KR100668794B1 - Hypersensitive EuIII Red Complexes for Light Emitting Diode - Google Patents

Abstract

Eu (III) complexes of formula (1) are β-diketone-based 4,4,4-trifluoro-1-phenyl-1,3-butanedione (tfpb) or 4,4,4-trifluoro-1- (2-naphthyl)- Ternary complex consisting of 1,3-butanedione (tfnb) and triphenylphosphine oxide (tppo). The Eu (III) complex not only has strong energy transfer from the ligand to Eu (III) at 350-440 nm UV region, but also strong excitation at 460-470 nm region corresponding to ⁷ F ₀ → ⁵ D ₂ electron transfer. Metastasis occurs, causing supersensitive red fluorescence. Therefore, it is excited by a light source generated from a blue or ultraviolet light emitting diode and is suitable for a red light emitting diode having excellent luminous luminance.

<Formula 1>

M [Eu (β-diketonato) ₄ (tppo)]

Where M = Na ⁺ , Cs ⁺ or K ⁺ .

Light emitting diode, Eu (III) complex red phosphor, β-diketone, triphenylphosphine oxide.

Description

Hypersensitive Eu (III) Red Complexes for Light Emitting Diode}

1 is a TGA / DT spectrum of a Cs [Eu (tfpb) ₄ (tppo)] complex according to the present invention.

2 is a TGA / DT spectrum of a Cs [Eu (tfnb) ₄ (tppo)] complex according to the present invention.

3 is an IR spectrum of Cs [Eu (tfpb) ₄ (tppo)] according to the present invention.

4 is an IR spectrum of Cs [Eu (tfnb) ₄ (tppo)] according to the present invention.

FIG. 5 shows the luminescence spectrum (λ _exc = 466.5 nm) of Cs [Eu (tfpb) ₄ (tppo)] in powder form.

FIG. 6 is an excited spectrum (λ _ems = 618 nm) of Cs [Eu (tfpb) ₄ (tppo)] in powder form.

FIG. 7 is an excited spectrum of crystalline Cs [Eu (tfpb) ₄ (tppo)] (λ _ems = 618 nm).

8 shows luminescence spectra of Cs [Eu (tfnb) ₄ (tppo)] (λ _exc = 466.5 nm).

9 is an excited spectrum (λ _ems = 613 nm) of Cs [Eu (tfnb) ₄ (tppo)].

10 is a time resolved spectrum of Cs [Eu (tfnb) ₄ (tppo)] (λ _exc = 337 nm).

11 is a light emission spectrum of a red light emitting diode using the red phosphor according to the present invention.

The present invention relates to a red phosphor for a light emitting diode and a manufacturing method thereof, and more particularly, to a red phosphor suitable for a red light emitting diode which is excited by a light source generated from a blue or ultraviolet light emitting diode and has excellent luminous luminance. It is about.

Light Emitting Diodes (LEDs) are futuristic color display devices, and are known as the research fields of recent interest due to their application to flat panel displays as well as various instrument panels and TVs. have. When the electroluminescence is applied to a light emitting material that emits light, electrons injected from the cathode and holes formed in the anode combine in the light emitting layer to form a so-called "single excition", which is a ground state. When transitioned, it is a phenomenon that emits various light. This is a semiconductor device having high luminous efficiency, low power consumption and good thermal stability as compared to the conventional light emitter, which has long life and good responsiveness.

Currently the most common LED is GaN, which emits blue light. However, in the case of the conventional Eu (III) phosphor, high luminance red luminescence cannot be induced from Eu (III) by ⁷ F ₀ → ⁵ D ₂ electron transition which absorbs GaN blue light. Therefore, up to now, no Eu (III) complex phosphor which emits luminescence by GaN has been developed.

The present invention provides a high-luminance red phosphor of Eu (III) that can be excited by blue light or ultraviolet light of GaN by selecting and synthesizing a ligand system that causes excess sensitivity.

