WO2022164412A1

WO2022164412A1 - A solid state lighting device including cdse and cspbbr3 quantum dot-doped glass nanocomposite layers and production method thereof

Info

Publication number: WO2022164412A1
Application number: PCT/TR2022/050071
Authority: WO
Inventors: Orhan KIBRISLI; Erdinc EROL; Ali Ercin ERSUNDU; Miray Celikbilek Ersundu
Original assignee: Yildiz Teknik Universitesi
Priority date: 2021-01-27
Filing date: 2022-01-27
Publication date: 2022-08-04
Also published as: TR202101278A1; EP4284762A1

Abstract

The present invention provides a multi-layered glass nanocomposite (100), comprising one or more first layers (101) being glass nanocomposites doped with one or more CdSe quantum dots (1), and one or more second layers (102) being glass nanocomposites doped with one or more CsPbBr3 quantum dots (2). The present invention also provides a device (1000) which is a solid state lighting system comprising the multi-layered glass nanocomposite (100) of the invention as a radiation color converter. The present invention also provides a method for obtaining said multi-layered glass nanocomposite (100) of the invention. In addition, the present invention provides a method for obtaining a device (1000) for solid state lighting systems comprising such a multi-layered glass nanocomposite (100).

Description

A SOLID STATE LIGHTING DEVICE INCLUDING CdSe and CsPbBr₃ QUANTUM DOT-DOPED GLASS NANOCOMPOSITE LAYERS AND PRODUCTION METHOD THEREOF

Technical Field of the Invention

The present invention relates to nanocomposites in the fields of materials science, optics, photonics and chemistry. In particular, the present invention relates to a solid state lighting device comprising quantum dot-doped glass nanocomposite layers, and production method thereof.

Background Art

Existing commercial solid state white-radiating diodes (white LED or WLED) are formed by combining a blue-radiating LED chip and a Ce:YAG phosphor which absorbs some of the blue light and radiates yellow light, with silicone or organic binders, in which systems, white light is obtained by mixing blue and yellow light. Considering the visible region of the electromagnetic spectrum, the spectrum having only blue and yellow radiation is considered to be heterogeneous. Therefore, the capacity of WLEDs obtained by this method to display the colors in an environment to the observer is regarded insufficient in terms of NTSC (National Television System Committee) standard and CRI (Color Rendering Index) parameter. Meanwhile, scattering losses due to the refractive index difference between silicon or organic binder and phosphorus, low chemical and thermal stability of phosphorus material (Ce:YAG), degradation of the binder under UV light and/or the heat generated by the LED chip in time are problems concerning commercial WLEDs, and accordingly there is a need to improve WLEDs.

Quantum dots are nanosized (1-20 mm), semiconductive crystal materials that are hotspot for their unique properties such as high absorption cross-section, size-dependent band gap energy, adjustable radiation wavelength and high photoluminescence quantum efficiency. With their superior properties, quantum dots have a high potential for use in solid state lighting applications. However, due to their strong ionic structure and high surface energy, quantum dots degrade when exposed to polar solvents such as water, to high temperature and high radiation intensity.

In order to improve the radiation color properties of the commercially used WLEDs, studies have been conducted to obtain a more homogeneous radiation spectrum by combining different materials that radiate separately red and green colors with blue LED chips. Most of these studies are based on the principle of depositing colloidal (wet chemistry, solution based) quantum dots on various substrate materials in the form of thin films. Also, various techniques have been developed, such as the production of quantum dots in organic or inorganic matrices such as polymers by means of surface modification and/or encapsulation. Although improvements are made with these methods in terms of radiation properties of quantum dots, the stability and degradation problems have not been solved at a desired level.

These colloidal based, quantum dot containing materials that is suitable to be prepared in the form of thin films are generally only stable at temperatures up to 200°C. Therefore, it can be said that their thermal resistance and stability are relatively low. Since colloidal based, quantum dot containing materials that is suitable to be prepared in the form of thin films are highly sensitive to moisture and oxygen, they start to degrade even in short time contacts in the order of minutes or hours; therefore, it can be said that the chemical stability thereof is relatively low. In addition, it can be said that the mechanical strength of colloidal based, quantum dot containing materials which can be prepared in the form of thin films is low. Quantum dots synthesized colloidally can also be embedded in various polymer matrices whose thermal and mechanical strength is considerably lower than inorganic glasses.

In order to combine the blue light from an LED chip with other primary colors (red, green) or the mixtures thereof, different glass layers doped with different quantum dots are disposed on the LED chip so as to obtain the white light.

