Copper-doped Glasses and Methods of Manufacture

Abstract

A copper dopant delivery powder comprising a fused silica powder and a Cu.sub.2S powder. A method of making the copper dopant delivery powder. A method of making a copper-doped glass comprising placing a target glass in a container, packing a composite SiO.CuS dopant powder around the target glass and heating the container and SiO.CuS dopant powder to a temperature of between 800° C. and 1150° C. A copper-doped glass comprising a glass comprising copper-doping wherein the copper-doped glass was formed by covering the glass with a fused silica powder and a Cu.sub.2S powder, wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x and heating to a temperature of between 800° C. and 1150° C.

Claims

1. A copper dopant delivery powder comprising: a fused silica powder; and a Cu.sub.2S powder; wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x.

2. The copper dopant delivery powder of claim 1 wherein the copper dopant delivery powder is ground upon cooling after heating to 1100° C. for about 5 hours to produce a uniformly mixed powder comprising particles in the range of 10 nm-50 μm.

3. The copper dopant delivery powder of claim 2 wherein the copper dopant delivery powder is chemically modified by heating and comprises SiO.sub.2, CuS, Cu.sub.2S, CuO and Cu.sub.2O with copper concentrations that can be varied from 0.01 weight percent to 10 weight percent and can be represented by the formula SiO.CuS.

4. A method of making a copper dopant delivery powder comprising the steps of: providing a fused silica powder; providing a Cu.sub.2S powder; mixing the fused silica powder and the Cu.sub.2S powder; and heating the fused silica powder and the Cu.sub.2S powder to a temperature of 1100° C.; wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x.

4a. The method of making a copper dopant delivery powder of claim 4 wherein the step of mixing the fused silica powder and the Cu.sub.2S powder comprises mixing the fused silica powder and the Cu.sub.2S powder in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x to a uniformly mixed powder and wherein the step of heating is for about 5 hours.

5. The method of making a copper dopant delivery powder of claim 4 further comprising the steps of: crushing and milling the heated copper dopant delivery powder mixture after it has cooled to yield a uniform dopant delivery powder with particle sizes between 10 nm to 4-50 microns.

6. A method of making a copper-doped glass comprising the steps of: placing a target glass in a container; packing a SiO.CuS copper dopant delivery powder around the target glass; and heating the container and the target glass and the SiO.CuS copper dopant delivery powder to a temperature of between 800° C. and 1150° C.

6a. The method of making a copper-doped glass of claim 6 wherein the step of heating the container and the target glass and the SiO.CuS copper dopant delivery powder is for a duration of between 1 and 10 hours.

7. The method of making a copper-doped glass of claim 6 wherein the temperature of between 800° C. and 1150° C. is below the softening point of the target glass.

8. The method of making a copper-doped glass of claim 7 further comprising the step of: exposing the copper-doped glass to ultraviolet light or ionizing radiation and wherein the copper-doped glass is sensitive to ultraviolet light or ionizing radiation.

8a. The method of making a copper-doped glass of claim 8 wherein the copper-doped glass is luminescent when exposed to the ultraviolet light or ionizing radiation.

8b. The method of making a copper-doped glass of claim 8 wherein the copper-doped glass is thermoluminescent and optically stimulable luminescent due to the presence of populated traps that are formed upon exposure to ultraviolet light and/or ionizing radiation.

9. The method of making a copper-doped glass of claim 8 wherein the SiO.CuS dopant powder comprises a fused silica powder and a Cu.sub.2S powder and wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x.

10. The method of making a copper-doped glass of claim 8 wherein the SiO.CuS dopant powder is made from providing a fused silica powder, providing a Cu.sub.2S powder, mixing the fused silica powder and the Cu.sub.2S powder, and heating the mixed fused silica powder and the Cu.sub.2S powder to a temperature of 1100° C. for a minimum of 5 hours, and grinding the heated mixed powder after it has cooled and wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x.

10a. The method of making a copper-doped glass of claim 8 wherein the copper-doped glass, when exposed to ionizing radiation, exhibits prompt radioluminescence and exhibits ionization of a fraction of the copper ions in the copper-doped glass and trapping of electrons at defects in the copper-doped glass.

