Indian Journal of Pure & App lied Physics Vol. 4 I. August 2003 , pp. 651-666

Optical and infrared absorption of gamma irradiated ternary silicate glasses containing NiO

Magda M I Khalil

Radiati on Physics Department, National Center for Radiati on Research & Technology, Nasr City, Cairo, Egypt

Fatma H A Elbatal

Glass Research Department , National Research Center, Dokki , Cairo, Egypt

N Nada & S A Desouky

Physics Department , College for Girls, Ain Shams University, Cairo, Egypt

Received 24 December 2002; revised 2 April 2003; accepted 28 April 2003

The optical and infrared absorption spectra of ternary sili cate glasses containing NiO were studied sys tematicall y. as function of glass composit ion . The same properties were measured after successive gamma ray irradiation . The induced spectra and the rate of formation of the intrinsic defect of the base glass and the extrinsic detect due to the nickel iom were calcu lated. The experimental opti cal results were analysed and explained by assuming that, ni ckel exists in glass as dival ent Ni ions in two different states of coordi nation, namely, octahedral and tetrahedral. The infrared spectra of the doped glasses reveal the same spectra of the undoped glasses retaining the main vibrational bands which indicate that the dopant oxide has no effect on the main structural bui lding groups. The rates of formati on and annihilation of the color centers produced by gamma irradiation are believed to approach saturation or equ ilibriu m with prolonged irradiation.

[Keywords: Infrared absorption spectra, Ternary silicate glasses , Gamma ray irradiation]

1 Introduction

There has been a cons iderab le amount of absorpt ion spectra analysis of various g lasses irradiated by gamma-rays devoted, almost exclusively, to the study of colour centers induced by radiation '·4 • It appeared that, these studies provide valuable infonnation about the intrinsic defects due to the base g lasses and the role of doping wi th transi tion-metal ox ide. Recently , in terest in radiation effects has been expanded, as glasses are being used in optics on board a spacecraft , in image guides fo r reactor inspection and nuc lear medicine, and m optical-fiber waveguides.

The spectra of nickel in glass was identified early by Zsigmondy\ in 190 I, to extend over the whole visib le spectrum and varied from one glass to another, depending on their composi tion . Later work elucidated variable interpretation for the nature of nickel ions in glasses. Wey l and his co-authors6

assumed that, the yell ow colour in nicke l glasses is due to the presence of NiOr, complexes , while the pink co lour is re lated to the presence of Ni04 groups

and that, both these colours in volve the nickel ions in a divalent state with different numbers of surrounding oxygen li gands. Moore & Winkelmann7

studied spectro-photometric and magnet ic properties of nickel ions in various host glasses and explained their results by assuming that, nickel ions ex ist in three states: octa-, tetra-, and a third undulatory form. Bamfordx and Bates~ re lated and di scussed the absorption spectra of nicke l glasses from the point of view of ligand fie ld theory and concluded that, nickel ex ists in glass, as Ni 2

+ ions mainly in octahedral and tetrahedral coordinations. Paul & Douglas 111 suggested that, divalent nicke l ions are present in alka li borate glasses in octahedral , square planar or tetrahedra l symmetry depending on the g lass composition . Turner & Turner 1 1 assumed that, the postulated tetrahedral species of nicke l ions in si licate glasses may, in stead, be cubic (8-coordinated). They further added that , mixing of the Ni2

+ 3T2~ (p) level with Ni 2

+ 4P and/or li gand e lectron transfer bands was observed .

Recent in vestigations 12.

14 demonstrate that, nickel ions ex ist in g lasses, mainly in octahedral and

652 INDIAN J PURE & APPL PHYS, VOL 41, AUGUST 2003

tetrahedral coordinations and the ratio of them depends on the type and composition of the host

g lass.

Table I -Chemi cal composition of ternary sili cate glasses

Glass Si0 2 No.

74 2 74 3 74 4 74 5 74 6 74

4.0

a> t) c 2 2.0 0 (/) .D <{

studied (mole %)

Na20

16 16 16 16 16 16

: I ·; I ·:I - :I , .. _,

Third oxide Co lorant oxide added NiO

IOCaO 0.07 lOBaO 0.07 lOSrO 0.07 lOZnO 0.07 I OM gO 0.07 10820 3 0 .07

---Before --- -2 MR

-4MR - · · - · · 6 MR

. ·. ~

\ ·. ' \ ·. .. .... , .... __ .....

':..

.... .

360

Wavenumber (em - 1)

Fig. I - Absorpt ion spectra of parent undoped glass

The present work was conducted to exp lore systematically the variation of the Ni 2

+ optical and infrared spectra in some ternary sil icate glasses of variable composition; to reveal, the effect of increasing gamma ray irradi ation on the spectra; and use the spectral data to infer inte rnal loca l structure

and the suitab lity of the doped NiO as colour radiation indicator.

---2 MR

0.9 -----·4MR

-----·SMR

~ Ill c <II

~ 0.6 0 u

:;;1 0. 0

c QJ

g' 0.3 ·o .c <.)

100 200 300 400 500

Wavelength ( n m )

Fig. 2- Induced spectra of parent undoped glass

---Before -2 MR -A-MR

6MR

c ·u; c (l)

0 2

Wavelength tnm)

Fig. 3- Absorption spectra of gamma - irradiated glass No. ( 1) containing 0.07 NiO for different radiat ion doses

KHALIL et al. : TERNARY SILICATE GLASSES 653

4 ---~-------------.

~A

z.. 'Vi c Q)

0

ro 2 .!::2 Q. 0

---Before --- -2 MR

f/ v.: fj ut r~ .:_)11 Ill

-4MR - · -· · 6 MR

t .• r ~

'y~ \\

I \

.. I

\\ \ .. \ ~\ \ \i \

~\ \\ I ,. \ 1\ I \\ \ .. ~ \ \'. \ \'. \ ' \ \ \ . ' , ., ' \ ' '-\ '·· ''-. ...... \,

\ ·., \ '\ . . \

' \ ' \\ ·....._ ··-.....

