TWI796516B - Phosphor converted led with high color quality - Google Patents

Abstract

A light emitting diode (LED) device may include an LED die having a first surface on a substrate. A first phosphor layer may be formed on a second surface and sides of the LED die. The second surface may be opposite the first surface. A second phosphor layer may be formed on the first phosphor layer. The second phosphor layer may have a peak emission wavelength (L_pk 2) located between a peak emission wavelength of the LED die (L_pk D) and a peak emission wavelength of the first phosphor layer (L_pk 1).

Description

Phosphor-converted LEDs with high color quality

This application relates to LEDs, and more particularly to phosphor converted LEDs.

Phosphor-converted white LED light-emitting diode (LED) devices typically use a blue LED covered by a layer of luminescent material that partially absorbs blue LED light and emits green, yellow, and red light. Luminescent materials usually contain a mixed powder of one of the inorganic materials. For high color quality as defined by the Commission on Illumination (CIE) as Color Rendering Index (CRI), the spectral power distribution (SPD) of the light emitted from the LED must closely follow the SPD of a white reference light. Avoiding sharp peaks and minima in SPDs can be especially important if the light emitted from the LED is used in combination with a camera system (eg, as a flash).

A light emitting diode (LED) device can include an LED die having a first surface on a substrate. A first phosphor layer can be formed on a second surface and sides of the LED die. The second surface may be opposite to the first surface. A second phosphor layer can be formed on the first phosphor layer. The second phosphor layer may have a peak emission wavelength (L pk 2) between a peak emission wavelength (L _pk D) _of the LED die and a peak emission wavelength (L _pk 1) of the first phosphor layer .

A light emitting diode (LED) device can include an LED die having a first surface on a substrate. A first phosphor layer can be formed on a second surface of the LED die. The second surface may be opposite to the first surface. A second phosphor layer can be formed on the first phosphor layer. The second phosphor layer may have a peak emission wavelength (L pk 2) between a peak emission wavelength (L _pk D) _of the LED die and a peak emission wavelength (L _pk 1) of the first phosphor layer . A reflective coating is formed on each side of the LED die, on each side of the first phosphor layer, and on each side of the second phosphor layer.

16: n-type region

18: Emitting or active region/p-type region

20: p-type region

21: p contact

22:n contact

24: Dielectric layer

25: Clearance

26: Interconnect

27: Clearance

28: Interconnects

102: Substrate

104: Light-emitting diode grain/light-emitting diode structure

202: first phosphor layer

300: light emitting diode device

302: second phosphor layer

402: lens

502: side wall

504: side wall

506: side wall

600: light emitting diode device

602: Reflective coating / first reflective coating

702: lens

802: First emission spectrum

804: Second emission spectrum

A more detailed understanding can be obtained from the following description, given by way of example in conjunction with the accompanying drawings, in which like element numbers in the various figures indicate like elements, and in which: FIG. 1 illustrates an LED die on a substrate 2 is a cross-sectional view illustrating the formation of a first phosphor layer on the LED; FIG. 3 is a cross-sectional view illustrating the formation of a second phosphor layer on the first phosphor layer to form an LED device; FIG. 4 is a cross-sectional view illustrating the optional formation of a lens around the LED device; FIG. 5 is a cross-sectional view illustrating the optional removal of the first phosphor layer and the second phosphor layer from the LED device; FIG. A reflective coating is formed on each side of the bead, the remainder of the first phosphor layer, and the remainder of the second phosphor layer to form a cross-sectional view of an LED device; FIG. 7 illustrates one of a lens optionally formed around the LED device cutaway Figures; Figure 8 is one of a graph illustrating the emission spectrum of an LED die coated with only the first phosphor layer compared to an LED die coated with both the first phosphor layer and the second phosphor layer; and 9 is a graph illustrating the emission spectrum of the second phosphor layer and LED die.

Cross References to Related Applications

This application claims the benefit of priority of European Patent Application No. 18201516.4, filed October 19, 2018, and U.S. Patent Application No. 16/119,688, filed August 31, 2018, in which The entire text of each is incorporated herein by reference.

Examples of various light emitting diode ("LED") implementations are set forth more fully hereinafter with reference to the accompanying drawings. These examples are not mutually exclusive, and features found in one example may be combined with features found in one or more other examples to arrive at additional implementations. Accordingly, it should be understood that the examples shown in the accompanying drawings are provided for illustrative purposes only and that they are not intended to limit the invention in any way. Like numbers refer to like elements throughout.

