- Email: [email protected]
The influence of oxide doping on some optical properties of fluoroaluminate glasses
LETTER TO THE EDITOR
J O U R N A L OF
NON-C SOI ELSEVIER
Journal of Non-Crystalline Solids 204 (1996) 196-201
Letter to the Editor
The influence of oxide doping on some optical properties of fluoroaluminate glasses V.D. Khalilev *, P. Ebeling, N.U. Vinogradova St. Petersburg's State Institute of Technology, St. Petersburg, Russia
Received 15 November 1995; revised 17 May 1996
Abstract The optical constants and transmission spectra of fluoroaluminate glasses from the system A1F3-YF3-~ZRF2 (R = Ba, Ca, Sr, or Mg) doped with small (0.25-1.00 tool%) amounts of oxides into the batch and with oxygen from the melting atmosphere were measured. The displacement of UV-transmission limit toward the longwave region, as compared to undoped glass, was observed to be slight (about 20 nm) in the case of oxide doped glasses and significant (about 100 nm) in the case of glass doped with oxygen from the melting atmosphere. It is concluded that fluoroaluminate glasses accept only limited quantity of oxides. The glasses concerned are transparent (up to 91%) in the range of wavelengths of 220 to 6300 rim.
1. Introduction Fluoride glasses are known for their high transparency in the range of wavelengths of 2 0 0 - 5 5 0 0 nm and for their low linear and non-linear refractive indices, which makes them attractive materials for fibre and laser optics [1]. The first fluoride glasses, fluoroberyllate glasses (FBG), were obtained. The influence of oxygen content in F B G on their optical properties, particularly on transparency, was studied in Ref. [2]. F B G materials were melted in an atmosphere containing oxygen. At first, transparency increased, caused by oxidative effect of oxygen on refractory nitrides forming in the glass in the pres-
* Corresponding author.
ence of ammonia residue after fluorination by ammonia bifluoride. With an increase of melting time in the same atmosphere, an absorption band of 270 nm appeared and bands at 350 and 430 nm were observed in the spectra of glasses of B e F 2 - K F - C a F 2 system containing no AIF 3. Research on F B G is restricted because of the high toxicity of beryllium fluoride. There are many publications on fluorozirconate glasses and there are significantly fewer publications on fluoroaluminate glasses (FAG), though the letter have a higher transformation temperature (about 450°C) and better chemical durability [3]. To produce transparent non-crystallizing F A G (of high quality), it is necessary to use additional fluorination. N H 4 H F 2 is one of the best fluorinating agents. A m m o n i a residue reacts with batch fluorides,
0022-3093/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S0022-3093(96)00531-5
ETTER TO THE EDITO[
V.D. Khalilet, et al. / Journal of Non-Co'stalline Solids 204 (1996) 196-201
particles of which decrease the transparency and crystallization resistance of glass. In this case, the doping of glass with small amounts of oxygen leads to oxidation of refractory nitrides and to an increase in transparency. A better method consists in melting a batch of monocrystalline fluorides (produced by vacuum high temperature technology with lead bifluoride being used) followed by remelting of crushed glass with addition of fluoride acid in a reactive dry mixed atmosphere of oxygen and argon of high purity. In this case, ammonia bifluoride is not used. This method increased the transparency of FAG and decreased the concentration of dispersing defects to the level of the best fluorozirconate glasses [4]. The question of the effects of oxygen is not solved. As shown in Ref. [4], oxygen content in FAG can reach 5 at.%. This paper presents the results of an investigation into the influence of oxygen doping into the batch
Table
and from the melting atmosphere on some optical properties of FAG.
2. Experimental The basic glass for this investigation has the composition A1F3-YF3-ERF 2 (R = Ba, Ca, Sr, or Mg) system containing 36 mol% A1F3 and will be called FAG-36. The starting composition for this glass was the mineral usovite Ba2CaMgA12F~4. The batches were prepared from monocrystalline raw materials, except A1F3. FAG-36 was doped with oxygen in two ways: (1) from the melting atmosphere (reactive mixture of argon of high purity and oxygen of superior purity in the ratio 2:1). These samples will be indicated by index (02); (2) as oxide compounds in small additions to the batch. The composition of synthesised glasses is given in Table 1. The doping of every oxide started from 0.10
1
Composition No.
