WO2013171660A1

WO2013171660A1 - Light-emitting device comprising an electroluminescent metal-organic framework

Info

Publication number: WO2013171660A1
Application number: PCT/IB2013/053889
Authority: WO
Inventors: Frederik Kapteijn; Jorge Gascon; Hossein KHAJAVI; Patrick John BAESJOU; Abraham Rudolf Balkenende; Johan Hendrik KLOOTWIJK; Hendrik Adrianus Van Sprang
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-05-14
Filing date: 2013-05-13
Publication date: 2013-11-21
Also published as: WO2013171659A1

Abstract

The invention relates to a light-emitting module comprising a light- generating layer on a carrier substrate, wherein the light- generating layer contains an electroluminescent compound comprising a metal-organic framework. The light-emitting module further comprises first and second electrodes between which a voltage can be applied to generate an electric field in at least a part of the light- generating layer. In operation the light-emitting module generates light from an emissive volume of the light- generating layer, wherein at least a part of the projected area of the emissive volume on the carrier substrate does not overlap with a projected area of one of the first and second electrodes on the carrier substrate. The light-emitting module of the invention can be easily manufactured with electrodes on only one side of the light- generating layer, and it allows the use of standard electrodes that do not necessarily have to be transparent.

Description

Light-emitting device comprising an electroluminescent metal-organic framework

FIELD OF THE INVENTION

The invention is directed to a light-emitting module having a light- generating layer containing an electroluminescent compound comprising a metal-organic framework, and to a light-emitting device comprising the light-emitting module. BACKGROUND OF THE INVENTION

Electroluminescent device technology forms a major opportunity for advanced materials development impacting a large number of technology-based applications. These, for example, include flat panel displays which offer significant advantages over liquid crystal displays including much lower power requirements, improved definition, broader viewing angles and faster response times. The technology for electroluminescent devices offers the potential for lower cost lighting sources compared to incandescent lighting as well as fluorescent lighting applications.

Organic light-emitting diodes (OLEDs) based on electroluminescent organic molecules (also known as small molecule OLEDs or SMOLEDs) are being commercialized to replace liquid crystal displays based on lower power requirements, faster response times, better definition and also easier fabrication.

OLEDs may also be based on electroluminescent polymeric materials. Such OLEDs are also known as polymer light-emitting diodes or PLEDs. The use of

electroluminescent polymeric materials enables the manufacture of flexible OLEDs using roll-to-roll wet chemical processing techniques such as inkjet printing.

The potential for flexible OLEDs is considered to be large offering unique flat or contoured display panels. The development of PLEDs has focused on polymeric materials which exhibit electroluminescence. These materials are generally conjugated polymers, such as poly(phenylene vinylene), polyfluorenes, polyphenylenes, polythiophenes and

combinations of such structures.

Furthermore, a large number of low molecular weight compounds exists which exhibit fluorescence and electroluminescence. Some of these materials are commonly referred to as laser dyes. Many of these compounds have very high fluorescence and electroluminescence efficiencies. However, the properties desired for light-emitting devices are generally only observed in solution or at low levels of doping in electro-optical or electro-active polymers. In the solid state, these materials can crystallize and lack the mechanical integrity to be utilized in PLEDs or SMOLEDs. Additionally (and more importantly), their excellent fluorescence and electroluminescence properties are lost upon crystallization. These problems have been well documented in various reviews on the subjects of materials for light-emitting devices.

Some attempts have been made to combine different components in order to profit from the advantages of each component. For example, light-emitting devices have been proposed wherein a polymer matrix hosts an emitter guest material, such as a light-emitting dye or light-emitting polymer. Another example of the combination of different components is the use of organic/inorganic hybrid materials, such as hybrid nanocrystal PLEDs, for example as described by Colvin et al (Nature 1994, 370, 354-357).

A metal-organic framework is a compound that typically comprises an organic structure coordinated to at least one metal ion or cluster. Such metal-organic frameworks have been described in, for example, US-A-5 648 508 and EP-A-0 790 253. More recently, several reviews have been published on the topic. Cui et al (Chem. Rev. 2012, 112,

1126-1162) published a review article concerning luminescent functional metal-organic frameworks. These materials are said to be very promising as multifunctional luminescent materials, such as for applications in light-emitting and display devices. In this review article it is mentioned that it is theoretically feasible to incorporate nanoscale electroluminescent metal-organic frameworks between two conductors to provide an electroluminescent device. However, it is mentioned that the realization of such important functionality first requires the realization of electroluminescent metal-organic frameworks.

