Diode-based illumination modules with magnesium aluminate spinel based color conversion elements

Abstract

Color conversion elements with improved optical performance and methods for fabrication thereof are described herein. In one aspect, a color conversion element is a sintered composite material including one or more phosphor materials dispersed in a magnesium aluminate spinel matrix material. Exemplary phosphor materials include an oxide based phosphor material, an α-type sialon phosphor material, a beta-type sialon phosphor, a silicon nitride based phosphor material, an aluminum garnet based phosphor material, or any combination thereof. In some examples, the overall efficiency of a diode based illumination device is increased using a color conversion element including a magnesium aluminate spinel matrix material. High sintering temperatures are known to degrade the color conversion efficiency of many phosphor materials. In some examples, a magnesium aluminate spinel based color conversion element fabricated at a lower sintering temperature improves the optical performance of LED based illumination devices operating at high optical power.

Description

DIODE-BASED ILLUMINATION MODULES WITH MAGNESIUM ALUMINATE SPINEL BASED COLOR CONVERSION ELEMENTS Ting Li Shih-Yu Chiu Yuanqiang Li CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application for patent claims priority to U.S. patent application serial number 19 / 188,993, entitled “Diode-Based Illumination Modules With Magnesium Aluminate Spinel Based Color Conversion Elements,” filed April 24, 2025, which, in turn, claims priority under 35 U.S.C. §119 from U.S. provisional patent application serial number 63 / 638,858, entitled “LED-Based Illumination Modules With Magnesium Aluminate Spinel Based Color Conversion Elements,” filed April 25, 2024, the subject matter of both applications is incorporated herein by reference in their entireties. TECHNICAL FIELD

[0002] The described embodiments relate to illumination modules that include diode-based illumination sources and one or more color conversion elements. BACKGROUND INFORMATION

[0003] Light emitting devices employing Light Emitting Diode (LED) or Laser Diode (LD) illumination sources have achieved broad market penetration due to their electrical efficiency, long lifetime, high reliability, relatively low cost of manufacture, and physical scalability. Markets addressed by LED based light emitting devices include vehicle lighting, indoor and outdoor building lighting, display lighting, etc. In particular, LED based light emitting devices are rapidly replacing traditional illumination sources such as incandescentbulbs and fluorescent bulbs in general illumination applications.

[0004] As narrowband emitters, LEDs are not directly suited to general illumination applications because LEDs cannot directly meet the specific requirements on the quality of white light emitted from the light emitting device. To resolve this problem an LED based light emitting device includes one or more LED illumination sources and one or more wavelength conversion structures. A wavelength conversion structure absorbs a portion of light emitted from an LED and converts the absorbed light into light having different wavelengths. The LED based light emitting device generates illumination light that combines light emitted directly from the LED mixed with wavelength converted light. Thus, wavelength conversion effectively broadens the spectrum of light emitted from the LED based light emitting device. In some examples, an LED based light emitting device is designed to emit light with a spectral power distribution that closely matches that of a blackbody radiator over a wavelength range of interest, e.g. the visible spectrum.

[0005] FIG. 1 illustrates a plot 10 including the normalized spectral response 11 of an LED illumination source, the normalized spectral response 12 of a LuAG:Ce phosphor, the normalized spectral response 13 of a Y3Al5O12:Ce (YAG) phosphor, and the normalized spectral response 14 of a CaAlSiN3:Eu phosphor.

[0006] As depicted in FIG. 1, the LED illumination source emits light with a peak emission near 450 nanometers. LEDs with a peak emission near 450 nanometers are typically selected as LED illumination sources because of the radiometric efficiency of LEDs in this peak wavelength regime. However, as illustrated in FIG. 1, the spectral response of the LED is very narrow and varies greatly from the spectral response of a blackbody radiator. To achieve light output from an LED-based light emitting device that more closely approximates a blackbody radiator, a portion of the narrow band emission of the LED isconverted to various higher wavelengths. As illustrated in FIG. 1, the emission spectra of the LuAG:Ce phosphor exhibits a peak emission at approximately 518 nanometers, the emission spectra of the Y3Al5O12:Ce (YAG) phosphor exhibits a peak emission at 555 nanometers, and the emission spectra of the CaAlSiN3:Eu phosphor exhibits a peak emission at approximately 650 nanometers. Each of the exemplary photo-luminescent materials has a unique chemical composition and may be blended to achieve a desired spectral emission from an LED based light emitting device. In general, these specific phosphors are exemplary and many other photo-luminescent materials, and combinations of photo- luminescent materials may employed to achieve a desired spectral emission from an LED based light emitting device.

[0007] In general, phosphor materials are not only selected for their emission properties, but also their temperature stability, long term reliability, and durability in the face of environmental conditions present in various lighting environments. Exemplary phosphors used in LED based light emitting devices include rare earth aluminate phosphors, e.g., (Y,Gd,Tb,Lu)3(Al,Ga)5O12:Ce and inorganic phosphors such as silicate phosphors, e.g., (Sr,Ca,Ba)2SiO4, α-sialon phosphors, e.g., Ca-α-SiAlON:Eu, etc.