197
of
of
sample
samples MgO
synthesised a (mol%)
CaO
1
0.25
.
2
0.50
.
a (mol%)
A1203
a (mol%)
.
SrO
.
" (mol%)
.
.
.
.
.
~ (mol%)
BaO
a (mol%)
PbO
.
.
.
Y203
.
3
0.75
.
4
-
0.10
.
.
. .
. .
.
5
-
0.25
.
.
.
.
.
6
-
0.50
.
.
.
.
.
7
-
0.75
.
.
.
.
.
8
-
1.00
.
.
.
.
9
-
0.25
0.25
10
-
-
0.25
-
-
-
11
-
-
0.50
-
-
-
12
-
-
-
0.25
-
-
-
13
-
-
-
0.50
-
-
-
14
-
-
-
0.75
-
-
-
15
-
-
-
1 . 0 0
-
-
-
16
-
-
-
0.25
-
-
17
-
-
-
0.50
-
-
.
.
.
. .
.
18
.
.
.
.
.
19
.
.
.
.
.
0.50
20
.
.
.
.
.
0.75
21
.
.
.
.
.
22
.
.
.
.
.
23
.
24(02
)
a
100
To
mol%
.
.
-
-
BaCaMgA12Ft4,
these
.
of
oxide
1.00 .
0.25
. -
mol%
0.25
were
0.50 0.50
added.
-
-
a (mol%)
.ETTER TO THE EDITOI
198
V.D. Khalilet, et al. / Journal of Non-C~stalline Solids 204 (1996) 196-201
or 0.25 mol% and finished when the next glass of the series was opalescent or milky. The glasses with additions of rare earth element oxides Ga, Ge, Hf, Zr were prepared, but the colour of the glasses was grey and opaque at 0.25 tool% oxide addition, so they were not investigated. Melting of glasses was carried out in vitreous carbon crucibles at 900-1000°C for 1 h and 1 h 20 min, in the atmosphere of high purity argon (except samples with index 02). The rate of cooling was about 2°C/s. The weight loss of the glasses did not exceeded 3%.
t~'(a)# /!
For a comparison, some fluoroberyllate glasses (FBG) doped with oxides were synthesised. The composition of basic glass FBG-54 was as follows (tool%): BeF 2 54, A1F3 10, KF 20, CaF 2 12. The batch containing BeO, A1203, KHF 2, CaF 2 was melted in platinum crucibles, NH4HF 2 was used as a fluorinating agent in 50 mass% excess. FBG-54 doped either with BeO or with AI203, K 2 0 or CaO were melted in argon atmosphere, other conditions being equal. Optical properties were determined by a refractometer (Hpqb-23). Transmission spectra were mea-
TT,
dO0
(b) .r
50
50
300
~00
~bO
,~ , n m
(c)
900
3do
~o0
(d)
400"
z -Z
"Z
P 50
,~, nm
5O
~
f ~6o
/ ~tbo
,l, nm
Jbo
#bo
.~, rvn
Fig. 1. UV transmission spectra of samples of FAG-36 (a) and of FAG-36 doped with following oxides: BaO (b) where the curve I corresponds to 0.25, II to 0.50, III to 0.75, IV to 1.00 mol%; A1203, Y203 (c) where curve I corresponds to 0.25 mol% of Y203, II to 0.25 mol% of AI203, III to 0.50 tool% of Y203 (A1203); mixture of CaO + A1203 (curve I) and PbO (II) (d).
