (2007)
023703.
[4] H. Kuroiwa et al., J. Phys. Soc. Jpn. 76 (2007)
124704.

Results and Discussion
We obtained pressure-dependent reflectivity
spectra [R( ,P)] of CeIn3 at 300K in the pressure
region from 0.7 to 5.6 GPa as shown in Fig. 1. The
spectra were divided by that at 0.7 GPa to emphasize
the pressure dependence. With increasing pressure,the R(,P) intensity around 0.75 eV was enhanced.
To explain the pressure-dependent of R(,P), aninterpretation using the periodic Anderson model(PAM) has been employed by Hancock et. al. [2] and

91

BL6B

Phonon-Polariton of Superconducting InN Observed by Far-Infrared
Synchrotron Radiation
T. Inushima1, Y. Ota1, T. Yanagawa2, K. Fukui2
1
Department of Electronics, Tokai University, Hiratsuka, 259-1292 Japan2
Department of Electronics and Electrical Engineering,
University of Fukui, Fukui 910-8507 Japan

Temperature dependence of the reflectivity ofsuperconducting InN with a carrier concentration of
3.5~4.71017cm3 is investigated from 50 to 750 cm-1
using infrared synchrotron radiation. E1 phonon isobserved separately from plasma oscillation, and in
the energy range below E1(TO), phonon-polariton isobserved up to 104 cm-1. The lifetime of the E1(TO)phonon is directly determined by the reflectivity
measurements. From the temperature dependence ofthe lifetime, it is concluded that the E1(TO) phonon
decays primarily into phonons with a renormalized
frequency of 177 cm-1. From the plasma edge
position the electron effective mass is estimated to be
me=0.076m0 for the intrinsic InN.
All of the InN films investigated had a hexagonal
structure and their c-axes were perpendicular to thesapphire (0001) planes. Therefore, one E1 opticalphonon was observed in this configuration. Figure 1
shows the reflectivity spectrum of GS1586
(ne=3.51017cm3). In the spectrum there is a clear
Reststrahren band around 500 cm-1, which is due tothe E1 optical phonon. A reflection edge due to theplasma oscillation is observed at 200 cm-1. The
reflectivity spectrum is analysed using a following
dielectric function, ( ) =  0 + p22

  i

+

2
TO
2
.
2
  TO + i2(1)

In-In nano-structure spread in the a-b plane was thecause of the occurrence of the superconductivity[1].
The results presented here show that there is no such
structure in InN. At present we have to conclude
that InN has strong electron-phonon andelectron-electroninteractions
andthesuperconductivity is induced by this effect.

Fig. 1. Reflection spectrum of GS1586 at 10 K. The
fitted line (blue line) is drawn using Eq. 1. The
fitting parameters are; p=0.03 eV, TO= 0.0594 eV,
0=10.3, =0.0002 eV, =0.008 eV, =6.7, d=4.2
m.

Using Eq. 1, the reflectivity spectrum is well
reproduced and fitting parameters are obtained.
As is seen in Fig.1, the oscillations below E1(TO)are due to the interference of the penetrating light in
the InN film.
In this case,the light with
momentum k is expressed by polariton and isexpressed using () of InN as follows,c 2 k ( ) 2N=  ( ); k ( ) =
2
2cd


.

(2)

The observed phonon-polariton dispersion isshown in Fig. 2.
In this experiment, thephonon-polariton is observed up to 1.2 eV (104 cm-1).
The ratio of /TO is the energy dissipation rate for
the E1 vibration. When we regard this as anunharmonic factor of the crystal, InN has 3.310-3,
which is comparable to those of III-V compounds,
indicating that the crystal growth technology of InN
has attained the level of major III-V compounds.
Nevertheless, the InN investigated here shows
superconductivity. Once it was proposed that theFig. 2. Phonon-polariton wavenumber q=ck isplotted against photon energy . The data points
are obtained at the peak positions shown in Fig. 1,
where the order starts at the peak at 300 cm-1, where
N=0.5. The dashed line is drawn using () given in
Eq. 2, and the dotted line is the dispersion of the light.
[1] T. Inushima, Phys. Stat. Sol. (c) 4 (2007) 660.