[0008] In some examples, phosphors are dispersed in a resin, and the resin containing the phosphors is cured within the LED based light emission device to form the wavelength conversion structure. Unfortunately, the resin materials currently available suffer from deterioration, particularly under high brightness operating conditions. This leads to undesirable loss of optical transmission efficiency and color degradation. In addition, resin materials typically have low thermal conductivity. This leads to overheating and deterioration of the resin material itself and the phosphor materials embedded within.

[0009] In some other examples, an α-Sialon phosphor is mixed with alumina particles and sintered to form a wavelengthconversion structure as described in detail in U.S. Patent Application No. 2022 / 0251444 by Yamaura et al. and Japan Patent Publication No. 2019-135543A by Fukui et al., the content of each is incorporated herein by reference in its entirety. However, the use of alumina particles as the primary base material of the sintered composite leads to a preference for sintering temperatures of 1,500 degrees Centigrade, or higher. This may lead to chemical reactions between the phosphor material and the alumina particles that reduce the color conversion efficiency of the phosphor materials.

[0010] Future lighting applications present challenges for LED based light emitting devices due to increasingly high brightness requirements and color quality requirements. Thus, methods and systems for improved wavelength conversion structures integrated as part of an LED based light emitting device are desired. SUMMARY

[0011] Color conversion elements with improved optical performance and methods for fabrication thereof are described herein. In one aspect, a color conversion element is a sintered composite material including one or more phosphor materials dispersed in a magnesium aluminate spinel matrix material, e.g.,MgAl2O4 and its solid solutions, Mg1-xAl2+yO4, where0 < x ≤ 0.7^^^and^^0 ≤ y ≤ 0.5.^Exemplary phosphor materials include an oxide based phosphor material, an α-type sialon phosphor material, a beta-type sialon phosphor, a silicon nitride based phosphor material, an aluminum garnet based phosphor material, or any combination thereof.

[0012] In some embodiments, the color conversion element is fabricated as a plate and assembled in an optical path of a diode based illumination source to form a diode based illumination device. The spectral content of light emitted from the diode based illumination device is dictated by the amount and color of unconverted pump light passed through the color conversion plate (if any) and the amount and color of convertedlight generated by the phosphor materials embedded in the color conversion plate.

[0013] In some examples, the overall efficiency of a diode based illumination device is increased using a color conversion element including a magnesium aluminate spinel matrix material, rather than alumina. High sintering temperatures are known to degrade the color conversion efficiency of many phosphor materials. The inventors have discovered that a magnesium aluminate spinel based color conversion element fabricated at a lower sintering temperature compared to an equivalent alumina based color conversion element achieves more efficient optical performance. The lower sintering temperature reduces the degradation of color conversion efficiency of the phosphor materials. The reduced degradation results in a relative increase in color conversion efficiency of the phosphor materials included in the magnesium aluminate spinel based sintered composite. In particular, the efficiency benefits accrue in devices employing an LED illumination source having a minimum blue photon excitation level of one radiometric Watt per one millimeter squared area.

[0014] In some embodiments, a color conversion element is fabricated from a sintered composite material including one or more phosphor materials dispersed in one or more matrix materials including a magnesium aluminate spinel matrix material. In some embodiments, the magnesium aluminate spinel matrix material is at least 35% of the mass of the sintered composite material. In some embodiments, the composite material includes magnesium aluminate spinel as the primary matrix material and one or more additional matrix materials, e.g., one or more sintering additives. In some embodiments, the magnesium aluminate spinel matrix material is at least 80% of the mass of the sum of the matrix materials of the sintered composite material. In some of these embodiments, a composite material includes magnesium aluminate spinel as the primary matrix material and a sintering additive, e.g. an oxide material suchas magnesium oxide (MgO), a fluoride material, a chloride material, etc.

[0015] In some embodiments, a color conversion element is fabricated from a composite material including an α-type sialon phosphor dispersed in a combination of matrix materials including a magnesium aluminate spinel matrix material. In these embodiments, the α-type sialon phosphor comprises 1% and 60% of the mass of the composite, and magnesium aluminate spinel matrix material is between 80% and 100% of the mass of all of the matrix materials of the composite, and a sintering additive material is between 0% and 20% of the mass of all of the matrix materials of the composite.

[0016] In some embodiments, a minimum grain size of the magnesium aluminate spinel matrix material and the one or more phosphor materials is greater than 1 micrometer and less than 50 micrometers.

[0017] In some embodiments, a composite is sintered at a temperature of 1500° Centigrade, or lower. In some embodiments, the composite is sintered at a temperature of 1400° Centigrade, or lower. In some embodiments, the composite is sintered at a temperature of 1300° Centigrade, or lower. In general, higher sintering temperatures increase the density of the sintered composite, but at a cost of further degradation of the color conversion performance of the phosphor materials.

[0018] In some examples, the densification of the sintered composite at a given sintering temperature is achieved by a sintering process, e.g., spark plasma sintering, hot press sintering, hot isostatic press sintering, gas-pressure sintering, etc. In some examples, the sintering process is undertaken in a process chamber in a controlled environment filled with a non-oxidizing inert gas, e.g., nitrogen, argon, xenon, etc., to prevent oxidation of the phosphor materials. In some examples, the sintering process is undertaken in a process chamber under vacuum conditions to prevent oxidation of the phosphor materials. In some examples, the sintering process isundertaken in a pressurized process chamber to improve densification of the sintered composite at a given sintering temperature.