It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element such as a layer, region, or substrate is referred to as being "on" or extending "on" another element, it can be directly on the other element. Or extend directly to another element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly to" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. It will be understood that these terms are intended to encompass different orientations of elements in addition to any orientation depicted in the figures.

Relative terms (such as "under" ... "below" or "on" ... "above", or "upper" or "lower", or "horizontal" or "vertical ”) to illustrate the relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

As explained above, for high color quality defined by the Commission on Illumination (CIE) as Color Rendering Index (CRI), the spectral power distribution (SPD) of the light emitted from the LED must closely follow the SPD of a white reference light. To achieve a high CRI, different phosphor materials may have to be applied in order to emit different wavelengths of light. Emission from a phosphor emitting at a shorter wavelength can be absorbed by a phosphor emitting at a longer wavelength. This phosphor-phosphor interaction can reduce efficiency due to loss of photons in the conversion process. Phosphor-phosphor interactions can also increase absorption losses in an LED package that includes the one or more LED dies due to redirection of emitted light back to the one or more LED dies.

In some applications, it may be desirable to reduce the blue emission peak close to the LED in the SPD The local minimum of the value. The emission peak of a phosphor element may have to be close to that of the blue LED. When a phosphor material absorbs a photon, it gains energy and enters an excited state. One way to relax the phosphor material is to emit a photon, thus losing its energy (another way would be to lose the energy as heat). When emitted photons have less energy than absorbed photons, this energy difference is Stokes shifted. Stokes fluorescence is the emission of a longer wavelength photon (lower frequency or energy) by a molecule that has absorbed a photon of a shorter wavelength (higher frequency or energy). In other words, the Stokes shift can be the distance between an absorption maximum wavelength and an emission maximum wavelength. Due to the Stokes shift, large amounts of phosphor material may be required. It may be desirable to minimize reabsorption of emitted light by other phosphors.

The following description includes systems, methods, and apparatus for using multiple phosphor layers formed on an LED to reduce reabsorption of light emitted by the outermost phosphor layer and increase the efficiency of the LED at high CRI. By using a second phosphor layer with an emission peak located between an emission peak of a first phosphor layer and an LED, the wavelength between the LED emission and the emission of the first phosphor layer can be effectively filled gap.

Referring now to FIG. 1 , a cross-sectional view illustrating an LED die 104 on a substrate 102 is shown. A first surface of the LED die 104 can be located on the substrate 102, and a second surface of the LED die can be located opposite the first surface. The LED die 104 can be any type of conventional semiconductor light emitting device and can be formed, attached or grown on the substrate 102 . Figure 1 shows an illustrative example of one type of LED die 104 that may be used and is not intended to limit the following description. LED die 104 may be a type III-nitride LED of one of the types known in the art. Typically, III-nitride LEDs are fabricated by depositing a sapphire, silicon carbide, III-nitride or Other semiconductor layers suitable for epitaxial growth of different compositions and dopant concentrations on substrates One stacks. The stack typically includes one or more n-type layers formed over a substrate doped with, for example, silicon, an active region (eg, a p-n diode) formed over the n-type layer(s). ), and one or more p-type layers formed over the active region doped with, for example, magnesium. Electrical contacts are formed on the n-type region and the p-type region.

In the following examples, LED die 104 may emit blue or UV light. However, instead of LEDs, it is also possible to use materials such as laser diodes and LEDs made of other material systems (such as other III-V materials, III-Phosphides, III-As, II-VI materials, ZnO or Si-based materials). Semiconductor light emitting devices such as fabricated semiconductor light emitting devices.

The device of FIG. 1 may be formed by growing a type III-nitride semiconductor structure on a substrate 102, as is known in the art. Substrate 102 may be sapphire or any suitable substrate such as, for example, SiC, Si, GaN, or a composite substrate. One of the surfaces of the substrate 102 on which Group III-nitride semiconductor structures of the type described can be grown can be patterned, roughened or textured prior to growth, which can improve light extraction from the device. The surface of the substrate 102 opposite the growth surface (i.e., the surface through which most light is extracted in a flip-chip configuration) can be patterned, roughened, or textured before or after growth, which can be improved from Device Light Extraction.