.ETTEFI T O T H E E D I T O I
V.D. Khalile~' et a l . / Journal of Non-Co:stalline Solids 204 (1996) 196-201
199
Table 2 Optical constants of glasses synthesised No. of sample
n,. (q-4 X 10 - 4 )
n d ( ± 4 X 10 - 4)
nf (-t-4 X 10 4)
v = (nd - l ) / ( n f - n c)
FAG-36(O 2) l 2 3 4 5 6 7
1.4253 1.4255 1.4249
1.4267 1.4269 1.4257
1.4297 1.4299 1.4285
98.5 97.3 99.4
opalescent
sample
1.4267 1.4252 1.4251 1.4254
1.4280 1.4264 1.4264 1.4268
1.4311 1.4295 1.4295 1.4297
97.6 98.7 98.1 99.4
1.4296 1.4296
96.6 97.6
1.4293 1.4297 1.4301 1.4310 1.4306
97.6 98.3 99.3 98.6 98.7
1.4294 1.4288 1.4312
98.9 99.3 96.9
1.4306 1.4308 1.4299
98.2 96.0 98.8
8
opalescent
sample
9 10
1.4252 1.4252
1.4266 1.4265
11
opalescent
sample
12 13 14 15 16
1.4250 1.4253 1.4258 1.4267 1.4263
1.4262 1.4267 1.4271 1.4280 1.4276
17
opalescent
sample
18 19 20
1.4251 1.4245 1.4268
1.4263 1.4258 1.4282
21
opalescent
sample
1.4263 1.4264 1.4256
1.4276 1.4277 1.4269
22 23 24(02 )
sured on samples of FAG, 7 and 0.5 mm thick, and on samples of FBG, l0 mm thick, with spectrometers (Hitachi and Shimadzu).
3. Results Optical constants of the glasses are given in Table 2. It should be mentioned that the ground glass, FAG-36, has stable optical constants, refractive index particularly n d = 1.4267 _ (4 × 10 4). The doping of FAG with small amounts of oxides has a small influence on the refractive index of FAG-36, for instance n a varies from 1.4257 to 1.4280. The density of oxide doped FAG lies between 3.81 and 3.88 g / c m 3. The highest density samples are those containing PbO. Ultraviolet transmission spectra of FAG-36 and oxide doped FAG are shown in Fig. 1. The samples are transparent (I, II, III, ~ 91%) at wavelengths
< 250 nm. In Fig. l(b) and (c), the spectra of opalescent samples (III, IV) are also shown (transparency < 40% at A > 400 nm).
~o0
50
20o
J
~
0~0
~, r~n
Fig. 2. UV transmission spectra of the samples of FAG-36(O2). Thicknesses of samples are (a) 7 and (b) 0.5 ram.
E T T E R TO T H E EDITOF
200
V.D. Khalileu et al. / Journal of Non-Crystalline Solids 204 (1996) 196-201
T,7.
samples 7 and 0.5 mm thick are shown in Fig. 3. Spectra of thick samples (a) have absorption band at 3600 cm -1 (2.8 p~m). For the samples with index (O2), another absorption band at 2170 cm -1 (4.6 ~m) is observed. UV transmission spectra of FBG samples are shown in Fig. 4. In the case of undoped FBG-54, an absorption band at 270 nm is resolved. In the case of FBG-54 (a) doped with K20, AI203 or CaO, the absorption at 270 nm is greater. Other bands at 350 and 430 nm occur only in samples with addition of BeO ((c), (d)), the absorption being greater when concentration of BeO increases from 0.2 to 0.4 tool%.
too
50
40';o
' 2ooo
~6oo
• 42oo
~ cm .a
Fig. 3. Typical IR transmission spectra of the samples of oxide doped FAG-36, 7 mm thick (dashed line) and of the samples FAG-36(O 2) and glass no. 24(02) (a) 7 and (b) 0.5 mm thick.
UV transmission spectra of samples FAG-36(O 2) with thickness 7 and 0.5 mm are shown in Fig. 2(a). The limit of UV transmission is shifted into the longwave region. In the spectrum of the thin sample of FAG-36, three absorption bands were observed: 215, 235, and 255 nm. Typical infrared transmission spectra of FAG with
~Z t00
d-
2~0
zb0
~k0
0/~0
a],n,,
Fig. 4. UV transmission spectra of the samples of FBG-54 (a) and FBG-54 doped with following oxides: 0.4 mol% of AI203 (CaO, K 2 0 ) (b); BeO (c) 0.2; and (d) 0.4 tool%.