. ·......._., ··-.. -. ~2~0-0-----3~6-0------5~4~0-------7~2~0--JSOO

Wavelength (nm)

Fig. 4 - Absorption spectra of gamma - irradi ated glass No.(2) containi ng 0.07 NiO for different radiation doses

2 Experimental Details

2.1 Preparation of glasses

The glasses were prepared from chemjcally pure materi als, in amounts suffic ient to produce 50 gm glass . Silica was introduced in the form of pulverized pure quartz of the highest grade available . Boric oxide was added as orthoboric acid l-1 3BO.~. whereas, :;ada, lime, magnesia, barium and strontium ox ides were introduced in the form of the ir respective anhydrous carbonates. Zinc oxide was added as such, and NiO was added as A.R. quality of the respect ive oxide.

Batches were melted in platinum 2% Rh cruc ihles. in e lectricall y heated SiC furnaces, at temperature of 1450±20 °C for 3 hr, after the last traces of batches had di sappeared . The melt was rotated several times to produce satisfactory homogeneity.

The melt was cast as rectangular slabs ( I by I by 4 em) for the optical absorption measurements and annealed, at 500 °C, in a muffle furnace. After I hr, the muffle was left to cool at a rate of 30 °C/h .

The annealed specimens were ground and highly polished to a sample thickness of =::0.3 em. Table I gives the chemical composition of the ternary silicate glasses studied .

z.. ·u; c: Q)

0

~ 2 :a 0

---Before ----2 MR

- · - · - --4 MR 6MR

0~----~----~------~--J 200 360 540 720 800

Wavelength (nm)

Fi g. 5- Absorption spectra of gamma- irradi ated glass No.(3) containing 0.07 NiO for di ffe rent radi ation doses

2.2 Optical absorption measurements

UV -vi sible optical absorption in the range 200-800 nm before and after irradiation was measured within 15 min after irradiation, using a recording Uvikon 860 spectrophotometer (Denmark).

2.3 Infrared absorption measurements

Infrared spectro-photometry was carried out on glass powder before and after irradiation by the KBr technique using an apparatus . JASKO (JAPAN)

654 INDIAN J PURE & APPL PHYS, VOL 4 1, AUGUST 2003

Ff/IR-300E recording spectrometer in the range 4000-200 cm-1. The ratio of the glass powder to KBr is 2: 200 mg. The mixture was subjected to a pressure of 5 tons/cm2 to prepare transparent discs. The infrared absorption spectra were measured immediate ly, after preparing the desired discs.

.b ·v; c <V

0

g 2 :c: CL 0

0 '200 360 540 720 BOO

WovelenSJI:"h ( nm

Fig. 6- Absorption spectra of gamma- irradiated glass No .(4) containi ng 0.07 NiO for di fferent radiation doses

2.4 Scanning electron microscopic investigation

Scanning e lectron microscope is used to study the surface morphology of differed glasses, before and after irradiation, to reveal the textural transfor­mation by radiation. A model JSM-5400 scanning electron mjcroscope was used in thi s investigati on.

2.5 X-ray diffraction analysis

X-ray diffraction studies were carried to follow the structural variations with gamma irradi ation. A Shimadzu (JAPAN) diffractometer type XD-D1 was used. The target was copper (A= I .542 A) with applied voltage of 40 k V and 30 rnA anode current. The pattern was recorded at a scanning rate of

4°/min . and angu lar range (28) of I 0- 100° with , di vergence slit I 0 , scatter-slit and receivi ng slit 0.3 mm, with a sample pitch 0. 12°. T hese operating conditions were sustained all over the examinati on.

4

~ ·u; c: (].)

0 ca .­-~ 0.2 0

---Before --- - 2 MR

- - · - · --4 MR

I

\ \ \ \

\.

' \.

6 MR

' , -~,

\

' \. ..... ...

0~---L----~------L---~ 200 360 540

Wavelength (nm)

720 BOO

Fig. 7-- Absorption spectra o f gamma- irradiated glass No.(5) contain ing 0 .07 Ni O for different radiatio n doses

2.6 Gamma irradiation

A wco source of the gamma cell was used fo r irradiation. It had a dose rate of 30 rad/s, at room temperature ( I 02 rad = I Gy).

3 Results

3.1 Ultraviolet and visible absorption spectra

The absorpti on spectra of the undoped and doped colored glasses containing NiO are represented in Figs 1-8.

KHALIL eta!.: TERNARY SILICATE GLASSES 655

i?;­·u; c Cll

0 2 -ro .~ a. 0

0~----~-------~L-----~--~ .200 360 540 720 BOO

Wavelength (nm)

Fig. 8- Absorption spectra of gamma· irradi ated glass No. (6) containing 0.07 NiO for differcni radi at ion doses

3.1.1 Absorption spectra of parent undoped glass

The undoped parent ternary silicate glass is colorless, with no obvious absorption bands in the vi sible part of the spectrum but, with marked ultraviolet absorption bands at about 270 nm. On subj ect ing the glass to gamma-rays irrad iation, the color changes to li ght amber, at first doses, which deepens afterwards, on prolonged irradi at ion. Fig. I shows the absorption spectra of the undoped parent ternary s ilicate g lass before and after gamma-rays irradiation.

The spectrum reveals a slight shift of the descending lobe of the charge-transfer absorption band with radiation . The intensttles of the absorption curves sharply increase at fi st dose 2Mr and the decreases with progress ive irradiation but, sti ll higher than the intensity before irradiation .

Q) 0 c "' -e 0

1l . <!: .