Llabres I Xamena et al (J. Phys. Chem. C 2007, 111, 80-85) discloses the use of metal-organic framework compound MOF-5 as component in an electroluminescence cell. MOF-5 has a three-dimensional structure consisting of zinc oxide structural units that are coordinated to benzene 1,4-dicarboxylate as organic structural units. In the

electroluminescence cell a uniform layer of 50 micrometers thickness comprising MOF-5 and DMF is sandwiched between a transparent ITO electrode and an aluminium counter electrode. When a square AC voltage is applied between the two electrodes, electroluminescence from the cell can be observed, originating from the zinc oxide structural units.

Further to the above there remains a need for further light-emitting modules that can be applied in light-emitting devices.

It is an object of the invention to address the aforementioned need and to provide a light-emitting module, which in turn can be incorporated in a light-emitting device.

SUMMARY OF THE INVENTION

In a first aspect of the invention, the object is achieved by a light-emitting module comprising a light- generating layer on a carrier substrate, wherein the light- generating layer contains an electroluminescent compound comprising a metal-organic framework. The light-emitting module further comprises first and second electrodes between which a voltage can be applied to generate an electric field in at least a part of the light- generating layer, and to generate light from an emissive volume of the light- generating layer. In the light-emitting module of the invention, at least a part of the projected area of the emissive volume on the carrier substrate does not overlap with a projected area of one of the first and second electrodes on the carrier substrate.

In the light-emitting module of the invention a light- generating layer comprising an electroluminescent compound is provided on a carrier substrate. The light- generating layer may either be provided directly on the carrier substrate, or with one or more intermediate layers in between. When a voltage is applied between the first and second electrodes, an electric field is generated in at least a part of the light- generating layer, so that the

electroluminescent compound in the layer is excited, and the light-emitting module starts to emit light. The part of the light- generating layer from which the emitted light originates is referred to as the emissive volume of the light- generating layer. Each of the first electrode, the second electrode, and the emissive volume of the light- generating layer, has a projected area on the carrier substrate. The term "projected area" refers to the two-dimensional area measurement of a three-dimensional object by projecting its shape on a plane in a direction parallel to the surface normal of the plane. In this case, the three-dimensional object is an electrode or an emissive volume, and the plane is formed by the carrier substrate of the light-emitting module. According to the invention, at least a part of the projected area of the emissive volume does not overlap with a projected area of one of the first and second electrodes. In other words, when the light-emitting module is in operation and light is emitted by the light- generating layer, at least a part of the light- generating layer has at least one side that is not covered by an electrode, so that light from this part of the light- generating layer can exit the light-emitting module without having to pass through an electrode. This represents an advantage of the light-emitting module according to the invention, in that electrodes may be used that do not have to be at least partially transparent to allow light to exit the light-emitting module. Instead, common electrodes such as aluminium electrodes may be used. It has been found that with the light-emitting module of the invention, a homogenous emission of can be obtained from an emissive volume of the light- generating layer without having to sandwich this emissive volume between two electrodes, which would be required for other types of light-emitting modules based on electroluminescent compounds.

The carrier substrate can be any kind of substrate on which electrodes can be provided, and that can subsequently be provided with a light- generating layer. The carrier substrate can be either small or large, such as a panel or a wall.

In an embodiment of the light-emitting module of the invention, the first and second electrodes are provided on the same side of the light- generating layer. This embodiment is advantageous from the point of view of manufacturability. One can simply provide two electrodes on a carrier substrate, cover the two electrodes with a light- generating layer containing an electroluminescent compound comprising a metal-organic framework, and by applying a voltage between the electrodes the light- generating layer will

homogeneously emit light. In this embodiment the first and second electrodes may have any shape, for example they may be formed as interdigitated electrodes.

In an embodiment of the light-emitting module of the invention, the first and second electrodes are provided on opposite sides of the light- generating layer, wherein at least one of the first and second electrodes is confined to an edge area of the light- generating layer. In this embodiment, the first and second electrodes may be formed as strips that are each located at an edge of the light- generating layer, for example at the same edge of the light-generating layer. In this embodiment, the first electrode may also be shaped as a plane, with the second electrode being shaped as a frame, wherein the perimeters of the plane and the frame are substantially aligned to each other. Alternatively, both the first and the second electrode may be shaped as a frame, wherein the perimeters of the two frames are substantially aligned to each other.

This particular electrode layout may be used in a photoframe device, wherein the second electrode is comprised in the frame and the first electrode is provided on the backplane of the photoframe device, with the light- generating layer in beween.

