Patent Publication Number: US-2007103078-A1

Title: Plasma display panel

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to plasma display panels (PDP). More particularly, to a PDP including phosphor layers and EL layers, and having improved brightness and luminance distribution.  
      2. Description of the Related Art  
      In plasma display panels (PDP), brightness and luminous efficiency are main factors which determine the performance of a PDP. In order to improve luminous efficiency and brightness of the PDP, a surface area of a phosphor layer can be increased. However, there is a limitation in increasing the surface area of the phosphor layer due to a structure of the PDP.  
      In addition, in order to improve brightness of the PDP, a discharge voltage applied to electrodes can be increased. However, when the discharge voltage is higher than a predetermined voltage, brightness may not be further improved and/or a ratio corresponding to the increasing brightness is reduced, whereby luminous efficiency of the PDP is lowered.  
      PDPs having pixels of 640×480 and 800×600 have been used. However, as PDPs having pixels of 1940×1035 are being developed, a more need for improving brightness and luminous efficiency of the PDP is required. That is, as the PDP has been made to display high definition images, the size of discharge cells of the PDP is being reduced and a surface area of a phosphor layer applied in the discharge cells is also reduced. As the surface area of the phosphor layer is reduced, the amount of visible light emitted from the phosphor layer is reduced, brightness of the PDP is lowered, whereby luminous efficiency of the PDP is lowered.  
     SUMMARY OF THE INVENTION  
      The invention is therefore directed to a plasma display panel, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.  
      It is therefore a feature of embodiments of the invention to provide a plasma display panel (PDP) having improved brightness relative to conventional PDPs.  
      It is therefore a separate feature of embodiments of the invention to provide a PDP having improved luminous efficiency without requiring a discharge voltage to be increased.  
      At least one of the above and other features and advantages of the invention may be realized by providing a plasma display panel including a first substrate, a second substrate opposing the first substrate, a plurality of discharge cells defined between the first substrate and the second substrate, a plurality of sustain discharge electrode pairs formed on the first substrate, a dielectric layer covering the sustain discharge electrode pairs electroluminescent (EL) layers formed on the dielectric layer at least partially within the discharge cells, a discharge gas disposed in the discharge cells, and phosphor layers formed in the discharge cells.  
      The EL layers may include at least one of inorganic EL material and quantum dots. The EL layers may emit light when a sustain voltage is applied between electrodes that form the sustain discharge electrode pairs. The EL layers may include ZnS:Mn, ZnS:Tb, SrS:Ce, Ca 2 S 4 :Ce, SrS:Cu, SrS:Ag, CaS:Pb, and/or BaAl 2 :Eu. A thickness of the EL layers may be about 500 Å to about 5000 Å. The quantum dots may include a core formed of CdSe, a shell formed of ZnS and surrounding the core, and caps formed of trioctylphosphine oxide (TOPO) and disposed outside the shell.  
      The EL layers may at least partially overlap with the sustain discharge electrodes. The EL layers may include a transparent material. Each of the discharge cells may include at least one of the EL layers arranged therein. The EL layers may correspond to each of the electrodes that form the sustain discharge electrode pairs and two EL layers may be disposed in each of the discharge cells. Respective portions of the two EL layers associated with each of the discharge cells may be substantially symmetrically arranged within the respective discharge cell. Each of the discharge cells may include two of the EL layers arranged therein, wherein each of the EL layers may only be within one of the of the discharge cells, wherein the EL layers may completely overlap with respective portions of the sustain discharge electrode pair of the respective discharge cell.  
      The plasma display panel may include address electrodes extending on the second substrate to cross the sustain discharge electrode pairs, and a second dielectric layer covering the address electrodes.  
      The first substrate may correspond to a front substrate of the plasma display panel, the EL layers may be arranged on the front substrate, and the EL layers may be formed of a transparent material. The first substrate may correspond to a rear substrate of the plasma display panel, the EL layers may be arranged on the rear substrate.  
      At least one of the above and other features and advantages of the invention may be separately realized by providing a display panel, including a first substrate, a second substrate, a plurality of discharge cells defined between the first substrate and the second substrate, a plurality of sustain discharge electrode pairs arranged on one of the first substrate and the second substrate, a dielectric layer covering the plurality of sustain discharge electrode pairs, first light emitting elements for emitting light toward the first substrate, and second light emitting elements for emitting light toward the first substrate, wherein for each of the discharge cells the second light emitting elements are arranged along a sustain discharge path of the plurality of sustain discharge electrode pairs, and the first light emitting elements and the second light emitting elements substantially simultaneously emit light toward the first substrate based on a voltage potential across a corresponding one of the plurality of sustain discharge electrode pairs.  