4000

Wavenumber (em_,)

Fig. 9 - Infrared absorption spectra of glass No.( I) containing 0.07%Ni0 with varying doses of gamma irradi ati on

4000 3000 2000 1500 1000 300

Wavenumber (em ·· ')

Fig. I 0- Infrared absorption spectra of glass No. (2) containing 0.07%Ni0 with varying doses of gamma irradiation

656 INDIAN J PURE & APPL PHYS , VOL 4 1, AUGUST 2003

Wavenumber (em _, )

Fig. II -Infrared absorption spectra of glass No. (3) containing 0.07%Ni0 with varying doses of gamma irradiation

"' 0 . c: "' € ~ .0 <{

100l 500 300

Wavenumber (em_, )

Fi g. 12 -Infrared absorption spectra of glass No. (4) containing 0.07%Ni0 with varying doses of gamma irradiation

Fig. 2 reveals the induced absorption spectra obtained by subtracting the absorpti on curve intensity of the irradiated glass, from the absorption of the sample after success ive irradiation . The induced spectra reveal an induced absorpti on band, at about 370 nm, with first dose and then with progressive irradiation reveal another UV absorption band, at abou t 250 nm.

. " u t:: ..

-e 0

"' .0 <{

'l:lOO 500 300

Wavenumber (cm1i

Fig. 13 - In fra red absorpti on spectra of glass No.(5) contain ing 0.07%Ni0 with varying doses of gamma irrad iat ion

3.1.2 Absorption spectra of glasses containing NiO .

The studied glasses contammg NiO (0.07 grn/ I 00 gm glass) show brown ish color, in the glasses Nos. 1-5 and purple color in glass No. 6. The absorption spectra of these glasses before and after gamma irradiation are illustrated in Figs 3-8 which can be outlined as follows:

(i) Before irradiation, the optical spectra of all the glasses containing NiO consist of four characteristic and repetttt ve absorption bands extending in the ultraviolet and visible regions. The

KHALIL eta!.: TERNARY SILICATE GLASSES 657

ultraviolet spectrum consists of a very sharp absorption band at about 280 nm, whi le the visib le spectrum is composed of three absorption bands. The first one is very sharp at about 420nm, and the second and third bands are small and located at about 560 and 650 nm.

~ " u <::

"' D

0 "' D

}~

3000 2000 1500 1000 300

Wavenumber (em_,)

Fig. 14- Infrared absorption spectra of glass No.(6) containing 0.07%Ni0 with varying doses of gamma irradiation

(i i) Careful examination of Figs 3-7 reveals that, the absorption bands menti oned remain unchanged, irrespective of the type of the divalent oxide introduced . Fig. 8 shows the appearance of the same main characteristic UV and visib le absorption bands, but the intensity of the absorption band at 420 nm is markedly reduced.

(iii ) Upon gamma irradiation, the following changes are observed:

I. The ultraviolet absorpt ion band shows slight increase in its intensity with radiation , but remains in its position .

2. Upon gamma irrad iation, the visible spectrum shows the appearance of an induced new absorption band, at about 380 nm and the obvious and marked

high increase in the intensities of the three characteristic absorption bands, together with shifting of their position, to reach 430, 530 and 680 nm.

3. The visible absorpti on is seen to shift increasingly, to longer wave lengths, with the f irst dose of radiat ion (2 Mr) and sli ghtly retard with pro longed irradiation.

>-:>.::: Vl c Q1

""0

0 v ..... 0. 0

. C

Q1

Ol c 0 .c u

4 250 ----· ·--• • 446

3 0 o- -o

2

630- 650

A------A

0 0 20 40 60

Dose of rad iation ( KGy) Fig. 15-Growth curves of gamma- irradiation gl ass

No .( I) with 0 .07%

3.2 Infrared absorption spectra

The infrared absorption spectra obtained for the undoped and doped si licate glasses containing NiO dopant can be represented by Figs 9-14 and the resu lts can be out lined as follows:

3.2.1 Infrared spectra of undoped parent glasses

Figs II and 12 illustrate the infrared absorption spectra of the parent and doped glasses , which reveal the following characteristics.

The absorption spectra of the studied glasses 1-5 resemble, in general, features the same absorption spectra, usually observed from si licate glasses and crystals. Glass No. 6 reveals the spectral characteristics of borosilicate glass family due to vibrations of both silicate and borate chains .

The principal absorption spectra of the glasses studied are concentrated in the mid-region of the infrared spectrum (2000-400) cm·1 in which , the

658 INDIAN J PURE & APPL PHYS, VOL 4 1, AUGUST 2003

infrared vibrations of the main structural groups are obtained and few absorpt ion bands are obtained in the near-in frared region (4000-2000) cm- 1 cons isting of the absorption bands due to water, hydroxyl and si lano l groups.

;>..

Ill c QJ

-u

0 u .... c. 0

c <lJ CJl c 0 .c. u

250 4

.-;::::-~ • 220 •

~0

0 3 560

A ·--. 650

2 6 6

0 20 30 40

DosE? of radiation ( KGy)

Fig. 16- Growth curves of gamma- irradiation glass No.(6) with 0.07%

The specific absorption bands of the glasses (Nos. 1-5), are visualized to be located at 460-470 nm, 730-720 nm, 880-820 nm, 11 00-9 10 nm, 1460-1250 nm, 1650- 1620 nm, 2400 nm and 3500 nm.

