4
Solid state
spectroscopy
I: IR and
VUV

63

BL1B

Vacuum-ultra Violet Reflectance Spectroscopy of Strongly CorrelatedElectron System
J. Fujioka1, S. Miyasaka2, Y. Tokura1,3,4
Department of Applied Physics, University of Tokyo, Tokyo 113-8656 Japan2
Department of Physics, University of Osaka, 560-0043, Osaka Japan
3
Correlated Electron Research Center (CERC), National Institute of Advance Industrial
Science and Technology (AIST), Tsukuba 305-8562
4
ERATO-SSS, Japan Science and Technology Agency (JST) Tsukuba 305-8562 Japan1

The spin, orbital and charge degrees of freedom inthe correlated electron system have been attracting
much attention. The interplay among them leads tothe versatile magnetic and/or electronic structure,even though the crystal structure is nearly cubic. One
interesting topic is the reconstruction of the electronic
structure in the course of the insulator-metaltransition,accompanying
thespin/orbital
ordering-disordering transition [1]. The investigationof the electronic structure over wide energy range by
the measurements of the reflectivity spectra isindispensable to reveal the spin-orbital-charge
coupled phenomena associated with the insulator tometal transition.
In this beamtime, we have measured thereflectivity spectra of the several transition metaloxides, including the V, Mn, Fe, Ni, and Cu ions, for
an energy range between 4eV and 35eV at room
temperature using the beam line BL1B. We connected
the measured spectra to the low energy ones below 4
eV and calculated the optical conductivity spectra by
the Kramers-Kronig analysis. As an example, we
focus on the optical conductivity spectra of the single
domain crystals of Y1-xCaxVO3 in this report.
The perovskite-type vanadium oxide YVO3, which
is known as the prototypical Mott-Hubbard insulator,
has two valence electrons in the 3d orbital of thenominally trivalent V ion with the spin configurationof S=1. The orthorhombic crystal distortion splits thetriply degenerate t2g levels into the lower lying dxylevel and the higher lying doubly degenerate dyz anddzx ones. With lowering temperature, the Jahn-Teller
distortion further lifts the degeneracy of the dzx anddyz, and the G-type orbital ordering (OO), where theoccupied dzx and dyz orbitals are staggered in all (x, y,z) directions, appears at TOO1=200K. Subsequently,
the C-type spin ordering (SO) appears at TSO1=116K,
where spins align ferromagnetically along the c axis
and antiferromagnetically in the ab plane. Withfurther lowering the temperature, the C-type orbital
and G-type spin ordered state appears at TSO2(=TOO2)=77K. Recent studies have revealed that the
low temperature C-type orbital and G-type spinordered phase is immediately suppressed by Ca
doping, i.e. the hole doping as shown in fig. 1 (a).
In Fig. 1(b), we show the optical conductivity
spectra of Y1-xCaxVO3 x=0 and x=0.10 for E || c,which was measured at room temperature. In both

TSO , TOO(K)

250

(a)

200

TOO1

150

TSO1

100
50

TSO2(=TOO2)

0
0
(b)
V3d

O2p

6

C Y4d

O2p

B

3

-1

-1

Conductivity (10  cm )8

0.05
Doping level x

0.1

E || c
D
V3d

O2s

E
Y4d

Y4p

4
Y1-xCaxVO3
room temperature
x=0
x=0.1

2
A

0
0

10

20

30

Photon energy (eV)Fig. 1: (a) The spin-orbital phase diagramof Y1-xCaxVO3. (b)The optical conductivity
spectra of Y1-xCaxVO3 x=0 (black line) and
x=0.1 (red line), respectively.
spectra, several peaks are observed. We assigned thepeak A around 2eV to the Mott-gap excitation. A
more intense peak (B) is observed around 7 eV, whichis assigned to the charge transfer excitation from O2p
to V3d level. Above 7eV, three peaks (C, D, and E)
are observed and we have assigned them to theexcitations from O2p to Y4d, from O2s to V3d, andfrom Y4p to Y4d, respectively, according to Ref. [2].
To see the Mott gap excitation in more detail, in fig. 2,
we show the magnified view of the opticalconductivity spectra for YVO3 in the low energy
region. With lowering the temperature, the intensityof the Mott gap excitation for E||c spectra increases
especially in the range of TSO2 (=TOO2) < T < TOO1,
while that for Ec shows minimal temperaturedependence. Such an anisotropic charge dynamics is
also observed in the similar system, LaVO3, and is
explained in terms of the quasi-one-dimensional
orbital exchange interaction, which is characteristic in

64

-1

Optical conductivity(

400

10K
70K

210K
293K

0
(b)E || b

400

10K
82K
293K

-1

300

-1

82K
120K
185K

-1

cm )

400
200

500

YVO3 (a)E || cOptical conductivity ( cm )

600

200
100
0
400
300

Y1-xCaxVO3 E || c(a)x=0.02
10K
60K
100K

200K
240K
293K

120K
140K
160K

(b) x=0.10

100K
120K

TOO=135K 10K
TSO=100K 90K

200

200

100

0
0

TSO1=113K
TOO1=185K

1

2

3

0
0

4

Photon energy (eV)

140K
160K
293K

1

2

3

4

Photon energy (eV)Fig. 2: (a)The temperature dependence of the
optical conductivity spectra of YVO3 for E || cand (b) for E? c. The open and closed triangle isthe lower-lying band (mg1) and higher-lying one(mg2), respectively.

Fig3 (a) The optical conductivity spectra
for x=0.02 and (b)x=0.10, respectively. The
open and closed triangle is the lower-lying
band (mg1) and higher-lying one (mg2),
respectively.

may be that, for x=0.02, the spin and orbital quantum
fluctuation is relatively enhanced compared to LaVO3,
since this system is located in the vicinity of thespin-orbital ordered phase boundary.
In the E || c spectra for x=0.10, the intensity of theMott gap excitation is reduced and the additional
bump structure (mid-IR peak) appears at ~1eV, which
results from the incoherent motion of the doped holeas shown in fig. 3(b). The mid-IR peak for E || cspectra has larger spectral weight than that for E cand increases its intensity in the low temperature
region, while that for E  c shows minimal
temperature dependence. Note that the spectral
weight is a good measure for the kinetic energy of theelectrons. For x=0.10, the orthorhombic crystal
distortion is still robust and, hence, the dxy level might
be lower in energy than dyz or dzx level. Thus, as the
explanation for the enhancement of the mid-IR peakfor E||c spectra, it is expected that the doped holes
mainly occupy the dyz and dzx orbitals and have a large
kinetic energy along the c-axis, reflecting thequasi-one-dimensional orbital exchange interaction.

the C-type spin and G-type orbital ordered state[3,4,5]. According to the ref. [4], in the C-type spin
and G-type orbital ordered phase, the Mott gap
excitation is decomposed into the two components.
The lower-lying band (mg1) is an allowed Mott-gap
excitation along the ferromagnetic chain (||c) in the
C-type spin ordered state. The higher-lying band(mg2) is the nominally forbidden one, which is
weakly allowed due to the imperfect spin-orbital
polarization. For T > TSO2 (=TOO2), the intensity of
mg2 seems to be larger than that of mg1, indicating
the large spin and orbital fluctuation. Such kind of thelarge spin and orbital fluctuation in the C-type spin
and G-type orbital ordered phase is also pointed out
by the neutron scattering experiment [6]. On the other
hand, for T < TSO2 (TOO2), the intense peak structurearound 2eV disappears and the spectral weight istransferred to above 3eV. Concomitantly, theanisotropic feature of the Mott gap excitation also
disappears. The disappearance of the anisotropic
electronic structure may be explained in terms of thenearly isotropic orbital exchange interaction in the
G-type spin and C-type orbital ordered phase.
For x=0.02, the ground state is the spin C-type /orbital G-type and the intensity of the Mott-gap
excitation around 2eV in the E||c spectra increases
monotonously with lowering the temperature asshown in fig. 3(a). In particular, the intensity of the
mg1 continues to increase down to 10K, while there
is still considerable contribution from that of mg2.
This contrasts with the case of LaVO3, where that of
mg2 is much smaller at 10K [4]. One explanation[1]M.Imada et al., Rev. Mod. Phys. 70 (1998)1039.
[2] T. Arima et al., J. Phys. Soc. Jpn. 64 (1995) 2488.
[3]Y. Motome et al, Phys. Rev. Lett. 90 (2003)
146602.
[4] S. Miyasaka et al, J. Phys. Soc. Jpn. 71 (2002)
2086.
[5]J. Fujioka et al., Phys. Rev. Lett. 97 (2006)
196401.

65

BL5B

Phase Change of EUV Reflection Multilayer by Total Electron Yield andReflection Spectra
T. Ejima, T. Harada, A. Yamazaki
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai
980-8577 Japancos  2  d   cos 

In the extreme ultraviolet (EUV) wavelength
region, normal incidence mirrors were made available
through the use of reflection multilayers and are
required to have extremely low aberrations [1]. To
achieve the aberration-free multilayer mirrors, thetechnique of surface milling has been proposed as an
accurate correction method of figure errors [2]. In
order to make an accurate correction, it is importantto first obtain information regarding the reflection
phase in multilayer mirrors. In this study, reflection
phase values for multilayer optics were obtained
according to the formula derived from the total
electron yield intensity and reflection in themultilayer. These phase values were found to changein accordance with increases in the thickness of the
top layer.
Total electron yield (TEY) is a spectroscopic
method used in X-ray regions for detecting the
wavelength-dependence of the number of emitted
electrons from a solid, and is proportional to theabsorbed energy of the incident light in the EUV
region [3]. The intensity of the photoelectrons emitted
from a reflection multilayer is optically represented
by three terms: incidence-, reflection-, andinterference- terms [4]. When the attenuation length Lof emitted photoelectrons from the top layer issmaller enough than the thickness d of the top layer,
the TEY intensity IT() is approximately representedby I    I T    T
 2 R .
I  
(2)Periodic [Mo 2.6nm/Si 4.1nm]20 multilayerswith different thicknesses of top Mo layer were
fabricated on a same Si substrate. Thicknesses of the
top Mo layer were accurately controlled by the
shutter that was placed in front of the sample, andwere deposited from 0.4nm to 3.2nm at 0.4nm
intervals. A Mo single layer (d > 200nm) was alsofabricated for normalization of the TEY spectra. TEY
spectra of these aperiodic multilayers were measured
with reflection spectra. In the measurement, acombination of the G2 grating and the M22 mirror
was used for the 10-20 nm wavelength region. The
incident wavelength was calibrated according to theposition of the Si-L2,3 absorption edge. The resolving
power of the wavelength / estimated from thewidth of the Si-L2,3 absorption edge was 200. The
incident light estimates include a higher order lightcomponent, with a 20% intensity component of firstorder light. The reflection and TEY spectra of theMo/Simultilayer
systemweremeasuredsimultaneously at 10 to the normal angle ofincidence.
TEY spectra of the aperiodic multilayers werenormalized using the TEY spectrum of the Mo single
layer. The TEY and reflection spectra are shown in
Figure 1. In the TEY spectra, the main peak isobserved clearly around 13.4 nm and the peak
position shifts from 13.2 nm to 13.6 nm as the
thickness of the top Mo layer increases. Smaller
peaks are observed either side of the main peak, andthe peak positions shift also to the longer wavelength
region. In the reflection spectra, the series of peaks
located at 13.4 nm, deviate little in their peak position
despite increases in the thickness of the Mo layer.
To obtain the phase term differences, thenormalized TEY spectra of each multilayer and thereflection spectra were substituted for IT()/I(),I’T()/I(), and R() in Eq. (2). In Figure 2, phasechanges obtained experimentally are represented withthose obtained numerically using the exact formula[4]. Here, the graph labels (+Mo xx nm) correspondto the top Mo layer thickness. In the calculation, theoptical constants were taken from data compiled byHenke and Palik [6, 7]. The thicknesses of theperiodic Mo (2.02 nm) and Si (4.76 nm) layers used

I T    I   1  R   2 R  cos  2 d  L  , (1)where I() is a TEY spectrum of the top-layermaterial, R is the real part of the complex reflectanceof the top layer,  is the reflection phase at one layer
below the top layer, and  is the real part of the
top-layer’s propagation-vector using angle ofincidence  , wavelength , and complex dielectric
function  of the top layer. The term  is represented
as =2(-sin2)/. Equation (1) resembles theformula applied to analyze surface structures using
X-ray standing waves generated by a single crystal in
the hard X-ray region [5]. A phase term will beobtained on the basis of the relation to determine
surface structures. As the same manner, the phaseterm in Eq. (1) can be represented by measurable
quantities. When the phase term 2(d+L) isrepresented by  in Eq. (1), the cosine term difference
between the thicknesses d and d of the top layers canbe obtained as66

reflection and TEY spectra are in accordance with thechange in thickness of the top Mo layer. This method
will be applied to evaluate the phase information for
accurate multilayer optics, for example microscopes,
telescopes, and photo-masks, in the EUV region.
Same phase information will be obtained from the
Kramers-Kronig analysis of a reflection spectrum.
The merit of this method is reliant on the TEY
intensity, which can be easily measured in accordancewith the corresponding reflection spectra, such thatthe associated phase information can be obtained fora given wavelength.

in reflection spectrum were determined bycomparison of the X-ray diffraction data andfabrication conditions. The attenuation length wastreated as the fitting parameter, based on NIST
Standards [8]. The value of 2L obtained from thefitting procedure was 0.3.

