EP3729526A1 - Porous micron-sized particles to tune light scattering - Google Patents
Porous micron-sized particles to tune light scatteringInfo
- Publication number
- EP3729526A1 EP3729526A1 EP18827330.4A EP18827330A EP3729526A1 EP 3729526 A1 EP3729526 A1 EP 3729526A1 EP 18827330 A EP18827330 A EP 18827330A EP 3729526 A1 EP3729526 A1 EP 3729526A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- light
- light emitting
- emitting device
- porous structure
- micron
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
- H01L33/52—Encapsulations
- H01L33/56—Materials, e.g. epoxy or silicone resin
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
- H01L33/58—Optical field-shaping elements
Definitions
- Light emitting diodes may be used as white light sources in various applications, such as flash sources for cellular telephone cameras and filament lamps. Such LEDs may be referred to herein as white LEDs.
- White LEDs may appear to emit white light from the perspective of the viewer when the LEDs are in an on state. However, they may actually be made up of light emitting semiconductor structures that emit non-white light, as well as wavelength converting structures that make the nonwhite light appear white to the viewer.
- a white LED may be formed from a blue light emitting semiconductor structure covered by a yellow emitting phosphor layer. Photons of blue light emitted by the light emitting semiconductor structure may either pass through the yellow emitting phosphor layer as blue photons or may be converted into yellow photons by the yellow emitting phosphor layer. The blue and yellow photons that are ultimately emitted out of the LED combine to make the light emitted from the LED appear white to the viewer.
- LEDs can also be used across a range of dimtone settings. However, an LED that appears to emit cooler light at a high dimtone setting for example, may also appear to emit cooler at a low dimtone setting. Likewise, an LED that appears to emit warmer light at a low dimtone setting for example, may also appear to emit warmer at a high dimtone setting.
- the optically functional porous structure comprises a non-light absorbing material structure, which may be a dielectric structure, comprising a plurality of sub-micron pores and a polymer matrix.
- the non-light absorbing material structure itself may be comprised of a plurality of micron-sized porous particles.
- the refractive index of the non-light absorbing material structure is different than a refractive index of the polymer matrix at a first temperature such that a refractive index difference between the refractive index of the non-light absorbing material structure and the refractive index of the polymer matrix configures the plurality of sub-micron pores within the optically functional porous structure to have a light scattering ability at the first temperature. Because the refractive index difference between the refractive index of the non-light absorbing material structure and the refractive index of the polymer matrix decreases as the temperature changes, the light scattering ability of the plurality of submicron pores also varies with these corresponding changes in temperature.
- FIG. 1A is a diagram of an example light emitting device (LED) that includes a light emitting semiconductor structure and an off state white material layer;
- LED light emitting device
- FIG. 1 B is a diagram of an exemplary off state white layer comprised of micronsized porous particles having an interconnected of sub-micron pores filled with a polymer matrix;
- FIG. 1 C is a diagram of another exemplary off state white layer comprised of a mesh slab having an interconnected of sub-micron pores filled with a polymer matrix;
- FIG. 2 is a scanning electron micrograph illustration of a cross section of a micronsized porous glass bead particle comprising sub-micron pores having silicon infused within the submicron pores;
- FIG. 3A is an illustration (photograph) of a drop-casted silicone layer loaded with micron-sized porous particles having a diameter of 25 - 45 m and comprising sub-micron pores, at 25 °C;
- FIG. 3B is an illustration (photograph) of a drop-casted silicone layer loaded with micron-sized porous particles having a diameter of 25 - 45 m and comprising sub-micron pores, at 200 °C;
- FIG. 4 is a graphical representation of light transmission at 450 nm through a 150 m layer of high index silicone comprising 25 weight % of 50 pm sized porous silica particles with an effective pore size of 100 nm as a function of temperature;
- FIG. 5 is a microscopic image of micron-sized porous particles filled with silicone and comprising air voids
- FIG. 6 is a graphical representation illustrating a shift in color point of the light generated from a 1202 COB chip light source whose drive current leads are shifted from 10 mAmp to 400 mAmp, the 1202 COB light source having a cover layer on top comprising micron-sized porous particles having interconnected sub-micron pores filled with a polymer matrix; and
- FIG. 7 is a flow diagram of a method of tuning light scattering using an optically functional porous structure.
