Patent Application
20070252527
The above and other features and advantages of the present 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:
Korean Patent Application No. 10-2006-0037715, filed on Apr. 26, 2006, in the Korean Intellectual Property Office, and entitled: “Phosphor for Plasma Display Panel and Plasma Display Panel Including Phosphor Layer Formed of the Phosphor,” is incorporated by reference herein in its entirety.
The present 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” 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.
An exemplary embodiment of a phosphor with an amorphous layer according to the present invention will now be described in detail below. The phosphor with an amorphous layer according to an embodiment of the present invention may include a core phosphor and an amorphous oxide layer having a positive polarity. In particular, the core phosphor may include a Mn-activated zinc silicate represented by Zn2SiO4:Mn, and the amorphous oxide layer may include a metal oxide, e.g., aluminum oxide (Al2O3), lanthanum oxide (La2O3), or yttrium oxide (Y2O3), adsorbed into a surface of the core phosphor to form a phosphor with an amorphous layer having improved discharge properties, resistance to plasma impact and lifespan as compared to the core phosphor.
The amorphous oxide layer may be formed on the core phosphor to a thickness of about 1 nm to about 30 nm, so that an amount of the metal oxide adsorbed into the core phosphor may be controlled to form a phosphor with an amorphous layer having a predetermined zeta potential. The amount of metal oxide adsorbed into the core phosphor may be in the range of about 0.01-10 parts by weight, and preferably about 0.03-2.0 parts by weight, based on 100 parts by weight of the core phosphor. An amount of metal oxide below about 0.01 parts by weight based on 100 parts by weight of the core phosphor may be insufficient to modify a surface polarity of the core phosphor, thereby providing no decrease in discharge voltage. On the other hand, an amount of metal oxide in excess of about 10 parts by weight based on 100 parts by weight of the core phosphor may absorb vacuum ultraviolet (VUV) light and/or visible light generated by the core phosphor and, thereby, decrease the luminance of the core phosphor.
Without intending to be bound by theory, it is believed that a metal oxide may have a positive charge and, therefore, reduce the overall surface polarity of a negatively polarized core phosphor upon adsorption thereto. Accordingly, the discharge voltage of the phosphor with an amorphous layer, i.e., a core phosphor adsorbed with an amorphous oxide layer, may be reduced. In addition, it is believed that a metal oxide may have a reduced reactivity as compared to the core phosphor and, thereby, provide a shield capable of minimizing contact between the core phosphor and emitted ions during sputtering to reduce deterioration of the phosphor with an amorphous layer.
The phosphor with the amorphous layer according to an embodiment of the present invention may be used as a single phosphor component or as a main component in a mixture of phosphors, e.g., YBO3:Tb, BaAl12O19:Mn, and so forth. However, when the phosphor with the amorphous layer is used in a mixture of phosphors, the other phosphors may be used in small amounts in order to improve the light properties of the PDP.
A zeta potential of the phosphor with the amorphous layer may be in the range of about 10 mV to about 50 mV, and preferably about 20 mV to about 40 mV. An average diameter of a particle of the phosphor with the amorphous layer may be in the range of about 1 μm to about 10 μm.
According to yet another embodiment of the present invention, a method of preparing a phosphor with an amorphous layer will now be described in detail.
In the method according to an embodiment of the present invention, a core phosphor may be synthesized in a reduction atmosphere at a high temperature to facilitate adsorption of materials having positive surface charges into a surface of the core phosphor by an adsorbing method and, thereby, to impart a positive polarity to the surface of the core phosphor.
In particular, the core phosphor may be synthesized from any phosphor forming components as determined by one of ordinary skill in the art by a conventional solid-state reaction, followed by a thermal treatment at a temperature in a range of about 1,000° C. to about 1,400° C. for about 10 hours or less. As a result, the core phosphor may be formed. Next, a metal oxide, e.g., aluminum oxide (Al2O3), lanthanum oxide (La2O3), or yttrium oxide (Y2O3), may be adsorbed onto a surface of the formed core phosphor at a predetermined ratio by an ion adsorption method to form an amorphous oxide layer thereon.
