Structures and Optical Properties of Pt and Pd Compounds with Charge-Density-Waves - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 20

Fig. 2.9 PA spectra with the
excitation of 3.2 eV and
polarized absorption
spectrum ( broken line )
measured at 77 K of (a)
Pt-Br-Pt-II and (b)
Pt-Br-Pd. Both the excitation
lights ( E ex ) and the
transmission lights ( E ) are
polarized parallel to the b
axis. Insets show PESR
spectra (derivative of
absorption) at 4 K for the
excitation of 3.1 eV.
(Reprinted figure from [ 52 ])

a

0.4

4 K

H ⊥ b
E ex // b

Pt-Br-Pt-II

0.3

g ⊥
= 2.299

α

0.2

4 5

1 2 3

77 K
E // b
E ex // b

Magnetic Field (kOe)

β

0.1

γ

× 10

0

E CT

b

6

H ⊥ b
E ex // b

Pt-Br-Pd

4 K

a 1

4

g ⊥
= 2.235

1 2 3 4 5

77 K
E // b
E ex // b

Magnetic Field (kOe)

2

a 2

0

E CT

-2

0 0.5 1.0 1.5 2.0 2.5

Photon energy (eV)

inverted triangles for band a 1 in Pt-Br-Pd. The thin solid line is the absorption
spectra ( e 2 ) due to the CT excitons obtained from the polarized reflectivity spectra

and their peaks correspond to E CT . As seen, in Pt-Br-Pt-II, CT excitons do not
contribute to the generation of band g , but contribute to band a . Band g in
Pt-Br-Pt-II and band a 1 in Pt-Br-Pd were generated only for the excitation
energies higher than E CT .
PESR measurements were also performed to investigate whether the

photoproducts have spins ( S ¼ 1/2) or not. In Pt-Br-Pt-II, an ESR signal was

observed in an as-grown single crystal. The ESR signal was enhanced by the
photoirradiations. The inset in Fig. 2.9a showed the increased component (the
PESR signal) for the 3.1 eV excitation. The excitation profile of the integrated
intensities of PESR signals was shown by solid squares in Fig. 2.10a . Paramagnetic
spins were produced by the 2.5-eV excitation. The same excitation did not generate
band g but enhances bands a and b so that the PESR signals in Pt-Br-Pt-II should
be related to bands a and b . In those measurements, it could not be determined
whether band g is related to a spin ( S ¼

1/2) or not.
In Pt-Br-Pd, on the other hand, no ESR signal was detected in an as-grown
single crystal. The PESR signal by the 3.1 eV excitation was shown in the inset of
Fig. 2.9b and the excitation profile of the integrated intensities of PESR signals was