[0019] In some embodiments, the porosity of the sintered composite structure of the color conversion element including a magnesium aluminate spinel matrix material and one or more phosphor materials is greater than 0.1% and less than 25% by volume.

[0020] In a further aspect, the one or more surfaces of a color conversion element are mechanically or chemically processed after sintering to achieve a desire surface finish. By way of non-limiting example, surface processes include grinding, polishing, lapping, plasma etch, deposition, or any combination thereof.

[0021] The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not limiting in any way. Other aspects, inventive features, and advantages of the devices and / or processes described herein will become apparent in the non-limiting detailed description set forth herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a plot illustrative of a normalized spectral response of an LED illumination source and three different phosphor materials.

[0023] FIG. 2 is a simplified diagram illustrative of a perspective view of an LED based illumination device including a color conversion element packaged in a flip-chip configuration.

[0024] FIG. 3 is a simplified diagram illustrative of a cross- sectional view of an LED based illumination device including a color conversion element packaged in a flip-chip configuration.

[0025] FIG. 4 is a simplified diagram illustrative of a cross- sectional view of an LED based illumination device including a color conversion element packaged in a wire bond configuration.

[0026] FIG. 5 is a simplified diagram illustrative of a cross- sectional view of an LED based illumination device including a color conversion element packaged in a chip-on-board configuration.

[0027] FIG. 6 is a table 130 illustrative of the mass percentage composition of a binary composite of magnesium aluminate spinel and a Ca-α-sialon phosphor material after sintering at three different temperatures.

[0028] FIG. 7 is a table 135 illustrative of the mass percentage composition of a binary composite of alumina and a Ca-α-sialon phosphor material after sintering at two different temperatures.

[0029] FIG. 8 is a table 140 illustrative of the optical total integrated scattering and optical conversion efficiency of a ceramic sintered from a magnesium aluminate spinel matrix material and a ceramic sintered from an alumina matrix material in one example.

[0030] FIG. 9 is a plot 145 of the spectral output of an LED based illumination device including an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 8.

[0031] FIG. 10 is a plot 150 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a single pulse mode in the two embodiments described with reference to FIG. 9.

[0032] FIG. 11 is a plot 155 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a continuous wave mode in the two embodiments described with reference to FIG. 9.

[0033] FIG. 12 is a table 160 illustrative of the optical total integrated scattering and optical conversion efficiency of a ceramic sintered from a magnesium aluminate spinel matrix material and a ceramic sintered from an alumina matrix material in another example.

[0034] FIG. 13 is a plot 165 of the spectral output of an LED based illumination device including an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 12.

[0035] FIG. 14 is a plot 170 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a single pulse mode in the two embodiments described with reference to FIG. 13.

[0036] FIG. 15 is a plot 175 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a continuous wave mode in the two embodiments described with reference to FIG. 13.

[0037] FIG. 16 is a plot 180 illustrative of surface temperature of a color converting element as a function of drive current from an LED based illumination device operated in a continuous wave mode.

[0038] FIG. 17 illustrates a flowchart of a method 200 for convering an amount of pump light to a different color using a color conversion element comprising a magnesium aluminate spinel matrix material in at least one example. DETAILED DESCRIPTION

[0039] Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0040] FIG. 2 is a simplified diagram illustrative of a perspective view of an LED based illumination device 100 packaged in a flip-chip configuration. FIG. 3 is a cross sectional view of the LED based illumination device 100 depicted in FIG. 2. As depicted in FIGS. 2 and 3, LED based illumination device 100 includes a mounting board 101, an LED based illumination source 103, a color conversion element 104, and die bonding structures 102. Die bonding structures 102, e.g., solder based contact pads, mechanically and electrically couplemounting board 101 to the LED based illumination source 103. Mounting board 101 mechanically and electrically interfaces LED based illumination device 100 with the application environment in which LED based illumination device 100 is installed. Color conversion element 104 is disposed over the light emitting surface of LED based illumination source 103.

[0041] FIG. 4 is a simplified diagram illustrative of a cross- sectional view of an LED based illumination device 110 packaged in a wire bond configuration. As depicted in FIG. 4, LED based illumination device 110 includes a mounting board 111, an LED based illumination source 113 mechanically mounted to mounting board 111, a color conversion element 115, electrodes 112, and wire bond structures 114. Wire bond structures 114 electrically couple electrodes 112 of LED based illumination source 113 to mounting board 101. Mounting board 101 mechanically and electrically interfaces LED based illumination device 110 with the application environment in which LED based illumination device 110 is installed. Color conversion element 115 is disposed over the light emitting surface of LED based illumination source 113.

[0042] FIG. 5 is a simplified diagram illustrative of a cross- sectional view of an LED based illumination device 120 including LEDs packaged in a chip-on-board (COB) configuration. As depicted in FIG. 5, LED based illumination device 120 includes a mounting board 121, a plurality of LED based illumination sources 123 mechanically and electrically mounted to mounting board 121, electrodes 122, a color conversion element 125, and mounting structures 124. Mounting board 122 mechanically and electrically interfaces LED based illumination device 120 with the application environment in which LED based illumination device 120 is installed. Color conversion element 125 is disposed over the light emitting surface of each of the plurality of LED based illumination sources 123.