[1] For example, D. Attwood, Soft X-rays andextreme ultraviolet radiation, (Cambridge University
Press, Cambridge, 2000) Chap. 4.
[2] M. Yamamoto, Nucl. Instrum. Meth. Phys. Res. A,
467-468 (2001) 1282.
[3] W. Gudat and C. Kunz, Phys. Rev. Lett., 29(1972) 169.
[4] T. Ejima, Jpn J. Appl. Phys. 42 (2003) 6459.
[5] J. Zegenhagen, Surf. Sci. Reports, 18 (1993) 199.
[6] “Handbook of Optical Constants of Solids I, II,
and III” ed. E. D. Palik, (Acad. Press. Inc., New York& London, 1985, 1991, and 1998).
[7] B. L. Henke, E. M. Gullikson, and J. C. Davis, At.
Data Nucl. Data Tables 54, 181 (1993), at
http://www.cxro.lbl.gov/optical_constants/.
[8] C. J. Powell and A. Jablonski, NIST Electron
Effective-Attenuation-Length
database,
NIST
standard reference database 82, (National Institute ofStandards and Technology, Gaithersburg, 2001).

Fig. 1. Total electron yield (solid curves) andreflection (broken curve) spectra of Mo/Si
multilayers with varying top Mo layer
thicknesses.

Fig. 2. Differences of the cos terms in Eq. (2). Red
curves represent the experimental results and black
curves, the calculation ones.
Experimental phase changes were reproduced wellby the numerical simulations at that the thickness ofthe top Mo layer is more than 1.2nm. This result
suggests that reflection phases of multilayer mirrors
will be observed by both reflection and TEY spectra
around reflection peaks. On the other hand, spectral
shapes of the phases resemble to those of thecalculation results but the values were disagreed atthat the thickness of the top Mo layer is less than
1.2nm. This disagreement will be caused by overlapof photoelectrons emitted from the layers below the
top layer. In other words, the assumption made on thederivation of Eq. (1), the photoelectrons are emitted
from the top layer only, will not applicable in thethinner top layers.
Simultaneous reflection and TEY measurements
have been obtained for aperiodic Mo/Si multilayers.
The phase term differences obtained from the

67

BL1B

Effect of Anionic Species in Ionic Liquids on Photostability
N. Inoue, M. Makita, T. Ishioka, A. Harata
Department of Molecular and Material Sciences, Kyushu University, Kasugakoen 6-1,
Kasuga-shi, Fukuoka 816-8680, Japan
appeared at 7.5ppm (d, C-H), 7.0ppm (d, C-H), and3.6ppm (s, N-CH3) after SR light irradiation. Thesechemical shifts show that compounds likemethylimidazole are formed. Similar changes wereobserved in [bmim][BF4]. Figure 2 shows IR spectraof [bmim][PF6]. New absorption peaks appeared at
1230cm-1, 1285cm-1, 1525cm-1. These are assigned toN-CH3 stretching vibration, N-CH3 stretchingvibration, imidazolium ring asymmetric stretchingvibration, respectively. Similar changes were observedin [bmim][BF4]. Compared to the IR spectra ofmethylimidazole, the products of the photolysis are
assigned to methylimidazolium hexafluorophosphate([mim][PF6]), or methylmidazolium tetrafluoroborate([mim][BF4]). In contrast, [bmim][Tf2N] did notshow any change in 1H-NMR and IR spectra.
It is considered that [bmim][PF6]([bmim][BF4])
photodecompose into [mim][PF6]([mim][BF4]), and1-butene. However, no photolysis was observed in[bmim][Tf2N]. Thus, it is apparent that photostabilityof ionic liquids are influenced largely by anionicspecies. It is considered that photolysis proceeds by
nucleophilic reaction or abstraction reaction of proton.
Further research including wavelength dependence
will be needed.

Photostability of ionic liquid compounds of
1-butyl-3-methylimidazolium salts was evaluatedusing synchrotron radiation. A remarkable change in
1
H-NMR and FT-IR spectra was observed for[bmim][PF6] and [bmim][BF4]. Production of
methylimidazolium ionic liquids was confirmed.
While no changes was observed for [bmim][Tf2N]. It
is suggested that photostability of ionic liquids arelargely influenced by anionic species.

Introduction
Ionic liquids are defined as salts which are in theliquid state at room temperature. Ionic liquids are
rapidly expanding topic of research because of theirfavorable properties such as negligible volatility; highchemical, thermal, and electrochemical stability; highionic conductivity; and, in some case, hydrophobicity.
These properties make them highly attractive
candidates for the use in solvent for chemical
reactions such as photochemistry, organic synthesis,
and photocatalysis. Especially, in photochemical
reaction, it is known that ionic liquids act as anelectron donor or an accepter. However,photochemical behavior and any potential toxicity
issues for most ionic liquids are not known,
particularly with respect to alkylimidazolium systems,
and preliminary data is only now being determined.
Recently, researches on water stability and thermo
stability are reported. Some ionic liquids possibly
decompose under moisture and high temperature
atmosphere. In the case of photoreactions, presence of
decomposed products might cause lowered
experimental accuracy and distorted results. It is
important to investigate photostability of ionic liquids
precisely.
In this report, photostability and photolysis of
1-butyl- 3-methylimidazolium hexafluorophosphate,tetrafluoroborate, bis(trifluoromethanesulfonyl)imide(
abbreviated[bmim][PF6],[bmim][BF4],[bmim][Tf2N], respectively ) were investigated usingsynchrotron irradiation.

PF6N

+

N

BF4Tf2N-

Transmittance / arb.units

Fig. 1
Structure of [bmim][PF6], [bmim][BF4],
and [bmim][Tf2N].

Experimental

( a)
( b)

( c)

1800 1600 1400 1200 1000 800-1Wavenumber / cm

The 0-th order diffraction of Seya-Namioka
monochromator ( 10eV>) was obtained from BL1B at
the UVSOR facility. The light was emitted from thechamber to a He-purged cell through an MgF2
window. The emitted light was reflected with an Al
mirror and vertically irradiated on the [bmim][PF6]surface for 30 minutes.
These kinds of ionic liquids ([bmim][PF6],[bmim][BF4], [bmim][Tf2N] (Figure 1)) weresynthesized according to the literature [1-3].

600

400

Fig. 2
IR spectra of (a) [bmim][PF6], (b) [bmim][PF6] after SR light irradiation, and (c) methyl
imidazole.
[1] J. G. Huddleston, R. D. Rogers, Chem. Commun(1998) 1765
[2] Rika. Hagiwara, Yasuhiko Ito, Journal of Fluorine
Chemistry 105 (2000) 221[3] M.J.Earle, C.M.Gordon, K.R.Seddon, Analytical
Chemistry (2006) 6

Results and Discussion

In 1H-NMR spectra of [bmim][PF6], new peaks

68

BL1B

Photoluminescence from Localized Excitonsin PbCl2, PbCl2:Br¯ and PbCl2:I¯ Crystals

1

S. Izuhara1, M. Kitaura2, H. Nakagawa1
Dep. of Electrical & Electronics Engineering, Fukui University, Fukui, 910-8507
2
Fukui National College of Technology, Sabae, 916-8507

The excitonic states of lead halides are represented
by the excited states of a Pb2+ ion in roughapproximation. Indeed, since the optical properties
are strongly dependent on halogen species, theexcitonic states certainly include significant
contribution from electronic orbitals of halogen. It
has been accepted that the outermost p orbitals of
halogen play an important role in self-trapping of
excitons in PbX2 (X=F, Cl, Br). As is well known, theinformation on absorption and luminescence of thehalide crystal doped with other halogen ion impurity
is indispensable to see the relaxed configuration ofself-trapped excitons (STE’s) in the host crystal. The
purpose of the present study is to investigate thelocalized exciton luminescence of PbCl2 crystals
doped with a small amount of Br¯ ions and I¯ ions.
Special reagent grade powder of 99.99% purity of
dehydrated PbCl2, PbBr2 and PbI2 were purchasedfrom Kojundo Chemical Laboraty. The single crystalsof
PbCl2,
PbCl2:Br¯(0.01mol%)and
PbCl2:I¯(0.01mol%) were grown from melt in sealed
quartz ampoules by the Bridgeman method. Samples
were cut in the size of 5×5×5 mm3 from crystal
ingots with a razor blade. The mesurements ofemission and excitation spectra were carried out at
BL1B using a normal incidence monochromator.
Photoluminescence from samples was guided into theincident slit of a grating monochromator by a opticalfiber, and then detected by a CCD detector or aphotomultiplier tube. The crystal samples were
mounted on the copper holder of a closed-cycle He
refigerator in order to perform measurements at 13K.
Figure 1 shows emission spectra of PbCl2,
PbCl2:Br¯, and PbCl2:I¯ at 13K (black lines). The
excitation spectra for the emission bands observed in
the three samples are also indicated by red lines. In
the crystal of PbCl2, two emission bands are observed
at 3.78eV (UV emission) and 2.89eV (B emission)under excitation at 4.6 eV. This spectrum is inagreement with the emission spectrum previously
reported [1] .
In the crystal of PbCl2:Br¯, three emission bands
are observed at 3.1eV (V1 emission), 2.32eV (Gemission) and 1.75eV (R emission) by
photostimulation at 4.3eV. The V1 emission isstrongly
excitedinthenarrowenergy13K

INTENSITY OF LUMINESCENCE

PbCl2

Exci. 4.6eV
Emis. 3.78eV

PbCl2:Br -Exci. 4.3eV
Emis. 3.15eV

PbCl2:I-

Exci. 4.0eV
Emis. 2.26eV

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Photon Ener gy [eV]Fig.1 Emission spectra (black lines) and excitation
spectra (red lines) of PbCl2, PbCl2:Br¯, and PbCl2:I¯.
region around 4.3eV (shaded area), which is locatedin the low energy tail of the fundamental abosrptionin PbCl2.
In the crystal of PbCl2:I¯, an emission band
appears at 2.26eV (Y emission) when the excitation
photon energy is adjusted at 4.0 eV. The Y emissionis also excited in the limited energy region around
4.0eV (shaded area), which separates from theintrinsic absorption edge.
It seems that the V1 emission in PbCl2:Br¯ and Y
emission in PbCl2:I¯ are similar to the luminescencefrom localized excitons in Br¯ or I¯ doped alkali
chlorides, in the sense that the excitation for theemission takes place in the energy region below theexcitonic absorption band of the host lattice. They are
assigned to the luminescence from localized excitons.
According to the cluster calculation, the excitonic
states of lead halide are described by a complex
molecule of lead and halogen ions. We expect that thewave function of an electron is localized on a lead ion
while that of a hole is distributed on the adjacenthalogen ions in PbCl2:Br¯ and PbCl2:I¯. The cluster
calculation by the DV-X method is now underproceeding to make sure of our expectation.
[1] M.Kitaura et al., J. Phys. Soc. Jpn. 70 (2001)
2462.