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BL6B

Solid State Spectroscopy of Proteins in Terahertz Region

X. Jin1, S. Kimura2, H. Kihara1
Department of Physics, Kansai Medical University, 18-89 Uyama-Higashi, Hirakata573-1136, Japan
2
UVSOR, Institute for Molecule Science, and School of Physical Sciences, The Graduate
University for Advanced Studies (SOKENDAI), Myodaiji, Okazaki 444-8585, Japan1

The terahertz (THz) region of the electromagnetic
spectrum has energies of approximately 1 - 10 meV,
which corresponds approximately to the frequency
range of the transition between rotational states ofmolecules. Due to the strong frequency-dependent
attenuation of water, dry, or partially hydrated
samples should be used in the THz study. THz
spectroscopy has been used to studying the dynamics
of DNA, polypeptide and proteins. [1.2] In order toinvestigate effects of secondary structures on THz
spectra of proteins, we measured the THz spectra of
representative proteins having various secondary
structures, myoglobin (-helix-rich), lysozyme (/protein), -lactoglobulin (-sheet-rich) and synuclein (unfolded).
All experiments were done at THz beam line BL6B
at UVSOR-II. The thickness of the samples wasaround 0.5 mm. The lyophilized samples were tightly
pressed to form a tablet. The measurements weredone at the wavenumber range of 10-200 cm-1 atroom temperature. Each spectrum was accumulated
500 times. The final spectra were divided by the cell
spectrum in order to subtract absorbance of the cell.
All measurements were repeated three times to getgood consistency. When the wavenumber is above
100 cm-1, absorbance of the protein become very highand noisy.
Figures 1-4 show these protein absorbance spectra.
The red lines are smoothed ones. Figures 1(myoglobin) and 2 (lysozyme) show a broad peakaround 20-25 cm-1, respectively, while Figures 3(-lactoglobulin) and 4 (-synuclein) do not show
specific peaks at the corresponding region. These
results seem to imply that proteins are classified into
two different groups, with and without -helix. It
would be more related to the over-all concerted
motion of the proteins.

Fig. 1. Absorbance spectrum of myoglobin.

Fig. 2. Absorbance spectrum of lysozyme.

Fig. 3. Absorbance spectrum of -lactoglobulin.

[1] B. Brooks and M. Karplus, Proc. Natl. Acad. Sci.
80 (1983) 6571.
[2] F. P. David et al., Chem. Phys. Chem. 8 (2007)
2412.

Fig. 4. Absorbance spectrum of -synuclein

93

94

BL7B

Comparative Study of Photoluminescence Properties between
ScPO4:Zr4+,Mn2+ and YPO4:Zr4+,Mn2+ Phosphors
Y. Inada1 , M. Kitaura2, K. Fukui1
1
Dep. of Elec. Elec. Eng., Univ. of Fukui, Fukui, 910-8507
2
Fukui National College Technology, Sabae, 916-8507
the peak shift is not due to the change in crystal fieldstrength at the Mn2+ site. One plausible effect for the
peak shift is the change in electrostatic interaction of
3d electrons in Mn2+ ions. In fact, the results inelectron spin resonance (ESR) measurement hasrevealed that the 3d wave function of Mn2+ spreads
out in ScPO4 lattice more than in YPO4 lattice.

Photoluminescence (PL) properties of divalentmanganese ions are sensitive for the structure of host
crystals. An adjustment of the environment aroundMn2+ ions by the choice of host materials leads to theimprovement of PL properties; the diversification ofemission color and the increase in PL intensity. It isthus expected that Mn2+ activated phosphors have thepotential controlling PL properties artificially on
demand. In the present study, we have synthesized
the phosphor of ScPO4:Zr4+,Mn2+, and the PL and PL
excitation (PLE) spectra of it have been measured
using vacuum ultraviolet photons.
Samples of ScPO4:Zr4+,Mn2+ were synthesized by
the solid state reaction with the regent of Sc2O3,(NH4)2HPO4, ZrO2, and MnC2O4. The concentrationof Mn2+ and Zr4+ ions were adjusted to be 2.5 mol%in preparation. The powders were mixed by a ballomill, and then fired at 800 C in air for 5 hours. The
powders thus obtained were sintered at 1200 oC in
nitrogen atmosphere for 3 hours.
The PL spectrum of ScPO4:Zr4+,Mn2+ at 14 K isshown in Fig. 1. In this figure, the PL spectrum of
YPO4:Zr4+,Mn2+ at 14 K was also shown as areference. These spectra were obtained under
excitation with 6.5 eV photons. The PL spectra of
ScPO4:Zr4+,Mn2+
and
YPO4:Zr4+,Mn2+
aredominated by the 2.34 eV (green) band and the2.53 eV (blue-green) bands, respectively. The PL
intensity of the G band is about twice as large as theintensity of the BG band. The PLE spectra for the G
and BG bands at 14 K are shown in Figs. 2(a) and2(b), respectively. The lowest energy peak is locatedat 3.08 eV in ScPO4:Zr4+,Mn2+ and at 3.15 eV in
YPO4:Zr4+,Mn2+. The peak energy is lower in
ScPO4:Zr4+,Mn2+ than in YPO4:Zr4+,Mn2+.
In the PL and PLE spectra, the G band of
ScPO4:Zr4+,Mn2+ is similar to the BG band of
YPO4:Zr4+,Mn2+. As generally accepted, the PL bandof Mn2+ originates from the transition from the 6A1(6S) ground state to the 4T1 (4G) excited state. Theenergies of the lowest PLE peaks in Figs.2(a) and2(b) are close to the energy difference between the 6S
and 4G states [1]. This indicates that the G and BG
bands originate from the intra-3d transition of Mn2+
ions.
As the host material is changed from YPO4 to
ScPO4, the lowest PLE peak slightly shifts into
low-energy side. Since the 6A1  4A1 + 4E transitionis scarcely influenced by the crystal field potential [2],Fig. 1. PL spectra of ScPO4:Zr4+,Mn2+ (red) andYPO4:Zr4+,Mn2+ (blue) at 14K under excitation withphotons at 6.5eV.