      The first light emitting elements may include a discharge gas and at least one phosphor layer, and the second light emitting elements may include an electroluminescent layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  illustrates an exploded perspective view of a plasma display panel (PDP) according to an exemplary embodiment of the invention;  
       FIG. 2  illustrates a cross-sectional view of the plasma display panel illustrated in  FIG. 1 , taken along line  11 -II of  FIG. 1 ;  
       FIGS. 3A and 3B  illustrate cross-sectional views of a portion of a discharge cell of the PDP illustrated in  FIG. 1  including a general charge distribution pattern according to respective charged states of sustain discharge electrode pairs;  
       FIG. 4  illustrates a plan view of electrodes and an EL layer of the PDP illustrated in  FIG. 1 ;  
       FIG. 5  illustrates a cross-sectional diagram of an exemplary quantum dot as an exemplary element for the EL layer of the PDP illustrated in  FIG. 1 ;  
       FIG. 6  illustrates an exploded perspective view of a PDP according to a second exemplary embodiment of the invention; and  
       FIG. 7  illustrates a cross-sectional view of the exemplary PDP illustrated in  FIG. 6 , taken along line VII-VII of  FIG. 6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Korean Patent Application No. 10-2005-0106391, filed on Nov. 8, 2005, in the Korean Intellectual Property Office, and entitled: “Plasma Display Panel,” is incorporated by reference herein in its entirety.  
      The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are illustrated. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
      In the figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” or “sandwiched between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout.  
       FIG. 1  illustrates an exploded perspective view of a plasma display panel (PDP)  100  according to an exemplary embodiment of the invention, and  FIG. 2  illustrates a cross-sectional view of the PDP  100  illustrated in  FIG. 1 , taken along line II-II of  FIG. 1 . Referring to  FIGS. 1 and 2 , the PDP  100  may include a front substrate  120 , a rear substrate  130 , a plurality of barrier ribs  137 , a plurality of sustain discharge electrode pairs  121 , a plurality of electroluminescent (EL) layers  127 , a discharge gas (not shown), and a plurality of phosphor layers  140 . The rear substrate  130  and the front substrate  120  may be arranged parallel to each other, may be separated from each other by a predetermined gap and sides thereof may be sealed for containing the discharge gas (not shown) therebetween.  
      In general, display devices transmit visible light toward the front substrate  120  to display images thereon. In embodiments of the invention, at least some visible light may be transmitted toward the rear substrate  130  to display images on the PDP  100 . The PDP  100  may be, e.g., a reflective-type, a transmissive-type or a transreflective-type.  
      At least one barrier rib  137  may be formed between the front substrate  120  and the rear substrate  130 . The barrier ribs  137  may be disposed on and/or correspond to a non-discharge portion of the PDP  100 . Together with the front substrate  120  and the rear substrate  130 , the barrier ribs  137  may at least partially define discharge cells  150 . The barrier ribs  137  may prevent cross-talk of charged particles amongst, e.g., adjacent discharge cells  150 . In embodiments of the invention, the barrier ribs  137  may be formed on a front surface of a rear dielectric layer  135 .  
      Each of the discharge cells  150  may constitute one unit pixel of the PDP  100 , and may include a group of different colored discharge cells. For example, in embodiments of the invention, the discharge cell  150  may include red discharge cells  150 R, blue discharge cells  150 B and green discharge cells  150 G.  
      The phosphor layers  140  may be arranged in the discharge cells  150 . More particularly, e.g., the red discharge cell  150 R may include a red phosphor layer  140 R, the blue discharge cell  150 B may include a blue phosphor layer  140 B, and the green discharge cell  150 G may include a green phosphor layer  140 G. The phosphor layers  140  may be disposed on side surfaces of the barrier ribs  137  and/or on the front surface of the rear dielectric layer  135  between, e.g., adjacent ones of the barrier ribs  137 .  
