LUMINESCENT OPTICAL DEVICE AND ILLUMINATING INK COMPOSITION

Abstract

A luminescent optical device, comprising an optical substrate that provides a wave guide, and an illuminating ink composition are disclosed. The device comprises a cured layer of said ink composition at an interface of said waveguide, substantially comprising a polymer matrix and a luminescence agent that is dispersed in said polymer matrix. The ink composition comprises a polymerizable acrylate compound, particularly a poly-di-acrylate matrix, preferably a poly-glycol di-acrylate matrix. The ink composition further contains a polymerization initiator that is configured and capable of releasing free radicals during polymerization of said acrylate compound and a polymerization promoter that comprises a thiol compound.

Claims

1. A luminescent optical device, comprising an optical substrate that provides a wave guide and a luminescent composition that is provided at an interface of said waveguide, wherein said luminescent composition substantially comprises a polymer matrix and a luminescence agent that is dispersed in said polymer matrix, wherein said luminescent composition comprises a cured ink layer, and in that said polymer matrix comprises a poly-acrylate matrix, particularly a poly-di-acrylate matrix, preferably a poly glycol di-acrylate matrix.

2. The luminescent optical device according to claim 1, wherein said substrate comprises at least a substantially transparent sheet having a main surface extending between opposite edges of said sheet, said main surface comprising said interface, in that at least one active optical component is coupled optically with at least one of said opposite edges, said optical component being one of a light source and a photo-voltaic converter.

3. The luminescent optical device according to claim 2, wherein said sheet is at least part of one of: a window pane of a window intended to be used in a facade of a building, a signage element, and a screen intended to be used in a ship, plane or vehicle.

4. The luminescent optical device according to claim 1, wherein said luminescence agent comprises one of a fluorophoric dye, quantum dots (nanocrystals) and phosphors.

5. The luminescent optical device according to claim 4, wherein said fluorophoric dye is one of an organic or organo-metallic dye.

6. The luminescent optical device according to claim 4, wherein said fluorophoric dye comprises Perylene-1,6,7,12-tetraphenoxy-3,4,9,10 tetracarboxylic acid-bis-(2′-6′ di-isopropylanilide), more particularly the fluorophoric dye that is commercially available as Lumogen F Red 305 by BASF.

7. The luminescent optical device according to claim 4, wherein said fluorophoric dye comprises benzoxanthene derivative based dye molecules.

8. The luminescent optical device according to claim 4, wherein said fluorophoric dye comprises perylene perinone based dye molecules.

9. The luminescent optical device according to claim 1, wherein said acrylate comprises a di-acrylate, preferably a glycol di-acrylate, particularly at least one of tri(propylene glycol diacrylate (TPGDA)), tri(ethylene glycol diacrylate (TEGDA)), 1,6-Hexanediol diacrylate (HDDA) and di(ethylene glycol diacrylate (DEGDA)), wherein most preferably said glycol di-acrylate comprises tri(propylene glycol diacrylate (TPGDA) or 1,6-Hexanediol diacrylate (HDDA).

10. The luminescent optical device according to claim 19, wherein the luminescent composition comprises between 0.01 and 25 wt %, particularly between 1 wt % and 20 wt %, more particularly around 10 wt %, of quantum dots as said luminescence agent.

11. The luminescent optical device according to claim 1, wherein the luminescent composition comprises between 0.01 and 5 wt %, particularly between 0.01 and 2.5 wt %, more particularly between 0.25 wt % and 1.25 wt %, even more particularly around 1 wt %, of a dye as said luminescence agent.

12. An illuminating ink composition comprising a polymerizable compound, a polymerization initiator and a luminescence agent, wherein said polymerizable compound comprises an acrylate compound, wherein said polymerization initiator is configured and capable of releasing free radicals during polymerization of said polymerizable compound, and wherein said ink composition comprises a polymerization promoter that comprises a thiol compound.

13. The-An illuminating ink composition according to claim 12, wherein said thiol compound is a thiol compound having multiple thiol functional groups.

14. The illuminating ink composition according to claim 12, wherein said thiol compound comprises 2,2′-(ethylenedioxy)diethanethiol.