69

BL1B

Luminescence and Excitation Properties of Host Lattice and Eu2+ Ions in
BaMgAl10O17:Eu Phosphor
H. Yoshida1,2, H. Kai1, S. Watanabe1, K. Ogasawara1
Department of Chemistry, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan
2
Research and Development Division, NEC Lighting, Ltd., 3-1 Nichiden, Minakuchi-cho, Koka,
528-8501, Japan
1

From the view points of the importance as anefficient blue-emitting phosphor, Ba1-xEuxMgAl10O17(BAM:Eu) is a material of great interest in the recent
research of phosphor. It is well known that BAM:Eu
phosphor used for 3-band fluorescent lamps (FLs)and color plasma displays (PDPs) exhibit a decreaseof luminescence and color shift due to thermal anddischarge damage. Therefore, their products havebeen many issues in using it.
The blue emission in BAM:Eu is due to the 4f65d1→
4f7 transition of Eu2+ ions. As substituted location of
Eu2+ ions, three sites are generally considered in thehost lattice. The Beevers-Ross(BR) site is originallylocated to the Ba2+ site, while the anti-Beevers-Ross(aBR) and the mid-oxygen (mO) sites are in theinterstitial positions[1]. According to recent reports,
the most dominant site of Eu2+ ions in BAM is
considered to be aBR[2-5]. However, this problem isstill in controversy.
In this report, we have investigated the excitation
properties of host lattice and Eu2+ ions in BAM:Eu
phosphor by using the technique of vacuum
ultraviolet measurements by synchrotron radiation
light and first-principles molecular orbital calculation
method developed for rare earth ions.
The luminescence bands at about 258 nm and 450
nm, which originate from the host lattice and the Eu2+
ions in BAM:Eu respectively, are observed. Figure 1
shows normalized excitation spectra of BAM:Eu. For
x = 0, two excitation peaks at 160 nm and 175 nm areobserved. They are considered to be due to the O 2p
→ Ba 5d transitions and the O 2p → Al 3dtransitions within spinel block, respectively [6]. The
excitation spectra at 450-nm emission band show asignificant absorption band at 200 nm as well as thetwo main structures peaking at 310 nm and 250 nm. It
is well known that the excitation band between 220
nm and 380 nm clearly increases with an increase of
the amount of Eu2+ ions, which is due to 4f7 →
4f65d1 transitions of Eu2+ ions. It is also found that theabsorption edge of host lattice at 190 nm is
unchanged with increase of Eu content, whichindicates that the absorption of Eu activator center in
BAM does not overlap that of the host lattice. On
the other hand, in the luminescence spectrum underthe excitation at 200 nm, the 388-nm emission bandwith an extrinsic characteristic was strongly observed,
while the electronic state calculation of Eu2+ site in
BAM:Eu suggested a possible contribution of the
mid-oxygen sites in BAM:Eu [4,5] to this 200-nm

structure. Therefore, in addition to the mO site, thepresent results indicate that some kind of defects or
impurities also contribute to the 200-nm structure.
[1] N. Iyi, Z. Inoue and S. Kimura, J. Solid State
Chem. 61 (1986) 236.
[2] K. C. Mishra, M. Raukas, A. Ellens and K. H.
Jhonson, J. Lumin. 96 (2002) 95.
[3] M. Stephan, P.C.schmidt, K.C. Mishra,
MRaukas, A. Ellens and P. Boolchand, Z. Phys.
Chem. 215 (2001) 1397.
[4] H. Toyoshima, S. Watanabe, k. Ogasawara andH. Yoshida, J. Lumin. 122-123 (2007) 104.
[5] H. Yoshida, T. Yamazaki, H. Toyoshima, S.
Watanabe, K. Ogasawara and H. Yamamoto, J.
Electrochem. Soc., submitted.
[6] B. Howe and A.L. Diaz, J. Lumin. 109 (2004)
51.

Ba1-xEuxMgAl10O17

Obs. 450 nm
x = 0.20

INTENSITY (arb. units)x = 0.10
x = 0.06
x = 0.03
x = 0.01
x = 0.003
x = 0.001
x = 0.0003
x = 0.0001
x = 0 (Obs. 243 nm)

150

200
250
300
350
WAVELENGTH (nm)400

Fig. 1 Excitation spectra of Ba1-xEuxMgAl10O17 (x= 0.0001, 0.0003, 0.001, 0.003, 0.01, 0.03,
0.06, 0.1, 0.2) observed at 450-nm emission
band. As reference, an excitation spectrumof the 243-nm emission in x = 0 is also
shown.

70

BL1B

Excitation Energy Transfer in CeF3 Crystals
Heavily Doped with Sr2+ Ions
Y. Tani, T. Katagiri, D. Iri, M. Itoh, M. Fujita1, A. Yoshikawa2, K. Aoki 3
Department of Electrical and Electronic Engineering, Shinshu University, Nagano 380-8553
1Japan Coast Guard Academy, Kure 737-8512
2
Institute of Multidiscriplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577
3
Stella Chemifa Corporation, 1-41 Rinkai-cho, Izumiootsu, Osaka 595-0075
Among single-component fluorides such as BaF2,
CaF2, CeF3, etc., CeF3 is one of the most commonlyused crystalline scintillating materials with fast
decaying luminescence. In the present paper, excitation energy transfer in CeF3 crystals doped with Sr2+
ions is discussed.

comparable with the decay time (17 ns at 8 K) of the
intrinsic Ce3+ luminescence.

(a)Experiment

CeF3 single crystals heavily doped with Sr2+ ions (3mol) were grown by the micro-pulling-down (PD) method [1]. Three dimensional emission (em)excitation (ex) spectra were measured using a
SpectraPro-300i monochromator equipped with an
LN/CCD camera. The decay kinetics of luminescence
was detected by an MCP with use of a time-correlated
single-photon counting technique when the UVSOR
storage ring was operating in single-bunch mode
(pulse width: 1.3 ns; pulse interval: 177.6 ns).

(b)

Results and Discussion
Figure 1 shows the contour plots of emissionexcitation spectra of CeF3:Sr at (a) 8 K and (b) 300 K.
In Fig. 1(a) an emission band peaking around 330 nm
is excited with UV light at ex  290 nm. This band
somewhat red-shifts relative to the Ce3+ 5d  4f
luminescence (287 and 304 nm) in pure CeF3. The
excitation threshold (290 nm) is also lowered ascompared to that (260 nm) for the intrinsic Ce3+
luminescence. These facts suggest that the 330 nm
band is ascribed to Ce3+ ions perturbed by nearby Sr2+
ions. The intrinsic Ce3+ luminescence locating on the
short-wavelength side of the main band at 330 nm isvery weak in intensity due to heavy doping.
In Fig. 1(b) an emission band appears at around
400 nm at the expense of the 330 nm band. The 400
nm band, which is excited at ex  295 nm, is probably attributed to some defect that was introduced by
Sr2+ doping. Therefore, it is supposed that excitationenergy is efficiently transferred from Ce3+ sites todefect sites when the CeF3:Sr crystal is warmed from
8 to 300 K.
Figure 2 shows the decay behaviors of (a) the 330
nm luminescence at 8 K and (b) the 400 nm luminescence at 300 K, both being excited at ex = 266 nm.
The two bands exhibit a single exponetial decay overtwo decades. The decay times of the 330 and 400 nm
bands are 26 and 40 ns, respectively. These values are

Fig. 1. Contour plots of the emission-excitation spectra of CeF3:Sr at (a) 8 K and (b) 300 K.

Fig. 2. Decay curves of (a) the 330 nm luminescenceat 8 K and (b) the 400 nm luminescence at 300 K.
[1] A. Yoshikawa, et al.: J. Cryst. Growth 270 (2004)
427.

71

BL1B

Energy Transfer to Pr3+ Ions in LuAG:Pr Crystals
2

2

1

T. Katagiri, D. Iri, M. Itoh, M. Fujita , A. Yoshikawa , H. Ogino , K. Kamada

2

Department of Electrical and Electronic Engineering, Shinshu University, Nagano 380-8553
1Japan Coast Guard Academy, Kure 737-8512
2
Institute of Multidiscriplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577
In the last decade, Lu3Al5O12 (LuAG) garnet dopedwith rare-earth ions attracts much attention as aneffective scintillating material. Pr3+-doped Lu3Al5O12
is a newly-grown crystal in the LuAG family.
Therefore, a search for its luminescence properties isvery interesting. In this work, we have investigatedthree dimensional (3-D) emission-excitation spectra
and luminescence decay kinetics of LuAG:Pr crystals.

behaviors at 300 K are almost the same as Fig. 2.

ExperimentSingle crystals of LuAG:Pr (0.3 mol) were grownby the micro-pulling-down (-PD) method [1]. The
3-D emission (em)-excitation (ex) spectra were measured by using an Acton SpectraPro-300i monochromator equipped with a camera (Roper Scientific
LNCCD-100EB-GI). Luminescence decay kinetics
was detected by an MCP (Hamamatsu R3809U-52)
with use of a time-correlated single-photon counting
technique under the single-bunch operation of the
UVSOR ring (duration: 1.3 ns; interval: 177.6 ns).

Results and Discussion
Figure 1 shows the 3-D spectrum of LuAG:Pr at 8 K.
Three broad emission bands are observed at 260, 310
and 370 nm. The 260 nm band is the intrinsic
luminescence of LuAG, because it is excited with UVlight above the fundamental absorption edge (ex 
172 nm). The 310 and 370 nm bands are ascribed to
the 5d  4f transitions of Pr3+ ions. In the region atem  400 nm, several weak emission lines are seen
and attributed to the 4f  4f transitions of Pr3+ ions.
The decay behaviors of the 310 nm luminescence
excited at 280 and 170 nm are shown in Figs. 2(a)and 2(b), respectively. Under the direct 4f  5d
excitaion of Pr3+ ions (a), the emission intensity
decays single-exponentially over two orders ofmagnitude, with a lifetime of 18.4 ns. When the host
crystal is photoexcited (b), two remarkable changes
take place in the decay kinetics. One is that a risecomponet appears in the initial stage at t = 0, as seenfrom the insets of Fig. 2. The other is that a piled-up
component apparently increases in intensity.
The above facts strongly suggest that there are twokinds of energy transfer mechanisms from the host
LuAG crystal to the Pr3+ ions; a fast process with atransfer time T of nanoseconds or less and a slow
process with T  1 s. These transfer processes are
not so sensitive to the temperature, because the decay

0

10

INTENSITY

Fig. 1. 3-D emission-excitation spectrum of LuAG:Pr
at 8 K, together with the contour plot of the upper
spectrum in the (em, ex) plane.
(a)

0
-2

0

2

4
6 8
TIME (ns)

0

2

4
6 8
TIME (ns)

-2

10

0

10

INTENSITY

INTENSITY (arb. units)

-1

10

1

(b)

1

0
-2

-1

10

0

20

40

60

80

100 120 140

TIME (ns)Fig. 2. Decay behaviors of the 310 nm luminescenceof LuAG:Pr excited at (a) 280 and (b) 170 nm at 8 K.
[1] H. Ogino, A. Yoshikawa, et al., J. Cryst. Growth287 (2006) 335.

72

BL1B

+
Luminescence Properties of Heavily Doped CsI:Tl Crystals
T. Kawai1, T. Hirai2, N. Ohno2,3
Graduate School of Science, Osaka Prefecture University, Sakai 590-0035, Japan
2
Academic Frontier Promotion Center, Osaka Electro-Communication University
3
Graduate School of Engineering, Osaka Electro-Communication University,
Neyagawa 572-8530, Japan

1

CsI crystals doped with Tl+ ions exhibit
complicated luminescence properties in the different
way from the Tl+ centers doped in NaCl-type alkali
halides. The two UV bands are attributed to intratransition of the Tl+ ion. The two visible-light bands
are considered to originate from the Tl+ perturbed
self-trapped excitons [1]. In order to determine thecharacteristics of the complicated luminescence andtheir origin, the luminescence properties of CsI:Tl+
crystals with various Tl+ concentrations have beenstudied [2]. In the present study, we have investigatedluminescence properties of the heavily doped CsI:Tl+
crystals in order to clarify an influence of the Tl+concentration on the luminescence characteristics.
Single crystals of the heavily doped CsI:Tl+ weregrown from a starting material with the concentrationof 1.0 mol% TlI by Bridgmann method.
Luminescence and excitation spectra of the CsI:Tl+
crystals were measured at the BL-1B beam line of
UVSOR.
Figure 1 shows the luminescence spectra of theheavily doped CsI:Tl+ crystal at 10K under theexcitation on 4.30 and 4.00 eV. Under the excitation
on 4.30 eV, which corresponds to the peak energy of
the A absorption band of CsI:Tl+, the luminescencebands are observed around 2.21, 2.52, and 3.05 eV.
The bands are the same ones of the CsI:Tl+ crystals
with the concentration of less than 10-3mol%. Whenthe concentration of the Tl+ ions is 1.0 mol%, theabsorption intensity around the energy region below
4.30 eV increases remarkably. In the heavily doped
CsI:Tl+ crystal, the 4.00 eV excitation causes the
new luminescence bands peaking at 2.05, 2.31 and
2.73 eV.
Figure 2 shows the excitation spectra 2.03 and 2.25
eV of the heavily doped CsI:Tl+ crystal. The
excitation spectrum for 2.25 eV is similar to that of
the CsI:Tl+ crystals with the concentration of lessthan 10-3mol%. On the other hand, the excitation
spectrum for 2.03 eV exhibits the strong response at
4.10 eV, which corresponds to the energy region
below the A absorption band.
In general, as the concentration of the Tl+ ionsincreases beyond 10-2 mol%, aggregate centers suchas dimer are created [3]. The absorption bands due tothe aggregate centers are observed in the energy
region below the A absorption band. Since the 2.05
eV luminescence band in the heavily doped CsI:Tl+
crystal has the strong response in the lower energy
region than the A band, the 2.05 eV band should be

attributed to the aggregate centers of the Tl+ ions. The
aggregate centers would exhibit the different
characteristics of the luminescence from the isolated
Tl+ centers.

Lumi. Int. (arb. units)

800 700

Wavelength (nm)
600
500

400
CsI:Tl+1.0 mol%

10 K

Exc. 4.30 eV
Exc. 4.00 eV

1.5

2.0
2.5
3.0
3.5
Photon Energy (eV)Fig. 1. Luminescence spectra of the heavily doped
CsI:Tl+ crystal under the excitation on 4.00 eV (redcurve) and 4.30 eV (blue curve).

