Method for preparing pmma composite fluorescent film for converting electroluminescence of led chip into white light

Abstract

The present application relates to the preparation method of PMMA composite fluorescent film for converting electroluminescence of LED chip into white light, which is composed of two or three of blue Bi2S3 quantum dots-B-PMMA, green Bi2S3 quantum dots-G-PMMA and red Eu2(TDAP)(DMB)6(Phen)2-PMMA. The film composed of blue, green and red three colors converts the electroluminescence of ultraviolet LED chip into white light with wavelength greater than 450 nm, and the proportion reaches 98%. The film composed of green and red two colors converts the electroluminescence of blue light LED chip into white light with wavelength greater than 450 nm, and the proportion reaches 99.6%. The efficiency of the PMMA composite fluorescent film of the present application in absorbing light less than 450 nm of LED lamp or LED display is much greater than that of traditional optical filter film; and the influence on the brightness, light stability and life of LED lamp or LED display is smaller.

Description

Technical Field

[0001] This invention relates to the field of fluorescent thin film preparation technology, and in particular to a preparation technology of a polymethyl methacrylate (PMMA) fluorescent composite thin film. The thin film technology converts commercial ultraviolet LEDs into white light and blue LEDs into white light through PMMA organic-inorganic composite fluorescent thin films of three colors or two colors. It can efficiently convert light with emission wavelengths less than 450nm into white light, and can eliminate the damage to the eyes caused by ultraviolet and blue-violet light from LED lamps or LED displays. Background Technology

[0002] Light-emitting diodes (LEDs), made from semiconductors such as gallium nitride, are gradually replacing traditional fluorescent mercury lamps and are widely used in daily life and industry due to their small size, high electro-optical conversion efficiency, long lifespan, and environmental friendliness. LED displays are also widely used due to their small size, high brightness, high energy efficiency, and environmental friendliness. Currently, there are two main types of commercially available LED chips: ultraviolet LED chips with electroemission peaks of 377nm and 405nm, and blue LED chips with an electroemission peak of 450nm. LED lights and LED displays typically contain light with wavelengths less than 450nm. This blue-violet light can damage the human retina, causing eye fatigue, tearing, and myopia. Therefore, in 2019, the State Administration for Market Regulation and the Standardization Administration of China jointly issued the standard "Technical Requirements for Light Health and Light Safety of Blue Light Protective Films" (GB / T 38120-2019). This standard specifies the following requirements for the light transmittance of blue light protective films: for wavelengths between 385nm and 415nm, the light transmittance should be less than 75%; for wavelengths between 415nm and 445nm, the light transmittance should be less than 80%. Light transmittance is the ratio of transmitted luminous flux to incident luminous flux. According to the data specified in this standard, traditional blue light removal films absorb only a small portion of the light from LEDs or LED displays with wavelengths less than 450nm (only about 25% of the light greater than 450nm), allowing more than 80% of visible light greater than 450nm to pass through. The absorbed ultraviolet and blue-violet light is converted into heat, which reduces the brightness of LEDs or LED displays. The generated heat also reduces the luminous stability and shortens the lifespan of LEDs or LED displays.

[0003] Therefore, there is an urgent need for a thin-film technology that can fully absorb ultraviolet and blue-violet light with wavelengths less than 450nm from LED lamps or LED displays and convert it into visible light with wavelengths greater than 450nm, thereby eliminating the harm of these electro-optical devices to the human eye. Summary of the Invention

[0004] This invention utilizes a PMMA organic-inorganic composite fluorescent film to fully absorb light smaller than 450nm from LED lamps or LED displays, converting it into visible light with a wavelength greater than 450nm, thereby eliminating the harm to the human eye caused by these electro-optical devices. Furthermore, this invention has minimal impact on the brightness of LED lamps or LED displays. This PMMA composite fluorescent film generates less heat, thus having a smaller impact on the luminous stability and lifespan of LED lamps or LED displays. The features of this invention are illustrated below using ultraviolet LED chips and blue LED chips as substrates, respectively. Three colors of PMMA fluorescent films are used to convert the light from ultraviolet LED chips into white light with a wavelength greater than 450nm, and two colors of PMMA fluorescent films are used to convert the light from blue LED chips into white light with a wavelength greater than 450nm.