- white LEDs may appear to emit white light in the on state, such LEDs may appear to be the color of the wavelength converting material when turned off.
- a white LED that includes a yellow emitting phosphor layer may appear yellow or green to a viewer when turned off, such as when being viewed on a store shelf.
- an ordinary consumer may expect a product that includes a white LED to appear white even in the off state.
- a person who walks into a store to purchase a white light bulb will usually expect the white light bulb to actually appear white and may think that the light bulb is defective if it appears yellow or green.
- the same may be true of a cellular telephone consumer who may expect the camera flash to appear white.
- Such products would be more marketable to the consumer if the LED appeared white in the off state as well as in the on state.
- Changes in color point of an LED light may also be preferred. For example, when
- LED lights are dimmed, a user may prefer to observe warmer colors at these lower dimtone settings. Conversely, when LED lights are bright, a user may prefer to observe cooler colors.
- By increasing the drive current, which leads to an increase temperature a change in the color point will occur if changes in light scattering are correlated with changes in temperature. This is in part because blue light, for example, scatters light more strongly than red light; therefore, by changing the relative amount of blue light that is scattered relative to the amount of red light that is scattered may change the color point of the perceived light emitted from the LED.
- granules of white, non-phosphor, inert materials have been used. These granules are often sub-micron sized granules because particles of this size may function as particularly effective light scattering elements. Examples of such materials include Titanium Dioxide (Ti0 2 ) and Zirconium Oxide (ZGOS). Sub-micron size particles of these materials may be mixed in with a transparent material, such as silicone, and applied over a non-white LED surface to make it appear whiter to a viewer in the LED off state for example. However, such granules of white, non-phosphor, inert materials may remain white while the device is on and may result in some scattering of light emitted from the LED in the on state, reducing the LED’s lumen output.
- a transparent material such as silicone
- the magnitude of light scattering in either state depends on the concentration of the sub-micron particles in optically functional layer, and on the refractive index difference between the sub-micron particles and the transparent material.
- concentration of the sub-micron particles may increase light scattering in the off state.
- concentration of these particles may lead to a decrease in the LED’s lumen output in the on state.
- there may be issues in processing the materials For example, mixing the materials becomes increasingly difficult as the viscosity of the mixture increases with increasing concentration of sub-micron particles. Another issue may be that the final layer is too brittle due to high particle loading.
- the refractive index difference between the refractive index of the sub-micron particle and the refractive index of the transparent layer it must be great enough so that sufficient light scattering from the sub-micron particles may occur.
- the refractive index difference must not be too great such 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 were so high compared with the refractive index of the sub-micron particle, then a decrease in the refractive index of the transparent layer may not sufficiently approach the refractive index of the sub-micron particle and light scattering would occur across all temperatures in the range of use.
- the temperature of an LED may increase in the on state relative to the off state, and because increased light scattering may reduce the LED’s lumen output, it would be ideal to have light scattering decrease with an increase in temperature.
- the most commonly used scattering particle is Ti0 2 .
- the refractive index of Ti0 2 is high while that of silicone, a commonly used transparent layer material is lower, wherein the refractive index difference between them is more than 0.5.
- An increase in temperature using this combination of materials may result in an even greater refractive difference between Ti0 2 and silicone, causing even greater light scatter in the on state. Accordingly, using a scattering particle having a lower refractive index relative to the transparent material may be better suited.
- MgF 2 which has a refractive index of 1.37. Its refractive index is smaller than, but close to that of a high refractive index silicone, which may have a refractive index of 1.55. Because the refractive index difference between the two materials is only 0.16, much greater concentrations of MgF 2 would be required to achieve sufficient light scatter in the off state, which may lead to issues in processing the materials as described in the foregoing.