Glass No. 6 belongs to the borosilicate family , which consists of both silicate and borate chai ns. The infrared absorpti on spectrum of thi s glass is somewhat different from the previous data of glasses 1-5 hr. The infrared absorption spectra of glass No . 6 of the compos ition Si02 74%, Na20 16%, B20 1 I 0%, Fig. 12 reveals several add itional absorpt ion bands in the mid-region, which can be related to various borate groups such as , that due to B01 tr iangles and/or B04 tetrahedra, which give absorption bands very close and coincide or interfere with the absorption bands due to silicate groups. The net result is that , the absorption bands of g lass sample No. 6, extending from 1200 to 700 cm- 1

, are really composite ones of the co llective two s ilicate and borate c hains (ma inl y BO~ groups). The extra absorpt ion bands, which are observed at 1500-1250 cm- 1

, are mainly due to BO, groups stretchi ng vibrati on, which are active in th is mentioned reg ion. Table 2 presents the detailed positions and

ass ignment of the infrared absorption obtained from the studied glasses.

;>. ..... VI c <ll u

Ci <)

..... Cl.. 0

c

en c 0 £: u

4.0 • • 2 MR

3.6 X 6 MR

X

3.2

2.8

2.4

2.0

1.6

1.2

0 .8

0.4

0 200 400 600 800

Wave length ( nm)

Fig. 17 - Induced spectra of gamma- irradi ation glasses No.( I) wi th 0.07%

bands

3.3 Infrared spectra of doped ternary silicate glasses

The doping of the different glasses with the addi tion of NiO is shown to have a lmost no effect o n the infrared absorption spectra. This means that, the colorant ox ide has no influence on the structural arrangement of the building g lass formi ng groups . The effect of the dop ing oxide seems to be effic ient on ly in the UY-visible reg ion and its use as color and/or rad iati on indicators is appreciated.

KHALIL et al.: TERNARY SILICATE GLASSES 659

>-

Vl c <ll "0

0 v .... 0. 0

c <ll Ol c 0 s: u

4.0 r---------------

3.6 • 2 MR

o 4 MR

3.2 x 6 MR

2.8

2.'-<

2.0

1.6

]. 2

0.8

0.4

Wave length ( n m)

Fig. 18 - Induced spectra of gamma - irradi ation glasses No.(6) with 0.07%

3.4 Induced spectra of doped glasses

Figs I 5 and 16 illu strate the induced spectra of glass No. I and No. 6, which represent the difference or the c hange in optical density of the irradi ated g lass subt racted from the optical density of the un-irrad iated base g lass versus wavelength at three different doses of gamma irradiati on.

The spectra reveal the appearance of one very sharp induced band. at about 360 nm in glass No. I and g lass No. 6, but shifts to about 400 nm with pro longed irrad iation in glass No. 6.

Figs 17 and 18 show the growth curves of the absorption bands, with increasing radiation dose. The absorption bands show, at first, marked growth with radiation fo llowed by a near stabili zation or equilibrium state, with continuous irradiation. The visib le absorption bands reveal fast changes than ultraviolet absorpti on band .

·2 ··c:

::l ..0 .... ~ >-1-Ci) z w 1-z

b) •...........,.; _.........;,__,_.,.-..,. ___________ ....,..__,._,

a)"v--~v••p ~·........,......

(3) C)

b)~ aJ:::.J'.v...__..,..,............,., --~ .... ..,. . .._,......__.._.....,... __ ................ ..,..

(2) c)­b )

a)

(I) c)

b)

a)

10 30 50 70

26 (deg) Fig. 19- X-ray di ffracti on analysis of doped glasses No( 1-6)

before and after Irradi ation . (a) before (b) O.SMR (c ) 6MR

3.5 X-ray diffraction analysis

X- ray diffracti on inves tigat ions of the undoped and doped glasses reveal no d iffraction peaks or lines indicating any c rystalline phases. The resu lts as shown in F ig. 19 indicate th at, the studied g lasses are amorphous, e ither the undopecl or el oped specimens . Also, the resul ts reveal that, irradiati on

660 INDIAN J PURE & APPL PHYS, VOL 41 , AUGUST 2003

Be ;:. 0 ,.,_,. - ' !< - ,""' ft e r

Glass No.(1)

Bef c e After

G css 'c.(6)

Fig. 20 - Scanning electron microscopic investigation of doped glasses before and after gamma irradi ation

of the glass gives no alteration of the diffraction pattern obtained showing no crystalline indication .

3.6 Scanning electron microscopic results

Scanning e lectron microscopic investigations show no visual differences in the microstructure between the undoped and doped glasses and even the same specimens Fig. 20 after gamma-ray irradiation.

4 Discussion

4.1 Discussion of spectrophotometric measurements

4.1.1 Origin of absorption bands in the spectra of nickel ions in ~lass

Nickel ion has 3dx configuration and it is generally accepted that, only divalent Ni 2

+ ions are stable in glass under normal atmospheric conditions .

Moore & Winkelmann7 measured the spectra of various glass systems containing Ni 2

+ ions and concluded that, there are three fonns of Ni 2

+ ions to be found in glasses, mimely, a ' green' form in which , Ni 2

+ has an average coordination of six , an 'undulatory' form in :vhich, Ni2

• is four coordinated, and a 'brown' form in which , Ni 2

+ occupies bridging positions between two o· ions . Wey l6 inter-related the spectra of glasses containing Ni 2

• in terms of an equilibrium between octahedral and tetrahedral coordinated Ni 2

+ ions. Later srudiesH1 have indicated that , all the spectra of Ni 2

• ions can be accounted for, in terms of an equilibrium between Ni z. ions in octahedral and tetrahedral symmetry, depending on the type and composition of the host glass, conditions of glass-melting and concentration ofNiO.

KHALIL eta!.: TERNARY SILICATE GLASSES 661

The energy diagram for dx system in octahedral system predicts that, the spectrum of nickel ion in octahedral state will consist of: (Refs 8 and 9)

Transition

3 T2 (F) --7 3T5 (F) 3 T2 (F) --7 3T4 (F) 3 T2 (F) --7 3T4 (P) 3 T2 (F) --7 3T3 (D)

!Position of absorption bGnd (nm)

1333 794 422 658

Type of absorption

Spin- all owed Spin-allowed Spin-allowed Spin-forbidden

The energy diagram for dx in tetrahedral symmetry predicts that, the spectrum of nickel ion in tetrahedral state will consist of (Refs 8 and 9).

