title effect of plastic deformation upon f-centers in alkali...

Title Effect of plastic deformation upon f-centers in alkali halides

Author(s) Kiyama, Ryo; Okamoto, Fumio

Citation The Review of Physical Chemistry of Japan (1955), 25(1): 1-5

Issue Date 1955-08-01

URL http://hdl.handle.net/2433/46717

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

The Review of Physical Chemistry of Japan Vol. 25 No. 1 (1955)

EFFECT OF PLASTIC DEFORMATION UPON F-CENTERS

IN ALKALI HALIDES*

Rv Rvo KtYn_vt ~ a~n FO~uo Ox.aHloro

Introduckion

On the basis of the assumption that vacant lattice sites are generated during plastic

flow'1 it is expected that plastic flow will affect the absorption spectrum of a crystal

containing color centers. Smekalz> and Schroeder3> hate found that the F-centers in

alkali halide crystals darkened by ionizing radiation are bleached by plastic How.

Jacobs'1 has demonstrated that the bleaching of F-centers does not occur when the

additive]y colored crystals are deformed by uniaxial strain at room temperature. We

have found in clectrolytically colored crystals that the blue color of a KI crystal

containing F-centers bleaches during plastic flow and the yellow color of a NaCI crystal

containing F-centers changes very rapidly to blue by irradiating with white light after

plastic deformation, whereas the undeformed crystals maintain their coloration for a

long time. Now the effect of plastic deformation upon electrolytically produced

F•centers in NaCI, KCI, Kl3r and KI crystals has been investigated in detail by measuring

the absorption spectra. The plastic deformation was carried out by die-casting with a

pressure of 5,000 kg/cm' at room temperature.

Experimentals

Preparation of samples The crystal pieces used in this work were cleaved from

large single-crystal blocks synthesized in this laboratory. F-centers were produced in

the respective crystals by means of electrolysis with a pointed cathode of nichrome and

a fiat anode of graphite in the furnace of 6(10-C and then rapidly quenched. The samples

suitable for measurement were cleaved from the inner region of colored crystal-

Procedure The pressure apparatus is shown in Fig. 1. The pressure vessel A is a

cylinder with a 6mm hole having closely fitted two pistons B. 1'he colored crystal

* Tkis iuvrstigntion kas bre>+ dmre by F. Okautotu. being en 11re Quslgrndrralc course, vndrr the directiar of Pro): X. h7ynn~a.

1) F. Seitz, Pkys. NcU., 80, ?39 (1950) 2) A. SmekaL Z. PGpsik, 5v, 289 (1929)

3) H. J. Schroeder, % Physik, 76, 60R (1952) 4) i. S, Jacobs, Phys. Rrw., 93. 993 (194)


2 R. Kiyama and F. Okamoto

cleaved to a square plate of abouC 4x4x2mm was set in

the sample region C, and deformed to a thin disk of 6 mm in

diameter by gradually compressing np to S,000kg/cm= with

pistons in the dark at room temperature, and then the defor-

med crystal was removed from the vessel and mounted on a

metal holder for absorption measurements by means of the

13ec6-man Model D U Spectrophotometer.

The absorption spectra of the deformed colored crystals

were measured, over the wavelength range from 350 to 1100m~~

at room temperature, on each step of [he successive treat•

ments as follows: (i) immediately after plastic deformation,

Qi) after preservation in the dark and (iii) after irradiation with

white light by using 100 watt ordinary incandescent lamp

situated apart at- a distance of ZOcm from the crystal. In

these absorption measurements, the deformed uncolored crys-

tals wese used as blank crystal.

In auxiliary experiments, the effect of preservation and ir-

radiation upon ttndeformed colored crystals was examined for

compazison with that upon deformed colored crystals.

1y

A

ipradiation upon ttndeformed colored crystals was examined for Fig. 1 Di

agram of the compazison with that upon deformed colored crystals. pressure apparatus

A :pressure vessel B : pislon5

C : samp]° region

Results

NaCI crystal containing F-centers was deformed in the dark and the deformed crys-

tal was preserved in the dark for 20 hours. The bleaching of the F-band was negligible

and there was no detectable growth of long wavelength bands (curves 2 and 3 in Fig. 2).