Fig. 2. PLE spectra for the G band in
ScPO4:Zr4+,Mn2+(a) and the BG band in
YPO4:Zr4+,Mn2+(b) at 14K.. The intensities arenormalized to unity at their maxima.
[1] J. W. Stout, J. Chem. Phys. 31 (1959) 709.
[2] H. Kamimura, S. Sugano, Y. Tanabe, Haiishiba
Riron to Sono Oyo (Ligand Field Theory and its
Applications) (Shokabo, Tokyo, 1990) 10th ed., 224(in Japanese).

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VUV Reflection Spectroscopy of PdO and PtO Thin Films

Y. Iwai, K. Nakagawa, T. Mizunuma, K. Nakatsuru, K. Chijiwa, K. Ohba, S. Matsumoto,
H. Matsumoto
School of Science & Technology, Meiji University, Kawasaki 214-8571 Japanside of valence band lies slightly lower in PtO is
considered stronger d-O2p hybridization due to thelarger radius of Pt. And now, energy position of the
dip-A observed in reflection spectra is higher in PtO
thin film. If there is no large difference in unoccupied
levels as final states between PdO and PtO, it isconsistent with the widths of valence bands and theenergy positions of the dips. And on the same
assumption, it can be thought that the fact that the
band-B is observed at higher energy on PtO
originates the downward diffusing of O2p orbital
compared to that of PdO.

Both PdO and PtO have the tetragonal cooperite
structure (space group D94h) and extremely nearlattice constants. Extensive experimental andtheoretical studies have been performed on theelectronic structures of PdO [1, 2]. On the other hand,
there are a few reports of PtO in experimental dataobtained by electric and optical measurements. To
discuss the electronic structures, researchers have
tried calculation and referred them [3]. However,
because of restricted experimental data, there areunresolved problems such as a behavior like a p-typesemiconductor with high conductivity, and an
absence of optical band gap.
The purpose of this work was to achieve opticalresponses of PdO and PtO thin films in wide-range
photon energy, and investigate electronic structuresby comparing experiment data and theoretical
calculation.
Thin films of PdO and PtO were deposited by RF
reactive sputtering on fused quartz, at a temperatureof 573 °C. Metal palladium and platinum plate wereused as the target, and the sputtering was carried out
in argon and oxygen mixture gases. The film
thickness was about 150 nm. Composition ratio,chemical bonding states and crystallinity of the films
were investigated by RBS, XPS and XRD.
Reflection spectra of the films were measured in
the vacuum ultraviolet region up to 30 eV with the
3-m normal incident monochromator (grating: G1 and
G2) at BL-7B of UVSOR-II. And a silicon
photodiode sensor was used as a detector for thereflection light.
According to the analyses, both palladium andplatinum oxide thin films are composed ofpolycrystalline PdO or PtO.
Figure 1 shows the reflection spectra of PdO andPtO thin films at room temperature. Similar
characters are involved in each spectrum: a dip
named dip-A in the figure located at about 11 eV, aband named band-B at about 6-8 eV in lower energy
side of the dip-A, and a broad band with somefeatures above the dip-A. However, these are atdifferent position in energy.
To analyze the differences, DV-X molecularorbital calculation was performed. Figure 2 showsenergy level diagrams of [M13O28]-30 (M=Pd, Pt)
clusters embedded in Madelung potential represented
by formal charges. Band gap arises from the splitting
off in the d orbital slightly hybridized with O2p. In
each oxide, lower side of d band and O2p band
construct the valence band. The reason that the lower

Fig. 1. Reflection spectra of PdO and PtO thin films.
The solid line is the data obtained at UVSOR, and thedotted line represents the data obtained elsewhere.

