Light conversion method and light emitting device

Abstract

Disclosed is a light conversion method in which light having a wavelength of 300 nm to 580 nm produced by a light source (1) converting electrical energy into light is subjected to a luminescent material (2) having graphitic-core quantum carbon dots dispersed in a matrix, said quantum carbon dots producing, in response to this illumination, red light having a wavelength of 625 nm to 740 nm.

Description

[0001] Description

[0002] Title: Light conversion method and light emitting device

[0003] Technical field

[0004] The present invention relates to a light conversion method and a light emitting device.

[0005] Prior art

[0006] Phosphor materials capable of converting blue light have been widely used since the advent of LEDs for lighting applications or imaging systems (screens). These materials generally use crystalline inorganic compounds, such as yttrium aluminum garnets (YAGs) or lutetium aluminum garnets (LuAGs). These phosphors can be doped with neodymium, chromium, ytterbium, erbium, cerium, praseodymium or gadolinium to modify their emission spectra and thus cover the entire range of visible light.

[0007] These so-called conventional phosphors have good optical properties. However, they are derived from ores and elements, some of which may become less available in the future.

[0008] US 2022 / 231202 discloses a light conversion method in which a phosphor material comprising graphitic-core quantum carbon dots that are insoluble in water and in low-polar solvents is subjected to wave light produced by LEDs.

[0009] The article by Zhan et al. titled "A solvent-engineered molecule fusion strategy for rational synthesis of carbon quantum dots with multicolor bandgap fluorescence" published in Carbon, volume 130, 2018, discloses a method for preparing carbon quantum dots.

[0010] Finally, the article by Zhu Zhijun et al. entitled “Red carbon dots: Optical property regulations and applications” published in Materials Today, volume 30, 2019, lists numerous devices comprising a light source and a phosphor material comprising graphitic-core quantum carbon dots.

[0011] Presentation of the invention There is therefore an interest in having a luminophore material capable of converting blue light in particular, without recourse to the aforementioned inorganic compounds or in smaller quantities.

[0012] Summary of the invention

[0013] The invention meets this need by proposing a light conversion method in which a luminophore material comprising graphitic core quantum carbon dots dispersed in a matrix is ​​subjected to light with a wavelength between 300nm and 580nm, produced by a light source converting electrical energy into light, the latter producing, in response to this illumination, a red light with a wavelength between 625nm and 740nm.

[0014] The invention makes it possible to emit red light under the effect of incident blue and / or green radiation and / or in the ultraviolet light range.

[0015] The quantum efficiency is preferably between 60% and 80%, depending on the wavelength.

[0016] The invention also relates, according to another of its aspects, to a light-emitting device, comprising

[0017] A light source converting electrical energy into light, emitting light with a wavelength between 300nm and 580nm, a material comprising graphitic-core quantum carbon dots dispersed in a matrix, the latter producing, in response to illumination by the light source, light, in particular red, with a wavelength between 625nm and 740nm.

[0018] Such a device can be used in the production of a lighting device or an imaging system.

[0019] H can be associated with light emitting devices emitting in green or blue, for example in order to generate white light.

[0020] Carbon dots

[0021] Carbon dots are also known by the Anglo-Saxon designation “Carbon Dots” or “CD”.

[0022] They are in the form of luminescent nanoparticles with a graphitic core, whose size is less than or equal to 50nm, and preferably less than or equal to 10nm. The carbon dots are preferably hydrophobic, which can facilitate their dispersion in a matrix polymerization precursor.

[0023] In exemplary embodiments, the carbon dots have traces of nitrogen, which originate from the synthesis process used. These traces of nitrogen can contribute to improving the emission efficiency of the carbon dots. Indeed, the nitrogen groups act as exciton traps, which results in an increase in the quantum efficiency of the carbon dots.

[0024] Carbon points can thus have a non-zero nitrogen content, in particular an atomic % content of NI of between 10 and 15%.

[0025] Carbon dots may have a non-zero oxygen content, including an atomic % Ois content of between 15 and 20%.

[0026] Carbon dots can have an atomic % Cl s content of between 65 and 75%.

[0027] The mass content of carbon dots can be between 0.01% and 0.5% relative to the total weight of the phosphor material (carbon dots plus matrix).

[0028] Matrix

[0029] The matrix can be thermoplastic or thermosetting. In particular, it can be cast or injected in a fluid state into a mold, then demolded after cooling. It can also be sprayed or deposited in the form of one or more layers by a printing process.

[0030] The matrix can still be mineral, for example glass.