The semiconductor structure includes a light emitting or active region sandwiched between n-type and p-type regions. An n-type region 16 may be grown first, and this n-type region may comprise multiple layers of different compositions and dopant concentrations. The n-type region 16 may include preparation layers (such as buffer layers or nucleation layers) and/or layers designed to facilitate removal of the growth substrate, which may be n-type or not intentionally doped and directed towards making the light emitting region highly efficient. n-type or even p-type device layers designed with specific optical, material or electrical properties desired to emit light. A light emitting or active region 18 is grown over the n-type region 16 . Examples of suitable light emitting regions 18 include a single thick or thin light emitting layer, or multiple quantum well light emitting regions that include multiple thin or thick light emitting layers separated by barrier layers. A p-type region 20 can then be grown over the light emitting region. Like the n-type region, the p-type region can contain Multiple layers comprising different compositions, thicknesses and dopant concentrations, including layers that are not intentionally doped or n-type layers.

After growth, a p-contact may be formed on the surface of p-type region 18 . The p-contact 21 may include multiple conductive layers, such as a reflective metal and a guard metal that prevents or reduces electromigration of the reflective metal. The reflective metal is typically silver, but any suitable material or materials may be used. Portions of p-contact 21 , p-type region 20 and active region 18 may be removed to expose a portion of n-type region 16 over which an n-contact 22 is formed. The n-contact 22 and the p-contact 21 may be electrically isolated from each other by a gap 25, which may be filled with a dielectric such as a silicon oxide or any other suitable material. A plurality of n-contact vias may be formed. The n-contact 22 and the p-contact 21 are not limited to the configuration illustrated in FIG. 1 . The n-contact 22 and p-contact 21 can be redistributed to form bond pads with a dielectric/metal stack, as is known in the art.

To form electrical connections to LED die 104 , one or more interconnects 26 and 28 may be formed on or electrically connected to n-contact 22 and p-contact 21 . Interconnect 26 may be electrically connected to n-contact 22 . Interconnect 28 may be electrically connected to p-contact 21 . Interconnects 26 and 28 may be electrically isolated from n-contact 22 and p-contact 21 and from each other by dielectric layer 24 and a gap 27 . For example, interconnects 26 and 28 may be solder, stud bumps, gold layers, or any other suitable structure. In the following figures, the semiconductor structure, n-contact 22 , p-contact 21 , and interconnects 26 and 28 are shown as LED structure 104 . Substrate 102 may be thinned or removed entirely. Patterning, texturing or roughening can improve light extraction by thinning the exposed surface of the substrate 102 .

Referring now to FIG. 2 , there is shown a cross-sectional view illustrating the formation of a first phosphor layer 202 on the LED die 104 . The first phosphor layer 202 can be applied to the second surface and sides of the LED die 104 . The first phosphor layer 202 may have a thickness ranging from about 1 μm to about 150 μm.

The first phosphor layer 202 can be formed using a conventional deposition procedure. In one example, the first phosphor layer 202 may be a thin sheet that is placed on top of the LED die 104 and then processed to conform to the shape of the LED die 104 . The first phosphor layer 202 may be laminated to the LED die 104 using a combination of vacuum and heat.

Those skilled in the art will recognize that the first phosphor layer 202 need not be in the form of a laminated sheet; it may be applied in liquid or paste form via spraying, molding, screen printing, or the like. For example, using a conventional deposition procedure such as chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), atomic layer deposition (ALD), evaporation, sputtering, chemical solution deposition, spin-on deposition or other Similar to the procedure, the first phosphor layer 202 can be conformally formed on the LED die 104 .

The first phosphor layer 202 may comprise a wavelength converting material which may be, for example, conventional phosphors, organic phosphors, quantum dots, organic semiconductors, Group 26 or 35 semiconductors, Group 26 or Group III and V semiconductor quantum dots or nanocrystals, dyes, polymers, or other materials that emit luminescence. The first phosphor layer 202 may comprise a transparent material, such as polysilicon, mixed with a wavelength converting material.

The wavelength conversion material can absorb light emitted by LED die 104 and can emit light at one or more different wavelengths. The unconverted light emitted by the LED die 104 may be part of the final spectrum of light extracted from the structure, although it need not be.

In one example, the LED die 104 may be a blue-emitting LED having a peak emission wavelength L _pk D .

In an example, the first phosphor layer 202 may include a yellow emission wavelength converting material, a green emission wavelength converting material, and a red emission wavelength converting material having a combined peak emission wavelength L _pk 1 .

The first phosphor layer 202 may include one or more phosphor powders in polysiloxane. For example, the first phosphor layer 202 may include GaLuAG, SCASN, and CASN. The mass ratio of materials in the first phosphor layer 202 may be about 20% SCASN:80% CASN. In the first phosphor layer 202, the ratio of GaLuAG to total red mass may be about 8.47.