[0005] Using o-phenylenediamine to stabilize the surface energy of Bi2S3 particles, the synthesized Bi2S3 quantum dots (Bi2S3 quantum dot-2) exhibit a broad excitation absorption band of 360 nm to 475 nm, which can fully absorb the electroluminescence of ultraviolet or blue LED chips and efficiently convert it into green fluorescence (Bi2S3 quantum dot-2 is named Bi2S3 quantum dot-G in this invention, with a quantum efficiency of 51%, and a national invention patent has been applied for, 202310399204.6). Referring to the paper, a red fluorescent material Eu2(TDAP)(DMB)6(Phen)2 (TDAP = terephthaloyl-benzophenone, DBM = dibenzoylmethane, Phen = 1,10-o-phenanthroline, solid-state quantum efficiency 54%, Journal of Luminescence, 2007, 127:297–301) was synthesized. The laser spectrum of solid Eu2(TDAP)(DMB)6(Phen)2 is located in a broad excitation absorption band of 350nm to 470nm, which can fully absorb the electroluminescence of ultraviolet LED chips or blue LED chips and efficiently convert it into red fluorescence.

[0006] PMMA, also known as plexiglass, has good transmittance in the visible region and exhibits excellent stability and high strength under natural conditions. PMMA is readily soluble in CHCl3 solvent, and PMMA films can be fabricated using simple experimental methods. The material is relatively inexpensive and can be mass-produced industrially.

[0007] To achieve the above objectives, the present invention adopts the following technical solution, comprising the following steps:

[0008] a. Synthesis of blue Bi₂S₃ quantum dots (named Bi₂S₃ quantum dot-B). Bi₂S₃ quantum dot-1 was synthesized according to Chinese invention patent application 202310399204.6. 5–8 mg of 1,8-diaminonaphthalene was added to 5–25 mL of the synthesized Bi₂S₃ quantum dot-1 solution, and the pH of the solution was adjusted to approximately 7 using NaOH solution. The solution was transferred to a polytetrafluoroethylene (PTFE) reactor and reacted at 160–200 °C for 4 h. After natural cooling to room temperature, the pH of the solution after the reaction was approximately 5. Dialysis was performed using a 3500 Da semi-permeable membrane for 48 h to remove small molecules, yielding a bright blue fluorescent solution of Bi₂S₃ quantum dot-B in isopropanol. The luminescence properties of Bi₂S₃ quantum dot-B were stable in the isopropanol solution, and its absolute fluorescence quantum yield was measured to be 55%.

[0009] b. Preparation of blue Bi₂S₃ quantum dot-B-PMMA fluorescent film. 2–5 mg of Bi₂S₃ quantum dots-B were dispersed in 5–6 mL of isopropanol, and 5 mL of CHCl₃ solution containing 2–4 g of PMMA was added. The mixture was ultrasonically dispersed for 30–60 minutes. Subsequently, the mixture was poured into a petri dish and allowed to stand at room temperature for at least 24 hours to obtain a blue Bi₂S₃ quantum dot-B-PMMA fluorescent film.

[0010] c. Preparation of green Bi₂S₃ quantum dot-G-PMMA fluorescent film. 3–6 mg of Bi₂S₃ quantum dots-G were dispersed in 5 mL of isopropanol, and 5 mL of CHCl₃ solution containing 2–4 g of PMMA was added. The mixture was ultrasonically dispersed for 30 minutes. Subsequently, the mixture was poured into a petri dish and allowed to stand at room temperature for at least 24 hours to obtain a green Bi₂S₃ quantum dot-G-PMMA fluorescent film.

[0011] d. Preparation of red Eu2(TDAP)(DMB)6(Phen)2-PMMA fluorescent film. 5–15 mg of Eu2(TDAP)(DMB)6(Phen)2 was dissolved in 5–10 mL of CHCl3, and 10 mL of CHCl3 solution containing 2–6 g of PMMA was added. The mixture was ultrasonically dispersed for 30 minutes. Subsequently, the mixture was poured into a petri dish and allowed to stand at room temperature for at least 24 hours to obtain a red Eu2(TDAP)(DMB)6(Phen)2-PMMA fluorescent film.

