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 14

Fig. 2.4 Energies of (a)CT-
exciton absorption peaks ( E CT )
and (b) STE luminescence
peaks ( E lm ) as a function of the
distortion parameter d .The
material for each number is
listed in Table 2.1 .Dataofthe
Pt compounds are represented
by circles .Dataofthe
heterometal compounds with
M

4

a

12

1

M = Pt, Pd

3

2

13

M = Pt

4

14

3

2

5

9

6

7

Pt and Pd are represented
by diamonds . Open and filled
marks indicate the compounds
with Y

¼

M = Pd

8

1

10

¼ ClO 4 and

11

Y halogen, respectively.

(Reprinted figure with
permission adapted from [ 5 ])

¼

0

b

2

12

M = Pt, Pd 13

1

2

14 4

M = Pt

3

1

5

6

7

9

M = Pd

10

0

0 0.1 0.2

d = 2 δ / L

Pt or Pd compounds is very small. It is because L is determined mainly by the
choice of the ligand (A), the counter anion (Y), and the bridging halogen ions (X),
and l 1 is almost equal to the sum of the ion radii of Pt 4 þ and X ions as mentioned
above.
It provides serious modifications to relaxation processes of photoexcited states in
the MX chains whether CDW is degenerate or nondegenerate; in degenerate CDW
states, solitons are the low-energy excitations and play dominant roles on the
relaxation processes but in nondegenerate CDW states, formations of solitons are
suppressed. Relaxation processes of photoexcited states associated with solitons are
discussed in Sect. 2.3.2 .

2.2.3 Control of Optical Gap Energies

In the MX-chain compounds, the lowest optical transition corresponding to the
optical gap is the charge-transfer (CT) exciton transition expressed as (M 2 þ ,M 4 þ !
M 3 þ ,M 3 þ )[ 13 , 32 ]. In Table 2.1 , the energies of those transitions ( E CT ) are listed for
the various compounds. In Fig. 2.4a , E CT is plotted for Pt and Pd compounds, and
the heterometal (M

¼ Pt and Pd) compounds as a function of the distortion parameter