JPH1012925A - Light-emitting diode with phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable emission of fluorescent lights of various colors using a single type of light-emitting diode, by causing a phosphor to absorb a light emitted by a light-emitting diode which emits an ultraviolet light or a near ultraviolet light and to convert the absorbed light to a visible light. SOLUTION: A phosphor film 2 which absorbs an ultraviolet light or a near ultraviolet light and emits a visible fluorescent light is applied onto a light- emitting diode 1 which emits an ultraviolet light or a near ultraviolet light, thus constituting a light-emitting diode with a phosphor. As the light-emitting diode which emits an ultraviolet light or a near ultraviolet light, a light-emitting diode made of pn junction of a GaInN semiconductor may be used. This light- emitting diode normally emits a light of blue color. However, by causing a pulse-like large current to flow through the lightemitting diode, it may be used as the light-emitting diode which emits an ultraviolet light or a near ultraviolet light. By providing a reflection board 3 on which an Al thin film is bonded by vacuum evaporation, the light emission efficiency of the phosphor may be improved approximately 15%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode that emits light of various colors by combining a light emitting diode emitting ultraviolet light or near ultraviolet light with a phosphor.
The present invention relates to a light-emitting element that performs display of different emission colors with the same drive voltage.

[0002]

2. Description of the Related Art Conventionally, a light emitting diode which has been widely used is a light emitting diode in which a minority carrier is injected by a voltage applied in a forward direction at a pn junction of a semiconductor, and recombination with a majority carrier or transition to a light emitting center is performed. It utilizes light emission transitions leading to the release of energy. The emission color of the light emitting diode, that is, the emission wavelength generally differs depending on the semiconductor material constituting the light emitting diode, and mainly depends on the forbidden body width of the semiconductor material. That is, in order to obtain light emission of different colors, it is necessary to form a junction using semiconductor materials having different forbidden body widths corresponding to the light emission wavelength. For example, a light emitting diode emitting red light is gallium aluminum arsenide (GaAlAs), which is a mixed crystal of gallium arsenide and aluminum arsenic, and a light emitting diode emitting green light is gallium phosphide (GaP).
However, a light emitting diode that emits blue light uses zinc selenide (ZnSe) or gallium indium nitride (GaInN) that is a mixed crystal of gallium nitride and indium nitride. On the other hand, in a thin-film electroluminescence element that obtains light emission by applying a voltage to an element having a structure in which thin films are stacked, a substance that absorbs this light emission and emits fluorescence such as green or red is applied to an electroluminescence element that emits blue light. An element with a wavelength conversion function of obtaining light emission with different wavelengths by stacking (Proceedings of the 15thInt
ernational Display Research Conference, S11-2, p.2
69) have been reported.

[0003]

However, in the light emitting diode comprising a pn junction made of the above-mentioned semiconductor material, different semiconductor materials must be used in order to manufacture a light emitting diode which emits light of different colors. In addition, since the manufacturing method and manufacturing conditions of the light emitting diode are different depending on each semiconductor material, and furthermore, the crystal used as the substrate is also different, it is difficult to integrate a large number of light emitting diodes having different emission wavelengths on the same substrate. It is. It is also known that, in a light emitting diode comprising a pn junction of a semiconductor, a threshold voltage at which a current flows when a voltage is applied to start light emission is determined by a junction barrier called a diffusion potential. It is also known that a threshold voltage is increased in a diode made of a semiconductor having a large forbidden width depending on the forbidden width of a material. That is, generally, the driving voltage of the green light emitting diode is higher than that of the red light emitting diode, and a higher driving voltage is required for the blue light emitting diode. Therefore, even if a large number of light emitting diodes with different colors of light emission can be integrated on the same substrate, it is difficult to select and emit light having different emission wavelengths by the same power supply voltage, and It is also difficult to perform matrix driving or the like. Furthermore, the above-mentioned thin-film electroluminescent elements generally have the disadvantage that the driving voltage is high and the luminance of light emission is low as compared with light-emitting diodes, and it is difficult to construct a high-luminance and bright light-emitting element. Since it is also difficult to manufacture an electroluminescent element that emits light, it is difficult to construct a display that emits high-luminance full-color fluorescent light by excitation with ultraviolet light. The present invention is intended to solve the above-described conventional problems, and a method of combining a light emitting diode emitting ultraviolet light or near ultraviolet light with a phosphor emitting fluorescent light of various colors to form a single type of light emitting diode. An object of the present invention is to provide a light emitting element which can emit fluorescent light of various colors by using the same, and which can emit light of various colors at the same driving voltage.

