JP2003347588A - White-light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a durable, small, lightweight white-light emitting device that can generate a low color-temperature white color. <P>SOLUTION: A fluorescent screen of a massive ZnSSe including 10<SP>17</SP>cm<SP>-3</SP>or more of either one of Al, Ga, In, Br, Cl, and I is combined with InGaN-LED that generates a blue color of 410 nm-460 nm to excite the ZnSSe fluorescent screen by the blue so as to generate a yellow color, and then the blue and the yellow generated are synthesized into a white color. The ZnSSe is turned massive, does not absorb water, and thus does not deteriorate. The InGaN-LED is durable, and the massive ZnSSe does not deteriorate, which will produce a durable white-light emitting device. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white light emitting device capable of generating white light having a single element structure and usable for illumination, display, liquid crystal backlight, and the like.

[0002] Numerous light emitting diodes (LEDs) and semiconductor lasers (LDs) have been manufactured and sold as small light emitting elements.
Red LEDs, yellow LEDs, green LEDs, blue LEDs, and the like are commercially available as high-brightness LEDs. Red LE
D is an LED having an active layer of AlGaAs, GaAsP or the like. Yellow and green LEDs with GaP as the light emitting layer
There is. Orange / yellow is L with AlGaInP as the light emitting layer
Can be created by ED.

Blue, which requires a wide band gap interband transition, has been the most difficult and difficult. SiC, ZnS
e, GaN-based ones were tried and competed, but it was found that GaN-based ones with high brightness and long life were overwhelmingly superior, and the win or loss was already attached. Since the active layer of InGaN-based LEDs is actually InGaN, InGaN-based LEDs and InGaN
-The substrate will be sapphire and the main body of the layer structure will be GaN, although it will be written as LED hereinafter. These LEDs and LD
Such a semiconductor light-emitting element uses a band gap transition to emit monochromatic light having a narrow spectrum width. As it is, a complex color cannot be created by a semiconductor device.

[0004]

BACKGROUND OF THE INVENTION Illumination light sources are useless with monochromatic light sources. A backlight for liquid crystal cannot be a monochromatic light source. Lighting requires a white light source. In particular, white having high color rendering properties is desirable. A backlight for liquid crystal also needs a white light source. Incandescent lamps and fluorescent lamps are still used exclusively as illumination light sources. Incandescent lamps are suitable for lighting because of their high color rendering properties, but have the disadvantages of poor efficiency and short life. A fluorescent lamp has a short life, requires a heavy object, and is a large and heavy device.

[0005] The emergence of smaller, longer-life, higher-efficiency, and less expensive white light sources is awaited.
If it is light weight, small size, long life and high efficiency, it seems that it is only a semiconductor element.

In fact, blue LED, green LED, red LE
Since D exists, white should be synthesized by combining these ternary colors of light. Blue, green, red 3
If the same type of LED is uniformly mounted on the panel and emits light simultaneously, it should be white. Such three color mixing LED
Seems to have already been proposed and partially implemented.
Although white can be produced by mixing three colors, it must not be seen as a separate single color, so that three kinds of LEDs must be distributed at high density.

[0007] In addition, since the three types of LEDs have different current, voltage and light emission characteristics, a separate power supply is required, resulting in three power supplies. Difficult to align because of variations in brightness.
Although there is such a problem, above all, a large number of three types of LEDs are densely arranged in parallel, so that it becomes an expensive light source.

[0008] Expensive light sources are not popular or useless. We would like to make a smaller white light emitting element at lower cost as a semiconductor device. There are two known techniques of a semiconductor light emitting device using a single light emitting device. One is a composite LED in which an InGaN-LED (light emitting element on a GaN substrate) is surrounded by a YAG phosphor. The other is to dope impurities into the ZnSe substrate of the ZnSe-LED to make it a phosphor and to excite the ZnSe phosphor by the blue color of the ZnSe-LED light-emitting part (ZnCdSe) (referred to as SA emission).
Then, yellow / orange is generated, and white is obtained by a combination of blue and yellow / orange. Briefly, the former is a GaN-based white light emitting device (A), and the latter is a ZnSe-based white light emitting device (B).
Let's call it. Each will be described.

(A) GaN-based white light emitting device (YAG + I
nGaN-LED; FIG. 1) This uses an InGaN-LED. For example, “Optical Functional Materials Manual”, Optical Functional Materials Manual Editing Board, edited by Optoelectronics, p457,
It was described in June 1997. FIG. 1 shows the structure.

A concave portion 3 is provided in a horizontal portion of the mold lead 2,
The InGaN-LED 4 is attached to the bottom of the recess 3. The concave portion 3 accommodates a resin 5 in which a Ce-added YAG fluorescent agent is dispersed. The YAG fluorescent agent has a property of absorbing blue light and generating yellow having lower energy. Such low-energy light that is emitted when a material absorbs high-energy light and is excited by electrons and the excited electrons return to the original level is called fluorescence. The material that emits it is called a fluorescent agent. It returns to the original level through various levels, so there is a spread of energy and the spectrum of fluorescence is wide. The loss of energy becomes heat.

The electrodes 6 and 7 of the InGaN-LED 4 are connected to the lead 2 and the lead 10 by wires 8 and 9, respectively.
The upper portions of the leads 2 and 10 and the fluorescent resin 5 are covered with a transparent resin 20. Thereby, a bullet-type white light emitting element is manufactured. Since an InGaN-LED uses an insulating sapphire substrate, an n-electrode cannot be provided on the bottom surface, and an n-electrode and a p-electrode are formed at two places on the upper surface, and two wires are required.

This involves surrounding the InGaN-based blue LED 4 with a resin layer 5 in which a YAG fluorescent agent is dispersed, and converting a part of the blue light B into yellow light Y by the fluorescent agent. And the yellow light Y, the white W
(= B + Y). White light can be produced with a single light emitting element. Here, a Ce-activated YAG fluorescent agent is used. 460 nm light is used as blue light B of the InGaN-LED. The center wavelength of the yellow light Y converted by YAG is about 570 nm. That is, YAG absorbs 460 nm blue light and converts it into yellow light having a broad peak at about 570 nm.

[0013] Since the InGaN-LED light emitting device has high luminance and long life, this white light emitting device also has the advantage of long life. However, since YAG is an opaque material, blue light is strongly absorbed, and the conversion efficiency is not good. This realizes a white light emitting element having a color temperature of about 7000K.