Transition

3 T4 (F) --7 3T5 (F) 3 T4 (F) --7 3T2 (F) 3 T4 (F) --7 3T4 IP) 3 T4 (F) --7 IT, (D)

!Position of Gbsorption band (n m)

2560 11 90 617 790

Type of absorption

Spin-allowed Spin-allowed Spin-all owed Spin-forbidden

Bates9 assumed that, the 3T 4 (P) band appears to be split probably because of L, S interaction effects . Several authorsx-lo believed that, Ni 2

+ ions should occur as octahedral si tes in preference to tetrahedral si tes in many glasses.

4.1.2 Interpretation of optical absorption spectra

The present result s indicate that, Ni 2+ ions are

assumed to be present in both octahedral and tetrahedral coordination . However, opt ical spectral absorption confirm that, in the first 5 glass compositions consisting of (a lkali oxide-divalent oxide-silica) with the mole percentage cited, initiate the prevalence of the Ni 2

+ in octahedral sites. With glass No. 6, consisting o f (S i02, B20 3 and Na20 ), the color is purple and the spectrum of the glass indicates the presence of tetrahedral Ni 2

+ ions as major sites. The fo ll owing assumptions are introduced to interpret the optical data .

I. The absence of marked change in the optical absorption of the nickel ions spectra of the first glasses (Nos 1-5) indicates that, the d-p orbital mixing remains the same with variation of the type of divalent oxide introduced . The glasses 1-5 contain Ni 2

+ ions mainly in octahedral sites. Glass No. 6, exhibits somewhat different spectrum and its

color is purple, indicating the dominance of the tetra-coordination Ni 2

+ ions, in this glass.

. 2. It has been suggested 15 that, the components of the characteristic and high intense 410 nm band arise from different tran sitions and cannot be ass igned to a single energy level with spin-orbit splitting. PauP 5 assumed that , as R20 is increased in alkali borate glasses, a shoulder develops on long­wavelength side of the 3A2 (F) 3T 1 (p) transition which is caused by the development of the 515 nm peak. The other r~markable difference caused by this tetragonal state is, the intens ification of the 410 nm band . It seems that, the assumption of Paul holds for alkali silicate glasses too .

3. Paul 15 added that, when R 20 concentration is further increased , an extra band at 6 L5 nm is also developed . This band can be assigned to the ·'T 1(F) 3T 1(p) transition of nickel Ni 2

+ ions, in a tetrahedra l symmetry.

4 . The band at 650 nm i · ascribed to Ni 2+, in tetrahedral symmetry, and assigned to 3T 1(F) 3T 1 (p).

5 . Spin-orbit coupling which removes the degeneracy of the ·'T 1 (p) state is assumed to split the visible bands9

.

6. The charge-transfer band in the studied glasses is , suggested to be, related to the presence of trace iron impurities, in the raw materials. Thi s can be supported by the presence of the ultraviolet absorption band in the blank, parent undoped g lass . Iron , usually occurs in both the ferrous and ferric states in glass. Both Fe3

+ and Fe2' have been

reported to have strong charge-transfer bands in the near-ultraviolet reg ion 15

• However, the fe rrous charge-transfer band has lower intensity than that of Fe3

+. The ultraviolet absorption of Fe3+ in g lass is characterized by a steep absorption edge and in silicate glasses, Fe3

+ is assumed to occur in four-fold coordinationr..

4.2 Discussion of infrared absorption spectra

The infrared absorption spectra of the studied g lasses are compared, in general , feature with the same absorption spectra usually observed from the traditional silicate g lasses. The principal absorption frequencies can be classified to occur in three regtons:

(I) The mid-region , extending from 2000-400 cm·1 and is characterized by the appearance of the

662 INDIAN J PURE & APPL PHYS, VOL 41, AUGUST 2001

characteri sti c and princ ipal absorpti on bands of the network forming S i O~ groups.

(2) The near-in fra red region, extending from 4000-2000 c m·1 and compri ses the absorpti on bands due to vibrati ons of water, hydroxy l and silanol groups.

(3) T he fa r-infrared region, extend ing from 400-100 c nr 1 and is characte ri zed by the presence of sharp and narrow, consecuti ve peaks, belonging to the vibrat ions of network-mod ifie r cat ions.

Table 2- Posi tions and assignment of the observed infrared abso rpti on band s

Peak position (cm. 1)

Silicate chain

Assignment References

1065-1095 Si -0 -Si anti-symmetric 17-20 stretching of bri dging oxygen wi thin the tet rahedral

940-970 Si-O.Stretching with I non- 17-20 bridging oxygen

860-940 Si -0 · stretch ing wi th 2 non- 17-20 bridging oxygens

750-820 Si-0-S i Symmetric stretching of bridging oxygen

460-510, GOO Si -0 -Si and 0-Si-0 bending 17-20 modes (V ~ )

Borate Chains BO~ stretching

1420- 1550 B-0 bonds vibrations 2 1-24

1550- 1400 B-0 vibrations of various 2 1-24 bo rate groups

1250 Roroxo l rings , tri-, tetra- and 2 1-24 pentaborate groups

1220-1250 pyro- and other borates 21-24

804 stretching

I 050 Tri-. tetra-, and pentahorate 2 1-24

900- 1000 Diborate

880 Tri- , tetra, and pentaborate 2 1··24

760-770 Oxygen bridges between 2 1-24 tetra- and trigona l boron atoms

690-730 Oxygen bridges between 2 1-24 trigona l atoms

Other group

1640 Molecu lar water 19.20

1460 Carbonate g roup 19.20

3000-3750 Hydrogen, mo lecu lar water, 19,20 silanol group(SiOH)

T he infrared absorption spectra obtained before irradiati on can be interpreted as fo ll ows:

The base ternary sili cate g lasses (Nos. 1-5) of the compos iti on S i02 74% Na20 16%, RO (d iva lent ox ide) I 0%, (mole %) show several abso rpti on bands extend ing in the th ree menti oned regions, of the spectrum studied. The observed abso rpti on bands can be attri buted to the specific groups or cati ons vibrati ons 17

.23 .