[0012] e. Fabrication of white LEDs using ultraviolet LED chips as substrates. Blue Bi₂S₃ quantum dot-B-PMMA fluorescent films, green Bi₂S₃ quantum dot-G-PMMA fluorescent films, and red Eu₂(TDAP)(DMB)₆(Phen)₂-PMMA fluorescent films are cut into sizes slightly larger than the diameter of the ultraviolet LED chip. These films are then bonded together in the order of blue, green, and red fluorescent films using CHCl₃ solvent to form a three-layer structure. The blue PMMA fluorescent film is tightly attached to the ultraviolet LED chip. Applying a 3V DC current to the LED chip yields a white LED, effectively eliminating light smaller than 450nm from the ultraviolet LED chip.

[0013] f. Fabrication of white LEDs using blue LED chips as substrates. Green Bi₂S₃ quantum dot-G-PMMA fluorescent films and red Eu₂(TDAP)(DMB)₆(Phen)₂-PMMA fluorescent films are cut into sizes slightly larger than the diameter of the blue LED chip. The green and red fluorescent films are then bonded together using CHCl₃ solvent to form a two-layer structure. The green PMMA fluorescent film is tightly attached to the blue LED chip. Applying a 3V DC current to the blue LED chip yields a white LED, effectively eliminating light smaller than 450nm from the blue LED chip. Attached Figure Description

[0014] Figure 1 The excitation spectrum of the blue Bi2S3 quantum dot-B prepared in this invention at a detection wavelength of 483 nm and the fluorescence emission spectrum under 388 nm light excitation are shown in the illustration. The illustration shows a photograph of its blue fluorescence under 365 nm light irradiation.

[0015] Figure 2 The blue Bi2S3 quantum dot-B-PMMA fluorescent film prepared in Example 1 of this invention has an excitation spectrum at a detection wavelength of 442 nm and a fluorescence emission spectrum under light excitation at 382 nm. The illustration shows a photograph of the PMMA fluorescent film under 365 nm light irradiation.

[0016] Figure 3 The green Bi2S3 quantum dot-G-PMMA fluorescent film prepared in Example 1 of this invention has an excitation spectrum at a detection wavelength of 499 nm and a fluorescence emission spectrum under light excitation at 452 nm. The illustration shows a photograph of the PMMA fluorescent film under 365 nm light irradiation.

[0017] Figure 4 The excitation spectrum of the Eu2(TDAP)(DMB)6(Phen)2-PMMA red fluorescent film prepared in Example 1 of this invention is shown in the excitation spectrum at a detection wavelength of 612 nm and the fluorescence emission spectrum under light excitation at 388 nm. The illustration shows a photograph of the PMMA fluorescent film under 365 nm light irradiation.

[0018] Figure 5 The first embodiment of the present invention shows the electroluminescence spectrum (a) of the ultraviolet LED chip driven by a 3V DC voltage; the second embodiment shows the electroluminescence spectrum (b) of the ultraviolet LED chip converted into a white LED by sequentially using a three-layer fluorescent film structure of Bi2S3 quantum dot-B-PMMA, Bi2S3 quantum dot-G-PMMA and Eu2(TDAP)(DMB)6(Phen)2-PMMA, with visible light with wavelengths greater than 450nm accounting for 98%.

[0019] Figure 6 This is a CIE coordinate diagram of the electroluminescence spectrum of a UV LED chip converted into a white LED by sequentially using a three-layer fluorescent film structure of Bi2S3 quantum dot-B-PMMA, Bi2S3 quantum dot-G-PMMA, and Eu2(TDAP)(DMB)6(Phen)2-PMMA.

[0020] Figure 7 The electroluminescence spectrum (a) of the blue LED chip driven by a 3V DC voltage in Embodiment 2 of the present invention; the electroluminescence spectrum (b) of the blue LED chip electroluminescence converted into white LED by sequentially using Bi2S3 quantum dot-G-PMMA and Eu2(TDAP)(DMB)6(Phen)2-PMMA two-layer fluorescent films, with visible light with wavelengths greater than 450nm accounting for 99.6%.