(B) ZnSe-based white light emitting device (ZnCd
Se emission, ZnSe substrate fluorescent agent; Fig. 2) This is ZnC instead of InGaN-LED as blue light source.
Use dSe-LED. Uses fluorescence but does not use a separate fluorescent agent. An excellent and clever element. Become the applicant,

Japanese Patent Application No. 10-316169 “White L
ED "

Has been proposed for the first time. 3 shows the structure of the LED shown in FIG. ZnS instead of GaN substrate
An e-substrate 22 is used. A light emitting layer composed of a ZnCdSe epitaxial layer is provided on the impurity-doped ZnSe substrate 22. ZnCdSe emits 485 nm blue.
Zn, Se, I, Al, In, Ga, Cl, Br
Is doped as a luminescent center. The impurity-doped ZnSe substrate 22 absorbs a part of blue and
Generates a broad yellow light centered at Blue light B and yellow light Y are combined to create white W (W = B +
Y).

Actually, the ZnCdSe-LED of FIG. 2 is also attached to the lead and surrounded by a transparent resin to form a shell-type light emitting element like the element of FIG. 1, but this is not shown. In this method, an n-type ZnSe substrate is doped with impurities and the n-type substrate itself is used as a fluorescent plate. The epi-layer ZnCdSe emits blue light, and the ZnSe substrate emits yellow fluorescence. Together, they form white W.

The substrate is essential because it is an LED. The substrate functions not only as a physical holding function of the light emitting layer but also as a fluorescent plate. That is, it has a sophisticated structure in which the substrate is effectively used twice. No separate fluorescent agent such as YAG is required. That is a great advantage.

The light emission of impurity-doped ZnSe is referred to as SA.
Called self-activated. This uses blue light at 485 nm and yellow light at a center wavelength of 585 nm,
A white color having an arbitrary color temperature between 00K and 2500K is realized. When the thickness of the ZnSe substrate is reduced or the impurity concentration is reduced, the fluorescence becomes inferior and the blue light of the ZnCdSe light emitting layer becomes effective. A white color with a high color temperature is obtained. When the thickness of the ZnSe substrate is increased or the impurity concentration is increased, fluorescence is superior, so that white with a low color temperature can be obtained. With such a little contrivance, white with various color temperatures can be obtained.

As described above, there are three semiconductors having a wide band gap: ZnSe, SiC, and GaN. SiC
Is inefficient because of indirect transition and does not compete from the beginning. ZnSe, which can produce a single crystal substrate, was the primary one, but currently, InGaN blue light from GaN and InGaN thin films on a sapphire substrate has long life, high brightness, and low cost.
He has won as ED. InGaN / sapphire-LEDs can produce shorter wavelength (higher energy) blue light, have longer lifetimes and are brighter.

Although ZnSe has a short life and low energy (long wavelength), it lags behind as a blue light LED. However, this white light emitting element B is economical because the substrate itself is a fluorescent plate, no special fluorescent agent is required, and economy is low. It may grow into a costly white light emitting device.

(C) Chromaticity diagram (FIG. 3) The rule of synthesis of white W = blue B + yellow Y is difficult to understand strictly by itself. Let's explain with a chromaticity diagram. FIG. 3 is a chromaticity diagram. The chromaticity diagram is a two-dimensional graph expressing the stimulus values to the human eye for the three primary colors red, green, and blue for the visible light source or the object color.
Speaking of the light source, among the light source light, x is a stimulus value that human eyes perceive as red, y is a stimulus value that perceives as green, and z is a stimulus value that perceives blue. It is difficult to understand, but human vision is the standard, and the energy of light (Nhν; N is the number of photons, ν
Is not the frequency). Even with the same energy, green visibility is high, and blue visibility is low. Two-dimensional display is not possible if there are three variables. Moreover, since the color tone is considered, the total stimulus amount does not matter.

Therefore, a two-dimensional coordinate space in which red and green are adopted and blue is omitted is assumed. X = x / (x
+ Y + z) and normalized green is given by Y = y / (x
+ Y + z). The chromaticity diagram shows the normalized red on the horizontal axis and the normalized green on the vertical axis. Naturally, X + Y <1 must be satisfied. Any color is represented by a point on its two-dimensional coordinates. The monochromatic (the spectrum becomes a δ function) is shown on a diagonal horseshoe-shaped curve (shown by a solid line; abcdefghijkmnpq). The limit a at the lower right of the horseshoe curve is the red limit. 620, 610
.. Represents the wavelength expressed in nm. 620
Although 530 nm (abcdef) is close to a straight line, since the blue component z is small, the portion becomes such a straight line as X + Y is close to 1.

The curve falls from 520 nm (g) of green,
510, 505, 500,... (Hi), but this has a shape along the Y axis since there are almost no red components and strong blue and green components. It can be said that the decrease from 520 nm is the blue component. The x component slightly increases from 495 nm (i) because the red component is included. Red and green are used for the x and y coordinates, and blue is discarded. So where did blue go? It actually appears on the chromaticity diagram as a value obtained by multiplying the distance between the oblique line of X + Y = 1 and the coordinate point by ^21/2 .

The end n of the horseshoe curve is purple. The straight line npqa connecting purple and red is called a pure purple curve. Monochromatic is this curve a
bcdefghijkmnpq. However, the pure purple curve npqa is not necessarily monochromatic and is difficult to explain. This part is not yet mature in color theory and is not an issue here.

All complex colors are inside this curve.
When colors are mixed intricately, they are represented by more interior points. The area surrounded by the broken line in the center is the white area W.
It is. The chromaticity diagram itself is originally only a device for displaying color components two-dimensionally, but since the linearity is maintained for blue, red and green from the above definition, a mixed tone of two or three colors There is an extremely convenient property that corresponds to the mixing operation on the chromaticity diagram.

Here, the color temperature will be briefly described. White, reddish, yellowish,
It is bluish and various. As a method of expressing white, there is a method of expressing the coordinates by coordinate points on a chromaticity diagram. It lacks intuition, however. As described above, the expression by the color tone of reddish or bluish is easy to understand, but lacks quantitativeness. Although it varies from person to person, there is also an expression based on color temperature.
In the present invention, since white is represented by color temperature, its definition will be described.

