TW202021156A - 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 conversion LED with high color quality

This application is related to LEDs, and more specifically 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. The cold light material usually contains a mixed powder of one of the inorganic materials. For the high color quality defined by the Lighting Commission (CIE) as the 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. If the light emitted from the LED is used in combination with a camera system (for example, as a flashlight), it may be particularly important to avoid sharp peeping and minimum values in SPD.

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 each side of the LED die. The second surface may be opposite to the first surface. A second phosphor layer may be formed on the first phosphor layer. The phosphor layer may have a second peak located one emission wavelength of the LED die (L _pk D) between a peak wavelength (L _pk 1) one of the first emission peak emission wavelength of the phosphor layer (L _pk 2) .

A light emitting diode (LED) device may 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 may be formed on the first phosphor layer. The phosphor layer may have a second peak located one emission wavelength of the LED die (L _pk D) between a peak wavelength (L _pk 1) one of the first emission peak emission wavelength of the phosphor layer (L _pk 2) . 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.

Cross-reference of related applications

This application claims the priority rights of European Patent Application No. 18201516.4 filed on October 19, 2018 and US Patent Application No. 16/119,688 filed on August 31, 2018. Among these patent applications The full text of each is incorporated by reference.

Examples of different light emitting diode ("LED") implementations will be explained more fully below with reference to the accompanying drawings. These examples are not mutually exclusive, and features found in one example can be combined with features found in one or more other examples to achieve additional implementations. Therefore, 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. Similar numbers throughout the text refer to similar components.

It should 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, without departing from the scope of the present invention, a first element can be referred to as a second element, and similarly, a second element can be referred to as a first element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

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

Relative terms (such as "in"... "below" or "in"..."above", or "upper" or "lower", or "horizontal" or "vertical" can be used in this article to illustrate The illustrated relationship between one element, layer or region and another element, layer or region. It should be understood that in addition to the orientations depicted in the various figures, these terms are also intended to cover different orientations of the device.

As explained above, in order to define high color quality as the color rendering index (CRI) by the Lighting Commission (CIE), 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, it may be necessary to apply different phosphor materials in order to emit light at different wavelengths. Emissions from the phosphor emitting at a shorter wavelength can be absorbed by the phosphor emitting at a longer wavelength. This phosphor-phosphor interaction can reduce efficiency due to photon loss in the conversion process. Due to the redirection of the emitted light back to one or more LED dies, the phosphor-phosphor interaction can also increase the absorption loss in an LED package that includes the one or more LED dies.

In some applications, it may be desirable to reduce the local minimum of the blue emission peak of the LED close to the LED. The emission peak of a phosphor assembly may have to be close to the emission peak 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 and therefore lose its energy (another method uses energy as heat to lose). When the emitted photon has less energy than the absorbed photon, this energy difference is Stokes shifted. Stokes fluorescence emits a longer wavelength photon (lower frequency or energy) from a molecule that has absorbed a photon of 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 Stokes shift, a large amount of phosphor material may be required. It may be necessary to minimize the reabsorption of the emitted light by other phosphors.

The following description includes systems, methods, and devices for using multiple phosphor layers formed on an LED to reduce the 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 having an emission peak between an emission peak of a first phosphor layer and an emission peak of 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 104 is shown. A first surface of the LED die 104 may be located on the substrate 102, and a second surface of the LED die 104 may be located opposite to 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. FIG. 1 shows an illustrative example of one type of LED die 104 that can be used and is not intended to limit the following description. The LED die 104 may be one of the group III nitride LEDs known in the art. Generally, Group III nitride LEDs are manufactured by the following operations: by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques in a sapphire, silicon carbide, group III nitride or One stack of other semiconductor layers suitable for epitaxial growth of different compositions and dopant concentrations on the substrate. The stack typically includes one or more n-type layers formed above the substrate doped with (for example) silicon, and an active region (eg, a pn diode) formed over the n-type layer(s). ) One or more of the light-emitting layers, and one or more p-type layers formed above 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, the LED die 104 may emit blue light or UV light. However, in addition to LEDs, materials such as laser diodes and other material systems (such as other Group III-V materials, Group III phosphides, Group III arsenides, Group II-VI materials, ZnO, or Si-based materials) can also be used Semiconductor light-emitting devices, such as fabricated semiconductor light-emitting devices.