[0021] Figure 8 This is a CIE coordinate diagram of the electroluminescence spectrum of a blue LED chip converted into a white LED by sequentially using a two-layer fluorescent film of Bi2S3 quantum dot-G-PMMA and Eu2(TDAP)(DMB)6(Phen)2-PMMA quantum dot-G-PMMA.

[0022] Figure 9 The emission spectra of the blue Bi2S3 quantum dot-B prepared in Example 1 of this invention at different excitation wavelengths are shown.

[0023] Figure 10 This is a high-resolution transmission electron microscope (HRTEM) image of the blue Bi2S3 quantum dot-B prepared in Example 1 of this invention, with the inset showing its characteristic lattice diffraction fringes.

[0024] Figure 11 This is the infrared absorption spectrum of the blue Bi2S3 quantum dot-B prepared in Example 1 of this invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, the raw materials or processing techniques used in the following embodiments and comparative examples are all conventional commercially available raw materials or conventional processing techniques in the art.

[0027] To fully convert the electroluminescence of the ultraviolet LED chip into white light with a wavelength greater than 450 nm, a PMMA blue fluorescent film needs to be added. 1,8-Diaminonaphthalene is reacted with the surface of Bi2S3 quantum dot-1 particles to stabilize their surface energy and modulate the surface energy levels of the Bi2S3 quantum dots, thus achieving a change in the fluorescence color of the Bi2S3 quantum dots from green to blue. The design and synthesis route of blue Bi2S3 quantum dot-B is as follows.

[0028] Synthesis Route 1:

[0029]

[0030] Example 1: Convert the electroluminescence of the ultraviolet LED chip into white light with a wavelength greater than 450nm.

[0031] a. Synthesis of blue Bi₂S₃ quantum dots-B. Bi₂S₃ quantum dots-1 were synthesized according to Chinese Invention Patent 202310399204.6. 8 mg of 1,8-diaminonaphthalene was added to 25 mL of the synthesized Bi₂S₃ quantum dot-1 solution, and the pH of the solution was adjusted to approximately 7 using NaOH solution. The solution was transferred to a polytetrafluoroethylene reactor and reacted at 200°C for 4 h. After natural cooling to room temperature, the pH of the solution after the reaction was approximately 5. Dialysis was performed using a 3500 Da semi-permeable membrane for 48 h to remove small molecules, yielding a bright blue fluorescent Bi₂S₃ quantum dot-B solution in isopropanol.

[0032] b. Preparation of blue Bi₂S₃ quantum dot-B-PMMA fluorescent film. 2 mg of Bi₂S₃ quantum dots-B were dispersed in 5 mL of isopropanol, and 5 mL of CHCl₃ solution containing 2.2 g of PMMA was added. The mixture was ultrasonically dispersed for 30 minutes. Subsequently, the mixture was poured into a petri dish and allowed to stand at room temperature for 24 hours to obtain a blue Bi₂S₃ quantum dot-B-PMMA fluorescent film with a thickness of 0.26 mm.

[0033] c. Preparation of green Bi₂S₃ quantum dot-G-PMMA fluorescent film. 4 mg of Bi₂S₃ quantum dots-G were dispersed in 5 mL of isopropanol, and 5 mL of CHCl₃ solution containing 2.2 g of PMMA was added. The mixture was ultrasonically dispersed for 30 minutes. Subsequently, the mixture was poured into a petri dish and allowed to stand at room temperature for 24 hours to obtain a green Bi₂S₃ quantum dot-G-PMMA fluorescent film with a thickness of 0.40 mm.

[0034] d. Preparation of a red Eu2(TDAP)(DMB)6(Phen)2-PMMA fluorescent film. 5 mg of Eu2(TDAP)(DMB)6(Phen)2 was dissolved in 5 mL of CHCl3, and 5 mL of CHCl3 solution containing 2.2 g of PMMA was added. The mixture was ultrasonically dispersed for 30 minutes. The solution was then poured into a petri dish and allowed to stand at room temperature for 24 hours to obtain a red Eu2(TDAP)(DMB)6(Phen)2-PMMA fluorescent film with a thickness of 0.46 mm.