[0043] In some embodiments, the LED based illumination source is a group III nitride semiconductor structure, including, by wayof non-limiting example, an n layer, a light emitting layer, and a p layer. In various examples, the group III nitride semiconductor structure is AlGaN-based, GaN-based, or InAlGaN- based. In general, a group III nitride semiconductor structure is configured to emit blue light in the visible spectrum.

[0044] In general, the color conversion element, e.g. color conversion elements 104, 115, and 125 depicted in FIGS. 3-5, respectively, is disposed over the light emitting surface of one or more diode based illumination sources. In some embodiments, e.g., the embodiments depicted in FIGS. 3 and 4, the color conversion element is in direct contact with the light emitting surface of one or more LED based illumination sources. In some examples, the color conversion element is fixed to the diode based illumination source by an adhesive, e.g., a silicone based adhesive. In other examples, the color conversion element is thermally bonded to the diode based illumination source, e.g., thermal fusion.

[0045] However, in other embodiments, the color conversion element is spaced apart from the light emitting surface of one or more diode based illumination sources, e.g., the embodiment depicted in FIG. 5. In some embodiments, the space between the color conversion element and a diode based illumination source, e.g., space 126 depicted in FIG. 5, is filled with an optically transparent material. In some other embodiments, the space between color conversion element 104 and diode based illumination source 103 is void of solid material, e.g., gas filled or sealed under vacuum.

[0046] In some examples, a color conversion element is individually located over one or more diode based illumination sources, and fixed into position to assemble an individual diode based illumination device. However, in other embodiments, a relatively large area color conversion element is located over more than one diode based illumination source, and fixed into position to assemble a group of diode based illumination devices. Each individual diode based illumination device issubsequently physically separated from the group by a subsequent manufacturing process, e.g., sawing, scribe and break, etc.

[0047] In the embodiment depicted in FIG. 2 the color conversion element 104 is rectangular in shape, i.e., a rectangular plate. As depicted in FIG. 2, color conversion element 104 is characterized by a thickness, T, and lateral dimensions, S1and S2, characterizing the length of the sides of the rectangular plate. In some other embodiments, the color conversion element is circular in shape, i.e., a circular plate. In these examples, the color conversion element is characterized by a thickness, T, and a diameter dimension characterizing the size of the circular profile. In general, the direction characterized by the thickness dimension is aligned with the direction normal to the light emitting surface of a diode based illumination source when the color conversion element is assembled as part of a diode based illumination device.

[0048] Color conversion elements manufactured by sawing of wafers are often shaped as rectangular plates to minimize material loss and manufacturing effort. However, circular plate shapes may be employed to reduce the risk of breakage, e.g., the corners of rectangular shaped plates are particularly vulnerable.

[0049] The thickness of a plate shaped color conversion element is determined by the process employed to manufacture the plate. In some examples, the sintering process is applied to a composite material that is already shaped to the desired thickness, e.g., in a mold. In other examples, the sintering process is applied to a composite material shaped thicker than the desired thickness, and the desired thickness is achieved by a subsequent process step, e.g., sawing, grinding, etc.

[0050] In some embodiments, the thickness of a color conversion element is greater than 50 micrometers. In other embodiments, the thickness of a color conversion element is greater than 500 micrometers.

[0051] In some embodiments, the diode based illumination device is encapsulated in a transparent sealant, e.g., silicone, to reduce the impact of the operational environment on degradation of the diode based illumination device.

[0052] In one aspect, a color conversion element is a sintered composite material including one or more phosphor materials dispersed in a magnesium aluminate spinel matrix material, e.g.,MgAl2O4 and its solid solutions, Mg1-xAl2+yO4, where0 < x ≤ 0.7^^^and^^0 ≤ y ≤ 0.5.^Exemplary phosphor materials include an oxide based phosphor material, an α-type sialon phosphor material, a beta-type sialon phosphor, a silicon nitride based phosphor material, an aluminum garnet based phosphor material, or any combination thereof.

[0053] As such, the color conversion plate acts as a wavelength converter to convert some or all pump light emitted from a diode based illumination source to converted light. Converted light typically includes longer wavelengths than the pump light. The converted light or combination of converted light and pump light include a range of wavelengths that result in broad spectrum light, e.g., white light or colored light meeting desired spectral characteristics. The spectral content of the light emitted from a diode based illumination device is dictated by the amount and color of unconverted pump light passed through the color conversion plate (if any) and the amount and color of converted light generated by the phosphor materials embedded in the color conversion plate.

[0054] Alumina is commonly employed as a matrix material because it has higher thermal conductivity compared to magnesium aluminate spinel. Thus, it is expected that an LED based illumination device employing alumina as the matrix material of a wavelength converter will be more thermally efficient, i.e., lower temperature per watt of electrical input. In particular, alumina is commonly employed as the matrix material in high power LED applications, e.g., devices employing an LEDillumination source having a minimum blue photon excitation level of one radiometric Watt per one millimeter squared area.