This crystal being irradiated with white light, the F•band was rapidly bleached and the

long wavelength bands were developed (curves 4 and 5). By about si_e hours irradiation,

the F-band was almost bleached and the long wavelength bands were enhanced (curve 6)-

KCI crystal containing F-centers was deformed in the dark. The bleaching of the

F•band was negligible and there was no detectable growth of long wavelength bands

(curve 2 in Fig. 3). This crystal being preserved in the dark for 21 hours, the F-band

was slightly bleached and the long wavelength bands were developed (curve 3). These

changes were mazkedly accelerated by irradiating with white light (curves 4 and 5). By

about six hours irradiation, the F-band was almost bleached and the long wavelength

bands were enhanced (curve 6).

KBr crystal containing F-centers was deformed in the dark. The F-band was con-

siderably bleached and the long wavelength bands were developed (curve 2 in Fiq.4).

These changes still continued during preservation in the dark (curve 3), and were

markedly accelerated by irradiating with white ]fight (curve 4). However, both F- and


EHec[ of Plas[ic Deformation upon P-centers in Alkali Halides

350 Wavelength, mp

40U 500 800 700 80U

0.3

C

v°

m 0 7. o?

N L

F u .a

01

G

127

i, , .,- .,-_. _ 1

F

~~/ 'rte ~ .~ i ~

i ; _.~ ~%6

MR. R

~ -~

\~_~ .~

\~~~ ~•.

0 3S S.0 2.5 2.0 1.5 eV

Fig. 2 Changes of the absorption spectrum of R-eenters in NaCI crystal after plastic deformation

Crystal thickness=0.82mnt

curve 1 : absorption spectrum of the crystal previous to plastic deformation

2 : immediately afrer plastic deformation in the dark

3 : after '20 hours preservation in the dark 4 : after 10 minutes irradiation with white

light 5 : after further 30 minutes irradiation

6 : after further 6 hours irradiation

long wavelength bands were considerably

(curves 5 and 6).

KI crystal containing F-centers was de

siderably bleached and the weak absorption 1

Fig. 5). These two bands in the deformed

d00

Wavefenglh, mµ 500 600 700 8W 1000

2S

Q.6 s

c

_T

Q~ J

7 U

v (L2

0

~s

s

1

/~\ % 5,-. \

/ % \\, !% ~~~

~~' ~ -,. ,`~i

F

R, R, M

11 1 :.,

.. _ '•.

.-. ~. .\ :, ~- ~ ~~~

3.0 25 2.0 1.5 eV

Pig. 3 Changes of the absorption spectrum of F-center in KCI crystal after plastic deformation

Cry'sta] thickness=Lllmm

curve 1 : absorption spectrum of the crystal pra vious to plastic deformation

2 timmediately after plastic deformation in the dark

3: after 21 hours preservation in the dark 9 : after 10 minutes irradiation with white light

5 : after further 'l0 minutes irradiation G: after further 6 hours irradiation

bleached by irradiating for a lon3 Cime

KI crystal containing F-centers was deformed in the dark. The F•band was con-

siderably bleached and the weak absorption band was formed at about 520m~.e(curve 2 in

Fig. 5). These two bands in the defonned crystal were unstable in the dark at room

temperature (curve 3), and were almost completely bleached after 20 hours (curve 4). In

this case the irradiation experiment was not performed because the deformed crystal

showed rapid spontaneous bleaching in the dark.

Summery

The F-centers in NaCI and KCl crystals are scarcely bleached by t}te treatment of

plastic deformation but those in KBr and KI crystals are considerably bleached, and

further the F-centers in deformed KCI, KBr and KI crystals except NaCI crystal are

spontaneously bleached during preservation in the dark at room temperature, whereas

those in the undeformed crystals are stable for a long time. From this rest7lt it is

revealed that the rate of spontaneous bleaching in the deformed crystals increases in the


4

900

0.0

500

R. Pipama

Wavelength, mk 600 700 800 1000

and F. Okamoto

1

900

0.5

0.4 c

a: 0.3 c L

y 0.~ •a d

0.]