(A) Mid-region

( I ) Strong absorpti on band at 500-480 cm·1,

which can be attribu ted to S i-0-S i or 0-S i-0 bending modes.

(2) Very weak infl ect ion or ki nk, at about 600 cm·1

, which can a lso be correlated to overtone of the same previous bend ing vibration.

(3) Small absorpti on b~nd at 800-700 cnr 1,

which can be ass igned to S i-0-S i symmet ri c stretching of bridging oxygens between tetrahed ra.

( 4) Strong broad absorpti on band, at 1250-880 cm·1

, which can be re lated to S i-0-S i anti-symmetric

stretchi ng of bridg ing oxygen w ithin the tetrahedra .

Thi s broad band reveal s a lso, a sma ll kin k at about 920-900 cm·1

, whic h can be re lated to Si-O· stretching with one or two non-bridging oxygen.

(5) Very weak inf lecti on at 1670- 1640 cm·1

which can be attributed to mo lecu lar water vibration.

(6) Small band or in flect ion at about 1460 c m·1

which can be re lated to carbonate group vibrat ion.

(B) Near infrared broad band

It is a characte ri sti c and fa mili ar broad-band, centered at 3300-3700 cnr 1

, whic h can be ass igned to hydroxy l, s ilano l group (SiOH) or watt:r molecule vibrations.

(C) Far infrared bands

The bands of thi s reg ion extend from 300-1 00 cm·1

, and they are not measu red in th is work and are accepted to originate from the vibra tion s of the mod ifiers cations such as that of. Na~ and ca~~

cations in their s its .

Table 2 dep icts the infr:.tred absorption spectra, the ir attribut ions and the re ferences of the ir assignment.

KH ALIL et al.: TERNARY SILICATE GLASSES 663

All the spectral curves of glasses 1-5 reveal the same previous absorption bands and these data reflect the stmctural silicate chains and the ir familiar arrangement which are nearly the same in the mentioned glasses ( 1-5), as it is obvious that, the divalent cations studied are most ly housed in interstiti al positi ons within the silicate network wi thout obvious disturbance on the main stmctural groups arrangement whatever the di valent ox ide introduced .

The infrared spectm m of g lass (No. 6) reveals add it ional absorption bands due to d ifferent borates (BO, and BOJ groups) beside that, due to the main silicate groups.

4.3 Effect of glass composition

When the optical absorpti on spectra of the ternary silicate g lasses containing nickel ions are compared with the predicted spectra given in the energy diagram for dx system in octahedral and tetrahedral symmetries9

• It would be suggested that, nicke l ions are present in both the coordinati ons. The sharp absorption band observed at 4 10-420 nm, can be re lated mostl y to nickel ions in octahedral state, while the absorption bands at 560 and 640 nm can be re lated to nicke l ions in the tetrahedral statex-10

• The two states of coordinati on are expected to be present in equilibrium and do not change with the change of the type of the di va lent ox ide introduced, (as seen in the spectra of glasses Nos 1-5. However, in glass No.6 contain ing 40% B20 3 and 74% Si0 2 and Na20 16% (mole%), the spectmm revea ls the decrease of the intensity of the absorption band at 410-420 nm, indicating the decrease of the percentage of the octahedral nickel ion. This resu lt is believed to be correlated with the increase of the ac id ic constituents of the host glass.

4.4 Effect of gamma irradiation

The effect of any radiation on a materi al depends not only on the energy of the irradi ati on, but on the nature of the irradiating species itself.

As an inc ident e lectron (or a secondary electron produced by an incident X-ray or y-ray photons) moves through a material, it forms defects through ionization of valence e lectrons; with enough energy, it can cause a cascade of secondary electrons, re leased through knock-on-collisions, with bound e lectrons, known ·as the Compton effect'A. The radi ati on damage processes that take pl ace in

glasses are, generally, the same as those, that occur in crystals. There are three bas ic processesJ: (i) radio lys is, (ii) displacement or (knock-on) damage, and (iii ) electron rearrangement.

Radi ation-induced ionizati on occurs when electrons in the va lence band of the mate ri al ga in enough energy from the inc ident radi ation to be excited into the conducti on band of the material. In insul ators, the bandgap energy is, between 5 and I 0 eV. An e lectron moving through a materia l in this manner will lose approx imate ly 20 eV per ionizati on, until it has too little energy to cause more ionization and will then be trapped by a positi ve ly charged defect. Alternati ve ly, an exciton can be fo rmed by a bound e lectron-hole pair. If the exc iton recombines non-radiati vely (i.e., a photon is not emitted), the energy given up by the atom upon recombination must be d irected into atomic motions, resulting in short-range structural rearrangements powered by thi s radiolys is process.

Gl asses dev iate from the ideal network struc ture and do cotain preexisting defects such as vacancies, nonbridging oxygens, impurities, e tc. The ex istence of such stmctural defects are assumed to occur in a solid because, the free energy is minimi zed by admitting a certain amount of di sorder in the stmcture4

•

Defects can be di vided into intrinsic defects. which arise fro m the glass matrix itse lf, and extrinsic defects, which are caused by dopants or impurities.

It is believed that, with the presence of impuri ties in the solid lattice, the optical and magnetic properties change. Mul ti-va lent impurities, such as transition or rare-earth ions, can easily trap electrons or holes when irradi ated . Induced color­centers formati on is a phenomenon in which, the ionizing radiat ion produces an e lectron-hole pair, which then becomes indi viduall y trapped at various defect sites in the glass structure.