11. The method of making a copper-doped glass of claim 8 further comprising the steps of: exposing the copper-doped glass to ionizing radiation; causing ionization of a fraction of the copper ions in the copper-doped glass; and trapping electrons at defects in the copper-doped glass.

12. The method of making a copper-doped glass of claim 11 further comprising the steps of: releasing the trapped electrons followed by luminescent recombination of the electrons with ionized Cu.sup.++ ions.

13. The method of making a copper-doped glass of claim 12 wherein the step of releasing the trapped electrons is induced by heating.

14. The method of making a copper-doped glass of claim 11 wherein the step of releasing the trapped electrons is induced by light stimulation.

15. A copper-doped glass comprising: a glass comprising copper-doping wherein the copper-doped glass was formed by covering the glass with a SiO.CuS copper dopant delivery powder and heating to a temperature of between 800° C. and 1150° C. for a duration of between 1 and 10 hours.

16. The copper-doped glass of claim 15 wherein the copper-doped glass has the capacity to store between 1×10.sup.10 and 1×10.sup.18 trapped charges per cubic centimeter.

17. The copper-doped glass of claim 16 wherein the copper-doped glass is transparent to its luminescent wavelength.

18. The copper-doped glass of claim 17 wherein the copper-doped glass is optically stimulable or UV-excitable luminescent glass.

19. The copper-doped glass of claim 15 wherein the SiO.CuS copper dopant delivery powder is a fused silica powder and a Cu.sub.2S powder, wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 illustrates copper-doped fused quartz rods prepared using different SiO.CuS composite concentrations and diffusion times.

DETAILED DESCRIPTION

[0022] Disclosed herein is a copper dopant delivery powder comprising a fused silica powder and a Cu.sub.2S powder. Further disclosed is a method of making the copper dopant delivery powder. Also disclosed herein is a method of making a copper-doped glass comprising placing a target glass in a container, packing a composite SiO.CuS dopant powder around the target glass and heating the container and SiO.CuS dopant powder to a temperature of between 800° C. and 1150° C. Disclosed herein is a copper-doped glass comprising a glass comprising copper-doping wherein the copper-doped glass was formed by covering the glass with a fused silica powder and a Cu.sub.2S powder, wherein the fused silica powder and the Cu.sub.2S powder are mixed in varying ratios of Cu.sub.2S to silica represented by the formula (SiO.sub.2).sub.(1-x)(Cu.sub.2S).sub.x and heating to a temperature of between 800° C. and 1150° C.

[0023] This invention describes an improved thermal diffusion method for the manufacture of low-concentration, copper-doped fused silica glasses. The invention provides an improved method for fabricating low-concentration, copper-doped fused silica glasses possessing large populations of trapping centers. These glasses have been used for radiation dosimetry applications that utilize OSL and TL phenomena.

[0024] The invention relates to the development of novel copper-doped glass materials that possess higher copper concentrations and improved uniformity of doping throughout the glass. The new thermal diffusion method for the fabrication of copper-doped glasses taught in this disclosure has allowed the fabrication of new copper-doped glasses possessing properties that previously could not be obtained.

[0025] The new method of fabricating copper-doped glasses has at least the following advantages: the copper dopant concentration can be controlled and can be much higher than was possible in the prior art; the new method of manufacture provides a uniform distribution of Cu.sup.+1 ions throughout the bulk of the silica glass; the new method of manufacture provides doped glasses with much higher radioluminescence yields; and the new method of manufacture retains all the positive features of the prior art.

[0026] It is an object of this invention to provide an improved method for preparing glasses that contain copper atoms, ions and clusters that are distributed throughout the volume of the glass without requiring the melting of the glass.

[0027] It is another object of the present invention to provide an improved method for diffusing copper into bulk glass objects.

[0028] It is another object of the present invention to provide an improved method for diffusing copper into high temperature glass types including, silica, fused silica, quartz, fused quartz, and aluminosilicate glass, where the softening point of the glass is greater than or equal to 800 C.

[0029] It is another object of the present invention to provide an improved method for diffusing copper into high temperature glasses at temperatures as low as 800 C.