- Embodiments described herein provide for a white LED that may appear white to the viewer in both the LED on and off states, yet also reduce or eliminate scattering in the LED on state, making products that include such LEDs more aesthetically pleasing to the viewer without impacting the quality of the LED itself or the structure of its materials.
- Embodiments described herein may also provide for an LED light whereby the color point can be adjusted such that at a low dimtone setting, the color point shifts to warmer colors, while at a high dimtone setting, the color point shifts to cooler colors.
- 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 the non-light absorbing material, which may be a dielectric material.
- the non-light absorbing material structure itself may be comprised of micron-sized porous particles dispersed throughout the optically functional layer, wherein the micron-sized porous particles comprise a network of interconnected sub-micron pores within the particle itself.
- the non-light absorbing material structure may instead be comprised of a mesh slab of porous dielectric material that itself comprises the network of the sub-micron pores. In each case the sub-micron pores are filled with the polymer matrix forming an interface between the polymer matrix and the non-light absorbing material in the shape of a submicron pore.
- the refractive index of the polymer matrix is greater than the refractive index of the non-light absorbing material structure in the LED off state, allowing for a light scattering effect to occur at the interface between the two materials.
- the refractive index of the polymer matrix decreases such that the refractive index difference between the non-light absorbing material, which outlines the shape of the sub-micron pores, and that of the polymer matrix, which fills the sub-micron pores, decreases resulting in decreased to no light scattering by the non-light absorbing material to sub-micron pores interface.
- These features may provide for an LED light that scatters light and appears white at a lower temperature such as room temperature when the LED is in the off state, and that does not scatter light or at least decreases the amount of light scattered, when the LED is in the on state at a higher temperature, which may translate into an increase in the output of the LED light.
- These refractive index properties may also provide for an LED that upon a change in intensity changes light scatter.
- temperature when the intensity of the LED is high, temperature may increase and scattering of light may decrease correspondingly. This may allow for a change in the color point setting of an LED light.
- blue light which contributes to cooler tones of light and which is scattered more strongly than red light, may be impacted more by these changes in temperature and light scattering ability.
- an increase in temperature which may decrease light scatter, may result in more blue light being detected causing a shift in the color point to cooler colors.
- temperature when the intensity of the LED is low, temperature may decrease and scattering of light may increase correspondingly. In this example, the decrease in temperature and increase in light scatter may result in less blue light being detected causing a shift in the color point to warmer colors.
- the refractive index of the non-light absorbing material is greater than the refractive index of the polymer matrix such that an increase in temperature decreases light scatter. This may impair a change in the color point setting of an LED light.
- This embodiment may be used at least for example to prevent or minimize a color shift that would otherwise occur that is undesirable as the temperature increases. By increasing light scatter as the temperature increases allows for a decrease in color change. This embodiment may also be used to shift the color point to warmer colors as higher temperatures.
- the non-light absorbing material structure itself may be comprised of a plurality of micron-sized porous particles that comprise a network of the sub-micron pores which are dispersed throughout.
- the non-light absorbing material structure may be comprised of a mesh slab of porous dielectric material that itself comprises the network of the sub-micron pores.
- the sub-micron pores are filled with the polymer matrix forming an interface between the polymer matrix and the non-light absorbing material structure in roughly the shape of a sub-micron pore.
- the refractive index of the polymer matrix is greater than the refractive index of the non-light absorbing material structure in the LED off state, allowing for a light scattering effect to occur at the interface between the two materials.
- the refractive index of the polymer matrix decreases such that the refractive index difference between the non-light absorbing material, which outlines the shape of the sub-micron pores, and that of the polymer matrix, which fills the sub-micron pores, decreases thereby resulting in decreased to no light scattering by the sub-micron pores-dielectric surface interface.
- These same inherent properties of the materials also allow for a change in the color point setting of an LED light. For example, at low intensity the LED light may shift towards warmer tones and at high intensity the LED light may shift towards cooler tones.
