The color-tunable light emitter has a first electrode and a light-generating layer adjacent the first electrode. The light-generating layer is operable to generate light in a band of wavelengths. The color-tunable light emitter also includes an electro-optical layer, a second electrode adjacent the electro-optical layer and a corrugated metal layer between the light-generating layer and the electro-optical layer. The corrugated metal layer couples a sub-band of the light from the light-generating layer to the electro-optical layer. The sub-band has a center wavelength dependent on a voltage applied to at least one of the electrodes.

TECHNICAL FIELD

The technical field of this disclosure is light emitters, particularly, color-tunable light emitters for color displays in which the color of the light emitted by the individual light emitters is tunable.

BACKGROUND OF THE INVENTION

Color pixels used in color displays are typically formed of three light sources, or subpixels, each emitting light of a different wavelength. Typically, one subpixel emits red light, one subpixel emits green light, and one subpixel emits blue light. The apparent color of the pixel depends on the relative intensities of the three colors. The apparent color is determined by the current applied to each of the three subpixels.

Packaging the subpixels into the pixels of a display is complex and costly. Light-emitting diodes are commonly used as subpixels. The light-emitting diodes of the subpixels are each formed from different semiconductor materials, so the individual light-emitting diodes of the subpixels cannot be combined. The size of pixels must be less than the resolution of the human eye to prevent the observer from discerning the individual pixels. The subpixels must be smaller than the individual pixel to fit within the individual pixel. Each subpixel typically also includes associated electronics to enable the subpixel to be individually addressable.

Use of subpixels emitting light at a particular wavelength also causes problems with color quality as the display ages. As light-emitting diodes age, the intensity emitted for a given applied current changes. Red, green, and blue light-emitting diodes typically age at different rates. Because the apparent color of the pixel depends on the relative intensities of the three colors and the intensity of the three light-emitting diodes shifts with time, the apparent color for a given relative current profile will shift over time.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a color-tunable light emitter operable to generate light whose color depends on an applied voltage. A light-generating layer generates light in a band of wavelengths. A sub-band of this light is coupled to an electro-optical layer by plasmons generated in a corrugated metal layer disposed between the light-generating layer and the electro-optical layer. The sub-band has a center wavelength determined by the refractive index of the electro-optical layer. The light coupled to the electro-optical layer passes through the electro-optical layer and is emitted by the color-tunable light emitter. Changing the electric field applied to the electro-optical layer changes the index of refraction of the electro-optical layer, which changes the center wavelength of the sub-band of light coupled through the corrugated metal layer. This changes the color of the light emitted by the color-tunable light emitter. Thus, the electric field applied to the electro-optical material tunes the color of the light emitted by the color-tunable light emitter.

One aspect of the present invention provides a color-tunable light emitter that includes a first electrode and a light-generating layer adjacent the first electrode. The light-generating layer is operable to generate light in a band of wavelengths. The color-tunable light emitter also includes an electro-optical layer, a second electrode adjacent the electro-optical layer, and a corrugated metal layer between the light-generating layer and the electro-optical layer. The corrugated metal layer couples a sub-band of the light generated by the light-generating layer to the electro-optical layer. The sub-band has a center wavelength dependent on voltage applied to at least one of the electrodes.

Another aspect of the invention provides a method of generating color-tunable light. In the method, an electro-optical layer and a corrugated metal layer are provided. The corrugated metal layer is juxtaposed with the electro-optical layer. The corrugated metal layer is illuminated with light in a band of wavelengths. A sub-band of the light is coupled through the corrugated metal layer to the electro-optical layer. The refractive index of the electro-optical layer is adjusted to tune the center wavelength of the sub-band of light coupled through the corrugated metal layer.