4.5 Effect of radiation on base silicate glasses

Bishay2 and FriebeleJ summari zed in the ir review, the collecti ve rad iati on stud ies of sil icate g lasses and concluded that, the fo llowing poss ible induced absorption bands can be reso lved .

Recently, Shkrob et af.25 conf irmed that, irradiation of a lkali silicate glasses results in the formation of metastable spin centers such as,

664 INDIAN J PURE & APPL PHYS, VOL 41 , AUGUST 2003

oxygen-hole centers (OHC 1 and OHC2) , silicon

peroxy radical s and a silicon dangling bond (£' center) . There are two absorption bands from the ho le centers, OHC2 reveals the band at (2eV) and OHC 1 reveals the band at (2.7 eV). In the OHC 1

centers, the =SiO· radical is strongly coupled to a sing le a lka li cati on. It is argued that, trapping of the hole by non-bridg ing oxygen atoms does not result in the re lease of a compensating alkali cation . The O HC2 center is a hole-trapped, on a tetrahedral =S i0 2

2·unit or a pl anar -Si02• unit. It is demonstrated that, silicon peroxy radicais are not formed by charge-trapping.

Table 3- Posi tions and origi ns of radiation induced bands

Origi n

Absorp ti on Bishay( 1970) Friebele ( 1990 ) band posi tion

1.7-2.0 eV Electron trap Electron trap (E 1)

2.0-2 .1 eY Posit ive hole Hole trap (HC2)

2.7-2 .9 eY Positive ho le Hole trap (HC 1)

4 .0eV Posi tive hole Electron trap (EJ) 5.4 eY Electron trap Electron trap (E' 2)

5.8 eY Electron trap (E' 1)

4.6 Effect of radiation on transition metal ion

When a glass, that contains transiti on meta l ions, is irradiated, these ions are available as poten ti a l traps fo r the radiolytic e lectrons and ho les. In most cases, the trapping of charges by the transition metal ions, seems to be favoured and the behaviour of g lass depends primaril y on the type and concentration of these dopants (or impurities) . It is important to note that, the presence of the dopants do not alter the intrinsic trapping sites of the glass. Rather by prov iding alternate sites, they retard the fo rmat ion rate and increase the recovery rate of the in trins ic co lor centers. Many multi-valent transition elements compete, successfully, with the intrinsic traps for the radi olyt ic charges. Ghone im et af.2'' has shown that, rad iation effec t can change the va lency of vanadium ions in phosphate glasses and manganese ions in cabal g lasses by photo-chemi cal reactions. However, nicke l ions are known to ex ist in g lasses, so lely, in the di va lent Ni2

+ state, under norma l atmospheric conditi ons. The authors pos tulate the same assumption of E hrt et a /.13

•27 that,

the ex trins ic defects observed in glasses containing nicke l ions could be ascribed to the photo-oxidation

of Ni2+ forming (Ni 2+) . It seems that, these induced

metastable states show absorption spectra in the same positions, expected for divalent Ni 2

+ ions. This explains the observed increase in the intensities of the characteri stic absorption bands of Ni 2

+ ions with radiation. It is obvious that, the high basicity of the studied g lass hosts ( 10 mol % alkali ox ide + 16 mol % divalent oxide) stabili zes the new ox idation states.

4.7 Effect of radiation on infrared spectra

To interpret the effect of gamma rad iati on on the infrared absorpti on spectra, the fol lowing crite ri a are introduced .

I . The infrared results obtained indicate that, after irradiation, the elementary network-forming units (SiO~ te trahedra) remain unchanged . In other words, the units maintain the ir shape and structu re. It seems that, the sma ll changes observed in the intensiti es of the absorpti on bands with radi ati on can be corre la ted with two parameters, name ly, the change in the bond angles or the de truction of the same bonds th rough successive irradi at ion. Piao et a/.2s arri ved to a simil ar conc lu sion on the effec t of irradiation on vitreous s ilica. They assumed that, the angles of Si-0 -Si bridg ing bond undergo essenti a l changes. These angles define the tightness of the structural package of the. whole glass and also are the randomizing factors in vitreous sil ica.

2 . During irradi ati on, ion izati on process produces e lectron-ho le pa irs, prov id ing paths fo r bond rearrangements, reduc ing the constra ints on structural relaxation . The relaxat ion process re leases some of the excess energy stored in the st ructure, accompanied by a decrease of the average bridg ing bond (Si-0 -Si) angle . Due to the absence of regular structure, the re laxation in vo lves long-range effects, essenti a ll y, the entire structu re partic ipati on.

3 Piao er a /. 2x fina lly conc luded that , even if there is some change in the most probable bond angle with radi ation, they expect this effec t to be second-order, in compari son to the thermodynamica ll y dri ven narrow111g of the di stributi on of the bridging bond angles. It is obvious that, the structure of th is si I icate glasses packing and the ir structural units are so mewhat res istant to radiation and the infrared spectra are seen to be quite pronounced with high doses . It seems that, the so-called induced defects are limited to optical spectroscopic investigati ons.

KHALIL eta/.: TERNARY SILICATE GLASSES 665

4.8 Rate of formation of color centers or growth rate

It is very important to point out that, ionizing radiation will not only create new defects, but can also convert pre-existing defects, including transition metals, to color centers.

Formation of the radiation-induced color centers is certainly not a simple capturing process at existing defects 1, which would contradict the linear relation of absorption and radiation dose found by Weeks & Sonders2~, It can, therefore, be assumed that, the radiation creates defects beside the already existing defects, which subsequently trap electrons or holes. Lell et al. 1 reported that, some authors distinguish between the two phases in the formation of color centers, an initial fast growth and a second slower rate, frequently reaching saturation . They also indicated that, some interactions between defect centers of various types are possible.

