Abstract:
A light emissive printed articles ( 101 ) include printing with ink that includes quantum dots in lieu of pigment. A pump light that emits light with photon energies sufficient to excite the quantum dot ink ( 102 ) is used to drive light emission.

Description:
FIELD OF THE INVENTION 
     The present invention relates to light emissive printed articles. 
     BACKGROUND 
     In today&#39;s competitive global market manufacturers and retailers must compete for consumers attention in an increasingly competitive environment. One form of advertisement uses posters. However, posters may not make much of an impression on consumers accustomed to high definition flat screen TV and computer displays. In order to make posters more memorable posters that include electroluminescent lamps that are patterned to show lighted areas of a product have been introduced. For example there are posters that use electroluminescent lamps as the lighted display of depicted cellular telephones. Electroluminescent lamps use multilayer structures that requires specialized equipment and techniques to manufacture them and so can not readily be made by local printers for use in a local retail market. Moreover, given the broad spectrum of electroluminescent lamps, finely tuned colors which are important for advertising materials can not be obtained without the added complexity of overlaid filters, which in any case would reduce brightness. 
     Thus, there is a need for luminescent posters with a broad color range and a simplified structure that lends itself to rapid production. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
         FIG. 1  is a schematic of a light emissive poster system including a light emissive poster printed with quantum dot ink and a pump light; 
         FIG. 2  is a schematic cross section of a functionalized core-shell quantum dot used in the ink of the light emissive poster shown in  FIG. 1 ; 
         FIG. 3  is a schematic sectional elevation view of a quantum dot light emitting device that is used as the pump light shown in  FIG. 1  according to an embodiment of the invention; 
         FIG. 4  is a schematic of a fluorescent lamp light box that is used as the pump light shown in  FIG. 1  according to an alternative embodiment of the invention; 
         FIG. 5  is a graph including plots of quantum dot absorbance versus wavelength for several sizes of quantum dots; 
         FIG. 6  is a graph including three lines of spectral emission for three size distributions of quantum dots; 
         FIG. 7  is a 1931 CIE chart showing a color range obtainable by mixing quantum dots of the three distributions have the spectral emissions shown in  FIG. 6 ; 
         FIG. 8  a schematic cross section of a light emissive poster including an ink including quantum dots and a UV transparent overcoating; and 
         FIG. 9  shows a product package with a light emissive label that is printed with ink that includes quantum dots. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     DETAILED DESCRIPTION 
     Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of and apparatus components related to quantum dot light emissive poster systems. Accordingly, the apparatus components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
       FIG. 1  is a schematic of a light emissive poster system  100  including a light emissive poster  101  printed with quantum dot ink  102  and a pump light  104 . Printed graphics  106  include the quantum dot ink  102 . The printed graphics  106  are printed on a backside  108  (a side that faces away from a viewer) of a substrate  110 . The pump light  104  is arranged to illuminate the printed graphics  106 . Alternatively, the printed graphics  106  are printed on a front side  109  of the substrate  109  and the pump light is positioned facing the front side  109 . The pump light  104  emits ultraviolet and/or visible light including photons that have photon energies greater than a band gap of quantum dots ( 202 ,  FIG. 2 ) in the quantum dot ink  102 . Accordingly illuminating the printed graphics  106  with the pump light  104  causes the quantum dot ink  102  to emit light. Other graphics (not shown) that are not printed with the quantum dot ink  102  can also be printed on the substrate  108 , so that only a portion of the poster  101  will be light emissive. The substrate  110  can be made out of a material, e.g., transparent plastic, that absorbs light (e.g., ultraviolet light) emitted by the pump light. The substrate  110  can be made out of a flexible and conformable material so that the poster  101  can be displayed in a non-planar configuration. Using a separate pump light  104  and poster  101  facilitates local design and printing of the poster  101 . The poster  101  can be used in a scrollable display, such as used for advertising. 
     Multiple colors of quantum dot ink  102 , each of which is characterized by a different band gap mean and peak color can be used so that the light emissive poster  101  will include multi-color light emissive printing. 
       FIG. 2  is a schematic cross section of a functionalized core-shell quantum dot  202  used in the ink of the light emissive poster shown in  FIG. 1 . The quantum dot  202  includes a core  204  and a shell  206 . The shell  206  is made of a material that has a higher band gap than a material of the core  204 . Using a higher band gap shell reduces a rate of non-radiative transitions thereby increase the efficiency and brightness of the quantum dot ink  102 . The core  204  can, for example, be made of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, AlP, AlSb, whilst the shell  206  can, for example be made of ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaAs, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP, InSb, AlAs, AlN, AlP, AlSb. Alternative quantum dot materials that may be used include but are not limited to tertiary microcrystals such as InGaP, which emits in the yellow to red wavelengths (depending on the size) and ZnSeTe, ZnCdS, ZnCdSe, and CdSeS which emits from blue to green wavelengths, (depending upon the size). Additional alternative materials that may be used in quantum dots include Zinc chalcogenides, such as ZnSe, doped with transition metal ions such as Mn or Cu. The quantum dot  202  is capped (functionalized) with organic molecules  208 . In as much as quantum dots are prepared in colloidal systems a variety of molecules can be attached to them via metal coordinating functional groups, including thiols, amines, nitrites, phosphines, phosphine oxides, phosphonic acids, carboxylic acids or others ligands. With appropriate molecules bonded to the surface, the quantum dots could be readily included in different ink systems, without degrading their quantum electronic properties (e.g., emission efficiency). The organic molecules  208  render the quantum dot miscible with an organic resin and solvent of the quantum dot ink  102 . The quantum dot ink  102  can be heat dryable or include a UV curable photochemical resin, for example. 