[0004]

According to the present invention, there is provided a light emitting diode comprising: a light emitting diode emitting ultraviolet light or near ultraviolet light; and a phosphor. (2) The phosphor-equipped light emitting diode according to claim 1, wherein the phosphor has a light scattering effect. (3) The light emitting diode according to claim 1, wherein the phosphor has a light scattering effect. (4) The light emitting diode with a phosphor according to (1), (2) or (3), which has a function of reflecting the fluorescence emitted by the phosphor. 4. A light emitting diode with a phosphor according to claim 1, wherein a plurality of light emitting diodes with a body are integrated and driven by the same power supply voltage. It is obtained as characterized by mixing or laminating a phosphor emitting fluorescence becomes colored.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To realize a light emitting diode with a phosphor according to the present invention, for example, the following method may be used.
As shown in FIG. 1, a phosphor film 2 that absorbs ultraviolet light or near ultraviolet light and emits visible fluorescence is applied to a light emitting diode 1 that emits ultraviolet light or near ultraviolet light used in the present invention. To form a light emitting diode. The light emitting diode that emits ultraviolet light or near ultraviolet light used in the present invention includes GaI manufactured by Nichia Corporation.
An NLPB500 light-emitting diode comprising a pn junction of an nN-based semiconductor is exemplified. The NLPB500 light emitting diode is a light emitting diode that normally emits blue light,
It can be used as a light emitting diode that emits ultraviolet light and near-ultraviolet light by passing a large pulsed current. For example, the emission spectrum when driven at a pulse width of 10 microseconds and a pulse repetition frequency of 1 kilohertz is as shown in FIG. 2, and the maximum ultraviolet light component output is obtained when driven at a peak current of 800 mA. Can be The phosphor used in the present invention includes ZnS: Ag (blue),
ZnS: CuAl (green), ZnCdS: Ag (red)
Powdered phosphors made of inorganic compounds such as above are dispersed in an aqueous solution of polyvinyl alcohol and solidified by evaporation.
Further, BOQP, PBBO, BisMSB, BBO which are organic substances used as reagents for liquid scintillation are used.
T, POPOP, etc. (above, blue), DPOT (green),
TB (EDTA) which is a rare earth chelate compound (SS
A) (green) and EuTTA (red) are dissolved in, for example, methyl methacrylate and polymerized and solidified to obtain polymethyl methacrylate (PMMA). FIG. 3 shows a fluorescence spectrum when these organic phosphors are irradiated with ultraviolet light. In addition, these phosphors are applied to the light emitting diode as shown in FIG. 1, or the phosphor is applied to glass or the like and arranged adjacent to the light emitting diode, so that the ultraviolet light from the light emitting diode or the near The fluorescent material absorbs ultraviolet light, and visible fluorescent light emission of a color characteristic of each fluorescent material is obtained. If a phosphor made of an inorganic compound that has a light scattering effect by itself or a material in which a medium having a light scattering effect is dispersed in the phosphor is used, ultraviolet or near-ultraviolet light for excitation emits fluorescent light. Fluorescence can be obtained efficiently by being scattered in the body, and the fluorescence emitted from the phosphor is scattered. In this case, there is an optimum value for the light scattering effect, and if there is an excessive light scattering effect, the overall efficiency will decrease. Further, if a reflecting mirror 3 having such a property as to reflect the fluorescence emitted from the phosphor forward in FIG. 1 is used,
The emission intensity of the apparent fluorescence is increased, and the emission efficiency is improved as a whole.