Another aspect of the invention provides a color display. The color display has opposed electrodes, and a layer structure comprising a light-generating layer, an electro-optical layer and a corrugated metal layer between the electrodes. At least one of the electrodes is composed of electrode segments that define respective color-tunable light emitters. The light-generating layer is operable to generate light in a band of wavelengths. The corrugated metal layer is located between the light-generating layer and the electro-optical layer, and couples a sub-band of the light generated by the light-generating layer to the electro-optical layer. The sub-band has a center wavelength. The center wavelength of each of the color-tunable light emitters depends on a voltage applied to the respective one of the electrode segments.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The invention is based on the observation that the above-described size and aging problems can be avoided by using for each pixel a single light emitter capable of emitting light in a range of colors and that does not rely on the relative light intensity from three individual light emitters, each emitting light of a single color. Such a light emitter, referred to herein as a color-tunable light emitter, is capable of emitting light of a color defined by an applied voltage. In accordance with the invention, the color-tunable light emitters used in a display are all the same and do not rely on different colored subpixels. Each color-tunable light emitter is individually addressable. Moreover, the color-tunable light emitter saves space, ages at the same rate as all the other color-tunable light emitters in the display, and maintains a consistent color quality as it ages.

FIG. 1is a schematic cross sectional view of a first embodiment of a color-tunable light emitter10in accordance with the present invention. A dielectric light-generating layer30is located adjacent a first electrode20. The light-generating layer30includes a matrix material31, such as a polymer, containing polyatomic luminescent molecules32. A second electrode70covers an electro-optical layer60. The second electrode70is transparent in the specified emission wavelength range of the color-tunable light-emitter10. A corrugated metal layer50is located between the dielectric light-generating layer30and the electro-optical layer60in contact with the electro-optical layer60. The period of the corrugations in the corrugated metal layer50is Λ.

When no voltage is applied between the first electrode20and second electrode70, no light is generated in light-generating layer30, so that the light emitter10is dark. A voltage applied between the first electrode20and second electrode70causes the light-generating layer30to generate light in a band of wavelengths that includes the specified emission wavelength range of the color-tunable light-emitter10. The band of wavelengths includes a first wavelength41, a second wavelength42, a third wavelength43, and a fourth wavelength44. The voltage excites the luminescent molecules32and causes them to generate light that they emit in random directions.

The word “light” as used in this disclosure refers to electromagnetic radiation in the wavelength range from ultraviolet to infrared. For color display applications, the wavelength range is the visible wavelength range from about 400 nm to 700 nm. Additionally or alternatively, the light emitter may be designed to emit in the ultra-violet and infrared regions.

In the absence of an electric field applied to the electro-optical layer60, the corrugated metal layer50is optically opaque in the band of wavelengths generated by the light-generating layer30, including wavelengths41through44. However, the voltage applied between the first electrode20and second electrode70that excites the luminescent molecules32also changes the index of refraction of the electro-optical layer60, which alters the cross coupling of the light generated by the light-generating layer30through the corrugated metal layer50to the electro-optical layer60in a sub-band of the band of wavelengths generated by the light-generating layer30. In the example shown inFIG. 1, the sub-band includes fourth wavelength44. Consequently, light of fourth wavelength44passes through the electro-optical layer60and the second electrode70and is output as the output light of color-tunable emitter10.

The cross-coupling in the corrugated metal layer50causes the transmission of light generated within the light-generating layer30through the corrugated metal layer50into the electro-optical layer60. This light transmission is effected by surface plasmons. A surface plasmon is a specific form of radiation in which an evanescent traveling wave is bound to a metal-dielectric interface. Cross coupling occurs when identical wave number vector components parallel to the corrugated metal layer50are supported in the light-generating layer30and in the electro-optical layer60.

The sub-band of light cross coupled through the corrugated metal layer50, passing through electro-optical layer60and the second electrode70and emitted by the color-tunable light emitter10is narrow in bandwidth. The light emitted by the color-tunable light emitter10can therefore be regarded as being monochromatic light having a wavelength equal to the center wavelength of the sub-band.