In general, the Eu (III) phosphor emits light in the 580-720 nm region as an electron transition occurs from the emission energy level ⁵ D ₀ to ⁷ F _J (J = 0-4) in the ground state. In particular, the ⁵ D ₀ → ⁷ F ₂ emission transition at 610-630 nm is characterized by an excess sensitivity in which the luminescence intensity is greatly influenced by the coordination environment of Eu (III). However, the absorption cross section of Eu (III) ions is so small that it does not absorb light in the ultraviolet-visible region. Of the absorption transitions of Eu (III) ions, the ⁷ F ₀ → ⁵ L ₆ transition in the 390-400 nm region shows the largest transition probability, but the oscillator intensity is very small, only 10 ^-6 , and the 460-470 nm region. The oscillator strength of the transition ⁷ F ₀ → ⁵ D ₂ is about 10 ^-8 , which is almost negligible. Therefore, in order to make up for this drawback, a ligand having a high absorbance is used to induce red light emission of Eu (III) ions through an energy transfer mechanism or a charge transfer mechanism from the ligand to Eu (III) ions. For energy transfer mechanisms, ligands with π-conjugation bonds are used, which act as antennas by having strong absorption in the UV region. Representative ligands include diphenyltone ligands substituted with phenyl groups, naphthyl groups, phenanthroline or terpyridine ligands, or mixed ligands thereof. However, since the absorption region of the ligands acting as these antennas is the UV region, the excitation of visible light cannot induce strong luminescence from Eu (III).

The present invention is characterized by the red phosphor represented by the following formula (1).

<Formula 1>

M _a [Eu (β-diketonato) _b (tppo) _c ]

Where M = Na ⁺ , Cs ⁺ or K ⁺

b = a + 3 and 2b + c = 9 (where 3 ≤ b ≤ 4)

 β-diketone is 4,4,4-trifluoro-1-phenyl-1,3-butanedione (tfpb) or 4,4,4-trifluoro-1- (2-naphthyl) -1,3-butanedione (tfnb) Is preferred.

Eu (III) complexes form the most stable complex when the coordination number is 9. Here, β-diketone has a monovalent charge and acts as a bidentate ligand, and tppo is neutral and acts as a monodentate ligand. Therefore, the condition for the total number of charges to be 0 is b = a + 3, and the condition for achieving stable coordination of the Eu (III) complex is 2b + c = 9.

In the above formula, M is preferably an alkali metal such as Na, Cs or K.

The red phosphor of the invention 460 of GaN - ⁷ F ₀ → of the Eu (III), which absorbs light at 470 nm when D region ⁵ of the _second electron transfer, and satisfy the selectivity of ΔJ = ± 2 in the second sensitization transition. Therefore, it can be used for red light emitting diodes using GaN LEDs. In addition, it can be used in the manufacture of a white light emitting diode because it can be excited with a known green phosphor by blue light or with a known green and blue phosphor by ultraviolet light to emit white.

Hereinafter, the present invention will be described in more detail with reference to the following examples and drawings, but the present invention is not limited thereto.

Example 1 Cs [Eu (tfpb) According to the Present Invention ₄ (tppo)] Preparation of Phosphor

1 mmol (0.352 g) of high purity Eu ₂ O _{3 is} dissolved in 1 mL of water, and dissolved in a small amount of hydrochloric acid. To this was added water to make a 2 mL aqueous solution of Eu (III). Dissolve 4 mmol (0.865 g) of ligand 4,4,4-trifluoro-1-phenyl-1,3-butanedione (tfpb) and 1 mmol (0.278 g) of triphenylphosphine oxide (tppo) in 20 mL methanol. To this was added dropwise the aqueous solution of Eu (III) prepared above. The pH of this mixed solution is adjusted to 6.5-7.5 using CsOH solution dissolved in methanol. The precipitate is filtered off. The filtered precipitate is washed several times with water and dried in an electric oven.

The molecular formula of the complex thus synthesized was confirmed by elemental analysis that Cs [Eu (tfpb) ₄ (tppo)]. Theoretical and experimental values for the mass% of representative elements are as follows.

Theory; Eu 11.7%, C 53.8%, H 3.4%, P 2.4%.

Experimental value; Eu 11.1%, C 55.3%, H 3.0%, P 3.5%.

In the synthesized Cs [Eu (tfpb) ₄ (tppo)] phosphor, tfpb acts as a coordination ligand and tppo acts as a coordination ligand, so Eu (III) ions satisfy the most stable 9 coordination number.

