High-temperature-resistant reflective layer for wavelength conversion device

Abstract

A wavelength conversion device (100) includes: a substrate (110), a reflective layer (120) on the substrate (110), and a wavelength conversion layer (130) on the reflective layer (120). The reflective layer (120) includes an adhesive (121) and reflective titanium dioxide nanoparticles (122). The nanoparticles (122) have a particle size of about 200 nanometers to about 500 nanometers. The reflective layer (120) has enhanced thermal stability. A method of manufacturing a wavelength conversion device is also disclosed herein.

Description

[0001] This application is a divisional application of the patent application with the application number 2019800941612, the application date of April 19, 2019, and the invention title of "High Temperature Resistant Reflective Layer for Wavelength Conversion Device". Technical Field

[0002] The present disclosure relates to wavelength conversion devices having a high temperature resistant reflective layer, such as a fluorescent wheel. Therefore, the wavelength conversion device is particularly suitable for projection display systems and optical light conversion devices using a solid state laser as a light source. Background Art

[0003] A fluorescent wheel can be used to generate light with different wavelengths from a single light source. The fluorescent wheel includes a circular substrate having surface segments of different colors. When the fluorescent wheel rotates together with the light incident thereon (from a light source), the surface segments convert the light into different wavelengths.

[0004] For a reflective fluorescent wheel, the substrate reflects light, and thus it is desirable to maximize the reflectivity of the substrate. For wavelengths from about 420 nm (nanometers) to about 680 nm, a substrate coated with aluminum (Al) typically has an average reflectivity of 94%, while a substrate coated with silver (Ag) has an average reflectivity of 98%.

[0005] However, stability and durability are also concerns for reflective wavelength conversion devices. After operating at a high temperature (greater than 150 °C) for hundreds of hours, burning phenomena were observed in the laser incident area on the substrate coated with silver (Ag). Migration of silver ions in the coating at high temperatures may be the cause of this effect. Silver ion migration may result in a loss of optical performance of about 9%.

[0006] Silicone having a high reflectivity (> 95%) has been used to form the reflective layer of a wavelength conversion device. However, silicone has poor thermal stability. At temperatures exceeding 200 °C, silicone degrades, usually starts to turn yellow, and gradually starts to burn. At temperatures exceeding 195 °C, the phosphor layer on the reflective layer also breaks after about 1000 hours. It is undesirable that the breakage of the phosphor layer results in a shorter service life of the fluorescent wheel, and a sharp decrease in the light conversion efficiency due to thermal quenching has been observed (> 10% at 200 °C). In high brightness applications (e.g., a laser power of 300 W), the operating temperature of the fluorescent wheel is generally expected to be higher than 200 °C, so it is not desirable to use silicone.

[0007] It is desirable to have a substrate with a high reflectivity throughout its entire service life. It is also desirable to increase the substrate reflectivity at a low cost while maintaining and increasing reliable service life performance. Such a substrate and reflective coating / layer can be advantageously used in various applications, such as light tunnels, projection display systems, and optical light conversion devices such as fluorescent wheels used in such systems. SUMMARY OF THE INVENTION

[0008] The present disclosure relates to a composition for forming a reflective layer in a wavelength conversion device such as a fluorescent wheel or a color wheel; a reflective layer containing certain materials; and a wavelength conversion device containing such a reflective layer. Such a reflective layer resists temperature degradation at high operating temperatures (e.g., greater than 200 °C and even up to 250 °C). Methods of preparing and using such compositions, layers, and devices are also disclosed herein.

[0009] Wavelength conversion devices are disclosed in various embodiments herein, including: a substrate; a reflective layer on the substrate; and a wavelength conversion layer on the reflective layer. The reflective layer includes an adhesive (A); and reflective nanoparticles (B) having a particle size of about 200 nanometers to about 500 nanometers.

[0010] In some embodiments, the reflective nanoparticles are pure titanium dioxide (TiO2), or aluminum oxide (Al2O3), or magnesium oxide (MgO). In other embodiments, the reflective nanoparticles are titanium dioxide (TiO2) surface-modified with an organic alcohol, a siloxane, aluminum oxide (Al2O3), zirconium dioxide (ZrO2), or silicon dioxide (SiO2).

[0011] The reflective layer may have a thickness of about 0.05 mm to about 0.15 mm. The weight ratio of the reflective nanoparticles (B) to the adhesive (A) may be from about 1:2.5 to about 1:0.8.

[0012] The adhesive can be an organic adhesive or an inorganic adhesive. Examples of organic adhesives include organosilicons such as octamethyltrisiloxane. Examples of inorganic adhesives include sodium silicate.