The first electrode20is a layer of a conductive material, such as aluminum, copper, or silver, having a thickness in the range from about 50 m to about several millimeters.

The light-generating layer30has a thickness in the range from about 50 nm to about 1,000 nm. Polyatomic luminescent molecules32are molecules that can be excited from the ground state to an excited state. Photons are emitted as the molecules revert to their ground state. The emitted light is called luminescence. Specifically, the emitted light is called electroluminescence when the molecules are excited by an electric field. The emitted light is called photoluminescence when the molecules are excited by absorption of photons, such as by optically pumping the photo-luminescent material. The light is called cathode-luminescence when the molecules are excited by bombardment with electrons in an electron beam.

Molecules that can be used as luminescent molecules32in the light-generating layer30include quinine, fluorescein, rhodamine B, and polynuclear aromatic hydrocarbons, such as anthracene and perylene. Suitable emissive polymer materials, in which at least 1% of the input electrical energy is converted to light, include poly p-phenylene vinylene (PPV) and classes of soluble conjugated polymers including the polyfluorene family, such as poly(9,9′-dioctylfluorene). The electrical properties of the polymer, such as band gap, electron affinity, and charge transport, can be tuned by modifying the constituent groups in the polymer and/or the molecular weight. The rheological properties, such as viscosity and solubility, can also be tailored in this manner for the desired application and deposition method. A broad spectral range can be obtained by blending different polymers together or by changing the chemical composition. Phosphors for cathode-luminescence can be chosen from several chemical compositions, including Y2O3:Eu, (Y,Gd)BO3:Eu, Zn2SiO4:Mn, BaO.6Al2O3:Mn and BaMg2Al16O27:Eu, which are commercially available from Phosphor Technology Ltd.

The material of the corrugated metal layer50is silver, gold, copper, platinum, or combinations thereof. The corrugated metal layer50has a thickness of about 50 nm and its grating period Λ is in the range from about 0.5 μm to about 20 μm.

The second electrode70is a layer of a conductive material, such as indium tin oxide, that is transparent in the specified emission wavelength range of the color-tunable light-emitter10having a thickness in the range from about 0.1 μm to about 1 μm.

The electro-optical layer60is a layer of electro-optical material such as nematic liquid crystal, electro-optic semiconductor, lithium niobate, or lithium tantalate. In one embodiment, the electro-optical material is a nematic liquid crystal material encapsulated in a porous silicon matrix. The electro-optical layer60has a thickness in the range from about 0.5 μm to about 1.0 μm. In one embodiment, applying an electric field strength about 107V/m across the electro-optical layer60changes the index of refraction n of the electro-optic material by 0.20.

Surface plasmons can be generated over a broad range of wavelengths. The exact range depends on the spectral characteristics of the surface plasmon excitation mechanism. When conditions are appropriate to support surface plasmons having the same wavelength on both sides of the corrugated metal layer50, as will be described below with reference toFIG. 2, surface plasmons supported at the interface between the corrugated metal layer50and the light-generating layer30excite surface plasmons at the same energy state on the opposite side of the corrugated metal layer50. Light in the sub-band is cross coupled across the corrugated metal layer50from the light-generating layer30to the electro-optical layer60. The cross-coupled sub-band of light propagates into and through the electro-optical layer60.

Dissimilar dielectric materials on opposite sides of the corrugated metal layer50limit the cross coupling to the above-mentioned sub-band of the band of wavelengths generated by the light-generating layer30. The center wavelength of the sub-band depends on the period Λ of the corrugated metal layer, of the corrugations of the corrugated metal layer50and the indices of refraction of the dielectric materials on each side of the corrugated metal layer. Surface plasmon cross coupling is a function of the wave number kzparallel to the corrugated metal layer50:
kz=2π(εdεm/εd+εm)1/2/λ
where λ is the wavelength of the surface plasmon, and εdis the permittivity of the dielectric material juxtaposed with the corrugated metal layer50and εmis the permittivity of the metal of the corrugated metal layer50. Index of refraction n is related to permittivity by:
n=(εd)1/2.