[0031] The matrix can have any shape, including polyhedral, for example cubic or parallelepiped, solid or hollow cylindrical, conical, toric, among other possibilities. It can be machined, if necessary, to the desired shape.

[0032] The matrix can also be in the form of a layer serving as a binder for the carbon dots, the matrix or a precursor of the matrix being for example deposited in a fluid state in the form of an ink by a printing technique.

[0033] The matrix is ​​preferably transparent, but can be translucent.

[0034] The matrix may be colorless and the phosphor material may have a color due to the presence of carbon dots.

[0035] The matrix may further include one or more dyes. It may incorporate a light-collecting element, if applicable, or form a light guide.

[0036] The matrix occupies any volume appropriate to the conditions of use. Its thickness ranges, for example, from 1 mm to 100 mm.

[0037] The matrix can be polymeric. The polymer can be a homopolymer or a copolymer.

[0038] The polymer can be chosen from PolyVinylToluene (PVT), PolyStyrene (PS), PolyMethylAcrylic Methacrylate (PMMA), among other materials.

[0039] The matrix can contain silicone, or be made of silicone.

[0040] The matrix is ​​preferably in contact with the aforementioned light source, in particular may encapsulate it at least partially. There may also be an interface of a gas, in particular air, or vacuum between the two.

[0041] The matrix can be formed with a flat or convex or concave surface, allowing light to be concentrated or diffused, depending on the applications.

[0042] The matrix may be arranged relative to the light source so as to intercept all of the light produced by the light source or at least more than 50% of it.

[0043] Light source

[0044] The source emitting blue and / or green and / or UV light which is converted by the phosphor material according to the invention operates by converting electrical energy into light.

[0045] It can be a light-emitting diode, a discharge lamp, a flash lamp or a laser, especially a laser diode.

[0046] Preferably, the light source is an electroluminescent source, in particular comprises at least one light-emitting diode.

[0047] The light source can emit in the range 300-350nm.

[0048] The light source can emit in the range 440-575nm.

[0049] The phosphor material can emit red light whether it is illuminated by light of wavelength 300-350nm or light of wavelength 450-575nm.

[0050] Carbon dot synthesis process

[0051] Carbon dots can be produced from the degradation (e.g. hydrothermal or microwave) of precursor molecules. These precursor molecules are preferably extracted from biomass, which is an advantage given the inexhaustible nature of the resources used to produce them.

[0052] The carbon dots advantageously result from a synthesis process involving the decomposition of trinitropyrene, previously solubilized in an organic solvent, which can be toluene, dimethylformamide (DMF), or better a toluene / DMF mixture.

[0053] The presence of DMF in a DMF / toluene mixture makes it possible to obtain a better mass yield of carbon points.

[0054] Manufacturing process

[0055] The invention also relates to a method for manufacturing the luminophor material according to the invention.

[0056] This process can involve two steps.

[0057] First, the carbon dots are synthesized. At the end of this step, the carbon dots are advantageously in the form of a powder.

[0058] In a second step, this powder can be dispersed either in a lithographic resin or in a monomer. After a time of crosslinking of the lithographic resin under UV light, or a polymerization reaction of the monomer, the carbon dots are found fixed in a plastic medium constituting said matrix.

[0059] Carbon dots can be synthesized by implementing the above synthesis method, in particular a synthesis method in which the decomposition of trinitropyrene, previously solubilized in an organic solvent, is carried out, this organic solvent comprising a mixture of toluene and dimethylformamide (DMF).

[0060] As mentioned above, the matrix can be polymerized in the presence of the carbon dots. Alternatively, the matrix can be dissolved in a solution containing the carbon dots suspended in an organic solvent, and then the organic solvent is evaporated, this evaporation taking place, for example, in a mold of the desired shape.

[0061] The invention also relates to a method for manufacturing the luminophore material of a light-emitting device comprising: a light source converting electrical energy into light, emitting light with a wavelength between 300nm and 580nm, a luminophore material comprising quantum carbon dots with a graphitic core dispersed in a matrix, the latter producing light in response to illumination by the light source, in which, to manufacture the carbon dots, the decomposition of trinitropyrene is carried out, preferably previously solubilized in an organic solvent, this organic solvent preferably comprising a mixture of toluene and dimethylformamide (DMF).

[0062] Applications

[0063] The invention finds applications in many fields.

[0064] The invention thus also relates to the use of a device according to the invention for horticultural lighting.