The ion adsorption method may include mixing the core phosphor with pure water at a predetermined ratio to form a first mixture, stirring the first mixture for about 30 minutes, adding a predetermined amount of an aqueous solution of a nitrate compound of an atom to be adsorbed, e.g., Al(NO3)3, La(NO3)3, or Y(NO3)3, to form a second mixture, and stirring the second mixture for about 30 minutes. Without intending to be bound by theory, it is believed that positive metal ions, e.g., Al3+, La3+, or y3+ ions, may be easily adsorbed to a negatively charged surface of the core phosphor in the aqueous solution, i.e., the second mixture. Next, since the aqueous solution may be highly acidic, i.e., have a pH in a range of about 4 to about 5, ammonia solution (NH3OH) may be added to the aqueous solution in an amount sufficient to impart an overall pH of about 7 to the aqueous solution. Addition of the ammonia solution to the aqueous solution may trigger interaction between the metal ions in the aqueous solution and the hydroxide group of the ammonia solution, as illustrated in reaction scheme 1, to facilitate metal ion adsorption into the surface of the core phosphor to form an intermediate phosphor.
The intermediate phosphor may be thermally treated at a temperature in a range of about 400° C. to about 600° C. to facilitate formation of an amorphous oxide layer on the surface of the intermediate phosphor to complete formation of the phosphor with the amorphous layer. The thermal treatment may be performed in an inert gas atmosphere, i.e., in a presence of a hydrogen gas (H2), a nitrogen gas (N2), or a mixture thereof. If luminance of the phosphor with the amorphous layer is decreased during the thermal treatment due to oxidation, the luminance may be adjusted by a thermal treatment in a reduction atmosphere.
A thickness of the amorphous oxide layer may be in the range of about 1 nm to about 30 nm. A thickness below about 1 nm may be insufficient to shield the phosphor with the amorphous layer from ion emission, thereby providing no lifespan enhancement. On the other hand, a thickness above about 30 nm, may be capable of absorbing vacuum ultraviolet (VUV) light and/or visible light generated by the phosphor with the amorphous layer and, thereby, decrease the luminance of the phosphor with the amorphous layer.
A particle diameter of the phosphor with the amorphous layer prepared according to an embodiment of the present invention may have an average diameter of about 1 μm to about 10 μm. An average particle diameter below about 1 μm may provide insufficient luminance and trigger particle agglomeration. On the other hand, an average particle diameter above about 10 μm may impede screen printing of the phosphor with the amorphous layer during application onto PDP emission cells and, thereby, reduce the fineness and precision of the PDP.
According to yet another exemplary embodiment of the present invention, a PDP having a phosphor layer will be described in detail below with respect to
The green phosphor layers 225b may be formed of the phosphor with the amorphous layer described previously. The phosphor with the amorphous layer may be prepared according to an embodiment described previously. Subsequently, the phosphor with the amorphous layer may be mixed with a binder and a solvent to form a paste phase composition. The paste phase composition may be screen printed with a screen mesh onto the emission cells 226. Next, the screen-printed composition may be dried and sintered to form a phosphor layer in the emission cells 226. The drying temperature may be in the range of about 100° C. to about 150° C. The sintering temperature may be in the range of about 350° C. to about 600° C., and preferably about 450° C., in order to remove organic materials from the paste phase composition.
The binder employed to form the phosphor layer may be ethyl cellulose, and the amount of binder may be in the range of about 10 to about 30 parts by weight, based on 100 parts by weight of the phosphor with the amorphous layer. An amount of binder below about 10 parts by weight based on 100 parts by weight of the phosphor with the amorphous layer may impart insufficient binding force to the phosphor layer. On the other hand, an amount of binder above about 30 parts by weight based on 100 parts by weight of the phosphor with the amorphous layer may reduce the relative amount of the phosphor with the amorphous layer and, thereby, decrease the color purity of the emitted light.