[0030] It is another object of the present invention to provide an improved dopant delivery powder for making doped glasses that upon absorbing ionizing radiation, emit prompt luminescence and store a fraction of the absorbed energy in the form of charges in metastable traps that persist for extended periods of time ranging from seconds to years.

[0031] It is another object of the present invention to provide an improved dopant delivery powder for making radiation-sensitive glasses that have the capacity to store between 1×10.sup.10 and 1×10.sup.18 trapped charges per cubic centimeter.

[0032] It is another object of the present invention to provide an improved dopant delivery powder for making glasses that are transparent to their luminescent wavelengths.

[0033] It is another object of the present invention to provide a dopant delivery powder material for making thermoluminescent glasses.

[0034] It is another object of the present invention to provide an improved dopant delivery powder for making optically stimulable luminescent glasses.

[0035] It is another object of the present invention to provide an improved dopant delivery powder for making UV-excitable luminescent glasses.

Example 1

[0036] The SiO.CuS dopant delivery powder of this invention was tightly packed around several ¼″ diameter fused quartz rods placed in an alumina crucible, insuring that there was at least a 5 mm covering of powder over all of the rods. The crucible was placed in a box furnace and heated to 1100 C. Individual rods were removed from the furnace after heating for differing times. The heating times used in this example were 1, 2, 5 and 10 hours. The weight percent of copper in the SiO.CuS powder was 1%, 2%, 5%, and 10%.

[0037] Photographs of cross-sections of the rods in room light and under UV illumination are shown in FIG. 1. The photograph taken under room light provides a simple visual indication of the dopant concentrations. The color of the glass is due to the formation of copper oxide and/or copper nanocrystals. As expected, nanocrystal formation is more likely to occur for the higher copper concentrations and for the longer heating times. The photograph taken under UV illumination shows the photoluminescence from the rods. As expected, the photoluminescence is reduced for the more highly doped samples due to absorption of light by the nanocrystals.

[0038] Diffusion of high concentrations of copper into high temperature glasses using the methods taught in this disclosure can result in the formation of copper oxide nanoparticles, or copper metal nanoparticles within the volume of the glass. The presence of such nanoparticles is indicated by visible optical absorption bands. The doping conditions that favor the formation of nanoparticles include high doping temperatures and long duration heating.

[0039] The method taught in this disclosure provides for the diffusion of copper into solid glass materials to yield copper-doped glasses. The method can also be used to diffuse copper ions into glasses that contain other dopant metal ions, such as transition metal ions or rare earth metal ions. This can result in glasses that are co-doped with more than one type of metal ion. Alternatively, the copper ions may displace the initial metal ion dopants from their defect sites.

[0040] There are several advantages and new features disclosed herein.

Example 2

[0041] The copper dopant concentration of the SiO.CuS dopant source can be varied and can be orders of magnitude higher than was possible in the prior art. The prior art [Huston, 1998] for thermal diffusion of copper into fused silica glass utilized other doped glasses as the source of copper ions, e.g. doped sol-gel silica films, and doped Vycor glass powder (Vycor glass is a 96% porous silica glass). The copper in the doped sol-gel silica films or Vycor powder was not immediately available to diffuse into the fused silica glass target material. Before the copper ions could diffuse into the fused silica glass target material they had to first diffuse out of the doped source material. The concentration of copper ions that was actually able to diffuse into the fused silica glass target depended on the specific properties of the doped source glass (sol-gel film or Vycor powder) and the temperature of the diffusion process. For example, in either the sol-gel film or the doped Vycor powder the concentration of copper dopant was limited to a value that was only a small fraction of a percent by weight. The low concentration, when combined with the relatively small volume, particularly in the thin sol-gel films, limited the total amount of copper that was available. Raising the diffusion temperature served to increase the effective doping concentration, but there was a fairly narrow range of acceptable diffusion temperatures for each type of glass that was doped. Diffusion at temperatures below the acceptable temperature range caused a dramatic decrease in the amount of copper that diffused into the target glass. Operation at temperatures above the acceptable range damaged the target glass surface and compromised the volume of the glass. Common symptoms of damage were increased roughness of the surface, increased brittleness of the bulk glass, and loss of Cu.sup.+1 activity (lowered photoluminescence yield and/or TL sensitivity, for example). Increasing the duration of the thermal diffusion procedure allowed more copper to enter the fused silica glass and increased the depth that the copper ions diffused. However, increasing the amount of time that the fused silica glass experienced the high diffusion temperature also caused damage to the glass, similar to what was observed if the temperature was too high.