15. The illuminating ink composition according to claim 12, wherein said luminescence agent comprises one of a fluorophoric dye, quantum dots and phosphors.

16. The illuminating ink composition according to claim 15, wherein said fluorophoric dye comprises an organic or organo-metallic dye, particularly a dye that is commercially available as RED 305 by BASF, a dye comprising benzoxanthene derivative or a perylene perinone based dye.

17. The illuminating ink composition according to claim 12, wherein said acrylate comprises a di-acrylate, preferably a glycol di-acrylate, particularly at least one of tri(propylene glycol diacrylate (TPGDA)), tri(ethylene glycol diacrylate (TEGDA)), 1,6-Hexanediol diacrylate (HDDA) and di(ethylene glycol diacrylate (DEGDA)), wherein most preferably said glycol di-acrylate comprises tri(propylene glycol diacrylate (TPGDA)) or 1,6-Hexanediol diacrylate (HDDA).

18. The illuminating ink composition according to claim 12, wherein the ink composition comprises between 0.01 and 25 wt %, particularly between 1 wt % and 20 wt %, more particularly around 10 wt %, of quantum dots as said luminescence agent.

19. The illuminating ink composition according to claim 18, wherein the ink composition comprises between 0.01 and 5 wt %, particularly between 0.01 and 2.5 wt %, more particularly between 0.25 wt % and 1.25 wt %, even more particularly around 1 wt %, of a dye as said luminescence agent.

20. The illuminating ink composition according to claim 12, wherein the ink composition comprises a cross-linking agent, particularly di-pentaerythritol penta-acrylate (DPPA).

21. The illuminating ink composition according to claim 12, wherein said polymerization initiator comprises at least one photo-initiator, particularly at least two photo-initiators that initiate at different wavelengths.

22. The illuminating ink composition according to claim 12, wherein said polymerization initiator comprises between 0.01 and 15 wt % diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and particularly a mixture of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) and phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide.

23. The illuminating ink composition according to claim 12, wherein said ink composition has a viscosity in a range of between 1 and 100 mPa.Math.s at an application temperature between 25° C. and 33° C., preferably between 5 and 30 mPa.Math.s at said application temperature.

24. (canceled)

25. A luminescent optical device comprising: an optical substrate that provides a wave guide; and a luminescent composition that is provided at an interface of said waveguide, wherein said luminescent composition comprises a polymerizable compound, a polymerization initiator and a luminescence agent, wherein said polymerizable compound comprises an acrylate compound, wherein said polymerization initiator is configured and capable of releasing free radicals during polymerization of said polymerizable compound, and wherein said luminescent composition comprises a polymerization promoter that comprises a thiol compound.

Description

[0027] Hereinafter, the invention will be described in further detail with reference to a specific embodiment and an accompanying drawing. In the drawing:

[0028] FIG. 1 shows the absorption and emission spectrum of Lumogen F Red 305;

[0029] FIG. 2 shows an assembly of a device according to the invention;

[0030] FIG. 3 shows a specific example of a device according to the invention; and

[0031] FIG. 4 is a graph of the minimum transmission plotted against the photon efficiency values of selected materials;

[0032] It is noted that the figures are drawn purely schematically and not necessarily to a same scale. In particular, certain dimensions may have been exaggerated to a more or lesser extent to aid the clarity of any features. Similar parts are generally indicated by a same reference numeral throughout the figures.

EXAMPLE

[0033] Preparation of the Glycol Diacrylates Fluorescent Ink Compositions

[0034] A 1.0 wt % Lumogen F RED 305 fluorescent dye is dissolved in a matrix of 1:6-7 weight mixture of di-pentaerythritol penta-acrylate (DPPA) and one of three glycol di-acrylate monomers: tri(propylene glycol)diacrylate (TPGDA), tri(ethylene glycol)diacrylate (TEGDA) and di(ethylene glycol)diacrylate. Instead of this organic dye (RED305) also quantum dots may be used as a luminescent agent in the coating. The concentration of the dye may vary preferably roughly between 0.01 and 25 wt % for quantum dots and between 0.01 and 2.5 wt % when the aforementioned dye is being used. The di-pentaerythritol penta-acrylate (DPPA) is used as a cross-linker for polymerisation of the glycol di-acrylate monomer compound into the corresponding poly-glycol di-acrylate.