In order to achieve superior radiation properties, the red, green and blue radiation bands of the white light components must cover a large part of the visible region. In the studies to obtain white light using lanthanide ions, the full width at half maximum (in short: FWHM) of rare earth ions is narrow, and the constant central wavelength values prevent a large part of the visible region of the electromagnetic spectrum to be covered. At this point, the radiation bands of quantum dots with broad and adjustable wavelengths make it possible to obtain radiation bands that cover the entire visible region.

In devices developed to produce white light using a blue LED chip and perovskite quantum dots (CsPbBr₃, green radiation), red radiation can be obtained by using CsPbI₃ PQDs (see Figure 1). However, although quantum dots such as CsPbI₃ can radiate red light, their quantum efficiency is quite low. Similarly, in devices developed to produce white light, red radiation may be obtained by using lanthanide ions (see Figure 2) with narrow FWHM and fixed central wavelength values, such as Eu³⁺, or phosphorus materials with low chemical and thermal resistance, such as Eu²⁺:CaAISiN₃ (see Figure 3). The white light produced using these materials cannot meet the properties expected from an ideal white light source.

Objects of the Invention

The main object of the invention is to eliminate the problems encountered in the prior art.

Another object of the invention is to prevent the degradation of quantum dots and to ensure that the radiation properties can be preserved for a long period time.

Another object of the invention is to provide nanocomposite layers in which improved radiation properties and a high quantum dot strength are provided in a radiation color converter. Accordingly, another object of the invention is to provide a multi-layered glass nanocomposite structure that radiates white light, by combining said nanocomposite layers in a suitable manner. Another object of the invention is to provide a solid state lighting device that radiates white light due to the incorporation of said multi-layered glass nanocomposite having the radiation converter property therein.

Still another object of the invention is to provide a method for obtaining such a multilayered glass nanocomposite. In connection, another object of the invention is to provide a method for providing a white radiating solid state lighting device comprising said multilayered glass nanocomposite.

Summary of the Invention

The present invention provides a multi-layered glass nanocomposite comprising a first glass nanocomposite layer doped with one or more CsPbBr₃ quantum dots and a second glass nanocomposite layer doped with one or more CdSe quantum dots, and a method for obtaining same.

The nanocomposite of the invention is suitable for use as a radiation color converter in a solid state lighting system.

Accordingly, the present invention also provides a solid state lighting system comprising the multi-layered glass nanocomposite of the invention as a radiation color converter, and a method for obtaining same.

Brief Description of the Drawings

The present invention is exemplified below with reference to the accompanying figures for better understanding thereof, which examples are only illustrative of the embodiments of the present invention and are not limiting other embodiments and general functions providing the solution of the technical problem.

Figure 1 is a schematic view of a next generation comparative WLED design that is suitable to be used for the generation of white light.

Figure 2 is a schematic view of another next generation comparative WLED design that is suitable to be used for the generation of white light.

Figure 3 is a schematic view of another next generation comparative WLED design that is suitable to be used for the generation of white light. Figure 4(a) is a schematic view of a possible WLED design presented within the scope of the present invention, for use in the generation of white light.

Figure 4(b) is a schematic view of another possible WLED design presented within the scope of the present invention, for use in the generation of white light.

Figure 5(a) is a schematic cross-sectional view showing an exemplary case where a quantum dot-doped multi-layered glass nanocomposite of the invention is included in a solid state lighting system, for example, together with an LED chip.

Figure 5(b) is a schematic cross-sectional view showing another exemplary case where a quantum dot-doped multi-layered glass nanocomposite of the invention is included in a solid state lighting system, for example, together with an LED chip.

Figure 6 is a photoluminescence (PL) graph of a solid state lighting device comprising a quantum dot-doped multi-layered glass nanocomposite of the present invention and a blue LED chip coupled thereto. The radiation wavelength of the blue LED chip used as the light source herein, i.e. the stimulation wavelength to which the multi-layered glass nanocomposite structure is exposed, is 450 nm.