- the refractive index of the non-light absorbing material may also decrease in response to increased temperature, the change in the refractive index between a first temperature and a second temperature is low relative to the change in the refractive index of the polymer matrix at the first and second temperature.
- Solid materials such as the non-light absorbing material, have a much lower expansion coefficient, and therefore a much smaller change in refractive index as a function of temperature than silicone for example. Accordingly, changes in temperature have a greater effect on the refractive index of a polymer matrix than on non-light absorbing materials. More details regarding the polymer matrix and the non-light absorbing material are described below and shown in FIG. 2.
- the difference between the refractive index of each material needs to be a certain minimum.
- this minimum can be affected by factors such as the concentration of light scattering particles within the optically functional layer.
- concentration of light scattering particles within the optically functional layer.
- concentration of light scattering particles can help to compensate for the relatively small difference in refractive indexes between materials to achieve greater levels of light scatter than at an equivalent refractive index difference with lower concentration of light scattering particles.
- concentration of particles that can be placed within the layer without compensating its form.
- the difference between the refractive index of each material can only be a certain maximum. If the refractive index difference between the two materials is too great and cannot be sufficiently decreased within any reasonable temperature change, a functionally effective decrease in light scatter cannot occur in the on state.
- the refractive index difference between the refractive index of the non-light absorbing material and the refractive index of the polymer matrix is 0.3 or less. In an embodiment, the refractive index difference between the refractive index of the non-light absorbing material and the refractive index of the polymer matrix is 0.2 or less. In an embodiment, the refractive index difference between the refractive index of the non-light absorbing material and the refractive index of the polymer matrix is 0.1 or less. In an exemplary embodiment, the refractive index difference between the refractive index of the non-light absorbing material and the refractive index of the polymer matrix is 0.07.
- FIG. 1A is a diagram of an example light emitting device (LED) 100 that includes a light emitting semiconductor structure 115, a wavelength converting material 1 10, and an off state white material, which may be an optically functional porous structure 105 comprising a plurality of micron-sized porous particles or mesh slab comprising sub-micron pores.
- Contacts 120 and 125 may be coupled to the light emitting semiconductor structure 115, either directly or via another structure such as a submount, for electrical connection to a circuit board or other substrate or device.
- the contacts 120 and 125 may be electrically insulated from one another by a gap 127, which may be filled with a dielectric material.
- the contacts or interconnects 120 and 125 may be, for example, solder, stud bumps, or gold layers.
- the optically functional porous structure 105 comprising the plurality of micron-sized porous particles, or mesh slab comprising submicron pores, is in contact with the LED.
- the light emitting semiconductor structure 1 15 emits blue light.
- the wavelength conversion material 1 10 may include, for example, a yellow emitting wavelength conversion material or green and red emitting wavelength conversion materials, which will produce white light when the light emitted by the respective phosphors combines with the blue light emitted by the light emitting structure 115.
- the light emitting semiconductor structure 1 15 emits UV light.
- the wavelength conversion material 1 10 may include, for example, blue and yellow wavelength converting materials or blue, green, and red wavelength converting materials. Wavelength converting materials emitting other colors of light may be added to tailor the spectrum of light emitted from the LED 100. In an embodiment, the color point of this LED 100 may be shifted based on the properties of the optically functional porous structure 105 described herein.
- FIG. 1 B is a diagram of a magnified view of an embodiment of the optically functional porous structure 105, wherein the optically functional porous structure 105 comprises a plurality of micron-sized porous particles 150.
- Dispersed throughout each micron-sized porous particle 150 is a network of sub-micron pores 165 (shown in FIG. 2), which in this illustration are filled with a polymer matrix 180 (shown in white).
- the plurality of sub-micron pores 165 form an interconnected network surrounded by the non-light absorbing material 160 (shown in white).
- the micron-sized porous particle 150 may be a micron-sized porous glass bead particle.
- the micron-sized porous particle 150 may be a micron-sized porous silica particle.