Light having a frequency of ν has energy of hν.
Because photons are bosons

[0029]

(Equation 1)

The Bose statistic is followed. We want to find the average value Em = <hν> of the photon energy per unit volume. There is one state for small volume _dk x _dk y _dk z = 1 in wave number space. The frequency ν is ν = c / λ = ck / 2
π. Since spherical symmetry in k-space _dk x _dk y d
Since k _z = 4πk ² dk = 32π ⁴ ν ³ dν / c ³ , the probability distribution is

[0031]

(Equation 2)

It can be written as follows. That is the energy distribution of photons of blackbody radiation. When hv is multiplied and integrated, the distribution becomes blackbody radiation (such as an incandescent light bulb). The denominator absolute temperature T is the color temperature.

Assuming that the frequency showing the maximum distribution is νmax or the average frequency νm, they are proportional to T. νma
x / T = const1, and νm / T = const2. In terms of an average value, νm = const2 × T.

If it is not blackbody radiation, the distribution is not equation (1). F (ν) in equation (1), where the spectrum is g (ν)
And calculate the average value of ν. The color temperature T can be calculated by dividing it by νm and dividing it by const2. The white color temperature of T means that the same average value as the energy distribution when the temperature of the distribution function is T by black body radiation is given. Therefore, it is possible to define and calculate the color temperature even in the white spectrum apart from blackbody radiation.

Another parameter for evaluating white is color rendering. It shows the deviation from blackbody radiation (3). Black body radiation naturally has a color rendering property of 100%, such as an incandescent light bulb. In the present invention, the color rendering property is not considered so much, so the color rendering property will not be described.

The (A) GaN-based white light emitting device described above
In the chromaticity diagram of FIG. 3, the GaN-LED emits blue light (point m) at 460 nm, and the Ce-doped YAG fluorescent agent absorbs blue light and generates yellow light (point d) having a peak at 568 nm. Therefore, (A) GaN-based white light emitting device (YAG
+ InGaN-LED) can generate complex colors corresponding to points on the straight line md. The straight line md crosses the left end of the white area W. So you can create white. 7 mentioned above
000K white color means X = 0.31, Y inside W
= 0.32. The reason why the color temperature is considerably high is that the wavelength of the light emitted from the InGaN-LED is short even though it is blue light.

Another (B) ZnSe-based white light-emitting device (ZnCdSe / ZnSe substrate) is a ZnCdS active layer.
e generates 485 nm blue light and corresponds to point j in the chromaticity diagram of FIG. Impurities (Al, In, Br, Cl, Ga,
I) Fluorescence of doped ZnSe generates fluorescence of yellow light of about 585 nm. In FIG. 3, it corresponds to the point c. When 485 nm blue light (point j) from the active layer and 585 nm yellow light (point c) from the ZnSe substrate are combined, an arbitrary color on the straight line jc can be created. Advantageously, this line jc crosses the white area W from left to right. This means that white with various color temperatures can be produced by changing the ZnSe thickness and the impurity concentration.

Here, 10,000K, 8000K, 700
0K, 6000K, 5000K, 4000K, 3000
K, the coordinates of white at a color temperature of 2500 K are indicated by dots. As described above, in the ZnSe-based white light emitting element, the slope of the straight line jc is gentle, and the ZnSe-based white light emitting element crosses the white region long. Thanks to this, it is possible to produce whites of various colors (color temperatures). In that respect, it is more convenient than the GaN-based white light emitting device (A).

[0039]

[Problems to be solved by the invention] [1. Advantages and Disadvantages of ZnSe-Based White Light-Emitting Element] The chromaticity diagram (FIG. 3) of the synthesis of the ZnSe-based white light-emitting element shows that the ZnCdSe-LED
A straight line jc connecting the blue light B (at 485 nm, j point) and the yellow light Y (at 585 nm, c point) of the ZnSe substrate almost coincides with the locus of white light (10000K to 2500K). By changing the ratio of the blue light B and the yellow light Y by changing the thickness of the ZnSe substrate or changing the impurity concentration, it is possible to obtain a white color having an arbitrary color temperature (10000K to 2500K). There are advantages such as a small and simple element structure and simple electrodes.

However, the disadvantage of ZnSe-based LEDs is that they tend to deteriorate and have a short life. Since a large current flows for light emission, defects increase and deterioration proceeds. When it deteriorates, the luminous efficiency decreases. Eventually, it stops emitting light. It is short-lived, which is a common disadvantage of light emitting devices on a ZnSe substrate.

When the white light W is synthesized by mixing the blue light B and the yellow light Y, a necessary ratio between the blue light B and the yellow light Y is a problem. When blue light having a wavelength near 445 nm, which has high energy, is used, the necessary ratio of blue light is the smallest. When blue light having a lower energy near 485 nm (point j) is used, about twice as much blue light as 445 nm blue light is required (B: Y = 2: 1).

Here, the blue light has a lower luminous efficiency than the yellow light, so that the smaller the ratio of the blue light, the higher the luminous efficiency.
Therefore, a ZnSe-based white light emitting element that requires more blue light is disadvantageous in terms of efficiency.

[2. Advantages and disadvantages of GaN-based white light emitting element] (A) GaN-based (InGaN-LED)
+ YAG) white light emitting element has a blue color of 460 nm to 44
The energy is high at 5 nm and the required power ratio is B: Y
= 1: 1, and the blue color needs only half the ZnSe-based color.
This is advantageous in terms of efficiency. Since a GaN-based light-emitting element has a long life, a white light-emitting element using it also has a long life. There are such advantages.

However, there are disadvantages. YAG + InG
The aN-LED white light emitting element, as can be seen from FIG.
A straight line md connecting the blue light m and the yellow light d is a white locus (1
(0000K-2500K), it has a gradient that makes contact at 7000K, so that white with an arbitrary color temperature cannot be synthesized. A white color having a color temperature lower than around 7000K (6000K, 5000K, 2500K, etc.) cannot be synthesized.

Generally, the color temperature of a white light bulb is a low color temperature around 3500K. An InGaN-based white light-emitting element can only realize white having a color temperature different from that of a white light bulb. That is, it cannot be used as a white light emitting element for illumination. Although it can be used for a liquid crystal backlight, there is a disadvantage that the color temperature is too high.

Therefore, despite having excellent characteristics (lifetime and efficiency), replacement of a white light bulb has not been sufficiently advanced.

A lower color temperature, specifically 6000K
It is a first object of the present invention to provide a small white light emitting device capable of producing a white color having a lower color temperature. It is a second object of the present invention to provide a long-life white light emitting device. Without long life, incandescent bulbs and fluorescent lamps cannot be replaced.