       FIG. 3  is a schematic sectional elevation view of a quantum dot light emitting device  302  that is used as the pump light  104  shown in  FIG. 1  according to an embodiment of the invention. The quantum dot light emitting device  302  includes a multilayer structure including, in sequence, a substrate (e.g., glass)  304 , a transparent conductor (e.g., ITO)  306 , an organic or inorganic hole transport layer (e.g., N,N0-diphenyl-N,N0-bis(3-methylphenyl)-(1,10-biphenyl)-4,40-diamine (TPD))  308 , a quantum dot layer  310 , an organic or inorganic electron transport layer (e.g., tris-(8-hydroxyquinoline)aluminum or 3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-1, 2, 4-triazole (TAZ))  312 , an electron source layer (e.g., Mg:Ag)  314  and an electrical contact (e.g. Ag)  316 . The light emitting device  302  emits photons  318  Alternatively, light emitting diodes that do not include quantum dots can be used. For example a GaN UV diodes can be used. 
       FIG. 4  is a schematic of a fluorescent lamp light box  402  that is used as the pump light  104  shown in  FIG. 1  according to an alternative embodiment of the invention. The light box  402  includes a number of fluorescent light bulbs  404 , such as those used in tanning beds or black lights, that emit UV light  406 . A back reflector  408  is used to collect and direct the UV light  406  emitted by the bulbs  404 . The UV light  406  passes out of the light box  402  through a protective window  410  that is made out of a UV transmissive material such as borosilicate glass or UV transmissive plastic such as a UV transmissive acrylic polymer such as Acrylite® H12-503 manufactured by Cyro Industries of Rockaway, N.J. According to an alternative embodiment of the invention a compact pump lamp such as a medium pressure arc lamp is used to illuminate the light emissive poster  101 . 
       FIG. 5  is a graph including plots  502  quantum dot absorbance versus wavelength for several sizes of quantum dots  202  that emit visible light. The plots  502  are for different sizes of quantum dots  202 . Each plot  502  includes a local peak  504  that corresponds to its peak emission wavelength. As shown in  FIG. 5  all of the quantum dots  202  represented in the plots  502  are able to effectively absorb pump light in the UVA range 
       FIG. 6  is a graph including three lines  602 ,  604 ,  606  of spectral emission for three size distributions of quantum dots. The lines  602 ,  604 ,  606  exhibit Gaussian line shapes that have a FWHM of 30 nm. The spectral FWHM is a function of the size distribution FWHM. A first blue line  602 , is centered at 450 nm, a second green line  604  is centered at 525 nanometers and a third red line  606  is centered at 600 nanometers. 
       FIG. 7  is a 1931 CIE chart  700  showing a color range  702  obtainable by mixing quantum dots of the three distributions have the spectral emissions shown in  FIG. 6 . One skilled in the art will appreciate that the use of quantum dots allows for fine control of the obtainable color space by controlling the center and FWHM of quantum dot size distributions used in the quantum dot ink  102 . Although as shown in  FIG. 7  only three color space points  704  are used to delineate the obtained color range  702 , one skilled in the art will appreciate that an expanded color range can be obtained by using more than three quantum dot inks, with each ink having a different mean quantum dot size. A variety of printing techniques, such as for example Flexo, Gravure, Screen, inkjet can be used. The Halftone method, for example, allows the full color range  702  to be realized in actual printing. 
       FIG. 8  a schematic cross section of a light emissive poster  800  according to an alternative embodiment. The light emissive poster  800  includes a UV transparent coating  802  covering the printed graphics  106 , so that the printed graphics  106  are disposed between the substrate  110  and the UV transparent coating  802 . The UV transparent coating can for example be a UV transmissive acrylic polymer such as Acrylite® H12-503 manufactured by Cyro Industries of Rockaway, N.J. The photons  318  and UV light  406  can activate the printed graphics  106  through the UV transparent coating  802 . The coating  802  serves to seal and protect the printed graphics  106 . 
     For some applications, the poster  101  can be affixed to another object, such as for example, a carton or a container. Elongated quantum dot rods, which emit polarized light may be used. Elongated quantum dot rods are disclosed by Liang-shi Li, J. Hu, W. Yang, and A. Paul Alivisatos in Nano Letters, 2001, Vol. 1 No. 7 pp 349-351. 
       FIG. 9  shows a product package  902  with a light emissive label  904  with printing  906  with quantum dot ink. The label overlies the pump light source  302  which is supported on the package  902 . A battery  908  in a battery case  910  is electrically coupled to and supplies electrical power to the pump light source 
     In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.