Detailed Description of the Invention

Hereinafter, the present invention is described in detail, based on the drawings, whose brief description given above. The list of reference symbols used in the drawings is as follows:

1 CdSe quantum dots

2 CsPbBr₃ quantum dots

50 characteristic photoluminescence peak of the CsPbBr₃ quantum dot

60 characteristic photoluminescence peak of the CdSe quantum dot

70 characteristic photoluminescence peak of the Dy⁺³ lanthanide ion

80 characteristic photoluminescence peak for blue LED chip 10 light source such as LED chip, such as blue LED chip or UV LED chip or violet LED chip

11 first glass nanocomposite layer doped with a PQD such as CsPbI₃ that has low red radiation quantum efficiency

12 a glass nanocomposite layer doped with green- radiati ng (CsPbBr₃) PQD

13 glass nanocomposite layer doped with a lanthanide such as red-radiating Eu³⁺ with narrow FWHM and fixed central wavelength values, and with CsPbBr₃ PQD

14 layer comprising red-radiating Eu²⁺:CaAISiN₃-based phosphor or consisting of red-radiating Eu²⁺:CaAISiN₃-based phosphor

100 multi-layered glass nanocomposite of the invention

101 (CdSe quantum dot-doped glass nanocomposite) first layer

102 (CsPbBr₃ quantum-dot doped glass nanocomposite) second layer

1000 device

AexCexc radiation wavelength of the light source

B blue light

G green radiation

R red radiation

W white light

L total thickness

PL photoluminescence

With the present invention, a multi-layered glass nanocomposite (100) is developed in order to eliminate the disadvantages mentioned in the background art section.

In order to prevent the degradation of quantum dots and to preserve their exceptional radiation properties for a long period of time, it is appropriate to encapsulate them in a thermally, chemically and mechanically stable material. In this context, glasses, such as silicate glasses stand out as the encapsulation material with the highest potential for their high optical transmittance, ease of production, 100% recyclability and exceptional thermal, chemical and mechanical resistance. Since the synthesis of quantum dots directly in glass matrices results in their zero contact with the outside environment and passivation of their surfaces, their radiation properties can be preserved for a long period time.

The multi-layered glass nanocomposite (100), which will be obtained as a result of synthesizing quantum dots in suitable glass matrices, will allow the development of new commercial products that is suitable to be used in WLED solid state lighting systems, with their thermal and chemical stability as well as the radiation color converting properties thereof.

Comparative example 1:

Figure 1 shows a device (1000) comprising a light source (10) (e.g., a blue LED chip) emitting blue light (B) and developed to produce white light (W) by the effect of doped nanocomposite.

The device (1000) includes a first glass nanocomposite layer (11) doped with perovskite quantum dots (in short: PQD) such as CsPbI₃, which have low red radiation (R) quantum efficiency, as a radiation color converter, and also a second glass nanocomposite layer (12) doped with green radiating (G) (CsPbBr₃) PQD. Thus, as the blue light (B) originating from blue radiation pass through the nanocomposite layers, PQDs in nanocomposite layers generate red radiation (R) and green radiation (G) so that white light (W) (or white color) is obtained.

The low efficiency of red radiation (R) due to CsPbI₃ doping is represented with a thin arrow.

Comparative example 2:

Figure 2 shows a device (1000) comprising a blue LED chip emitting blue light (B) and developed to produce white light (W) by the effect of doped nanocomposite.

The device (1000) includes a glass nanocomposite layer (13) doped with a red radiating (R) lanthanide such as Eu³⁺, as a radiation color converter, and green radiating (G) (CsPbBr₃) PQD. Thus, as the blue rays or blue light (B) pass through the nanocomposite, EU³⁺ ions in nanocomposite generate a red radiation (R) and PQDs generate a green radiation (G) so that white light (W) (or white color) is obtained.

Here, the absorption cross-sectional area, quantum efficiency and FWHM values of Eu³⁺ ions used for red radiation (R) are low.

Comparative example 3:

Figure 3 shows a device (1000) comprising a blue LED chip emitting blue light (B), which is also developed to produce white light (W) by the effect of a first layer (101) and a second layer (102) being doped nanocomposite.

The device (1000) includes a layer (14) consisting of red radiating Eu²⁺:CaAISiN₃-based phosphorus or red radiating Eu²⁺:CaAISiN₃-based phosphorus, as a radiation color converter, and also a glass nanocomposite layer (12) doped with green radiating (G) (CsPbBr₃) PQD. Thus, as the blue light (B) pass through the red radiating layer (14) and the green radiating layer , said layers separately emit red radiation (R) and green radiation (G) so that white light (W) (or white color) is obtained. The red radiating phosphor material used herein has low chemical and thermal resistance.