~.

Znti

,~~ f/3 iI

l~ ,~ f ~: a/

~• i ~~ 5~•' 6

R; R: M

i~

t) ~ J.c~_ _...r 3.0 2S 20 1.5 v1.0 eV

Pig. d Changes of the absorpton spectrum of P-centers in KBr crystal after plastic deformation

Crystal thickness=0.91mm

curve 1 : absorption spectrum of the crystal previous to plastic deformation

2 : immediately after plastic deformation in the dark

3 : aY.er !? hours preservation in the dark. 4: af[en 30 minutes irradiation tvi[h white light

5: after further 2 hours irradiation 6: aher further 4 hours irradiation

Navelength, mu 350 900 500 fi00 700 800

500R'avelength, mp

600 i00 800 1000

0.8

c

os m 0

_a T y 0.4

U

G C U.2

i

,~

~~ r ~

r ~ 3~ ,

5.'~Om'. ~ / ~.

l ~% i ~~.~ // F ~.\ \\ a \~. i

01 ~ - ~ 3.0 Y.5 'l.0 1.5 1.0 eV

Fig. 5 Changes of the absorption specirum of F-centers in KI crystal after plastic deformation

Crystal thickness=1.03mm

curve 1 : absorption speetmm of the crystal pr agous to plastic deformation

'l:immediately after plastic defornation in

the dark 3 : after 1 hour preservation in the dark

4 : after further 'LO hours preservation

0.9

c

x o.a r :~

c •~ o.~

u

z~

i ~

F

R, R,

~~! 1M

~~

400Wa~•elengt6, mN

500 600 700 800 1000

0.8

c

=os a

i. ~N ~ 0.9

Y ~ 0.2

0

r• i~. F-cen tvith

curve

~1`

1 ~1

F

~̀`~ ~~

\J

mt

~~ / ~

\_

35 30 2.5 2.0 L5 eV Fig. 6 Change of the absorptioq spectrum of

Fomenters in undeformed \*aCl crystal by irradia-tion with white light Crystal thickness=0.82mm

curve L : absorptioq spectrum of the crystal previous to irradiation

2 : after 4 hours irradiation with white light

30 2fi 20 1.5 eV

Fig. 7 Change of [he absorption spectrum of F-centers in tmdeformed IiCI crystal by irradiation with white ]igh[ Crystal thickness=LLlmm

:urve ].:absorption spectrum of the crystal pre- ~~ous to irradiation-

'L :after 4 hours irradiation with white Iight


?OU

0.6

liffect of Plastic Urfonnatiou

Wavelength, mp FiOU ti00 'OU 800 ]UUU

upon F-centers in Alkali Halides

'

~ ~ os

o.~

0.3

u

0,'L v

.. 0.1

0

1R. R,

~~ ~ p' . \~

2.5 1.0 eV

Fig. 8 Change of the absorption spectrum nt F-centers in undeforn:ed KRr cr_vs.al by i rradia[ion with whiie light

Crystal thickness=0.91 mm

curve 1 : absorptimt spectrum of the crystal previous to irradiation

2 : after 4 hours irradiation with white light

3.0 2-0 IS

order : NaCI <KCI <KBr <KI. D4oreover, when the deformed crystals are irradiated

with white light, the bleaching of the F-band and the enhancement of the long wave-

length bands which may be probably the Kr; R._- and 1\I•bands, are more rapid that[

those in the undefornied crystals (curves 2 in Figs. 6, 7 and S). This result can

probably be ascribed to the large density of clusters of positive-and negative-ion

vacancies which are formed during plastic flowl•sl. Fo'r reference the positions of

the Rt-, R.- and :11-bands are noted with arrows in each figure.

The authors are partly indebted to the Department of Education for the Grant

in Aid for Fundamental Scientific Research.

The Laboratory of Physical Chemistry,

Kyalo University

5) P. Seitz, Reu. bfaJ.

title effect of plastic deformation upon f-centers in alkali...

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