4. Discussion Upon analysis of 'oxide-fluoride' phase equilibrium diagrams [5], for instance of AIzO3-CaF2 system, when even the smallest addition of AI203 to CaF 2 decreases the melting temperature of the system, we assume that addition of a small amount of oxides to FAG would decrease their tendency to crystallization, because the reduction of liquidus temperature of composition leads to an increase in the possibility of glass formation. Experimental data had confirmed this hypothesis only partly. As mentioned in Ref. [4], oxygen content in FAG36(02) is about 5 at.% (according to XPS data). The calculated content of 'batch' oxygen in our FAG is not above 0.45 at.%. It should be noted that the glasses were milky or opalescent when the calculated oxygen content was about 0.29 at.%. We believe that in FAG the solubility of oxide is limited quantity, and the oxide over this amount increases crystallization. We do not think that slight displacement of the UV transmission limit toward the longwave region for oxide doped FAG, as compared to undoped FAG-36, as we observed, can be a result of the doped cation. Logically, UV transmission limit should shift into the longwave region with addition of heavy cations, such as PbO and Y203, and to the shortwave region with addition of light ones. These shifts are not observed in the spectra. So we attribute the limit displacement observed to the effects of oxygen. Based on the data obtained, it seems diffi-
.ETTER TO THE EDITOI
V.D. Khalilec et al. / Journal of Non-Crystalline Solids 204 (1996) 196-201
cult to determine the form of this relation between either UV transmission limit shifts, or the variations of optical constants, and calculated oxygen content; we note that there is a small uncontrolled pick-up of air oxygen during some of the operations, and the content of A I 2 0 3 residue in commercial A1F3 of high purity fluctuates. The combined state of oxygen in F A G - 3 6 ( O 2) (so-called 'atmospheric' oxygen) and the combined state of ' b a t c h ' oxygen might differ. The displacement of UV transmission limit in the case of 'atmospheric' oxygen is significant and three absorption bands (215, 235 and 255 nm) are resolved in the spectra of thin samples. W e assign the bands concerned to the influence of 'atmospheric' oxygen. The maximum transparency was observed for the glasses no. 23 and 9 doped with 0.5 mol% PbO and 0.25% CaO + 0.25% A I 2 0 3, respectively. These two additions have the lowest melting temperature, as compared to the other ones. Absorption bands in IR transmission spectra seem to be caused by the presence in the glass of structurally bound water (3600 cm E) and oxygen linked to carbon as CO (2170 cm - l ) [6], because of the interaction between 'atmospheric' oxygen and the vitreous carbon crucible. In the case of FBG, absorption bands at 350 and 430 nm are caused by the presence of oxygen linked to beryllium in the glass. In the case of F B G containing no A1F3, and its increased hydroscopicity, the same absorption bands (350 and 430 nm) are caused by the formation of B e - O bond as a result of pyrohydrolysis of glass melt.
201
5. Conclusions Oxide solubility in fluoroaluminate glasses ( F A G ) is limited (up to oxygen content in glass, ~ 0.29 at.%). The optical quality of F A G - 3 6 remains after doping the batch with Y203, A1203, MgO up to 0.25 mol%; PbO, CaO + A120 3 up to 0.50 tool%; BaO, CaO up to 0.75 mol%; SrO up to 1.00 mol%. The fundamental absorption limit (the wavelength corresponding to 50% of transmission with the sample thickness 7 mm) is ~ 6.4 Ixm in the IR-region, and ~ 245 nm in the UV-region for oxide doped F A G and 315 nm for F A G - 3 6 ( O 2) and glass no. 24(02). 'Atmospheric' and ' b a t c h ' oxygen exist in F A G in different states and influence the optical properties of F A G differently. In fluoroberyllate glasses, the absorption bands at 350 and 430 nm are caused by presence of oxygen linked to beryllium in the glass.
References [1] M. Weber, D. Milan and W. Smith, Engineering 5 (17) (1978) 468. [2] V.D. Khalilev, Steklo, Trudy instituta stecla (Russia) 1 (1966) 101. [3] V.D. Khalilev and L.V. Bogdanov, Vysokochistye veshestva (Russia) 4 (1992) 50. [4] L.D. Bogomolova, N.A. Krasil'nikova, O.A. Trul. V.L. Bogdanov, V.D. Khalilev, K.V. Panfilov and F. Caccavale, J. Non-Cryst. Solids 175 (1994) 84. [5] N.A. Toropov and V.P. Brakovski, Diagrammy sostojanija silikatny sistem, Spravochnik 'Dvojnye sistemy' (Nauka, Moscow, 1965) p. 468. [6] C. Nakamoto, Infrakrasnye spectry neorganicheski i coordinacionny soedineni (Mir, Moscow, 1966) p. 106.