In the light-emitting module of the invention, the metal-organic framework may comprise metallic structural units linked by organic structural units, wherein the

electroluminescent compound further comprises a luminescent moiety that is comprised in at least a part of the organic structural units, and/or resides in a pore of the metal-organic framework, and/or is grafted to a coordinatively unsaturated metal site of the metal-organic framework.

The luminescent moiety is chosen from the group consisting of inorganic compounds, inorganic-organic compounds such as metal-organic compounds, and organic compounds.

In the context of the present invention, the term "metal-organic framework" refers to a one-, two-, or three-dimensional coordination polymer including metallic structural units (sometimes also referred to as "inorganic connectors") and organic structural units (sometimes also referred to as "linkers"), wherein at least one of the metallic structural units is chemically bonded to at least one bi-, tri-or poly-dentate organic structural unit. It is noted that a "metallic structural unit" may refer to any structural unit comprising a metal or a metal oxide, and that an "organic structural unit" may also refer to a modified unit that contains an inorganic moiety coupled to an organic moiety.

In the context of the present invention, the term "luminescent moiety" refers to a moiety or compound which is capable of emitting light, for example by fluorescence or by phosphorescence, or by both.

In the context of the present invention, the term "pore " refers to any kind of opening in the metal-organic framework that contributes to the framework's porosity.

In the context of the present invention, the term "metal-organic compound" refers to a compound comprising one or more metal ions surrounded by organic ligands. Such metal-organic compounds are sometimes also referred to as "coordination complexes" or "coordination compounds" .

In the light-emitting module of the invention, the electroluminescent compound may comprise a combination of a luminescent moiety and a structured support in the form of a metal-organic framework. The luminescent moiety may be chemically combined with the organic structural units of the metal-organic framework, or it may reside within pores of the metal-organic framework as a guest molecule, or it may be grafted to the metallic structural units of the metal-organic framework, or any combination of these options.

The metal-organic framework comprised in the light-emitting module of the invention may comprise a single type of metallic structural unit, or different types of metallic structural units.

The metal-organic framework comprised in the light-emitting of the invention may comprise a variety of metallic structural units. For example, at least part of the metallic structural units may comprise one or more elements selected from the group consisting of Al, Zn, Cu, Cr, In, Ga, Fe, Sc, Ti, V, Co, Ni, La, Ce, Pr, Nb, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No and Lr, such as one or more elements selected from the group consisting of Al, Zn, Ga, In, Fe, Cr and Sc, or one or more elements selected from the group consisting of Al, In, and Ga. When at least part of the metallic structural units comprise a rare earth element it is possible to tune the emission wavelength of the electroluminescent compound.

The metal-organic framework comprised in the light-emitting module of the invention may comprise a variety of organic structural units. For example, at least part of the organic structural units may comprise a moiety chosen from the group consisting of porphyrins, perylenes, and carboxylates. Examples of suitable carboxylates are

nitrogen-containing carboxylates such as pyridine-like moieties having one nitrogen atom (pyridines), two nitrogen atoms (imidazoles, bipyridines), three nitrogen atoms (triazoles) or more nitrogen atoms. Nitrogen-containing carboxylates may be used in combination with dicarboxylates and/or tricarboxylates. Further examples of suitable carboxylates are oxalic acid, malonic acid, succinic acid, glutaric acid, phthalic acid, isophthalic acid, terephthalic acid, citric acid, trimesic acid, and mixtures thereof.

Suitable examples of the light-emitting module of the invention may comprise a metal-organic framework that is based on aluminium or aluminium carboxylates as metallic structural units, such as MIL-53, MIL-69, MIL-88, MIL-96, MIL-100, MIL-101, and MIL-110, wherein the acronym "MIL" refers to "Materiaux de Vlnstitut Lavoisier" .

Particularly suitable examples of the light-emitting module of the invention comprise one or more of the metal-organic frameworks MIL-53, MIL-69, MIL-88, and MIL-101. From a practical point of view it is preferred that the light-emitting module of the invention comprises a metal-organic framework that is flexible, but it may also be rigid.

To prevent diffusion of the luminescent moiety out of the metal-organic framework, it is preferred that the luminescent moiety is chemically bonded to the metal-organic framework. Furthermore, by chemically binding luminescent moieties to the metal-organic framework it is possible to provide an electroluminescent compound with a higher content of luminescent moieties. Also, chemically binding moieties to the

metal-organic framework may result in an enhancement of luminescence through

conjugation.