[0048]

[Means for Solving the Problems] The present invention relates to InG
We propose a white light-emitting device in which ZnSSe bulk fluorescent plates are stacked on an aN-LED. A part of the InGaN-LED emission that emits blue light having a short wavelength is converted to yellow light by a bulk phosphor plate made of ZnSSe crystal, and white W (W = B + Y) is obtained by mixing blue light B and yellow light Y.
Are synthesized.

2. The wavelength of blue light generated by the InGaN-LED is set to 410 nm to 460 nm. This is a shorter wavelength even in blue light, and corresponds to light emission in the lower left portion of mn in the chromaticity diagram of FIG. Such short-wavelength blue light is a ZnSe-based (ZnCdSe active layer: 485n).
m; j point) cannot be made. Therefore, GaN-based (InGaN
(Active layer) LED is used. InGaN / Sapphire
LEDs are easy to use in terms of track record, lifetime, cost and reliability. Therefore, the present invention is common to the above-described prior art (A) YAG + InGaN-LED in terms of LED. However, the fluorescent material is not YAG. Use new substances.

3. The wavelength of yellow light is 570 nm to 580
nm. This expresses the novel concept of the present invention by wavelength. The aforementioned prior art (A) YAG + I
Since the nGaN-LED uses Ce-doped YAG that emits 568 nm (d point) fluorescence, it can synthesize only 7000K white. Point d is closer to yellow-green than yellow light. The present invention produces a longer wavelength near red light. In the chromaticity diagram, 570 nm (point v) and 580 nm (u
Produces a yellow that is closer to red in the range between (dots). In that case, the blue light emits light in the range of the line segment nm,
The yellow light emits fluorescence in the range of the line segment uv. Line segment n
The straight line connecting m and the line segment uv corresponds to the light emission of the white light emitting device of the present invention. A straight line (dashed-dotted line) connecting the line segment nm and the line segment uv enters a white region deeper than the line segment md corresponding to YAG. One of the ideas of the present invention is where the yellow side of the straight line is slightly lowered.

4. In order to slightly lower the yellow light side (shift to the red side), a new fluorescent material other than YAG is required. The present invention relates to ZnSSe, which is a mixed crystal of ZnSe and ZnS.
Use crystals. High purity ZnSSe does not emit fluorescence.
A dopant that becomes an emission center is required. The dopant is any of Al, In, Ga, Cl, Br, and I.
The fluorescent material used in the present invention contains Al, I in ZnSSe crystal.
An impurity (dopant) of at least one element of n, Ga, Cl, Br, and I is contained at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more. If it is less than this, fluorescence is not sufficiently generated. The specific gravity of yellow light (uv) can be changed by changing the dopant concentration or the thickness of the fluorescent material. In other words, a point indicating a color in the blue light / yellow light line segment (mn to uv) on the chromaticity diagram can be moved up and down along the line segment. Conventional example using YAG (A; md)
Since the stranded line penetrates deeply into the white region, white with various color temperatures can be synthesized. By increasing the thickness of the fluorescent material and the dopant concentration, the specific gravity of yellow light (uv) can be increased to produce white with a low color temperature.

Al, In, Ga, C as dopants
The use of any one of l, Br, and I is the same as the conventional example (B) using a ZnSe substrate as a fluorescent plate. However, the present invention uses ZnSSe instead of ZnSe as the fluorescent plate. Further, the LED is InGaN instead of ZnCdSe.

5. ZnSe has a narrow band gap,
Since ZnS has a wide band gap, depending on the mixed crystal ratio x
Band gaps in between can be made.
The phosphor material of the present invention is made of ZnS in ZnSSe crystal.
The composition ratio is x, the composition ratio of ZnSe is (1-x), and x is
0.1 to 0.4. To be exact, ZnS
_xSe_1-x(0.1 ≦ x ≦ 0.4)
However, the mixed crystal ratio x is omitted for simplicity. If x = 0, Z
nSe becomes a fluorescent plate, which is the same as the fluorescent plate of the conventional example (B).
You. However, if it is used as a fluorescent screen, blue kn and yellow c
Only the color of the line segment (kn-c) connecting
It shifts to the lower side of the color area W. Wide range of any color temperature
I can't make a good white. So ZnSe (x =
0) is negated.

On the other hand, if the whole is made of ZnS (x = 1), the fluorescence wavelength is too short and the conventional example (A) YAG + InGaN
-Only white with a high color temperature can be produced, like the LED. Therefore, the present invention sets the mixed crystal ratio to x = 0.1 to 0.4. The wavelength of the fluorescence is not the band gap itself. The relationship will be described later.

6. As described above, ZnSSe is used in a lump shape. This is an important device of the present invention. Should not be in powder form. Furthermore, ZnSS that constitutes the fluorescent screen
It is desirable that the average particle size of the e crystal be larger than the thickness of the phosphor screen. In the conventional example (A), YAG is YAG (yttrium aluminum).
Inum garnet) powder is dispersed in a transparent resin and used as a fluorescent agent. In the first place, a fluorescent plate is often a material in which fine powder of a material that emits fluorescent light is dispersed in transparent glass or resin. If it is made into a lump rather than a powder, the light does not enter the inside, so the internal fluorescent agent is useless. The fluorescent agent is made into a fine powder and dispersed in a transparent resin or glass so that the light can be easily irradiated and the conversion efficiency is improved as much as possible. This is because light passes through the transparent resin, the light easily hits the fluorescent powder, the concentration of the fluorescent substance can be easily adjusted, and it can be formed (formed) into an arbitrary shape.

However, ZnSS doped with the above impurities
It has been found that dispersing fine powder of e-polycrystal in resin has disadvantages not found in YAG or the like. ZnSSe has water absorption. When the powder is dispersed in the resin, water enters the resin, and the powder ZnSSe easily absorbs water and is easily deteriorated. Unless such difficulties are overcome, they cannot be used as fluorescent agents.
Therefore, unlike conventional fluorescent agents, bulk polycrystalline or single crystal ZnSSe is used instead of powder. This is important in the present invention. When it is made into a lump, the surface area is small, so that water hardly enters and stays near the surface even if it enters. Deterioration due to water absorption is also limited to near the surface. That's why the mass Z
nSSe is used.