In the present study, it is observed that, in almost all glasses, an initial fast growth is followed by a second slower growth, frequently reaching saturation.

The results of the authors can be explained by suggesting that, before irradiation , the lattice structure of the glasses contains a large number of intrinsic defects, which may trap electrons or holes, and thus, form color centers, as the glass sample is irradiated . In the meantime, new, induced defects may be formed, and their number will increase at first with increasing radiation dose. On the other hand, the number of intrinsic defects that have not trapped electrons or holes decreases with increasing irradiation . The predominant effect is associated with the intrinsic defects and the rate of formation and annihilation of the color centers associated with these defects. When the rates of formation and annihilation become nearly equal after prolonged irradiation, equilibrium is assumed to be established.

Another suggestion may be advanced, which would also explain the different growth behavior and is simply based on the assumption that, there are numerous color centers with different growth rates contributing to the absorption at a given wavelength . Another postulation may be recognized that, there are several rate-determining processes operating concurrently during irradiation. Similar conclusions were arrived at by several workers 2 •2 ~·.1 11 ··11 .

5 Conclusion

Experimental results of thi s study establish the presence of characteristic radiation-induced colour centers in undoped and doped gamma-irradiated ternary silicate glasses, containing nickel. The induced bands slightly change with radiation dose and chemical composition of the base glass.

Electron microscopic and X-ray analysis confirm the stability of glass structure and that , induced colour centres are identified quite by optical absorption, but not by infrared spectroscopic investigation . Nickel-containing glasses are, therefore, considered to be suitable as radiat ion­sensitive indicator glasses.

Interpretation of the growth rate relati onship between induced bands growth and the applied dose is not so simple, but includes several possibilities in formation and annihilation of the colour centers.

References

Lcll E, Kreidl N J & Hensler J R, Progress in ceramic science (Pergamon Press, Oxford), Vol. 4, 1966, pp. 1-93.

2 Bishay A, J Non-Cryst Solids, 3 ( 1970) 54.

3 Griscom D L & Friebele E J, Treatise on materials science & technology, (Ed) M Tomozawa & R H Doremus, (Academic Press, New York), Vol. 17, 1979, pp. 25 7-351.

4 Friebele E J, Optical properties of glass, (Ed) D R. Uhlmann & N J Kreidl , (American Ceramic Society, Westerville, Ohio, USA), 1991 , p. 205 .

5 Zsigmondy R, Ann Phys , 4 ( 190 I) 60.

6 Weyl W A, Coloured glasses, reprinted by (Dawson's of Pall Mall , London), 1959.

7 Moore H & Winkelmann H, J Soc Glass Tecllllol, 39 (1955) 213 .

8 Bamford C R, Phys Chem Glasses, 3 ( 1962) 189.

9 Bates T, Modem aspects of the vitreous state, Ch 2, (Ed) J D Mackenzie (Butterworths, London), 1962, pp. 195-254.

10 Paul A & Douglas R W, Phvs Chem Glasses , 8 ( 1967) 233.

II Turner W H & Turner J A, J Am Ceram Soc, 55 ( 1972) 201.

12 Moncke D & Ehrt D, Proceedings 5'" European Society for Glass Technology Conference, B4 ( 1999) 49-56.

13 Moncke D & Ehrt D. Glastech Ber Glass Sci Lll Teclll!ol. 74 (200 I) 65 .

14 EI- Hadi Z A & EI-Baki M A. Phys Chem Glasses , 40 ( 1999) 90.

IS Paul A, Chemistry of glass , (2"d Ed), (Chapman & Hall. New York), 1990.

666 INDIAN 1 PURE & APPL PHYS, VOL 41, AUGUST 2003

16 Steele F N & Doug las R W, Phvs Chem Glasses, 6 ( 1965) 246 .

17 Wong J & Angell C A, Glass structure by spectroscopy, (Marcel Dek kar, New Yo rk), 1976.

18 Merzbacher C I & White W B, J Non-Ctyst Solids , 130 ( 199 1) 18.

19 Dun ken H & Doremu s R H, J Non-Crvst Solids, 92 ( 1987) 61.

20 Hu sung R D & Doremus R H, J Mater Res , 25 ( 1990) 2209.

2 1 Krogh-Moe J, Pln•s Chem Glasses, 6 ( I 965) 46.

22 Kami tsos E I, Patsis A P. Karakassides M A & Chryssikos G D, J Non-Ctyst So lids, 126 ( 1990) 26.

23 Kamitsos E I, Pat sis A P & Ch ryss ikos G D . .I Non-Crvst Solids , 152 ( 1993) 246.

24 El Batal H A. Khalifa FA & Azooz M A, Indian./ Pure & Appl Phys, 39 (200 I ) 565 . .

25 Shkrob I A, Tadjikov B M & Trifunac A D, .I Non-Cryst Solids , 262 (2000) 35 .

26 El Batal H A & Ghoneim A, Nucl lnstmm Meth Phys Res (B) 124 ( 1997) 8 1; Ghoneim N A, \lloustatTa FA & Ezz El-Din F M, Phys Chem Glasses, 26 t I 985) 55.

27 Natura U & Ehrt D, Clastech Ber Glass Science & Tee/mol, 72 ( 1999) 295 .

28 Pi ao F, Oldham W G & Haller E E, J Non-Crvst Solids , 276 (2000) 6 1.

29 Weeks R & Sonders E, Parm11agnetic resonance (Ed) Low W (Academ:c Press, New York), Vol. 2, 1963, p. 869.

30 Levy P W, .I Am Cerwn Soc, 43 ( 1960) 389.

3 1 Barker R S, McConkey E A G & Richardson D A. Pln•s Chem Glasses, 6 ( 1965) 24.