Example 4, the effect of the nanocomposite of the invention:

In Figure 4(a) and Figure 4(b), an example of possible configurations of a device (1000) is shown comprising a light source (10) (e.g., a blue LED chip) emitting blue light (B) and developed to produce white light (W) by the effect of a multi-layered glass nanocomposite (100) according to the present invention. As seen in Figure 4(a) and Figure 4(b) (similarly, in Figure 5(a) and Figure 5(b)), the order in which the first layer (101) and the second layer (102) are disposed on top of each other in such a way that their distance from the light source (10) is different from each other does not make any difference in terms of the operation of the invention. In the invention, the device (1000) includes an exemplary multi-layered glass nanocomposite (100), as a radiation color converter, comprising a first layer (101), which is a glass nanocomposite doped with red radiating (R) CdSe (cadmium selenide) QD, and a second layer (102) which is a glass nanocomposite doped with green radiating (G) CsPbBr₃ (cesium lead bromide) perovskite quantum dots (in short: PQD). Thus, as the blue light (B) originating from the blue radiation pass through the multi-layered glass nanocomposite (100) which is the subject of the invention, CdSe quantum dots (1) in the multi-layered glass nanocomposite (100) emit red radiation (R) and CsPbBr₃ (perovskite) quantum dots (2) emit green radiation (G) so that white light (W) (or white color) is obtained. With the CdSe doping, the red radiation (R) efficiency is high.

One or more first layers (101) of glass nanocomposite containing one or more CdSe quantum dots (1) may also contain one or more lanthanide ions such as Dy³⁺. In this way, both the quantum efficiency is increased and the homogeneity of the radiation spectrum is improved.

In light of the above, the present invention provides a multi-layered glass nanocomposite (100) comprising one or more first layers (101) of glass nanocomposite doped with CdSe quantum dots (1) and one or more second layers (102) of glass nanocomposite doped with CsPbBr₃ quantum dots (2). With the CdSe quantum dots (1), red and preferably also yellow radiation is provided from one or more first layers (101). As mentioned above, one or more first layers (101) of glass nanocomposite containing one or more CdSe quantum dots (1) may also contain one or more lanthanide ions such as Dy³⁺, thus, both the quantum efficiency is increased and the homogeneity of the radiation spectrum is further improved. With the CsPbBr₃ quantum dots (2), green radiation (G) is provided from one or more second layers (102). With the improvement of the present invention, each of one or more first layers (101) of glass nanocomposite containing green radiating CsPbB_r3 quantum dots (2) and one or more second layers (102) doped with red and yellow radiating CdSe quantum dots (1) with a high FWHM value, and the multi-layered glass nanocomposite (100) containing them, have high thermal, chemical and mechanical resistance. In this context, a radiation color converter having ideal properties is proposed by synthesizing CdSe quantum dots (1) and CsPbBr₃ quantum dots (2), which radiate in red and green regions with high efficiency, in glass matrices (first layer(s) (101) and second layer(s) (102), respectively). Glass nanocomposite first layer(s) (101) and glass nanocomposite second layers (102) of the invention can be classified as silicate glass nanocomposites.

The inventive multi-layered glass nanocomposite (100) radiates red radiation (R) and green radiation (G) with blue light (B) emitted from a light source (10) (e.g., an LED chip) coupled with it, and radiation of all colors are combined to provide the radiation color properties expected from an ideal white light (W) source.

The multi-layered quantum dot glass nanocomposite (100) of the present invention has at least the following advantages compared to colloidal-based materials containing quantum dots, which can be prepared in thin film form:

- After repeated heating-cooling cycles up to 400°C, it preserves its initial original radiation properties, therefore said nanocomposite provides a high thermal stability.

- Even when it is immersed in water for more than 60 days no adverse effects on the radiation properties were observed, thus said nanocomposite has a high chemical stability.

- Quantum dot-doped glass nanocomposites have very high mechanical strength compared to colloidal-based thin films and quantum dot-doped polymers;

- CdSe quantum dots (1) and CsPbBr₃ quantum dots (2) are quantum dots having the most advantageous properties for obtaining red/yellow and green radiation (G), respectively. Therefore, with the subject of the present invention, a radiation with ideal white light (W) parameters is obtained by using these two materials together.

Possible exemplary configurations of the inventive multi-layered glass nanocomposite (100) containing CdSe quantum dots (1) and CsPbBr₃ quantum dots (2) simultaneously are shown schematically in Figure 5(a) and Figure 5(b). In Figure 5(a) and Figure 5(b), dashed lines are used to symbolize that the multi-layered glass nanocomposite (100) of the invention can be coupled with, for example, a light source (10). In addition to its superior and adjustable radiation properties, the multi-layered glass nanocomposite (100) of the invention, due to its thermal, chemical and mechanical resistance, has the potential for as a radiation color converter in durable solid state lighting devices (1000), as exemplified in Figure 4(a), Figure 4(b), Figure 5(a) and Figure 5(b).