Even in the case of polycrystal, the larger the particle size, the better.
This is because water can easily enter the grain boundaries, but it is not the only one. Light may be irregularly reflected and absorbed at the grain boundaries, causing optical loss. Therefore, the larger the grain boundary, the better. It is more suitable that the average particle size of the polycrystal is equal to or larger than the thickness of the fluorescent plate. In this case,
n) also keeps a single crystal in the thickness direction, and the average particle size is defined in the plane direction of the phosphor plate.

7. More preferably, the ZnSSe fluorescent plate is made of single-crystal ZnSSe. Polycrystalline grain boundaries (bo
Undary) causes optical loss, so it is better not to have grain boundaries. A single crystal is ideal if it has no grain boundaries. Therefore, an impurity-doped ZnSSe single crystal is optimal as the fluorescent plate of the present invention. Nevertheless, ZnSSe single crystals cannot be easily made. It can be made by chemical transport but is time consuming and expensive. In terms of cost reduction, massive polycrystalline ZnSSe will be used.

8. Emission wavelength 4 as blue light emitting LED
An InGaN LED of 10 nm to 460 nm is used.
This is because, as already described, in the chromaticity diagram, the blue light emitting region is set to mn, and the line connecting the yellow light and the blue light crosses the white region W deeply. Thereby 700
A white color with a color temperature below 0K is obtained.

9. When the composition ratio of ZnS in the ZnSSe crystal is x, the composition ratio of ZnSe is (1-x), and the emission wavelength of the blue light emitting LED is λ _LED , λ _LED ≧ 1
239 / (2.65 + 1.63x-0.63x 2) nm
It is desirable that The band gap of ZnSe is 2.
The absorption edge wavelength is 460 nm at 7 eV. The band gap of ZnS is. At 3.7 eV, the absorption edge wavelength is 335 nm. The equation for the emission wavelength λLED is 2.65, and the band gap is 2.7. Mixed ZnS
the band gap of _x Se _1-x is approximately Eg = 2.7
+ Provided by 1.63x-0.63x ^2. When 1239 (= hc) is divided by the band gap, the absorption edge wavelength is expressed in nm. In other words, the above equation says that it is better to excite the fluorescent material with blue light (of a longer wavelength) having an energy lower than the band gap of the mixed crystal ZnSSe of the fluorescent material used in the present invention. It is a completely different story from mn-uv traversing the white area W on the chromaticity diagram. Although slightly complicated, this condition
The condition is that the blue light of the N-LED is not absorbed by the surface of the ZnSSe fluorescent material but reaches the inside and is absorbed inside to generate fluorescence. Semiconductors readily absorb light with energy (short wavelength) higher than the band gap. Even if it is made into a lump, the surface of the fluorescent material may be deteriorated due to water absorption. So I don't want to use the surface. It is desired that blue light reaches the inside and excites the dopant therein to emit light. Therefore, Zn that is hardly absorbed
That is, blue light having energy lower than the band gap of SSe is used.

10. Zn heat treated in Zn atmosphere
It is preferable to use an SSe crystal as the fluorescent plate. This is because the heat treatment reduces defects and reduces scattering and non-fluorescence absorption.

[0062]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above-mentioned problem of generating a white color having a color temperature lower than 7000K,
It suffices if there is a fluorescent material that converts a part of the blue light emitted from the LED near the light emission wavelength of 445 nm (the midpoint of mn) to light near the center wavelength of 575 nm (the midpoint of uv).

InGaN-LEDs emitting 445 nm exist and are commercially available. The fluorescent material is the problem. A fluorescent material emitting a wavelength of 575 nm is required. The fluorescence of Ce-YAG of the conventional example (A) has a center wavelength of 568 nm.
(Point d). It is too short. As described in the conventional example (B), a group 3 element or a group 7 element (Al,
When In, Ga, Br, Cl, and I) are mixed, the emission wavelength is around 585 nm (point c). This is too long. I want fluorescence with a wavelength between u and v between points d and c.

A common fluorescent agent such as Ce-YAG is Ce
Since there is only a parameter such as the dopant concentration, the center wavelength of the fluorescence cannot be changed. When the Ce concentration is increased, only the color coordinates on the line segment md approach the point d, and the point d itself cannot be moved. This is because Ce itself works as an isolated color center in the YAG matrix.

However, Zn which is a mixed crystal of ZnSe and ZnS
In the S _x Se _1-x crystal, dopants (Al, In, G
In addition to a, Br, Cl, and I), the mixed crystal ratio x exists as a freely selectable parameter. ZnSe with x = 0 has a band gap of Eg _ZnSe = 2.7 eV, and ZnS with x = 1 has a band gap of Eg _ZnS = 3.7 eV. That is, it is larger by about 1 eV. The band gap changes depending on x. It has been found that the fluorescence of ZnSSe is likely due to the donor-acceptor transition. The addition of Group 3 and Group 7 dopants produces both relatively deep donors and acceptors. Fluorescence is emitted by the donor-acceptor transition. Therefore, the fluorescence center wavelength Δq is considerably longer than the band gap wavelength λg (= hc / Eg).

Then, when the band gap Eg is changed, the wavelength Δq of the fluorescence due to the donor-acceptor transition can be changed. It is a convenient point of ZnSSe that the fluorescence center wavelength Δq depends on the band gap Eg. This is not a case of using ZnSe as an active LED in terms of passive fluorescence. It's complicated, but don't confuse them.

The fluorescence center wavelength Δq of impurity-doped ZnSe
_ZnSe = 585 nm and the desired fluorescence center wavelength is 5
80 nm to 570 nm (between u and v), so 10 nm
It just needs to be as short as possible. The fluorescent wavelength when ZnS is used as the fluorescent material is around 470 nm. The ZnSSe band gap and fluorescence wavelength will change continuously with x. If so, the desired fluorescence wavelength is 570 nm to 5 nm.
80 nm should be obtained with a mixed crystal ZnS _x Se _{1-x where x} is chosen appropriately.

Therefore, if the composition ratio x of ZnS is appropriately selected and the group 3 element or group 7 element is mixed in the ZnS _x Se _1-x crystal, it should be possible to obtain fluorescence at around 575 nm. Suitable values of x will be described later.

Here, if the mixing density is low, sufficient light emission cannot be obtained. It is necessary to mix (dope) impurities (dopants) of about 1 × 10 ¹⁷ cm ⁻³ or more. If the density is higher than this, increasing the density can increase the specific gravity of yellow light, and decreasing the density can increase the specific gravity of blue light. Such a thing is also possible by changing the thickness of the fluorescent material.