      At least portions of the sustain discharge electrode pairs  121  and address electrodes  133  may overlap the discharge cells  150 . The sustain discharge electrode pairs  121  include X electrodes  122  and Y electrodes  123 , or respective portions thereof, associated with each of discharge cell may cause a sustain discharge. In embodiments of the invention, the X electrodes  122  and the Y electrodes  123  may include transparent electrodes  122   a  and 123   a  and bus electrodes  122   b  and  123   b,  respectively. The X electrodes  122  and the Y electrodes  123  may extend parallel to each other on, e.g., a rear surface of the front substrate  120 . A front dielectric layer  125  may cover the X electrodes  122  and the Y electrodes  123  and/or exposed portions of the front substrate  120 .  
      Each of the sustain discharge electrode pairs  121  may be associated with one of the address electrodes  133 . The address electrodes  133  may be arranged on, e.g., a front surface of the rear substrate  130 . The address electrodes  133  may extend parallel to each other and along a direction that crosses a direction along which the sustain discharge electrode pairs  121  extend. In embodiments of the invention, the address electrodes  133  may extend substantially perpendicular to the sustain discharge electrode pairs  121 . The address electrodes  133  and/or exposed portions of the rear substrate  130  may be covered by the rear dielectric layer  135 .  
      The EL layers  127  may be formed on a rear surface of the front dielectric layer  125 . The EL layers  127  and exposed portions of the rear surface of the front dielectric layer  125 , e.g. portions of the rear surface of the front dielectric layer  125  where the EL layers  127  are not formed, may be covered with a protective layer  129 . While the protective layer  129  is not an essential element, the protective layer  129  may prevent charged particles from colliding with the EL layers  127  and the front dielectric layer. The protective layer  129  may also emit a relatively large amount of secondary electrons during a discharge operation, and may enable a sustain discharge voltage to be reduced.  
      The EL layers  127  may overlap with respective portions of the sustain discharge electrode pairs  121 . For example, the EL layers  127  may overlap with respective portions of the X electrodes  122  and the Y electrodes  123 . More particularly, e.g., the EL layers  127  may overlap with respective portions of the transparent electrodes  122   a  and 123   a  and/or the bus electrodes  122   b  and  123   b.  That is, in embodiments of the invention, the EL layers  127  may partially, substantially and/or completely overlap with at least portions of the sustain discharge electrode pairs  121 , and may be sandwiched between the sustain discharge electrode pairs  121  and portions of the address electrodes  133  and/or portions of the rear substrate between adjacent ones of the barrier ribs  137 . That is, the EL layers  127  may be formed along a sustain discharge path between the sustain discharge electrode pairs  121 .  
      Further, in embodiments of the invention, one, some, or all of the discharge cells  150  may include and/or be associated with one or more EL layers  127 . Thus, in embodiments of the invention, some of the discharge cells  150  may not include and/or be associated with any of the EL layers  127 .  
       FIGS. 3A and 3B  illustrate cross-sectional views of a portion of a discharge cell of the PDP  100  illustrated in  FIG. 1 , including a general charge distribution pattern according to respective charged states of the sustain discharge electrode pairs  121 . As illustrated in  FIGS. 3A and 3B , the EL layers  127  may be arranged along the sustain discharge path between the X electrodes  122  and the Y electrodes  123 . As a result, when, e.g., the X electrodes  122  and the Y electrodes  123  are charged, electrons may pass through the EL layers  127 , thereby producing light. That is, when a sustain discharge between the X electrodes  122  and the Y electrodes  123  occurs in respective ones of the discharge cells  150  to be turned on, charges may move along the sustain discharge path in a discharge space of the discharge cell(s). The discharge space in the discharge cells  150  in which the X electrodes  122  and the Y electrodes  123  are disposed may have an electrically low resistance during a sustain period. Accordingly, a current i may flow along the sustain discharge path.  
      Referring to  FIGS. 3A and 3B , polarities of the X electrodes  122  and the Y electrodes  123  may be alternately changed during the sustain period(s).  FIG. 3A  illustrates a charged stated where a high voltage is applied to the X electrode  122  and a low voltage is applied to the Y electrode  123 .  FIG. 3B  illustrates another charged state where the low voltage is applied to the X electrode  122  and the high voltage is applied to the Y electrode  123 . As illustrated in  FIGS. 3A and 3B , charges may move along the sustain discharge path from the X electrodes  122  to the Y electrodes  123  or from the Y electrodes  123  to the X electrodes  122 , and may collide with the discharge gas in the respective discharge cell  150 . When the charges collide with the discharge gas, UV light may be emitted. The emitted UV light may collide with the phosphor layers  140 , and visible light may be produced from the phosphor layers  140 .  