In suitable examples of electroluminescent compounds wherein the luminescent moieties are chemically bonded to the organic structural units, the metal-organic framework comprises luminescent organic structural units that are the reaction product of (i) an organic structural unit provided with a functional group, and (ii) one or more luminescent moieties chosen from the group consisting of inorganic compounds, inorganic-organic compounds such as metal-organic compounds and organic compounds. Herein, the term "functional group " refers to its usual and ordinary meaning in organic chemistry, namely an

interconnected group of atoms that is responsible for a characteristic chemical reaction of the molecule to which the group is bonded. A functional group may comprise a leaving group.

The preparation of such luminescent organic structural units can be done by using various functional groups. For instance, the organic structural unit can be modified with one or more functional groups selected from the group consisting of amines, nitro groups, imines, pyridyls or derivatives thereof, haloformyls, haloalkyls, halogens including acyl halides such as acid chlorides. Good results have been achieved by modifying the organic structural unit with an amine functional group, but other functional groups may be used as well.

A functional group may be used to couple an inorganic compound, an inorganic-organic compound such as a metal-organic compound and/or an organic compound to an organic structural unit so as to produce a luminescent organic structural unit. The functional group may comprise a leaving group, which may be replaced with the inorganic compound, the inorganic-organic compound, or the organic compound.

Examples of inorganic compounds, inorganic-organic compounds, and organic compounds suitable for use as luminescent moiety are organic laser dyes and compounds that comprise a phosphorus atom, such as phosphine and phosphinates. Examples of metal-organic compounds suitable for use as luminescent moiety are compounds that comprise silver, gold, a rare earth element such as a lanthanide, or a ferrocene.

When the luminescent moiety is chemically bonded to the organic structural units of the metal-organic framework, 50 % or more of the organic structural units may be functionahzed with the luminescent moiety, such as 60 % or more or 70 % or more. For example, 70 % to 80 % or 70 % to 90 % of the organic structural units may be functionahzed with a luminescent moiety. It may also be possible that substantially all of the organic structural units of the metal-organic framework have been functionahzed with a luminescent moiety.

In an example of the electroluminescent compound of the invention, at least some of the organic structural units of the metal-organic framework have a functional group in the form of an amino group that is functionahzed with a phthalic acid, such as an amino group functionahzed with isophthalic acid, or an amino group functionahzed with terephthalic acid. It has been found that such functionahzed amino groups can be readily reacted with a suitable luminescent moiety. Examples of resulting luminescent organic structural units are those of formula (I) and formula (II) below.

In formula (I), R can be hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an amino group, an alkoxy group, an aryloxy group, a heterocyclic oxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a heterocyclic thio group or a heterocyclic group. R' can be the same as R" and can be a phenyl ring which may optionally be substituted.

In general formula (II), R can be hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an amino group, an alkoxy group, an aryloxy group, a heterocyclic oxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an alkoxycarbonylamino group, an

aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a heterocyclic thio group or a heterocyclic group. R' can be the same as R" and can be a phenyl ring which may optionally be substituted. M' is a metal ion, for example a rare earth metal ion, such as a rare earth metal ion selected from the group consisting of yttrium, lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. X¹, X², X³, X⁴, X⁵, and X⁶ can each independently be a halogen atom, such as fluorine, chlorine, or bromine. X¹, X², X³, X⁴, X⁵, and X⁶ can be the same.

The light-emitting module of the invention may comprise an electroluminescent compound wherein a luminescent moiety resides in the pores of the metal-organic framework. The luminescent moiety can, for example, be adsorbed to the inner surface of the metal-organic framework. The luminescent moiety can be intercalated after preparation of the metal-organic framework via known methods such as vapor deposition and/or adsorption and/or post-synthetic functionalization. It is also possible to prepare the metal-organic framework in the presence of a luminescent moiety which will then be incorporated

(encapsulated or embedded) in the porous structure of the metal-organic framework.

Advantageously, the size restrictions imposed by the metal-organic framework prevent (or at least reduce) the formation of crystals of the luminescent moiety. Accordingly, luminescence quenching by crystal formation is significantly reduced and relatively high luminescence quantum yields are obtained. Additionally, the close proximity and regular organization of the luminescent moieties may lead to the occurrence of charge (electron) hopping mechanisms. Furthermore, luminescent moieties can be used that lack a reactive group thereby extending the range of possible luminescent moieties that can be used in the electroluminescent compound of the invention.

When the luminescent moiety resides in pores of the metal-organic framework, the latter may be loaded with the luminescent moiety to an extent of at least 0.8 luminescent moieties per organic structural unit of the metal-organic framework.