The present invention also provides a method for providing the multi-layered glass nanocomposite (100) of the invention. The method includes the following steps: a) preparing a first blend of glass and a second blend of glass, b) melting the first glass blend and the second glass blend prepared in step a separate from each other, c) pouring the first glass blend melted in step b and the second glass blend melted in step b into one or more separate molds to obtain one or more first molded samples and one or more second molded samples, d) annealing one or more first molded samples and one or more of the second molded samples obtained in step c, thereby obtaining one or more first annealed samples and one or more second annealed samples, e) controlled crystallization of CdSe quantum dots (1) in one or more annealed first samples and CsPbBr₃ quantum dots (2) in one or more second annealed samples through heat treatment of one or more annealed first samples and one or more annealed second samples obtained in step d at a temperature above their glass transition temperature, thereby obtaining one or more first glass nanocomposite samples containing CdSe quantum dots (1) and one or more second glass nanocomposite samples containing CsPbBr₃ quantum dots (2), f) controlled cooling of one or more first glass nanocomposite samples containing CdSe quantum dots (1) and one or more second glass nanocomposite samples containing CsPbBr₃ quantum dots (2), obtained in step e, thereby obtaining one or more first layers (101) of glass nanocomposite doped with one or more CdSe quantum dots (1) and one or more second layers (102) of glass nanocomposites doped with one or more CsPbBr₃ quantum dots (2), g) placing one or more first layers (101) and one or more second layers (102) obtained in step f on top of each other, thereby obtaining a multi-layered glass nanocomposite (100). The first glass blend in step a of the method is prepared to contain the following components, with the total mole percent concentrations of each constituent component that being 100:

SiO₂ in the range of 40% to 60% by mole; one or more alkali metal oxides in the range of 15% to 25% by mole; AI₂O₃ in the range of 2% to 10% by mole, ZnO in the range of 5% to 15% by mole, as well as

- CdO in the range of 0.5% to 5% by mole and ZnSe in the range of 0.5% to 5% by mole, or

- Cdse in the range of 0.5% to 5% by mole.

The second glass blend in step a of the method is prepared to contain the following components, with the total mole percent concentrations of each constituent component being 100:

SiO₂ in the range of 40% to 60% by mole; alkali metal oxide in the range of 15% to 25% by mole; AI₂O₃ in the range of 2% to 10% by mole; ZnO in the range of 5% to 15% by mole, CsBr in the range of 3% to 7% by mole, PbBr₂ in the range of 6% to 14% by mole.

Starting from the second glass blend, one or more second nanocomposite layers (102) of glass nanocomposite are obtained at the end of the method.

Said one or more alkali metal oxides may be one or more selected from l_i₂O, Na₂O, and K₂O.

As can be understood, the first glass blend may contain CdO and ZnSe together, and as a result of the chemical reaction that will take place between them during the performance of the method, CdSe (thus CdSe quantum dots (1)) is formed as a product. Alternatively, CdSe can be directly included in the glass blend and does not experience chemical transformation while the method is performed. Starting from the first glass blend, one or more first nanocomposite layers (101) of glass nanocomposite are obtained at the end of the method. Therefore, the mole percent composition of the first glass blend can be formed by considering the components appearing in either Table 1 and Table 2 below, and the corresponding mole percent concentrations for these components. In a preferred case where the first layer (101) to be obtained is intended to contain one or more lanthanide ions, the first glass blend may contain one or more lanthanide oxides selected from, for example, Dy₂O₃, Eu₂O₃, Er₂O₃, Ho₂O₃ and Tm₂O₃, as a source of lanthanide. In such a case, the total concentration of one or more lanthanide oxides in the first glass blend is up to 1% by mole, with the total mole percent concentrations of each component making up the first glass blend being 100. The lanthanide oxide is preferably Dy₂O₃.

The mole percent composition of the second glass blend can be formed by considering the components shown in Table 3, and the mole percent concentrations corresponding to the said components. Here, the term mole percent concentration is the proportion of each component in the total number of moles of components in the glass blend.

The first glass blend and the second glass blend may contain other components, provided that they provide the compositional properties described herein which are also shown in Table 1, Table 2 and Table 3, for example. Thus, the first glass blend and the second glass blend may also contain one or more other components not mentioned herein, provided that the mole percent concentration ranges of each component described in this specification are maintained, with the total of the mole percent concentrations of each constituent component being 100.