The electric field applied to the electro-optical layer60determines the permittivity of the electro-optical layer60and hence its index of refraction, so that the center wavelength of the sub-band of light that is cross coupled depends on the applied electric field, i.e., the voltage between the first electrode20and the second electrode70.

FIG. 2shows dispersion curves for the interface between the corrugated metal layer50and the light-generating layer30, and the interface between the corrugated metal layer50and the electro-optical layer60. The dispersion curves56and57are for the interface between the corrugated metal layer50and the electro-optical layer60at two different voltages applied between first electrode20and second electrode70. Dispersion curve56applies when the electro-optical layer60has an index of refraction n1corresponding to an applied voltage V1and dispersion curve57applies when the electro-optical layer60has an index of refraction n2corresponding to an applied voltage V2. The dispersion curve56approaches dispersion curve57, as shown by dashed arrow58, as the applied voltage is increased from V1to V2. Dispersion curve55is for the interface between the corrugated metal layer50and the light-generating layer30. Dispersion curve55is fixed, since the index of refraction of light-generating layer30does not change in response to a change in the applied voltage.

In the following description, references to the wavelength of light are to be understood to refer to the center wavelength of the sub-band of light cross coupled through the corrugated metal layer50. Surface plasmon cross coupling occurs at a wavelength λ1at which the separation between the dispersion curves55and56is equal to ±2π/Λ. As the applied voltage is changed from V1to V2, the dispersion curve56approaches dispersion curve57, and the wavelength at which the separation of dispersion curve56from dispersion curve55is equal to ±2π/Λ changes to wavelength λ2as shown by dashed arrow59. Thus, as the applied voltage is changed from V1to V2and dispersion curve56approaches dispersion curve57, the center wavelength of the cross coupled sub-band of light shifts from λ1to λ2to maintain Δkz=±2π/Λ.

In operation, the voltage applied between the first electrode20and the second electrode70excites the luminescent molecules32, generating electroluminescent light in a band of wavelengths that includes wavelengths λ1and λ2. The voltage applied between the electrodes20and70also determines the refractive index of the electro-luminescent layer60and, hence, the center wavelength of the sub-band of light cross coupled by the corrugated metal layer50from the light-generating layer30to the electro-optical layer60. Light at the wavelength satisfying the wave number differential condition Δkz=±2π/Λ is cross-coupled into the electro-optical layer60, passes through the electro-optical layer and the second electrode70and is emitted by the color-tunable light emitter10as output light. In the example shown inFIG. 1, the output light is of fourth wavelength44. Changing the voltage applied between the electrodes20and70changes the index of refraction of the electro-optical layer60, which changes the wavelength that satisfies the wave number differential condition Δkz=±2π/Λ and hence, the wavelength of the output light emitted by the color-tunable light emitter10. Thus, the wavelength of the output light emitted by the color-tunable light emitter10is tuned by the voltage applied between the electrodes.

FIG. 3, in which like elements share like reference numbers withFIG. 1, is a schematic cross-sectional view showing a second embodiment of a color-tunable light emitter11in accordance with the present invention. Light emitter11is similar to light emitter10except for a dielectric waveguide51interposed between the light-generating layer30and the corrugated metal layer50. The waveguide51is formed of dielectric material, such as fused silica or nitrides, and has a thickness in the range from about 500 nm to about 1 μm. Waveguide51supports the propagation of light in the band of wavelengths generated by the light-generating layer30, including first wavelength41, second wavelength42, third wavelength43, and fourth wavelength44. Waveguide51increases the probability that light generated by the light-generating layer30generates surface plasmons in the corrugated metal layer50by increasing the interaction between luminescent molecules32and the surface plasmons. This enhances the radiated decay mechanism resulting in the excitation of surface plasmons. The presence of the waveguide layer also prevents the quenching of the radiative decay mechanism of the luminescent molecules32. Cross coupling also occurs between the waveguide mode on one side of the corrugated metal layer to surface plasmon modes on the opposite side of the corrugated metal layer.