[0035] The absorption and emission spectrum of the dye that is used in this example (Lumogen F Red 305) are shown in FIG. 1. This dye is based on perylene bisimides as luminescent agent. The core structure, perylene bisimide, gives an intense fluorescence and photostability, strongly dependent on the substituents. The absorbency of the dye contains three peaks (A,B,C) when the dye is dissolved in a polystyrene matrix. The absorption maxima are found at the wavelengths 442 nm (A), 553 nm (B) and 575 nm (C), with an emission maximum (E) around 640 nm.

[0036] To polymerise the monomeric mixture to form a coating, initiators are added. These molecules are capable of forming very reactive species (radicals) upon a stimulus, which initiates a chain reaction to form a cross-linked macromolecule. These initiators produce radical species under certain conditions and promote radical reactions. Next, the initiator radicals will merge with the monomer, which results in the formation of primary radicals that subsequently propagate through additional monomer units to create a polymer network.

[0037] Several ways are capable of forming these radicals, such as chemical, thermal or photo-initiation. In this example, however, photo-initiators are applied as the thermal and chemical initiators are more difficult to control and implement in the process. The reactive species created by the photo-initiators are formed by absorbing the incident UV light and photo-cleavage into the initiation of radicals. Two photo-initiators are used that initiate at different wavelengths. This results in a more controlled polymerization process of the coating. Specifically 1.0 wt % Irgacure 819 (bis(2,4,6-trimethyl(benzoyl)-phenylphospineoxide) and 2.5 wt % Irgacure 184 (1-hydroxy-cyclohexyl-phenyl-ketone) are added to the mixture.

[0038] Oxygen is found to have a significant impact on the photo-polymerization. Oxygen inhibits the polymerization by reacting with the initiator, primary and polymer radicals to form peroxy radicals. The peroxy radicals do not readily and rapidly reinitiate the polymerization. In this way, oxygen scavenges and effectively terminates radicals. With a view on a rapid solidification and low photon re-absorption, the ink is preferable applied as a relatively thin layer starting with a low velocity. Such layer is especially prone to oxygen diffusing into the layer while it polymerises and cures.

[0039] In this example the adverse effect of oxygen during polymerization is counteracted by the addition of one or more thiols to the ink composition, particularly thiols having two or more functional thiol groups. The introduction of thiols reduces the inhibiting effects of oxygen. This is due to the hydrogen atom that is taken away from the thiol by the peroxy radicals, forming a new reactive radical on the thiol. With this technique, the polymerization can be performed even in the presence of oxygen, as the reaction can continue. This renders the ink particularly suitable to be used in industrial processes and on an industrial scale.

[0040] In this example the thiols pentaerythritol tetrakis(3-mercaptopropionaat) (PETMP) and 2,2′-(ethylenedioxy)diethanethiol (EDDE) are being added to the ink composition having multiple thiol functional groups for an enhance oxygen suppression. The advantages of using these thiols is that solidification and curing of the ink may be accomplished in open air. The thermal stability increases as the number of mercapto groups increases. Increasing the thiol concentration also increases the solidification rate. The viscosity of the ink preferably below 30 mPa.Math.s. The ink has a viscosity of around 20.8 mPa.Math.s at 25° C. without the dye and initiators, and can be adjusted by changing the composition. At 50° C., the viscosity is around 7.3 mPa.Math.s. The ink compositions for the coatings that are prepared in this example, are summarized in table 1, while their luminescent performance is shown in FIG. 4.