[0013] Desirably, the reflective layer has a reflectivity of at least 95% for light having a wavelength of about 420 nm to about 680 nm. The phosphor layer may include phosphor particles dispersed in glass, or in crystals, or in ceramic materials. The substrate may have a disc shape. The wavelength converter may further include a motor for rotating the substrate. The substrate can be of a metal or non-metal material or a composite material.

[0014] An optical projection system including the wavelength conversion device described herein is also disclosed herein.

[0015] Methods of manufacturing a wavelength conversion device are also disclosed in various embodiments, the method including: applying a composition to a substrate to form a reflective layer on the substrate, the composition including an adhesive (A); and reflective nanoparticles (B) having a particle size of about 200 nanometers to about 500 nanometers; and forming a wavelength conversion layer on the reflective layer.

[0016] When applied to a substrate, the composition may have a viscosity of from about 0 centipoise (cP) to about 1500 centipoise (cP). The method may further include curing the composition at a temperature of from about 85 °C to about 150 °C. The composition may be applied by dispersion, spraying, brushing, flowing, coating, or screen printing.

[0017] These and other non-limiting features of the present disclosure will be disclosed more specifically hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following is a brief description of the drawings for illustrating the exemplary embodiments disclosed herein and not for limiting the scope of the present disclosure.

[0019] Figure 1A is a schematic diagram of an exemplary optical light conversion device according to the present disclosure, the device including a substrate, a high reflectivity layer, and a phosphor layer.

[0020] Figure 1B is Figure 1A a side cross-sectional view of the exemplary optical light conversion device.

[0021] Figure 1C is an exploded view of the layers of the optical light conversion device.

[0022] Figure 2A is a graph showing the relationship between the reflectivity and the thickness of the reflective layer of the first fluorescent wheel of the present disclosure.

[0023] Figure 2B is a graph showing the relationship between the reflectivity and the thickness of the reflective layer of the second fluorescent wheel of the present disclosure. DETAILED DESCRIPTION

[0024] A more complete understanding of the components, methods, and devices disclosed herein can be obtained by referring to the accompanying drawings. These drawings are merely schematic diagrams for conveniently and easily showing the present disclosure, and thus are not intended to indicate the relative sizes and dimensions of the device or its components and / or to define or limit the scope of the exemplary embodiments.

[0025] Although specific terms are used in the following description for the sake of clarity, these terms are only intended to refer to the specific structures of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the present disclosure. In the drawings and the following description, it should be understood that the same reference numerals denote components having the same functions.

[0026] Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" include plural objects.

[0027] As used in the specification and claims, the terms "comprising," "including," "having," "capable of," "containing," and variations thereof as used herein are intended to be open transitional phrases, terms, or words that require the presence of the specified element / step and allow the presence of other elements / steps. However, such descriptions should also be construed to describe the composition or method as "consisting of the recited elements / steps" and "consisting essentially of the recited elements / steps," which allow only the named elements / steps, together with any unavoidable impurities that may result therefrom, and exclude other elements / steps.

[0028] The numerical values in the specification and claims of this application should be understood to include the same numerical values when reduced to the same number of significant figures, and values that differ from the set value by less than the experimental error of the conventional measurement techniques of the type described in this application for determining that numerical value.

[0029] All ranges disclosed herein include the recited endpoints as well as intermediate values that can be independently combined (e.g., a range of "2 grams to 10 grams" includes the endpoints 2 grams and 10 grams, as well as all intermediate values).

[0030] The terms "about" and "approximately" can be used to include any numerical value that can vary without changing the basic function of that value. When used in conjunction with a range, "about" and "approximately" also disclose the range defined by the absolute values of the two endpoints, e.g., "about 2 to about 4" also discloses the range "2 to 4." Generally, the terms "about" and "approximately" can refer to plus or minus 10% of the specified number.

[0031] As used herein, the terms "excitation light" and "excitation wavelength" refer to the input light that is subsequently converted, e.g., light generated by a laser-based illumination source or other light source. The terms "emission light" and "emission wavelength" refer to the converted light, e.g., the synthetic light generated by a phosphor that has been exposed to excitation light.

[0032] As used herein, the term "inorganic" refers to an "inorganic" object that does not contain any carbon. To avoid doubt, the terms "inorganic binder" and "inorganic coating" in this disclosure do not contain carbon.