[0006]

According to the present invention, instead of a light emitting diode comprising a pn junction manufactured using a semiconductor material having a forbidden band width corresponding to each emission wavelength, a light emitting diode emitting ultraviolet light or near-ultraviolet light is used. By using a single type of light emitting diode, it is possible to construct a light emitting diode that emits a variety of colors of fluorescent light by combining a phosphor that emits fluorescent light of a different color. It is possible to integrate a light emitting diode that can emit light of the above.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings. Example 1 As shown in FIG.
NLPB500 light emitting diode 1 consisting of junction
S: A solution in which the Ag phosphor powder is dispersed in a 10% aqueous solution of polyvinyl alcohol at a weight ratio of 1: 4 is applied,
After drying, the thin phosphor film is coated. Similarly, a ZnS: CuAl phosphor or a ZnCdS: Ag phosphor powder is dispersed in a 10% aqueous solution of polyvinyl alcohol at a weight ratio of 1: 4 and applied, thereby emitting green or red fluorescent light, respectively. A diode is configured. The NLPB500 light emitting diode coated with these phosphors has a peak current of 800 mA and a pulse width of 1
FIG. 4 shows respective emission spectra when driven by a pulse current of 0 microsecond. Blue, green,
A red fluorescent light emitting diode was constructed. Example 2 ZnS: Ag phosphor powder, ZnS: CuAl
A phosphor powder obtained by mixing a phosphor powder and a ZnCdS: Ag phosphor powder at a weight ratio of 1: 1, 1: 2,
Similarly, a solution dispersed in a 10% aqueous solution of polyvinyl alcohol at a weight ratio of 1: 4 is applied to an NLPB500 light emitting diode, and dried to form a thin film coating. The peak current is 800 mA and the pulse width is 10 microseconds. , A light-emitting diode that emits white fluorescent light in which red, green, and blue primary colors are mixed is formed. Blue light, green light, red light emitted from these phosphor-equipped light emitting diodes shown in Example 1 and Example 2
FIG. 5 shows the chromaticity coordinates of the white fluorescent light emission. It can be seen that although the purity of the green fluorescent light emission is somewhat poor, light emission close to the NTSC chromaticity coordinates is obtained. In addition, the phosphor film prepared from the polyvinyl alcohol dispersion solution of these inorganic phosphors is in a state in which the phosphor powder is dispersed and has a light scattering effect, so that light emission having a wide viewing angle dependency can be obtained. Was. Example 3 BBOT which is a dye for scintillation,
DPOT and EuTT, a rare earth chelate compound
A is added to methyl methacrylate to which azobisisobutyronitrile as a polymerization initiator is added in an amount of 1 to 3% by weight, respectively.
Dissolve and polymerize each. When the solution in which the polymerization started and the viscosity became high was applied to an NLPB500 light emitting diode and further polymerized and solidified to obtain polymethyl methacrylate,
A transparent phosphor film is formed. Similarly, when the light emitting diode provided with the phosphor film is driven by a pulse current having a peak current of 800 mA and a pulse width of 10 microseconds, the blue, green, and red fluorescent light having a spectrum similar to the fluorescent spectrum shown in FIG. A light-emitting diode emitting light was constructed. Further, by dispersing titanium oxide powder or zinc oxide powder in methyl methacrylate and polymerizing and solidifying the same, a phosphor having a light scattering effect was obtained, and a uniform and highly efficient phosphor was obtained. Example 4 In the light-emitting diode with a phosphor shown in FIG. 1, by providing a reflector with an aluminum thin film by a vacuum evaporation method as a reflector shown by 3, light emitted from the phosphor is efficiently reflected forward. As a result, the luminous efficiency from the phosphor was apparently improved by about 15%. In the above embodiment, the case where the phosphor film is directly coated on the light emitting diode is described. However, various configurations other than these embodiments can be performed. For example, ZnS: Ag
Phosphor powder, or ZnS: CuAl phosphor powder, or Z
Phosphor powders obtained by mixing nCdS: Ag phosphor powders alone or at a weight ratio of 1: 1, 2: 2 were similarly dispersed in a 10% aqueous solution of polyvinyl alcohol at a weight ratio of 1: 4. The solution was thinned on a glass substrate by a spin coating method, and the glass substrate provided with the phosphor film was NL
By placing it adjacent to the PB500 light emitting diode,
An element that uniformly emits fluorescence over a much larger area than light emitted from a light emitting diode that emits light in the form of a point light source could be constructed. Further, it is also easy to configure a full-color display by arranging NLPB500 light-emitting diodes provided with phosphors that emit red, green, and blue fluorescent light in a matrix and applying a current pulse in order to drive them. In the light emitting diode, a phosphor film can be directly provided on a semiconductor chip serving as a light emitting portion, or a polymer such as polymethyl methacrylate in which a phosphor composed of an organic compound is dissolved can be provided in a dome shape or a lens shape. It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0008]