J O U R N A L OF
NON-C SOI ELSEVIER
Journal of Non-Crystalline Solids 204 (1996) 196-201
Letter to the Editor
The influence of oxide doping on some optical properties of fluoroaluminate glasses V.D. Khalilev *, P. Ebeling, N.U. Vinogradova St. Petersburg's State Institute of Technology, St. Petersburg, Russia
Received 15 November 1995; revised 17 May 1996
Abstract The optical constants and transmission spectra of fluoroaluminate glasses from the system A1F3-YF3-~ZRF2 (R = Ba, Ca, Sr, or Mg) doped with small (0.25-1.00 tool%) amounts of oxides into the batch and with oxygen from the melting atmosphere were measured. The displacement of UV-transmission limit toward the longwave region, as compared to undoped glass, was observed to be slight (about 20 nm) in the case of oxide doped glasses and significant (about 100 nm) in the case of glass doped with oxygen from the melting atmosphere. It is concluded that fluoroaluminate glasses accept only limited quantity of oxides. The glasses concerned are transparent (up to 91%) in the range of wavelengths of 220 to 6300 rim.
1. Introduction Fluoride glasses are known for their high transparency in the range of wavelengths of 2 0 0 - 5 5 0 0 nm and for their low linear and non-linear refractive indices, which makes them attractive materials for fibre and laser optics [1]. The first fluoride glasses, fluoroberyllate glasses (FBG), were obtained. The influence of oxygen content in F B G on their optical properties, particularly on transparency, was studied in Ref. [2]. F B G materials were melted in an atmosphere containing oxygen. At first, transparency increased, caused by oxidative effect of oxygen on refractory nitrides forming in the glass in the pres-
* Corresponding author.
ence of ammonia residue after fluorination by ammonia bifluoride. With an increase of melting time in the same atmosphere, an absorption band of 270 nm appeared and bands at 350 and 430 nm were observed in the spectra of glasses of B e F 2 - K F - C a F 2 system containing no AIF 3. Research on F B G is restricted because of the high toxicity of beryllium fluoride. There are many publications on fluorozirconate glasses and there are significantly fewer publications on fluoroaluminate glasses (FAG), though the letter have a higher transformation temperature (about 450°C) and better chemical durability [3]. To produce transparent non-crystallizing F A G (of high quality), it is necessary to use additional fluorination. N H 4 H F 2 is one of the best fluorinating agents. A m m o n i a residue reacts with batch fluorides,
0022-3093/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S0022-3093(96)00531-5
ETTER TO THE EDITO[
V.D. Khalilet, et al. / Journal of Non-Co'stalline Solids 204 (1996) 196-201
particles of which decrease the transparency and crystallization resistance of glass. In this case, the doping of glass with small amounts of oxygen leads to oxidation of refractory nitrides and to an increase in transparency. A better method consists in melting a batch of monocrystalline fluorides (produced by vacuum high temperature technology with lead bifluoride being used) followed by remelting of crushed glass with addition of fluoride acid in a reactive dry mixed atmosphere of oxygen and argon of high purity. In this case, ammonia bifluoride is not used. This method increased the transparency of FAG and decreased the concentration of dispersing defects to the level of the best fluorozirconate glasses [4]. The question of the effects of oxygen is not solved. As shown in Ref. [4], oxygen content in FAG can reach 5 at.%. This paper presents the results of an investigation into the influence of oxygen doping into the batch
Table
and from the melting atmosphere on some optical properties of FAG.
2. Experimental The basic glass for this investigation has the composition A1F3-YF3-ERF 2 (R = Ba, Ca, Sr, or Mg) system containing 36 mol% A1F3 and will be called FAG-36. The starting composition for this glass was the mineral usovite Ba2CaMgA12F~4. The batches were prepared from monocrystalline raw materials, except A1F3. FAG-36 was doped with oxygen in two ways: (1) from the melting atmosphere (reactive mixture of argon of high purity and oxygen of superior purity in the ratio 2:1). These samples will be indicated by index (02); (2) as oxide compounds in small additions to the batch. The composition of synthesised glasses is given in Table 1. The doping of every oxide started from 0.10
1
Composition No.