[0065] Brief description of the drawings

[0066] The invention may be better understood by reading the detailed description which follows, non-limiting examples of its implementation, and by examining the attached drawing, in which:

[0067] [Fig 1] schematically and partially illustrates the light conversion method according to the invention,

[0068] [Fig 2] schematically and partially represents an example of a light-emitting device according to the invention,

[0069] [Fig 3] shows transmission electron microscopy (TEM) images of carbon dots (images A and B) and a diffractogram of the carbon dots (image C),

[0070] [Fig 4] is a 2D diagram representing the emission properties of an example of a phosphor material according to the invention, indicating the emission intensity and the emission wavelength as a function of the excitation wavelength

[0071] [Fig 5] schematically and partially represents an example of an imaging system comprising the phosphor material according to the invention,

[0072] [Fig 6] illustrates the XPS spectrum of the carbon dots used for light conversion (left) and the associated Carbon (C), Nitrogen (N) and Oxygen (O) content, and [Fig 7] illustrates the deconvolution of the XPS spectra associated with the carbon dots used for light conversion and the identification of the functions present in the carbon dots using fitting curves (“Fits”).

[0073] Detailed description

[0074] Figure 1 illustrates the conversion of light using a phosphor material 2 according to the invention, comprising a transparent or translucent matrix and carbon dots.

[0075] This phosphor material 2 is illuminated by a light source 1 at a wavelength λ in the blue or UV range, and re-emits light in the red at a wavelength λ2.

[0076] The phosphor material 2 is for example integrated into a lighting device as illustrated in FIG. 2, which comprises a light source in the form for example of an electroluminescent chip 1, in particular a light-emitting diode, the matrix of the phosphor material being for example cast or injected in contact with the chip.

[0077] The manufacture of the phosphor material 2 can be done in two stages.

[0078] First, the carbon dots are synthesized in the form of a powder. In a second step, this powder is dispersed in a liquid monomer in the presence of a polymerization initiator. After a waiting time necessary for the polymerization of the monomer, the carbon dots are fixed in the transparent plastic matrix. The carbon dots can be synthesized from trinitropyrene with the following formula: [Chem 1]

[0079] The synthesis is preferably carried out in DMF because it is better to obtain hydrophobic carbon points, which are easier to disperse later in the matrix medium or its precursor, for example in the monomer which serves as a precursor to the transparent plastic matrix.

[0080] A solution of trinitropyrene is prepared, for example, at a concentration of 10 mg / mL in dimethylformamide (DMF). This solution can then be placed either in a microwave oven at 200°C for 1 hour or in an autoclave at 200°C for 8 hours. At the end of the reaction, a blackish-purple solution is obtained. This solution is slowly evaporated, for example, at 70°C for 72 hours. Following the evaporation step, a black powder is collected. This black powder can be redispersed in 5 mL of ethanol. These 5 mL are then dialyzed, for example, for 24 hours in a tube specific to IkDa to remove the unreacted species. The ethanol solution containing the purified carbon dots is then evaporated, for example, at 70°C overnight.

[0081] After this final evaporation step, a black powder of purified carbon dots is obtained. It is this black powder that can then be used for the preparation of the phosphor material.

[0082] Figure 3 shows TEM images and the diffractogram of the carbon dots thus prepared. The size distribution of the carbon dots is polydisperse, ranging from a few nm to 50 nm (images A and B). The XRD analysis (image C) gives a classic diffractogram of what is generally obtained with carbon dots, with a broad peak around 25° relative to the (002) plane of the graphitic core of the carbon dots.

[0083] To produce a block of phosphor material 2, a mass of, for example, between 5 mg and 15 mg of carbon dots is taken and then dispersed in, for example, 20 mL of styrene with stirring. Then, a mass of a polymerization initiator such as benzoyl peroxide, for example, between 0 and 20 mg, is added. Then the viscous liquid is placed in a mold intended to give its shape to the phosphor material, and left to mature at a temperature of, for example, between 70°C and 110°C for a time of, for example, between 5 and 25 days. The matrix can also be dissolved in a solution containing the carbon dots suspended in an organic solvent, then this organic solvent is evaporated, this evaporation taking place, for example, in a mold of the desired shape.

[0084] Figure 6 shows the XPS spectrum of the carbon dots and their calculated content of Carbon (69.5%), Nitrogen (12.4%) and Oxygen (18.1%). The deconvolution of the peaks of the XPS spectrum presented in Figure 7 allows the identification of the various groups present on the surface of the carbon dots.