[0035] e. Fabrication of white LEDs (WLEDs) using ultraviolet LED chips as substrates. Ten layers of blue Bi₂S₃ quantum dot-B-PMMA fluorescent film, one layer of green Bi₂S₃ quantum dot-G-PMMA fluorescent film, and two layers of red Eu₂(TDAP)(DMB)₆(Phen)₂-PMMA fluorescent film are sequentially bonded together using CHCl₃ solvent to form a blue, green, and red tricolor PMMA film. The blue PMMA fluorescent film is tightly attached to the ultraviolet LED chip. Applying a 3V DC current to the LED chip yields a white LED.

[0036] Example 2: Convert the electroluminescence of a blue LED chip into white light with a wavelength greater than 450nm.

[0037] The six-layer green Bi2S3 quantum dot-G-PMMA fluorescent film and the three-layer red Eu2(TDAP)(DMB)6(Phen)2-PMMA fluorescent film prepared in Example 1 were bonded together with CHCl3 solvent to form a green and red bicolor PMMA fluorescent film. The green PMMA fluorescent film was attached to a blue LED chip, and a white LED (WLED) was obtained by applying a 3V DC current to the LED chip.

[0038] Figure 1 The images show the fluorescence excitation (Ex) and emission (Em) spectra of the isopropanol solution of Bi2S3 quantum dots-B prepared in Example 1. The maximum emission wavelength is 483 nm. The inset is a fluorescence photograph under 365 nm UV light illumination, and the absolute fluorescence quantum yield reaches 55%. Its excitation spectrum can cover the entire electroemission spectrum of a UV-LED chip (see...). Figure 5(a)) can convert the electroluminescence of the ultraviolet-LED chip into blue light with a wavelength greater than 450nm.

[0039] Figure 2 This shows the fluorescence excitation and emission spectra of the blue Bi₂S₃ quantum dot-B-PMMA fluorescent film prepared in Example 1, with a maximum emission wavelength of 442 nm. Its excitation spectrum exhibits a broad excitation absorption band from 350 nm to 425 nm, covering the entire electroluminescence spectrum of the UV-LED chip, thus converting the electroluminescence of the UV-LED chip into blue light with a wavelength greater than 400 nm. The illustration shows a photograph of the PMMA fluorescent film under 365 nm UV light illumination.

[0040] Figure 3 This image shows the fluorescence excitation and emission spectra of the green Bi₂S₃ quantum dot-G-PMMA fluorescent film prepared in Example 1. The maximum emission wavelength is 499 nm, and its emission spectrum consists entirely of visible light with wavelengths greater than 450 nm. Its excitation spectrum is a broad excitation absorption band from 350 nm to 475 nm, covering the entire electroluminescence spectrum of the UV-LED chip, enabling the conversion of the UV-LED chip's electroluminescence into green light with wavelengths greater than 450 nm. Its maximum excitation wavelength is 452 nm, covering the emission spectrum region of the blue Bi₂S₃ quantum dot-B-PMMA fluorescent film with wavelengths less than 450 nm, allowing for the efficient conversion of the inner blue Bi₂S₃ quantum dot-B-PMMA fluorescent film's emission light with wavelengths less than 450 nm into visible light with wavelengths greater than 450 nm. The illustration shows a photograph of the PMMA fluorescent film under 365 nm UV light illumination.

[0041] Figure 4 This is the fluorescence excitation and emission spectrum of the red Eu2(TDAP)(DMB)6(Phen)2-PMMA fluorescent film prepared in Example 1. The maximum emission wavelength is 612 nm, and its emission spectrum consists entirely of red light with wavelengths greater than 580 nm. Its excitation spectrum is a broad excitation absorption band from 300 nm to 450 nm, covering the entire electroluminescence spectrum of the UV-LED chip, enabling the conversion of the UV-LED chip's electroluminescence into red light with wavelengths greater than 580 nm. Its excitation spectrum also covers the emission spectrum region of the blue Bi2S3 quantum dot-B-PMMA fluorescent film with wavelengths less than 450 nm, efficiently converting the emission light from the inner blue Bi2S3 quantum dot-B-PMMA fluorescent film with wavelengths less than 450 nm into red light with wavelengths greater than 580 nm. The illustration shows a photograph of the PMMA fluorescent film under 365 nm UV light illumination.

