Optical colored glass, its use, and an optical long-pass...

Details Optical colored glass, its use, and an optical long-pass... Optical colored glass, its use, and an optical long-pass...

2002-08-20

2003-12-23

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S065000, C501S077000, C501S079000, C501S059000, C501S067000, C501S900000

Reexamination Certificate

active

06667259

ABSTRACT:

The subject matter of the invention is an optical colored glass, it use, as well as an optical long-pass cutoff filter.
Optical long-pass cutoff filters are distinguished by characteristic transmission properties. In the short-wave range, they have a lower transmission, which increases to a higher transmission over a narrow spectral range and remains high in the long-wave range. The lower transmission range is called the stop band, and the higher transmission range is called the pass band or the transmission band.
Optical long-pass cutoff filters are characterized by certain parameters. For example, the absorption edge of such a filter is generally given as the so-called edge wavelength □
c
. It corresponds to the wavelength at which the spectral internal transmission factor between the stop band and the transmission band equals half of the maximum value.
Optical long-pass cutoff filters are generally made of colored glass, in which the coloring is caused by the colloidal precipitation of semiconductor compounds during the cooling of the melt or by the later heat treatment. This is also sometimes called starting glass.
The long-pass cutoff filters that are customary in the marketplace are produced by a doping of the base glass with cadmium-semiconductor compounds or raw materials that form in situ the named compounds. Depending on the edge position, CdS, CdSe, CdTe, or a mixed combination of these semiconductors is used. Based on the toxic and carcinogenic properties of the cadmium and the tellurium, it is desirable to be able to avoid these compounds and use other dopants instead. In order to obtain the same or similar glass absorption properties, alternative dopants must also be made of semiconductors or raw materials, which form semiconductors in situ, with direct optical transitions. The sharp transitions between the absorption and transmission range of the glass and, thus, the filter properties of the glass are only determined by the special band structure of the semiconductor, the energy gap between the valence band and the conduction band.
The I-III-VI semiconductor system, e.g., copper indium disulfide and copper indium diselenide, could also represent an alternative to the CdS, CdSe, CdTe compounds.
These long-known semiconductors have only had much practical meaning in the field of photovoltaics.
In a series of Russian and Soviet patent applications, CuInS
2
-doped glass to be used as a filter is already described for a very narrow glass composition range: SU 1677026A1, SU 1527199A1, RU 2073657C1, SU 1770297A1, SU 1770298A1, SU 1678786A1, SU 1678785A1, SU 1701658A1, SU 1677025, SU 1675239A1, SU 1675240A1, and SU 1787963A 1. All of this glass is similar in that they all contain large amounts of SiO
2
at rates of up to 79 percent by weight. Thus, it is necessary to produce the glass at very high temperatures of approx. 1400° C. to 1500° C., which is particularly disadvantageous due to the highly volatile and oxidation-sensitive doping agent. According to synthesis, this type of glass contains large amounts of this compound, with up to 0.99 percent by weight of CuInS
2
. This type of glass is B
2
O
3
-free or -poor. It does not have good chemical resistance.
The purpose of the invention is to make available optical chemically resistant colored glass, which possesses long-pass cutoff filter properties, that can be produced at low temperatures and, thus, energy-efficiently and that has absorption edges up to 1.2 &mgr;m.
It is also the purpose of the invention to make such long-pass cutoff filters available.
The purposes are fulfilled through a glass in accordance with the following composition by weight percentage:
SiO
2
30-75
K
2
O 5-35
B
2
O
3
>4-17
ZnO 5-37
F 0.01-10
M
I
M
III
Y
II
2
, whereby M
I
=Cu
+
, Ag
+
0.1-3
M
III
=In
3+
, Ga
3+
, Al
3+
Y
II
=S
2−
, Se
2−
.
Te
2−
.
The purposes are further fulfilled through use of the glass as an optical long-pass cutoff filter.
With 30 to 75 percent by weight, preferably 40 to 65 percent by weight, and most preferably 40 to 56 percent by weight, SiO
2
is the main component of the glass.
The glass based on the invention has a B
2
O
3
content between >4 and 17 percent by weight. This improves the chemical resistance as well as the processability and drying of the green body during production via a sintering process. Contents higher than 17 percent by weight would have a disadvantageous affect on the glass quality. Moreover, the solubility of H
3
BO
3
in H
2
O, a possible raw material for the boroxide, is limited to the named B
2
O
3
content. Contents between 5 percent by weight and 16 percent by weight are preferred. Particularly preferred is a B
2
O
3
content of at least 8 percent by weight.
The H
3
BO
3
raw material is particularly advantageous when K
2
O is brought in as a component of the glass via the raw material KOH, since the very high pH value of the suspension, caused by the KOH, is lowered when the sintering process is used.
An important component is ZnO. This oxide is present at 5 to 37 percent by weight. ZnO supports homogenous nanocrystal formation of the doping material in the glass. This means that, a homogenous crystallite growth of the semiconductor doping is ensured with the tempering of the glass. The very pure and bright color and the sharp absorption edge of the glass are the result of these monodispersive crystallites. At a ZnO content lower than 5 percent by weight, the glass displays poor or no starting behavior. The named upper limit for ZnO is meaningful, since glass that has a higher content of ZnO has a tendency to form drop-like areas of precipitation and, thus, to segregate. A ZnO share of at least 5 percent by weight is preferred, especially preferred from at least 9 percent by weight and a ZnO share of at the most 30 percent by weight especially preferred from at the most 23 by weight. The segregation tendency of this type of “zinc silicate glass” can be lowered by the use of the K
2
O network converter. Thus, the glass contains 5 to 35 percent by weight, preferably 15 to 29 percent by weight in order to prevent micro-dispersions of ZnO-enriched areas and to reduce their processing temperature. In particular, with a ZnO content >5 percent by weight, a K
2
O content >5 percent by weight is preferred, and, with a ZnO content >10 percent by weight, a K
2
O content >17 percent by weight is preferred. Highly transparent glass is obtained in this manner.
It is also possible to further improve the starting properties of the glass by adding the additional crystal creators CdS and CdSe. The content of CdS and CdSe should not exceed individually and in total 0.5 percent by weight. Based on the toxic properties of these components, it is preferable to avoid them; Cd-free glass is preferred.
Furthermore, the glass also contains between 0.01 and 10 percent by weight of F. This is especially advantageous if the glass is produced via sintering processes, since the sinter temperature is reduced by the F shares and the strength of the green bodies is increased. At least 0.3 percentage by weight is particularly preferred. More than 3 percent by weight is even more preferred, since this improves the bubble quality of the glass produced via the sintering process. During production via a melting process, the presence of F reduces the melting temperature.
A high strength of the green body is significant for its processing, its transport, and its handling. The strength of the green bodies is determined in that hydrogen bonds form between the neighboring SiOH groups and thus interlace the green bodies. If F is present, besides the hydrogen bonds, bonds also form between —SiF and —SiOH that are stronger than the hydrogen bonds between —SiOH and —SiOH. Low amounts of fluorine can thus increase the strength. However, the drying properties of the green body are impaired when the F content is too high (>10 percent by weight). Moreover, the expansion factor becomes too high and the transformation temperature, too low. F conc

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