In another example, the first phosphor layer 202 may include a mixture of a green emission wavelength conversion material and a red emission wavelength conversion material. The green emitting wavelength conversion material may comprise garnet activated with cerium, which has a chemical composition of (Y,Gd,Lu) ₃ (Al,Ga) ₅ O ₁₂ :Ce. Green emitting wavelength conversion materials may include silicates and oxynitrides activated with europium, such as SiAlON. Red-emitting wavelength converting materials may include nitrides activated with europium, such as CASN, SCASN, and BSSN, and quantum dots.

In another example, the first phosphor layer 202 may include a mixture of one of a green-emitting wavelength converting material and a red-emitting wavelength converting material. The green emitting wavelength conversion material may include GaLuAG and GaYAG. The red emitting wavelength conversion material may comprise SCASN and CASN, wherein the mass ratio of SCASN to CASN is about 20:80. The ratio of the total mass of green-emitting wavelength converting material to the total mass of red-emitting wavelength converting material is about 8.47 and may range from 5-10.

Referring now to FIG. 3 , there is shown a cross-sectional view illustrating the formation of a second phosphor layer 302 on the first phosphor layer 202 to form an LED device 300 . A second phosphor layer 302 may be applied to the top and sides of the first phosphor layer 202 . Second phosphor layer 302 may be formed using any of the techniques described above with reference to the formation of first phosphor layer 202 . The second phosphor layer 302 may have a thickness ranging from about 10 μm to about 150 μm.

The second phosphor layer 302 may comprise a wavelength converting material which may be, for example, a conventional phosphor, an organic phosphor, a quantum dot, an organic semiconductor, a Group 3 or 5 semiconductors, group 26 or group 35 semiconductors quantum dots or nanocrystals, dyes, polymers, or other materials that emit luminescence. The second phosphor layer 302 may comprise a transparent material, such as polysilicon, mixed with a wavelength converting material.

The wavelength conversion material can absorb light emitted by LED die 104 and/or first phosphor layer 202 and can emit light at one or more different wavelengths. The unconverted light emitted by the LED die 104 and/or the first phosphor layer 202 may be part of the final spectrum of light extracted from the structure, although it need not be.

The second phosphor layer 302 may include one or more phosphor materials having a peak emission wavelength L _pk 2 between L _pk D and L _pk 1 (ie, L _pk D<L _pk 2<L _pk 1 ). . In an example, the peak emission wavelength L _pk 2 may be approximately 100 nm greater than L _pk D and approximately 100 nm smaller than L _pk 1 (ie, L _pk D+100 nm<L _pk 2<L _pk 1-100 nm). In another example, the peak emission wavelength L _pk 2 may be about 50 nm greater than L _pk D and about 50 nm smaller than L _pk 1 (ie, L _pk D+50 nm<L _pk 2<L _pk 1-50 nm).

1之一質量比之一混合物時，L_pk2之此範圍可係較佳的。 In another example, the peak emission wavelength L _pk 2 may be about 10 nm greater than L _pk D and about 10 nm smaller than L _pk 1 (ie, L _pk D+10 nm<L _pk 2<L _pk 1-10 nm). When the first phosphor layer 202 includes a green emission wavelength conversion material (green) and a red emission wavelength conversion material (red) with green: red

When a mixture of a mass ratio of 1, this range of L _pk 2 can be preferred.

In another example, the peak emission wavelength of the second phosphor layer is about 460 nm. The peak emission wavelength of the second phosphor layer may be approximately 10 nm, 20 nm, 30 nm, or 40 nm greater than _LpkD . The peak emission wavelength of the second phosphor layer may be about 10 nm to 20 nm longer than L _pk D. In another embodiment, L _pk 2 may be about 10 nm to 30 nm longer than L _pk D. In another embodiment, L _pk 2 may be about 20 nm to 40 nm longer than L _pk D. Preferably, L _pk 2 is within 440nm to 490nm, more preferably within 450nm to 470nm and most preferably within 455nm to 465nm.

The second phosphor layer 302 may include Sr ₃ MgSi ₂ O ₈ :Eu powder in polysiloxane. The mass of phosphor of the second phosphor layer 302 may be equal to 1 for the mass of polysiloxane.