[0042] Figure 5(a) is the electroemission spectrum of the ultraviolet-LED chip used in this embodiment. Its electroemission spectrum region is 375nm to 425nm, with two emission peaks at 377nm and 405nm. Figure 5 (b) is the electroluminescence spectrum of the white LED (WLED) prepared in this embodiment, which can efficiently convert the electroluminescence of the ultraviolet-LED chip into white light with a wavelength greater than 450nm.

[0043] Figure 6 This is the CIE coordinate diagram of the white LED chip prepared in Example 1, with coordinates at (0.36, 0.39), which is white light with a color temperature of 4500K.

[0044] Figure 7 (a) is the electroemission spectrum of the blue LED chip used in this embodiment 2. Its electroemission spectrum region is 425nm~475nm, with an emission peak at 450nm. Figure 7 (b) is the electroluminescence spectrum of the white LED (WLED) prepared in this embodiment, which can efficiently convert the electroluminescence of the blue LED chip into white light with a wavelength greater than 450nm.

[0045] Figure 8 This is the CIE coordinate diagram of the white LED chip prepared in Example 2, with coordinates at (0.32, 0.36), which is white light with a color temperature of 6000K.

[0046] Figure 9 The images show the emission spectra of the isopropanol solution of Bi2S3 quantum dots-B prepared in Example 1 under different excitation wavelengths. The shape of the fluorescence emission spectrum remains unchanged under excitation from 360 to 430 nm light, and the fluorescence color is independent of the excitation wavelength.

[0047] Figure 10 This is a high-resolution transmission electron microscope (HRTEM) image of the Bi₂S₃ quantum dots-B prepared in Example 1. The particles are spherical and uniformly dispersed. The inset shows the characteristic lattice diffraction fringes of Bi₂S₃ quantum dots-B, and their interplanar spacing. The

[520] interplanar spacing corresponding to Bi2S3 (Journal of Physical Chemistry C, 2014, 118: 30244-30252) demonstrates the successful synthesis of Bi2S3 quantum dots-B.

[0048] Figure 11 This is the infrared absorption spectrum of the Bi2S3 quantum dot-B prepared in Example 1. As shown in the figure, at 2500 cm⁻¹... -1 ~3600cm -1The broad absorption peak is the stretching vibration absorption peak of -COO-H of mercaptoacetic acid, at 1629 cm⁻¹. -1 and 1413cm -1 They are thioglycolic acid-COO - Absorption peaks for both asymmetric and symmetric stretching vibrations. 2921 cm⁻¹ -1 and 2852cm -1 The absorption peak is due to the asymmetric and symmetric stretching vibrations of the -CH2- group of mercaptoacetic acid. It is located at 3361 cm⁻¹. -1 The narrow singlet is the characteristic absorption peak of -NH- on 1,8-diaminonaphthalene. Normally, -NH2 has two weak absorption peaks, while -NH- has one weak and narrow absorption peak, indicating that 1,8-diaminonaphthalene reacts with Bi on the surface of Bi2S3 particles. 3+ During the reaction, the -NH2 group loses one hydrogen atom and reacts with the Bi on the surface of the Bi2S3 particles in the form of -NH-. 3+ Combined. Located at 1573cm -1 The strong absorption peak is the vibrational absorption peak of the naphthalene ring skeleton of 1,8-diaminonaphthalene, located at 3191 cm⁻¹. -1 The weak and narrow absorption peak is due to the CH stretching vibration on the naphthalene ring. Typically, -COO... - The asymmetric and symmetric stretching vibration absorption peaks are very strong, while the vibration absorption peaks of the naphthalene ring skeleton are of medium intensity. Figure 10 This indicates that most of the mercaptoacetic acid molecules on the surface of Bi2S3 particles are replaced by 1,8-diaminonaphthalene molecules.