Fig. 2. Energy level diagrams of [M13O28]-30 cluster(M=Pd, Pt). The energy is referred to the top of thevalence band. The broken lines represent unoccupied
levels.
[1] H. A. E. Hagelin et al., J. Electron. Spectrosc.
Relat. Phenom. 124 (2002) 1.
[2] R. Ahuja et al., Phys. Rev. B 50 (1994) 2128.
[3] J. Uddin et al., Phys. Rev. B 71 (2005) 155112.

96

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Angle Dependence of Polarized Excitation Spectra in AlGaN
M. Kishida1, F. Suzuki1, K. Fukui1, H. Miyake2, K. Hiramatsu2
1
Dept. Elec. Elec. Engi., Univ. of Fukui, Fukui 910-8507, Japan
2
Dept. Elec. Elec. Engi. Mie Univ., Mie 514-8507, Japan

AlGaN alloys are becoming important opticalmaterials which have the UV emission bands with thevariable photon energies from 3.4 to 6.28 eV, therefore
the studies of mechanisms of UV emissions require
wide energy range of the excitation photons, and the
SR is well-suited.
The band structures of both AlN and GaN are shownin Figure 1. The valence band at the  point issplitting into three bands by the crystal field effect (cr)
and the spin orbit interaction (so). The three bands
are called as crystal field split off hole (CH) band,heavy hole (HH) band, and light hole (LH) band,
respectively, and the transitions from CH, HH and
LH bands to the conduction band are labeled as A, B
and C transitions, respectively. Furthermore, sincethese bands have the anisotropy, the A transition isallowed under E//c condition, and both B and C are E
 c, where E and c represent the electric field vectorof the excited light and the crystal axis, respectively.
Usually, the AlGaN (including GaN and AlN)
crystalline thin films become wurtzite structure, andc-axis is perpendicular to the surface. Therefore theminimum band gap excitation is allowed in the caseof GaN (B transition), but is not in the case of AlN (Atransition). These conditions directly affect to theoptical properties, and the experimental research offinding the band inversion Al fraction is important.
Then, we have been measured the angle dependence
polarized photoluminescence excitation spectra.
AlxGa1-xN (x = 0.46, 0.54, 0.65, 0.74, 0.763)
samples were grown on the sapphire substrates via
1Am AlN single crystal films by MOVPE method at
Mie University. The thicknesses of AlGaN thin films
are about 1Am. All measurements were performed atabout 20K.
Figure 2 shows the excitation spectra of
Al0.763Ga0.237N at 0 degree of the incidence angle (E c) and 60 degree. The E // c spectra is calculatedusing these two spectra. The intensity of the E // cspectrum is higher than that of the E  c, and the red
shift of the peak energy is observed in the E  cspectrum. These results represent that the A transitionis allowed at x = 0.763, so is not clear (small), andthe shift represents cr.
Figure 3 shows the Al fraction dependence of cr .
The crs at x = 0 and 1 are taken from ref. 1. Fig. 3
results shows the band inversion is occurred at aroundx = 0.5. Fig. 3 also indicates that there is the negative
bowing which is similar to the x dependence of theband gap itself, though the bowing parameters aredifferent with each other.

Conduction bandB
A C   //HH band
LH band
CH bandA
B //
C
 
 
 so

 cr

GaN

AlGaN

AlN

Fig. 1. Band structures of AlN, GaN and AlGaN.

Fig. 2. Angle dependence of the polarized
photoluminescence exciton spectra (PLE) of
Al0.763Ga0.237N.

Fig. 3. Al fraction dependence of cr.
[1] A. Shikanai et al., J. Appl. Phys, 81 (1997) 417.