[0033] For reference, red generally refers to light having a wavelength of about 780 nanometers to about 622 nanometers. Green generally refers to light having a wavelength of about 577 nanometers to about 492 nanometers. Blue generally refers to light having a wavelength of about 492 nanometers to about 455 nanometers. Yellow generally refers to light having a wavelength of about 597 nanometers to about 577 nanometers. However, this may depend on the context. For example, these colors are sometimes used to label various components and distinguish these components from each other.

[0034] The present disclosure relates to a wavelength conversion device including a reflective layer having a specific composition. Specifically, the reflective layer includes an adhesive (A), which can be organic or inorganic; and reflective nanoparticles (B) having a particle size of about 200 nanometers to about 500 nanometers (including about 350 nanometers to about 450 nanometers). These reflective layers will operate at high temperatures (e.g., greater than 200 °C or 250 °C) while maintaining other optical and mechanical parameters such as the total reflectance percentage.

[0035] Whether the reflective layer maintains high stability can be determined by either of two methods. In the first method, a fluorescent wheel using the reflective layer is placed in an oven and the fluorescent wheel is aged at 250 °C. The reflectance is tested every 100 hours for at least 500 hours, and any cracks in the reflective layer are observed. If the change in reflectance measured between the 300th, 400th, and 500th hours is less than 2%, and the reflective layer has no cracks, the reflective layer is considered to have maintained high stability. In the other method, a fluorescent wheel using the reflective layer is placed in an oven and the fluorescent wheel is aged at 250 °C. The conversion efficiency is tested every 100 hours for at least 500 hours, and any cracks in the reflective layer are observed. If the change in conversion efficiency measured between the 300th, 400th, and 500th hours is less than 2%, and the reflective layer has no cracks, the reflective layer is considered to have maintained high stability. By just one of these two methods, the reflective layer can be considered to have maintained high stability.

[0036] Please refer to Figure 1A and Figure 1B , which depicts the wavelength conversion device of the present disclosure. The wavelength conversion device is shown in the form of a fluorescent wheel 100. Figure 1A is a schematic diagram of the fluorescent wheel 100, Figure 1B is a side cross-sectional view of the fluorescent wheel 100. The fluorescent wheel 100 includes a substrate 110 on which a reflective layer 120 is formed, and a phosphor layer 130 is applied on the reflective layer 120. The reflective layer is formed of the composition further described herein. As shown here, the reflective layer 120 is formed of an inorganic adhesive or silicone (A) labeled with reference numeral 121 and reflective nanoparticles labeled with reference numeral 122.

[0037] The substrate 110 is typically a metal with high thermal conductivity, such as aluminum or aluminum alloy, copper or copper alloy, silver or silver alloy, or other metals with high thermal conductivity. For example, the substrate can also be made of non-metallic materials or composite materials such as glass, sapphire, or diamond. The substrate is typically disc-shaped or annular. The smoothness or roughness of the substrate surface is not important. However, it is desirable that the surface of the substrate on which the reflective layer 120 is formed is clean and free of stains, oil, organic residues, or biological residues. For low surface energy surfaces, adhesion can be improved by applying a primer or by special surface treatment (such as chemical or plasma etching or ozone cleaning).

[0038] The phosphor layer 130 contains at least one phosphor. Examples of suitable phosphors include yttrium aluminum garnet (YAG), silicates, and nitrides. The phosphor can have a particle size of about 10 to about 30 microns. The phosphor layer is typically in the form of an annular phosphor segment that contains different types of phosphors to convert the excitation light into green, yellow, or red light. Typically, a blue laser (with a wavelength of about 440 nm to about 460 nm) is used to excite the phosphor segment on the fluorescent wheel. The fluorescent wheel can also have one or more gaps to allow the blue source light to pass through without being converted.

[0039] The fluorescent wheel 100 can be used by mounting the substrate on a motor and rotating it at high speed Figure 1A and Figure 1B . Typically, the substrate is rotated during use, although the device can also be used in a static (non-rotating) configuration, in which case the device may not be referred to as a fluorescent wheel. In Figure 1A , the rotation of the fluorescent wheel is depicted by an arrow rotating about axis A-A, which passes through the substrate 110 and is perpendicular to the planar surface of the substrate 110. Thus, light of different wavelengths is sequentially generated.

[0040] As Figure 1A and Figure 1BAs shown, excitation light 123 (i.e., excitation light or input light) having an excitation wavelength from a light source (not shown) (e.g., a laser-based illumination source) is focused on a phosphor layer. Emission light 124 (i.e., emission light or converted light) having an emission wavelength is generated by the phosphor layer. In this way, the phosphor layer converts the spectrum of the excitation light from a first spectral wavelength range to an emission light (or re-emission) in a second spectral wavelength range, where the first spectral wavelength range and the second spectral wavelength range have different spectral wavelength ranges. When light (e.g., a laser beam blue light) having an excitation wavelength 123 is focused on the phosphor layer, light having an emission wavelength 124 (e.g., yellow light) will be emitted in all directions (including towards the substrate). The reflective layer 120 is used to reflect and redirect this emission light away from the substrate, such that the light is emitted on the same side of the substrate as the side that receives the excitation light. The emission light can be collected (e.g., by a lens) and used for subsequent downstream processes.