Table 1: Components in the first glass blend in step a of the method and the first alternative for their percent concentration based on the total number of moles in the first glass blend, with the total mole concentrations thereof in the first glass blend being 100%.

Component Concentration of the component in the glass blend (% mole)

SiO₂ in the range of 40% to 60% alkali metal oxide in the range of 15% to 25%

AI₂O₃ in the range of 2% to 10%

ZnO in the range of 5% to 15%

CdO in the range of 0.5% to 5% ZnSe in the range of 0.5% to 5%

Preferably, Lanthanide oxides (e.g., Dy₂O₃) up to 1%.

Table 2: Components in the first glass blend in step a of the method and the second alternative for their percent concentration based on the total number of moles in the first glass blend, with the total mole concentrations thereof in the first glass blend being 100%.

Component Concentration of the component in the glass blend (% mole)

SiO₂ in the range of 40% to 60% alkali metal oxide in the range of 15% to 25%

AI₂O₃ in the range of 2% to 10%

ZnO in the range of 5% to 15%

CdSe in the range of 0.5% and 5%

Preferably, Lanthanide oxides (e.g., Dy₂O₃) up to 1%.

Table 3: Components in the second glass blend in step a of the method and their percent concentration based on the total number of moles in the second glass blend, with the total mole concentrations thereof in the second glass blend being 100%.

Component Concentration of the component in the glass blend (% mole)

SiO₂ in the range of 40% to 60% alkali metal oxide in the range of 15% to 25%

AI₂O₃ in the range of 2% to 10%

ZnO in the range of 5% to 15%

CsBr in the range of 3% to 7%

PbBr₂ in the range of 6% to 14%.

In the melting process in step b of the method, both the first glass blend and the second glass blend can preferably be raised to a temperature value in the range of 1000°C to 1450°C. Said temperature may be referred to as the melting temperature. The first glass blend and the second glass blend can each be placed in a pot for the melting process, said pots may be made from a material resistant to temperatures above 1000°C, such as quartz, alumina or platinum. Preferably, in step c of the method, the molds may be preheated to a temperature in the range of 350°C to 550°C prior to the casting process. The temperature preferred for preheating may be referred to as the preheating temperature. The molds may be formed from a metallic material such as stainless steel, brass or copper.

The annealing in step d of the method is preferably carried out for a period of 1 to 5 hours. Said period in which the annealing process is carried out may be referred to as an annealing period. The glass transition temperature of the first glass blend and the second glass blend prepared according to the description in step a of the method is expected to be 20°C to 100°C higher than a temperature in the range 350°C to 550°C. In this context, the annealing process may preferably be performed at a temperature value below 20°C to 100°C of the glass transition temperature of the first molded sample and the second molded sample, i.e., for example in the range of 350°C to 550°C. The temperature in the annealing process may be referred to as an annealing temperature. The purpose of the annealing process is to eliminate internal stress resulting from rapid cooling.

The heat treatment in step e of the method may, for example, have a single stage or for example two stages or more. The heat treatment in step e of the method may preferably be carried out for a period in the range of 1 to 72 hours. Said period in which the heat treatment is carried out may be referred to as a heat treatment period. The heat treatment in step e of the method may preferably be carried out at a temperature in the range of 400°C to 600°C; therefore, in this case, the temperature of the heat treatment corresponds to a temperature value above the glass transition temperature. The temperature value during heat treatment may be referred to as a heat treatment temperature.

The controlled cooling in step f of the method may preferably be continued to a temperature corresponding to a temperature below 30°C, more preferably to a temperature corresponding to room temperature (20°C). The temperature reached at the end of the said controlled cooling may be referred to as an operating temperature. Preferably, step f of the method may be followed by step fl below: fl) preparing at least one surface of one or more first glass nanocomposite samples and one or more second glass nanocomposite samples cooled in step f at an optical quality.

Here, the process of preparing at least one surface at optical quality may include any of the methods applied and known in the field of optics. The process of preparing at optical quality may be carried out by means of grinding and polishing, and may, for example, correspond to the reduction of the average roughness of said at least one surface to 1 micrometer or less.