[0049] In summary, the technical features of the PMMA fluorescent film prepared by this invention are as follows:

[0050] 1. Compared with traditional filter films, the PMMA fluorescent film of the present invention can fully absorb light less than 450nm from LED lamps or LED displays and convert it into visible light with a wavelength greater than 450nm. The efficiency of absorbing light with a wavelength less than 450nm is much greater than that of traditional filter films.

[0051] 2. This invention converts the absorbed light into visible light with a wavelength greater than 450nm, which has little impact on the brightness of LED lamps or LED displays.

[0052] 3. This PMMA fluorescent film generates less heat, thus having a smaller impact on the luminous stability and lifespan of LED lamps or LED displays.

[0053] 4. White LEDs can be achieved by adjusting the thickness of the three-color PMMA fluorescent films (blue, green, and red) or by changing the concentration of Bi2S3 quantum dots-B, Bi2S3 quantum dots-G, or Eu2(TDAP)(DMB)6(Phen)2-PMMA in the PMMA film.

[0054] 5. By flexibly combining one, two, or three of the three colors of PMMA fluorescent film (blue, green, and red), LEDs of various colors can be realized, such as blue LEDs, green LEDs, and red LEDs.

[0055] 6. The light conversion efficiency of PMMA fluorescent films in blue, green and red colors all exceed 50%.

[0056] 7. The excitation spectrum of red Eu2(TDAP)(DMB)6(Phen)2-PMMA does not overlap with the emission spectrum of green Bi2S3 quantum dot-G-PMMA. Therefore, the emission spectrum of green Bi2S3 quantum dot-G-PMMA is not affected by red Eu2(TDAP)(DMB)6(Phen)2-PMMA, making it easy to achieve color control of LEDs.

[0057] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A PMMA composite fluorescent thin film for converting the electroluminescence of an LED chip into white light, characterized in that, The PMMA composite fluorescent film fully absorbs the electroluminescence of the ultraviolet LED chip and converts it into white light with a wavelength greater than 450nm. The visible light with a wavelength greater than 450nm accounts for 98%. The PMMA composite fluorescent film is composed of three films: blue Bi2S3 quantum dot-B-PMMA, green Bi2S3 quantum dot-G-PMMA, and red Eu2(TDAP)(DMB)6(Phen)2-PMMA. The blue Bi2S3 quantum dot-B-PMMA: A1. Synthesis of Bi2S3 quantum dots-1: 0.116g H3Bi2Br9 was dissolved in 20mL isopropanol, 30μL mercaptoacetic acid was added, and the mixture was reacted under nitrogen protection at 30-40℃ for 30-60min. The temperature was then raised to 90℃, and an isopropanol solution containing 11.3mg thioacetamide was added. The mixture was refluxed for 1-1.5h, cooled naturally to room temperature, and then reacted at 130℃ for 1h. The pH was adjusted to 4-5 with NaOH solution. B1. Synthesis of blue Bi2S3 quantum dots - B: Add 5-8 mg of 1,8-diaminonaphthalene to 5-25 mL of Bi2S3 quantum dot-1 solution, adjust the pH to 7 with NaOH solution; react at 160-200℃ for 4 h; cool naturally to room temperature, the pH of the solution after reaction is 5; dialyze with a semipermeable membrane with a molecular weight of 3500 Da for 48 h; C1. Disperse 2-5 mg of Bi2S3 quantum dots-B in 5-6 mL of isopropanol, add 5 mL of CHCl3 solution containing 2-4 g of PMMA, and sonicate for 30-60 minutes; pour the mixed solution into a petri dish and let it stand at room temperature for more than 24 hours. The green Bi2S3 quantum dot-G-PMMA: A2. Synthesis of green Bi2S3 quantum dots-G: Add 5-8 mg of o-phenylenediamine to the Bi2S3 quantum dot-1 solution synthesized in A1, react at 130℃ for 1-1.5 h, cool naturally to room temperature, adjust the pH to 5-6 with NaOH solution, and dialyze with a semipermeable membrane with a molecular weight of 3500 Da for 48 h. B2. Disperse 3-6 mg of Bi2S3 quantum dots-G in 5 mL of isopropanol, add 5 mL of CHCl3 solution containing 2-4 g of PMMA, and sonicate for 30 minutes; pour the mixed solution into a petri dish and let it stand at room temperature for more than 24 hours. The red Eu2(TDAP)(DMB)6(Phen)2-PMMA: Dissolve 5-15 mg Eu2(TDAP)(DMB)6(Phen)2 in 5-10 mL CHCl3, add 10 mL of CHCl3 solution containing 2-6 g PMMA, and sonicate for 30 minutes; pour the mixed solution into a petri dish and let it stand at room temperature for at least 24 hours.