- the micron-sized porous particle 150 is a micron-sized porous magnesium fluoride particle.
- FIG. 1 C is a diagram of a magnified view of an embodiment of the optically functional porous structure 105, wherein the optically functional porous structure 105 comprises a mesh slab formed of a non-light absorbing material 160 having a plurality of sub-micron pores (not shown), which in this illustration are filled with a polymer matrix 180.
- an interconnected network of polymer matrix 180 is formed throughout the mesh slab, having an interface (similar to interface 170 of FIG. 2) between the polymer matrix 180 and the non-light absorbing material 160 of the mesh slab that surrounds it.
- FIG. 2 is a scanning electron micrograph illustrating a cross section of an exemplary micron-sized porous particle 150.
- Dispersed throughout micron-sized porous particle 150 are sub-micron pores 165 surrounded by the non-light absorbing material 160 structure forming an interconnected network within the micron-sized porous particle 150.
- the submicron pores 165 are filled with a polymer matrix 180.
- Light that encounters a micron-sized porous particle 150 comprising sub-micron pores 165 will be multiply scattered, not excluding transmission, but limiting it to only a fraction of the light that would otherwise pass through a fully transparent structure.
- the micron-sized porous particle 150 may be a micron-sized porous glass bead particle.
- the polymer matrix 180 may be any optically functional material, including silicone; a temperature and light resistant matrix, such as an optical grade silicone matrix; or any other suitable material, such as a sol-gel material, an organically modified ceramic (ormocer), or a polysilizane based matrix.
- the polymer matrix 180 may be a high refractive index silicone.
- silicone may include phenylated silicones (i.e., methylphenyl), and silicones filled with high index nanoparticles.
- the refractive index of the polymer matrix 180 may be greater than the refractive index of the non-light absorbing material 160 of the micron-sized porous particle 150 or the mesh slab network. In an embodiment, the refractive index of the polymer matrix 180 may be less than the refractive index of the non-light absorbing material 160 of the micron-sized porous particle 150 or the mesh slab network.
- the polymer matrix is silicone having a refractive index ranging from at least 1.4 to 1.7 at room temperature. In an embodiment, the polymer matrix is silicone having a refractive index ranging from at least 1.46 to 1.56 at room temperature. In an embodiment, silicone has a refractive index ranging from at least 1.50 to 1.56 at room temperature.
- the refractive index of the polymer matrix 180 may decrease as the temperature increases.
- the refractive index of a silicone at the elevated temperature may decrease and have range from at least 1.46 to a temperature lower than an upper temperature disclosed for the refractive index at room temperature.
- the refractive index of the polymer matrix decreases by 0.1 or less at the elevated temperature compared with the refractive index of the polymer matrix at room temperature.
- the micron-sized porous particles 150 may include glass bead particles formed from any material including a porous silica particle or any other suitable material having a refractive index less than the refractive index of the polymer matrix 180.
- the micron-sized porous particle 150 may be a porous silica.
- a non-limiting example of a non-glass bead micron-sized porous particle 150 is a micron-sized porous magnesium fluoride particle.
- the lower limit diameter of the micron-sized porous particles 150 must be large enough to have a sufficient amount material, including the sub-micron pores 165 within such that a sufficient level of light scatter can be achieved.
- the upper limit diameter of the micronsized porous particles 150 must be small enough to maintain the optically functional layer as thin as possible, In an embodiment the micron-sized porous particle 150 may have a diameter larger than the thickness of optically functional layer. In an embodiment, the micron-sized porous particles 150 may have a diameter in the range of 3 m to 700 pm. In an embodiment, the micron-sized porous particles 150 may have a diameter in the range of 3 m to 150 pm. In an embodiment, the micronsized porous particles 150 may have a diameter in the range 50 m to 150 pm. In an embodiment, the micron-sized porous particles 150 may have a diameter in the range 3 m to 50 pm.