97

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Temperature Dependence of the Photoluminescence of the SrScCuOS
Layered Oxysulfide
T. Nakazato1, Y. Furukawa1, H. Ogino2, S. Saito1, S. Ono3, N. Sarukura1, K. Kishio2
1
Institute of Laser Engineering, Osaka University, Osaka 565-0871 Japan2
Department of Applied Chemistry,University of Tokyo, Tokyo 113-8656, Japan
3
Faculity of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, JapanThe development and engineering of the wide gap
semiconductors are important for optoelectronics.
Electrical and optical properties of various III-V or
II-V compounds have become clear that thephotoabsorption and the emission near the band gap
are dominated by excitons. It is said that the excitons
enhance emission efficiency because of their large
oscillator strengths and room temperature excitonic
emission is crucial for light emitting diode operation.
Unfortunately,
excitons
areusually
only
experimentally observed in high quality crystals andat low temperatures. Ueda et al.[1], investigated thetemperature dependence of the photoluminescence(PL) spectra of LaCuOS and found that the emission
from excitons can be observed at room temperature.
They also mentioned that the Cu-S bonding in Cu-S
layer defines the electronic structures near band gap.
We are interested in SrScCuOS because it has Cu-S
layer as LaCuOS. This suggests that it could also be apotential UV material. In the present study, we havemeasured the temperature dependence of the PL
spectra of SrScCuOS to evaluate the opticalproperties.
We have measured the PL spectra of 3 SrScCuOS
crystals, labeled sample A, B, C and E at the BL7B
port of the UVSOR. The excitation wavelength was
340 nm. In order to investigate the temperaturedependence of PL spectra, these measurements havebeen carried out at 24-120 K and room temperature.
Figure 1 shows the temperature dependence of the
PL spectra. The peaks exist at about 370 nm in all
samples. The peak intensities become stronger withlower temperature. These spectra have interesting
temperature dependence as will be discussed below.
In the case of sample A and E, only one broad peak
was found for each temperature setting. A blue shift
is observed and the width becomes narrower at lower
temperature. Samples B and C showed not only anarrowing of the peak width but a splitting wasobserved, as well. A temperature dependent relative
blue shift between the two peaks could not be
observed due to limitations in the spectral resolution.
The shorter wavelength peak relatively becomesstronger as compared with the longer wavelengthfeature as temperature is increased in both samples, B
and C. At present, we cannot conclude whether thesepeaks in each sample are excitonic in nature.
Nonetheless, the prospects are interesting because
excitonic emission in oxides has not been reported sooften. The differences in the PL spectra of A, B, C
and E might originate from anisotropy in the defects,
impurities, or structures of the Cu-S layers.
We have measured the temperature dependence of

the PL spectra of SrScCuOS to evaluate the opticalproperties. An intensive temperature-dependent PL
and absorption study is necessary to confirm theexcitonic nature of the observed UV emission.

Fig. 1. PL spectra of the SrScCuOS at 20-120 K androom temperature. The excitation wavelength is 340
nm.
[1] Ueda et al., Appl. Phys. Lett. 78 (2001) 2333.

98

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Energy and Temperature Dependences of Time Resolved Decay Curves in
AlGaN Alloys
T. Sakai1, M. Suzuki1, T. Kondo1, K. Fukui1, S. Naoe2, H. Miyake3, K. Hiramatsu3
1
Dept. Elec. Elec. Engi., Univ. of Fukui, Fukui910-8507, Japan
2Dept. Mech. Sys. Engi., Kanazawa Univ., Kakuma, Kanazawa 920-1192, Japan
3
Dept. Elec. Elec. Engi.Mie Univ., Mie 514-8507, Japan
three components of Al0.54Ga0.46N. The hot colors
represent the high intensity regions. The intensity
alternation from slow component to middle one withincreasing temperature is clearly seen at the lowtemperature, and similar behavior is also seen
between middle to fast at higher temperature side.
The intensity alternation between slow and middle
components reveals that there is the energy transfer
path between them and the thermal energy makes theexcited electrons at the energy level corresponded tothe slow component move to that corresponded to the
middle component. These kinds of the intensity
alternations are seen in all Al fraction samples, andwe think we can confirm our model at the various Al
fraction samples.