Lumi. Int. (arb. units)

350

300

10 K

3.5

Wavelength (nm)250

200
CsI:Tl+1.0 mol%
For 2.25 eV
For 2.03 eV

4.0

4.5
5.0
5.5
6.0
6.5
Photon Energy (eV)Fig. 2. Excitation spectra for 2.03 eV (red curve) and2.25 eV (blue curve) of the heavily doped CsI:Tl+
crystal.

[1] V. Nagirnyi, S. Zazubovich, V. Zepelin,
M. Nikl and G. P. Pazzi, Chem. Phys. Lett.
227 (1994) 533.
[2] V. Babin, A. Krasnikov, H. Wieczorek andS. Zazubovich, Nucl. Instr. and Meth. in Phys.
Res. A 486 (2002) 486.
[3] T.Tsuboi and P.W.M.Jacobs, J. Phys. Chem.
Solids 52 (1991) 69.

73

BL1B

Luminescence Properties of YPO4:Bi3+
N. Ohno, T. Hirai
Academic Frontier Promotion Center,
Osaka Electro-Communication University, Neyagawa, Osaka 572-8530, Japanand 1P1 excited states, respectively. Kang et al. havereported that the A and C bands appear at 3.7 and ~6.0 eV, respectively, in the absorption spectrum of
KCl:Bi3+ at low temperatures [2].
In Bi3+ ions doped in phosphate and fluoride hosts,
the absorption bands would shift to the higher energyside, as compared to those in chloride hosts. In
YPO4:Bi3+ crystals, the excitation band appearing at
5.4 eV is tentatively assigned as the A band nature
due to 1S0 → 3P1 transition in Bi3+ ions. The excitation
bands at 6.5–10 eV show composite structures, which
is a common feature of the C band of Tl+-type ions.
Therefore, these structures in the VUV region is
ascribed to the C band origin ascribed to 1S0 → 1P1
transitions in Bi3+ ions.

INTENSITY (arb. units)

Metal ions with s2 electronic configurations dopedin wide-gap materials such as alkali halides, which
are called Tl+-type ions, show several strong
absorption bands due to s2 → sp transitions. Since
these optical transitions are dipole-allowed, theabsorption is expected to be much stronger than that
due to the dipole-forbidden f-f transitions in rare-earth
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 fluoride and phosphate hosts aretransparent up to ~ 10 eV, so that the VUV light candirectly excite impurity activators in these hosts. The
strong absorption would give efficient conversion of
the VUV light from the Xe2 discharge fluorescentlamps.
In the present study, luminescence properties oftrivalent Tl+-type Bi3+ centers in phosphate andfluoride hosts have been studied in the UV and VUVregion. The YPO4:Bi3+ and YF3:Bi3+ phosphors wereprepared by amounts of the appropriate starting
compound powders of YPO4 and YF3 adding BiF3 (~2 mol %), mixing and firing in a carbon crucible at
900ºC in argon atmosphere. Impurity Bi3+ 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 YPO4:Bi3+
measured at room temperature. Luminescence peaks
located at 3.1 eV and 3.6 eV and a small hump at 4.9eV are observed for the excitation of VUV light at 7.8
eV. The 3.1 and 3.6 eV luminescence is excited withphotons of 5.4 eV and the luminescence energies of
Xe discharge lamp in the VUV region. These excitation peaks are located at lower energies than theabsorption edge of the host YPO4 (~ 12 eV). Therefore, the observed luminescence bands of YPO4:Bi3+
would be responsible for intra-ionic transitions in
impurity Bi3+ ions.
Tl+-type ions doped in alkali-halide crystals with ahigh symmetry crystal structure exhibit threecharacteristic absorption bands arising from thes2→sp transitions, namely, A, B and C bands [1].
These absorption bands have been attributed to theoptical transition from the 1S0 ground state to 3P1, 3P2,

YPO 4:Bi3+

RT

1
emissionexc. 7.8 eV
0.50excitation
emi. 3.1 eV

2

3

4
5
6
7
8
PHOTON ENERGY (eV)910Fig. 1. Luminescence (blue curve) and excitation(red curve) spectra of YPO4:Bi3+ at room temperature.
[1] W.B. Fowler, Physics of Color Centers, Academic
Press Inc., New York, 1968.
[2] J.G. Kang, H.M. Yoon, G.M. Chun, Y.D. Kim and
T. Tsuboi, J. Phys.: Condens. Matter 6 (1994) 2101.

74

BL1B

Photoluminescence of Hydroxyapatite Irradiated by Ultraviolet
Synchrotron Orbital Radiation Light (3)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 is also
useful as a contrast medium for magnetic resonanceimaging, restriction enzyme, biocatalyst, and so on infields of biochemistry, physiology, medicine, etc.
However, the behavior of rare earth in the living bodysystem 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 rare earth ion is also found to
substitute easily for calcium ion in hydroxyapatitewhich is soaked in rare earth chloride aqueous
solution, and to play on emission center.
In this study, hydroxyapatite samples doped withrare earth phosphate were prepared in order to apply
to phosphor. Their characteristics were investigatedby photoluminescent property of rare earth ion-doped
hydoxyapatite samples excited by ultraviolet
synchrotron orbital radiation light.
Eu-dopedhydroxyapatite
andGd-dopedhydroxyapatite samples were prepared as follows:hydroxyapatite was added with EuPO4 or GdPO4 andmixed homogeneously, and then heated at 1373K for
1 hr. EuPO4 or GdPO4 was prepared by reaction of
GdCl3 or YbCl3 and Na3PO4· 12H2O and then fired at
1373K for 1 hr. GdCl3 or YbCl3 was prepared byreaction of Eu2O3 or Gd2O3 and HCl.
The photoluminescent property of each sample
exited by ultraviolet synchrotron orbital radiation
light (BL-1B) was detected by using with amulti-channel analyzer.
Figure 1 shows photoluminescence spectra of rareearth ion-doped hydroxyapatite samples excited by
BL-1B.
The data of X-ray powder diffraction indicated thatthe rare earth ion substituted for calcium ion inhydroxyapatite.
Figure 1 shows the photoluminescent spectra ofrare earth ion-doped hydroxyapatite samples excitedby ultraviolet synchrotron orbital radiation light. In
Eu ion-doped sample, 4 peaks due to 5D0→7F1(595nm), 5D0→7F2 (612nm), 5D0→7F3 (654nm), and
5
D0→7F4 (700nm) of Eu3+, and 3 broad peaks (at near
330nm, 430nm and 580nm) due to hydroxyapatite
matrix. The emission intensity of Eu3+ ion was veryweak.
In Gd ion-doped sample, a peak due to 6P7/2→8S(320nm) and 3 broad peaks (at near 330nm, 430nm

and 580nm) due to hydroxyapatite matrix.
[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.

Eu(5mol%)
ex=100nm
ex=120nm
ex=140nm

Intensity / Relative value

A B

ex=160nm
C D

ex=180nm
ex=200nm
ex=220nm

EGd(5mol%)

ex=100nm
ex=120nm
ex=140nm
ex=160nm
ex=180nm
ex=200nm
ex=220nm
300

400 500 600
Wavelength / nm

700Fig. 1 Photoluminescent spectra of rare earth
ion-doped hydroxyapatite samples excited byultraviolet synchrotron orbital radiation light.
Eu3+:
A: 5D0→7F1, B: 5D0→7F2
C: 5D0→7F3, D: 5D0→7F4
Gd3+:
E: 6P7/2→8S

75

BL1B

Temperature Dependence of Absorption Spectra for Pr3+ in LiYF4
S. Watanabe1, H. Kai1, H. Yoshida1,2, K. Ogasawara1
Department of Chemistry, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337 Japan
2
Research and Development Division, NEC Lighting, Ltd., 3-1 Nichiden, Minakuchi-cho, koka,
528-8501, Japan1

The trivalent or divalent lanthanides in crystals andglasses have drawn attentions due to their application
for luminescent materials in UV and VUV regions
such as tunable solid-state lasers or phosphors. In
those materials, transitions between the multiplet
energy levels were used. In case of trivalentpraseodymium ion (Pr3+) in various host crystals, the4f2-4f15d1 transitions lie in UV and VUV regions.
Therefore, Pr3+ in host crystals or glasses hold thepromise of good luminescent materials in UV or
VUV regions.
The excitation spectrum for Pr3+ in LiYF4 wasreported by Pieterson et al [1]. They measured theexcitation spectrum at 6 K using the DESY
synchrotron facility. According to their report, 3 main
peaks and 2 sub-peaks were observed in the
excitation spectrum.
In this report, we have investigated the temperaturedependence of absorption spectra for Pr3+ in LiYF4.
And we also analyzed the spectra based on thefirst-principles calculation for multiplet energy andabsorption spectrum using the 4-component
relativistic configuration interaction (CI) method [2].
This calculation method has been successfully
applied to calculation of the multiplet energy levels
and optical absorption spectrum between multiples
for impurity ions in host crystals [3]. By
measurements of the absorption spectrum at low
temperature, we could directly compare thetheoretical absorption spectrum to that obtained by
the first-principles calculation. Therefore, thecombination of measurements of the absorption
spectrum at low temperature and first-principles
calculations is very effective procedure for analysis of
optical properties.
The LiYF4 single crystal doped with Pr3+ weregrown by Bridgeman-Stockbarger method. The
concentration of Pr3+ ion in the sample was 0.3 mol%.
Fig. 1 shows the temperature dependence ofabsorption spectra for Pr3+ in LiYF4. The absorption
spectra were measured at 10, 50, 100, 150, 200 and
300 K. The 3 main peaks, A, B, C, were observed ineach spectrum at 5.8, 6.7 and 7.6 eV. The
first-principles relativistic CI calculation indicatesthat the splitting of those 3 peaks A, B, C is due to the
crystal field splitting of Pr-5d levels. On the other
hand, the 2 sub-peaks, A’, B’, were observed inspectrum at 10, 50, 100 and 150 K at about 6.0 and
7.2 eV. The first-principles relativistic calculation
indicates that the splitting between peak A and A’ andthat between peak B and B’ are due to the spin-orbit
interaction of Pr-4f levels. These splittings areobserved only in the spectra measured at low
temperature measurements. We should point out thatobservation of peaks A’ and B’ originating form
spin-orbit interaction also significantly depend on the
Pr3+ concentration.

C
300 K

A
B
B’

A’

200 K

Intensity /arb. units

150 K

100 K

50 K

10K

5.5

6

6.5

7

Energy /eV

7.5

8Fig. 1 The temperature dependence of absorption
spectra for Pr3+ in LiYF4. The concentration of Pr3+
ion is 0.3 mol%.
[1] L. van Pieterson, M. F. Reid, R. T. Wegh, S.
Soverna and A. Meijerink, Phys. Rev. B65 (2002)
045113.
[2] K. Ogasawara, T. Iwata, Y. Koyama, T. Ishii, I.
Tanaka and H. Adachi, Phys. Rev. B64 (2001)
143.
[3] K. Ogasawara, S. Watanabe, H. Toyoshima, T.
Ishii, M. G. Brik, H. Ikeno and I Tanaka, J.
Sol.Stat.Chem. 178 (2005) 412

76

BL1B

Optical Spectroscopy of Ce-doped Oxides
Y. Ohsumi, M. Yoshida, T. Hasegawa, M. Yamaga,
Faculty of Engineering, Gifu University, Gifu 501-1193 Japan
Ce3+-doped crystals are attractive for applications tolasers, scintillators, and phosphors. The 4f  5dtransitions of Ce3+ are parity- and spin-allowed so thatthe transition probabilities are very large. The
lifetimes of Ce3+ in crystals are in the range of 10-60
ns [1-3]. Recently, Lu2SiO5 (LSO) doped with Ce3+
was developed as a new scintillator with highconversion efficiency from high energy to visible
light. However, when there are deficits in the crystal,
the emission efficiency is degraded. In addition, theafterglow is observed. This report describes optical
spectra of LSO and CaYAl3O7 (CYAM) single
crystals doped with Ce3+, which were grown using the
Czochralski method.
Figure 1 shows the vacuum ultraviolet (VUV) and
UV absorption/excitation and visible fluorescence
spectra in CYAM:Ce3+ and LSO:Ce3+ crystals. The
optical absorption spectra of Ce3+ consist of five
broadbands due to the transitions from the 4f groundstate to the five 5d excited states. However, theabsorption spectra could not be resolved because ofstrong absorption coefficient. Although CYAM andLSO have different crystal structure, the peakwavelengths of the fluorescence bands are about 440
nm. These fluorescence spectra have large Stokes
shift. On the other hand, both excitation spectra
consist of two groups: one is in the range of 200-400
nm and the other is in the range of 100-200 nm. The
former corresponds to the five absorption bands of
Ce3+, whereas the latter may be due to band-to-band
transitions with band edges around 200 nm.
The decay curves of the Ce3+ fluorescence in CYAM
and LSO fit single exponential curves with lifetimesof about 40 ns. However, the fluorescence spectra
have background intensities, which are drasticallyenhanced with an increase of temperature. This iscalled as afterglow.
Figure 2 shows the decay curve of the long-lasting
phosphorescence in CYAM:Ce3+ at 300 K in the time
range of 1-300 s in log-log scales. The decay curve
does not fit a single exponential curve, but a functionof t-n (n  1). In order to examine a radiative processof the phosphorescence, it is very useful to measure
the excitation spectra of the phosphorescence in the
VUV region. The excitation spectra for CYAM andLSO have peaks around 200 nm as the same as thoseof the fluorescence in Fig.1. The wavelength of 200
nm in Fig. 1 is corresponding to the band edge energy.
This result suggests that electron-hole pairs produced
by VUV/UV light are trapped at deficits in the
crystals, such as color centers, and recombineradiatively when temperature is elevated up to room
temperature.

absorption

2

3+

CaYAl3O7:Ce

excitation
em=440nm

1emission
 =200nm
ex

0
100

200

300

400

500

600

Wavelength (nm)absorption

2

Lu2SiO5:Ce

1

3+

excitation
em=450 nm

0
100

200

emissionex=360 nm

300

400

500

600

Wavelength(nm)Fig. 1. Absorption, excitation and emission spectra in
CaYAl3O7:Ce3+ and Lu2SiO5:Ce3+ measured at 17K.