The waveguide51shown inFIG. 3is corrugated on both sides. This occurs as the result of forming a grating in surface of the light-generating layer30before deposition of the dielectric material to form waveguide51. In an alternative embodiment, no grating is formed in the surface of the light-generating layer30before the waveguide material is deposited. A grating pattern is then formed in the exposed surface of the waveguide51and the corrugated metal layer50deposited on the grating pattern. In this embodiment, the interface between the waveguide51and the light-generating layer30is relatively smooth. In some embodiments, the grating patterns are formed by chemical etching.

FIG. 4, in which like elements share like reference numbers withFIG. 1, is a schematic cross sectional view showing a third embodiment of a color-tunable light emitter12in accordance with the present invention. Light emitter12is similar to light emitter10except that an optical diffuser80is interposed between the electro-optical layer60and the second electrode70. Light cross coupled through the corrugated metal layer50is transmitted through the electro-optical layer60at a wavelength-dependent angle that is not necessarily normal to the surface of the second electrode70. The emission angle is randomized by the optical diffuser80, which increases the range of viewing angles of the light emitter12. Several types of diffuser are commercially available, including holographic diffusers, opal glass diffusers, and ground glass diffusers. Opal glass diffusers produce a near Lambertian source, but have high scatter loss. Ground glass diffusers are less diffusive and have less loss. Color-tunable light emitter12may additionally include a dielectric waveguide similar to dielectric waveguide51shown inFIG. 3.

FIG. 5, in which like elements share like reference numbers withFIG. 4, is a schematic cross-sectional view showing a fourth embodiment of a color-tunable light emitter13in accordance with the present invention. Light emitter13is similar to light emitter12except that optical diffuser81is located on the side of the second electrode70remote from the electro-optical layer60, instead of interposed between the electro-optical layer60and the second electrode70. Color-tunable light emitter13may additionally include a dielectric waveguide similar to dielectric waveguide51shown inFIG. 3.

FIG. 6, in which like elements share like reference numbers withFIG. 5, is a schematic cross-sectional view showing an embodiment of an optical display15in accordance with the present invention. The optical display15is composed of color-tunable light emitters13A through13D. The color-tunable light emitters13A through13D have a structure based on that of light emitter13shown inFIG. 5, but could alternatively have a structure based on those of any of the light emitters10,11, or12shown in the other figures. The light-generating layer30is located adjacent an array of first electrodes20. The first electrodes are electrically isolated from one another by insulators21. The electro-optical layer60is located adjacent an array of second electrodes70disposed opposite the array of first electrodes20. The corrugated metal layer50is located between the light-generating layer30and the electro-optical layer60in contact with the electro-optical layer. The second electrodes70are isolated from one another by insulators71. Spacers90located between the array of first electrodes20and the array of second electrodes70maintain a uniform distance between the electrodes20and70. The diffuser81overlies the second electrodes70. In an alternative embodiment, a common electrode (not shown) serves as the array of first electrodes20and no insulators21are required. In another alternative embodiment, a common electrode (not shown) serves as the array of second electrodes70and no insulators71are required.

The spacers90are dielectric beads of about equal diameter. The density of spacers90is kept to the minimum needed to provide uniform spacing of the first electrodes20from the second electrodes70over the area of the display15, because the spacers90prevent the individual light emitters where they are located from emitting light.

The optical display15is formed by forming an array of first electrodes20. In the example shown inFIG. 5the first electrodes are shown electrically isolated from one another by insulators21. In an embodiment, the electrodes are supported on a nonconductive substrate. The first electrodes20are formed by depositing a layer of a conductive material such as aluminum, copper, or gold by a deposition process such as sputtering, electroplating or electron beam evaporation.