      As discussed above, in embodiments of the invention, EL layers  127  may be arranged along the sustain discharge path of the X and Y electrodes  122 ,  123 , and thus, in the respective discharge cell(s)  150  to be turned on, the current i may pass through the EL layers  127 , wherein electrons may move in a direction opposite to a direction of flow of the current i. Thus, electron transfer or tunneling may occur in the EL layers  127 , and light may be produced. Thus, in embodiments of the invention, light produced from the EL layers  127  and the visible light emitted from the phosphor layers  140  may be emitted through the front substrate  120 , and, thus, brightness and luminous efficiency of the PDP  100  may be improved. That is, in embodiments of the invention, brightness and luminous efficiency of the PDP  100  may be improved by providing multiple sources of light emission, e.g., phosphor layers  140  and EL layers  127 .  
       FIG. 4  illustrates a plan view of electrodes and an EL layer of the PDP illustrated in  FIG. 1 . As illustrated in  FIG. 4 , in embodiments of the invention, two of the EL layers  127  may be arranged in one, some or all of the discharge cells  150 . The EL layers  127  may extend along a same direction as the direction along which the sustain discharge electrode pairs  121  extend. Although the exemplary embodiment illustrated in  FIG. 4 , illustrates two of the EL layers  127  in each discharge cell  150 , embodiments of the invention are not limited to two EL layers  127  for each of the discharge cells  150 , and the discharge cells  150  may include one or more than two EL layers.  
      In embodiments of the invention by providing independent EL layers  127  in the discharge cells  150 , the possibility of light being produced from portions of the EL layers  127  overlapping the barrier ribs  137  and/or cross-talk among adjacent ones of the discharge cells  150  may be reduced and/or minimized.  
      In other exemplary embodiments of the invention, e.g., the EL layers  127  may correspond to each of the X electrodes  122  and the Y electrodes  123 , extending along multiple discharge cells  150 . Manufacture of such EL layers  127  may be advantageous, e.g., simpler. In such embodiments, cross-talk among adjacent ones of the discharge cells  150  may be higher relative to embodiments with independent EL layers  127  in the discharge cells  150 .  
      The sustain discharge path of the sustain discharge electrode pairs  121  may generally correspond to an upper portion of the discharge cell  150  associated with the respective one of the sustain discharge electrode pairs  121 . Thus, the EL layer(s)  127  may be arranged substantially anywhere in the respective discharge cell  150  between, e.g., the sustain discharge electrode pair  121  and the phosphor layer  140 . For example, the EL layer(s)  127  may be arranged on portions of the front dielectric layer  125  exposed to the respective discharge cell  150 . That is, as illustrated in  FIG. 2 , the EL layers  127  may also be arranged along a path of the visible light produced from the phosphor layers  140  in the discharge cells  150 .  
      More particularly, in embodiments of the invention, the EL layers  127  may be symmetrically or substantially symmetrically arranged in each of the discharge cells  150 . For example, in embodiments including two of the EL layers  127 , i.e., independent layers or portions of continuous layers, each of the discharge cells  150 , one of the EL layers  127  symmetrically arranged on each side of the discharge cells  150 . Thus, light from the EL layers  127  may be emitted from both sides of the discharge cell  150 . That is, by symmetrically arranging the EL layer(s)  127  in the discharge cells, it may be possible for the discharge cells  150  to emit substantially uniformly distributed light.  
      A general description of exemplary materials that may be employed for different layers or elements of the PDP  100  is provided below. Referring to  FIGS. 1 and 2 , the discharge gas (not shown) may be filled in the discharge cells  150 . A penning mixture such as, e.g., Xe—Ne, Xe—He, or Xe—Ne—He may be used as the discharge gas. Xe may be used as a main discharge gas because, e.g., Xe is a chemically stable inert gas, generally does not dissociate by a discharge, has a relatively high atomic number, may enable an excitation voltage to be reduced, and a wavelength of emitted light may be relatively long. He and/or Ne may generally be used as a buffer gas because a voltage reduction effect caused by penning due to Xe and a sputtering effect caused by high pressure may be reduced. The main discharge gas may include, e.g., a rare gas such as Kr.  
      The front substrate  120  and the rear substrate  130  may include a material having excellent light transmission characteristics, such as glass.  