Example 2: Na [Eu (tfpb) according to the invention ₃ (tppo) ₃ ] Preparation of Phosphor

As in Example 1, 1 mmol (0.352 g) of high purity Eu ₂ O ₃ was added to 1 mL of water, dissolved with hydrochloric acid, and then water was added to form a 2 mL solution of Eu (III). Dissolve 3 mmol (0.649 g) of ligand tfpb (0.834 g) in 20 mL methanol. To this was added dropwise aqueous solution of Eu (III). The pH of this mixed solution is adjusted to 6.5-7.5 using aqueous NaOH solution. The filtered precipitate is washed several times with water and dried in an electric oven.

The molecular formula of the complex thus synthesized was confirmed by elemental analysis that Na [Eu (tfpb) ₃ (tppo) ₃ ]. Theoretical and experimental values for the mass% of representative elements are as follows.

Theoretical values: Eu 9.3%, C 61.7%, H 4.1%, P 5.7%.

Experimental Value: Eu 10.0%, C 59.5%, H 3.1%, P 5.0%.

In the synthesized Na [Eu (tfpb) ₃ (tppo) ₃ ] phosphor, tfpb acts as a coordination ligand and tppo acts as a coordination ligand so that Eu (III) ions satisfy the most stable 9 coordination number.

Example 3: Cs [Eu (tfnb) according to the present invention ₄ (tppo)] Preparation of Phosphor

Make 2 mL of 1 mmol Eu (III) aqueous solution as in Example 1. Dissolve 4 mmol (1.065 g) of 4,4,4-trifluoro-1- (2-naphthyl) -1,3-butanedione (tfnb) and 1 mmol (0.278 g) of tppo in 20 mL methanol. In the same manner as in Example 1, Cs [Eu (tfnb) ₄ (tppo)] Phosphor was synthesized and the molecular formula of the complex was confirmed by elemental analysis. Theoretical and experimental values for the mass% of representative elements are as follows.

Theoretical values: Eu 10.2%, C 59.5%, H 3.4%, P 2.1%.

Experimental Value: Eu 10.2%, C 57.7%, H 3.2%, P 2.2%.

In the phosphor, tfnb acts as a coordination ligand, tppo acts as a coordination ligand, and Eu (III) ions satisfy the most stable ninth coordination number.

Example 4 M _a Eu (β-diketonato) _b (tppo) _c TGA / DT Spectrum of Complex

In order to investigate the thermal stability and the coordination of solvent molecules in the dry powder form of Cs [Eu (tfpb) ₄ (tppo)] phosphor prepared in Example 1 by measuring the weight change (TGA / DT) with temperature Shown in According to FIG. 1, mass reduction of the phosphor did not occur until 250 ° C. FIG. This shows that no water molecules or methanol molecules used as the solvent were included in the prepared Eu (III) complex, and the complex was thermally stable up to 250 ° C. Most of the mass loss occurred sharply in the temperature range of 275-325 ° C, with a final mass loss of about 50%. This mass loss is due to the dissociation of C and H atoms by pyrolysis of the Cs [Eu (tfpb) ₄ (tppo)] molecule. The molecular weight of Cs [Eu (tfpb) ₄ (tppo)] is 1427.81, and 58 moles of C and 43 moles of H atoms are contained in 1 mole of molecules. The mass fraction of these C and H elements in the Cs [Eu (tfpb) ₄ (tppo)] molecule is 52%. It can be seen that this value exactly matches the mass loss.

In the same manner, the TGA / DT of Cs [Eu (tfnb) ₄ (tppo)] in dry powder form prepared in Example 3 was also measured and shown in FIG. 2. As shown in Figure 2, the mass loss did not occur to 250 ℃ as in the case of Cs [Eu (tfpb) ₄ (tppo)]. This shows that no water or methanol molecules used as the solvent are included in the complex, and the synthesized complex is thermally stable up to 250 ° C. Most of the mass loss occurred sharply in the temperature range of 275-325 ° C, with a final mass loss of about 35%. This mass loss is less than that of Cs [Eu (tfpb) ₄ (tppo)]. The molecular weight of Cs [Eu (tfnb) ₄ (tppo)] is 1628.06 and a mass loss of 35% corresponds to about 570 g. This corresponds to the mass of carbon and hydrogen contained in 2 moles of tfnp and tppo of the 4-mole bond tfnp. Therefore, it can be seen from this result that Cs [Eu (tfnb) ₄ (tppo)] is more thermally stable than Cs [Eu (tfpb) ₄ (tppo)].