Referring now to FIG. 4 , there is shown a cross-sectional view illustrating the optional formation of a lens 402 around the LED device 300 . The lens 402 may be in contact with the substrate 102 and the second phosphor layer 302 . The lens 402 can extend laterally outward beyond the LED device 300 . Lens 402 may comprise a transparent material for improved light extraction from LED device 300 . Lens 402 may be formed using conventional deposition techniques. The lens 402 may include one or more of the following: PMMA, polycarbonate, silicone, HRPC. One or more portions of the lens may be aluminum coated.

Referring now to FIG. 5 , there is illustrated a cross-sectional view of portions of the first phosphor layer 202 and the second phosphor layer 302 optionally removed from the LED device 300 shown in FIG. 3 .

Portions of the first phosphor layer 202 and the second phosphor layer 302 may be removed using a conventional etch or sand etch process. For example, portions of first phosphor layer 202 and second phosphor layer 302 may be removed using reactive ion etching (RIE), plasma etching, or a selective etching process.

The remainder of the first phosphor layer 202 can have sidewalls 504 that are substantially flush with the sidewalls 502 of the LED die 104 . The remainder of the second phosphor layer 302 can have sidewalls 506 that are substantially flush with the sidewalls 502 of the LED die 104 .

Referring now to FIG. 6 , a cross-sectional view of forming a reflective coating 602 on each side of the LED die 104 , the remainder of the first phosphor layer 202 , and the remainder of the second phosphor layer 302 to form an LED device 600 is illustrated.

Reflective coating 602 may be formed using a conventional deposition procedure. In one instance, Reflective coating 602 may be placed on each side of LED die 104 and the remainder of first phosphor layer 202 and second phosphor layer 302 and then processed to adhere to LED die 104 and first phosphor layer 202 and second phosphor layer 302. One flake of the remainder of the two phosphor layers 302 . A combination of vacuum and heat may be used to laminate reflective coating 602 to LED die 104 and the remainder of first phosphor layer 202 and second phosphor layer 302 .

Those skilled in the art will recognize that the reflective coating 602 need not be in the form of a laminated sheet; it may be applied in liquid or paste form via spraying, molding, screen printing, dropping, or the like. For example, using a conventional deposition process, such as CVD, PECVD, ALD, evaporation, sputtering, chemical solution deposition, spin-on deposition, or other similar processes, the first reflective coating 602 .

Reflective coating 602 may include a metal such as Ti, Au, Ag or the like. In one example, reflective coating 602 may include TiO ₂ powder in a polysiloxane matrix.

The reflective coating 602 may have an upper surface that is substantially flush with an upper surface of the remainder of the second phosphor layer 302 .

Referring now to FIG. 7 , there is shown a cross-sectional view illustrating the optional formation of a lens 702 around the LED device 600 . Lens 702 may be in contact with substrate 102 , reflective coating 602 and second phosphor layer 302 . Lens 702 may extend laterally outward beyond LED device 600 . Lens 702 may comprise a transparent material for improved light extraction from LED device 600 . Lens 702 may be formed using conventional deposition techniques. The lens 702 may include one or more of the following: PMMA, polycarbonate, silicone, HRPC. One or more portions of the lens may be aluminum coated.

Referring now to FIG. 8, there is shown a first emission spectrum 802 illustrating a first emission spectrum 802 of an LED die 104 coated with only the first phosphor layer 202 and an LED die coated with both the first phosphor layer 202 and the second phosphor layer 302. 104 is a graph of a second emission spectrum 804 . first emitted light Spectrum 802 and second emission spectrum 804 may exhibit the same LED wavelength and the same color coordinate system.

The first emission spectrum 802 and the second emission spectrum 804 may be normalized to blue LED die 104 emission. As can be seen, both the LED die 104 in combination with the first phosphor layer 202 and the LED die 104 in combination with both the first phosphor layer 202 and the second phosphor layer 302 emit light having a wavelength in the blue (450nm to 490nm) Light with one of the spectral peaks between red light (635nm to 700nm). It should be noted that the first phosphor layer 202 used to generate the first emission spectrum 802 and the first phosphor layer 202 used to generate the second emission spectrum 804 may be composed of the same phosphor material. However, the particular phosphor concentration in each first phosphor layer 202 can be varied to produce the same color point. Furthermore, it should be noted that the application of the second phosphor layer 302 may alter the emission of the first phosphor layer 202 due to the reflection of light that may be absorbed and converted by the first phosphor layer 202 .

The local minimum in the SPD at 470 nm after the blue emission peak of the LED die 104 can be increased with two phosphor layers compared to the case with only the first phosphor layer 202 . This can be seen in Table 1 below.