[0041] The reflective layer 120 includes an adhesive (A), which can be organic or inorganic; and reflective nanoparticles (B) having a particle size of from about 200 nanometers to about 500 nanometers. In a more specific embodiment, the reflective nanoparticles have a particle size of from about 350 nanometers to about 450 nanometers.

[0042] For the adhesive (A), suitable materials should work for a long time (at least 20,000 hours) within a temperature range of -45°C to 250°C (-49°F to +482°F). Desirably, the adhesive can work at a temperature above 200°C for a long time. The adhesive (A) can be an organic adhesive or an inorganic adhesive.

[0043] An example of an organic adhesive is silicone, such as a reflective resin octamethyltrisiloxane. This silicone is commercially available from Dow or Sumitomo Chemical. Before coating, the silicone can be mixed with an organic solvent, which can include methyl siloxane. An example of the organic solvent is OS-20 sold by Dow Corning Corporation, which is a volatile solvent and used as a diluent to adjust the solution viscosity. The mixed silicone / solvent is uniformly prepared according to process requirements. Before putting it into a mixer for mixing, silicone oil diluent can be added to adjust the viscosity.

[0044] Alternatively, the adhesive (A) can be an inorganic adhesive having certain properties. Desirably, the inorganic adhesive has a coefficient of thermal expansion (CTE) of from about 0.5 to about 25 ppm / °C. In a specific embodiment, the inorganic adhesive is sodium silicate. Sodium silicate is the common name of the compound of the formula (Na2SiO3) n and can also be considered a polymer, as shown in the following formula (I).

[0045]

[0046] Sodium silicate exists in anhydrous form and hydrated form Na2SiO3·nH2O, where n = 5, 6, 8 or 9. The characteristics of sodium silicate can be represented by the weight ratio of silicon dioxide (SiO2) to sodium oxide (Na2O). SiO2:Na2O can vary from 2:1 to 3.75:1. In specific embodiments, SiO2:Na2O can range from about 2.5:1 to about 3.75:1, or from about 2:1 to about 3:1. Sodium silicate is usually provided in aqueous solution form.

[0047] In other embodiments, the inorganic binder can be made of other inorganic materials other than sodium silicate. These inorganic materials can be silicates, aluminates, phosphates, borates or inorganic sol-gels. Examples of inorganic sol-gels include sol-gels made of silicon dioxide (SiO2) or alumina (Al2O3).

[0048] In another exemplary embodiment, the inorganic binder is formed from a first component and a second component. The total dissolved solids (TDS) characteristics of the inorganic binder used are provided in the following table:

[0049]

[0050] This specific inorganic binder is prepared by mixing the first component and the second component and stirring for about 2 to about 3 hours at a temperature of about 25 to about 30 °C. The ratio of the first component to the second component ranges from about 1:1 to about 7:3.

[0051] Desirably, the inorganic binder (A) is substantially optically transparent (e.g., the light transmittance of the inorganic binder is at least 80%, including 90% and at most 98%). It is measured, for example, using a spectrophotometer with a thickness of about 0.1 to about 0.2 mm available from Idea Optics. In contrast, many inorganic binders are opaque.

[0052] In specific embodiments, the inorganic binder of the present disclosure can withstand high temperatures (e.g., greater than 200 °C, including 300 °C or higher, or up to 400 °C), has a high light transmittance (e.g., at least 98%), has a high tensile shear strength (e.g., at least 100 psi at a temperature of 300 °C), can be applied by a flexible coating process (e.g., dispersion, screen printing, spraying), and has a low curing temperature (e.g., below 185 °C).

[0053] The reflective layer also contains reflective nanoparticles (B). It is believed that the presence of the reflective nanoparticles reduces the shrinkage rate of the binder (A), thereby reducing the formation of cracks and bubbles. This avoids stress during assembly and increases the adhesion strength between the reflective layer and the substrate. Ideally, the coefficient of thermal expansion of the reflective nanoparticles should be as close as possible to that of the binder (A), and their densities should also be as close as possible to avoid compositional delamination.