Since Na, K or Cs ions are present in the crystal space only to balance charges, the thermal stability and spectroscopic properties are almost similar even if Na or K is used in place of Cs in the Eu (III) complex.

Example 5 M _a Eu (β-diketonato) _b (tppo) _c IR spectrum of the complex

A small amount of the Cs [Eu (tfpb) ₄ (tppo)] phosphor prepared in Example 1 was mixed with KBr powder to make pellets. The IR spectrum of this pellet is shown in FIG. No band was measured at a frequency above 2000 cm ⁻¹ . Absorption bands of OH groups of water and methanol molecules, which are solvents, are usually very strong at 3000 cm ⁻¹ , whereas only absorption traces of the absorption bands of OH groups are shown in FIG. 3. This is considered to be due to the water adsorbed on KBr. The main peaks can be assigned as follows.

Wavenumber (cm ⁻¹ ): 1626 (C═O); 1580, 1535, 1489 (aromatic); 1438 (CH ₂ ); 1288 (CC (= 0) -C); 1173, 1122 (Ar ₃ P═O); 724, 693 (CF ₃ )

From the above results, it can be seen that Eu ions form coordination bonds with ligands tfpb and tppo.

A small amount of Cs [Eu (tfnb) ₄ (tppo)] phosphor prepared in Example 3 was mixed with KBr powder and pellets were prepared. 4 shows the IR spectrum of this pellet. Since no band was measured at a wavenumber of 2000 cm ⁻¹ or more, it can be seen that the water and methanol molecules used as solvents were not included in the complex. The main peaks can be assigned as follows.

Wavenumber (cm ^-1 ): 1612 (C = O); 1532 (aromatic); 1296 (CC (= 0) -C); 1202, 1135 (Ar ₃ P═O); 792 (CF ₃ )

From the above results, it can be seen that Eu ions form coordination bonds with ligands tfnb and tppo.

Example 6 M _a Eu (β-diketonato) _b (tppo) _c Luminescence and excitation spectra of complexes

The luminescence and excitation spectra of the Cs [Eu (tfpb) ₄ (tppo)] complexes in powder form prepared in Example 1 were measured. FIG. 5 is a luminescence spectrum of Cs [Eu (tfpb) ₄ (tppo)] emitted by 466.5 nm excitation light corresponding to ⁷ F ₀ → ⁵ D ₂ excitation transition. FIG. The measured spectra can be classified into four emission transitions as summarized in Table 1.

Table 1. Properties of Cs [Eu (tfpb) ₄ (tppo)] luminescence

No. Peak position (nm) Assignment Century relative ratio 1 2 3 4     590, 595.5 618 654 694.5, 703.8 ⁵ D ₀ → ⁷ F ₁ ⁵ D ₀ → ⁷ F ₂ ⁵ D ₀ → ⁷ F ₃ ⁵ D ₀ → ⁷ F ₄     0.05, 0.06 1 0.03 0.03, 0.03

In general, the ⁵ D ₀ → ⁷ F ₁ transition is not affected by the ligand coordination environment because it is an emission transition that is allowed by the magnetic moment. On the other hand, the ⁵ D ₀ → ⁷ F ₂ transition depends on the excess sensitive selectivity of ΔJ = ± 2, so the intensity of this transition is strongly influenced by the coordination environment. For EuCl ₃ , only ⁵ D ₀ → ⁷ F ₁ emission transitions are observed. In the case of _{Cs [Eu (tfpb) 4 (} tppo)], 5 D 0 → ⁷ F ₂ transition intensity of the ⁵ D ₀ → ⁷ F ₁ transition was greater by 20 times as much as the intensity.

FIG. 6 is an excited spectrum of the 618 nm emission band of Cs [Eu (tfpb) ₄ (tppo)] in powder form. The strong broad band in the 250-450 nm region corresponds to the band of energy transfer from the ligand to Eu (III) ions. In particular, in the 350-440 nm range, the intensity is large and it can be seen that it is excited in the ultraviolet range of this range. And the excitation band shown at 460-470 nm corresponds to the ⁷ F ₀ → ⁵ D ₂ excitation transition of Eu (III) ion. In general, for most Eu (III) phosphors, the intensity of this excitation band is negligibly small. However, as shown in Figure 6, the excitation intensity of the Cs [Eu (tfpb) ₄ (tppo)] phosphor according to the present invention is about 0.6 times the energy transfer band. This is because the coordination environment of tfpb and tppo mixed ligands on Eu (III) ions causes an oversensitive excitation transfer that is not seen in other phosphors. Therefore, the Cs [Eu (tfpb) ₄ (tppo)] complex can induce strong red luminescence by the GaN diode of blue light as well as ultraviolet light due to this supersensitive ⁷ F ₀ → ⁵ D ₂ excitation transition. In addition, the 537 nm excitation band corresponds to the transition from ⁷ F _{1 to} ⁵ D ₁ .

