Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1998-07-27
2001-05-08
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C252S30140R, C252S30140F, C252S30140P, C501S064000, C501S073000, C501S045000
Reexamination Certificate
active
06228787
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fluorescent photosensitive glass compositions and processes for making them. More specifically, this invention relates to silicate or phosphate glasses exhibiting both fluorescent and photosensitive properties. These fluorescent and photosensitive properties are imparted to the glass by the inclusion of certain rare earths in the glass composition.
BACKGROUND OF THE INVENTION
Glass, as a material, has advantageous characteristics for many applications including: isotropy; considerable flexibility as to the shape and size of the finished glass objects; amenability to uniform doping at high concentrations; flexibility in achieving desired physical properties by virtue of the good solubility of the various glass composition constituents; and relatively low production costs.
Generally, glass is obtained by cooling a melt in such a way that crystallization is suppressed. Glass also can be produced by the known sol-gel method.
Most glasses are oxide glasses. The structure of oxide glasses consists of a continuous network of glass-forming oxides in which long range order is missing. Glass-forming oxides such as SiO
2
, P
2
O
5
, GeO
2
, Al
2
O
3
, B
2
O
3
and Ga
2
O
3
have the strongest bonding strength among glass-forming oxides. Such glass-forming oxides are known as glass network formers. Oxides with weak bonding strength, such as oxides of alkali, alkaline earth, and rare earths cannot form a glass network and are known as modifiers.
Some glasses are fluorescent. Fluorescent glasses, when exposed to ultraviolet light, convert that ultraviolet light into visible light. The fluorescence of rare earth metal ions in glass was first observed in the 1880s (see W. A. Weyl, “The Fluorescence of Glasses”, in “Coloured Glasses”, Society of Glass Technology, Sheffield, England, 1951). Fluorescent glasses are used in lasers, and the discovery of the lasing phenomenon gave a strong impetus to the development of rare earth activated fluorescent glasses. Various fluorescent glasses and their industrial applications are disclosed in U.S. Pat. Nos. 3,549,554; 3,846,142; 4,075,120 and 4,076,541.
Some glasses are photosensitive. When photosensitive glasses are irradiated with short wave radiation such as ultraviolet radiation or X-rays, the optical properties of the glass in the irradiated areas are modified. Photosensitive glasses generally contain photosensitive elements such as copper (Cu), silver (Ag) and gold (Au). The photosensitive elements in the glass, upon exposure to the incident radiation, absorb that radiation. Upon heat treatment of the glass (typically at or above the annealing point of the glass), metal particles are precipitated thus changing the color of the glass in the irradiated areas. Upon cooling of the glass, the colored areas remain colored unless the glass is subsequently reheated to a high temperature.
Photosensitivity was initially observed by Dalton and described in U.S. Pat. Nos. 2,326,012 and 2,422,472. Development of photosensitive glasses is described in U.S. Pat. No. 2,515,937.
While fluorescent glasses are known in the art, and while photosensitive glasses also are known in the art, it was not previously known to combine fluorescent properties with photosensitive properties in the same glass. Accordingly, it is desirable to provide a glass having both fluorescent and photosensitive properties.
It is also be desirable to be able to control the degree of fluorescence of the glass.
It further is desirable to be able to control the degree of fluorescence of the glass in selected areas of the glass.
It is also desirable to provide a glass having both fluorescent and photosensitive properties for use in photography and fluorescent displays.
It is desirable, moreover, to provide a glass in which the degree of fluorescence can be selectively controlled for use in computer memories.
SUMMARY OF THE INVENTION
The inventive fluorescent photosensitive glass combines the characteristics of two known glass types—fluorescent glasses and photosensitive glasses.
In the inventive glass, the degree of fluorescence can be manipulated via controlled irradiation of the glass. When the glass is irradiated in a specific area, the fluorescence in that area can be inhibited by the photosensitive agents in the glass. The unirradiated areas retain their fluorescence.
It is an object of this invention to provide a glass having both fluorescent and photosensitive properties.
It is also an object of this invention to be able to control the degree of fluorescence of the glass.
It is a further object of this invention to be able to control the degree of fluorescence of the glass in selected areas of the glass.
It is a further object of this invention to provide a glass having both fluorescent and photosensitive properties for use in photography and fluorescent displays.
It is a further object of this invention to provide a glass in which the degree of fluorescence can be selectively controlled for use in computer memories.
In accordance with this invention, glasses are prepared which also include two or more rare earths. In particular, silicate or phosphate glasses are prepared which also include two or more rare earths. One or more of the rare earths imparts fluorescent properties to the glass while the other of the rare earths included in the glass impart photosensitive properties to the glass. Suitable rare earths for imparting fluorescent properties to the glass include ytterbium (Yb), samarium (Sm), europium (Eu) and combinations thereof. Suitable rare earths for imparting photosensitive properties to the glass include erbium (Er), thulium (Tm), praseodymium (Pr), ytterbium (Yb), holmium (Ho), samarium (Sm), cerium (Ce), dysprosium (Dy), terbium (Tb), neodymium (Nd) and combinations thereof.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of this invention, silicate or phosphate glasses are prepared which also include two or more rare earths. One or more of the rare earths imparts fluorescent properties to the glass while other of the rare earths included in the glass impart photosensitive properties to the glass.
Suitable base silicate glass compositions comprise about 10 mole percent to about 80 mole percent SiO
2
, up to about 54 mole percent K
2
O, up to about 58 mole percent Na
2
O, up to about 35 mole percent Li
2
O, up to about 40 mole percent BaO, up to about 40 mole percent SrO, up to about 56 mole percent CaO, up to about 42 mole percent MgO and up to about 48 mole percent ZnO.
Suitable base phosphate glass compositions comprise about 20 mole percent to about 80 mole percent P
2
O
5
, up to about 47 mole percent K
2
O, up to about 60 mole percent Na
2
O, up to about 60 mole percent Li
2
O, up to about 58 mole percent BaO, up to about 56 mole percent SrO, up to about 56 mole percent CaO, up to about 60 mole percent MgO and up to about 64 mole percent ZnO. Additionally, yttrium (Y) may be included in amounts up to about 5 mole percent.
The inventive fluorescent photosensitive glass is made by including two types of rare earths in a silicate or phosphate base glass. These two types of rare earths are (1) fluorescence-imparting rare earths (e.g., ytterbium (Yb), samarium(Sm), europium (Eu)) and (2) rare earth photosensitive agents (e.g., erbium (Er), thulium (Tm), praseodymium (Pr), ytterbium (Yb), holmium (Ho), samarium (Sm), cerium (Ce), dysprosium (Dy), terbium (Tb), neodymium (Nd)). These rare earths may be incorporated in oxide form into the glass in amounts up to about 5 mole percent of the rare earth oxides.
When a specific area of the inventive glass is irradiated at a wavelength sufficient to photoionize the photosensitive rare earth in the glass, fluorescence in that specific area diminishes. Areas which have not been so irradiated continue to exhibit a strong fluorescence.
Without being bound by theory, it is believed that fluorescence is diminished in areas exposed to the photoionizing radiation because the resulting photoionized photosensitive rare earths inhibit the fluorescence in that area.
The present i
Dubno Herbert
Koslow C. Melissa
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