In an embodiment, such as that shown inFIG. 5, in which a common electrode is not used as the array of first electrodes20, the first electrodes20are formed in an array by the placement of insulators21between islands of metal. The insulators are formed from silicon nitride, silicon dioxide or other dielectric materials. To form the insulators21, the layer of metal for the first electrode20is deposited on a substrate (not shown). The deposited metal layer of the first electrodes20is then coated with photoresist. The photoresist is developed to expose the metal where the insulators21are to be formed. The metal is etched by ion etching in the pattern of the insulators21. The insulators21are deposited in the etched pattern by plasma deposition, spin coating or evaporation of nitrides or fused silica. The light-generating layer30is deposited on the array of first electrodes20by a deposition process such as vacuum deposition, spin coating or printing.

A grating having a period Λ is formed in the exposed surface of the light-generating layer30. In an embodiment, the grating is formed by chemical etching or ion etching.

A thin layer of metal, such as silver or gold, is then deposited by a deposition process such as sputtering or resistive evaporation on the grating formed in the light-generating layer30to form the corrugated metal layer50.

The electro-optical layer60is then deposited over the corrugated metal layer50by a deposition process such as spin coating.

In an alternative embodiment in which the electro-optical layer60is a layer of liquid crystal material, the array of second electrodes70is formed, as will be described below. The liquid crystal material is then deposited on the array of second electrodes70by spin coating. The stack composed of the first electrode20, the light-generating layer30and the corrugated metal layer50is then inverted and placed over the electro-optical layer60deposited on the array of second electrodes70.

The array of second electrodes70is a segmented layer of transparent conductive material, such as indium tin oxide. The second electrodes70are formed in an array by the placement of insulators71between islands of metal. The insulators are formed from nitrides, fused silica or other dielectric materials. To form the insulators71, the layer of conductive material for the second electrodes70is deposited on a sacrificial substrate (not shown) or on the diffuser80. The layer of the conductive material is then coated with photoresist. The photoresist is developed to expose the conductive material where the insulators71are to be formed. The conductive material is etched by ion etching in the pattern of the insulators71. The insulators71are deposited in the etched pattern by a deposition process such as plasma deposition, spin coating or evaporation of such dielectric materials as nitrides or fused silica. When the second electrode70with insulators71is formed on a sacrificial substrate, the substrate is removed by a removal process such as chemical or ion etching.

The spacers90are evenly distributed over the surface of the array of first electrodes20before the layers30,50, and60are deposited. Alternatively, the layers30,50and60are deposited on the array of first electrodes20, and the spacers90are evenly distributed with a low area density on the surface of the electro-optical layer60. The spacers are pressed into the layers30,50and60until they contact the array of first electrodes20. In another alternative, the layers30,50and60are deposited on the array of first electrodes20, widely-separated holes having a diameter equal to that of the spacers90are etched through the layers30,50and60and the spacers90are positioned in the etched holes.

Applying a voltage between the first electrodes20and second electrodes70of each of the color-tunable light emitters13A–13D causes display15to emit output light having a wavelength that depends on the voltage applied to each of the light emitters. The voltage is typically applied using thin film transistors that individually address the first electrodes20and/or the second electrodes70of the color-tunable light emitters13A–13D. To ensure the electric field for one light emitter does not spread to adjacent light emitters, the first electrode20and second electrode70are separated by a distance that is small relative to the dimensions of the light emitter in the plane parallel to the major surface of electrodes20. These dimensions are of the order of micrometers, for example 4 μm by 4 μm. The layers between the first electrode20and second electrode70have a total thickness of about 2 μm or less, so spacers90have a diameter of about 2 μm or less. When the display15incorporates an embodiment of light emitter11shown inFIG. 3having a 1 μm-thick waveguide51, the layers between the first electrode20and second electrode70have a total thickness of about 3 μm or less. In this case, spacers90have a diameter of about 3 μm or less.