The metal-organic framework may have a one-dimensional porous structure (at least prior to functionalization). Luminescent moieties residing in the pores of such a one-dimensional porous metal-organic framework are highly ordered. The metal organic framework host can give rise to second-harmonic generation (also known as frequency doubling). In accordance with this phenomenon, a material is capable of generating photons with twice the frequency (half the wavelength) of incident photons. The metal-organic framework may also have a two-dimensional porous structure or a three-dimensional porous structure (at least prior to functionalization).

The light-emitting module of the invention may comprise an electroluminescent compound wherein a luminescent moiety is be grafted to a free coordination site within a metallic structural unit of the metal-organic framework. When the metal-organic framework comprises metallic structural units with one or more free coordination sites, these free coordination sites can be occupied by a luminescent moiety.

The light-emitting module of the invention may comprise an electroluminescent compound that is based on abundant elements which are not (or hardly) harmful for the environment, or poisonous. The electroluminescent compound may substantially consist of elements selected from the group consisting of hydrogen, oxygen, carbon, aluminium, and phosphorus.

The light-emitting module of the invention may comprise a light-emitting layer that is formed from a blend of the electroluminescent compound with a matrix material, wherein the metal-organic framework is embedded as particles in the matrix material.

Preferably, the matrix material is at least a partially transparent material. Depending on the intended application, the matrix material may comprise one or more compounds selected from the group consisting of polymers (such as electrically conductive polymers or electrically non-conductive polymers), amalgamate pastes, and liquid electrolytes.

The matrix material may comprise one or more electrically conductive polymers. Many different electrically conductive polymers are known in the art, for example polythiophenes, polyanilines, polycarbazoles, polypyrroles, and substituted derivatives thereof. As specific examples can be mentioned poly(3-butylthiophene-2,5-diyl (optionally with a phosphor-based dopant), poly(thiophene-2,5-diyl) which may optionally be bromine terminated, poly(3,4-ethylenedioxythiophene)-polystyrenesulphonate), poly(p-phenylene vinylene), polyaniline doped with BF₃, polyphenylene sulphide, conductive nylon, polyester urethane, and polyether urethane.

The matrix material may also comprise one or more non-conductive polymers. Some examples thereof include epoxy resin without hardener and Nafion. Non-conductive polymers can be used in small scale electroluminescent devices. For example, a small scale device can be designed using point electrodes, which each are in direct contact with luminescent metal-organic framework crystals.

The matrix material may comprise a polymer that is doped with a dopant with the purpose of changing the electrically conductive properties of the matrix material.

The blend of matrix material and electroluminescent compound may comprise 2 % to 70 % of the metal-organic framework based on the total volume of the blend, such as 4 % to 40 %, for example 5 % to 30 %, or 5 % to 25 %.

The blend of matrix material and electroluminescent compound may comprise two or more electroluminescent compounds, each of the electroluminescent compounds having a different emission spectrum, wherein the different emission spectra may be partly overlapping. By selecting different emission spectra, the overall emission spectrum of the blend can be tuned to the specific needs of the user.

The blend of matrix material and electroluminescent compound may comprise further components such as conventional additives including dopants, and charge transport compounds (such as solid or liquid electrolytes). Furthermore, laser dyes may be included as optional additives for changing or tuning the wavelength of the emitted light, wherein the laser dye can be physically separate from the electroluminescent compound. An example of a laser dye that may be used for this purpose is Coumarin 540A. The light-emitting module may further comprise an auxiliary layer that is located between the light- generating layer and at least one of the first and second electrodes. An example of such an auxiliary layer is a dielectric layer, which can prevent direct interaction between the light- generating layer and the at least one of the first and second electrodes.

The light- generating layer of the light-emitting module may have a layer thickness in the range of 5 micrometers to 100 micrometers, such as in the range of 10 micrometers to 80 micrometers or in the range of 20 micrometers to 50 micrometers.

The light-emitting module of the invention may comprise additional layers, such as charge injection layers and charge transfer layers.

The light-emitting module of the invention may be prepared by a wet chemical process wherein a blend comprising the electroluminescent compound is applied as a paste.

