Abstract:
A material that phosphoresces may be controlled and the phosphorescence may be terminated when desired. A phosphorescing material may be exposed to an energy source that causes the material to stop phosphorescing. Thus, a pattern may be written on a surface, which is phosphorescing using a coherent energy source. The written pattern, represented by darkened regions, may be recognized by users as a symbol, a graphics or text.

Description:
This is a divisional of prior application Ser. No. 09/785,917 filed Feb. 17, 2001 now U.S. Pat. No. 6,595,826. 
    
    
     BACKGROUND 
     This invention relates generally to phosphorescent materials. 
     Materials that are phosphorescent glow in the dark after being exposed to an energy source generating sufficient energy to create phosphorescence. Phosphorescence is the result of electrons associated with molecules changing orbitals in a fashion, which results in the generation of light. Some phosphorescent materials glow after being exposed to energy in the ultraviolet range. Since sunlight may include sufficient ultraviolet energy, sunlight exposure may be sufficient to cause some materials, such as zinc sulfide, to glow. 
     As one example, zinc sulfide, after having been exposed to ultraviolet light, may emit a pale green light for a period of up to eight hours. Thus, zinc sulfide is utilized in a variety of products including children&#39;s glowing toys and dolls, as well as a variety of non-toy products including signs and safety equipment. 
     Phosphorescent materials may be provided in the forms of paints, pigments, and films. Many of these films are utilized as lambertian backgrounds to uniformly light displays while others may be used for foreground elements such as shapes or text. Phosphors are available that emit a wide variety of colored light when exposed to energy within a phosphor&#39;s absorption band. 
     Among the known phosphorescent materials are ZnS (green), CaAl 2 O 4  (blue), SR 4 Al 14 O 25  (blue-green), SRAl 2 O 4  (green), and Y 2 O 2 S (orange-yellow). Each of these phosphorescent materials may emit different wavelengths of light and yet may require different energy levels in order to initiate phosphorescence. Moreover, the period of time that they phosphoresce after being exposed to sufficient energy may vary. 
     Typically phosphorescent materials are considered “one way” materials—they may be turned on to phosphoresce. It is then generally considered that these materials will continue to phosphoresce until such time as they reach their ground state. Generally, it is believed that this period of phosphoresce is a function of the characteristics of the material. 
     Thus, there is a need for better ways to control phosphorescent materials and particularly better ways to control the way that these materials phosphoresce. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of the present invention; 
     FIG. 2 is an enlarged cross-sectional view taken generally along the line  2 — 2  in FIG. 1; 
     FIG. 3 is a depiction of the display screen of the device shown in FIG. 1 in one situation in accordance with one embodiment of the present invention; and 
     FIG. 4 is a depiction of the display screen shown in FIG. 3 in another situation in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, one application of the principles set forth herein is in connection with a wide variety of toys. As a toy example, shown in FIG. 1, a drawing toy  10  may include a housing  12  with an inclined drawing surface  13 . A child may use an erasable marker  18  to draw on the drawing surface  13 . However, in this embodiment, the child&#39;s drawing may be guided by a pattern  14  that has been formed on the drawing surface  13  to guide the child&#39;s depiction of the object. Thereby, the child may simply trace over the pattern  14  to create a suitable design on the toy  10 . 
     Turning to FIG. 2, the child&#39;s eye, indicated as E, may view the drawing surface  13  from one side. On the opposite side of the surface  13  may be coated a phosphorescent layer or film  20 . In one embodiment, the layer  20  may be opaque. The layer  20  may be formed of any phosphorescent material that glows for an extended amount of time in one embodiment. In one embodiment, the surface  13  may be formed of a transparent material such as a plastic sheet having the phosphorescent layer  20  merely coated on one side. 
     When the phosphorescent layer  20  is exposed to a sufficient energy source, it will emit light as indicated at L. The layer  20  will continue to glow, enabling the surface  13  to glow in the dark. As one example, the layer  20  may be zinc sulfide. 
     An energy source  22  may include a laser  24  and a laser driver  26 , which positions the beam B of the laser  24  at a desired position on the surface  13 . The laser  24  may generate a light beam B of insufficient energy to cause the layer  20  to glow but of sufficient energy to actually discharge the layer  20  and to thereby terminate or accelerate the phosphorescence of the layer  20 . When exposed to energy of appropriate frequency characteristics, the glowing layer  20  may emit the remaining energy in the form of a flash of light, thereafter extinguishing the glowing light emission. 
     In this way, the laser beam B may be driven across the surface  13  by the laser driver  26  in two dimensions to draw features on the surface  13  in one embodiment. The laser  24  may do this by exposing the glowing layer  20  to energy that causes the glowing in the exposed spot to be extinguished. Thus, the surface  13  may continue to glow except for those regions exposed to the beam B which regions may go dark. 
     For example, referring to FIG. 3, the surface  13   a  may be entirely glowing, having been exposed to a sufficient energy source to initiate phosphorescence. For example, in the case of a layer  20  of zinc sulfide, exposure to ultraviolet light, such as sunlight, initiates phosphorescence. Thus, the entire surface  13  may glow. 
     However, when the layer  20  is exposed to the beam B produced by the laser  24  in a pattern  14 , the portions of the surface  13   b  exposed to the light beam B no longer glow and appear relatively dark compared to the surrounding regions which continue to glow with pale green light. 
     In the case of a laser beam  24  that is a deep red laser having a wavelength of 6000 Angstroms, the phosphorescence may be caused to immediately discharge. It appears to discharge by emitting a flash of pale green light and then going dark. Thus, instead of continuing to glow for an extended period, such as eight hours as normally associated with zinc sulfide phosphorescence, the phosphorescence is caused to quickly or immediately terminate when the layer  20  is exposed to sufficient energy to discharge the energy responsible for phosphorescence. 
     It is believed that an energy source that does not deliver sufficient energy to cause phosphorescence but instead provides energy with the right frequency characteristics may immediately or substantially immediately terminate the phosphorescence of areas exposed to the energy source. If a relatively coherent light source is used to deliver the discharging energy, the phosphorescent layer  20  may be effectively written on since the unexposed regions of the phosphorescent layer  20  continue to phosphorescence while the exposed regions, which may be a relatively coherent dot, line or curve, may go dark. 
     In this way, the phosphorescence may be controlled to create a variety of visual effects. For example, in addition to children&#39;s toys, whiteboard images may be generated from a distance using a laser pointing device to write information on a glowing phosphorescent layer on the whiteboard. While relatively simple graphical symbols are illustrated in the figures in the present application, it may be possible in some applications to write relatively complex information including numbers and text using the discharging effect. For example, relatively low data rate displays may be implemented using the discharging technology. 
     With each phosphorescent material, a specific range or band of energy may be utilized to discharge the phosphorescence in the fashion described herein. That range or band will generally be less than the energy needed to initiate phosphorescence. It is believed that the discharging energy source “pushes” the remaining energized molecules over the activation energy barrier so that they quickly discharge, en masse, creating dark spots thereafter whose phosphorescence has been extinguished. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.