      The phosphor layers  140  may be classified into red phosphor layers  140 R, green phosphor layers  140 G, and blue phosphor layers  140 B, according to colors of visible light. The red phosphor layers  14 OR may include phosphor such as, e.g., Y(V,P)O 4 :Eu, the green phosphor layers  140 G include phosphor such as, e.g., Zn 2 SiO 4 :Mn, and the blue phosphor layers  140 B include phosphor such as, e.g., BAM:Eu.  
      The red discharge cells  150 R in which the red phosphor layers  140 R are disposed may serve as red subpixels, the green discharge cells  150 G in which the green phosphor layers  140 G are disposed may serve as green subpixels, and the blue discharge cells  150 B in which the blue phosphor layers  140 B are disposed may serve as blue subpixels. As discussed above, the red subpixels, the green subpixels, and the blue subpixels may form one unit pixel, thereby representing a wide range of colors according to various combinations of the primary R, G, B colors.  
      The EL layers  127  may include an inorganic EL material. The inorganic EL material may be a light transmissive material, which may, e.g., transmit visible light. When voltages having different polarities are applied to two sides of the inorganic EL material, electron transfer may occur in the inorganic EL material, and light may be produced. Thus, if voltages are applied between the sustain discharge electrode pairs  121 , light may be produced in the EL layers  127 , which may include, e.g., inorganic EL material. As discussed above, the light emitted from the EL layers  127  may be combined with visible light produced from the phosphor layers  140 , and emitted so that brightness and luminous efficiency of the PDP  100  may be improved. A more detailed description of exemplary material(s) that may be employed for the EL layers  127  is provided below.  
      A general description of an exemplary operation of the PDP  100  is provided below. To drive the PDP  100 , an address discharge and a sustain discharge may be initiated in the discharge cells  150 . To initiate an address discharge, an address voltage may be applied between the address electrodes  133  and the Y electrodes  123 . More particularly, the address voltage may be applied between respective ones of the address electrodes  133  and the Y electrodes  123  associated with discharge cells  150  that are to be turned on during a subsequent sustain discharge operation. As a result of the address discharge, the discharge cell(s)  150  in which a sustain discharge is to occur during the subsequent sustain discharge operation, may be selected. Then, to initiate a sustain discharge operation between the X electrodes  122  and the Y electrodes  123 , an AC sustain discharge voltage may be applied between the X electrodes  122  and the Y electrodes  123  of the selected discharge cells  150 . As a result, an energy level of a discharge gas excited by the sustain discharge may be reduced and UV light may be emitted. The UV light may excite the phosphor layers  140  in the discharge cells  150 . The energy level of the excited phosphor layers  140  may be reduced, visible light may be emitted, and the emitted visible light may enable an image(s) to be realized on the PDP  100 .  
      In embodiments of the invention, the sustain discharge voltage may be about 150V to about 180 V, and the sustain discharge voltage may be alternately applied between the X electrodes  122  and the Y electrodes  123  during a sustain period of a frame. In the discharge space in the discharge cells  150  selected during the prior addressing period, charges having signs opposite to signs of the applied sustain discharge voltage may move in the discharge space of the selected discharge cells  150  and on and/or toward the rear dielectric layer  135 , corresponding to the X electrodes  122  and the Y electrodes  123 . Accordingly, when the sustain discharge voltage is applied to the X electrodes  122  and the Y electrodes  123 , current may flow from the X electrodes  122  to the Y electrodes  123  or from the Y electrodes  123  to the X electrodes  122  along the front dielectric layer  125  and the discharge space in the discharge cells  150 .  
      Further, when sustain discharge occurs in the selected ones of the discharge cells  150 , voltages having opposite polarities may be applied to front and rear surfaces of the EL layers  127 . When sustain discharge occurs, current does not flow in the discharge cells  150  that were not selected during the prior addressing operation. Thus, in such non-selected ones of the discharge cells  150 , light may not emitted from the EL layers  120  associated therewith.  
      As discussed above, the EL layers  127  may include inorganic EL material and may be arranged on the rear surface of the front dielectric layer  125 , i.e., along the sustain discharge path of the sustain discharge electrodes  121 . Thus, when the sustain discharge occurs in the selected discharge cells  150 , UV, visible and/or infrared light may be emitted from the EL layers  127  of those selected discharge cells  150 . Such UV light may collide with the phosphor layers  140  and generate additional visible light, i.e., visible light in addition to visible light generated by collision of UV light generated by the discharge gas (not shown) and the phosphor layers  140 . The visible light emitted form the EL layers  127  together with the visible light emitted from the phosphor layers  140  may be transmitted to the front substrate  120  where an image(s) may be realized on the PDP  100 . Thus, the light emitted from the inorganic EL layers  127  may be combined with the visible light produced from the phosphor layers  140 , and the combined light may be emitted through the front substrate  120 , thereby increasing an amount of light emitted from the discharge cells  150  and improving a brightness of the PDP  100 .  