The solvent employed to form the phosphor layer may be butyl carbitol (BCA) or terpineol, and the amount of solvent may be in the range of about 70-300 parts by weight based on 100 parts by weight of the phosphor with the amorphous layer. An amount of solvent below about 70 parts by weight based on 100 parts by weight of the phosphor with the amorphous layer may cause insufficient dispersion of phosphor with the amorphous layer and excessively increase a viscosity of the paste phase composition, thereby providing non-uniform luminance and trigger printing difficulties, respectively. On the other hand, an amount of solvent above about 300 parts by weight based on 100 parts by weight of the phosphor with the amorphous layer may provide a low amount of phosphor with an amorphous layer per unit area, thereby decreasing the luminance of the PDP.
The viscosity of the paste phase composition may be in the range of about 5,000 cps to about 50,000 cps, and preferably about 20,000 cps. When the viscosity of the paste phase composition is less than about 5,000 cps, the printing solution may leak out of the emission cells during the printing process, thereby providing non uniform printed phosphor layers in terms of thickness and location precision. On the other hand, when the viscosity of the paste phase composition is greater than about 50,000 cps, the viscosity of the paste may be too high, thereby rendering the printing difficult.
The red and blue phosphor layers 225a and 225c of the PDP may be any red and blue phosphors as determined by one of ordinary skills in the art. For example, the red phosphor may be (Y,Gd)BO3:Eu or Y(V,P)O4:Eu, and the blue phosphor may be BaMgAl10O17:Eu or CaMgSi2O6:Eu.
The front panel 210 of the PDP may include a transparent front substrate 211, e.g., a glass substrate, a plurality of pairs of sustain electrodes 214 disposed on a lower surface 211a of the front substrate 211 and positioned along the emission cells 226, a front dielectric layer 215 on the front substrate 211, such that the plurality of pairs of sustain electrodes 214 are between the front dielectric layer 215 and the front substrate 211, and a protective layer 216. The front substrate 211 may have high light transmittance.
The rear panel 220 may include a transparent rear substrate 221, e.g., a glass substrate, in parallel to the front substrate 211, a plurality of address electrodes 222 positioned on a front surface 221 a of the rear substrate 221 and perpendicularly to the plurality of pairs of sustain electrodes 214, a rear dielectric layer 223 covering the address electrodes 222, and a plurality of barrier ribs 224 positioned on the rear dielectric layer 223 and defining the plurality of emission cells 226.
The address electrodes 222 of the rear panel 220 may be formed of a metal having high electrical conductivity, e.g., aluminum (Al). The address electrodes 222 may be used with a sustain electrode 212 to generate an address discharge. The address discharge may be a discharge employed to select emission cells 226 to be activated, i.e., emit light, by a sustain discharge, as will be described in detail below.
The rear dielectric layer 223 of the rear panel 220 may be on the address electrodes 222 to minimize collision between the address electrodes 222 and charged particles generated during the address discharge. The rear dielectric layer 223 may be formed of a dielectric material capable of inducing discharged particles, e.g., lead oxide (PbO), bismuth oxide (B2O3), silicon oxide (SiO2), and so forth.
The barrier ribs 224 of the rear panel 220 may be positioned to define the emission cells 226 therebetween. Accordingly, the barrier ribs 224 may be interposed in a discharge space between the front substrate 211 and the rear substrate 221. The barrier ribs 224 may minimize contact between adjacent emission cells 226 and enlarge a surface area of phosphor layers 225 applied inside the emission cells 226. The barrier ribs 224 may be formed of glass including any suitable property enhancing material, e.g., lead (Pb), boron (B), silicon (Si), aluminum (Al), or oxygen (O), a filler, e.g., zirconium oxide (ZrO2), titanium oxide (TiO2), or aluminum oxide (Al2O3), and/or a pigment, e.g., chromium (Cr), copper (Cu), cobalt (Co), iron (Fe), or titanium oxide (TiO2).