197
of
of
sample
samples MgO
synthesised a (mol%)
CaO
1
0.25
.
2
0.50
.
a (mol%)
A1203
a (mol%)
.
SrO
.
" (mol%)
.
.
.
.
.
~ (mol%)
BaO
a (mol%)
PbO
.
.
.
Y203
.
3
0.75
.
4
-
0.10
.
.
. .
. .
.
5
-
0.25
.
.
.
.
.
6
-
0.50
.
.
.
.
.
7
-
0.75
.
.
.
.
.
8
-
1.00
.
.
.
.
9
-
0.25
0.25
10
-
-
0.25
-
-
-
11
-
-
0.50
-
-
-
12
-
-
-
0.25
-
-
-
13
-
-
-
0.50
-
-
-
14
-
-
-
0.75
-
-
-
15
-
-
-
1 . 0 0
-
-
-
16
-
-
-
0.25
-
-
17
-
-
-
0.50
-
-
.
.
.
. .
.
18
.
.
.
.
.
19
.
.
.
.
.
0.50
20
.
.
.
.
.
0.75
21
.
.
.
.
.
22
.
.
.
.
.
23
.
24(02
)
a
100
To
mol%
.
.
-
-
BaCaMgA12Ft4,
these
.
of
oxide
1.00 .
0.25
. -
mol%
0.25
were
0.50 0.50
added.
-
-
a (mol%)
.ETTER TO THE EDITOI
198
V.D. Khalilet, et al. / Journal of Non-C~stalline Solids 204 (1996) 196-201
or 0.25 mol% and finished when the next glass of the series was opalescent or milky. The glasses with additions of rare earth element oxides Ga, Ge, Hf, Zr were prepared, but the colour of the glasses was grey and opaque at 0.25 tool% oxide addition, so they were not investigated. Melting of glasses was carried out in vitreous carbon crucibles at 900-1000°C for 1 h and 1 h 20 min, in the atmosphere of high purity argon (except samples with index 02). The rate of cooling was about 2°C/s. The weight loss of the glasses did not exceeded 3%.
t~'(a)# /!
For a comparison, some fluoroberyllate glasses (FBG) doped with oxides were synthesised. The composition of basic glass FBG-54 was as follows (tool%): BeF 2 54, A1F3 10, KF 20, CaF 2 12. The batch containing BeO, A1203, KHF 2, CaF 2 was melted in platinum crucibles, NH4HF 2 was used as a fluorinating agent in 50 mass% excess. FBG-54 doped either with BeO or with AI203, K 2 0 or CaO were melted in argon atmosphere, other conditions being equal. Optical properties were determined by a refractometer (Hpqb-23). Transmission spectra were mea-
TT,
dO0
(b) .r
50
50
300
~00
~bO
,~ , n m
(c)
900
3do
~o0
(d)
400"
z -Z
"Z
P 50
,~, nm
5O
~
f ~6o
/ ~tbo
,l, nm
Jbo
#bo
.~, rvn
Fig. 1. UV transmission spectra of samples of FAG-36 (a) and of FAG-36 doped with following oxides: BaO (b) where the curve I corresponds to 0.25, II to 0.50, III to 0.75, IV to 1.00 mol%; A1203, Y203 (c) where curve I corresponds to 0.25 mol% of Y203, II to 0.25 mol% of AI203, III to 0.50 tool% of Y203 (A1203); mixture of CaO + A1203 (curve I) and PbO (II) (d).