[0055] However, the inventors have discovered that employing magnesium aluminate spinel as a matrix material may result in an overall increase in efficiency of a diode based illumination device. High sintering temperatures are known to degrade the color conversion efficiency of many phosphor materials. The inventors have discovered that a magnesium aluminate spinel based color conversion element fabricated at lower sintering temperatures compared to an equivalent alumina based color conversion element achieves more efficient optical performance. The lower sintering temperatures reduce the degradation of color conversion efficiency of the phosphor materials, compared to higher sintering temperatures employed when alumina is employed as a matrix material. The reduced degradation results in a relative increase in color conversion efficiency of the phosphor materials included in the magnesium aluminate spinel based sintered composite. Counterintuitively, this may result in an overall increase in optical efficiency of the diode based illumination device employing a magnesium aluminate spinel based color conversion element. In particular, the efficiency benefits accrue in devices employing a diode based illumination source having a minimum blue photon excitation level of one radiometric Watt per one millimeter squared area.

[0056] FIG. 6 is a table 130 illustrative of the mass percentage composition of a binary composite of magnesium aluminate spinel and a Ca-α-sialon phosphor material after sintering at three different temperatures.

[0057] Table 130 illustrates three different sintering temperature scenarios. In the first scenario, a mass combination of 60% magnesium aluminate spinel and 40% Ca-α-sialon phosphor material is sintered at a temperature of 1200 degrees Centigrade. In the second scenario, the same mass combination (60% magnesium aluminate spinel and 40% Ca-α-sialon phosphor material) is sintered at a temperature of 1250 degreesCentigrade. In the third scenario, the same mass combination (60% magnesium aluminate spinel and 40% Ca-α-sialon phosphor material) is sintered at a temperature of 1300 degrees Centigrade.

[0058] As depicted in FIG. 6, at a sintering temperature of 1200 degrees Centigrade, the resulting ceramic includes two main phases: the magnesium aluminate spinel phase and the Ca-α- sialon phosphor material phase. Similarly, at sintering temperatures of 1250 and 1300 degrees Centigrade, the resulting ceramic includes the same two main phases in approximately the same mass proportion. As illustrated in table 130, the mass proportion of Ca-α-sialon phosphor material slightly decreases with increasing temperature.

[0059] FIG. 7 is a table 135 illustrative of the mass percentage composition of a binary composite of alumina and a Ca-α-sialon phosphor material after sintering at two different temperatures.

[0060] Table 135 illustrates two different sintering temperature scenarios. In the first scenario, a mass combination of 60% alumina and 40% Ca-α-sialon phosphor material is sintered at a temperature of 1250 degrees Centigrade. In the second scenario, the same mass combination (60% alumina and 40% Ca-α-sialon phosphor material) is sintered at a temperature of 1500 degrees Centigrade.

[0061] As depicted in FIG. 7, at a sintering temperature of 1250 degrees Centigrade, the resulting ceramic includes only two phases: the alumina phase and the Ca-α-sialon phosphor material phase. However, at a sintering temperature of 1500 degrees Centigrade, the resulting ceramic includes an alumina phase and a Ca-α-sialon phosphor material phase, and a Ca2SiO4phase at a mass percentage of 14%. As illustrated in table 135, the ceramic sintered from an alumina matrix material includes a third phase at a significant mass percentage only at a sintering temperature of approximately 1500 degrees Centigrade, and doesnot include a third phase at any detectable amount at a sintering temperature of approximately 1250 degrees Centigrade.

[0062] FIG. 8 is a table 140 illustrative of the optical total integrated scattering and optical conversion efficiency of a ceramic sintered from a magnesium aluminate spinel matrix material and a ceramic sintered from an alumina matrix material in one example.

[0063] As depicted in FIG. 8, the Total Integrated Scatter (TIS) is the ratio of the total power generated by all contributions of scattered radiation into the forward half-space, the backward half-space, or both, to the power of the incident radiation from a pump light source. In the embodiments described with reference to FIG. 8, the pump light source is a blue laser having a peak emission at approximately 446 nanometers with a maximum output power of 5 Watts. The blue laser is pointed to a sample stage holding a color converting sample on top of an integrating sphere at a 45-degree angle. In these embodiments, the thickness of the sintered composite material is approximately 100 micrometers. In general, the higher the TIS value, the greater amount of converted light corresponds to spectral intensity at longer wavelengths.

[0064] As depicted in FIG. 8, conversion efficiency is evaluated based on an LED based illumination device. A sintered composite platelet is attached to a blue LED pump illumination source having a peak emission at approximately 445 nanometers. The conversion efficiency is the ratio of the radiometric power in the spectral range of 585 to 615 nanometers (a portion of the electromagnetic spectrum that is visible as an amber color) to the total power of the incident light from the blue LED pump illumination source operated at a drive current of approximately 6.5 Ampere and a junction temperature of 25 degrees Centigrade in both a single pulse (SP) measurement mode and a continuous wave (CW) measurement mode.

[0065] Table 140 illustrates two different sintering scenarios differing in both material and sintering temperature. In thefirst scenario, a mass combination of 60% magnesium aluminate spinel and 40% Ca-α-sialon phosphor material is sintered at a temperature of 1300 degrees Centigrade. In the second scenario, a mass combination of 60% alumina and 40% Ca-α-sialon phosphor material is sintered at a temperature of 1500 degrees Centigrade.