[0054] The reflective nanoparticles have a particle size of from about 200 nanometers to about 500 nanometers (including from about 300 nanometers to about 500 nanometers and from about 350 nanometers to about 450 nanometers). The reflective nanoparticles can be made of pure titanium dioxide (TiO2) or modified TiO2. The modified TiO2 nanoparticles can be surface-modified with organic alcohols, siloxanes, alumina (Al2O3), zirconia (ZrO2), or silica (TiO2). In a preferred embodiment, the reflective nanoparticles are pure TiO2.

[0055] The weight ratio of the reflective nanoparticles to the (A) binder can be from about 1:2.5 to about 1:0.8 (including from about 1:2 to about 1:1). The reflective nanoparticles (B) should be mixed with the binder (A), and then the mixture should be refrigerated before use. For example, the nanoparticles can be mixed with the binder twice, each time for about 2 minutes at 800 rpm, before refrigerating at a temperature of about 4 °C for about 24 hours. It is desirable that the reflective nanoparticles be uniformly dispersed throughout the mixture so that the reflective nanoparticles are also uniformly dispersed throughout the reflective layer.

[0056] The reflective layer can be formed by applying a mixture of the binder (A) and the reflective nanoparticles (B) to a substrate. The mixture can be applied by dispersion, spraying, brushing, flowing, pattern coating, or screen printing.

[0057] In applications where the mixture is applied by dispersion or screen printing, the mixture should have a suitable viscosity of from about 0 to about 1,500 centipoise (cP) (including from about 100 cP to about 800 cP, or from about 100 cP to about 600 cP, or from about 200 to about 500 cP, or from about 1,000 cP to about 1,500 cP). The viscosity is measured using a Brookfield DVE SLVTJO viscometer or in accordance with ASTM D1084. The inorganic binder itself (i.e., without TiO2 nanoparticles) can also have a suitable viscosity of from about to about 1,500 centipoise (cP) (including from about 0 to about 8, or from about 100 cP to about 800 cP).

[0058] In some cases, it is expected that the reflective layer will be built up over multiple application rounds. For example, in the first round, a mixture of an adhesive (A) and reflective nanoparticles (B) is stirred and then sprayed onto a substrate to form a reflective layer with a thickness of about 0.025 mm to about 0.075 mm. Then the first layer is left at room temperature for about 0.5 hours and then cured at a temperature of about 85 °C for about 0.5 hours. In the second round, the mixture of adhesive (A) and reflective nanoparticles (B) is stirred again, then the mixture is sprayed onto the first layer, then left at room temperature for about 0.5 hours and then cured at a temperature of about 85 °C for about 0.5 hours. The above steps result in the reflective layer ultimately having a total thickness of about 0.05 mm to about 0.15 mm.

[0059] It is desirable that the reflective layer is configured to reflect in the wavelength range of about 380 nm to about 800 nm, and more preferably configured to reflect in the range of about 420 nm to about 680 nm. The reflectivity of the reflective resin layer is typically at least (or greater than) 90%, and more preferably at least (or greater than) 94%, or 95%, or 96%, or 97%, or 98%, or 99%.

[0060] The reflective layer can have a total thickness of about 0.05 mm to about 0.15 mm. In a specific embodiment, the reflective layer has a thickness of about 0.07 mm to about 0.12 mm. The set thickness is to maximize the reflectivity of the light output within the desired wavelength range. A thicker layer provides a higher reflectivity, but may also lead to long-term failure, for example due to peeling or cracking of the reflective layer. Therefore, the optimal thickness can be determined by some compromise between the optimal reflectivity and / or reflectivity and durability.

[0061] The reflective layer is typically distinguished (and distinguishable) from the phosphor layer by its composition and / or structure. In particular, the reflective layer is typically significantly more reflective than the phosphor layer. The phosphor layer is typically not reflective. Generally, the reflective layer does not include wavelength-converting materials (e.g., phosphors).

[0062] The reflective layer of the present disclosure containing reflective nanoparticles can maintain at least 95% of the total reflectivity at temperatures above 200 °C. The reflective layer can be cured at relatively low temperatures of 85 °C to 150 °C. The reflective layer shows reliable operation at high laser irradiance and temperature. The reflective layer can also be flexibly made into various sizes, shapes, and thicknesses. The reflective layer can also withstand high operating temperatures, that is, operating temperatures exceeding 200 °C, up to 250 °C. The reflective layer can be used in high-power laser projection display systems, where solid-state laser projectors can be equipped with laser powers of about 60 watts to about 300 watts (including over 100 watts). The operating temperature of such devices can reach above 200 °C, resulting in high luminous brightness.

