JP7224355B2 - Porous, micron-sized particles for tuning light scattering - Google Patents

Description

Light emitting diodes can be used as white light sources in various applications such as flash light sources and filament lamps for mobile phone cameras. Such LEDs are sometimes referred to herein as white LEDs.

A white LED may appear to emit white light from an observer's point of view when the LED is in an ON state. However, these LEDs may actually consist of a light-emitting semiconductor structure that emits non-white light and a wavelength-converting structure that makes the non-white light appear white to an observer. For example, a white LED may be formed from a blue-emitting semiconductor structure covered with a yellow-emitting phosphor layer. Photons of blue light emitted by the light-emitting semiconductor structure can pass through the yellow-emitting phosphor layer as blue photons or be converted to yellow photons by the yellow-emitting phosphor layer. The combination of the blue and yellow photons ultimately emitted from the LED makes the light emitted from the LED appear white to an observer.

LEDs are also available over a range of dimtone settings. However, for example, an LED that appears to emit cooler light at high dimtone settings may appear to emit cooler light at low dimtone settings. Similarly, for example, an LED that appears to emit a warmer light at low dimtone settings may appear to emit a warmer light at high dimtone settings.

Described herein are optically functional porous structures for use in LEDs and methods of making such optically functional porous structures. The optically functional porous structure comprises a non-absorbing material structure which may be a dielectric structure comprising a plurality of submicron pores and a polymer matrix. The non-absorbing material structure itself may be composed of a plurality of micron-sized porous particles. Further, at the first temperature the refractive index of the non-absorbing material structure differs from the refractive index of the polymer matrix, and the refractive index difference between the refractive index of the non-absorbing material structure and the refractive index of the polymer matrix is the optical A plurality of sub-micron pores within the porous structure functioning as are configured to have light scattering capability at a first temperature. Since the refractive index difference between the refractive index of the non-absorbing material structure and the refractive index of the polymer matrix decreases with changes in temperature, the light-scattering ability of multiple submicron pores is also affected by these corresponding temperature changes. change with

1 is a diagram of an exemplary light emitting device (LED) including a light emitting semiconductor structure and a layer of material that is white in the off state; FIG.

FIG. 4 is an illustration of an exemplary off-state white layer composed of micron-sized porous particles with interconnections of submicron pores filled with a polymer matrix.

FIG. 10 is another exemplary off-state white layer composed of mesh slabs with submicron pore interconnections filled with a polymer matrix.

FIG. 2 is a scanning electron micrograph of a cross-section of a micron-sized porous glass bead particle containing sub-micron pores with silicon implanted therein.

FIG. 10 is a diagram (photograph) of a drop-casted silicone layer at 25° C. loaded with micron-sized porous particles of 25-45 μm diameter containing sub-micron pores.

FIG. 10 is a diagram (photograph) of a drop-cast silicone layer at 200° C. doped with micron-sized porous particles of 25-45 μm in diameter containing sub-micron pores.

FIG. 2 is a graphical representation of light transmission as a function of temperature in a 4 nm to 150 μm layer of high refractive index silicone containing 25% by weight of 50 μm sized porous silica particles with an effective pore size of 100 nm.

1 is a microscopic image of micron-sized porous particles filled with silicone and containing air voids.

A graphical representation showing the shift in color point of light generated from a 1202 COB chip light source whose drive current lead is shifted from 10mAmp to 400mAmp, the 1202 COB light source consists of interconnected submicron pores filled with a polymer matrix. is overlaid by a cover layer comprising micron-sized porous particles having a

1 is a flow diagram of a method for tuning light scattering using an optically functional porous structure.

White LEDs may appear to emit white light in the on state, but such LEDs may appear to be the color of the wavelength converting material when turned off. For example, a white LED that includes a yellow emitting phosphor layer may appear yellow or green to an observer when turned off, such as when viewed on a store shelf. Nonetheless, a typical consumer may expect products containing white LEDs to appear white even in the off state. For example, a person who goes into a store to buy a white light bulb usually expects the white light bulb to actually appear white, and if the bulb appears yellow or green, assumes the bulb is defective. can be The same may be true for mobile phone consumers, who may expect camera flashes to appear white. Such products would sell better to consumers if the LEDs looked as white in the off state as they did in the on state.

A change in the color point of the LED light may be desirable. For example, when the LED lights are dimmed, users may prefer to see warmer colors at these lower dim tone settings. Conversely, when the LED light is bright, users may prefer to see cooler colors. Increasing the drive current leads to an increase in temperature, resulting in a change in color point if the change in light scattering correlates with temperature change. This is due in part to changing the relative amount of scattered blue light to the amount of red light emitted from the LED, for example because blue light scatters light more strongly than red light. This is because the perceived color point of the light may change.

Granules of white, non-phosphor, inert material to provide a white appearance in the off state for LEDs in the off state, or to provide a warmer color when the illumination is dimmed to dark has been used. These granules are often submicron sized granules. This is because particles of this size can serve as particularly effective light scattering elements. Examples of such materials include titanium dioxide ( _TiO2 ) and zirconium oxide ( _ZrO2 ). Sub-micron sized particles of these materials can be mixed with transparent materials such as silicones and applied over non-white LED surfaces to make them appear whiter to an observer, e.g. in the LED off state. can be done. However, such granules of white, non-phosphor, inert material may remain white while the device is on, resulting in some scattering of the light emitted by the LED in the on state. , can reduce the lumen output of the LED.