As described in detail above, according to the light emitting diode with phosphor of the present invention, by changing the kind of phosphor, a single type of light emitting diode that emits ultraviolet light or near-ultraviolet light can be used. Light emitting diodes that emit fluorescent light of various colors can be used, and it is not necessary to adopt different manufacturing techniques and manufacturing conditions in order to integrate a large number of light emitting diodes having different colors. Further, there is a problem in driving a conventional light emitting diode that light emitting diodes emitting different colors must be driven at different voltages. However, this difficulty can also be driven by the same power supply voltage according to the present invention. So it is resolved. In addition, it is very easy to increase the area by using a phosphor film, so that it is economical. For example, it is possible to solve various obstacles and problems in the conventional light emitting diode manufacturing. Can be demonstrated.

[Brief description of the drawings]

FIG. 1 is a schematic view of a light emitting diode with a phosphor showing an embodiment of the present invention.

FIG. 2 is an NL emitting ultraviolet light or near ultraviolet light of the present invention.
It is an emission spectrum when a PB500 light emitting diode is pulse-driven.

FIG. 3 is a fluorescence spectrum of an organic phosphor for organic scintillation and a rare earth chelate compound phosphor used in the present invention.

FIG. 4 is an emission spectrum when an NLPB500 light emitting diode provided with an inorganic phosphor film according to the first embodiment of the present invention is pulse-driven.

FIG. 5 is chromaticity coordinates of three primary colors and white fluorescent light emission shown in the first embodiment and the second embodiment of the present invention. here,
R, G, and B indicate chromaticity coordinates of red, green, and blue in NTSC, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light emitting diode which emits ultraviolet light or near ultraviolet light 2 Phosphor 3 Reflector 4 Drive power supply

Claims (5)

[Claims] 1. A light-emitting diode with a phosphor, comprising: a light-emitting diode that emits ultraviolet light or near-ultraviolet light; and a phosphor, wherein the light emitted by the light-emitting diode is absorbed by the phosphor and converted into visible light. 2. The light emitting diode with a phosphor according to claim 1, wherein the phosphor has a light scattering effect. 3. The light-emitting diode with a phosphor according to claim 1, wherein the light-emitting diode with a phosphor has a function of reflecting fluorescence emitted from the phosphor. 4. A light emitting diode with a phosphor according to claim 1, wherein a plurality of light emitting diodes provided with phosphors emitting different colors of fluorescence are integrated and driven by the same power supply voltage. A light emitting diode with a phosphor. 5. The light emitting diode with a phosphor according to claim 1, 2 or 3, wherein phosphors emitting fluorescent lights of different colors are mixed or laminated.