3+

CaYAl3O7:Ce

-2

2x10

Intensity (arb. units)

T=300 K
ex=200 nm

-2

10

-3

5x10

-3

2x10

-3

10

10

20

50

100

200

Time (s)Fig. 2. Decay curve of the phosphorescence in
CaYAl3O7:Ce3+ measured at 300 K.
[1] E. Hayashi, K. Ito, S. Yabashi, M. Yamaga, N.
Kodama, S. Ono, N. Sarukura, J. Lumin. 119-120(2006) 67.
[2] E. Hayashi, K. Ito, S. Yabashi, M. Yamaga, N.
Kodama, S. Ono, N. Sarukura, J. Alloys andCompounds 408-412 (2006) 883.
[3] M. Yamaga, E. Hayashi, N. Kodama, K. Itoh, S.
Yabashi, Y. Masui, S. Ono, N. Sarukura, T.P.J. Han,
H.G. Gallagher, J. Phys. Condens. Matter 18 (2006)
6033.

77

BL4B, BL1A

Excitation Energy Dependence of Time Resolved Decay Curves in AlGaN
AlloysT.Sakai1, S.Suzuki1, N.Nakagawa1, K.Fukui1, S.Naoe2, H.Miyake3, K.Hiramatsu3
1
Research Center for Development of Far-Infrared Region, University of Fukui,
Fukui910-8507, Japan
2
Faculty of Engineering, Kanazawa University, Kanazawa 920-1192, Japan
3
Faculty of Engineering, Mie University, Mie 514-8507, JapanThe III-V nitride semiconductors are promisingmaterials for visible-UV opto electronic devices, suchas LEDs, LDs and photo detectors. To expand theoperation wavelength of LEDs and LDs into
ultraviolet (UV) regions, research efforts are being
made for the growth of device quality AlGaN alloys,
since their band gaps spread from 3.39eV (GaN) to
6.2 eV (AlN). However, investigations into themechanisms of near band-edge photoluminescence(PL) in AlGaN alloys are also hardly adequate. We
have been measuring PL, photoluminescence
excitation (PLE) and time resolved decay (TRD)
curves at the excitation energy of not only nearband-gap but also high photon energy up to 1.5 keV
to investigate the effects of both core electron
excitation and multi-electron excitation. Since all of
TRD curves can be fitted as the sum of three different
single exponential components (fast, middle and slow
components in the order corresponding to their
lifetime), we have been considering that threecomponents suggest the existence of threeenergetically adjacent decay processes. In this report,
we present TRD curves and their excitation energy
dependence from 30 eV to 1 keV.
AlxGa1-xN (x=0.34 - 0.76) samples have been
made by MOVPE method at Mie University. The
thicknesses of AlGaN thin films are about 1μm on
1μm AlN single crystal films with Al2O3 substrates.
The measurement was performed in BL4B at the timeof single bunch operation. A conventional 30cm
VIS-UV monochromator with liquid N2 cooled CCD
detector is used for PL measurements of all samples.
Figure 1 shows time integrated PL intensity ratios
among three decay components of Al0.76Ga0.24N.
Measurement temperature is 9.9 K and excitation
photon energy is 85 eV. The vertical line at 5.27 eV
indicates the PL peak position. Below this photon
energy, the contribution of LO phonon replica bands
becomes dominant relative to the main PL band. It isclear that slow component is dominant and stable in
the replica band region, in other words, decay processof LO phonon replicas mainly consists of slow
component. However, in the main band region,
intensity ratios are continuously shifted. This
probably reflects inhomogeneity of cation
distribution. These behaviors are similar to thoseresults under near band-edge excitation.
Figure 2 shows TRD curves of Al0.76Ga0.24N atvarious
excitationenergies.
Measurement

temperature is 9.9 K and emission photon energy is
5.27 eV. The contribution of fast component which isshown in fig. 2 as a sharp peak at 2 ns becomes large
with increasing excitation photon energy. Thistendency is also observed near 1.5 keV excitation.
Even though the contribution of fast component
becomes large, this contribution smoothly depends onthe excitation photon energy and shows no drasticchanges between below and above core levels. It is
probably indicated that the main effect of the highenergy excitation photons is multi electron-hole paircreation effect.

100

Integrated Intensity Ratio

90
80
Slow
Middle
Fast

70
60
50

exci. 85eV
temp 9.9K

40
30
20
10
0
4.90

4.95

5.00

5.05

5.10

5.15

5.20

5.25

5.30

5.35

5.40

Photon Energy(eV)Fig. 1 Integrated intensity ratio of Al0.76Ga0.24N at
9.9K
Normalized LOG PL Intensity

Al0.76Ga0.24N
temp 9.9K

1000eV
700eV
500eV G1
350eV
250eV

350eV
250eV
200eV G2
150eV
100eV

150eV
120eV
100eV G3
60eV
30eV

0

20

40

60

80

100

Time(ns)Fig.2 Time resolved decay curves of Al0.76Ga0.24N atvarious excitation energies.

78

BL5B

Vacuum Ultraviolet Transmission Spectra of Substrate-Free Evaporated
Amorphous Thin Films
K. Hayashi, K. Kimata
Department of Electrical and Electronic Engineering, Gifu University, Gifu 501-1193, Japan
membranes by conventional evaporation technique.
The removal of the polymer membrane tried two
kinds of methods of a thermal method and a methodby organic solvent. The measurement of the VUVtransmission spectra were carried out at room
temperature at the BL5B beam line of the UVSOR
facility of the Institute for Molecular Science. And thespectrum was measured by using the silicon
photodiode as a detector. To eliminate the higher
order light from the monochromator, an aluminum
thin film was inserted between the monochromatorand sample.

Introduction
Amorphous semiconductor materials are very
expected as a potential material for optoelectronic
devices because these materials are very sensitive tothe light and show a variety of photoinduced
phenomena [1-3]. For the device application, it isnecessary to sufficiently understand the physicalproperty of these materials. Although a large numberof studies have been done on the photoinduced
phenomena of these materials, little is known about
the details of these mechanisms. These phenomena
were studied by exciting outer core electrons with theirradiation of light with the energy corresponding tothe optical bandgap or sub-bandgap. The interest has
been attracted for the change of the optical properties
in the energy region of the visible light. We areinteresting for the change of the optical properties in
the higher energy region. To obtain a wide knowledgeof the photoinduced phenomena, it is necessary toinvestigate to the photoinduced effects on wide
energy region. In previous reports, we reported thephotoinduced change at the VUV reflection spectra of
the amorphous chalcogenide semiconductor films
induced by bandgap light [4]. Recently, we measure
the VUV transmission spectra of amorphous thinfilms prepared onto polymer membrane substrates [5].
In present work, we report the VUV transmission
spectra of substrate-free evaporated amorphous thinfilms.
Until now, we have measured the transmission
spectrum by using amorphous thin film which
evaporated on the ultrathin polymer membrane
substrate. However, there are some problems in thismethod. For example, the problems are effective
decreases of the transmitted light intensity by theabsorption of the polymer membrane and uncertaintyof the thickness of the polymer membrane. The
detection accuracy in the measurement becomes bad,when the transmitted light intensity decreases. And, it
is not possible to obtain true transmission spectrum of
the sample, when the thickness of polymer membrane
can not be accurately measured. Then, we thought out
the method for removing the polymer from thesample of the amorphous thin film which evaporated
on the polymer membrane substrate.

Results and Discussion
Figure 1 shows the spectra of the incident light(without polymer) and the transmitted light of thepolymer membrane (with polymer). As shown in the
figure, the intensity of the incident light decreases
under the half by the polymer membrane. Therefore,
it seems to be possible to obtain the two times thesignal intensity by removing the polymer membrane.
Actually, it was possible to obtain the result along the
expectation.

Intensity [a. u.]

1

without ploymer
with polymer

0.8
0.6
0.4
0.2
0
10

20

30

40

50

Wavelength [nm]Fig. 1 Spectra of the incident light (without polymer)
and the transmitted light of the polymer membrane(with polymer).
[1] Ke. Tanaka, Rev. Solid State Sci. 4 (1990) 641.
[2] K. Shimakawa, A.Kolobov, and S. R. Elliott, Adv.
Phys., 44 (1995) 475.
[3] Ke. Tanaka, Encyclopedia of Nanoscience andNanotechnology, 7 (2004) 629.
[4] K. Hayashi, UVSOR Activity Report 2001 (2002)
126.
[5] K. Hayashi, UVSOR Activity Report 2004 (2005)
79.

Experimental
The ultrathin polymer membranes were preparedonto stainless steel metal plates in which two pinholesof the 1.0mm diameter opened. Thin films ofamorphous chalcogenide semiconductor (a-As2S3 anda-As2Se3) were prepared onto the ultrathin polymer

79

BL6B&7B

Optical Response of a New Type of CaRh2O4 & NaRh2O4
T.Iizuka, K.Iizuka,A.Irisawa, T.Nanba, 1K.Yamaura
Kobe University, nada-ku, Kobe 657-8501, Japan
1
National Research Institute for Metals, 1-2-1 Sengen, Tsukuba, 305-0047, Japan
Introduction
Recently, CaRh2O4 & NaRh2O4 have been newly
synthesized by a high-pressure method in Tsukuba [1].
The oxides crystallize in a CaFe2O4-type structure.
The recent electrical resistivity experiment revealed
that at atmospheric pressure, NaRh2O4 exhibits a
metallic property (Rh3.5+;Rh4+(t2g5) and Rh3+ (t2g6)) but
CaRh2O4 is an insulating and non-magnetic material(Rh3+;t2g6). Up to now, there exist no optical study
except macroscopic studies such as specific heat andelectrical resistivity. To study its fundamental
electronic states close to the Fermi level at ambientpressure, we measured the temperature dependence of
optical reflectivity spectra R() of NaRh2O4 &CaRh2O4 .

Experimental

Fig.1 Temperature dependence of R-spectra ofNaRh2O4 at 300 & 8 K.

The optical reflectivity spectra R() at ambientpressure were measured in the wide photon energy
range from 7 meV to 30 eV in the temperature range of
8-300 K. The measurements were performed using a
Fourier-transform interferometer combined with athermal light source and synchrotron radiation sourceat the beam line BL6B & 7B of UVSOR. The opticalconductivity 1()and complex dielectric function
1() were obtained from a standard Kramers-Kronig(K-K) transformation of the measured reflectivity(R)spectrum.

Results and Discussions
Fig.1 shows the temperature dependence of the
R-spectra of NaRh2O4. The spectra in the low energy
region exhibit a strong Drude component due to thefree conduction electrons which grows with cooling.
The peaks at 2.6, 6.0 and 15 and 20 eV from a visible
to vacuum ultraviolet originate to the electronicinterband transition.
Fig.2 shows the temperature dependence of the
R-spectra of CaRh2O4.The whole spectra exhibits aninsulating property. In the low energy part of the
R-spectra, twelve distinct peaks were resolved whichcorrespond to the phonon bands. They have a very
weak temperature dependence. The structure in thehigher energy region corresponds to the electronicinterband transitions of which spectral profile issimilar with NaRh2O4 but shows an additional finestructure superposed on the main peaks. Such finestructure might result from the super lattice structure
due to the charge ordering states between Rh4+(t2g5)
and Rh3+ (t2g6). The analysis is now on progress.

Fig.2 Temperature dependence of R-spectra of
CaRh2O4 at 300 & 8 K.
[1] K.Yamaura et al., Chem.Mater. 17 (2005) 359.

80

BL6B

Far-infrared Spectroscopy of Iodides Doped Silver Phosphate
Superionic Conducting Glasses
T. Awano
Department of Electronic Engineering, Tohoku Gakuin University, Tagajo 985-8537, JapanThe far-infrared spectral change showed themechanism of the enhancement of ionic conductivity
in iodides doped silver phosphate glasses. A doped
metal ion substitutes a silver ion which is connectedwith a non-bonding oxygen. The released silver ion iscoordinated weakly with an iodine ion and conducts
easily. This mechanism is the same as that in
PbI2-AgPO3 glass. The correlation effect seems toexist in lower wave number region.