In these examples, the magnitude of light scattering in either state depends on the concentration of submicron particles in the optically functional layer and the refractive index difference between the submicron particles and the transparent material. Regarding the former, increasing the concentration of submicron particles can increase off-state light scattering. However, as the concentration of these particles increases, this can lead to a decrease in the lumen output of the LED in the ON state. Additionally, there may be problems in processing the material. For example, mixing of materials becomes increasingly difficult as the viscosity of the mixture increases with increasing concentration of submicron particles. Another problem can be that the final layer is too brittle due to high particle loading.

Regarding the refractive index difference between the refractive index of the submicron particles and the refractive index of the transparent layer, the difference must be large enough so that sufficient light scattering from the submicron particles can occur. Conversely, the refractive index difference should not be too large so that light scattering does not occur at all temperatures within the possible range of use. For example, if the refractive index of the transparent layer was very high compared to the refractive index of the submicron particles, the lowering of the refractive index of the transparent layer may not be sufficiently close to the refractive index of the submicron particles, and the range of use Light scattering will occur over all temperatures within.

Since the temperature of an LED can increase in the on state compared to the off state, and increased light scattering can reduce the lumen output of the LED, light scattering increases with increasing temperature. Ideally it should be reduced. As mentioned above, the most commonly used scattering particles are _TiO2 . However, the refractive index of _TiO2 is high, while the refractive index of silicone, a commonly used transparent layer material, is low, and the refractive index difference between the two is greater than 0.5. Using this combination of materials, an increase in temperature can result in a larger refractive index difference between TiO ₂ and silicone, leading to greater light scattering in the on-state. Therefore, it may be more suitable to use scattering particles with a lower refractive index relative to transparent materials.

An example of such particles is _MgF2 with a refractive index of 1.37. Its refractive index is smaller than, but close to, high index silicone, which can have a refractive index of 1.55. However, since the refractive index difference between the two materials is only 0.16, a much higher concentration of _MgF2 is required to achieve sufficient light scattering in the off-state, which is similar to It can lead to problems in processing the material.

Embodiments described herein provide white LEDs that may appear white to an observer in both the ON and OFF states of the LED, yet may reduce or eliminate scattering in the ON state of the LED. This makes products containing such LEDs more aesthetically pleasing to the observer, without affecting the quality of the LEDs themselves or the structure of their materials. The embodiments described herein adjust the color point such that at low dimtone settings the color point shifts to warmer colors, while at high dimtone settings the color point shifts to cooler colors. It can also provide an adjustable LED light. Such embodiments may rely on the refractive index difference between the refractive index of a transparent material, which may be a polymer matrix, and the refractive index of a non-absorbing material, which may be a dielectric material. .

In some embodiments, the non-absorbing material structure itself may be composed of micron-sized porous particles dispersed throughout the optically functional layer, the micron-sized porous particles within the particles themselves. contains a network of interconnected submicron pores. In some embodiments, the non-absorbing material structure may instead consist of a mesh slab of porous dielectric material that itself contains a network of submicron pores. In each case, the submicron pores are filled with the polymer matrix forming an interface between the polymer matrix and the non-absorbing material in the shape of the submicron pores. This, combined with the different temperatures of the LED in the on versus off state, or low versus high intensity (the refractive index of the materials described in this article can vary as a function of temperature), results in the properties disclosed in this article. relied on to form LEDs with

In some embodiments, the refractive index of the polymer matrix is greater than the refractive index of the non-absorbing material structure in the LED off state, allowing light scattering effects to occur at the interface between the two materials. However, in the LED-on state, as the temperature increases, the refractive index of the polymer matrix decreases, leading to a refractive index difference between the non-absorbing material delineating the shape of the submicron pore and the polymer matrix filling the submicron pore. is reduced, resulting in reduced or no light scattering by non-absorbing materials to submicron pore interfaces. These features scatter light at lower temperatures, such as room temperature, when the LED is in the off state and appear white, and do not scatter light, or at least are scattered, when the LED is in the on state at a higher temperature. LED light can be provided that reduces the amount of light (which can lead to an increase in LED light output).

These refractive index properties can also provide LEDs in which changes in intensity change light scattering. For example, if the intensity of the LED is high, the temperature will increase and light scattering may decrease accordingly. This may allow changing the color point setting of the LED lights. For example, blue light, which contributes to cooler light tones that are scattered more strongly than red light, may be more affected by changes in their temperature and light scattering capabilities. In this case, an increase in temperature, which can reduce light scattering, can result in more blue light being detected, causing a shift of the color point to cooler colors. Conversely, when the intensity of the LED is low, the temperature may drop and light scattering may correspondingly increase. In this example, a decrease in temperature and an increase in light scattering can result in less blue light being detected, shifting the color point to warmer colors.

In some embodiments, the refractive index of the non-absorbing material is greater than the refractive index of the polymer matrix, and increasing temperature reduces light scattering. This can impair changing the color point setting of LED lights. This embodiment can at least be used, for example, to prevent or minimize undesirable color shifts that would otherwise occur as temperature increases. Color change can be reduced by increasing light scattering as the temperature increases. This embodiment can also be used to shift the color point to warmer colors as the temperature increases.

In some embodiments, the non-absorbing material structure itself may be composed of a plurality of micron-sized porous particles containing a network of sub-micron pores dispersed throughout. Alternatively, the non-absorbing material structure may itself consist of a mesh slab of porous dielectric material containing a network of submicron pores. In each of these embodiments, the submicron pores are filled with a polymer matrix to form an interface between the polymer matrix and a non-absorbing material structure that is approximately in the shape of the submicron pores.