- the micron-sized porous particles 150 may have a diameter in the range 10 m to 50 pm. In an embodiment the micron-sized porous particle 150 may have a diameter in the range 10 pm to 100 pm. In an exemplary embodiment the micron-sized porous particle 150 may have a diameter of 50 pm. Notably, the strongest effects may be observed with the largest particles; however, thickness of the optically functional layer 105 must also be considered.
- the packing density of the micron-sized porous particle 150 in the optically functional layer it is preferably as high as possible to be able to obtain as much scattering as possible in as thin a layer as possible, (where a preferred layer thickness can be 50 pm, up to
- the random packing limit of monodisperse spheres is 64 vol%. If a bimodal distribution is used, the voids between the micronsized porous particles 150 can be filled up with smaller sized micron-sized porous particles 150, increasing the maximum packing fraction further, for example up to 70% or 80%. In an embodiment, where the micron-sized porous particle 150 used are not monodisperse, or not completely monodisperse, packing volume fractions between 40% and 55% are reached. Lower packing density is also possible, but it will reduce the off state white effect and may also necessitate increasing the layer thickness.
- the size of the sub-micron pore 165 of the micron-sized porous particle 150 may have a diameter in the range of 50 to 400 nm. In an exemplary embodiment the sub-micron pore 165 has a diameter of 200 nm. In an embodiment, the sub-micron pore 165 has a diameter of 100 nm.
- the volume occupied by the sub-micron pores 165 is within the range of approximately 0.6 cm 3 /gram to 1.5 cm 3 /gram of the micron-sized porous particle 150. In an embodiment, the volume occupied by the sub-micron pores 165 is within the range of approximately 0.8 cm 3 /gram to 1.2 cm 3 /gram of the micron-sized porous particle 150. In an exemplary embodiment, the volume occupied by the sub-micron pores 165 is approximately 0.9 cm 3 /gram of the micron-sized porous particle 150.
- the volume occupied by the sub-micron pores 165 within the optically functional porous structure 105 may vary outside of the range provided, depending on at least the materials used and their respective properties, the number of micron-sized porous particles 150 required for optimal light scatter at room temperature, and the integrity of the optically functional porous structure 105.
- the surface area to pore volume may be from approximately 10 m 2 /gram to 40 m 2 /gram.
- the surface area to pore volume occupied by the sub-micron pores 165 within the optically functional porous structure 105 may vary outside of the range provided, depending on at least the materials used and their respective properties, the number of micron-sized porous particles 150 required for optimal light scatter at room temperature, and the integrity of the optically functional porous structure 105.
- the non-light absorbing material 160 forms a mesh slab
- the non-light absorbing material 160 (as shown in FIG. 1 C)
- the material may be formed from any material including a porous silica particle or any other suitable material having a refractive index less than the refractive index of the polymer matrix 180.
- the non-light absorbing material 160 should be stable at high light flux, temperature, and humidity.
- inorganic materials are preferred.
- the mesh slab of porous non-light absorbing material 160 may be formed from a porous silica.
- FIGS. 3A and 3B are microscopic images of a droplet of the optically functional porous structure 105 comprising of a mixture of silicone as the polymer matrix 180 (as shown in FIGS 1 B and 2) and porous silica as the micron-sized porous particles 150 (also shown in FIGS. 1 B and 2).
- the mixture was prepared by combining a solvent, the silicone, and the porous silica together to form a droplet. Following mixing, the solvent was evaporated and the droplet cured at 150 °C forming an optically functional material 105. Dispersed throughout each droplet of optically functional material 105 are micron-sized porous silica particles whose sub-micron pores 165 (as shown in FIG. 2) are filled with silicone.
- FIG. 3A represents the droplet sample at 25 °C.
- the porous silica particles are illustrated by the plurality of small particles within the droplet itself.
- the silicone-loaded porous silica particles scatter white light due at least in part to the differences in the refractive index between porous silica and the silicone filling the sub-micron pores 165 (as shown in FIG. 2).
- the image of FIG. 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 at least in part due to the decrease in the refractive index difference between the refractive index of porous silica and the refractive index of silicone at the elevated temperature.