The light-emitting module may be incorporated in a light-emitting device, together with a controller for applying a voltage between the first and second electrodes. Preferably, the controller is arranged to apply an AC voltage, for example an AC voltage having a frequency in a range between 100 Hz and 10,000 Hz. The lower limit of this frequency range is chosen to avoid flicker, and the upper limit to make optimal use of charge generation processes in the light-emitting module. The AC voltage preferably has a waveform wherein the transition between minimum to maximum takes place in a relatively short period of time, because it has been experimentally determined that for such waveforms the light-emitting device has the best performance. Examples of such preferred waveforms are a square wave, a triangle wave, and a pulsed wave. The AC voltage may consist of negative or positive voltages only, by applying a DC bias on the AC signal. This has the advantage that only one type of amplifier can be used.

The light-emitting device of the invention may be used in various applications, such as lighting applications, photovoltaic applications, and photocatalytic applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically shows an example of a preparation of a light-emitting module of the invention by a wet chemical process;

Figures 2(a) to 2(e) schematically show several layouts that are possible for light-emitting modules according to the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

An example of a preparation of a light-emitting module according to the invention by a wet chemical process is schematically shown in Figure 1.

In Figure 1(a) first and second electrodes 201 and 202, respectively, are provided by cutting a sheet of a suitable electrode material such as aluminium in two pieces. In Figure 1(b) the first and second electrodes 201 and 202 are both attached on a non-conductive epoxy support 203. In Figure 1(c) the epoxy support 203 with the first and second electrodes 201 and 202 is secured on the work surface by using chemically inert tape 204, such as Scotch tape obtainable from 3M. It is advisable that an antistatic agent such as antistatic foam cleanser is applied to the work surface prior to use. In Figure 1(d) a blend 205 is applied as a paste onto the first and second electrodes 201 and 202 using a doctor blade technique such that the blend 205 at least bridges the first electrode 201 with the second electrode 202. The blend 205 has been prepared by mixing phosphine amino MIL-53 (Al) and

poly(thiophene-2,5-diyl) (CAS No. 25233-34-5) in chloroform in a weight ratio of 1:4. Excess blend 205 and excess epoxy support 203 may be removed, together with the chemically inert tape 204, before drying and removing any remaining solvent to create a light-generating layer of about 38 micrometers thickness. In Figure 1(e) first and second contacts 206 and 207, respectively, are provided for applying a voltage between the first and second electrodes 201 and 202 to create an electric field in at least a part of the

light-generating layer. The resulting light-emitting module 200 may then be sealed (for example by lamination) for optimal protection against environmental influences.

It is noted that in the light-emitting module 200 the first and second electrodes 201 and 202 are provided on the same side of the light- generating layer that has been formed from the blend 205.

An electroluminescent compound for use in the light-emitting module according to the present invention can be prepared by using amino MIL-53 (Al) as metal-organic framework for the introduction of diphenyl phosphine oxide, which was chemically anchored at the amines to the terephthalic acid of the metal-organic framework.

The post-functionalization of the amino MIL-53 (Al) changed many aspects of the metal-organic framework structure. From high-quality X-ray diffraction patterns it was observed that the metal-organic framework lattices were permanently expanded to accommodate the organo-phosphines that were introduced. More significant, electronic changes occur through this functionalization, causing a shift and enhancement of light emission, brought about by visible light illumination.

Phosphinated amino MIL-53 (Al) can be excited with radiation of 400 nm, resulting in a light blue photoluminescence with a maximum emission at a wavelength of 466 nm. Under the same excitation conditions non-functionalized amino MIL-53 (Al) has significantly lower emission intensity with a maximum emission at a wavelength of 616 nm. When phosphine oxide functionalized amino MIL-53 (Al) is used as electroluminescent compound in the light-emitting module of the invention, electroluminescence similar to the photoluminescence described above may be obtained when a sufficient potential difference is applied. AC potential differences with peak-to-peak voltages in the range of 30 V to 600 V AC have been explored.

It was found that the device lifetime is increased if during the first operation the voltage is slowly increased to the desired long-term operating voltage, which during the lifetime of the device is preferably not exceeded.

Applying AC voltage resulted in light emission starting at about 10 V. Up to 260

V and 600 V have been tested while exposed to a non-inert atmosphere.

The emission of the light was homogeneous over the entire surface. No dark area was seen at the separation line between the two electrode surfaces.

Device efficiency was determined using an Ulbricht integrating sphere to count the photon emission rate and using the wavelength distribution, the emitted energy relative to the electrical energy input (product of current and voltage) amounted to about 1 %.

Figure 2 shows several layouts that are possible for light-emitting modules according to the invention.

In Figure 2(a), first and second electrodes 811 and 812, respectively, are present on carrier substrate 813. The first and second electrodes 811 and 812 each have the form of a strip, and they are located at opposite sides of the carrier substrate 813.

