Radiant energy – Invisible radiation responsive nonelectric signalling – Luminescent device
Reexamination Certificate
1998-09-30
2001-04-03
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiation responsive nonelectric signalling
Luminescent device
C250S484300, C250S330000
Reexamination Certificate
active
06211526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to invisibly marking articles and materials for a dual mode readout, using luminescent and optically stimulable glasses. More particularly, the invention relates to using metal ion dopants in a glassy matrix in inks, dyes, and the like, for marking articles and materials, and for detecting these materials by fluorescence and optically stimulated readout of trapped states. Particular aspects of the invention include luminescent doped glasses, including copper-, europium-, and cerium-doped glasses such as Vycor™ (a registered trademark of Corning Corporation, Corning, N.Y.) and fused quartz.
2. Description of the Related Art
Labels that are not apparent to the naked eye are desired for many manufactured articles and materials. It is also desired to make such labels as flexible in applicability and as robust as possible. For instance, it is desirable to make labels that can be applied with dyes, inks, stains, shellacs, varnishes, glazes, polymer coatings such as polyurethane coatings, and other coatings or materials for application to an article. It is also desirable to make such labels robust so that, for instance, they can survive exposure to moderately high temperatures and exposure to common solvents. It is also desired to make labels that are non-toxic.
It is also desired to make labels that have some type of redundancy built into them. That is, it is desired to make labels that can be read in more than one way, as a double check on the authenticity of a labeled article.
Since labels generally require some type of coding (bar coding, alphanumeric coding, etc.), it is desired to have such coding on a label that is likewise not visible to the naked eye. In practice today, this is often done by putting a “hidden” number such as a serial number in some out of the way place in an article, such as inside a case or housing. The difficulty is that such placement is almost inherently not readily accessible, and so it is difficult to get to when it is desired to read the label. It would be preferred to have coding that is hidden in plain sight. Coding that requires stimulation for readability would satisfy this need.
It is often desirable to have a way of monitoring some time relating to labeled articles, such as shipping time or shelf time. A label that included some type of timing capability would satisfy this need. Optimally, such a timing system would have a broad range, being able to time over scales of days, weeks, months, or years, as needed.
Materials used for detecting infrared light by stimulating upconverted visible luminescence have been intensively studied for decades. Early work during the 1940's determined that the most efficient materials were polycrystalline alkaline earth sulfides such as SrS or CaS doped with trivalent rare earth activator and coactivator ions such as Sm paired with Ce or Eu. Presently, the most widely used optically stimulable luminescent (OSL) phosphors have evolved very little from the early formulations. These phosphors are typically micron-sized powders or polycrystalline films that absorb ionizing radiation (&ggr;-ray, x-ray, &bgr;-particle) or UV radiation and store a portion of the absorbed energy in the form of trapped charges. The trapped charges are stable until the phosphor is illuminated with a light source capable of stimulating luminescent electron-hole recombination.
Traditional OSL phosphors are highly scattering to visible light, due to the micron-sized features of the powders or films. The OSL is severely attenuated due to the scattering, thereby not only reducing the brightness of the emission, but also placing a practical limitation on the thickness and functionality of the phosphor for many applications. However, for applications where the phosphor is expected to be very thin, this scattering will be less critical.
The inventors have recently disclosed patents and published papers that describe several types of optically transparent, thermoluminescent, and optically stimulable glasses that operate through a charge trapping mechanism. For the thermoluminescent glasses, luminescent recombination of electron-hole pairs is induced by applying enough heat (by external heating or laser heating) to overcome the thermal barrier to recombination. In the case of an optically stimulable glass, recombination is induced by exposure to a light source with a wavelength that overlaps the optical stimulation band in the OSL material. Optical stimulation has a number of advantages over thermal stimulation, such as little or no bulk heating of the glass and a very rapid readout.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a method for invisibly marking articles and materials.
It is a further object of this invention to provide such marking with dyes and inks.
It is a further object of this invention to provide such marking in a robust manner that is not sensitive to moderate temperatures or common solvents.
It is a further object of this invention to provide such marking with non-toxic materials.
It is a further object of this invention to provide such marking with redundant, dual-mode readout (that is, having two methods for viewing the normally invisible mark).
It is a further object of this invention to provide such marking with invisible coding, such as bar-coding, alphanumeric coding, other symbols, or graphic images.
It is a further object of this invention to provide such marking with the ability to monitor transit or shelf time, or some other time relating to that article that may span days, weeks, months, or years.
It is a further object of this invention to provide such marking with a method of distinguishing the marking from conventional fluorescent dye marking, by the time scale of the fadeout of phosphorescence.
It is a further object of this invention to provide such marking with a transparent, non-scattering label.
It is a further object of this invention to provide such marking with a material that is not widely available commercially, and therefore not easily duplicated, especially in comparison to conventional fluorescent dyes.
It is a further object of this invention to provide such marking with a material that undergoes optically stimulated luminescence.
These and additional objects of the invention are accomplished by the structures and processes hereinafter described.
An aspect of the present invention is a material that contains, as a component, a glass matrix with luminescent centers and trapping centers. The trapping centers are capable of storing charges (electrons or holes) for extended periods of time. The trapped charges may be stimulated to recombine by the application of optical energy, resulting in the emission of light energy. In several embodiments, the present invention includes a glass (e.g., porous glass such as Vycor™, fused quartz, fused silica, alumina glass, or borate glass) matrix including an alkaline earth sulfide doped with an activator/co-activator pair of samarium and another rare earth element, typically europium or cerium. In other alternative embodiments, the glass matrix includes ZnS doped with copper, lead, manganese, or cerium. In yet another embodiment, the glass matrix is doped with Cu, Ag, Eu, or Ce. This doped glass will luminesce under excitation by an appropriate light source (typically a UV source). In other alternative embodiments, the glass matrix has other defects that provide luminescence centers, such as crystalline defects, gaps, etc.
Unlike the fluorescent luminescence of conventional fluorescent dyes, this luminescence includes a phosphorescent component that does not fade out for several seconds after the excitation source is removed. This combination of a prompt fluorescence with a lifetime of microseconds and a phosphorescence that decays over a period of tens of seconds to minutes may be used as a “fingerprint” to distinguish these materials from conventional fluorescent dyes. Moreover, if previously exposed to an excitation source that po
Huston Alan L.
Justus Brian L.
Gabor Otilia
Hannaher Constantine
Karasek John J.
Ketner Philip E.
The United States of America as represented by the Secretary of
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