[0042] In summary, the prior art [Huston, 1998] provided extremely limited ability to vary the concentration of the copper ions that diffused into the fused silica glass. The concentrations that could be achieved were extremely low, and the only two parameters that could be varied during the diffusion process were the temperature and duration of the diffusion. Unfortunately, these two parameters had very limited acceptable ranges, and variation of these parameters did not provide effective control of the outcome of the process. Variation of these parameters outside their narrow acceptable ranges resulted in significant damage to the fused silica target glass.

Example 3

[0043] The invention of this disclosure provides a novel material that functions as the source of copper ions for the thermal diffusion of copper into fused silica glasses. The new material is a powder dopant delivery composite that contains a mixture of SiO.sub.2, CuS, Cu.sub.2S, CuO, and Cu.sub.2O and can be prepared with up to 10 weight percent of copper. The concentration of the copper in the composite is orders of magnitude higher than that in the prior art copper sources (doped sol-gel silica glass and doped Vycor glass). The concentration of silica in the new SiO.CuS dopant delivery powder composite is lower than that in the prior sources, which are 96% to almost 100% silica. Therefore, the amount of diffusion that the copper ions must undergo to leave the dopant source material is significantly reduced compared to the prior art. When heated, the dopant delivery powder of this invention provides a concentration of copper ions that can be easily varied over a wide range and that is much higher than was available in the prior art sources.

Example 4

[0044] For example, the diffusion temperature and the amount of time that is required for the diffusion to be completed can both be independently optimized. As described above, the concentration of the copper ions provided by the new composite SiO.CuS dopant delivery powder can be controlled and can be orders of magnitude higher than that of the prior art sources of copper ions (doped sol-gel silica glass film and doped Vycor powder). In the prior art, the concentration of copper in the target glass could be increased primarily by increasing the diffusion temperature. In the prior art, the depth of diffusion could be increased primarily by increasing the duration of the diffusion. Unfortunately, increasing the temperature and/or increasing the duration of the diffusion often caused irreversible damage to the doped target glass.

[0045] The new SiO.CuS dopant delivery powder provides a much higher concentration of copper ions than was possible in the prior art. In addition, the new dopant delivery powder can provide high copper ion concentrations at lower temperatures than were used in the prior art. In the prior art, diffusion times of up to 24 hours were typically needed to achieve significant diffusion of copper ions throughout the fused silica target glass. The times required for effective doping of similar fused silica glasses using the method of this invention are on the order of 1-2 hours. The significant reduction in the diffusion time significantly reduces the risk of damage to the doped target glass.

Example 5

[0046] The SiO.CuS dopant delivery powder of this invention also can function as the source of copper ions for the thermal diffusion of copper into silicate-based glasses, such as aluminosilicate and borosilicate non-silica glasses. The prior art methods required high diffusion temperatures, above 1000 C, and preferably 1100 C, in order to promote the diffusion of copper ions out of the dopant source glasses (doped sol-gel silica glass films and doped Vycor powder) and diffusion of the those copper ions into the fused silica target glass.

[0047] The SiO.CuS composite material of this invention has a much lower concentration of silica glass and provides high copper concentrations at lower temperatures. Doping of glasses that soften at lower temperatures, such as aluminosilicate glasses, is now possible and has been demonstrated. This was impossible using the prior art because the concentrations of copper ions from the doped silica sources at temperatures of ˜800 C were too low to allow significant diffusion of metal in silicate-based target glasses. However, increasing the diffusion temperature to that taught in the prior art, ˜1100 C, exceeds the softening point of the silicate-based target glasses, and results in the loss of the material.

Example 6

[0048] The new method of manufacture provides the ability to control the parameters of the diffusion process to achieve a more uniform distribution of Cu.sup.+1 ions throughout the bulk of the silica glass.