- the effect of using a silicone having a different refractive index than that of another silicone was assessed keeping temperature constant.
- FIG. 4 illustrates a quantitative assessment of the ability of an optically functional porous structure 105 (as shown in FIG. 1A, 1 B, and 1 C), comprising 25 percent by weight porous silica beads having a diameter of 50 m as the micron-sized porous particles 150.
- the sub-micron pores 165 (as shown in FIG. 2) of the porous silica beads, having an effective pore size of 100 nm, are filled with a high refractive index silicone as the polymer matrix 180 (as shown in FIGS. 1 B and 2), to scatter light as a function of temperature.
- Direct transmission of light having a wavelength of 450 nm and an intensity of 10 W/cm 2 is transmitted through the optically functional porous structure 105 layer comprising the micron-sized porous silica beads distributed throughout, at various temperatures.
- the intensity of transmitted light detected at each of the temperatures is determined.
- the laser spot on the layer is 1.3 mm in diameter and detection of light occurs though the use of an integrating sphere having a 5 mm opening placed approximately 2 cm behind the layer, which is aligned with the 450 nm laser.
- the percent of light transmitted through the layer at a first temperature is 0.75%. This intensity is determined and normalized against itself to be 1.0 units, as illustrated in FIG. 4.
- the intensity of transmitted light detected at a second temperature is determined, which is normalized to the intensity of light detected at the first temperature.
- the intensity of light transmitted is measured for each subsequent temperature that the layer is subjected to and normalized to the intensity of transmitted light detected at the first temperature. As illustrated in FIG. 4, the intensity of light transmitted through the layer increases as the temperature increases such that the intensity of transmitted light is 30-fold higher when the layer is subjected to 200 °C versus the intensity of transmitted light when the layer is subjected to 30 °C.
- the intensity of transmitted light is approximately 10 fold higher that the intensity of light transmitted at 30 °C in this embodiment.
- FIG. 5 is a light microscope image illustrating the presence of air voids 185 (as shown by the wider arrows) within the micron-sized porous particles 150. These are visible under the microscope as an internal structure within the micron-sized porous particles 150.
- the air voids 185 also contribute to the scattering of light, from a optically functional layer 105 made with the materials described herein.
- the air voids 185 can be formed a result of incomplete filling of the sub-micron pores 165 with the polymer matrix 180 (i.e., silicone), but they can also be formed upon curing of the silicone for example, inside the sub-micron pores 165 followed by the subsequent cooling down.
- silicone is cured at elevated temperatures (i.e., 150 °C) the silicone expands considerably, because the expansion coefficient is high.
- the silicone expands again and fills up the air voids 185 completely or partially such that the air voids disappear. The net effect is that the switching amplitude in light output between samples at two different temperatures is increased.
- the micron-sized porous particles 150 having submicron pores 165, or the mesh slab formed of non-light absorbing material 160 and having submicron pores, described herein for off state white may be used in other applications.
- color point regulation, filament lamps, and switchable lenses may be used in other applications.
- a color point shift can be observed with an increase in temperature. For example, by increasing the drive current leads, which increases the temperature of the LED, the color point of the LED light can be shifted to cooler light colors. Conversely, by decreasing the drive current leads, which decreases the temperature, the color point of the LED light can be shifted to warmer colors. This is at least in part due to the differing abilities of each color of light to scatter light. For example, blue light is more strongly scattered than red light; therefore, in the layers described in the foregoing, upon an increase in temperature, light scatter decreases such that relatively more blue light is emitted. In this embodiment, the color point shifts to cooler white light.
- the 1202 COB chip light comprising the additional layer described herein was subject to drive current leads of 10 mAmp, which was associated with temperatures of about 25 °C.
- FIG. 6 also illustrates a relatively smaller shift along the v’ axis, which is representative of primarily green light color, when the drive current leads are shifted from 10 mAmp to 400 mAmp.