The device of FIG. 1 can be formed by growing a type III-nitride semiconductor structure on a substrate 102, as is known in the art. The substrate 102 may be sapphire or any suitable substrate such as, for example, SiC, Si, GaN, or a composite substrate. The surface of one of the substrates 102 on which the group III nitride semiconductor structure of the type described above is grown can be patterned, roughened, or textured before growth, which can improve light extraction from the device. The surface of the substrate 102 opposite to the growth surface (ie, the surface through which most light passes through in a flip-chip configuration) can be patterned, roughened, or textured before or after growth. This can be improved from Light extraction from the device.

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 the n-type region may include multiple layers of different compositions and dopant concentrations. The n-type region 16 may include a preliminary layer (such as a buffer layer or a nucleation layer) and/or a layer designed to facilitate removal of the growth substrate, which may be n-type or unintentionally doped and targeted to make the light emitting region highly efficient N-type or even p-type device layers designed for the specific optical, material or electrical properties desired to emit light. A light emitting or active region 18 grows above the n-type region 16. Examples of suitable light emitting regions 18 include a single thick or thin light emitting layer, or a multiple quantum well light emitting region including multiple thin or thick light emitting layers separated by a barrier layer. Then, a p-type region 20 can be grown above the light-emitting region. Like the n-type region, the p-type region may include multiple layers of different compositions, thicknesses, and dopant concentrations, the multiple layers 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 a plurality of conductive layers, such as a reflective metal and a protective metal that can prevent or reduce electromigration of the reflective metal. The reflective metal is usually silver, but any suitable material or materials can be used. A part of the p-contact 21, the p-type region 20 and the active region 18 can be removed to expose a part of the n-type region 16 where an n-contact 22 is formed. The n-contact 22 and the p-contact 21 can be electrically isolated from each other by a gap 25, which can be filled with a dielectric such as a silicon oxide or any other suitable material. Multiple n-contact vias can 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 the p-contact 21 can be redistributed to form a bonding pad with a dielectric/metal stack, as is known in the art.

To form an electrical connection to the LED die 104, one or more interconnects 26 and 28 may be formed on the n-contact 22 and p-contact 21 or electrically connected to the n-contact 22 and p-contact 21. The interconnect 26 may be electrically connected to the n-contact 22. The interconnect 28 may be electrically connected to the p-contact 21. The interconnects 26 and 28 can be electrically isolated from the n-contact 22 and p-contact 21 and are electrically isolated from each other by the 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 structures 104. The substrate 102 may be thinned or completely removed. Patterning, texturing, or roughening can expose the surface of the substrate 102 by thinning to improve light extraction.

Referring now to FIG. 2, a cross-sectional view illustrating the formation of a first phosphor layer 202 on the LED die 104 is shown. The first phosphor layer 202 may 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 process. In one example, the first phosphor layer 202 may be a sheet placed on top of the LED die 104 and then processed to conform to the shape of the LED die 104. A combination of vacuum and heat may be used to laminate the first phosphor layer 202 to the LED die 104.

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

The first phosphor layer 202 may include a wavelength conversion material, which may be, for example, a conventional phosphor, an organic phosphor, a quantum dot, an organic semiconductor, a group two or three or five group semiconductor, a group two or six group or Group III-V semiconductor quantum dots or nanocrystals, dyes, polymers or other materials that emit cold light. The first phosphor layer 202 may include a transparent material mixed with a wavelength conversion material, such as polysilicon.

The wavelength conversion material can absorb the light emitted by the LED die 104 and can emit light of 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 with a peak emission wavelength L _pk D.

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

The first phosphor layer 202 may include one or more phosphor powders in polysilicon. For example, the first phosphor layer 202 may include GaLuAG, SCASN, and CASN. The mass ratio of the material in the first phosphor layer 202 may be approximately 20% SCASN: 80% CASN. In the first phosphor layer 202, the ratio of GaLuAG to the total red mass may be approximately 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 emission wavelength conversion material may include garnet activated with cerium, which has one of the chemical compositions of (Y, Gd, Lu) ₃ (Al, Ga) ₅ O ₁₂ :Ce. The green emission wavelength conversion material may include silicate and nitrogen oxide activated with europium, such as SiAlON. The red emission wavelength conversion material 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 emission wavelength material and a red emission wavelength conversion material. The green emission wavelength conversion material may include GaLuAG and GaYAG. The red emission wavelength conversion material may include SCASN and CASN, where the mass ratio of SCASN to CASN is approximately 20:80. The ratio of the total mass of the green emission wavelength conversion material to the total mass of the red emission wavelength conversion material is approximately 8.47, and may range from 5 to 10.