In each of these embodiments, the refractive index of the polymer matrix is greater than the refractive index of the non-absorbing material structure in the LED off state, allowing light scattering effects to occur at the interface between the two materials. However, in the LED-on state, as the temperature increases, the refractive index of the polymer matrix decreases, leading to a refractive index difference between the non-absorbing material delineating the shape of the submicron pore and the polymer matrix filling the submicron pore. is reduced, resulting in reduced or no light scattering by the submicron pore-dielectric surface interface. These same inherent properties of the material also allow for varying color point settings of the LED light. For example, at low brightness the LED light may shift towards warmer tones and at high brightness the LED light may shift towards cooler tones.

The refractive index of non-absorbing materials can also decrease with increasing temperature, but the change in refractive index between the first and second temperatures is similar to that of the polymer at the first and second temperatures. Low compared to the change in refractive index of the substrate. A solid material, such as a non-absorbing material, has a much lower coefficient of expansion than, for example, silicone, and thus a much smaller change in refractive index as a function of temperature. Thus, changes in temperature have a greater effect on the refractive index of polymer matrices than non-absorbing materials. Further details regarding polymer matrices and non-absorbing materials are described below and shown in FIG.

Furthermore, with respect to the refractive index difference between the two materials, there should be a minimum difference between the refractive indices of each material in order to achieve sufficient light scattering in the off-state. Notably, this minimum value can be influenced by factors such as the concentration of light scattering particles in the optically functional layer. For example, if the difference in refractive index between materials is smaller, a higher concentration of light scattering particles will compensate for the relatively small difference in refractive index between materials, equivalent to a lower concentration of light scattering particles. It can help achieve greater levels of light scattering than at even refractive index differences. However, there is a limit to the concentration of particles that can be placed in a layer without compensating for its shape. Conversely, to sufficiently reduce ON-state light scattering, the difference between the refractive indices of each material can be only some maximum value. If the refractive index difference between the two materials is too large to be sufficiently reduced within any reasonable temperature change, no functionally effective reduction of light scattering can occur in the on-state.

In some embodiments, the refractive index difference between the refractive index of the non-absorbing material and the refractive index of the polymer matrix is 0.3 or less. In some embodiments, the refractive index difference between the refractive index of the non-absorbing material and the refractive index of the polymer matrix is 0.2 or less. According to an embodiment, the refractive index difference between the refractive index of the non-absorbing material and the refractive index of the polymer matrix is 0.1 or less. In one exemplary embodiment, the refractive index difference between the refractive index of the non-absorbing material and the refractive index of the polymer matrix is 0.07.

The features described herein provide an LED that scatters light at room temperature when the LED is in the OFF state, appears white, and reduces the amount of light scattered when the LED is in the ON state. Other embodiments, such as color point adjustment, rely on the same principles of refractive index difference and refractive index change as a function of temperature described herein.

FIG. 1A shows an exemplary light emitting device (LED) 100 including a light emitting semiconductor structure 115, a wavelength converting material 110, and a material that is white in the off state. The off-state white material may be an optically functional porous structure 105 comprising a plurality of micron-sized porous particles or mesh slabs containing sub-micron pores. Contacts 120 and 125 may be coupled to light emitting semiconductor structure 115, either directly or via other structures such as submounts, for electrical connection to a circuit board or other substrate or device. In embodiments, contacts 120 and 125 may be electrically isolated from each other by gap 127, which may be filled with a dielectric material. Contacts or interconnects 120 and 125 may be, for example, solder, stud bumps, or gold layers. An optically functional porous structure 105 comprising a plurality of micron-sized porous particles or mesh slabs containing sub-micron pores is in contact with the LED.

In some embodiments, light emitting semiconductor structure 115 emits blue light. In such embodiments, wavelength converting material 110 may include, for example, a yellow emitting wavelength converting material, or a green and red emitting wavelength converting material, which emits light emitted by the respective phosphors. Produces white light when combined with the blue light emitted by 115 . In other embodiments, light emitting semiconductor structure 115 emits UV light. In such embodiments, wavelength converting material 110 may include, for example, blue and yellow wavelength converting materials or blue, green and red wavelength converting materials. To adjust the spectrum of light emitted from LED 100, wavelength converting materials that emit other colors of light may be added. In some embodiments, the color point of this LED 100 may be shifted based on the properties of the optically functional porous structure 105 described herein.

FIG. 1B is an enlarged view of an embodiment of an optically functional porous structure 105, wherein the optically functional porous structure 105 comprises a plurality of micron-sized porous particles 150. FIG. Distributed throughout each micron-sized porous particle 150 is a network of submicron pores 165 (shown in FIG. 2), which are filled with a polymer matrix 180 (shown in white) in this figure. ing. A plurality of submicron pores 165 form an interconnected network surrounded by non-absorbing material 160 (shown in white). In some embodiments, the micron-sized porous particles 150 may be micron-sized porous glass bead particles. In an exemplary embodiment, the micron-sized porous particles 150 may be micron-sized porous silica particles. In one embodiment, the micron-sized porous particles 150 are micron-sized porous magnesium fluoride particles.

FIG. 1C is an enlarged view of an embodiment of an optically functional porous structure 105, wherein the optically functional porous structure 105 is a non-absorbing material having a plurality of submicron pores (not shown). It includes a mesh slab formed at 160, the pores of which are filled with polymer matrix 180 in this view. In this embodiment, an interconnected network of polymer matrix 180 is formed throughout the mesh slab, and the interface between polymer matrix 180 and the non-absorbing material 160 of the surrounding mesh slab (interface in FIG. 2). 170).

FIG. 2 is a scanning electron micrograph showing a cross-section of an exemplary micron-sized porous particle 150 . Submicron pores 165 are dispersed through the micron-sized porous particles 150 . Submicron pores 165 are surrounded by non-absorbing material 160 structures to form an interconnected network within micron-sized porous particles 150 . In this embodiment, submicron pores 165 are filled with polymer matrix 180 . Light encountering micron-sized porous particles 150 containing submicron pores 165 is multiply scattered. Transmission is not eliminated, but limited to only a portion of the light that would otherwise pass through a completely transparent structure. In some embodiments, the micron-sized porous particles 150 may be micron-sized porous glass bead particles.