The pairs of sustain electrodes 214 of the front panel 210 may extend along the emission cells 226 and perpendicularly to the address electrodes 222. The pairs of sustain electrodes 214 may include first, i.e., Y electrodes, and second, i.e., X electrodes, sustain electrodes 212 and 213 at equal intervals, so that each second sustain electrode 213 may be positioned between two first sustain electrodes 212 and parallel thereto. Application of voltage to the first and second electrodes 212 and 213 may generate a potential difference therebetween and, thereby, trigger a sustain discharge.
The first and second electrodes 212 and 213 may include first and second transparent electrodes 212b and 213b, respectively, and first and second bus electrodes 212a and 213a, respectively. The first and second bus electrodes 212a and 213a may be used without the first and second transparent electrodes 212b and 213b, respectively, to form a scanning electrode and a common electrode.
The first and second transparent electrodes 213b and 212b may be formed of a transparent conductive material, e.g., indium tin oxide (ITO), so that light emitted from the phosphor can be transmitted towards the front substrate 211 without being blocked. However, formation of the first and second transparent electrodes 213b and 212b of a transparent conductive material, such as ITO, may impart high resistance thereto, thereby triggering a large voltage drop in a lengthwise direction of the transparent electrodes 213b and 212b, increase in power consumption of the PDP, and decrease in a response speed of images. Accordingly, the first and second bus electrodes 212a and 213a may be formed of a highly conductive metal, e.g., silver (Ag), on outer edges of the first and second transparent electrodes 212b and 213b, respectively.
The front dielectric layer 215 of the front panel 210 may be disposed on the pairs of sustain electrodes 214 to prevent a direct electrical connection between the first and second electrodes 212 and 213, and to prevent collisions between charged particles with the sustain electrodes 214 during the sustain discharge. The front dielectric layer 215 may be formed of a dielectric material with a high light transmittance, e.g., lead oxide (PbO), bismuth oxide (B2O3), silicon oxide (SiO2), and so forth.
The protective layer 216 of the front panel 210 may be formed on the front dielectric layer 215. The protective layer 216 may shield the front dielectric layer 215 from electron collisions and secondary electrons during the sustain discharge. The protective layer 216 may be formed of magnesium oxide (MgO).
The emission cells 226 of the PDP may be filled with a discharge gas, e.g., neon (Ne), xenon (Xe), or a mixture thereof. For example, if a gaseous mixture of neon and xenon is used, the xenon gas may be used in an amount of about 5%-10% of the gaseous mixture. Additionally, a portion of the neon gas may be replaced with a helium (He) gas.
The decay time of the PDP according to an embodiment of the present invention may be less than about 1 ms, and preferably in a range of about 400 μs to about 1 ms. The color temperature of the PDP may be about 8500 K, and the PDP may exhibit white color coordinate of (x=0.285, y=0.300) based on a CIE (Commission Internationale de l'Eclairage) color system.
The present invention will be described in further detail with reference to the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention.
zinc (Zn), silicon (Si), and manganese (Mn) in a mole ratio of 2:1:0.11 were mixed and ground to form a phosphor mixture. The phosphor mixture was placed in a crucible and thermally treated at 1550° C. in an electric furnace for 5 hours at air atmosphere. The thermally treated phosphor mixture was further thermally treated at 1,200° C. for 10 hours at an atmosphere of 5% of H2 and 95% of N2 to form a Zn2SiO4:Mn phosphor.
Subsequently, 0.05 parts by weight of aluminum oxide (Al2O3) was adsorbed to a surface of 100 parts by weight of the Zn2SiO4:Mn phosphor by ion adsorption method to form a Zn2SiO4:Mn phosphor with an amorphous layer with an average particle diameter of 3.0 μm and an average amorphous oxide layer thickness of about 2-5 nm.
Next, 40 wt % of the Zn2SiO4:Mn phosphor with an amorphous layer, 8 wt % of ethyl cellulose, and 52 wt % of terpineol were mixed to form a phosphor layer composition.