The CRI(Ra) of the SPD of the LED die 104 with two phosphor layers increases to one CRI(Ra) compared to the color rendering index CRI(Ra) of 91.4 for the LED die 104 with only the first phosphor layer 202 94.2. Local minimum in SPD after blue emission peak for LED die 104 with two phosphor layers compared to 38.2% of LED peak height for LED die 104 with only first phosphor layer 202 Can be increased to 48% of LED peak.

Referring now to FIG. 9 , there is shown a graph illustrating the emission spectra of the second phosphor layer 302 and the LED die 104 . As set forth above, the second phosphor layer 302 may include a peak emission wavelength L pk 2 having a peak emission wavelength between L _pk D of the LED die 104 and L _pk 1 of the first phosphor layer ₂₀₂ (ie, L _pk D< One or more phosphor materials of L _pk 2<L _pk 1). The graph shows an example where _Lpk 2 is about 460nm or _Lpk D+20nm. L _pk 2 may also be approximately L _pk D + 10 nm.

Although features and elements are described above in particular combinations, those skilled in the art will appreciate that each feature or element can be used alone or in any combination with other features and elements. Furthermore, the methods described herein can be implemented in a computer program, software or firmware incorporated into a computer readable medium for execution by a computer or processor. Examples of computer readable media include electronic signals (transmitted over wired or wireless connections) and computer readable storage media. Examples of computer readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a scratchpad, cache memory, semiconductor memory devices, magnetic media such as , internal hard disks and removable disks), magneto-optical media and optical media (such as CD-ROM disks and digital versatile disks (DVD)).

102: Substrate

104: Light-emitting diode grain/light-emitting diode structure

202: first phosphor layer

300: light emitting diode device

302: second phosphor layer

Claims (13)

A light emitting diode (LED) device comprising: an LED die configured to emit blue light having a peak emission wavelength; a first phosphor layer disposed on the LED die on-die and configured to emit green, yellow and red light by excitation of the blue light emitted from the LED die; and a second phosphor layer disposed on the first phosphor layer Opposite the LED die and including a Sr ₃ MgSi ₂ O ₈ :Eu phosphor, the second phosphor layer is configured to emit more light than that of the LED die excited by the blue light emitted from the LED die. Light having a peak emission wavelength approximately 10 to 50 nanometers longer, the Sr ₃ MgSi ₂ O ₈ :Eu phosphor configured to increase in Spectral power distribution (SPD) of the LED device at a local minimum at about 470 nm, the Sr ₃ MgSi ₂ O ₈ :Eu phosphor configured to produce an LED device with and without the second phosphor layer substantially the same x color coordinate of the spectral emission of the LED device. The LED device of claim 1, wherein the peak emission wavelength of the second phosphor layer is about 10 nanometers longer than the peak emission wavelength of the LED die. The LED device of claim 1, wherein the peak emission wavelength of the second phosphor layer is about 10 nm to 20 nm shorter than the peak emission wavelength of the first phosphor layer. As the LED device of claim 1, it further comprises: A lens surrounds the LED die, the first phosphor layer and the second phosphor layer. The LED device according to claim 1, wherein the first phosphor layer comprises Y ₃ (Al, Ga) ₅ O ₁₂ , Lu ₃ (Al, Ga) ₅ O ₁₂ , SCASN and CASN in polysiloxane. The LED device of claim 5, wherein the mass ratio of SCASN to CASN is about 20:80. The LED device of claim 5, wherein the ratio of Lu ₃ (Al,Ga) ₅ O ₁₂ to SCASN and CASN is about 8.47. The LED device of claim 1, further comprising: a reflective coating formed on each side of the LED die, each side of the first phosphor layer, and each side of the second phosphor layer. The LED device according to claim 8, wherein the reflective coating comprises TiO ₂ in polysiloxane. The LED device of claim 1, wherein the peak emission wavelength of the LED die is about 440 nm. The LED device of claim 1, wherein the peak emission wavelength of the second phosphor layer is about 20 nm to 40 nm longer than the peak emission wavelength of the LED die. The LED device according to claim 5, wherein the ratio of Y ₃ (Al,Ga) ₅ O ₁₂ and Lu ₃ (Al,Ga) ₅ O ₁₂ to SCASN and CASN is greater than 5 and less than 10. The LED device of claim 1, wherein the peak emission wavelength of the second phosphor layer is about 460 nm.

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