TABLE-US-00001 TABLE 1 Weight (mg) Component DEGDA TEGDA TPGDA Monomer 3681.3 3679.6 3674.1 DPPA 554.1 550.7 548.5 Irgacure 819 49.7 49.8 50.1 Irgacure 814 125.0 124.5 124.9 EDDE 152.9 157.2 157.3 PETMP 409.8 406.5 401.4 L-RED 305 49.9 50.1 50.1

[0041] Preparation of the Optical Device:

[0042] The prepared ink composition may be applied to a suitable substrate in various manners, like spin coating, dipping and lacquering. These techniques are particularly useful for creating a continuous film of the ink, covering substantially the entire surface of the substrate. However, the ink composition of the present example was also found particularly suitable to be used for digital printing techniques, notably ink jet printing. The viscosity of the ink may be tailored to meet the specific printer equipment requirements and specifications by adjusting the amount of cross-linker in the ink. Digital printing techniques are particularly useful for creating specific patters or images on a substrate using the florescent ink composition of the present invention. In either case, the ink may be applied either directly on the substrate or indirectly through an intervening layer or foil. In the latter case the ink is first printed on a suitable carrier, for instance on a flexible foil, that is subsequently transferred to the surface of the substrate while carrying the ink layer or pattern.

[0043] In this example the ink 15 is printed on a flexible transparent foil 10 of a suitable plastic, as shown in FIG. 2. Suitable foil 15 materials are for instance poly-vinyl-butyral (PVB) or polyethylene terephthalate (PET). In this example a PVB foil 10 is being used as a first substrate. The ink 15 is printed on the foil 10 in a desired pattern or image with the help of a commercially available inkjet printer by Meyer Burger. Examples of print heads that are capable of depositing the ink are the KM512 MH (16 pL) head by Konica Minolta and the Dimatix Materials Cartridge DMC-11610 (10 pL). Printing the ink can be performed at a ink temperature as low as between 15 and 50° C., specifically around 30° C. This allows a great variety of substrate and foil materials to be used. The printed layer thickness is typically around 30 micron, but may range between 1 and 60 micron, or may even be thicker is so desired. The ink 15 is polymerized by means of a high-intensity UV-lamp (max output 5 W/cm2) underneath the substrate in open air during printing, operating the lamp at between 10 and 20% of its maximum power. The device may be post-cured subsequently, by illumination in an inert nitrogen atmosphere for about 2 minutes at an exposure of around 35 mW/cm2 UV illumination dose.

[0044] The foil 10, carrying the ink pattern 15, is subsequently laminated to a transparent substrate 30 as shown in FIG. 2. The substrate 30 is for instance a glass panel or a solid sheet of a translucent/transparent plastic material, like poly-methyl-methacrylate (PMMA), poly-carbonate (PC) or polyethylene terephthalate (PET). Other transparent or translucent substrates are however also feasible to act as a waveguide for photons re-emitted by the ink layer upon excitation by incident primary radiation (light) or for incident light coupled into the waveguide directly from one or more of the edges. In this example two sheets of glass 30,40 are used as solid substrates.

[0045] The PVB foil 10 carrying the ink pattern 15 is laminated between the two sheets of glass 30,40 using vacuum at elevated temperature. A second flexible PVB foil 20 is used to protect and seal the ink layer 15 in between the sheets 30,40. This results in a visible print and light concentrating optical assembly, see FIG. 3, of several transparent sheets or layers 10,20,30,40 enclosing a luminescent ink film or pattern 15.

[0046] The transparent foils 10,20 and glass sheets 30,40 serve as optical wave guides that capture luminescent radiation emanating from the luminescent ink 15 and guide the radiation to the side edges of the assembly 10.40. Conversely, light that is coupled in at a side edge may be guided by the same wave guides to the ink pattern 15, resulting in luminescence of the ink that is (partly) coupled out at the main surfaces of the assembly to give an illuminating pattern or image. To both ends, active optical components are provided at these side edges to interact with the luminescent pattern 15 or layer. A lights source 50 comprising one or more light emitting diodes is applied at one of the side edges, while a photo-voltaic solar cell 60 is applied at one or more of the other sides of the assemble. Alternatively a light source and converter may also be combined at one or more of the side edges.