- the magnitude of the shift along the v’ axis less than the magnitude of shift along the u’ axis, but the degree to which a change in green light detection will affect warmer versus cooler light is much less than the degree to which an equivalent shift in red light detection will affect warmer versus cooler light.
- the degree of shift from the generation of more red light to the generation of less red light which corresponds to a shift from warmer light to cooler light, respectively, is considerably more when the micron-sized porous particle layer comprising porous silica dispersed in silicone is placed over the 1202 COB chip light.
- FIG. 7 is a flow diagram 700 of a method of tuning light scattering using an optically functional porous structure 105 comprising a plurality of sub-micron pores 165 (as shown in FIGS. 1 B and 2).
- the method 700 includes filling 705 the sub-micron pores 165 (as shown in FIG. 2) formed within the non-light absorbing material 160 (as shown in FIGS. 1 B, 1 C, and 2), with a polymer matrix 180 (as shown in FIG. 2).
- the sub-micron pores 165 are filled 705 with the polymer matrix 180 forming an interface 170 (as shown in FIG.
- the temperature is changed 715, such that the optically functional porous structure 105 is exposed to light at the second temperature 720. Because the refractive index difference between the non-light absorbing material 160 and the polymer matrix filling the sub-micron pores 165 changes as a function of temperature, the amount of light scattering that occurs at the second temperature changes.
- the refractive index of the polymer matrix 180 decreases as the temperature increases. This results in decreased light scattering, as long as the refractive index of the polymer matrix 180 is greater than that of a non-light absorbing material 160.
- Si0 2 is the non-light absorbing material 160 that forms the micron-sized porous particles 150 and silicone is used as the polymer matrix 180 that fills the sub-micron pores 165 (as shown in FIG. 2).
- the refractive index of the silicone is lower than that of the S1O2; therefore, the refractive index difference between the refractive index of the Si02 and the refractive index of the silicone would increase with increasing temperature, which would lead to increased light scattering.
- the polymer matrix 180 is polydimethylsiloxane (PDMS), a lower refractive index silicone.
- light can be further tuned beyond a refractive index difference through the existence of air voids 185 (as shown in FIG. 5) in the micron-sized porous particles 150 as described herein.
- air voids 185 as shown in FIG. 5
- silicone is cured and expands considerably, because it has a high coefficient of expansion.
- the silicone shrinks again, and if insufficient crosslinked silicone can be infused back into the micron-sized porous particles 150 air voids 185 may form and the remaining silicone in the micron-sized porous particles 150 is under stress and may demonstrate local delamination or cohesive failures.
- the optically functional porous structure 105 may be used to shift the color point of LED lights during operation, when the LED lights are on as described herein. This may occur as a first temperature of the LED is changed to a second temperature.
- the second temperature of the LED wherein the second temperature is greater than the first temperature, light scattering may decrease, which in this instance would allow for a proportionally greater decrease in light scattering of the blue light versus the red light for example. Because more blue light would be emitted in this instance, the color point of the LED shifts to a cooler white light.
- this method may also be used in other applications, for example, filament lamps and switchable lenses.
- the method may also be used in applications where an increase in temperature increases the refractive index difference between materials and increases light scatter.
Abstract
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US15/852,822 US10761246B2 (en) | 2017-12-22 | 2017-12-22 | Light emitting semiconductor device having polymer-filled sub-micron pores in porous structure to tune light scattering |
EP18163955 | 2018-03-26 | ||
PCT/US2018/065937 WO2019126000A1 (en) | 2017-12-22 | 2018-12-17 | Porous micron-sized particles to tune light scattering |
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JP2003131001A (en) * | 2001-05-25 | 2003-05-08 | Shipley Co Llc | Porous optical materials |
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TWI280673B (en) * | 2004-09-22 | 2007-05-01 | Sharp Kk | Optical semiconductor device, optical communication device, and electronic equipment |
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CN101661983B (en) * | 2008-08-26 | 2012-03-14 | 富准精密工业(深圳)有限公司 | Light emitting diode (LED) and preparation method thereof |
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