However, ZnSe, ZnSSe and ZnS
There is a problem that the fluorescent material of the system lacks water resistance. Absorbs water and degrades over time. Because of that, Z
A white light emitting device in which an nSSe-based material is used as a fluorescent agent in combination with an InGaN-based LED has not been put to practical use.
Ordinary fluorescent agents such as YAG are used by dispersing powder in transparent resin or transparent glass. The fine powder ZnSSe immediately absorbs water and immediately deteriorates and becomes unusable. The problem of water absorption degradation must be overcome.

Here, the problem of water resistance becomes a problem when the surface area of the fluorescent agent is relatively large. In order to increase the water resistance, it is effective to reduce the surface area as much as possible. The surface area of a sphere of radius r is 4πr ² and the volume is 4πr ³ /
3. The surface area / volume ratio is 3 / r. To lower the ratio, the radius r should be increased.

For this purpose, a bulky single crystal or polycrystalline ZnSSe is used rather than using powdery ZnSSe.
Fluorescent plate may be used. Lumped phosphors are self-contradictory and unfamiliar to hear, but ZnSSe could be used as a phosphor if lumped. Then, since the ratio of the surface area to the volume of the fluorescent material becomes very small, the water resistance should be remarkably improved.

Usually, it is written as "fluorescent agent" because it is a powder. In the present invention, since a lump of ZnSSe which is not a fine powder is used, the term "fluorescent material" or "fluorescent plate" will be used.

However, even if the above-described fluorescent plate is used, all of the blue light is absorbed in the vicinity of the fluorescent plate surface, and the blue light does not enter the fluorescent plate, and only the surface of the fluorescent plate emits fluorescence. In this case, the effect of the surface is strong, so that the problem of water resistance also becomes apparent. In addition, if the LED light is almost absorbed on the surface of the fluorescent plate, the internal fluorescent material is wasted and inefficient. In the first place, making a fluorescent agent into a powder with a normal fluorescent material and dispersing it in a resin was a device for allowing all the fluorescent agents to be exposed to light. In the present invention, since the fluorescent plate is formed as a block, it is necessary to allow the light to enter the inside instead of staying at the surface. That is where the situation is different from that of ordinary fluorescent agents. How do I get LED light inside?

It suffices that ZnSSe is almost transparent to the blue light of the LED. Normal fluorescent agents are opaque and this is not the case, but in the present invention, since a massive fluorescent plate is used, L
One that is transparent to ED light is used. So how do you make it transparent? The present inventor has considered that Zn constituting the fluorescent screen
It has been noticed that blue light having energy smaller than the forbidden band width (band gap; Eg) of the SSe crystal may be used.

Fortunately, ZnS has a wide band gap and is higher than the energy of the LED light emitted from the InGaN-LED. The band gap of ZnSe is InGaN-
It is lower than the light energy of the LED. With an appropriate mixed crystal ratio x,
ZnSS having a band gap Eg equal to the energy corresponding to the emission wavelength λ _LED of the InGaN blue light emitting device
e exists. If ZnSSe having a mixed crystal ratio x larger than the critical mixed crystal ratio is used as the fluorescent material, the band gap is widened and the LED is transparent to LED light. The LED light should be able to penetrate inside the phosphor screen. The task of making the bulk phosphor transparent to LED light is thereby vividly solved.

Then, the absorption coefficient of the fluorescent plate for the blue light is reduced, and the blue light enters the inside of the fluorescent plate,
Blue light is emitted from the entire phosphor plate. The influence of the deteriorated surface is reduced, and the fluorescent material inside can be effectively used.

On the contrary, the emission wavelength λ _LED of the blue LED may be longer (the energy is lower) than the band gap of the ZnSSe mixed crystal phosphor.

If the ZnS composition in the ZnSSe crystal is x (ZnS _x Se _1-x ), the forbidden band width is

Eg _ZnSSe = 2.7 + 1.63 × −0.63 × ² (eV) (4)

Is given by When the energy is expressed in eV and the wavelength is expressed in nm, they are inversely proportional. Since the proportionality constant is 1239, the LED blue light wavelength λ
_As the relationship between _LED and ZnS composition x,

[0082]

(Equation 3)

Should be satisfied. This is an inequality that determines the wavelength range of the InGaN-LED assuming that the composition x of the fluorescent material is determined. The ZnSSe band gap Eg and band gap wavelength λg are calculated by (5) by changing the mixed crystal ratio x as follows.

[0084]

[Table 1]

The emission wavelength of the In _y Ga _1-y N-LED can be changed by changing the mixed crystal ratio y of In. As described above, the preferred emission wavelength of InGaN is 410 nm to 460 nm.
Can emit light of up to 480 nm. I
When the ratio y of n is high, the emission wavelength shifts to the longer wavelength side, and Ga
If the ratio 1-y of the above is high, the emission wavelength changes to the shorter wavelength side.
The ZnS mixed crystal ratio corresponding to 410 nm is x = 0.252. Band gap wavelength λ for larger x
g becomes shorter than 410 nm. So 1>x> 0.2
In the range of 52, equation (5) is no longer a condition for limiting the emission wavelength λ _LED of the InGaN-LED. 0 <x ≦
In the range of 0.252, the band gap wavelength is 410 nm.
From the above, equation (5) is a condition for limiting the emission wavelength λ _LED of the InGaN-LED.

Since the λ _LED has a wavelength of 410 nm to 460 nm, for example, when x = 0.1, 460 nm> λ _LED
> 441 nm, and 460 nm> λ when x = 0.2
_LED > 420 nm. In the case of x = 0, λ _LED > 467 nm from equation (5), but does not satisfy the condition of 460 nm or less. Therefore, x = 0 is inappropriate. In the chromaticity diagram, the fluorescence wavelength is 570 nm to 580 nm.
Although x = 0 is unsuitable in that it must be (u to v), it is also unsuitable under an independent condition (the LED light enters the inside of the phosphor plate).

On the contrary, the equation (5) can be interpreted as if the wavelength λ _LED of the InGaN-LED was previously determined and the ZnS mixed crystal ratio x of the fluorescent plate was limited thereto.

The ZnS composition x of the fluorescent plate is not limited to this, and as described above, the fluorescent wavelength Δq is 570 nm to 580 nm.
Should be determined so that all such conditions are satisfied. The fluorescence wavelength Δq of ZnSSe is determined by the band gap Eg, but the relationship is not yet analytically clear. This will be explained later based on the results of experiments.