Preferably, prior to step fl of the method, a thickness of each of one or more first glass nanocomposite samples and one or more second glass nanocomposite samples cooled in step f is adjusted such that a total thickness (L) of the multi-layered glass nanocomposite (100) obtained in step g is in the range of 0.1 to 2 mm. In order to bring the total thickness (L) of the multi-layered glass nanocomposite (100) to a value in the range of 0.1 to 2 mm, adjusting the thickness of said first glass nanocomposite sample(s) and said second glass nanocomposite sample(s) may be performed, for example, by known sample preparation techniques. Sample preparation techniques include, for example, any of the methods of grinding, cutting, mechanical or chemical etching. Here, the term total thickness (L) may be considered to correspond to a length of a light transmittance path between a first surface and a second surface of the glass nanocomposite of the invention. Preferably said total thickness (L) term may be preferably considered in that a light transmittance path orthogonal to at least one of these surfaces, i.e., in the perpendicular direction (see Figure 4(a) and Figure 4(b)) corresponds to a total length across the multilayered glass nanocomposite (100) of the invention. More preferably, the term of total thickness (L) may be considered in that a light transmittance path orthogonal to both of these surfaces, i.e., in the perpendicular direction (see Figure 5(a) and Figure 5(b)) corresponds to a total length across the multi-layered glass nanocomposite (100) of the invention. Such total thickness (L) value may be considered a minimum value at which the light path is the shortest.

With the method of the invention, a multi-layered glass nanocomposite (100) is obtained which comprises CdSe quantum dots (1) and CsPbBr₃ quantum dots (2) dispersed homogenously in the glass matrix, with a quantum efficiency above 10%. The diameters of the resulting quantum dots (2 and 3) can be in the range of 1.5 nm to 10 nm.

Preferably, after step g of the method, said multi-layered glass nanocomposite (100) may be coupled with a light source (10) (for example, a UV light source, or a blue light (B) source, or a violet light source, such as a blue LED chip), for example, the multi-layered glass nanocomposite (100) may be placed above a light source (10) providing blue light (B), thus a device (1000) which is a solid state lighting system comprising the multilayered glass nanocomposite (100) is obtained. Thus, within the scope of the present invention, a method for obtaining a device (1000) for solid state lighting systems is provided, said method comprises coupling one or more multi-layered glass nanocomposites (100) obtained from any of the method versions described above with one or more light sources (10). Said light source (10) may be, for example, a UV light source, or a blue light (B) source or a violet light source, for example a blue LED chip.

Therefore, the present invention also proposes use of the multi-layered glass nanocomposite (100) of the invention in solid state lighting applications. A solid state lighting application suitable for this specification may for example be a WLED or a white LED. As the rays originating from the light source (10) pass through the multi-layered glass nanocomposite (100), red radiation (R) (red-yellow) and green radiation (G) of CdSe quantum dots (1) and CsPbBr₃ quantum dots (2), respectively, is allowed. White light (W) (or white light) is obtained as a mixture of all the resulting radiations (R+G+B). In other words, the present invention also provides a solid state lighting system comprising the multi-layered glass nanocomposite (100) of the invention as a radiation color converter.

Claims

1. A multi-layered glass nanocomposite (100), comprising one or more first layers (101) being glass nanocomposites doped with one or more CdSe quantum dots (1), and one or more second layers (102) being glass nanocomposites doped with one or more CsPbBr₃ quantum dots (2).

2. The multi-layered glass nanocomposite (100) according to claim 1, wherein said one or more CdSe quantum dots (1) and one or more CsPbBr₃ quantum dots (2) have a radius in the range of 1.5 nm to 10 nm.

3. The multi-layered glass nanocomposite (100) according to any one of claim 1 or 2, wherein the first layer (101) comprises one or more lanthanide ions.

4. The multi-layered glass nanocomposite (100) according to claim 3, wherein said lanthanide ion is Dy⁺³.

5. A device (1000) which is a solid state lighting system, comprising the multi-layered glass nanocomposite (100) according to any one of claims 1 to 4 and a light source (10) coupled thereto.

6. The device (1000) according to claim 5, wherein said light source (10) is a UV light source, or a blue light (B) source, or a violet light source.