Referring now to FIG. 3, 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 is shown. The second phosphor layer 302 may be applied to the top and sides of the first phosphor layer 202. The second phosphor layer 302 may be formed using any of the techniques described above with reference to the formation of the 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 include a wavelength conversion material, which may be, for example, conventional phosphors, organic phosphors, quantum dots, organic semiconductors, Group II or III-V semiconductors, II-VI or Group III-V semiconductor quantum dots or nanocrystals, dyes, polymers, or other materials that emit cold light. The second phosphor layer 302 may include a transparent material mixed with a wavelength conversion material, such as polysilicon.

The wavelength conversion material can absorb the light emitted by the LED die 104 and/or the first phosphor layer 202, and can emit light of 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 (ie, L _pk D<L _pk 2<L _pk 1) between L _pk D and L _pk 1 . In one example, the peak emission wavelength L _pk 2 may be larger than L _pk D by about 100 nm and smaller than L _pk 1 by about 100 nm (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 larger than L _pk D by about 50 nm and smaller than L _pk 1 by about 50 nm (ie, L _pk D + 50 nm<L _pk 2<L _pk 1-50 nm ).

In another example, the peak emission wavelength L _pk 2 may be larger than L _pk D by about 10 nm and smaller than L _pk 1 by about 10 nm (ie, L _pk D + 10 nm<L _pk 2<L _pk 1-10 nm ). When the first phosphor layer 202 includes a mixture of a green emission wavelength conversion material (green) and a red emission wavelength conversion material (red) having a green: red ≥ 1 mass ratio, this range of L _pk 2 may be preferred of.

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

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

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

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

A conventional etching or sanding process may be used to remove portions of the first phosphor layer 202 and the second phosphor layer 302. For example, reactive ion etching (RIE), plasma etching, or a selective etching process may be used to remove portions of the first phosphor layer 202 and the second phosphor layer 302.

The remaining portion of the first phosphor layer 202 may have a sidewall 504 that is substantially flush with the sidewall 502 of the LED die 104. The remaining portion of the second phosphor layer 302 may have a sidewall 506 that is substantially flush with the sidewall 502 of the LED die 104.

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

The reflective coating 602 can be formed using a conventional deposition process. In one example, the reflective coating 602 may be placed on each side of the LED die 104 and the remaining portions of the first phosphor layer 202 and the second phosphor layer 302 and then processed to adhere to the LED die 104 and the first A thin slice of the remaining portions of the phosphor layer 202 and the second phosphor layer 302. A combination of vacuum and heat may be used to laminate the reflective coating 602 to the LED die 104 and the remaining portions of the first phosphor layer 202 and the 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 can be applied in liquid or paste form by spraying, molding, screen printing, drip coating, and the like. For example, using a conventional deposition process, such as CVD, PECVD, ALD, evaporation, sputtering, chemical solution deposition, spin coating deposition, or other similar processes, the first can be formed on the substrate 102 adjacent to the LED die 104 Reflective coating 602.

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

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

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

Referring now to FIG. 8, there is shown a diagram illustrating a first emission spectrum 802 of only one of the LED dies 104 coated with the first phosphor layer 202 and LED dies coated with both the first phosphor layer 202 and the second phosphor layer 302 104 is a chart of a second emission spectrum 804. The first emission spectrum 802 and the second emission spectrum 804 may show 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, the LED die 104 combined with the first phosphor layer 202 and the LED die 104 combined with both the first phosphor layer 202 and the second phosphor layer 302 both emit light with a blue light (450 nm to 490 nm) and one of the spectral peaks between red light (635 nm and 700 nm). 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 specific phosphor concentration in each first phosphor layer 202 can be varied to produce the same color point. In addition, it should be noted that the application of the second phosphor layer 302 may change the emission of the first phosphor layer 202 due to the reflection of light that can be absorbed and converted by the first phosphor layer 202.

表1：發射特性Compared to the case with only the first phosphor layer 202, the local minimum in the SPD at 470 nm after the blue emission peak of the LED die 104 with two phosphor layers can be increased. This can be seen in Table 1 below.