1500

A B S O R P T IO N C O E F F IC IE N T (c m -1)

Enhancement of ionic conductivity by doping of
PbI2 in AgPO3 glass was reported previously.
Swenson et al. investigated mechanism of theenhancement on the PbI2-AgPO3 glass by diffraction
measurements and reverse Monte Carlo simulation[1].
They explained the increase of ionic conductivity bythat the doped Pb2+ substitute Ag+ which wasconnected with non-bonding oxygen and the released
Ag+ contribute to ionic conduction.
The enhancement of ionic conductivity by metal
iodide doping has also been reported on BiI3, CdI2
and other metal iodides[2]. The increase of ionic
conductivity is proportional to dopant concentrationand valence number of the metal ion. This abstract
reports results of far-infrared spectra of high-density
metal iodides doped silver phosphate glasses toinvestigate correlation effect of released silver ion on
the enhancement of ionic conductivity, besides theabove mentioned model.
Fig. 1 shows absorption spectra obtained by
Kramers-Kronig analysis from the reflectivity spectraof (AgI)0.5(AgPO3)0.5, (BiI3)0.03(AgPO3)0.97 and(CdI2)0.1(AgPO3)0.9 glasses. As previously reported,
Ag-O vibration absorption in AgPO3 glass is observed
at 135cm-1. In iodides doped glasses, it was observed
at different position with different band strength. In(CdI2)0.1(AgPO3)0.9, the peak was at 128 cm-1 andshift slightly toward low wave number. In(BiI3)0.03(AgPO3)0.97, the strength is more than that in(CdI2)0.1(AgPO3)0.9 as shown in fig. 1. In(AgI)0.5(AgPO3)0.5, the peak was at 115 cm-1 which israther lower than that in AgPO3.
In the above mentioned model of structuralchange of the glass, the number of the released silver
ions is proportional to the dopant concentration andalso the valence number of the doped metal ion.
Therefore intensities of newly induced absorption
band by Ag-I is expected to proportional to the
product of the dopant concentration and the valence
number. On the other hand, intensities of newly
induced absorption band by Cd- or Bi-O is expected
to proportional only to the dopant concentration. The
intensity of Ag-O vibration should also decrease withthe product of the dopant concentration and thevalence number. The simulation curves in fig. 1
shows the sum of each Gaussian component of Ag-O,
Ag-I and Cd- or Bi-O vibration, which are centered at
135, 100 and 165 cm-1[3]. The intensity of each bandis added or subtracted as above mentioned. Net
absorption spectra by these component bands areshown by dashed lines in fig. 1. These simulation
spectra well agree with the observed one.

78K

1000

500

(BiI3)0.03(AgPO 3)0.97(CdI2)0.10(AgPO 3)0.90
00(AgI) 0.50(AgPO 3)0.50
100-1WAVE NUMBER (cm )200

Fig. 1. Absorption spectra of iodides doped silver
phosphate glasses. Absorption coefficients wereobtained from reflectivity spectra by K-K
transformation. Simulation curves (thin lines) by
Gaussian components of Ag-I, Ag-O and Bi- or Cd-O
vibration were drawn as described in the text.

[1] J. Swenson, A. Matic, C. Gejke, L. Boerjesson, W.
S. Howells and M. J. Capitan, Phys. Rev. B 60
(1999) 12023.
[2] H. Takahashi, H. Nakanii and T. Sakuma, Solid
State Ionics 176 (2005) 1067.
[3] B. N. Nelson and G. J. Exarhos, J. Chem. Phys. 71(1979) 2739.

81

BL6B

Terahertz Spectroscopy of SmS under Pressures
T. Mizuno1, S. Kimura2,1, K. Matsubayashi3, K. Imura3, H.S. Suzuki4, N.K. Sato3
1
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Physics, Nagoya University Nagoya 464-8602, Japan
4 National Institute for Materials Science, Tsukuba 305-0047, Japanand all parameters in the Lorentz function) are fixed.
The obtained Neff is plotted in Fig. 1(b). The logNeff is
proportional to the pressure up to 0.65 GPa. The
pressure dependence indicates that the energy gap
closes with increasing pressure. The energy gap size(2) at the ambient pressure was evaluated to beabout 1000 K [3]. By evaluating the gap size from Neff,the energy gap at the black-golden phase boundary is
850 K and then the gap suddenly closes to 100 K in
the golden phase by the first order transition. This
result indicates that the charge instability occurs at
the phase boundary with the gap size of 850 K.

Introduction
SmS is a strongly correlated insulator (namely“black phase”) with the gap size of 1000 K at ambientpressure.[1] Above about 0.7 GPa, the sample color
changes to golden-yellow (golden phase) and theSm-ion changes from the divalence to mixed
valence.[2] To investigate the mechanism of theblack-golden phase transition, we developed theterahertz (THz) reflection spectroscopic method
under pressures and applied to this material.

Experimental
The THz reflection spectroscopy under pressures was
performed at the THz microspectroscopy end stationof BL6B. A membrane-type diamond anvil cell was
employed to produce high pressures to samples. The
pressure applied to samples is controlled by thehelium gas pressure filled in the membrane. Since theareas of the culet plane of diamond and of themembrane are 1.13 mm2 and 103 mm2, respectively,
the pressure of samples is about 103 times larger thanthe helium gas pressure. The sample with a typicalsize of 0.40.40.05 mm3 was set in a diamond anvil
cell with Apiezon-N grease as the pressure medium
and with a gold film as a reference and ruby tips as
for a pressure reference. The pressure was calibrated
by a ruby fluorescence measurement.

Fig.1. (a) Pressure dependence of reflectivity
spectrum [R()] of SmS (thick lines) in the blackphase at 300 K. The fitting curve of the combinationof a Drude and a Lorentz functions are also plotted bythin solid lines. Successive curves are offset by 0.5
for clarity. (b) Pressure dependence of energy gap
evaluated by the Drude and Lorentz fitting of R()spectra.

Results and Discussion

The obtained reflectivity spectrum [R()] of SmS at
300 K as a function of pressure are shown by thicklines in Fig. 1(a). At the ambient pressure, thespectrum indicates the insulating character because
the low energy limit does not approach to unity and aclear large peak due to the TO-phonon between Sm2+
and S2- ions appears. When pressures were applied,the background intensity increases with increasingpressure. The background that originates from theDrude component indicates the existence of carriers.
Therefore the carrier density increases withincreasing pressure. The fitting curve of the
combination of a Drude and a Lorentz functions isshown by thin solid lines in the same figure. The
Lorentz function was set to reproduce the TO-phonon
absorption. To fit the obtained spectra, the Neff in the
Drude function is only changed and the otherparameters (the relaxation time in the Drude function[1] K. Matsubayashi, K. Imura, H.S. Suzuki, T.
Mizuno, S. Kimura, T. Nishioka, K. Kodama, and
N.K. Sato, J. Phys. Soc. Jpn. (2007) in press.
[2] J.L. Kirk, K. Vedam, V. Narayanamurti, A.
Jayaraman, and E. Bucher, Phys. Rev. B 6 (1972)3023.
[3] T. Mizuno, S. Kimura, K. Matsubayashi, K. Imura,
H.S. Suzuki, and N.K. Sato, submitted.

82

BL6B(IR)Dielectric Spectroscopy of Ba4R9.33Ti18O54 (R=La and Sm) Ceramics
K. Wada, Y. Yamada, I. Kagomiya, K. Kakimoto, H. Ohsato
Graduate School of Engineering, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555 Japan
Ba4R9.33Ti18O54 is a paraelectric material withtungsten-bronze-like crystal structure. Characteristics
of Ba4R9.33Ti18O54-based material with both highpermittivity (r) and the temperature stability at GHz
frequency range are proper to a resonator or filter
application for the wireless telecommunication
devices. In general, temperature coefficient ofpermittivity () of high-permittivity paraelectricmaterial shows large negative value, e.g. SrTiO3 (r =304,  ≈ -3200 ppm/°C), CaTiO3 (r = 162,  ≈-1700 ppm/°C) and TiO2 (r = 104,  ≈ -900 ppm/°C).
On the other hand, the  of Ba4R9.33Ti18O54 strongly
depends on the R species in spite of the crystal
symmetry retention. Ba4La9.33Ti18O54 (r = 114;
BLaT) shows  of about -800 ppm/°C whereas
Ba4Sm9.33Ti18O54 (r = 78; BSmT) demonstrates  ofalmost zero. Understanding of this difference is not
sufficient despite much investigation for thedevelopment of dielectric property has been
performed.
IR reflectivity spectra give us useful information,i.e. the lattice vibration, which essentially correlates
to the dielectric behavior at high frequency. Dielectric
spectroscopy at the frequency range fromsub-millimeter to THz can be obtained by the analysis
of IR reflectivity. In this study, we measured thereflectivity spectra of BLaT and BSmT to examine
the dielectricity of Ba4R9.33Ti18O54.
Reflectivity spectra of BLaT and BSmT dense
ceramics were obtained in the temperature range of
10-300 K at the BL6B beam line of UVSOR. The
spectra below 150 cm-1 were corrected byMartin-Puplett interferometer (JASCO, FARIS-1) andsynchrotron radiation source. Measurement at higher
frequency range (>150 cm-1) was carried out using
Michelson interferometer (Bruker, IFS66v) andglow-bar source. Each peak of the imaginary part ofdielectric
spectroscopy
obtainedfrom
Kramers-Kronig transformation of experimental
spectra was used as an initial parameter (TO mode)
for the fitting. Then, the experimental spectra werefitted by Drude-Lorentz model.
Fig.1 shows far-infrared reflectivity spectra (circle)
and their fits (solid line) of BLaT and BSmT at 300
and 10 K, respectively. Observed spectra are similar
to that of Pr-analogy reported in the literature [1]. The
portion of the spectra above 1000 cm-1 is not shownsince no reflection bands were observed. Because of
the complexity of the crystal structure in BLaT and
BSmT, the spectra showed much dip resulted fromthe many vibration modes. From the factor group
analysis based on the crystal structure data, BLaT and
BSmT have 203 IR active modes. Actually, fitting

was carried out by use of less than 30 modes because
small number of strong modes and/or bundled modes
can represent the dielectric behavior approximately.
The fitted spectra are good agreements with theobserved ones. Usually, low-frequency modes inhigh-permittivity paraelectric material show softening
toward to the Currie temperature. However, in thisstudy, the softening was not confirmed for the lesschange in the spectra of BLaT and BSmT. The lack of
distinct changes in the spectra suggests that no
ferroelectric phase transition occurs in both materials
at least down to 10 K. Fig. 2 shows real part ofpermittivity obtained from the fitting of spectra of
BLaT. Although BLaT shows large temperaturedependence of permittivity below at several GHz
ranges [2], the permittivity obtained from IR
reflectivity exhibits small temperature dependence.
These phenomena can be well connected if BLaT has
broad dielectric dispersion. Therefore, Ba4R9.33Ti18O54
probably belongs not to normal paraelectrics but torelaxor dielectrics with broad dielectric dispersion.
[1] K. Fukuda, R. Kitoh and I. Awai, J. Mater. Sci. 30(1995) 1209.
[2] A. Belous, O. Ovchar, M. Valant and D. Suvorov,
J. Appl. Phys. 92 (2002) 3917.

Fig. 1. Far-infrared reflectivity spectra together with
their fits of Ba4La9.33Ti18O54 and Ba4Sm9.33Ti18O54
ceramics at 10 and 300 K.

Fig. 2. Real part of permittivity of BLaT calculated
from IR reflectivity measured at 10 and 300 K.

83

BL6B(IR)Optical Properties of Bismuth Clusters
S. Yoshida, A. Goyo, H. Ikemoto
Faculty of Science, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
It is well known that small clusters of atoms will
have a local structure and a property different fromtheir elemental crystalline equilibrium.
Raman-scattaring measurements of cluster of Bi
exhibit phase transition from rhomdohedral Bi
nanocrystalline to amorphouselike clusters depending
on cluster size[1]. They also suggest that amorphousclusters are semiconducting and covalent interactions
increase with decreasing size.
The Raman studies are good tools but indirect
evidences for the transition. So it is very important toinvestigate the optical property directly to reveal themechanism of the phase transition. In the present
study we report results of optical absorption
coefficients for Bi clusters.