7 is an excited spectrum of the crystalline Cs [Eu (tfpb) ₄ (tppo)] complex grown in acetone solution. Compared to the powder form, the intensity of the oversensitive ⁷ F ₀ → ⁵ D ₂ excitation transition was increased more than the powder for the crystalline complex. Compared to energy transfer, the relative strength of this transition is 0.86. In addition, it can be seen that the intensity of the excitation band in the 350-440 nm range is large and is excited in the ultraviolet range of this range.

The luminescence spectrum and the excitation spectrum of the Cs [Eu (tfnb) ₄ (tppo)] complex in powder form prepared in Example 3 were measured. 8 is a luminescence spectrum of Cs [Eu (tfnb) ₄ (tppo)] emitted by 466.5 nm excitation light corresponding to ⁷ F ₀ → ⁵ D ₂ excitation transition. The measured spectra can be classified into five emission transitions as summarized in Table 2.

Table 2. Properties of Cs [Eu (tfnb) ₄ (tppo)] luminescence

No. Peak position (nm) Assignment Century relative ratio 1 2 3 4 5 580 585-600 605-635 645-660 690-715 ⁵ D ₀ → ⁷ F ₀ ⁵ D ₀ → ⁷ F ₁ ⁵ D ₀ → ⁷ F ₂ ⁵ D ₀ → ⁷ F ₃ ⁵ D ₀ → ⁷ F ₄      0.06 0.08 1 0.05 0.07

The ⁵ D ₀ → ⁷ F ₀ transition, which was not seen for Cs [Eu (tf p b) ₄ (tppo)], was measured very weak at 580 nm for Cs [Eu (tfnb) ₄ (tppo)]. The emission intensity of the ⁵ D ₀ → ⁷ F ₂ transition was about 12 times stronger than that of the ⁵ D ₀ → ⁷ F ₁ release transition, which was not significantly affected by the ligand.

Figure 9 is an excitation spectrum for the 613 nm emission band of Cs [Eu (tfnb) ₄ (tppo)]. The strong broad band in the 250-500 nm region corresponds to the band of energy transfer from the ligand to Eu (III) ions. In particular, the intensity of the excitation band in the 350-440 nm range shows that the excitation band is excited in the ultraviolet region, and the excitation band shown at 460-470 nm corresponds to the ⁷ F ₀ → ⁵ D ₂ excitation transition. Overlapping with the energy transfer band caused the intensity of the excitation transition to be stronger than that of the energy transfer band. As in the case of Cs [Eu (tfpb) ₄ (tppo)], Cs [Eu (tfnb) ₄ (tppo)] complexes also exhibited hypersensitivity in the ⁷ F ₀ → ⁵ D ₂ transition. Therefore, the Cs [Eu (tfpb) ₄ (tppo)] complex can induce strong red luminescence by GaN diodes as well as ultraviolet light due to this supersensitive ⁷ F ₀ → ⁵ D ₂ excitation transition.

Example 7 M _a Eu (β-diketonato) _b (tppo) _c ] Luminescence Decomposition Spectrum of Complexes

The time resolution spectrum of the Eu (III) complex according to the present invention was measured using an N ₂ laser (337 nm). 10 shows the time resolved spectra of Cs [Eu (tfnb) ₄ (tppo)] complexes. Excitation of 337 nm induces luminescence by energy transfer process from ligand to Eu (III) ion. As shown in FIG. 10, the luminescence increased from 0.2 ms after the pumping N ₂ laser light flickered to maximum intensity at 2.5 ms, and decreased exponentially thereafter. The rising part corresponds to the energy transfer process. The rise and decay times calculated using the exponential function are summarized in Table 3 below. The synthesized Eu (III) complexes have a decay time of 0.6-1 ms, which is typically the decay time of most Eu (III) phosphors.