.ETTEFI T O T H E E D I T O I
V.D. Khalile~' et a l . / Journal of Non-Co:stalline Solids 204 (1996) 196-201
199
Table 2 Optical constants of glasses synthesised No. of sample
n,. (q-4 X 10 - 4 )
n d ( ± 4 X 10 - 4)
nf (-t-4 X 10 4)
v = (nd - l ) / ( n f - n c)
FAG-36(O 2) l 2 3 4 5 6 7
1.4253 1.4255 1.4249
1.4267 1.4269 1.4257
1.4297 1.4299 1.4285
98.5 97.3 99.4
opalescent
sample
1.4267 1.4252 1.4251 1.4254
1.4280 1.4264 1.4264 1.4268
1.4311 1.4295 1.4295 1.4297
97.6 98.7 98.1 99.4
1.4296 1.4296
96.6 97.6
1.4293 1.4297 1.4301 1.4310 1.4306
97.6 98.3 99.3 98.6 98.7
1.4294 1.4288 1.4312
98.9 99.3 96.9
1.4306 1.4308 1.4299
98.2 96.0 98.8
8
opalescent
sample
9 10
1.4252 1.4252
1.4266 1.4265
11
opalescent
sample
12 13 14 15 16
1.4250 1.4253 1.4258 1.4267 1.4263
1.4262 1.4267 1.4271 1.4280 1.4276
17
opalescent
sample
18 19 20
1.4251 1.4245 1.4268
1.4263 1.4258 1.4282
21
opalescent
sample
1.4263 1.4264 1.4256
1.4276 1.4277 1.4269
22 23 24(02 )
sured on samples of FAG, 7 and 0.5 mm thick, and on samples of FBG, l0 mm thick, with spectrometers (Hitachi and Shimadzu).
3. Results Optical constants of the glasses are given in Table 2. It should be mentioned that the ground glass, FAG-36, has stable optical constants, refractive index particularly n d = 1.4267 _ (4 × 10 4). The doping of FAG with small amounts of oxides has a small influence on the refractive index of FAG-36, for instance n a varies from 1.4257 to 1.4280. The density of oxide doped FAG lies between 3.81 and 3.88 g / c m 3. The highest density samples are those containing PbO. Ultraviolet transmission spectra of FAG-36 and oxide doped FAG are shown in Fig. 1. The samples are transparent (I, II, III, ~ 91%) at wavelengths
< 250 nm. In Fig. l(b) and (c), the spectra of opalescent samples (III, IV) are also shown (transparency < 40% at A > 400 nm).
~o0
50
20o
J
~
0~0
~, r~n
Fig. 2. UV transmission spectra of the samples of FAG-36(O2). Thicknesses of samples are (a) 7 and (b) 0.5 ram.
E T T E R TO T H E EDITOF
200
V.D. Khalileu et al. / Journal of Non-Crystalline Solids 204 (1996) 196-201
T,7.
samples 7 and 0.5 mm thick are shown in Fig. 3. Spectra of thick samples (a) have absorption band at 3600 cm -1 (2.8 p~m). For the samples with index (O2), another absorption band at 2170 cm -1 (4.6 ~m) is observed. UV transmission spectra of FBG samples are shown in Fig. 4. In the case of undoped FBG-54, an absorption band at 270 nm is resolved. In the case of FBG-54 (a) doped with K20, AI203 or CaO, the absorption at 270 nm is greater. Other bands at 350 and 430 nm occur only in samples with addition of BeO ((c), (d)), the absorption being greater when concentration of BeO increases from 0.2 to 0.4 tool%.
too
50
40';o
' 2ooo
~6oo
• 42oo
~ cm .a
Fig. 3. Typical IR transmission spectra of the samples of oxide doped FAG-36, 7 mm thick (dashed line) and of the samples FAG-36(O 2) and glass no. 24(02) (a) 7 and (b) 0.5 mm thick.
UV transmission spectra of samples FAG-36(O 2) with thickness 7 and 0.5 mm are shown in Fig. 2(a). The limit of UV transmission is shifted into the longwave region. In the spectrum of the thin sample of FAG-36, three absorption bands were observed: 215, 235, and 255 nm. Typical infrared transmission spectra of FAG with
~Z t00
d-
2~0
zb0
~k0
0/~0
a],n,,
Fig. 4. UV transmission spectra of the samples of FBG-54 (a) and FBG-54 doped with following oxides: 0.4 mol% of AI203 (CaO, K 2 0 ) (b); BeO (c) 0.2; and (d) 0.4 tool%.