The ternary AlGaN alloys are promising materials
for ultraviolet (UV) optical devices. They are known
as the wide band gap semiconductors with thefeatures of the high melting point and the highhardness. The mechanisms of the near band edge
photoluminescence (PL) are not clarified enoughthough the qualitative improvements of the AlGaN
emission devices are remarkable. We have beenmeasuring PL, PL excitation (PLE) and time resolved
decay (TRD) curves. These results suggest that thenear band edge emission band consists of threeadjacent emission components (bands) which interact
with each other, especially lower two components
show the highly efficient energy transfer between
them. In this experiment, we have been carried out
both the energy and temperature dependence TRD
curves of the various Al fraction samples to confirm
this model.
AlxGa1-xN (x=0.370.85) samples were made by
the MOVPE method at Mie University. The
thicknesses of AlGaN thin films are about 1m on
1m AlN single crystal films with Al2O3 substrates.
The TRD measurements were performed at single
bunch operation modes. A conventional 30cm
VIS-UV monochromator with liquid N2 cooled CCD
detector is used for PL measurements of all samples.
The time region of our TRD measurements using
TAC method (time correlated single photon counting
method) is 0~178 ns and the resolution is about 1 ns.
Figure 1 shows PL spectra of the three adjacentcomponents and the total of various Al fraction
samples at ~ 10K. Three components are called as theslow (in the order of 100 ns or less), middle (10 ns
order), and fast (less than 1 ns : under the time
resolution of our TAC system). The total spectrum
represents the sum spectrum of these threecomponents, and it must be in good agreement with
the normal (time integrated) PL spectra, conversely,
the agreements between the total spectra in Fig. 1 andthe normal PL spectra of the various Al fraction
samples are good validation checks of our model. In
fig.1, it is quite obvious that the slow component
become dominant with increasing Al fraction. Thisbehavior is similar to the Al fraction dependence of
the PL band width. Since the PL band widthcorresponds to the classical alloy broadening, thecompositional inhomogeneity is increasing withincreasing Al fraction up to x = 0.85 and probably
introduces some kinds of defects.
Figure 2 shows the temperature dependences ofFig. 1. PL spectra of each element in all samples.

Fig. 2. Temperature dependence of time resolved PL
spectra of Al0.54Ga0.46N.

99

BL7B

Photoabsorption Cross Section of C60 Thin Film from 1.3 to 42 eV

H. Yagi1, K. Nakajima2, K. R. Koswattage3, K. Nakagawa3, C. Huang1,
Md. S. I. Prodhan1, B. P. Kafle1, H. Katayanagi1, K. Mitsuke1
1
Department of Photo-molecular Science, and Grad. Univ. Adv. Studies,
Institute for Molecular Science,Okazaki 444-8585,Japan
2
Science Research Center, Hosei University, Chiyoda-ku, Tokyo 102-8160, Japan
3
Faculty of Human Development, Kobe University, Nada-ku, Kobe 657-8501, Japan
7 eV and the width of the peak at 22 eV is muchlarger in the solid phase.
Smith has shown that absorption spectra of C60 in
the gas phase and solution resemble each other [5] byintroducing the Chako factor [6]s/g = (n2+2)2/9n.
(2)Here, s and g are the absorption coefficient insolution and in the gas phase, respectively, and n is
the refractive index of the solution. Linder shows thatwhen the solvent is not transparent, Chako factor
should be replaced by [7]s/g = [(n2+2-k2)2+(2nk)2]/9n.
(3)Here, k is the extinction coefficient of the solution.
These factors are derived by considering the effect ofvan der Waals interaction and Lorentz local field.
Solid C60 is a molecular solid which is bonded byweak van der Waals forces with a cubic structure.
Therefore this relation is probably applicable to thesolid C60. Present data multiplied by the the Linder
factor is shown in Fig. 1 (blue curve). Here, n and k
are calculated from the EELS spectra [3]. After thecorrection of the Linder factor, the present data agrees
very well with  in the gas phase except in the energy
range 24-34 eV.