      Thus, in embodiments of the invention including the EL layers  127 , e.g., a light emitting inorganic material, brightness and luminous efficiency of the PDP  100  may be improved without requiring any additional voltage beyond a minimum sustain discharge voltage applied between the X electrodes  122  and the Y electrodes  123  for initiating discharge of the discharge gas (not shown) in the selected ones of the discharge cells  150 . Thus, when the sustain discharge voltage is about 150V to about 180 V for initiating discharge of the discharge gas (not shown) in the selected ones of the discharge cells  150 , when a potential difference of about 150V to about 180 V exists between the inorganic EL layers  127  of 150-180 V occurs, the inorganic EL layers  127  may also emit light.  
      In embodiments of the invention, the EL layers  127  may include inorganic material including at least one of ZnS:Mn, ZnS:Tb, SrS:Ce, Ca 2 S 4 :Ce, SrS:Cu, SrS:Ag, CaS:Pb, and/or BaAl 2 :Eu. For example, the EL layers  127  may include, e.g., ZnS:Mn, ZnS:Tb having a brightness of about 4000 cd/m 2  to about 5000 cd/m 2 .  
      Referring to  FIG. 2 , a thickness D of the EL layers  127  may be about 500 Å to about 5000 Å. When the thickness D of the EL layers  127  is greater than about 5000 Å, light transmission may be lowered, and when the thickness D of the EL layers  127  is less than about 500 Å, a sufficient amount of light may not produced from the EL layers  127 .  
      In embodiments of the invention, the EL layers  127  may include a plurality of quantum dots  128 .  FIG. 5  illustrates a cross-sectional diagram of an exemplary quantum dot  128 , as an exemplary element, for the EL layers  127 . Theoretically, quantum efficiency of the quantum dots  128  may be improved up to 100%, and electrons may be excited even at a low voltage, so that luminous efficiency may be improved. In embodiments of the invention, the EL layers  127  including such quantum dots  128  may be formed using, e.g., a printing process. This exemplary process of forming the EL layers  127  may be advantageous for making larger display apparatus.  
      As illustrated in  FIG. 5 , the quantum dots  128  may include a core  128   a,  a shell  128   b  surrounding the core  128   a,  and caps  128   c  disposed outside the shell  128   b.  The core  128   a  may be formed of, e.g., CdSe. The shell  128   b  may be formed of, e.g, ZnS. The caps  128   c  may be formed of, e.g., trioctylphosphine oxide (TOPO).  
      The EL layers  127  including the quantum dots  128  may be a single layer structure or a multi-layer structure. However, luminous efficiency of EL layers  127  having a single layer structure may be higher than the luminous efficiency of EL layers  127  having a multi-layer structure.  
      As discussed above, the EL layers  127  may be arranged along the path along which visible light travel from the phosphor layers  140  toward the front substrate  120 , and thus, the EL layers  127  may include light transmissive material(s).  
       FIG. 6  illustrates an exploded perspective view of a PDP according to a second exemplary embodiment of the invention, and  FIG. 7  illustrates a cross-sectional view of the exemplary PDP illustrated in  FIG. 6 , taken along line VII-VII of  FIG. 6 . In the following description of the exemplary PDP illustrated in  FIGS. 6 and 7 , to avoid repetition a detailed description of like features, having like reference numbers, among the illustrated exemplary embodiments will be avoided.  
      Referring to  FIGS. 6 and 7 , a second exemplary PDP  200  employing one or more aspects of the invention is illustrated. The PDP  200  may be a transmissive-type PDP. The PDP  200  may include a rear substrate  230  and a front substrate  220 , which oppose each other. The rear substrate  230  and the front substrate  220  may be separated from each other by a predetermined gap and sides thereof may be sealed for containing a discharge gas (not shown) therebetween.  