The ZnSSe fluorescent plate is most preferably a single crystal. Single crystals have the advantage that there are no grain boundaries. In addition to this, there is an advantage that processing is easy in producing a fine ZnSSe fluorescent plate. In other words, by cleaving a (100) ZnSSe substrate having an appropriate thickness and a plane orientation, a cubic ZnSSe having an arbitrary size is obtained.
A fluorescent plate can be easily created. However, it does not necessarily have to be a single crystal. It may be polycrystalline. In the case of polycrystal, it cannot be divided by cleavage, but may be cut mechanically. Since light absorption and light scattering at the polycrystalline grain boundaries reduce the conversion efficiency, it is preferable that the polycrystalline grain boundaries be large.
Preferably, the average grain boundary is larger than the thickness of the ZnSSe fluorescent plate.

It is desirable that the surface of the ZnSSe phosphor plate on the side where blue light is incident be mirror-polished in order to increase the incidence efficiency. This is because a rough surface causes irregular reflection. ZnSSe
It is not always necessary to perform mirror polishing on the other surface of the phosphor plate, but mirror polishing may be performed as required for processing. In addition, it is considered more preferable to form an antireflection film on the incident surface. The antireflection film is formed of a transparent dielectric film. Although a single layer is possible, a multilayer film improves the antireflection performance.

It is also useful to perform surface processing to enhance the emission efficiency of yellow light generated in the ZnSSe fluorescent plate.

The wavelength of blue light has been described as being advantageous around 445 nm. However, it does not always have to be 445 nm. Since there is also a change in the luminous efficiency due to the difference in the emission wavelength of the blue light of the LED and a change in the conversion efficiency of the fluorescent plate, the really optimum wavelength changes according to the technical trend of the blue light emitting LED.

However, since part of the blue light is converted to yellow light using the ZnSSe fluorescent plate, the wavelength of the blue light emission is 410 nm or more from the viewpoint of conversion.
Must be in the 480 nm range. Any deviations will obviously reduce efficiency. So 410nm ~
Blue light with a wavelength in the range of 480 nm should be used.
However, considering that a white color is formed by looking at the chromaticity diagram, the wavelength of the InGaN-LED blue light is 410 nm to 460.
nm.

In order to realize white using blue light in this range, the center wavelength of light emitted from the ZnSSe phosphor plate is 57
It should be between 0 nm and 580 nm. This can be seen from the chromaticity diagram.

In order to exhibit fluorescence having such a center wavelength, the ZnS composition ratio x in the ZnSSe crystal is set to 0.1 to 0.4.
What should I do? The grounds will be described later.

When an InGaN-based LED is used as a blue LED, the current technology has the highest luminous efficiency at a wavelength near 400 nm, and the luminous efficiency decreases at longer wavelengths. From the viewpoint of luminous efficiency, the wavelength of blue light is 46
It is preferably shorter than 0 nm. Therefore, when an InGaN-LED is used as the blue light LED, the emission wavelength is 410 nm to 460 nm. Therefore, 460 nm to 480 nm in the above-mentioned range of blue light can emit 570 nm to 580 nm fluorescent light for producing white light, but is omitted because the efficiency of the LED is reduced.

The absorption coefficient of ZnSSe crystal for blue light can be adjusted by the temperature of the heat treatment in a Zn atmosphere. The heat treatment increases the absorption of blue light. Therefore, in order to convert an appropriate amount of blue light into yellow light to synthesize white, it is useful to adjust the absorption coefficient.

[0098]

EXAMPLES Example 1 (Change in Fluorescence Wavelength Due to ZnS Mixed Crystal Ratio x) ZnS Composition Ratio (x) of ZnSSe Phosphor Emission
To check for dependencies, x = 0, 0.1, 0.2, 0.
3, 0.4, 0.5, and 0.6 ZnSSe crystals were produced by a chemical transport method using iodine as a transport medium. A ZnSSe substrate cut out from the crystal was heat-treated at 1000 ° C. in a Zn atmosphere for 50 hours to produce a ZnSSe fluorescent plate.

The center wavelength (point on the chromaticity diagram) was estimated from the wavelength distribution of fluorescence emitted when the ZnSSe substrate was irradiated with light having a wavelength of 440 nm. Table 2 shows the results.

[0100]

[Table 2]

From the analysis of the chromaticity diagram, the fluorescence was 570 nm to 5 nm.
The condition is that it is 80 nm. ZnS mixed crystal ratio of 0.4
Exceeds 570 nm. If it is less than 0.1, it exceeds 580 nm. From this result, it was found that the ZnS composition ratio x was optimally 0.1 to 0.4. The center wavelength of the fluorescence does not have a sharp peak like the emission wavelength of the LED. Because it is fluorescent, it becomes a gentle mountain and its central wavelength.

Example 2 (x = 0.4, λ _LED = 42
0 nm, Δq = 570 nm)] A thickness 20 cut out of a ZnS _0.4 Se _0.6 single crystal having a ZnS composition x = 0.4
0 micron, ZnSSe substrate with plane orientation (100)
Heat treatment was performed at 1000 ° C. in an atmosphere. The heat treatment was performed to adjust the absorption coefficient of blue light. This ZnSSe substrate was mirror-polished on both sides to a thickness of 100 microns. This Z
The nSSe substrate was scribe-breaked to produce a 300 μm square, 100 μm thick ZnSSe phosphor plate.

InGaN using a sapphire substrate
A blue LED chip having an active layer and an emission wavelength of 420 nm was prepared. As shown in FIG. 4, this LED chip was mounted in a flip-chip type, and a ZnSSe fluorescent plate was adhered to the upper side of the LED (the upper side of the sapphire substrate) via a transparent resin. In FIG. 4, a large {type lead 24, a small}
The mold leads 25 are combined. The leads are in a complicated combination, and the small lead 25 is inserted into the hole of the large lead 24. Γ type lead 24
Has an indentation 26 in which an InGaN-LED 27
Is implemented. Since the sapphire substrate is InGaN, the electrodes 30 and 32 are provided on the epitaxial growth surface.