[0066] As illustrated in table 140, the optical performance of the ceramic employing a magnesium aluminate spinel matrix material exceeds the optical performance of the ceramic employing an alumina matrix material across all illustrated measurement performance metrics. This result is achieved even though the ceramic employing a magnesium aluminate spinel matrix material is sintered at a sintering temperature that is 200 degrees Centigrade lower than the ceramic employing alumina as the matrix material.

[0067] FIG. 9 is a plot 145 of the spectral output of an LED based illumination device including an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 8. Plotline 146 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 140. Plotline 147 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 140. As depicted in FIG. 9, the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element in the amber portion of the electromagnetic spectrum, e.g., within the range of wavelengths spanning 585 nanometers to 615 nanometers.

[0068] FIG. 10 is a plot 150 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a single pulse mode. LEDbased illumination device includes an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 8.

[0069] Plotline 151 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 140. Plotline 152 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 140. As depicted in FIG. 10, the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element over the plotted range of drive currents, and particularly at higher drive currents.

[0070] FIG. 11 is a plot 155 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a continuous wave mode. LED based illumination device includes an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 8.

[0071] Plotline 156 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 140. Plotline 157 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 140. As depicted in FIG. 11, the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element over the plotted range of drive currents, and particularly at higher drive currents.

[0072] In addition, FIGS. 10 and 11 illustrate that the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element especially at higher drive currents operating in a continuous wave mode.

[0073] FIG. 12 is a table 160 illustrative of the optical total integrated scattering and optical conversion efficiency of a ceramic sintered from a magnesium aluminate spinel matrix material and a ceramic sintered from an alumina matrix material in another example. As depicted in FIG. 12, the total integrated scattering is evaluated as a ratio of the total scattered flux divided by the total incident flux. The optical conversion efficiency percentage is evaluated in a spectral range between 585 nanometers and 615 nanometers (a portion of the electromagnetic spectrum that is visible as an amber color) at a drive current of 6.5 Ampere and junction temperature of 25 degrees Centigrade in both a single pulse (SP) measurement mode and a continuous wave (CW) measurement mode.

[0074] Table 160 illustrates two different sintering scenarios differing in material. In the first scenario, a mass combination of 60% magnesium aluminate spinel and 40% Ca-α-sialon phosphor material is sintered at a temperature of 1250 degrees Centigrade. In the second scenario, a mass combination of 60% alumina and 40% Ca-α-sialon phosphor material is sintered at a temperature of 1250 degrees Centigrade.

[0075] As illustrated in table 160, the optical performance of the ceramic employing a magnesium aluminate spinel matrix material exceeds the optical performance of the ceramic employing an alumina matrix material across all illustrated measurement performance metrics.

[0076] FIG. 13 is a plot 165 of the spectral output of an LED based illumination device including an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference toFIG. 12. Plotline 166 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 160. Plotline 167 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 160. As depicted in FIG. 13, the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element in the amber portion of the electromagnetic spectrum, e.g., within the range of wavelengths spanning 585 nanometers to 615 nanometers.

[0077] FIG. 14 is a plot 170 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a single pulse mode. LED based illumination device includes an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 12.

[0078] Plotline 171 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 160. Plotline 172 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 160. As depicted in FIG. 14, the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element over the plotted range of drive currents, and particularly at higher drive currents.

[0079] FIG. 15 is a plot 175 illustrative of the radiometric intensity output as a function of drive current from an LED based illumination device operated in a continuous wave mode.LED based illumination device includes an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 12.

[0080] Plotline 176 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 160. Plotline 177 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 160. As depicted in FIG. 15, the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element over the plotted range of drive currents, and particularly at higher drive currents.

[0081] FIGS. 14 and 15 illustrate that the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element exceeds that of an alumina color converting element especially at higher drive currents operating in a continuous wave mode.

[0082] Furthermore, comparing FIGS. 8-11 and 12-15, respectively, illustrates that the optical performance of an LED based illumination device employing a magnesium aluminate spinel based color converting element dramatically exceeds that of an LED based illumination device employing an alumina color converting element when a sintering temperature of 1250 degrees Centigrade is employed.

[0083] FIG. 16 is a plot 180 illustrative of surface temperature of a color converting element as a function of drive current from an LED based illumination device operated in a continuous wave mode. The LED based illumination device includes an LED based illumination source emitting blue light through color converting elements corresponding to the two samples described with reference to FIG. 8.

[0084] Plotline 181 depicts the intensity of the radiometric output of the LED based illumination device employing a magnesium aluminate spinel based color converting element as described with reference to table 140. Plotline 182 depicts the intensity of the radiometric output of the LED based illumination device employing an alumina based color converting element as described with reference to table 140. As depicted in FIG. 16, the surface temperature of the color converting element employing a magnesium aluminate spinel based matrix material is lower that of an alumina based matrix material at higher drive currents.

[0085] In some embodiments, a color conversion element is fabricated from a sintered composite material including one or more phosphor materials dispersed in one or more matrix materials including a magnesium aluminate spinel matrix material. In some embodiments, the magnesium aluminate spinel matrix material is at least 35% of the mass of the sintered composite material. In some embodiments, the composite material includes magnesium aluminate spinel as the primary matrix material and one or more additional matrix materials, e.g., one or more sintering additives. In some embodiments, the magnesium aluminate spinel matrix material is at least 80% of the mass of the sum of the matrix materials of the sintered composite material. In some of these embodiments, a composite material includes magnesium aluminate spinel as the primary matrix material and a sintering additive, e.g. an oxide material such as magnesium oxide (MgO), a fluoride material, a chloride material, etc.