7. The device (1000) according to claim 6, wherein said light source (10) is a blue LED chip.

8. A method for obtaining a multi-layered glass nanocomposite (100) comprising one or more first layers (101) being glass nanocomposites doped with one or more CdSe quantum dots (1) and one or more second layers (102) being glass nanocomposites doped with one or more CsPbBr₃ quantum dots (2), wherein the method comprises the following steps: a) preparing a first blend of glass and a second blend of glass, b) melting the first glass blend and the second glass blend prepared in step a separate from each other, c) pouring the first glass blend melted in step b and the second glass blend melted in step b into one or more separate molds to obtain one or more first molded samples and one or more second molded samples, d) annealing one or more first molded samples and one or more of the second molded samples obtained in step c, thereby obtaining one or more first annealed samples and one or more second annealed samples, e) controlled crystallization of CdSe quantum dots (1) in one or more annealed first samples and CsPbBr₃ quantum dots (2) in one or more second annealed samples through heat treatment of one or more annealed first samples and one or more annealed second samples obtained in step d at a temperature above their glass transition temperature, thereby obtaining one or more first glass nanocomposite samples containing CdSe quantum dots (1) and one or more second glass nanocomposite samples containing CsPbBr₃ quantum dots (2), f) controlled cooling of one or more first glass nanocomposite samples containing CdSe quantum dots (1) and one or more second glass nanocomposite samples containing CsPbBr₃ quantum dots (2), obtained in step e, thereby obtaining one or more first layers (101) of glass nanocomposite doped with one or more CdSe quantum dots (1) and one or more second layers (102) of glass nanocomposites doped with one or more CsPbBr₃ quantum dots (2), g) placing one or more first layers (101) and one or more second layers (102) obtained in step f on top of each other, thereby obtaining a multi-layered glass nanocomposite (100); preparing the first glass blend in step a of the method such that it contains the following components, with the total of the mole percent concentrations of each constituent component being 100:

SiO₂ in the range of 40% to 60% by mole; one or more alkali metal oxides selected from l_i₂O, Na₂O and K₂O in the range of 15% to 25% by mole; AI₂O₃ in the range of 2% to 10% by mole; ZnO in the range of 5% to 15% by mole; and - CdO in the range of 0.5% to 5% by mole and ZnSe in the range of 0.5% to 5% by mole, or

- Cdse in the range of 0.5% to 5% by mole; and preparing the second glass blend in step a such that it contains SiO₂ in the range of 40% to 60% by mole; one or more alkali metal oxides selected from Li₂O, Na₂O and K₂O in the range of 15% to 25% by mole; AI₂O₃ in the range of 2% to 10% by mole; ZnO in the range of 5% to 15% by mole, CsBr in the range of 3% to 7% by mole and PbBr₂ in the range of 6% to 14% by mole, with the total mole percent concentrations of each constituent component being 100.

9. The method according to claim 8, wherein the first glass blend comprises one or more lanthanide oxides selected from Dy₂O₃ , Eu₂O₃, Er₂O₃, Ho₂O₃ and Tm₂O₃, the total concentration of said one or more lanthanide oxides in the first glass blend being up to 1% by mole.

10. The method according to claim 9, wherein said lanthanide oxide is Dy₂O₃.

11. The method according to any one of claims 8 to 10, wherein in the melting process in step b, the first glass blend and the second glass blend are raised to a temperature value in the range of 1000°C to 1450°C.

12. The method according to any one of claims 8 or 11, wherein in step c, prior to the casting process, said molds are preheated to a temperature in the range of 350°C to 550°C.

13. The method according to any one of claims 8 to 12, wherein in step d the annealing process is carried out for a period of 1 to 5 hours.

14. The method according to any one of claims 8 to 13, wherein during the annealing process in step d, the temperature value is in the range of 350°C to 550°C. -21-

15. The method according to any one of claims 8 to 14, wherein the heat treatment in step e is carried out for a period of 1 to 72 hours.

16. The method according to any one of claims 8 to 15, wherein the heat treatment in step e is carried out at a temperature in the range of 400°C to 600°C.

17. The method according to any one of claims 8 to 16, wherein the controlled cooling in step f is continued until a temperature below 30°C is reached.

18. The method according to any one of claims 8 to 17, wherein the controlled cooling in step f is continued until the temperature of 20°C is reached.

19. The method according to any one of claims 8 to 18, comprising the following step after step f: fl) preparing at least one surface of the sample cooled in step f such that the average roughness thereof is 1 micrometer or less.

20. The method according to any one of claims 8 to 19, comprising, prior to step fl, a thickness of each of one or more first glass nanocomposite samples and one or more second glass nanocomposite samples cooled in step f is adjusted such that a total thickness (L) of the multi-layered glass nanocomposite (100) obtained in step g is in the range of 0.1 to 2 mm.

21. A method for obtaining a device (1000) for solid state lighting systems, comprising coupling one or more multi-layered glass nanocomposites (100) obtained by the method according to any one of claims 8 to 20 with one or more light sources (10).

22. The method according to claim 21, wherein said light source (10) is a UV light source, or a blue light (B) source, or a violet light source.

23. The method according to claim 22, wherein said light source (10) is a blue LED chip.