      The rear substrate  230  may be, e.g., a glass substrate. A plurality of sustain discharge electrode pairs  231  may be formed on a front surface of the rear substrate  230 . The sustain discharge electrode pairs may  221  may extend parallel to each other. The sustain discharge electrode pairs  231  may be disposed in such a manner that at least a portion of a pair of X electrodes  232  and Y electrodes  233  may be disposed in and/or associated with each discharge cell  250 . A rear dielectric layer  235  may cover the sustain discharge electrode pairs  231  and exposed portions of the front surface of the rear substrate  230 . The rear dielectric layer  235  may be formed by applying a dielectric material on the front surface of the rear substrate  230 , and may have a thickness of about 15 μm to about 40 μm.  
      A plurality of EL layers  237  may be formed on the front surface of the rear dielectric layer  235 . The EL layers  237  may be formed of a light emitting material that may emit light when a sustain discharge voltage is applied between the X electrodes  232  and the Y electrodes  233 . As discussed above with regard to the EL layers  137  of the exemplary PDP  100 , the EL layers  237  may be formed along a sustain discharge path between the X electrodes  232  and the Y electrodes  233 . In embodiments of the invention, e.g., two independent EL layers  237  may be formed in each discharge cell  250  and may completely or partially overlap with the X electrodes  232  and the Y electrodes  233 . As discussed above with regard to EL layers  137 , embodiments of the invention are not limited to such a structure.  
      The EL layers  237  may be formed of an inorganic EL material. The inorganic EL material include at least one of, e.g., ZnS:Mn, ZnS:Tb, SrS:Ce, Ca 2 S 4 :Ce, SrS:Cu, SrS:Ag, CaS:Pb, and/or BaAl 2 :Eu. In embodiments of the invention, the function and/or structure of the EL layers  237  is similar to the EL layers  137  described above, and thus, a detailed description thereof will be omitted. For example, the EL layers  237  may include the quantum dots  128 .  
      In the exemplary embodiment of the PDP  200  illustrated in  FIGS. 6 and 7 , because visible light produced from phosphor layers  240  do not transmit through the EL layers  237 , the EL layers  237  may include non-transparent materials and/or transparent materials. As a result of the arrangement of the EL layers on the rear substrate  230 , a thickness D′ of the EL layers  237  may be greater than the thickness D of the EL layers  127  of the PDP  100  illustrated in  FIG. 1 . Thus, a manufacturing process for forming the EL layers  237  may be easier than a manufacturing process for forming the EL layers  137 . In embodiments of the invention, the thickness D′ of the EL layers  237  may be several μm.  
      The EL layers  237  may be disposed along sustain discharge path between the rear dielectric layer  235  and the front substrate  220 . The sustain discharge path of the sustain discharge electrode pairs  221  may generally correspond to a lower portion, i.e., portion closer to rear substrate  230 , of the discharge cell  250  associated with the respective one of the sustain discharge electrode pairs  221 . Thus, when voltages having different polarities are applied to two sides, e.g., upper and lower sides, of the EL layers  237  in discharge cells  250  to be turned on, electrons may be excited in the EL layers  237  and light may be emitted. In the discharge cells  250  to be turned or maintained off, wall charges are not generated in the discharge space and light is not emitted from EL layers  237  associated with the respective non-selected ones of the discharge cells  250 .  
      A protective layer  239  may cover the EL layers  237  and exposed portions of a front surface of the rear dielectric layer  235  and/or the rear substrate  230 . The protective layer  239  may prevent charged particles from colliding with and damaging the rear dielectric layer  235  and the sustain discharge electrode pairs  231  as a result of, e.g., sputtering of plasma particles, may emit secondary electrons and may reduce a discharge voltage and a sustain voltage. The protective layer  239  may be formed by applying magnesium oxide (MgO) on the front surface of the rear dielectric layer  235 . The protective layer  239  may have a thickness of about 0.2-2 μm. In embodiments of the invention, the protective layer  239  may not be provided.  
      The front substrate  220  may be a transmissive substrate through which visible light may be transmitted to realize an image(s) on the PDP  200 . The front substrate  200  may be formed of, e.g., a transparent glass. A plurality of address electrodes  223  may be formed on a bottom surface of the front substrate  220 . The address electrodes  223  may extend along a direction crossing a direction along which the sustain discharge electrode pairs  231  extend. A front dielectric layer  225  may cover the address electrodes  223  and/or exposed portion(s) of the bottom surface of the front substrate  220 .  