[0063] In some embodiments, the reflective layer 120 can also serve as an adhesive layer between the substrate 110 and the phosphor layer 130. Alternatively or additionally, an auxiliary adhesive layer (such as glue or tape) can also be used to adhere the phosphor layer to the reflective layer. This is useful for certain solid-state phosphor layers made of, for example, phosphor particles dispersed in glass, crystal, or ceramic materials.

[0064] Return reference Figure 1A and Figure 1C , it can be noted that the width of the reflective layer 120 (measured in the radial direction on the substrate) can vary. In Figure 1A , the width of the reflective layer 120 is much greater than the width of the phosphor layer 130. However, as Figure 1C shown, the width of the reflective layer 120 can also be approximately equal to the width of the phosphor layer 130. Generally, the width of the reflective layer 120 is at least equal to the width of the phosphor layer 130 and can be greater than the width of the phosphor layer.

[0065] It is contemplated that the reflective layers described herein can be used in fluorescent wheels and laser projection display systems. They can also be used in combination with solid-state lighting sources (such as automotive headlights).

[0066] The following examples are used to illustrate the methods of the present disclosure. The examples are illustrative only and are not intended to limit the present disclosure with the materials, conditions, or process parameters described herein.

[0067] Example

[0068] Example 1

[0069] Two fluorescent wheels are fabricated having a reflective layer composed of an inorganic binder and TiO2 nanoparticles. The inorganic binder of the reflective layer is formed from a first and a second component. The characteristics of the total dissolved solids (TDS) of this inorganic binder are provided in the following table:

[0070]

[0071] The weight ratio of the inorganic binder to the TiO2 nanoparticles is 1:1.7. The first fluorescent wheel labeled PT01 uses TiO2 nanoparticles having a particle size of 0.4 - 0.45 μm (i.e., 400 - 450 nm). The second fluorescent wheel labeled PT02 uses TiO2 nanoparticles having a particle size of 0.36 μm (i.e., 360 nm).

[0072] The inorganic binder and the TiO2 nanoparticles are mixed twice in a mixer at 800 rpm for two minutes each to prepare the inorganic scattering layer material (ISLM).

[0073] Interestingly, ISLM acts as a shear-thinning fluid, i.e., when stirred, its viscosity decreases. PT02 powder also tends to agglomerate, resulting in incomplete absorption of the glue. Therefore, ISLM was placed in a 4°C refrigerator for 24 hours to ensure complete absorption of the inorganic binder by PT02 powder. After 24 hours, ISLM was gently stirred by hand to ensure uniform mixing of the materials. The viscosity of ISLM is 1000 - 1500 centipoise (cP).

[0074] ISLM was applied using an automatic sprayer (PVA350). The spray air pressure was adjusted to 3.5 MPa. ISLM was sprayed onto an Al (aluminum) disk twice to obtain a wet reflective layer. The wet reflective layer was left at room temperature for 0.5 hours and cured at 85°F for 0.5 hours to obtain a reflective layer with a thickness of 0.045 mm. A second layer was applied over the first layer to obtain a reflective layer with a total thickness of 0.09 mm. The reflective layer was cured at 185°F for 0.5 hours to ensure complete curing of the reflective layer.

[0075] First, the diffuse reflectance of PT01 and PT02 fluorescent wheels was measured at different reflective layer thicknesses. The results of the PT01 fluorescent wheel are shown in Figure 2A and Table A below, and the results of the PT02 fluorescent wheel are shown in Figure 2B and Table B below. From these results, it can be seen that when the thickness is above 0.08 mm (PT01) or 0.07 mm (PT02), the reflectance stabilizes at greater than 94%.

[0076] Table A. PT01

[0077] Thickness (mm) Diffuse reflectance (%) 0.02 84.2 0.02 90.6 0.04 92.6 0.08 94.2 0.09 94.7 0.09 94.4 0.10 94.5

[0078] Table B. PT02

[0079] Thickness (mm) Diffuse reflectance (%) 0.050 93.0 0.070 94.5 0.075 94.5 0.080 94.4 0.082 94.8 0.093 94.6

[0080] Next, two fluorescent wheels PT01 and PT02 were compared with two other fluorescent wheels. The first control wheel labeled G1 used only an inorganic binder in the reflective layer (i.e., no TiO2 nanoparticles). The second control wheel labeled G1.5 used only an organic binder in the reflective layer (no TiO2 nanoparticles).

[0081] Output power tests were conducted at different thicknesses to compare the PT02 fluorescent wheel and the G1 fluorescent wheel. The results of the PT02 fluorescent wheel are shown in Table C, and in the last column, 100% of the results were obtained from the G1 fluorescent wheel.