Since the discovery of the method for bulk
synthesis of C60 [1], optical properties of solid C60
have been studied by various techniques. But most of
the studies were restricted to photon energies below 7
eV. Above 11 eV, only EELS measurements werecarried out. In the present study, we have measured
absorption spectra of C60 thin films from 1.3 eV to 42eV.
C60 films were prepared by vacuum deposition on
collodion thin film substrates. The deposition rate andthe amount of deposited C60 were estimated from thereadings of the crystal-oscillator surface thickness
monitor (Inficon, XTM/2). Collodion substrates andthe thickness monitor were located 90 mm above thesample holder and at symmetrical positions withrespect to the molecular beam axis. We prepared
three samples with the thickness d = 11, 28, and 57
nm. The deposition rate was 0.16-0.29 Å/s. Opticalabsorption measurements were carried out at BL7B of
the UVSOR facility. The photoabsorption crosssection of C60 film was estimated by using theLambert-Beer law
=0exp(-d).
(1)Here,  is the photoabsorption cross section, N is
the number density of C60 molecules and calculated
from the mass density 1.65 g/cm3 [2], d is the C60 film
thickness, I0 is the light intensity after passing
through a substrate, and I is the light intensity after
passing through a C60 film and a substrate. I0 and I
were measured succesively and normalized by thering current in the storage ring.
The  values obtained from the results of 28 and57 nm thick films show good agreement at h  12.5
eV. In the energy range 12.5-27.5 eV, I was so small
for the 57 nm thick film that we could not estimate
correct  values. The  from the results of 11 nm
thick film also shows good agreement with those of
the other films if multiplied by a factor of 0.85. Thisis probably due to the uncertainty of the film
thickness of 11nm thick film. Figure 1 shows thus
estimated photoabsorption cross section of C60 thinfilm (black curve) in comparison with that calculated
from EELS spectra of C60 thin film (green curve) [3].
The two curves are almost consistent with each other.
Photoabsorption cross section of gaseous C60 is also
shown in Fig. 1 (red curve) [4]. The positions of thepeaks and shoulders on the  curve for the C60 thinfilm agree well above 10 eV with those for gaseous
C60. This agreement, however, becomes worse below

Fig. 1. Photoabsorption cross section of C60.
[1] W. Kratschmer et al., Nature 347 (1990) 354.
[2] K. Prassides, H. W. Kroto, Phys. World 5 (1992)
44.
[3] E. Sohmen et al., Z. Phys. B Condens. Matter 86(1992) 87.
[4] B. P. Kafle et al., J. Phys. Soc. Jpn 77 (2008)
014302.
[5] A. L. Smith, J. Phys. B 29 (1996) 4975.
[6] N. Q. Chako, J. Chem. Phys. 2 (1934) 644.
[7] B. Linder and S. Abdulnur, J. Chem. Phys. 54(1971) 1807.

100

BL7B

Photoabsorption Cross Section of C70 Thin Film from 1.3 to 39 eV

H. Yagi1, K. Nakajima2, K. R. Koswattage3, K. Nakagawa3, C. Huang1,
Md. S. I. Prodhan1, B. P. Kafle1, H. Katayanagi1, K. Mitsuke1
1
Department of Photo-molecular Science, and Grad. Univ. Adv. Studies,
Institute for Molecular Science,Okazaki 444-8585,Japan
2
Science Research Center, Hosei University, Chiyoda-ku, Tokyo 102-8160, Japan
3
Faculty of Human Development, Kobe University, Nada-ku, Kobe 657-8501, Japan
crystal structure, or there may be other reason for thedisagreement between the three  curves.

The optical properties of solid C70, the second moststable and abundant fullerene, have been studied by avariety of techniques, though most of the studies wererestricted to photon energies below 6 eV. Even in thisenergy range, the values of the photoabsorption crosssection of solid C70 differ between different literature.
In the present study, we have measured the absorption
spectra of C70 thin films from h = 1.3 eV to 39 eV.
In the vacuum, C70 films were deposited on
collodion thin film substrates. The details of sample
preparation are described elsewhere [1]. We prepared
three samples with the thicknesses of d = 11, 29,
and 57 nm. The deposition rate ranges between
0.19-0.26 Å/s. Optical absorption measurements werecarried out at BL7B of the UVSOR facility. The
photoabsorption cross section of the C70 film wasestimated by using the Lambert-Beer law
=0exp(-d).
(1)Here,  is the photoabsorption cross section, N is
the number density of C70 molecules and calculated
from the mass density 1.64 g/cm3 [2], d is the
thickness of the C70 film, I0 and I are the intensities ofthe light measured with a photodiode by inserting,respectively, the film of neat collodion and that ofcollodion covered with C70 across the photon beamaxis. The intensity was measured successively at
wavelength intervals of 1 nm and normalized by thestorage-ring current.
Figure 1 shows the photoabsorption cross sectionof the three C70 samples with different thicknesses.
Their  values do not agree with each other. Figure 1
also contains the  curve calculated from the reported
EELS spectra of C70 thin film with the thickness of
200 nm (green curve) [3]. Our  curve for the 29 nm
C70 film and that calculated from EELS show good
agreement at h  25 eV. Figure 2 shows the
expanded spectra of Fig. 1 at h  6 eV. The  values
determined from EELS [3], ellipsometry [4], andoptical absorption spectroscopy [5] are also plotted.
These results and our present data are not consistent
with each other. This is possibly due to the differenceof the crystal structure. At room temperature, solid
C70 adopts face-centered cubic (fcc) or hexagonalclose packed (hcp) structures depending on thehistory of its formation [2]. A number of effects
determine the relative abundances of hcp and fcc
phases. In the present study, the conditions of sample
preparation were almost the same for all the samples.
Therefore, the thickness of the C70 film may affect theFig. 1. Photoabsorption cross sections of C70 thinfilms from 1.3 to 39 eV.