      At least one barrier rib  227  may be formed between the front substrate  220  and the rear substrate  230  at predetermined intervals. The barrier ribs  227  may partition the space between the front substrate  220  and the rear substrate  230 . Together with the front substrate  220  and the rear substrate  230 , the barrier rib(s)  227  may define the discharge cells  250 , and may prevent electrical and optical interference amongst adjacent ones of the discharge cells  250 .  
      The discharge gas such as Ne, Xe or a mixture thereof is filled in the discharge space. Phosphor layers  240  may be provided on a rear surface of the front dielectric layer  225  and/or side surfaces of the barrier ribs  227 , to a predetermined thickness.  
      In the PDP  200  having the above structure, pairs of the X and Y electrodes  232  and  233  are disposed on the rear substrate  230 , and a discharge may occur on a plane of the rear substrate  230 . As such, visible light emitted from the phosphor layers  240  may transmit the phosphor layers  240  and the front substrate  220 , and may be emitted from the front substrate  220 .  
      In such PDPs, e.g. PDP  200 , the rear dielectric layer  235  may be formed on the rear substrate  230 , and may cover the sustain discharge electrode pairs  231  and/or exposed portions of the rear substrate  230 . The rear dielectric layer  235  may be formed of a reflective, e.g., white dielectric material so that visible light emitted from the phosphor layers  240  in the discharge space can be reflected. The front dielectric layer  225  may be formed on the rear surface of the front substrate  220 , and may cover the address electrodes  223  and/or exposed portion(s) of the front substrate  220 . The front dielectric layer  225  may be formed of a transparent dielectric material so that visible light may transmit through to the front substrate  220 .  
      The address electrodes  223  disposed on the rear surface of the front substrate  220  may be formed of a transparent conductive material, such as indium tin oxide (ITO), so that visible light may transmit the front substrate  220 . In embodiments of the invention, the address electrodes  223  may be formed of ITO which is a transparent conductive material having a relatively high resistance. Thus, in order to reduce a line resistance, bus electrodes  224  formed of a metallic material having high conductivity may be coupled with the address electrodes  223 , respectively.  
      The sustain discharge electrode pairs  231  disposed on the front surface of the rear substrate  230  may be formed of, e.g., transparent or non-transparent material. For example, the sustain discharge electrode pairs may be formed of a conductive metallic material.  
      Driving of the transmitted type PDP  200  having the above structure may include driving for an address discharge and driving for a sustain discharge. The address discharge may occur between the address electrodes  223  disposed on the front substrate  220  and the Y electrodes  233  disposed on the rear substrate  230 . As a result of the address discharge, wall charges may be formed on selected ones of the discharge cells  250 . A sustain discharge may occur as a result of a potential difference between the X electrodes  232  and the Y electrodes  233  associated with the selected ones of the discharge cells  250  in which the wall charges may be formed. The phosphor layers  240  in the discharge space may be excited by UV light generated from the discharge gas during the sustain discharge, thereby emitting visible light. The visible light may transmit through the phosphor layers  240  and the front substrate  220 , and may be emitted from the front substrate  220  so that an image(s) may be realized on the PDP  200 .  
      In the PDP having the above structure, in addition to the existing phosphor layers, the EL layers that emit light simultaneously with the phosphor layers may be formed such that brightness of a PDP capable of displaying high definition images may be improved and high brightness may be obtained.  
      In embodiments of the invention, additional power is not required to drive the EL layers, and voltages employed for initiating sustain discharge operations and applied to the X electrodes and the Y electrodes may be simultaneously employed to create a voltage difference across two sides of the EL layers. Thus, embodiment of the invention need not employ additional power to increase brightness and/or improve a luminance distribution. That is, in embodiments of the invention, luminous efficiency of the PDP may be improved while employing a minimum amount of power necessary for initiating a sustain discharge in the discharge gas of the discharge cells of the PDP.  
      In embodiments of the invention, when sustain discharge occurs, current does not flow in the discharge cells that were not selected during the prior addressing operation. Thus, in such non-selected ones of the discharge cells, light may not emitted from the EL layers associated therewith.  
      In embodiments of the invention, a thickness of the phosphor layers formed on, e.g., a rear dielectric layer, may be larger than a thickness of a phosphor layer formed on side surfaces of the barrier ribs such that brightness of a PDP may be improved and discharge stability and luminous efficiency thereof may be improved.  
      Exemplary embodiments of the invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the invention as set forth in the following claims.