These results suggest the semimetal-semiconductortransition of Bi clusters.
0.8
experimentcalculated by ML model
calculated by EM modelTransmittance

0.6

0.4

0.2

0

Experimental
Bismuth of 99.999 % purity was slowly deposited
onto the substrates from a melting crucible. The Bi
film was discontinuous with isolated island formation.
Then, KBr of 99.99 % purity was deposited to cover
the Bi islands. By repeating these procedures, asample of Bi clusters isolated in a KBr matrix was
obtained. The size of the islands was adjusted bycontrolling the thickness deposited on the substrates,
which was monitored with a quartz oscillator. The
thickness ratio of the Bi and the matrix is about 1:20.
As mentioned above the Bi clusters are formed in thinfilms, and samples are represented by their average
thickness of the Bi thin films in this paper. The
measurements of reflectivity and transmissivity were
performed in the energy range of 0.05~0.8 eV withthe rapid-scan Michelson interferometer (Bruker,
IFS-66v) and a HgCdTe detector at the UVSOR. All
measurements were performed at room temperature.

0

0.2

0.4

0.6

0.8

Photon Energy (eV)Fig. 1. Transmittance of the 10 nm-thick films.
Measured transmittance (blue), transmittances
calculated by ML models(black) and EM model(red).

2 10

5

-1

α (cm )

10nm
2nm
0.5nm
crystalline
1 10

5Results and Discussion
Figure 1 shows the measured transmittance spectraof the Bi 10nm thick films with comparison withthose calculated by two models. In a multilayer(ML)model the layers of Bi and KBr are assumed to beuniform respectively. In an effective medium(EM)model it is assumed that there is a single layercomposed of mixture of Bi clusters and KBr matrix,
and optical constants of the layer are mixed opticalconstants of Bi[2] and those of KBr[3] are mixed in
the ratio of the thickness. The EM model is better
than that the ML models for 10nm thick films.
The absorption coefficients are calculated by
Hong’s expression[4]. The absorption coefficients of
10nm thick films are close to those of crystalline Bi,
suggesting that 10nm thick films are semimetal.
Meanwhile the absorption coefficients of the 2nm and
0.5nm thick films are smaller than those of bulk Bi.

0

0

0.2

0.4

0.6

0.8

1

Photon Energy (eV)Fig. 2. Variations in optical absorption coefficients of
the as-deposited Bi clusters for different thickness.
Open circles denote those of polycrystalline [2].

[1] M. G. Mitch, S.J.Chase, J Fortner, R.Q. Yu, and J.
S. Lannin, Phys. Rev. Lett. 67 (1991) 875-878.
[2] A.D.Lenham,et al. J.Opt.Soc.Am.55 (1965) 1072.
[3] Handbook of optical constants of solids II.
Academic Press (1991).
[4] W.Q.Hong, J.Phys.D:Appl.Phys.22(1989)1384.

84

BL6B

Infrared Reflection Absorption Spectroscopy of Potassium
Doped Alq3 Thin Film Using Synchrotron Radiation
Y. Sakurai1, S. Kimura1,2, K. Seki3
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan
2
School of Physical Sciences, Graduate University for Advanced Studies, Okazaki444-8585 Japan3
Department of Chemistry, Graduate School of Science, Nagoya University, 464-8602 Japan
Tris-(8-hydroxyquinoline) aluminum (Alq3) (figure1) is most widely used as the electron transport/lightemitting layer in organic light emitting diodes(OLEDs). A typical OLED consists of indium tinoxide (ITO) as the anode on which organic thin films
are sequentially deposited, with low work function
metals finally deposited as the cathode. The propertyof the interface between cathode metals and Alq3
affect the performance of the devices. Doping is on
way to modify the electronic property of the interface.
Infrared reflection absorption spectroscopy (IRAS)
is a powerful probe for the structure and chemistry of asurface and interface. Al-N and Al-O vibrationalmodes of Alq3 which are expected to be significantly
affected by alkali metals appear in the wavenumber
region lower than 600 cm-1. Since a conventional
FTIR system using a globar light source cannot cover
the wavenumber region because of its low brilliance,
we have performed IRAS measurement of potassium
doped Alq3 thin film using a high brilliant synchrotron
radiation, UVSOR-II, in the region between 300 and
500 cm-1. The change of the Al-N stretching modewith the potassium doping was observed [1]. In thisstudy, we measured IRAS spectra in the region
between 400 and 700 cm-1 to observe Al-N and Al-O
stretching modes.
Experiments including the sample preparation andmeasurement were performed in an ultrahigh vacuum
chamber specially designed for this experiment [2].
Alq3 films were prepared by vacuum evaporation onto
Ag films deposited on Si substrates. Potassium wasevaporated on the Alq3 films from SAES gettersources. IRAS spectra were obtained with the SR
light through CsI windows at the incident angle of 80°
relative to the surface normal. The reflected light was
detected by a liquid-helium-cooled Si bolometer.
Figure 2 shows the potassium doping dependence of
the IRAS spectra of an Alq3 film of 20 nm thickness inthe wavenumber region between 400 and 700 cm-1.
In the pristine Alq3 spectrum, four strong peaks at 422,
458, 552 and 655 cm-1 are observed. These peaks
are assigned to Al-N stretching, pyramidalization
modes of the nitrogen atom, Al-O stretching andpyramidalization modes, respectively, as previously
assigned by absorption spectra of powder Alq3
samples [3]. The intensity of these peaks gradually
decreases and new peaks additionally appeare around440 and 502 cm-1 with increasing potassium
evaporation amount. These new peaks are assigned

to Al-N and Al-O stretching modes, respectively, bycomparing with calculated vibrational modes.
Therefore the frequency of Al-N stretching modechanged to higher frequency, and that of Al-O
stretching mode changed to lower frequency, i.e., the
Al-N bond strengthens and the Al-O bond weakens by
the potassium doping. These changes are believed tobe caused by the charge transfer from the potassium
atom to the Alq3 molecule which is predicted bytheoretical investigation.

Fig. 1 The chemical structure of Alq3.

Fig. 2 The potassium doping dependence of the
IRAS spectra of an Alq3 film.
[1] Y. Sakurai, S. Kimura and K. Seki, UVSOR
Activity Report 2005 (2006) 81.
[2] S. Kimura, Y. Sakurai, E. Nakamura and T.
Mizuno, AIP Conf. Proc. 879 (2007) 595.
[3] M. Cölle, S. Forero-Lenger, J. Gmeiner and W.
Brütting: Phys. Chem. Chem. Phys., 5 (2003) 2958

85

BL7B

Reflectivity of YbAl2 in Visible to VUV Regions
1

H. Okamura1, S. Nagano1, T. Nanba1, M. Kosaka2
Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan.
2
Department of Physics, Saitama University, Saitama, Japan.

At ambient pressure, the average 4f electron
configuration of Yb in YbAl2 is (4f)13.8, hence theaverage valence of Yb is 2.2. It has been shown thatYbAl2 undergoes a valence crossover under externalpressure, from 2.2 at ambient pressure to nearly 3 at
16 GPa [1]. When the valence of Yb is 3+, it has ahole within the 4f shell; hence it possesses a localized
magnetic moment. Namely, as the applied pressure
is increased, the number of localized 4f holes
increases. This can be viewed as a pressure-induced
crossover from itinerant to localized character of the
4f electrons through the electron-hole symmetry.
Associated with this crossover, there should be alsochanges in the strength of the hybridization between
the conduction and 4f electron (c-f hybridization).
This is an interesting system where the degree of felectron localization can be tuned continuously by theapplied pressure. We are planning an infrared studyof YbAl2 under pressure, to explore the crossover ofelectronic states under pressure. To do so, it isimportant to measure its optical spectra in detail atambient pressure in a wide photon energy range. As
a part of this, we have carried out reflectivity
measurements of YbAl2 at BL7B from visible tovacuum UV regions.
Fig. 1 shows the measured reflectivity spectrumof YbAl2 single crystal.
It is seen that thereflectivity decreases rapidly above 2 eV, reaching aminimum (plasma edge) at 8 eV. We are alsomeasuring the reflectivity in the infrared region, so
the spectrum in the entire region can be analyzed via
the Kramers-Kronig analysis to obtain the opticalconductivity spectrum of YbAl2.

Reflectivity (uncalibrated)

0.5
0.4

YbAl2
300 K

0.3
0.2
0.1
0

0

10
20
Photon Energy (eV)30

Fig. 1. Reflectivity spectrum of YbAl2 at room
temperature. Note that since the sample size wassmaller than the SR beam spot size on the sample, theabsolute value of the reflectivity is not correct(uncalibrated).

[1] C. Dallera et al., Phys. Rev. B 68 (2003) 245114.

86

BL7B

Reflection Spectra of Polyimide (CBDA/BAPP) Films
Exposed to Polarized UV Radiation
T. Mizunuma, K. Nakagawa, T. Tsuda, S. Matsumoto
School of Science and Technology, Meiji University, Kawasaki 214-8571 Japan
Polyimides compounds based on aromatic
dianhydrides and diamines are widely used as basematerials for electronic devices, becouse of their
thermal stability and chemical resistance. Recently it
has been reported that polyimide films exposed tolinearly polarized Ultraviolet (UV) radiation arecapable of aligning liquid crystal(LC) molecules on
their surface. This technique, named photo alignment,is remarkable for fabricating Liquid Crystal Displays(LCD’s). But the detailed mechanism of photoalignment of LC molecules has not been clear.
Optical spectra of polyimide films in the UV-VIS and
IR regions give important clues to infer the photoalignment mechanism[1][2][3]. But few spectroscopic
investigation has been made about higher energy
regions such as vacuum ultraviolet (VUV) region. In
this paper, we report VUV reflection spectra ofpolyimide (CBDA/BAPP) films exposed to linearlypolarized UV radiation.

linearly UV radiation, DV-Xα molecular orbital
calculation was performed. Figure 2 shows Density ofState (DOS) spectra calculated. Peak A has beenreported to π-π* transition on a benzene ring. And it
is already known that n-π* transitions is dominant foralicylic polyimides, which implies the peaks B, C, D
and E may be attributed to n-π* transitions ofcarbonyl groups contained in CBDA/BAPP as drawn
in Fig 2.

Reflectivity (a.u.)

30

A
20

Experimental

0

An amic acid form of CBDA/BAPP from Nissanchemical Industries, Ltd was used and suitableconcentrations of the poly (amic acid) (PAA) form
was spin coated on quartz substrates. Spin conditionwas 3500 rpm for 40 s and film thickness was about
50 nm. They were soft baked for 10 min at 100 oC toremove the solvents and hard baked 250 oC in aconvection oven to accomplish imidization for 2
hours. UV irradiation was accomplished using a
He-Xe lamp based irradiator. The intensity of the UV
radiation was about 5.5 mW/cm2 around 365 nm.
Reflection spectra of polyimide (CBDA/BAPP) films
exposed and without exposed to linearly polarized
UV radiation were measured in the vacuum
ultraviolet region up to 25.0 eV with the 3-m normal
incident type monochromator (grating: G1 and G2) at
BL-7B of UVSOR-II.

D

C
B

10

0

5

E

10

15

20

25

Photon energy (eV)Fig. 1 Reflection spectra of polyimide (CBDA/
BAPP) films exposed (red line) and without exposed(blue line) to linearly polarized UV radiation.
E
D
C

Intensity(a.u.)-20

Results and Discussion

total
A site(benzen)
C site(cycrlobutane)benzencycrlobutane
other site

B

A

-15

-10

-5

0

5

Binding Energy (eV)

10

15

20

Fig. 2 DOS spectra of polyimide (CBDA/BAPP)
calculated by DV-Xα method.

Figure 1 shows the reflection spectra of polyimide(CBDA/BAPP) films exposed to linearly polarized
UV radiation compared with that of no exposed film.
Peaks in the figure are named as indicated forconvenience. In the reflection spectra, five peaks
named as A, B, C, D and E were observed at about
6.0 eV, 9.5 eV, 13.0 eV, 16.0eV and 20.0eV,
respectively. Therefore both reflection spectra show
some remarkable peaks at same energies. But peakintensities of spectrum exposed to UV radiation
becomes stronger than that of without exposed except
peak A. It is considered that molecular reorienteation
occurred by linearly polarized UV radiation. To
analysis of spectra changes caused by exposed to

Acknowledgements
The authors would like to thank H. Shitomi of AIST
for his support.
[1] H. Endo, T. Shinozuka, H. Fukuro, Y. Imura andS. Kobayashi, AM-LCD(1996)341.
[2] H. Shitomi, T. Ibuki, S. Matsumoto and
H. Onuki, Jpn.J.Appl.Phys. 38 (1999)176.
[3] K. Sakamoto, K. Usami, T. Araya and
S. Ushioda, Jpn.J.Appl.Phys. 38 (1999)1435.

87

BL7B

Optical Investigation of the Charge Gap Opening in FeSb2
M. Marutzky, S. Kimura1, J. Sichelschmidt, A. Bentien, F. Steglich
Max-Planck Institut für Chemische Physik fester Stoffe, Dresden, Germany
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Introduction
FeSb2 is characterized as a Kondo-insulator withsimilar physical properties to FeSi [1, 2]. It shows acrossover from a diamagnetic to a paramagnetic statearound 100 K [3, 4]. In the literature, a semiconducting
behaviour for two crystal axes and a
metal-semiconductor crossover for the third axis wasreported [3]. We have grown single crystals and founda semiconducting behaviour for all three axis and acolossal Seebeck coefficient [2]. In order to study thecorrelation effects in FeSb2, we started an opticalinvestigation over a large energy range from the FIR(3meV) to the VUV (30 eV).