In some embodiments, polymer matrix 180 is any optically functional material including silicone; heat and light resistant substrates such as optical grade silicone matrices; or sol-gel materials, organically modified ceramics. (ormocer), or any other suitable material such as a polysilizane-based matrix. In one exemplary embodiment, polymer matrix 180 may be a high refractive index silicone. Non-limiting examples of silicones can include phenylated silicones (ie, methylphenyl), and silicones loaded with high refractive index nanoparticles.

According to some embodiments, the refractive index of the polymer matrix 180 may be greater than the refractive index of the micron-sized porous particles 150 or the non-absorbing material 160 of the mesh slab network. In some embodiments, the refractive index of the polymer matrix 180 may be less than the refractive index of the micron-sized porous particles 150 or the non-absorbing material 160 of the mesh slab network. In some embodiments, the polymer matrix is silicone with a refractive index in the range of at least 1.4 to 1.7 at room temperature. In some embodiments, the polymer matrix is silicone having a refractive index at room temperature in the range of at least 1.46-1.56. In some embodiments, the silicone has a refractive index at least in the range of 1.50-1.56 at room temperature. In some embodiments, the refractive index of polymer matrix 180 may decrease as temperature increases. In some embodiments, the refractive index of the silicone may decrease at elevated temperatures and may range from at least 1.46 to temperatures below the upper temperature limit disclosed for refractive index at room temperature. In some embodiments, the refractive index of the polymer matrix decreases by no more than 0.1 at elevated temperatures compared to the refractive index of the polymer matrix at room temperature.

As mentioned above, not only the material's refractive index at room temperature, but also the material's coefficient of expansion influences which materials should be chosen for each layer. For example, a solid material, eg, non-absorbing material 160 in its final state, has a much lower coefficient of expansion than, for example, silicone, and thus a much smaller change in refractive index as a function of temperature. Thus, changes in temperature have a greater effect on the refractive index of polymer matrix 180 than non-absorbing material 160 in the embodiments described herein.

In some embodiments, micron-sized porous particles 150 are glass formed from any material including porous silica particles or any other suitable material having a refractive index less than that of polymer matrix 180. It may contain bead particles. In one exemplary embodiment, the micron-sized porous particles 150 may be porous silica. A non-limiting example of non-glass bead micron-sized porous particles 150 is micron-sized porous magnesium fluoride particles.

The lower diameter limit of micron-sized porous particles 150 must be large enough to have a sufficient amount of material containing submicron pores 165 therein such that a sufficient level of light scattering can be achieved. . Conversely, the upper diameter limit of micron-sized porous particles 150 should be small enough to keep the optically functional layer as thin as possible. In some embodiments, the micron-sized porous particles 150 can have a diameter greater than the thickness of the optically functional layer. In some embodiments, micron-sized porous particles 150 can have diameters in the range of 3 μm to 700 μm. In some embodiments, micron-sized porous particles 150 can have diameters in the range of 3 μm to 150 μm. In some embodiments, micron-sized porous particles 150 can have diameters in the range of 50 μm to 150 μm. In some embodiments, micron-sized porous particles 150 can have diameters in the range of 3 μm to 50 μm. In some embodiments, micron-sized porous particles 150 can have diameters in the range of 10 μm to 50 μm. In some embodiments, micron-sized porous particles 150 can have diameters in the range of 10 μm to 100 μm. In an exemplary embodiment, micron-sized porous particles 150 may have a diameter of 50 μm. In particular, the strongest effect can be observed with the largest particles, but the thickness of the optically functional layer 105 must also be considered.

Regarding the packing density of the micron-sized porous particles 150 in the optically functional layer, as much It is preferred to be as large as possible so that a lot of scattering can be obtained. In one embodiment, the random packing limit of monodisperse spheres is 64 vol%. When a bimodal distribution is used, the voids between the micron-sized porous particles 150 may be filled with smaller sized micron-sized porous particles 150, with a maximum filling factor of, for example, 70% or Increase to 80%. In embodiments where the micron-sized porous particles 150 used are not monodisperse, or not completely monodisperse, a filling volume fraction of between 40% and 55% is reached. Lower packing densities are possible, but it reduces the off-state white effect and may also require increasing the layer thickness.

In some embodiments, the size of the sub-micron pores 165 of the micron-sized porous particles 150 can have diameters in the range of 50-400 nm. In an exemplary embodiment, submicron pores 165 have a diameter of 200 nm. In one embodiment, submicron pores 165 have a diameter of 100 nm.

In some embodiments, the volume occupied by submicron pores 165 is in the range of about 0.6 cm ³ /g to 1.5 cm ³ /g for grams of micron-sized porous particles 150 . In some embodiments, the volume occupied by submicron pores 165 is in the range of about 0.8 cm ³ /g to 1.2 cm ³ /g for micron-sized porous particles 150 . In one exemplary embodiment, the volume occupied by submicron pores 165 is about 0.9 cm ³ /g for micron-sized porous particles 150 . The volume occupied by submicron pores 165 within the optically functional porous structure 105 is at least as large as the materials used and their respective properties, the micron-sized porosity required for optimal light scattering at room temperature. Depending on the number of particles 150 and the integrity of the optically functional porous structure 105, it may vary outside the ranges given.