[0082] Table C.

[0083] Thickness (mm) Diffuse reflectance (%) Output power 100W % of G1 0.07 94.7 48.0 106.3 0.08 94.7 48.2 106.6 0.09 94.6 48.0 106.2

[0084] Next, a reliability test was conducted to compare the PT02 fluorescent wheel and the G1 fluorescent wheel at 100W and 50W. The test conditions are shown in Table D. Three samples were run for each test. The results of the PT02 fluorescent wheel are shown in Table E. Similarly, 100% of the results were obtained by the G1 fluorescent wheel.

[0085] Table D.

[0086]

[0087] Table E.

[0088] Input power Thermal shock High humidity % of G1 output power 100W 106.2％ 105.9％ 106.3％ 50W 106.1％ 106.1％ 106.2％

[0089] Finally, the PT02 fluorescent wheel and the G1 fluorescent wheel were compared at 100W and 50W. The samples were placed in a muffle furnace at 250°C, and the output performance was tested over time. The results of the PT02 fluorescent wheel are shown in Table F. Similarly, 100% of the results were obtained by the G1 fluorescent wheel. The results show that the PT02 fluorescent wheel is stable and no cracks have occurred between the reflective layer and the phosphor layer.

[0090] Table F.

[0091] Time (hours) 100W 50W 0 106.3％ 106.2％ 115 105.9％ 106.0％ 206 106.3％ 105.8％ 349 106.1％ 106.1％ 513 106.0％ 105.9％

[0092] The output power test was conducted at different thicknesses to compare the PT01 fluorescent wheel and the G1 fluorescent wheel. The results of the PT01 wheel are shown in Table G. In the last column, 100% of the results were obtained by the G1 fluorescent wheel.

[0093] Table G.

[0094]

[0095] Next, a reliability test was conducted to compare the PT01 fluorescent wheel and the G1 fluorescent wheel at 100W and 50W. The test conditions are as shown in Table D above. Three samples were run for each test. The results of the PT01 fluorescent wheel are shown in Table H. Similarly, 100% of the results were obtained by the G1 fluorescent wheel.

[0096] Table H.

[0097] Input power Thermal shock High humidity Low temperature % of G1 output power 100W 106.0％ 106.1％ 106.3％ 106.4％ 50W 106.0％ 105.5％ 106.3％ 106.1％

[0098] Finally, compare the PT01 fluorescent wheel and the G1 fluorescent wheel at 100W and 50W. Place the sample in a muffle furnace at 250 °C and test the output performance over time. The results of the PT01 fluorescent wheel are shown in Table I. Similarly, 100% of the results were obtained with the G1 fluorescent wheel. The results show that the PT01 fluorescent wheel is stable and no cracks are generated between the reflective layer and the phosphor layer.

[0099] Table I .

[0100] Time (hours) 100W 50W 0 106.2％ 106.3％ 230 106.1％ 106.1％ 350 106.1％ 106.1％ 500 105.4％ 106.1％

[0101] Example 2

[0102] Diffusivity tests were carried out with different types of nanoparticles: TiO2, Al2O3 and Al. The binder is an inorganic binder. Layers of different thicknesses were prepared and the diffusivity (i.e., diffuse reflectance) was tested. Table J describes five different mixtures and Table K provides the diffusivity results for three mixtures. It can be noted that since the mixtures were spray-coated by hand, the given layers can have different thicknesses.

[0103] Table J.

[0104]

[0105] Table K.

[0106] Mixture # Layer thickness (mm) Diffusivity (%) 2 0.05-0.07 84-86,89,89 2 0.06-0.08 89-90 2 0.08-0.09 89.5 2 >0.08 90-92 2 >0.1 88.9 3 0.1-0.15 76-86 3 0.13-0.18 91-92 3 0.2-0.3 87-89 3 >0.2 88 4 0.05-0.07 89-90 4 0.09 91-92 4 >0.1 92-96 4 0.15-0.17 86-94 4 0.18 94 4 0.15-0.2 89-94 4 0.2 95.9 4 >0.2 94-97

[0107] The results in Table K show that when the layer thickness exceeds 0.15 mm, the diffusivity of Al2O3 nanoparticles exceeds 94%. However, the reflectivity of Al2O3 is unstable (i.e., varies greatly), and the thickness of Al2O3 required is greater than that of TiO2 nanoparticles with the same reflectivity. Al2O3 is also prone to cracking. Therefore, it is concluded that TiO2 is the best nanoparticle for high-reflectivity layers.