1.0
300 K
100 K
50 K
10 K

reflectivity

0.8
0.6
0.4
0.2
FeSb2
0.0
1E-3

0.01

Experimental

0.1

1

10

100

photon energy [eV]Single crystals of FeSb2 were grown by flux method.
The optical anisotropic crystals have a large [110]surface which was polished in order to allow opticalmeasurements with the E vector parallel andperpendicular to the c-axis. Michelson- andMartin-Puplett Fourier transform spectroscopy wasused in the IR where the contribution of the
conduction carriers to the optical properties can beobserved. Additionally, reflectivity measurements
were made from 1 to 30 eV at BL7B of the UVSOR
which was necessary in order to investigate theinterband transitions and to enable an exact
Kramers-Kronig transformation (KKT) of thereflectivity. The latter is needed to calculate thecomplex optical conductivity.

Fig. 1 Reflectivity of single crystalline FeSb2 with E
parallel to the c-axis in the [110] plane. For 100 and
300 K, the reflectivity was extrapolated down to zerowith the Hagen-Rubens relation in order to enable a
KKT. Above 30 eV, R ~ -4 was used for extrapolation.

1 [-1cm-1]

10000

Results and Discussion

In Figure 1 the reflectivity of FeSb2 with E  c from 3
meV to 30 eV is depicted at various temperatures. At
300 K, the reflectivity in the FIR is predominant
metal-like. Remarkable is the fact that at 24 meV apeak is visible arising from phonon absorption whichis unusual for a metal. At 50 K, the reflectivity haschanged dramatically and dropped from approx. 0.9 at
300K down to 0.7. This is similar to the situation in
FeSi where a charge excitation gap opens [5]. Very
distinctive phonon structures appear with a minimum
reflectivity of 0.1 at 10 K. The drastic depletion of thereflectivity and the absorptive part of the opticalconductivity was also observed in [6]. Qualitatively
the same behaviour occurs for E  c, not shown here.
A quantitative analysis of these optical spectra will
help to answer the question if the intriguing physicalproperties of FeSb2 can be understood in theframework of a Kondo model.

FeSb2

1000
300 K
100 K
50 K
10 K

100

10
1E-3

0.01

0.1

1

10

photon energy [eV]Fig.2 Real part of the optical conductivity, obtained by
Kramers-Kronig transformation of the reflectivity data
in Fig. 1.
[1] C. Petrovic et al., Phys. Rev. B 72 (2005) 045103.
[2] A. Bentien et al., submitted to Nature Physics[3] C. Petrovic et al., Phys. Rev. B 67 (2003) 155205.
[4] Ronwei Hu et al., Phys. Rev B 74 (2006) 195130.
[5] Z. Schlesinger et al., Phys. Rev. Lett. 71 (1993)
1748.
[6] A. Perucchi et al, Eur. Phys. J. B 54 (2006)
175-183.

88

BL7B

Temperature Dependence of Time Resolved Decay Curves in AlGaN Alloys
M .Suzuki1, T.Sakai1, N.Nakagawa1, K.Fukui1, S.Naoe2, H.Miyake3, K.Hiramatsu3
1
Research Center for Development of Far-Infrared Region, University of Fukui,
Fukui910-8507, Japan
2
Faculty of Engineering, Kanazawa University, Kanazawa 920-1192, Japan
3
Faculty of Engineering, Mie University, Mie 514-8507, Japanthat the other ‘another process’ is the radiative
process by middle component. Similar intensity
exchange is also found between middle and fastcomponents.

AlGaN alloys have a great potential for UV
opt-electronic devices, because AlGaN alloys cancover their band gap energies from 3.39 to 6.2 eV bychanging a compositional rate of Al and Ga. Then, tounderstand the decay processes of near band edge
ultraviolet (UV) photo luminescence (PL) in AlGaN,
we have been performing the measurement of thetime resolved decay (TRD) curves of AlGaN alloys.
In this report, temperature dependence of TRD curves
in AlGaN alloys is presented.
All samples are made by the MOVPE method. The
thicknesses of AlGaN thin films are about 1μm on
1μm AlN single crystal thin films with Al2O3
substrates. The all measurements were carried out at
BL7B under single-bunch operations. A optical fiberis used for guiding PL in the vacuum sample chamber
to a spectrometer with CCD. Time resolved decay
curve measurements are carried out by using timecorrelated single photon counting (TCSPC) method.
Figure 1 shows TRD curves at various
temperatures (from 10 to 170 K) of Al0.67Ga0.33N.
Excitation energy is 5.01 eV where PL excitation
spectrum becomes maximum intensity. As shown infig. 1, these curves can not be analyzed as a single
exponential decay process. We have been consideringthat TRD curves consist of three different single
exponential decay components. Decay times of first,
middle and slow components are less than 1 ns (lessthan resolution limit of TCSPC), order of ns ~ 10 ns,
and order of 10 ns ~ 100 ns, respectively. Decay timeof each component also decreases with increasing
temperature as shown in fig. 1. Time integrated PL
intensity of each component is calculated from theproduct of decay time with initial intensity, and fig. 2
shows normalized time integrated PL intensity ofeach component which is derived from the analyzed
results of TRD curves shown in fig. 1. The curvelabeled as ‘total’ in fig. 2, which represents simple
sum of three components, is in good agreement withtemperature dependence of PL intensity obtained
from time integrated PL measurement at 5.01 eV. The
temperature dependence of slow component indicatesthat the decay process corresponds to the slow
component is dominant process at low temperatureand this decay process basically shows temperature
quenching; there are potential barriers which connect
another processes, and the role of the radiative
process by slow component decreases with increasing
temperature. One of ‘another processes’ is a
non-radiative process, but the temperaturedependence of middle component clearly suggests

Normalized LOG PL Intensity

Al0.65Ga0.35N
10K
40K
60K
80K
100K
120K
140K
150K
170K

5.01eV

0

20

40

60

80

Time(ns)

Fig.1 Time resolved decay curves of
Al0.67Ga0.33N at 5.01eV

Normalized Intensity

Slow
MiddleFast
total
Al0.65Ga0.35N(2)5.01eV

0

20

40

60

80

100

120

140

Temperature (K)Fig.2 Temperature dependence of area strengthat PL energy peak position(5.01eV)

89

BL7B

Angle Dependence of Polarized Reflectance Spectra in AlN

1F.Suzuki1, M.Kishida1, K.Fukui1
Research Center for Development of Far-Infrared Region, University of Fukui,
Fukui910-8507, JapanAlN has a large bandgap of about 6 eV and a highthermal resistance, and is expected in fields such as
lasers and LED in the ultraviolet and the deep
ultraviolet. Usually, high quality AlN single crystal isfabricated as a thin film by MOCVD method. AlN
thin film has the wurtzite structure and c-axis isperpendicular to the surface. In this restriction,reflectance measurements are usually carried out
under E  c condition, where E represents the electricfield of incident light. In this condition, opticaltransition which corresponds to the minimum
bandgap becomes forbidden transition due to theselection rule, and first allowed transition is observed
at 6.2 eV. For this reason, the true bandgap has beenreported using unobtainable bulk crystals even though
crystal quality of the bulk sample is lower than that ofthin film. However, it is possible to investigate opticalproperties around true bandgap of high quality AlN
thin film by using the reflectance spectra withincidence angle dependency and high linear
polarization incident light. In this report, we present
angle dependence of polarized reflectance spectra in
AlN by using BL7B.
High quality AlN thin film has a wurtzite structure
which is evaporated on the sapphire substrate by
MOVPE method. Thickness of AlN film is 1μm.
Reflectance measurement at 10 K has been carriedout in the range between 5.8-7eV, and the incidence
angles to the surface normal are 6, 15, 30, 45, and 60
degrees.
Figure 1 shows the reflectance spectra of AlN at 6,
15, 30, 45, and 60 degrees. In all spectra, wave-likefeatures by interference are shown in the transparance
region (below 6.2eV), and the peak with dip
structures due to exciton absorption are also seen near
6.2 eV. However, wave-like features become
discontinuous near 6.0 eV with increasing incidence
angle. This is caused by the exciton absorption atminimum bandgap, since E // c component ofincident light becomes increasing with increasing
incidence angle. Although band edge absorption
begins at 6.0 eV by E // c component of incident light,
AlN is still transparance under E  c condition. Then,wave-like features still exist up to 6.2 eV with its
intensity decreasing.
Figure 2 shows the refractive index n and theextinction coefficient k derived from reflectancespectra shown in Fig. 1 by using the characteristic
matrix of the single-layer thin film model. Clear
jumps of k which corresponds to optical absorption
can be seen in not only ~ 6.2 eV but also ~ 6.0 eV atgrazing incidence conditions.

6°
15°
30°
45°
60°

0.30

Reflectance

0.25
0.20
0.15
0.10
0.05
0.00
6.0

6.5

Photon Energy (eV)Fig. 1 Reflectance spectra of AlN of 6, 15, 30,
45, and 60 degrees

1000

3.6

6°n
15°n
30°n
45°n
60°n

3.4
3.2
3.0

10

2.6

1

k

n

2.8

100

2.4

6° k 0.1
15° k
30° k
45° k 0.01
60° k

2.2
2.0
1.8
1.6

1E-3
5.6

5.8

6.0

6.2

6.4

6.6

6.8

Photon Energy (eV)Fig. 2 Optical constant n and k to each incidence
angle

90

BL7B

Photoluminescence of Forsterite Single Crystals Excitedby Vacuum Ultraviolet Radiation
M. Kitaura1, S.Izuhara2, H.Nakagawa2, A.Ohnishi3
Fukui National College of Technology, Sabae, 916-8507, Japan
2
Dept. of Electrical and Electronics Engineering, Fukui University, Fukui, 910-8507,Japan3
Deparment of Physics, Yamagata University, yamagata, 990-8560, Japan
1

Magnesium
silicate(Mg2SiO4)
isorthorhombic at normal condition, which is named
forsterite. This material has been used as the host ofradiation dosimeter. The application of it extends tothe other optical materials, e.g., laser, phosphor andso on. Because of its industrial importance, most of
the studies concentrate in optical properties ofactivator ions. There are few reports on opticalproperties of forsterite, except for our optical constantdata [1]. It seems valuable to investigate the opticalproperties of forsterite from the viewpoint offundamentals and applications.
In the present experiment, we havemeasured the emission spectra of forsterite single
crystals under excitation with synchrotron radiation at
low temperatures. In addition, excitation spectra werealso measured for the observed emission peaks. The
correction for the distribution of excitation lightsource was carried out for the excitation spectra
observed.
Figures 1(a) and 1(b) show the emission
spectra at 10K and 150K, respectively. In Fig.1(a),one can see the two emission peaks at around 2.60 eV
and 2.82 eV. Since the 2.60 eV peak begins to quench
thermally even at 10K, it cannot be found in Fig.1(b).
The 2.82 eV peak is clearly observed at 300K. The
other peaks below 2 eV may be connected to extrinsic
origin, because their features vary for each sample.
The excitation spectra for the 2.60 eV and 2.82 eV
emission peaks are presented in Fig.2, together withthe absorption tail spectrum. The threshold of
excitation for the 2.60 eV peak is in good agreementwith the fundamental absorption edge. This result
indicates that the 2.60 eV peak is of an intrinsic of
forsterite. The 2.82 eV peak is stimulated withultraviolet photons below the fundamental absorption
edge, and thus it originates in lattice imperfections. It
is to be noted that both spectra resemble each other inthe energy above 10 eV. This fact is explained asfollows. The energetic e-h pairs produced by vacuum
ultraviolet photons immediately relax into excitonic
states. Excitons will migrate to be trapped at the sitesof lattice imperfection. As a result, the 2.82 eV
emission peak originates from the latticeimperfections excited. We thus suppose that theexcitation of lattice imperfections by the inelastic
scattering of hot photoelectrons is negligible in theenergy region investigated here.

EMISSION INTENSITY (arb. units)

4

Forsterite(a)10K
ex. 9.54eV
ex. 7.29eV

2

0

2

3

4

5

4

(b)150K2

ex. 9.54eV
ex. 7.29eV

0

2

3

4

5

PHOTON ENERGY (eV)Fig.1: Emission spectra of forsterite at (a) 10K and(b) 150K. The red and blue lines correspond to
the emission spectra measured under excitation
below and above the fundamental absorption
edge, respectively.
10.0

INTENSITY (arb. units)

Forsterite
8.0
6.0
4.0
2.0
0

0

5

10

15

20

25

30

PHOTON ENERGY (eV)Fig.2: Excitation spectra for 2.60 eV emission peak at
10K (Blue line) and 2.82 eV one at 150 K (redline). The absorption tail spectrum at 10K is
also presented by a green line for comparison.
[1] M. Kitaura et al., J. Phys. Soc. Jpn. 71 (2002)
2736.

91