The phosphor layer composition was screen printed onto emission cells of a PDP, dried, and sintered at 480° C. to form a green phosphor layer. The PDP included a discharge gas having a mixture of 93 wt % of Ne and 7 wt % of Xe.
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.05 parts by weight of lanthanum oxide (La2O3), as opposed to aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.5 parts by weight of yttrium oxide (Y2O3), as opposed to aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.03 parts by weight of aluminum oxide (Al2O3), as opposed to 0.05 parts by weight of aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.3 parts by weight of yttrium oxide (Y2O3), as opposed to aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.1 parts by weight of lanthanum oxide (La2O3), as opposed to aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 1 part by weight of yttrium oxide (Y2O3), as opposed to aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that an amorphous oxide layer, i.e., aluminum oxide (Al2O3), was not adsorbed to the Zn2SiO4:Mn phosphor.
The green phosphor layer was prepared in a same manner as the green phosphor layer of Example 1, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.005 parts by weight of aluminum oxide (Al2O3), as opposed to 0.05 parts by weight of aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Comparative Example 2, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.005 parts by weight of lanthanum oxide (La2O3), as opposed to 0.005 parts by weight of aluminum oxide (Al2O3).
The green phosphor layer was prepared in a same manner as the green phosphor layer of Comparative Example 2, with the exception that the Zn2SiO4:Mn phosphor was formed with 0.005 parts by weight of yttrium oxide (Y2O3), as opposed to 0.005 parts by weight of aluminum oxide (Al2O3).
All green phosphor layers obtained in Examples 1-7 and Comparative Examples 1-4 were tested to determine a zeta potential and a relative luminance. A thickness of each amorphous oxide layer in Examples 1-7 was determined from Transmission Electron Microscopy (TEM) images.
A zeta potential was determined as follows. Each of the phosphor layers prepared in Examples 1-7 and Comparative Example 1-4 was dispersed in pure water (pH: 5.8) and subjected to ultrasonic waves for about 2 minutes. Next, each sample was loaded into a Zetamaster device (MALVERN Co.) to measure a zeta potential. The zeta potential of each sample was measured five times and an average seta potential was calculated and reported.
A relative luminance of each sample was measured using CA100 CRT color analyzer (MINOLTA Co.).
The green phosphor layers obtained in Examples 1-7 are illustrated in
As can be seen in Table 1, the green phosphor layers prepared according to Examples 1-7 exhibit positive zeta potential values, while the green phosphor layers prepared according to Comparative Examples 1-4 exhibit negative zeta potential values. Accordingly, green phosphor layers prepared according to an embodiment of the present invention, e.g., Examples 1-7, may provide improved brightness, minimized permanent afterimage, and increased lifespan.
Additionally, as can be seen in
Accordingly, a PDP including green phosphor layers prepared according to an embodiment of the present invention may exhibit enhanced and uniform luminance, in addition to improved overall life span of the PDP. In particular, the green phosphor layers according to an embodiment of the present invention may include an amorphous oxide layer to improve discharge and luminous properties and to minimize deterioration of the phosphor due to ion bombardments.
By using the phosphor with the amorphous layer prepared according to an embodiment of the present invention, surface charge properties of the green phosphor layer in a PDP may be improved and, thereby, the panel discharge voltage may be controlled to provide uniform luminance levels of red and green lights, i.e., minimize or eliminate low gray-level and low discharge problems. Additionally, the amorphous oxide layer adsorbed to the core phosphor may shield the resultant phosphor with the amorphous layer/and, thereby, minimize deterioration of the phosphor with the amorphous layer due to ion bombardment. Minimized phosphor deterioration may provide a PDP with a high luminance retention rate and, therefore, enhanced lifespan. In particular, a permanent afterimage initiation time of a PDP may be extended.
Exemplary embodiments of the present 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 present invention as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0037715 | Apr 2006 | KR | national |