Table 1: Emission characteristics

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

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

Although the features and elements are described above in specific combinations, those skilled in the art will understand that each feature or element can be used alone or in any combination with other features and elements. In addition, the methods described herein may 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 register, cache memory, semiconductor memory devices, magnetic media (such as , Internal hard drives and removable disks), magneto-optical media and optical media (such as CD-ROM disks and digital versatile disks (DVD)).

16:n type area 18: luminous or active area/p-type area 20: p-type area 21: p contact 22:n contact 24: Dielectric layer 25: clearance 26: Interconnect 27: clearance 28: Interconnect 102: substrate 104: Light emitting diode grain/light emitting diode structure 202: first phosphor layer 300: LED device 302: second phosphor layer 402: lens 502: sidewall 504: sidewall 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 explanation given by way of example in conjunction with the accompanying drawings, in which similar element symbols in each figure indicate similar elements, and in which:

1 is a cross-sectional view illustrating an LED die on a substrate;

2 is a cross-sectional view illustrating the formation of a first phosphor layer on the LED;

3 is a cross-sectional view illustrating the formation of a second phosphor layer on the first phosphor layer to form an LED device;

4 is a diagram illustrating a cross-sectional view of a lens formed around the LED device according to circumstances;

5 is a cross-sectional view illustrating a portion where the first phosphor layer and the second phosphor layer are removed from the LED device according to circumstances;

6 is a cross-sectional view illustrating forming a reflective coating on each side of the LED die, the remaining portion of the first phosphor layer, and the remaining portion of the second phosphor layer to form an LED device;

7 is a cross-sectional view illustrating the formation of a lens around the LED device as appropriate;

8 is a graph illustrating an emission spectrum comparing an LED die coated with only the first phosphor layer and 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 the LED die.

102: substrate

104: Light emitting diode grain/light emitting diode structure

202: first phosphor layer

300: LED device

302: second phosphor layer

Claims (20)

A light emitting diode (LED) device, including: An LED die configured to emit blue light or UV light having a peak emission wavelength; A first phosphor layer, which is disposed on the LED die and configured to emit green light, yellow light, and red light; and A second phosphor layer is disposed on the first phosphor layer and is configured to emit light having a peak emission wavelength that is approximately 10 nm to 50 nm different from the peak emission wavelength of the LED die. 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 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 is approximately 10 nm to 20 nm 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 is approximately 20 nm to 40 nm 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 460 nm. The LED device of claim 1 further includes: A lens surrounds the LED die, the first phosphor layer and the second phosphor layer. The LED device of claim 1, wherein the first phosphor layer is composed of GaLuAG, GaYAG, SCASN, and CASN in polysilicon. As in the LED device of claim 8, wherein the mass ratio of SCASN to CASN is approximately 20:80. The LED device of claim 8, wherein one ratio of total green quality to total red quality is approximately 8.47. The LED device of claim 8, wherein a ratio of total green quality to total red quality is greater than 5 and less than 10. The LED device of claim 1, wherein the second phosphor layer is composed of Sr ₃ MgSi ₂ O ₈ :Eu in polysilicon. The LED device of claim 1 further includes: The LED die has a first surface in contact with the first phosphor layer; The first phosphor layer has a second surface in contact with the second phosphor layer, the second surface being opposite to the first surface; and A reflective coating is 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 of claim 13, wherein the reflective coating includes TiO _{2 in} polysilicon. The LED device of claim 1, wherein the spectral power distribution (SPD) of the LED device contains a local minimum at about 470 nm. The LED device of claim 15, wherein at about 470 nanometers, the SPD emission of the LED device is increased compared to the SPD emission of the LED device without the second phosphor layer. A light emitting diode (LED) device, including: An LED die configured to emit blue light or UV light; A first phosphor layer, which is disposed on the LED die and configured to emit green light, yellow light, and red light; and A second phosphor layer disposed on the first phosphor layer and configured to emit light having a peak emission wavelength greater than 440 nanometers and less than 490 nanometers. The LED device of claim 17, wherein the peak emission wavelength of the second phosphor layer is greater than 450 nanometers and less than 470 nanometers. The LED device of claim 17, wherein the peak emission wavelength of the second phosphor layer is greater than 455 nm and less than 465 nm. The LED device of claim 17, wherein the peak emission wavelength of the second phosphor layer is about 460 nm.

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