[0086] In some embodiments, a color conversion element is fabricated from a composite material including an α-type sialon phosphor dispersed in a combination of matrix materials including a magnesium aluminate spinel matrix material. In these embodiments, the α-type sialon phosphor comprises 1% and 60% of the mass of the composite, and magnesium aluminate spinel matrix material is between 80% and 100% of the mass of all ofthe matrix materials of the composite, and the sintering additive is between 0% and 20% of the mass of all of the matrix materials of the composite.

[0087] A color conversion element is fabricated by mixing and sintering the composite materials to generate a dense composite structure. The matrix materials, including magnesium aluminate spinel, and phosphor materials are prepared as powder materials. In some embodiments, a minimum grain size of the magnesium aluminate spinel matrix material and the one or more phosphor materials is greater than 1 micrometer and less than 50 micrometers.

[0088] The powders are mixed thoroughly to disperse the phosphor materials in the magnesium aluminate spinel matrix using wet or dry mixing methods. In the matrix phase of the composite, the phosphor particles are dispersed between crystal grains of the magnesium aluminate spinel, within the crystal grains of the magnesium aluminate spinel, or both. In general, it is preferable that high purity magnesium aluminate spinel powder and phosphor powder are employed to form the composite material. In some examples, contamination of the magnesium aluminate spinel powder and phosphor powder by elements other than the desired constituent elements is less than 0.1%.

[0089] The composite is then sintered to uniformly disperse the phosphor particles in the magnesium aluminate spinel sintered matrix to form a relatively dense composite structure. In some embodiments, the mixture of the composite is sintered at a temperature of 1500° Centigrade, or lower. In some embodiments, the mixture of the composite is sintered at a temperature of 1400° Centigrade, or lower. In some embodiments, the mixture of the composite is sintered at a temperature of 1300° Centigrade, or lower. Higher sintering temperatures increase the density of the sintered composite, but at a cost of further degradation of the color conversion performance of the phosphor materials.

[0090] The densification of the sintered composite at a given sintering temperature is achieved by a sintering process, e.g.,spark plasma sintering, hot press sintering, hot isostatic press sintering, gas-pressure sintering, etc. In some examples, a spark plasma sintering system is employed to achieve densification of the sintered composite at a given sintering temperature. In some examples, the sintering process is undertaken in a process chamber in a controlled environment filled with a non-oxidizing inert gas, e.g., nitrogen, argon, xenon, etc., to prevent oxidation of the phosphor materials. In some examples, the sintering process is undertaken in a process chamber under vacuum conditions to prevent oxidation of the phosphor materials. In some examples, the sintering process is undertaken in a pressurized process chamber to improve densification of the sintered composite at a given sintering temperature.

[0091] In some embodiments, the porosity of the sintered composite structure of the color conversion element including a magnesium aluminate spinel matrix material and one or more phosphor materials is greater than 0.1% and less than 25% by volume.

[0092] In a further aspect, the one or more surfaces of the color conversion element are mechanically or chemically processed after sintering to achieve a desire surface finish. By way of non-limiting example, surface processes include grinding, polishing, lapping, plasma etch, deposition, or any combination thereof.

[0093] FIG. 17 illustrates a method 200 for generating illumination light by color conversion of pump light in at least one novel aspect. Method 200 is suitable for implementation by diode based illumination devices, e.g., LED based illumination device, laser diode based illumination devices, or both, such as diode based illumination devices 100, 110, and 120, illustrated in FIGS. 2-5 of the present invention. It is recognized herein that the particular structural aspects of illumination device 100, 110, and 120 do not represent limitations and should be interpreted as illustrative only.

[0094] In block 201, an amount of pump light is generated from one or more diode based illumination sources, e.g., light emitting diodes (LEDs), laser diodes, (LDs), etc.

[0095] In block 202, the amount of pump light is transmitted through a light color conversion element. The light color conversion element converts a portion of the amount of pump light to a different color. The light color conversion element includes a magnesium aluminate spinel matrix material and one or more phosphor materials dispersed in the magnesium aluminate spinel matrix material.

[0096] Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. For example, although LEDs 103, 113, and 121 are described as LEDs with a peak emission in the blue range, the LEDs can emit different or the same colors, either by direct emission or by phosphor conversion, e.g., where phosphor layers are applied to the LEDs as part of the LED package. Thus, the illumination device 100 may use any combination of colored LEDs 102, such as red, green, blue, amber, or cyan, or the LEDs 102 may all produce the same color light or may all produce white light. In the embodiments described, specific phosphors were described for exemplary purposes, but any number of phosphors each with peak emission in the UV, visible, and infrared ranges may be employed. Furthermore, in the embodiments described, specific ratios of matrix materials and phosphors were described for exemplary purposes, but these ratios may be varied to produce similar results. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

CLAIMS What is claimed is:

1. A light color conversion element comprising: a magnesium aluminate spinel matrix material; and one or more phosphor materials dispersed in the magnesium aluminate spinel matrix material, wherein a blue photon excitation level of light incident on the light color conversion element is at least one radiometric Watt per one millimeter squared area.