[0047] Preferably use is made of highly efficient multi junction solar cells to convert light into electricity at at least one of the sides. In this example use is made of thin film flexible CIGS (Copper Indium Gallium Selenide) solar cells. In a practical application the glass sheets 30,40 may have a thickness of the order of a few millimetre and the assembly may advantageously be applied as a component in a window pane for use in a facade of a building to collect solar radiation. A bright light source like a LED or laser device may be used at one of the sides to convert the device into an illuminating surface or specific display.

[0048] This renders the device suitable for both illumination/signage applications, wave guiding light from the edges towards the luminescent material, and for harvesting solar energy, capturing incident sunlight and re-emitting photons to the edges where one or more photo-voltaic solar cells are attached. The first application does not in itself require the presence of solar cells, although the combination with solar cells allows the gaining and accumulation of electrical energy from incident sunlight and to use this as an (auxiliary) power source for one or more illuminating light sources. Field of use of such devices may be in auto-motive, signage and building integrated photo-voltaic's.

[0049] Performance:

[0050] In FIG. 4 the photon efficiencies are shown on the x-axis and the minimum transmission on the y-axis of the different ink composition described above. The different points that can be found in the graph are individual samples that were made by using different spin speeds, ranging from 1000 to 5000 rpm. The ink layer show a transmissivity roughly over 90%, while the photon efficiency ranges between 70% and over 95%. Clearly TPGDA is superior to the other materials in photon efficiency. The highest scores happen to be formed at spin speeds between 3000 and 4000 rpm. Thicker layer may result in lower quantum yield. This may be minimized by using quantum dot material as the luminescent compound. These materials show a quantum yield of between 60 and 80% in an acrylate ink composition according to the invention, which is very high.

[0051] Although the invention has been described hereinbefore with reference to merely a number specific examples, it will be appreciated that the present invention is by no means limited to those examples. On the contrary, many other embodiments and variation are feasible to a skilled person within the scope of the present invention.

[0052] As an example an luminescent solar concentrator device may also be assembled using fewer, more or other layers than used in the example. Particularly PMMA or poly carbonate (PC) panels may be used instead of the glass panes to save weight. The ink may also be applied directly on one or both of the solid panes in which case these panes will act as an optical wave guide. Also other flexible foils may be used for printing or coating with the ink composition. Particularly a PET foil may be used in this respect for printing. The printed PET foil may be layers with PVB foils at opposite sides while being laminated in between a set of solid transparent substrates.

[0053] As far as the luminescent composition is concerned, the invention offers a wide variety of suitable materials. As such, fluorescent dyes can be organic from the classes, but are not limited to: Xanthene derivatives: fluorescein, rhodamine, Oregon green, eosin, and Texas red; Cyanine derivatives: cyanine, indocarbocyanine, oxacarbocyanine, thiacarbocyanine, and merocyanine; Squaraine derivatives and ring-substituted squaraines, including Seta and Square dyes; Squaraine Rotaxane derivatives: SeTau dyes; Naphthalene derivatives (dansyl and prodan derivatives); Coumarin derivatives; oxadiazole derivatives: pyridyloxazole, nitrobenzoxadiazole and benzoxadiazole; Anthracene derivatives: anthraquinones, including DRAQ5, DRAQ7 and CyTRAK Orange; Pyrene derivatives: cascade blue, etc.; Oxazine derivatives: Nile red, Nile blue, cresyl violet, oxazine 170, etc.; Acridine derivatives: proflavin, acridine orange, acridine yellow, etc.; Arylmethine derivatives: auramine, crystal violet, malachite green; Tetrapyrrole derivatives: porphin, phthalocyanine, bilirubin; and perylene derivatives.

[0054] Examples of quantum dots are typically made of binary compounds such as: lead sulfide; lead selenide; cadmium selenide; cadmium sulfide; cadmium telluride; indium arsenide; indium phosphide. Quantum dots may also be made from ternary compounds such as cadmium selenide sulfide.

[0055] Further, inorganic phosphors may be used as luminescent component, usually consisting of a host material, e.g. an oxide, nitride, oxynitride, silicate, sulfide, selenide, halide or oxyhalide, doped with small amounts of activator ions like rare-earth and/or transition metal ions. Examples include Mn2+, Eu2+ and Ce3+ ions where d-electrons are involved.