Normally, the electrode and the lead are connected by two wires as shown in FIG. 1, but here, the electrode 30 is connected to the large O
In addition, the electrode 32 is attached to the small lead 25 upside down. The leads 24, 25 penetrate each other but are not in contact. Since the InGaN-LED 27 is turned upside down, blue light is emitted upward from the sapphire substrate. A ZnSSe fluorescent plate 28 is mounted on a sapphire substrate. The depression 26 is filled with a transparent resin in which a diffusing agent (SiC powder) is dispersed. These were molded with a molding resin 36 to produce a shell-type light emitting device. When electricity is supplied to the LED, blue light is emitted from the InGaN-LED 27, which turns yellow on the fluorescent screen. It is spread by the transparent resin and spreads. As a result, a white color having a color temperature of 5000 K was obtained. FIG. 5 shows a state in which the yellow light Y is excited by the blue light B, and the blue light B and the yellow light Y are mixed and go outside to become white.

One reason that such a low color temperature white can be obtained while using an InGaN-LED is that the fluorescence wavelength is not 568 nm (Ce-YAG) but 569 nm.
(ZnS _0.4 Se _0.6 ). Another reason is that the wavelength of the InGaN-LED is shortened to 420 nm.

Example 3 (x = 0.25, λ _LED = 4
40 nm, Δq = 575 nm)] A white light-emitting device as shown in FIG. 4 was manufactured in the same manner as in Example 2 except that the composition ratio x of ZnS was changed to 0.25, the emission wavelength of the blue LED was changed to 440 nm, and the other conditions were the same. did. When the white light emitting element was energized to emit light, white light having a color temperature of 3500 K was obtained.

[0107]

According to the present invention, an InGaN-LED emitting at 410 nm to 460 nm is used as a blue light source,
ZnSSe that emits fluorescence with a center wavelength at ~ 580 nm
A white light-emitting device that emits white light by converting a part of blue light of a blue LED into yellow light by a fluorescent plate and combining with blue using a bulk crystal fluorescent plate is provided. YAG / I
A white color having a lower color temperature than an nGaN-LED can be created. White with a color temperature lower than 5000K can also be synthesized. Small size because of using InGaN-LED
Lightweight, with little deterioration and long life. Color rendering is not good because it is a combination of two colors. However, since it generates white light with high luminance and low color temperature, it can be used for a liquid crystal backlight or the like.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conventional example in which a transparent resin in which a Ce-doped YAG fluorescent material is dispersed surrounds a blue light-emitting InGaN-LED, and a white color with a high color temperature can be generated by a combination of blue of the LED and yellow of YAG. White LE
Sectional drawing which shows the structure of D (YAG / InGaN-LED).

FIG. 2 shows that a ZnCdSe epitaxial layer is formed on a ZnSe substrate containing any of Al, Ga, In, Br, Cl, and I as a dopant, and an impurity of the ZnSe substrate is excited by blue from a ZnCdSe light emitting unit to emit yellow light. A white L according to a conventional example that generates white by combining the blue of ZnCdSe with the yellow of SA emission
FIG. 4 is a cross-sectional view illustrating a structure of an ED (ZnSe / ZnCdSe).

FIG. 3 is a chromaticity diagram for explaining a white principle of a white light emitting element that generates white by a combination of blue of an LED and yellow of a fluorescent light.

FIG. 4 is an InGaN-LED that emits blue light having a short wavelength.
And a ZnSSe fluorescent plate containing any one of Al, Ga, In, Br, Cl, and I as a dopant.
FIG. 2 is a cross-sectional view showing a structure of a white LED of the present invention that can excite a ZnSSe fluorescent plate with blue light of a GaN-LED to generate yellow light and generate white light having a color temperature of 5000 K or less.

FIG. 5 shows that the blue light of an InGaN-LED provides ZnS
FIG. 5 is an enlarged cross-sectional view of a part of the LED and the fluorescent material of FIG. 4 for explaining the principle of the present invention in which a Se fluorescent plate is excited to generate yellow fluorescent light and obtain white by mixing blue light and yellow light.

[Explanation of symbols]

2Γ type lead 3 recess 4 InGaN-LED 5 Resin in which YAG fluorescent agent is dispersed 6 electrodes 7 electrodes 8 wires 9 wires 10 Straight lead 20 Transparent resin 22 Impurity-doped ZnSe substrate 24 mm lead 25mm type lead 26 recess 27 InGaN-LED 28 ZnSSe fluorescent plate 29 Transparent resin with diffusing agent dispersed 30 electrodes 32 electrodes 36 Mold resin

Continuation of front page    F-term (reference) 4H001 CA04 CA05 CF02 XA07 XA16                       XA30 XA31 XA34 XA49 YA13                       YA17 YA31 YA35 YA49 YA53                 5F041 AA11 AA14 AA44 AA47 CA13                       CA40 CA46 CB36 DA04 DA09                       DA12 DA16 DA43 DA56 DB01                       FF16

Claims (6)

[Claims] 1. An InGaN-based LED that emits blue light having a wavelength of 410 nm to 460 nm, and Al, In, Ga, C
impurities of at least one element of l, Br and I
ZnS _x Se containing at a concentration of × 10 ¹⁷ cm ⁻³ or more
_A lump-shaped fluorescent plate made of _1-x crystal;
A part of the blue light emission of the InGaN-based LED is converted to yellow light having a wavelength of 570 nm to 580 nm by the bulk ZnS _x Se _1-x crystal phosphor plate, and the InGaN-based LED is 410 nm to 460 n.
A white light-emitting device, which combines white light by mixing blue light of m and yellow light of 570 nm to 580 nm of a fluorescent plate to synthesize white. 2. The composition ratio of ZnS in the ZnSSe crystal is x, the composition ratio of ZnSe is (1-x), and x is 0.1 to 2.
The white light emitting device according to claim 1, wherein the white light emitting device is set to 0.4. 3. The white light emitting device according to claim 1, wherein the ZnSSe crystal constituting the phosphor plate has an average particle size larger than the thickness of the phosphor plate. 4. The white light emitting device according to claim 3, wherein the ZnSSe fluorescent plate is made of single crystal ZnSSe. 5. A blue light emitting LE having a ZnS composition ratio of x and a ZnSe composition ratio of (1-x) in a ZnSSe crystal.
When the emission wavelength of D is λ _LED , λ _LED ≧ 1239
White light emitting device according to any one of claims 1 to 4, characterized in that a /(2.65+1.63x-0.63x ²⁾ nm. 6. A ZnSS heat-treated in a Zn atmosphere.
The white light emitting device according to any one of claims 1 to 5, wherein the e crystal is used as a fluorescent plate.