2. A PMMA composite fluorescent thin film for converting the electroluminescence of an LED chip into white light, characterized in that, The electroluminescence of the blue LED chip is fully absorbed and converted into white light with a wavelength greater than 450nm. The visible light with a wavelength greater than 450nm accounts for 99.6%. The PMMA composite fluorescent film is composed of two films: green Bi2S3 quantum dot-G-PMMA and red Eu2(TDAP)(DMB)6(Phen)2-PMMA. The green Bi2S3 quantum dot-G-PMMA: A3. Synthesis of Bi2S3 quantum dots-1: Dissolve 0.116g H3Bi2Br9 in 20mL isopropanol, add 30μL mercaptoacetic acid, under nitrogen protection, react at 30-40℃ for 30-60min, raise the temperature to 90℃, add isopropanol solution containing 11.3mg thioacetamide, reflux for 1-1.5h, cool naturally to room temperature, then react at 130℃ for 1h, adjust pH to 4-5 with NaOH solution; B3. Synthesis of green Bi2S3 quantum dots-G: Add 5-8 mg of o-phenylenediamine to the Bi2S3 quantum dot-1 solution synthesized in A3, react at 130℃ for 1-1.5 h, cool naturally to room temperature, adjust the pH to 5-6 with NaOH solution, and dialyze with a semipermeable membrane with a molecular weight of 3500 Da for 48 h. C3. Disperse 3-6 mg of Bi2S3 quantum dots-G in 5 mL of isopropanol, add 5 mL of CHCl3 solution containing 2-4 g of PMMA, and sonicate for 30 minutes; pour the mixed solution into a petri dish and let it stand at room temperature for more than 24 hours. The red Eu2(TDAP)(DMB)6(Phen)2-PMMA: Dissolve 5-15 mg Eu2(TDAP)(DMB)6(Phen)2 in 5-10 mL CHCl3, add 10 mL of CHCl3 solution containing 2-6 g PMMA, and sonicate for 30 minutes; pour the mixed solution into a petri dish and let it stand at room temperature for at least 24 hours.

3. A method for preparing a PMMA composite fluorescent thin film for converting the electroluminescence of an LED chip into white light as described in claim 1, characterized in that, The PMMA composite fluorescent film is used to convert the electroluminescence of the ultraviolet LED chip into a white LED with a wavelength greater than 450 nm, and includes the following steps: Blue Bi2S3 quantum dot-B-PMMA, green Bi2S3 quantum dot-G-PMMA, and red Eu2(TDAP)(DMB)6(Phen)2-PMMA are cut into sizes slightly larger than the diameter of the UV LED chip. Then, they are bonded together with CHCl3 solvent in the order of blue, green, and red fluorescent films to form a three-layer structure. The blue PMMA fluorescent film is attached tightly to the UV LED chip. By applying a 3V DC current to the UV LED chip, a white LED can be obtained.

4. A method for preparing a PMMA composite fluorescent thin film for converting the electroluminescence of an LED chip into white light as described in claim 2, characterized in that, The PMMA composite fluorescent film is used to convert the electroluminescence of a blue LED chip into a white LED with a wavelength greater than 450 nm, and includes the following steps: Green Bi2S3 quantum dot-G-PMMA and red Eu2(TDAP)(DMB)6(Phen)2-PMMA are cut into sizes slightly larger than the diameter of the blue LED chip. Then, the green and red fluorescent films are bonded together with CHCl3 solvent to form a two-layer structure. The green PMMA fluorescent film is closely attached to the blue LED chip. When a 3V DC current is applied to the blue LED chip, a white LED can be obtained.

Images