2. The light conversion element of Claim 1, wherein the one or more phosphor materials include an oxide based phosphor material, an α-type sialon phosphor material, a beta-type sialon phosphor, a silicon nitride based phosphor material, an aluminum garnet based phosphor material, or any combination thereof.

3. The light conversion element of Claim 1, wherein a geometric shape of the light color conversion element is a rectangular plate characterized by a thickness and lateral dimensions.

4. The light conversion element of Claim 1, wherein a composite of the magnesium aluminate spinel matrix material and the one or more phosphor materials is generated by sintering at a temperature less than 1,500 degrees Centigrade.

5. The light conversion element of Claim 4, wherein the sintering of the composite is performed by a sintering system selected from a group consisting of a spark plasma sintering system, a hot press sintering system, a hot, isostatic press sintering system, and a gas pressure sintering system.

6. The light conversion element of Claim 4, wherein a porosity of the composite of the magnesium aluminate spinelmatrix material and the one or more phosphor materials is greater than 0.1% and less than 25%.

7. The light conversion element of Claim 4, wherein a minimum grain size of the magnesium aluminate spinel matrix material and the one or more phosphor materials is greater than 1 micrometer and less than 50 micrometers.

8. The light conversion element of Claim 4, wherein the magnesium aluminate spinel matrix material is at least 35% of the mass of the sintered composite material.

9. The light conversion element of Claim 4, wherein the sintered composite material includes magnesium aluminate spinel as a primary matrix material and one or more additional matrix materials, and wherein the magnesium aluminate spinel matrix material is at least 80% of the mass of the sum of the matrix materials of the sintered composite material.

10. A diode based illumination device comprising: a mounting board; one or more diode based illumination sources electrically and mechanically coupled to the mounting board, each of the one or more diode based illumination sources having a light emitting surface; a light color conversion element disposed above the light emitting surface of the one or more diode based illumination sources, the light color conversion element comprising: a magnesium aluminate spinel matrix material; and one or more phosphor materials dispersed in the magnesium aluminate spinel matrix material.

11. The diode based illumination device of Claim 10, wherein the one or more diode based illumination sources generate a blue photon excitation level of light incident on thelight color conversion element that is at least one radiometric Watt per one millimeter squared area.

12. The diode based illumination device of Claim 10, the one or more phosphor materials including an oxide based phosphor material, an α-type sialon phosphor material, a beta-type sialon phosphor material, a silicon nitride based phosphor material, an aluminum garnet based phosphor material, or any combination thereof.

13. The diode based illumination device of Claim 10, wherein the light color conversion element is physically coupled to the light emitting surface of each of the one or more diode based illumination sources.

14. The diode based illumination device of Claim 10, wherein a geometric shape of the light color conversion element is a rectangular plate characterized by a thickness and lateral dimensions.

15. The diode based illumination device of Claim 10, wherein a composite of the magnesium aluminate spinel matrix material and the one or more phosphor materials is generated by sintering at a temperature less than 1,500 degrees Centigrade.

16. The diode based illumination device of Claim 15, wherein the sintering of the composite is performed by a sintering system selected from a group consisting of a spark plasma sintering system, a hot press sintering system, a hot, isostatic press sintering system, and a gas pressure sintering system.

17. The diode based illumination device of Claim 15, wherein a porosity of the composite of the magnesium aluminatespinel matrix material and the one or more phosphor materials is greater than 0.1% less than 25%.

18. The diode based illumination device of Claim 15, wherein a minimum grain size of the composite of the magnesium aluminate spinel matrix material is greater than 1 micrometer and less than 50 micrometers.

19. A method comprising: generating an amount of pump light from one or more diode based illumination sources; and transmitting the amount of pump light through a light color conversion element, wherein the light color conversion element converts a portion of the amount of pump light to a different color, the light color conversion element comprising: a magnesium aluminate spinel matrix material; and one or more phosphor materials dispersed in the magnesium aluminate spinel matrix material.

20. The method of Claim 19, the one or more phosphor materials including an oxide based phosphor material, an α-type sialon phosphor material, a beta-type sialon phosphor material, a silicon nitride based phosphor material, an aluminum garnet based phosphor material, or any combination thereof.

21. The method of Claim 19, further comprising: sintering a composite of the magnesium aluminate spinel matrix material and the one or more phosphor materials at a peak temperature less than 1,500 degrees Centigrade.

22. The method of Claim 21, wherein the sintering of the composite involves a sintering system selected from a group consisting of a spark plasma sintering system, a hot press sintering system, a hot, isostatic press sintering system, and a gas pressure sintering system.

23. The method of Claim 21, wherein a porosity of the composite of the magnesium aluminate spinel matrix material and the one or more phosphor materials is greater than 1 micrometer and less than 50 micrometers.

24. The method of Claim 21, wherein a minimum grain size of the magnesium aluminate spinel matrix material and the one or more phosphor materials is greater than 1 micrometer and less than 50 micrometers.

25. The method of Claim 19, wherein a geometric shape of the light color conversion element is a rectangular plate characterized by a thickness and lateral dimensions.

Images