Fig. 2. Photoabsorption cross section of C70 thin films
below 6 eV in comparison with those of other studies[3-5].
[1] H. Yagi et al., UVSOR Activity Report 2007(2008).
[2] G. B. M. Vaughan et al., Science 254 (1991) 1350.
[3] E. Sohmen et al., Z. Phys. B Condens. Matter 86(1992) 87.
[4] Ren et al., Appl. Phys. Lett. 61 (1992) 124.
[5] Zhou et al., J. Appl. Phys. 80 (1996) 459.

101

FEL

Pumped Wavelength-Dependence of Ce:LuLiF4 as Fast Scintillator Using
Storage Ring Free-Electron Lasers
Y. Furukawa1, T. Nakazato1, M. Cadatal2, M. Pham2, T. Tatsumi1, A. Saiki1, Y. Arikawa1,
S. Saito1, N. Sarukura1, H. Nishimura1, H. Azechi1 , K. Mima1, T. Fukuda3,
M. Hosaka4, M. Katoh4, N. Kosugi4
1
Osaka university, Yamadaoka2-6, Suita, Osaka565-0871, Japan
2
The Graduated University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
3
Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
4
Institute for Molecular Science, Myodaiji, Okazaki, Aichi 444-8585, Japan

There is an emerging demand for the developmentof fast neutron scintillator for laser confined nuclear
fusion with a fast ignition scheme [1]. For the precise
measurement of ignition timing, a scintillator with afast response time to the high-energy neutron whileproviding sufficient contrast to the gamma ray is still
under investigation. Li 6 is known to have a large
cross section for high-energy neutrons. Therefore,
lithium-rich compounds with high quantum
efficiency light emitting ion are the prominent
candidates. From this aspects, we have considered
Ce:LuLiF4.
For the development of such scintillation devices,
the characterization of the response time for different
neutron or photon excitation energies is extremely
important for the optimum design of the material anddoping concentration.
For this purpose, free electron lasers (FEL) are
attractive for their flexible tunability. Among such
FELs, storage ring free-electron lasers (SRFEL)
should be the appropriate choice because of theiradequately high repetition rate [2].
In this presentation, Ce:LuLiF4 as a fast scintillator
is evaluated using a SRFEL operated in deep UV
region. The response time is found to remarkably
shorten for the excitation of the lower level of theabsorption band.
The SRFEL at the UVSOR facility in the Institutefor Molecular Science, Japan was used as theexcitation light source. The excitation wavelengths
used are 216 nm and 243 nm. The repetition rate of
FEL is 11.3 MHz. The SRFEL was focused on thesample. The fluorescence spectrum and thefluorescence lifetime of the Ce:LuLiF4 sample aremeasured using the spectrograph coupled to a streak
camera. The two peaks in streak camera image asshown in Fig. 1 are attributed to the 11.3 MHz laser
repetition rate. Fig. 2 shows that the fluorescencedecay time for excitation wavelengths of 290 nm, 243
nm, and 216 nm are 43 ns, 32 ns, and 35 ns,
respectively.
In conclusion, the response time is found to beremarkably shortened for the excitation oflower-level of the absorption band of Ce:LuLiF4 as
fast scintillator. This response time is alreadyacceptable for the scintillator for the diagonastic
device for the laser fusion with fast ignition scheme.
The SRFEL operated in deep UV region is shown to
be powerful tool for the material survey of neutron
scintillation devices.

Fig. 1. Streak camera images of Ce:LuLiF4 emission
when excited with 216 nm.

Fig. 2. Fluorescence lifetimes for 290 nm, 243 nm,
and 216 nm excitation.
[1] R. Kodama et al., Nature 432 (2004) 1005.
[2] M. Hosaka et al., Nucl. Inst. Methods in Phys.
Res. A 483 (2002) 146.

102