A light- generating layer 814 is provided on top of the first and second electrodes 811 and 812. Each of the first and second electrodes 811 and 812 is confined to an edge of the light- generating layer 814.

When a voltage is applied between the first electrode 811 and the second electrode 812 an electric field is generated in at least a part of the light- generating layer 814. As a result, light is generated from an emissive volume of the light- generating layer 814, wherein the emissive volume is substantially equal to the part of the light- generating layer 814 that is enclosed by the first and second electrodes 811 and 812. Each of the first electrode

811, the second electrode 812, and the emissive volume has a projected area on the carrier substrate 813. The projected area of the emissive volume only overlaps with the projected area of the first electrode 811 at an edge, while the larger part of the projected area of the emissive volume does not overlap with the projected area of the first electrode 811. The same is true for the projected area of the emissive volume relative to that of the second electrode

812. In other words, the emissive volume of the light- generating layer 814 is only covered by electrodes at two opposite edges, and only on one side of the emissive volume.

In Figure 2(b), first and second electrodes 821 and 822, respectively, are present on carrier substrate 823. The first and second electrodes 821 and 822 are formed as interdigitated electrodes, each electrode having an outer "supply" part and inner "digit" parts. A light- generating layer 824 is provided on top of the first and second electrodes 821 and 822.

When a voltage is applied between the first electrode 821 and the second electrode 822 an electric field is generated in at least a part of the light- generating layer 824. As a result, light is generated from an emissive volume of the light- generating layer 824, wherein the emissive volume is substantially equal to the part of the light- generating layer 824 that is enclosed by the outer "supply" parts of the electrodes. Each of the first electrode 821, the second electrode 822, and the emissive volume has a projected area on the carrier substrate 823. It is noted that in Figure 2(b) the various constituents are not drawn to scale, and the interdigit distance (i.e. the distance between a digit of the first electrode 821 and an adjacent digit of the second electrode 822) may be relatively large, for example in the order of 10 or 100 micrometers. Each of the first and second electrodes 821 and 822 has a projected area that overlaps only a part of the projected area of the emissive volume.

In Figures 2(a) and 2(b) electrodes are present on only one side of the light- generating layer 814 or 824. Although for practical purposes it is preferred to have both electrodes on the carrier substrate 813 or 823, for each of the layouts shown in Figures 2(a) and 2(b) the second electrode 812 or 822 may also be provided on top of the light- generating layer 814 or 824.

In Figure 2(c) first electrode 831 is present on carrier substrate 833, and has the form of a plane. Light- generating layer 834 is provided on top of the first electrode 831. Second electrode 832 is provided on top of the light-generating layer 834, wherein the second electrode 832 has the form of a frame, and wherein the perimeters of the plane and the frame are substantially aligned with each other. It is noted that the layout of Figure 2(c) is shown in an exploded view for the sake of clarity. In this Figure 2(c), first and second electrodes 831 and 832 are provided on opposite sides of the light-generating layer 834. The second electrode 832 is confined to an edge of the light- generating layer 834, leaving a central part of the light- generating layer 834 exposed.

When a voltage is applied between the first electrode 831 and the second electrode 832 an electric field is generated in at least a part of the light- generating layer 834. As a result, light is generated from an emissive volume of the light- generating layer 834, wherein the emissive volume is substantially equal to the part of the light- generating layer 814 that is enclosed by the perimeters of the first and second electrodes 831 and 832. Each of the first electrode 831, the second electrode 832, and the emissive volume has a projected area on the carrier substrate 833. The projected area of the emissive volume overlaps almost completely with the projected area of the first electrode 831. However, the projected area of the emissive volume only overlaps with the projected area of the second electrode 832 at the edges, while the larger part of the projected area of the emissive volume does not overlap with the projected area of the first electrode 832. In other words, electrodes are present on opposite sides of the light-generating layer 834, but the emissive volume of the

light-generating layer 834 is on one side only covered by an electrode at the edges.

Figure 2(d), also in exploded view for the sake of clarity, shows a layout that is comparable to that of Figure 2(c) but now the first electrode 841 also has the shape of a frame, similar to the second electrode 842. The perimeters of the two frames are substantially aligned with each other. First and second electrodes 841 and 842 are provided on opposite sides of the light- generating layer 844, and both are confined to an edge of the

light-generating layer, leaving a central part of the light- generating layer 844 exposed.