[0108] Example 3

[0109] Diffusivity tests were carried out using different TiO2 nanoparticles from different suppliers, as well as Al(OH)3 and MgO. The binder is an inorganic binder. Layers of different thicknesses were prepared and the diffusivity was tested. Table L describes six different mixtures and Table M provides the diffusivity results for five mixtures. It can be noted that the MgO particles are large and cannot be uniformly mixed.

[0110] Table L.

[0111]

[0112] Table M.

[0113]

[0114] Mixture #5 can achieve a diffusivity greater than 94%. The results also show that diffuse reflectivities greater than 90% can be achieved using TiO2 nanoparticles of 0.2 μm and 0.5 μm.

[0115] The subject matter of the present disclosure has been described with reference to preferred embodiments. After reading and understanding the foregoing detailed description, others may conceive of modifications and variations. As long as the above modifications fall within the scope of the appended claims or their equivalents, the present disclosure is to be construed as including all such modifications and variations.

Claims

1. A wavelength conversion device, comprising: substrate; A reflective layer on the substrate, the reflective layer comprising: Binder (A), wherein the binder (A) is an inorganic binder comprising an inorganic sol-gel made of silica or alumina; and reflective titanium dioxide (TiO2) nanoparticles (B), the reflective titanium dioxide (TiO2) nanoparticles (B) being surface-modified with an organic alcohol, a siloxane, aluminum oxide (Al2O3), zirconium dioxide (ZrO2) or silicon dioxide (SiO2), the reflective titanium dioxide (TiO2) nanoparticles (B) having a particle size of 200 nm to 500 nm, wherein the weight ratio of the reflective titanium dioxide (TiO2) nanoparticles (B) to the binder (A) is from 1:2 to 1:1; and a wavelength conversion layer on the reflective layer; The reflective layer is thermally stable at a working temperature of 250°C.

2. The wavelength conversion device according to claim 1, wherein: The reflective layer has a thickness of 0.05 mm to 0.15 mm.

3. The wavelength conversion device according to claim 1, wherein: The reflective titanium dioxide (TiO2) nanoparticles (B) have a particle size of 350 nm to 450 nm.

4. The wavelength conversion device according to claim 1, wherein: The reflective layer has a reflectivity of at least 95% for light with a wavelength of 420 nm to 680 nm.

5. The wavelength conversion device according to claim 1, wherein: The wavelength conversion layer is a phosphor layer, and the phosphor layer includes phosphor particles dispersed in glass, crystal, or ceramic material. The wavelength conversion device according to claim 1 , wherein: The substrate has a disk shape. 7 . The wavelength conversion device according to claim 1 , further comprising a motor for rotating the substrate.

8. The wavelength conversion device according to claim 1, wherein: The substrate is made of metal, non-metal or composite materials. 9 . A light projection system, comprising the wavelength conversion device according to claim 1 .

10. A method for manufacturing a wavelength conversion device, the method comprising: A composition is applied to a substrate to form a reflective layer on the substrate, the composition comprising: Binder (A), wherein the binder (A) is an inorganic binder comprising an inorganic sol-gel made of silica or alumina; and reflective titanium dioxide (TiO2) nanoparticles (B), the reflective titanium dioxide (TiO2) nanoparticles (B) being surface-modified with an organic alcohol, a siloxane, aluminum oxide (Al2O3), zirconium dioxide (ZrO2) or silicon dioxide (SiO2), the reflective titanium dioxide (TiO2) nanoparticles (B) having a particle size of 200 nm to 500 nm, wherein the weight ratio of the reflective titanium dioxide (TiO2) nanoparticles (B) to the binder (A) is from 1:2 to 1:1; curing the composition at a temperature of 85°C to 150°C; and forming a wavelength conversion layer on the reflective layer; The reflective layer is thermally stable at a working temperature of 250°C.

11. The method according to claim 10, wherein: The composition has a viscosity of up to 1500 centipoise (cP).

12. The method according to claim 10, wherein: The composition is applied by dispensing, spraying, brushing, flowing, coating or screen printing.

13. The method according to claim 10, further comprising: Before applying the composition to the substrate, the surface of the reflective titanium dioxide (TiO2) nanoparticles (B) is modified with the organic alcohol, the siloxane, aluminum oxide (Al2O3), zirconium dioxide (ZrO2) or silicon dioxide (SiO2).

14. The method according to claim 10, further comprising: The composition is formed by the following steps: mixing the reflective titanium dioxide (TiO2) nanoparticles (B) with the binder (A) to form a mixture, and The mixture is refrigerated to form the composition before applying the composition to the substrate to form the reflective layer.

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