In some embodiments, depending on the pore size, the surface area to pore volume can be from about 10 m ² /g to 40 m ² /g. The surface area to pore volume occupied by submicron pores 165 within the optically functional porous structure 105 is at least as large as the materials used and their respective properties, the micron size required for optimal light scattering at room temperature. , and the integrity of the optically functional porous structure 105, may vary outside the ranges given above.

In the example where porous non-absorbing material 160 forms a mesh slab, non-absorbing material 160 (shown in FIG. 1C), the material has a refractive index lower than that of porous silica particles, or polymer matrix 180. It may be formed from any material, including any other suitable material having a For applications in LEDs, non-absorbing material 160 should be stable at high flux, temperature, and humidity. In some embodiments, inorganic materials are preferred. In one exemplary embodiment, the mesh slab of porous non-absorbing material 160 may be formed from porous silica.

Figures 3A and 3B show an optical mixture of silicone as the polymer matrix 180 (shown in Figures 1B and 2) and porous silica as the micron-sized porous particles 150 (also shown in Figures 1B and 2). 10 is a microscopic image of a droplet of functional porous structure 105. FIG. A mixture was prepared by combining the solvent, silicone, and porous silica together to form droplets. After mixing, the solvent was evaporated and the droplets were cured at 150°C to form optically functional material 105 . Micron-sized porous silica particles are dispersed throughout each droplet of optically functional material 105, and sub-micron pores 165 (shown in FIG. 2) of the micron-sized porous silica particles are Filled with silicone.

The image in Figure 3A represents the droplet sample at 25 °C. Porous silica particles are indicated by multiple small particles within the droplet itself. At this temperature, the silicone-loaded porous silica particles exhibit a , scatters white light.

The image in Figure 3B represents the droplet sample at 200 °C. At this temperature, the silicone-loaded porous silica particles scatter less white light than the silicone-loaded porous silica particles observed at 25°C. This is due, at least in part, to the reduction in refractive index difference between the refractive indices of porous silica and silicone at elevated temperatures.

In one embodiment, the temperature is held constant and the effect of using a silicone with a refractive index different from that of other silicones is evaluated. Micron-sized porous particles 150, consisting of porous silica beads with a diameter of 25 μm to 40 μm and an average submicron pore size of about 200 nm, dispersed in silicone with a refractive index of 1.56 to scatter light at 25°C. An optically functional layer with a thickness of 200 μm having a porous structure was formed. There was no detectable light scattering at 25°C when silicone was substituted, which has a refractive index of 1.46, which is close to that of porous silica. (Data not shown.) This effect can be attributed, at least in part, to a reduction in the refractive index difference between the materials, where the refractive index difference between the materials was near zero.

FIG. 4 shows an optically functional porous structure 105 (shown in FIGS. 1A, 1B, and 1C) containing 25% by weight of porous silica beads having a diameter of 50 μm as micron-sized porous particles 150. Provides a quantitative assessment of competence. The submicron pores 165 of porous silica beads with an effective pore size of 100 nm (shown in Figure 2) are filled with high refractive index silicone as the polymer matrix 180 (shown in Figures 1B and 2) and the scatters light as Direct transmission of light having a wavelength of 450 nm and an intensity of 10 W/cm ² is transmitted at various temperatures through a layer of optically functional porous structure 105 containing micron-sized porous silica beads dispersed throughout. be done. The intensity of transmitted light detected at each temperature is measured. In one embodiment, the laser spot on the layer is 1.3 mm in diameter and light detection is through the use of an integrating sphere with a 5 mm aperture positioned approximately 2 cm behind the layer, aligned with the 450 nm laser. done.

The percentage of light transmitted through the layer at the first temperature (ie 30°C) is 0.75%. This intensity is determined and normalized to itself to give 1.0 units as shown in FIG. The intensity of transmitted light detected at the second temperature is determined and normalized to the intensity of light detected at the first temperature. The intensity of transmitted light is measured for each subsequent temperature to which the layer is exposed and normalized to the intensity of transmitted light detected at the first temperature. As shown in Figure 4, the intensity of light transmitted through the layer increases with increasing temperature, and the intensity of transmitted light when the layer is exposed to 200°C is greater than that when the layer is exposed to 30°C. 30 times higher than the intensity of the transmitted light. Even at temperatures below 200°C, the intensity of transmitted light increases as the temperature rises above 70°C to 80°C. For example, at 130° C., the intensity of light transmitted through the layer is approximately ten times higher than the intensity of light transmitted at 30° C. in this embodiment.

Apart from refractive index variations, air voids are often observed to exist inside micron-sized porous particles 150 . FIG. 5 is an optical microscope image showing the presence of air voids 185 (indicated by the thicker arrows) within micron-sized porous particles 150 . These are visible under a microscope as internal structures within micron-sized porous particles 150 .

Air voids 185 also contribute to scattering of light from optically functional layer 105 made of the materials described herein. Air voids 185 may be formed as a result of incomplete filling of submicron pores 165 by polymer matrix 180 (i.e., silicone), e.g., curing of the silicone inside submicron pores 165 followed by cooling. can also be formed when When silicone cures at high temperatures (ie 150°C), it expands significantly due to its high coefficient of expansion. As the temperature decreases, the silicone shrinks again, and insufficient cross-linked silicone can inject back into the micron-sized porous particles 150, causing the silicone in the micron-sized porous particles 150 to shrink. are stressed and may exhibit local delamination or cohesive failure. When the layer is heated again, for example by switching on the LED, the silicone expands again and completely or partially fills the air void 185 and the air void disappears. The net effect is to increase the switching amplitude of the optical power between samples at two different temperatures.