4. Discussion Upon analysis of 'oxide-fluoride' phase equilibrium diagrams [5], for instance of AIzO3-CaF2 system, when even the smallest addition of AI203 to CaF 2 decreases the melting temperature of the system, we assume that addition of a small amount of oxides to FAG would decrease their tendency to crystallization, because the reduction of liquidus temperature of composition leads to an increase in the possibility of glass formation. Experimental data had confirmed this hypothesis only partly. As mentioned in Ref. [4], oxygen content in FAG36(02) is about 5 at.% (according to XPS data). The calculated content of 'batch' oxygen in our FAG is not above 0.45 at.%. It should be noted that the glasses were milky or opalescent when the calculated oxygen content was about 0.29 at.%. We believe that in FAG the solubility of oxide is limited quantity, and the oxide over this amount increases crystallization. We do not think that slight displacement of the UV transmission limit toward the longwave region for oxide doped FAG, as compared to undoped FAG-36, as we observed, can be a result of the doped cation. Logically, UV transmission limit should shift into the longwave region with addition of heavy cations, such as PbO and Y203, and to the shortwave region with addition of light ones. These shifts are not observed in the spectra. So we attribute the limit displacement observed to the effects of oxygen. Based on the data obtained, it seems diffi-
.ETTER TO THE EDITOI
V.D. Khalilec et al. / Journal of Non-Crystalline Solids 204 (1996) 196-201
cult to determine the form of this relation between either UV transmission limit shifts, or the variations of optical constants, and calculated oxygen content; we note that there is a small uncontrolled pick-up of air oxygen during some of the operations, and the content of A I 2 0 3 residue in commercial A1F3 of high purity fluctuates. The combined state of oxygen in F A G - 3 6 ( O 2) (so-called 'atmospheric' oxygen) and the combined state of ' b a t c h ' oxygen might differ. The displacement of UV transmission limit in the case of 'atmospheric' oxygen is significant and three absorption bands (215, 235 and 255 nm) are resolved in the spectra of thin samples. W e assign the bands concerned to the influence of 'atmospheric' oxygen. The maximum transparency was observed for the glasses no. 23 and 9 doped with 0.5 mol% PbO and 0.25% CaO + 0.25% A I 2 0 3, respectively. These two additions have the lowest melting temperature, as compared to the other ones. Absorption bands in IR transmission spectra seem to be caused by the presence in the glass of structurally bound water (3600 cm E) and oxygen linked to carbon as CO (2170 cm - l ) [6], because of the interaction between 'atmospheric' oxygen and the vitreous carbon crucible. In the case of FBG, absorption bands at 350 and 430 nm are caused by the presence of oxygen linked to beryllium in the glass. In the case of F B G containing no A1F3, and its increased hydroscopicity, the same absorption bands (350 and 430 nm) are caused by the formation of B e - O bond as a result of pyrohydrolysis of glass melt.
201
5. Conclusions Oxide solubility in fluoroaluminate glasses ( F A G ) is limited (up to oxygen content in glass, ~ 0.29 at.%). The optical quality of F A G - 3 6 remains after doping the batch with Y203, A1203, MgO up to 0.25 mol%; PbO, CaO + A120 3 up to 0.50 tool%; BaO, CaO up to 0.75 mol%; SrO up to 1.00 mol%. The fundamental absorption limit (the wavelength corresponding to 50% of transmission with the sample thickness 7 mm) is ~ 6.4 Ixm in the IR-region, and ~ 245 nm in the UV-region for oxide doped F A G and 315 nm for F A G - 3 6 ( O 2) and glass no. 24(02). 'Atmospheric' and ' b a t c h ' oxygen exist in F A G in different states and influence the optical properties of F A G differently. In fluoroberyllate glasses, the absorption bands at 350 and 430 nm are caused by presence of oxygen linked to beryllium in the glass.
References [1] M. Weber, D. Milan and W. Smith, Engineering 5 (17) (1978) 468. [2] V.D. Khalilev, Steklo, Trudy instituta stecla (Russia) 1 (1966) 101. [3] V.D. Khalilev and L.V. Bogdanov, Vysokochistye veshestva (Russia) 4 (1992) 50. [4] L.D. Bogomolova, N.A. Krasil'nikova, O.A. Trul. V.L. Bogdanov, V.D. Khalilev, K.V. Panfilov and F. Caccavale, J. Non-Cryst. Solids 175 (1994) 84. [5] N.A. Toropov and V.P. Brakovski, Diagrammy sostojanija silikatny sistem, Spravochnik 'Dvojnye sistemy' (Nauka, Moscow, 1965) p. 468. [6] C. Nakamoto, Infrakrasnye spectry neorganicheski i coordinacionny soedineni (Mir, Moscow, 1966) p. 106.