[0085] Figure 4 shows that the phosphor material can emit red light, both when excited by blue light and when excited by UV light. This figure shows that the phosphor material in this example emits visible photons at 650nm with intensity maxima for excitation ranges at 300-350nm and 450-575nm. The mechanism responsible for the luminescence of this phosphor material therefore responds to a double excitation phenomenon, which allows it to be luminescent under the effect of a UV lamp or a blue LED.

[0086] Of course, the invention is not limited to the exemplary embodiments which have just been described.

[0087] For example, the phosphor material can be used to make an imaging system, as shown in Figure 5.

[0088] In this figure, we see a support carrying a network of luminous pixels, each comprising a light source constituted for example by an electroluminescent chip 1. At least part of these sources can be covered by a layer of the phosphor material 2 according to the invention. The source 1 can emit in the blue or UV, and the presence of the phosphor material makes it possible to convert this light into red light.

[0089] Other pixels can emit in other colors, for example green and blue.

Claims

Claims 1. Light conversion method in which a luminophore material (2) comprising graphitic core quantum carbon dots, resulting from a decomposition of trinitropyrene, dispersed in a matrix, is subjected to light with a wavelength between 300nm and 580nm, produced by a light source (1) converting electrical energy into light, the latter producing, in response to this illumination, a red light with a wavelength between 625nm and 740nm.

2. Method according to claim 1, the light source (1) being an electroluminescent source, in particular comprising at least one light-emitting diode.

3. Method according to one of claims 1 and 2, the light source emitting in the range 300-350nm.

4. Method according to one of claims 1 and 2, the light source emitting in the range 450-575nm.

5. Method according to one of the preceding claims, the phosphor material (2) emitting red light whether it is illuminated by light of wavelength 300-350nm or by light of wavelength 450-575nm.

6. Method according to any one of the preceding claims, the quantum yield of the carbon dots being between 60 and 80%.

7. Method according to any one of the preceding claims, the carbon points having a non-zero nitrogen content, in particular an atomic % content of NI s of between 10 and 15%.

8. Method according to any one of the preceding claims, the carbon points having a non-zero oxygen content, in particular an atomic % content of Ois of between 15 and 20%.

9. Method according to any one of the preceding claims, the carbon points having an atomic % content of Cls of between 65 and 75%.

10. Method according to any one of the preceding claims, the mass content of carbon points being between 0.01% and 0.5% relative to the weight of the luminophor material (2).

11. Method according to any one of the preceding claims, the carbon dots being hydrophobic.

12. Method according to any one of the preceding claims, the matrix comprising or consisting of PVT, PS or PMMA or silicone.

13. Light emitting device, comprising A light source (1) converting electrical energy into light, emitting light with a wavelength between 300nm and 580nm, a luminophore material (2) comprising quantum carbon dots with a graphitic core, resulting from a decomposition of trinitropyrene, dispersed in a matrix, the latter producing in response to illumination by the light source a red light with a wavelength between 625nm and 740nm.

14. Device according to claim 13, the light source (1) being an electroluminescent source, in particular comprising at least one light-emitting diode.

15. Device according to one of claims 13 and 14, the light source emitting in the range 300-350nm.

16. Device according to one of claims 13 and 14, the light source emitting in the range 450-575nm.

17. Device according to any one of claims 13 to 16, the carbon points having a non-zero nitrogen content, in particular an atomic % content of NI s of between 10 and 15%.

18. Device according to any one of claims 13 to 17, the carbon points having a non-zero oxygen content, in particular an atomic % content of Ois of between 15 and 20%.

19. Device according to any one of claims 13 to 18, the carbon points having an atomic % content of Cls of between 65 and 75%.

20. Device according to any one of claims 13 to 19, the mass content of carbon points being between 0.01% and 0.5% relative to the weight of the material.

21. Device according to any one of claims 13 to 20, the carbon dots being hydrophobic.

22. Device according to any one of claims 13 to 21, the matrix comprising or consisting of PVT, PS, PMMA or silicone.

23. Use of a device according to any one of claims 13 to 22 for horticultural lighting.

24. A method of manufacturing the phosphor material of a light-emitting device, in particular a device according to any one of claims 13 to 22, comprising: a light source (1) converting electrical energy into light, emitting light with a wavelength between 300nm and 580nm, a phosphor material (2) comprising graphitic core quantum carbon dots dispersed in a matrix, the latter producing light in response to illumination by the light source, in which, to manufacture the carbon dots, the decomposition of trinitropyrene is carried out, preferably previously solubilized in an organic solvent, this organic solvent preferably comprising a mixture of toluene and dimethylformamide (DMF).

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