As previously described, the micron-sized porous particles 150 having submicron pores 165 described herein for off-state white or formed from a non-absorbing material 160 with submicron pores. A mesh slab with a mesh may be used in other applications. For example, color point control, filament lamps, switchable lenses.

Regarding color point control, a color point shift can be observed with increasing temperature. For example, increasing the drive current leads can increase the temperature of the LED, thereby shifting the color point of the LED light to cooler light colors. Conversely, decreasing the drive current lead lowers the temperature, which can shift the color point of the LED light to warmer colors. This is at least in part because each color of light has a different ability to scatter light. For example, blue light is scattered more strongly than red light, so in the aforementioned layers, increasing temperature reduces light scattering and relatively more blue light is emitted. In this embodiment, the color point shifts to cooler white light. Conversely, as the temperature decreases, light scattering increases and relatively less blue light is emitted. In this embodiment, the color point shifts to warmer white light.

In one embodiment, porous silica as micron-sized porous particles 150 (shown in FIGS. 1B and 2) dispersed in silicone as the polymer matrix 180 (shown in FIGS. 1B and 2). The containing layer was deposited on a 1202 COB chip. This chip is a light source that provides bright light and can be used in place of LED light sources. A 1202 COB chip write including the additional layers described herein was subjected to a drive current lead of 10 mAmp associated with a temperature of approximately 25°C. Increasing the drive current lead to 400 mAmp caused a corresponding temperature rise to 85°C. As shown in FIG. 6, a color point shift occurred along the u′ axis, which is primarily representative of the color of red light. More red light was detected at 25°C and less red light was detected at 85°C.

FIG. 6 also shows a relatively smaller shift along the v' axis, representing predominantly green light color, as the drive current lead is shifted from 10 mAmp to 400 mAmp. However, not only is the magnitude of the shift along the v' axis smaller than that along the u' axis, but also the degree to which changes in green light detection affect warmer versus cooler light is The equivalent shift in red light detection is much less than it affects warmer versus cooler light.

Although not shown in this figure, the degree of shift from more red light generation to less red light generation corresponding to the shift from warmer to cooler light was distributed in the silicone. A significant increase occurs when a layer of micron-sized porous particles containing porous silica is placed on the 1202 COB chip light.

FIG. 7 is a flow diagram 700 of a method for tuning light scattering using an optically functional porous structure 105 containing a plurality of submicron pores 165 (shown in FIGS. 1B and 2). In one embodiment, the method 700 includes submicron pores 165 (shown in FIG. 2) formed in non-absorbing material 160 (shown in FIGS. 1B, 1C, and 2) through polymer matrix 180 (shown in FIG. 2), including a step 705 of filling. In each case, the submicron pores 165 are filled with a polymeric matrix 180 to form an interface 170 (shown in FIG. 2) between the polymeric matrix 180 and the non-absorbing material 160 in the shape of the submicron pores 165 . Examples of properties and characteristics of non-absorbing material 160, micron-sized porous particles 150, mesh slab network, plurality of sub-micron pores 165, and polymer matrix 180 are described above. Based on material properties and texture, light scattering can be tailored using a non-absorbing material structure 160 containing submicron-sized pores 165 filled with the polymer matrix 180 described herein. .

Once submicron pores 165 are filled with polymer matrix 180 (705), optically functional porous structure 105 is exposed to light at a first temperature (710). Due to the intrinsic properties and texture of the optically functional porous layer 105, including the refractive index difference between the non-absorbing material 160 and the polymer matrix filling the submicron pores 165, at the first temperature Light scattering occurs.

To adjust or change the relative amount of light scattering in response to exposure to light, the temperature is changed (715) and the optically functional porous structure 105 is exposed to light at a second temperature (720). . Because the refractive index difference between the non-absorbing material 160 and the polymer matrix filling the submicron pores 165 changes as a function of temperature, the amount of light scattering that occurs at the second temperature changes.

In some embodiments, the refractive index of polymer matrix 180 decreases as temperature increases. To the extent that the refractive index of polymer matrix 180 is greater than the refractive index of non-absorbing material 160, this reduces light scattering. In one embodiment, _SiO2 is the non-absorbing material 160 that forms the micron-sized porous particles 150, and silicone is used as the polymer matrix 180 that fills the submicron pores 165 (shown in FIG. 2). be. In this example, the refractive index of silicone is lower than that of _SiO2 , so the difference in refractive index between the refractive index of _SiO2 and that of silicone increases with increasing temperature, leading to a reduction in light scattering. lead to an increase. In one embodiment, polymer matrix 180 is polydimethylsiloxane (PDMS), which is a low refractive index silicone.

In some embodiments, the light is further tuned beyond the refractive index difference through the presence of air voids 185 (shown in FIG. 5) in the micron-sized porous particles 150, as described herein. can As the temperature rises, the silicone cures and expands appreciably since it has a high coefficient of expansion. As the temperature decreases, the silicone shrinks again and air voids 185 can form if insufficient cross-linked silicone can re-inject into the micron-sized porous particles 150, resulting in micron-sized particles. The remaining silicone within the porous particles 150 is stressed and may exhibit local delamination or cohesive failure. This, in addition to refractive index differences between materials within micron-sized porous particles 150, can contribute to scattering of light from layers made of the materials described herein. When the layer is heated again, for example by switching on the LED, the silicone expands again and completely or partially fills the air voids 185 . The net effect is to increase the switching swing.

In an embodiment, the optically functional porous structure 105 is used to shift the color point of the LED light during operation when the LED light is on, as described herein. may This can occur when the LED's first temperature changes to a second temperature. At a second temperature of the LED (the second temperature being greater than the first temperature), the light scattering may decrease, which in this case, for example, is proportional to the light scattering of blue light with respect to red light. typically allow a greater reduction. In this case, more blue light is emitted, so the color point of the LED shifts to cooler white light.