[0049] The thermal diffusion method of the prior art often failed to uniformly dope the entire volume of the fused silica glass. For example, the cross section of a fused silica rod that had been doped often revealed a doping pattern in the shape of a donut, with a hole in the middle where the glass had not been doped. The appearance of a donut-shaped doped region was related to the diffusion parameters. The cause might have been because the copper ion concentration was too low, or that the diffusion temperature was too low, or that the duration of the diffusion was too short. Another possible reason could be depletion of the copper source in the thin, sol-gel glass film. As discussed above, in the prior art, it is not possible to significantly increase the copper concentration from the source, and the risk of damage to the glass is high if the temperature is increased or the duration of the diffusion is increased. In the prior art, it was often not possible to systematically change the temperature and/or the time spent at high temperature, within the acceptable range of values, and achieve a uniformly doped fused silica sample. The invention of this disclosure provides for higher concentrations of copper ions at a given temperature and it also insures a much greater amount of copper in the SiO.CuS dopant delivery powder such that source depletion is a very unlikely problem.

[0050] The method of this invention allows the systematic variation of the temperature and time diffusion parameters over a wide range of values such that uniform doping is successfully achieved. The uniformity of doped silica glass rods has been demonstrated to be extremely high using the invention of this disclosure. The uniformity of the doping is illustrated in the photos in FIG. 1. The photo on the right side of the FIGURE shows ¼″ diameter fused silica rods that have been doped at various concentrations of copper in the dopant delivery powder and various heat profiles. The rods are illuminated with an ultraviolet light, causing photoluminescence from the Cu.sup.+1 ions. The diffusion temperature was fixed at 1100 C for all samples. It is readily apparent upon inspection of the photo that several sets of parameters provide for excellent uniformity. It is also apparent that some parameter pairs resulted in poor uniformity in other samples. The advantage of the method of this disclosure is that such an investigation of the parameter space is feasible. The prior art provided very little or no ability to change the doping concentration. A systematic study changing a variable related to concentration over a useful range simply was not possible in the prior art.

Example 7

[0051] The new method of manufacture provides novel doped glasses with much higher radioluminescence yields. The thermal diffusion method of the prior art provided glasses that exhibited outstanding OSL and TL sensitivity, but did not provide glasses with high radioluminescence yields. Compared to other well-known inorganic or organic scintillators, the radioluminescence yields were much smaller. The new method of this invention, as expected, yields doped glasses with outstanding OSL and TL sensitivity, but the method also provides the additional advantage of higher radioluminescence sensitivity. The likely reason for the improved radioluminescence yield is the higher concentration of the copper dopants. The higher radioluminescence yield is expected to have a significant impact on radiation detection applications based on the detection of radioluminescence.

Example 8

[0052] The new method of manufacture of this invention retains all the positive features of the prior art methods. The new method allows doping of bulk pieces of glass that have excellent optical transparency, indicating that the copper ions in the glass are predominantly Cu.sup.+1 ions. There is no visible absorption due to the presence of Cu.sup.+2 ions.

Example 9

[0053] The new method of manufacture of this invention enables the formation of Cu.sub.2O nanocrystals in the target glasses. Such glasses may exhibit plasmon resonance features that are of interest for their nonlinear optical properties and may have novel applications in nonlinear optical devices. The prior art method did not provide copper concentrations high enough to yield nanocrystals.

Example 10

[0054] The new method of manufacture of this invention does not generate toxic byproducts. The prior art methods required the generation of toxic H.sub.2S, and had to be performed using specialized safety equipment, such as fume hoods. In addition, there is no production of liquid organic hazardous waste.

Example 11

[0055] The new method of manufacture of this invention is significantly simpler, cheaper, and less labor intensive than the prior art. For example, the new method eliminates the need to use porous Vycor glass as a source for the copper. Vycor glass has become increasingly more expensive and less readily available. The prior art method that used Vycor glass was the preferred embodiment. A significant motivation for the development of the invention of this disclosure was the desire to abandon Vycor glass due to the expense and the complex procedures required to prepare the doped Vycor powder.

[0056] Many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that the claimed invention may be practiced otherwise than as specifically described. Any reference to claim elements in the singular, e.g., using the articles “a,” “an,” “the,” or “said” is not construed as limiting the element to the singular.