Table 3. Rise time and decay time of Cs [Eu (β-diketonato) _b (tppo) _c ] (p373 N ₂ laser with light source).

Sample λ _ems (nm) τ (ms) Cs [Eu (tfnb) ₄ (tppo)] powder 613.6 Decay time 0.64 Rise time 0.08 crystal 613.6 Decay time 0.66 Rise time 0.09 Cs [Eu (tfpb) ₄ (tppo)] powder      619 Decay time 0.94 Rise time 0.13

Example 8 M _a Eu (β-diketonato) _b (tppo) _c Light yield of complexes

The light efficiency of Eu (III) complex was measured using the integrating sphere of Labsphere. The light efficiency is the ratio of the total number of photons emitted to the total number of photons absorbed. To calculate the correct number of photons, the whole optical system was calibrated using a calibrated halogen lamp approved by NIST. In addition, in order to obtain more reliable results, the incident light reflected or passed by the sample was separately measured and corrected. The light yields measured in Table 4 are summarized. In general, the luminescence light efficiency obtained by directly exciting Eu (III) ions is very low, less than 1%. In particular, the light efficiency due to the ⁷ F ₀ → ⁵ D ₂ transition in the 460-470 nm region is almost negligible. However, in the red phosphor of the present invention, the light efficiency due to 466 nm excitation is 5% or more, which is almost the same as the light efficiency of energy transfer.

Table 4. Light yield of Eu (III) complexes

sample λexc (nm) Light yield (%) Cs [Eu (tfpb) ₄ (tppo)] (powder) 379 18.8 466 5.7 Cs [Eu (tfnb) ₄ (tppo)] (powder) 379 7.5 466 7.4 Cs [Eu (tfnb) ₄ (tppo)] (crystal) 379 8.8 466 11.4

Example 9 Preparation of Red Light Emitting Diode and Its Luminescence Spectrum

A light emitting diode was manufactured using the Eu (III) red phosphor prepared in Examples 1 to 4. On the sapphire substrate, a GaN nucleation layer 25 nm, n-GaN layer (metal: Ti / Al) 1.2 μm, five InGaN / GaN multiquantum well layers, InGaN layer 4 nm, GaN layer 7 nm and p-GaN layer (metal (Ni / Au) 0.11 μm was formed in order to prepare a blue light LED. Subsequently, the phosphor prepared in Example 3 on the surface of the blue light LED was dispersed in an epoxy to prepare a red light emitting device. The emission spectrum of the prepared red light emitting diode is illustrated in FIG. 11.

As shown in Fig. 11, the broad bands in the 400-500 nm wavelength range are the emission spectra of GaN, and the sharp bands in the 580-740 nm region are the luminescence bands emitted from Eu (III) ions. Accordingly, the red phosphor of the present invention can be utilized as a molecular light conversion device capable of converting blue light emitted from a GaN diode into red light. In addition, it can be used for white light emitting diodes.

According to the present invention, by selecting and synthesizing a ligand system inducing excess sensitivity, a red phosphor of Eu (III) having high luminance that can be excited by blue light of GaN can be provided. In addition, the red phosphor may be used to produce a red light emitting diode that is excited with light in the ultraviolet and visible light region and emits red light, and may be used in combination with a green or yellow phosphor to be variously applied to a white light emitting diode.

Claims (7)

Red phosphor represented by the following formula (1): <Formula 1> M [Eu (β-diketonato) ₄ (tppo)] Where M = Na ⁺ , Cs ⁺ or K ⁺ . The method of claim 1, M [Eu (β-diketonato) ₄ (tppo)] is M [Eu (4,4,4-trifluoro-1-phenyl-1,3-butanedionato) ₄ (tppo)] or M [Eu (4,4 , 4-trifluoro-1- (2-naphthyl) -1,3-butanedionato) ₄ (tppo)]. The method according to claim 1 or 2, The red phosphor is in powder form or crystalline red phosphor. A light emitting diode comprising the red phosphor of claim 1. The method of claim 4, wherein Wherein the red phosphor is excited by a wavelength in the range of 460-470 nm. The method of claim 4, wherein Wherein said red phosphor is excited by a wavelength in the range of 350-440 nm. The method of claim 4, wherein The red phosphor is excited by the blue light emitted from the GaN diode emits red light.

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