In some embodiments, the method may be used in other applications, such as filament lamps and switchable lenses. This method may be used in applications where increasing temperature increases the refractive index difference between materials, increasing light scattering.

Although embodiments have been described in detail, those skilled in the art will appreciate that modifications may be made to the embodiments described herein without departing from the spirit of the inventive concept. Accordingly, the scope of the invention is not intended to be limited to the particular embodiments illustrated and described.
Some aspects are described.
[Aspect 1]
a light-emitting semiconductor device that emits primary light during operation;
a wavelength converting structure disposed on the light emitting semiconductor structure and configured to absorb at least a portion of the primary light and, in response, emit secondary light of a longer wavelength than the primary light;
a submicron pore disposed on the wavelength converting structure opposite the light emitting semiconductor device, formed from a material substantially transparent to the primary light and secondary light, having a first refractive index, and having a submicron pore a porous structure comprising;
a polymer that fills the submicron pores in the porous structure and has a second refractive index different from the first refractive index at 25°C;
luminous device.
[Aspect 2]
A light emitting device according to aspect 1, wherein in operation of said light emitting device secondary light and optionally a portion of said primary light are transmitted through said porous structure to form a light output from said light emitting device. .
[Aspect 3]
3. The light emitting device of aspect 2, wherein the light output appears white to a human observer.
[Aspect 4]
At 25° C. when the light-emitting device is in the off state, the polymer forms an optically scattering interface with the porous structure, and when the porous structure is under external illumination with white light, the porous structure A light emitting device according to aspect 1, wherein the structure causes the structure to appear white to a human observer.
[Aspect 5]
Aspect 1. The light emitting device of Aspect 1, wherein the second refractive index is greater than the first refractive index.
[Aspect 6]
Aspect 1. The light emitting device of Aspect 1, wherein the first refractive index is greater than the second refractive index.
[Aspect 7]
the polymer forms an optical scattering interface with the porous structure that scatters primary and secondary light;
the magnitude of the difference between the first refractive index and the second refractive index decreases as the temperature of the porous structure increases during operation of the light emitting device;
As a result, during operation of the light emitting device, the scattering of the primary and secondary light by the scattering interface decreases as the temperature of the porous structure increases.
A light emitting device according to aspect 1.
[Aspect 8]
during operation of the light emitting device, secondary light and optionally a portion of the primary light are transmitted through the porous structure to form a light output from the light emitting device;
said light output appears white to a human observer;
As the temperature of the porous structure increases during operation of the light emitting device, the color point of the light output shifts to cooler colors.
A light emitting device according to aspect 6.
[Aspect 9]
the polymer forms an optical scattering interface with the porous structure that scatters primary and secondary light;
the magnitude of the difference between the first refractive index and the second refractive index increases as the temperature of the porous structure increases during operation of the light emitting device;
Consequently, during operation of the light emitting device, as the temperature of the porous structure increases, the scattering of the primary and secondary light by the scattering interface increases.
A light emitting device according to aspect 1.
[Aspect 10]
2. The light emitting device of Claim 1, wherein said porous structure comprises micron-sized particles containing said submicron pores.
[Aspect 11]
Aspect 1. The light emitting device of Aspect 1, wherein the porous structure comprises a mesh slab of porous dielectric material containing the pores.
[Aspect 12]
during operation of the light emitting device, secondary light and optionally a portion of the primary light are transmitted through the porous structure to form a light output from the light emitting device;
said light output appears white to a human observer;
At 25° C. when the light-emitting device is in the off state, the polymer forms an optically scattering interface with the porous structure, and when the porous structure is under external illumination with white light, the porous structure cause the structure to appear white to a human observer,
A light emitting device according to aspect 1.
[Aspect 13]
said second refractive index is greater than said first refractive index;
the polymer forms an optical scattering interface with the porous structure that scatters primary and secondary light;
the magnitude of the difference between the first refractive index and the second refractive index decreases as the temperature of the porous structure increases during operation of the light emitting device;
As a result, during operation of the light emitting device, the scattering of the primary and secondary light by the scattering interface decreases as the temperature of the porous structure increases.
13. A light emitting device according to aspect 12.
[Aspect 14]
14. The light emitting device of Claim 13, wherein the color point of the light output shifts to cooler colors as the temperature of the porous structure increases during operation of the light emitting device.
[Aspect 15]
said second refractive index is less than said first refractive index;
the polymer forms an optical scattering interface with the porous structure that scatters primary and secondary light;
the magnitude of the difference between the first refractive index and the second refractive index increases as the temperature of the porous structure increases during operation of the light emitting device;
Consequently, during operation of the light emitting device, as the temperature of the porous structure increases, the scattering of the primary and secondary light by the scattering interface increases.
13. A light emitting device according to aspect 12.