Applying different voltages to the color-tunable light emitters13A–13D in the optical display15causes the light emitters to emit light of different colors. Each of the light emitters13A–13D is individually addressable, typically by a thin film transistor circuit (not shown).

Independent control of the brightness and color of the light emitted by each of the color-tunable light emitters13A–13D can be obtained by using the corrugated metal layer50as a third electrode common to all the light emitters13A–13D. This allows independent voltages to be applied to the light-generating layer30and to the electro-optical layer60. The brightness of the light generated by the light-generating layer30of each of the light emitters13A–13D is controlled by the voltage applied between the first electrode20and the corrugated metal layer50and the color of the light emitted by each of the light emitters13A–13D is independently controlled by the voltage applied between the second electrode70and the corrugated metal layer. In an alternative embodiment, the duty cycle of a drive pulse applied to each light emitter controls the brightness while the amplitude of the drive pulse independently controls the color.

Electrode configurations different from that exemplified inFIG. 5are possible. In one embodiment, a thin film transistor circuit (not shown) is electrically connected to each of the first electrodes20, and the second electrodes70are electrically connected to a common voltage, such as ground. In another embodiment, a thin film transistor circuit (not shown) is electrically connected to each of the second electrodes70, and the first electrodes20are electrically connected to a common voltage, such as ground. In such embodiments, a common electrode may be used instead of the electrodes connected to a common voltage. In another embodiment, a thin film transistor circuit (not shown) is electrically connected to each of the first electrodes20segmented by insulators21and another thin film transistor circuit (not shown) is connected to each of the second electrodes70segmented by insulators71.

FIG. 7, in which like elements share like reference numbers withFIG. 5, is a schematic cross sectional view showing a second embodiment of an optical display16in accordance with the present invention. Optical display16is composed of color-tunable light emitters13E through13H. The color-tunable light emitters13E through13H have a structure based on that of light emitter13shown inFIG. 5, but could alternatively have a structure based on those of any of the light emitters10,11, or12shown in the other figures. The individual light emitters13E through13H are separated from each other by insulators22which extend from the first electrodes20to the second electrodes70through the light-generating layer30, the corrugated metal layer50, and the electro-optical layer60. The insulators22are formed of a nonconductive material such as silicon dioxide, silicon nitride or a polymer.

In one embodiment, an array of insulators22is formed to define an array of cavities. The light-generating material of light-generating layer30is injected into the cavities defined by the insulators22. An inkjet printing system, such as one commercially available from Seiko-Epson and Litrex Corporation (a CDT subsidiary), is used to inject the light-generating material into the cavities. A grating is chemically etched into the surface of the light-generating layer30in each cavity and the metal of the corrugated metal layer50is deposited on the surface of the gratings by a deposition process such as vacuum deposition. The electro-optical layer60is deposited on the corrugated metal layer50by a deposition process such as evaporation or ink jet deposition. The second electrodes70are deposited on the liquid crystal layer60by a deposition process such as sputtering, and the diffuser81is mounted on the second electrodes70.

Applying different voltages to the color-tunable light emitters13E–13H in the optical display16causes the light emitters to emit light of different colors. Each of the light emitters13E—13E is individually addressable, typically by a thin film transistor circuit (not shown).

Electrode configurations different from that exemplified inFIG. 7are possible. In one embodiment, a thin film transistor circuit (not shown) is electrically connected to each of the first electrodes20, and the second electrodes70are electrically connected to a common voltage, such as ground. In this embodiment, the insulator22does not extend completely through the second electrodes70so that the second electrodes are electrically interconnected. In another embodiment, a thin film transistor circuit (not shown) is electrically connected to each of the second electrodes70, and the first electrodes20are electrically connected to common voltage, such as ground. The isolator22does not extend completely through the first electrodes20so that the first electrodes are electrically interconnected.