When a voltage is applied between the first electrode 841 and the second electrode 842 an electric field is generated in at least a part of the light- generating layer 844. As a result, light is generated from an emissive volume of the light- generating layer 844, wherein the emissive volume is substantially equal to the part of the light- generating layer

844 that is enclosed by the perimeters of the first and second electrodes 841 and 842. Each of the first electrode 841, the second electrode 842, and the emissive volume has a projected area on the carrier substrate 843. The projected area of the emissive volume only overlaps with each of the projected areas of the first and second electrodes 841 and 842 at the edges, while the larger part of the projected area of the emissive volume does not overlap with the projected areas of the first and second electrodes 841 and 842. In other words, electrodes are present on opposite sides of the light- generating layer 844, but the emissive volume of the light-generating layer 844 is on both sides only covered by an electrode at the edges.

In Figure 2(e) light- generating layer 854 is provided on carrier substrate 853. First and second electrodes 851 and 852, respectively, are provided against opposite side walls of the light- generating layer 854. Although both electrodes are shown to fully cover the entire width of the light- generating layer 854, this does not have to be the case and the light-generating layer 854 may also extend above and/or below the two electrodes.

When a voltage is applied between the first electrode 851 and the second electrode 852 an electric field is generated in at least a part of the light- generating layer 854. As a result, light is generated from an emissive volume of the light- generating layer 854, wherein the emissive volume is substantially equal to the part of the light- generating layer

854 that is enclosed by the first and second electrodes 851 and 852. Each of the first electrode 851, the second electrode 852, and the emissive volume has a projected area on the carrier substrate 853. The projected area of the emissive volume only overlaps with each of the projected areas of the first and second electrodes 851 and 852 at the edges, while the larger part of the projected area of the emissive volume does not overlap with the projected areas of the first and second electrodes 851 and 852.

The device layouts shown in Figures 2(c) to 2(e) may be used in a photoframe device. For example, for the layout of Figure 2(c) the second electrode 832 can be comprised in the frame and electrically isolated from the first electrode 831 that is provided on the backplane of the photoframe device.

In each of the layouts shown in Figure 2, the light- generating layers 814, 824, 834, 844 and 854 will show homogeneous emission of light upon application of a voltage between the first and second electrodes. All these layouts have the advantage that there is no need for a transparent electrode because the viewing side of the light- generating layer is completely (in Figures 2(a), 2(b) and 2(e)) or almost completely (in Figures 2(c) and 2(d)) unobstructed by an electrode surface.

Although the layouts shown in Figure 2 have symmetric electrode configurations, also asymmetric electrode configurations may be used, all being capable of providing a homogeneous emission without a relation to the relative sizes of the electrode areas.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. Light-emitting module comprising:

- a light- generating layer on a carrier substrate, the light- generating layer containing an electroluminescent compound comprising a metal-organic framework, and

- first and second electrodes between which a voltage can be applied to generate an electric field in at least a part of the light- generating layer, and to generate light from an emissive volume of the light- generating layer,

wherein at least a part of the projected area of the emissive volume on the carrier substrate does not overlap with a projected area of one of the first and second electrodes on the carrier substrate.

2. Light-emitting module according to claim 1, wherein the first and second electrodes are provided on the same side of the light- generating layer.

3. Light-emitting module according to claim 2, wherein the first and second electrodes are formed as interdigitated electrodes.

4. Light-emitting module according to claim 1, wherein the first and second electrodes are provided on opposite sides of the light- generating layer, and wherein at least one of the first and second electrodes is confined to an edge area of the light-generating layer.

5. Light-emitting module according to claim 4, wherein the first electrode is shaped as a plane, and wherein the second electrode is shaped as a frame, the perimeters of the plane and the frame being substantially aligned.

6. Light-emitting module according to claim 4, wherein the first and second electrodes are each shaped as a frame, the perimeters of the frames being substantially aligned.

7. Light-emitting module according to any of the previous claims, wherein the metal-organic framework comprises metallic structural units linked by organic structural units, and wherein the electroluminescent compound further comprises a luminescent moiety that:

(i) is comprised in at least a part of the organic structural units, and/or

(ii) resides in a pore of the metal-organic framework, and/or

(iii) is grafted to a coordinatively unsaturated metal site of the metal-organic framework.

8. Light-emitting device comprising the light-emitting module according to any of the previous claims, and a controller for applying the voltage between the first and second electrodes, wherein the voltage is an AC voltage.

9. Light-emitting device according to claim 8 wherein the AC voltage has a waveform chosen from the group consisting of square waves, triangle waves, and pulsed waves.

10. Light-emitting device according to claim 8 or 9, wherein the AC voltage has a frequency in a range between 100 Hz and 10,000 Hz.