Claims (21)

a light emitting semiconductor device configured to emit primary light in response to a drive current flowing through the light emitting semiconductor device;
a wavelength converting structure positioned on the light emitting semiconductor device and configured to absorb at least a portion of the primary light and emit secondary light of a longer wavelength than the primary light in response to the absorption;
positioned on the wavelength converting structure opposite the light emitting semiconductor device and formed of a material transparent to the primary and secondary light, having a first refractive index and having a porous structure with submicron pores; quality structure;
and a polymer filling the submicron pores in the porous structure and having a second refractive index different from the first refractive index at 25°C, wherein
With no drive current flowing through the light-emitting semiconductor device and under external illumination of white light at 25° C., the porous structure exhibits light scattering from the interface between the porous structure and the polymer; the polymer appears white to a human observer,
luminous device. a light emitting semiconductor device configured to emit primary light in response to a drive current flowing through the light emitting semiconductor device;
a wavelength converting structure positioned on the light emitting semiconductor device and configured to absorb at least a portion of the primary light and emit secondary light of a longer wavelength than the primary light in response to the absorption;
positioned on the wavelength converting structure opposite the light emitting semiconductor device and formed of a material transparent to the primary and secondary light, having a first refractive index and having a porous structure with submicron pores; quality structure;
and a polymer filling the submicron pores in the porous structure and having a second refractive index different from the first refractive index at 25°C, wherein
The magnitude of the difference between the first refractive index and the second refractive index decreases with increasing temperature, and light scattering from the interface between the porous structure and the polymer increases with increasing temperature of the porous structure. Decrease,
luminous device. The porous structure exhibits light scattering in the absence of a drive current flowing through the light emitting semiconductor device when the drive current flows through the light emitting semiconductor device and the primary light is emitted therefrom. 3. The light emitting device of claim 2, exhibiting less light scattering than . With no drive current flowing through the light-emitting semiconductor device and under external illumination of white light at 25° C., the porous structure exhibits light scattering from the interface between the porous structure and the polymer; 3. The light emitting device of Claim 2, wherein the polymer appears white to a human observer. The porous structure is configured such that, in a state in which the driving current flows through the light emitting semiconductor device and the primary light is emitted therefrom, at least part of the secondary light is emitted from the porous structure as light output from the light emitting device. 5. A light emitting device according to any one of claims 1 to 4, wherein the light emitting device is transmissive through a thin structure. 6. The light emitting device of Claim 5, wherein the light output appears white to a human observer. 6. The claim 5, wherein the primary light is blue light and the wavelength converting structure comprises one or more of a yellow emitting wavelength converting material, a green emitting wavelength converting material or a red emitting wavelength converting material. luminous device. a light emitting semiconductor device configured to emit primary light in response to a drive current flowing through the light emitting semiconductor device;
a wavelength converting structure positioned on the light emitting semiconductor device and configured to absorb at least a portion of the primary light and emit secondary light of a longer wavelength than the primary light in response to the absorption;
positioned on the wavelength converting structure opposite the light emitting semiconductor device and formed of a material transparent to the primary and secondary light, having a first refractive index and having a porous structure with submicron pores; quality structure;
and a polymer filling the submicron pores in the porous structure and having a second refractive index different from the first refractive index at 25°C, wherein
The magnitude of the difference between the first refractive index and the second refractive index decreases with increasing temperature, and light scattering from the interface between the porous structure and the polymer increases with increasing temperature of the porous structure. Decrease,
The porous structure, in a state in which the driving current flows through the light-emitting semiconductor device and the primary light is emitted therefrom, (i) at least a portion of the secondary light, or (ii) a portion of the secondary light. at least a portion and/or a portion of the primary light is transmitted through the porous structure as light output from the light emitting device;
light emission wherein the color point of the light output shifts to cooler colors as the temperature of the porous structure increases with the drive current flowing through the light emitting semiconductor device and the primary light emitted therefrom. device. 5. A light emitting device according to any preceding claim, wherein at 25[deg.]C said second refractive index is greater than said first refractive index. 5. A light emitting device according to any preceding claim, wherein at 25[deg.]C said first refractive index is greater than said second refractive index. a light emitting semiconductor device configured to emit primary light in response to a drive current flowing through the light emitting semiconductor device;
a wavelength converting structure positioned on the light emitting semiconductor device and configured to absorb at least a portion of the primary light and emit secondary light of a longer wavelength than the primary light in response to the absorption;
positioned on the wavelength converting structure opposite the light emitting semiconductor device and formed of a material transparent to the primary and secondary light, having a first refractive index and having a porous structure with submicron pores; quality structure;
and a polymer filling the submicron pores in the porous structure and having a second refractive index different from the first refractive index at 25°C, wherein
With no drive current flowing through the light-emitting semiconductor device and under external illumination of white light at 25° C., the porous structure exhibits light scattering from the interface between the porous structure and the polymer; The polymer appears white to a human observer,
The magnitude of the difference between the first index of refraction and the second index of refraction increases with increasing temperature, and light scattering from the interface between the porous structure and the polymer increases increases with increasing temperature,
luminous device. With the driving current flowing through the light emitting semiconductor device and the primary light emitted therefrom, the porous structure exhibits light scattering exhibited by the porous structure in the absence of a driving current flowing through the light emitting semiconductor device. 12. The light emitting device of claim 11, exhibiting light scattering greater than . 5. A light emitting device according to any preceding claim, wherein the submicron pores have a pore size of less than 400 nm. 5. A light emitting device according to any one of the preceding claims, wherein said porous structure comprises micron-sized particles having said submicron pores. 15. The light emitting device of Claim 14, wherein said micron-sized particles have a particle size between 3 [mu]m and 150 [mu]m. 15. The light emitting device of Claim 14, wherein the micron-sized particles comprise one or more of porous glass bead particles, porous silica particles, or porous magnesium fluoride particles. 5. A light emitting device according to any preceding claim, wherein said porous structure comprises a mesh slab of porous dielectric material having said submicron pores. 5. A light emitting device according to any preceding claim, wherein the polymer comprises one or more of silicones, sol-gels, organically modified ceramics or polysilazanes. 5. A method of fabricating a light emitting device according to any one of claims 1 to 4, the method comprising placing the porous structure on the wavelength converting structure opposite the light emitting semiconductor device. method, including 20. The method of claim 19, further comprising filling said submicron pores with said polymer. 20. The method of Claim 19, further comprising curing the polymer that fills the submicron pores.

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