WO2015190242A1 - Light-emitting device - Google Patents

Abstract

Provided is a light-emitting device using quantum dots which has little colour tone unevenness. The light-emitting device (1) comprises a light-emitting part (30) and a light source (20). The light-emitting part (30) includes the quantum dots. The light source (20) is disposed in a central part of the light-emitting part (30) in a plan view. The light source (20) irradiates the light-emitting part (30) with light of a quantum dot excitation wavelength. In at least the peripheral edge part of the light-emitting part (30), the thickness of the light-emitting part (30) gradually decreases towards the outside.

Description

Light emitting device

The present invention relates to a light emitting device.

In recent years, light-emitting devices using light-emitting diodes have made remarkable progress and have been adopted for liquid crystal backlights, large displays, and the like. In particular, with the development of semiconductor materials for light emitting elements with short wavelength light, it has become possible to obtain short wavelength light, so that phosphors can be used to obtain light of various wavelengths. Became.

Conventionally, light emitting devices using quantum dots are known. For example, Patent Document 1 describes a light-emitting device that includes a blue LED and a sealing portion that seals the blue LED and is made of a resin composition that includes quantum dots.

JP 2010-126596 A

Incidentally, in a light emitting device using quantum dots, it is required that the color tone of light emitted from the light emitting device does not differ depending on the light emitting direction. Specifically, for example, the light emitted from the light emitting device along the optical axis direction and the light emitted along the direction inclined with respect to the optical axis are required not to have different color tones. .

However, the light-emitting device disclosed in Patent Document 1 contains a dispersant in the resin composition and uniformly irradiates light emitted from the blue LED to the quantum dots to improve the conversion efficiency. It has not led to improvement.

The present invention provides a light emitting device using quantum dots and having a small color unevenness.

The light emitting device according to the present invention includes a light emitting unit and a light source. The light emitting unit includes quantum dots. The light source is arranged at the center of the light emitting unit in plan view. The light source emits light having an excitation wavelength of the quantum dot to the light emitting unit. At least at the peripheral edge of the light emitting part, the thickness of the light emitting part gradually decreases toward the outside.

The light-emitting device according to the present invention may further include a device main body having a concave portion that accommodates the light source and the light-emitting portion, and a cover member that covers the concave portion and seals the light source and the light-emitting portion together with the device main body. In that case, it is preferable that the light emission part is provided on the surface at the side of the recessed part of a cover member.

The light-emitting device according to the present invention includes a first main wall portion, a second main wall portion facing the first main wall portion at an interval, a first main wall portion, and a second main wall portion. It may further include a cell having a side wall portion connected to the wall portion and arranged separately from the light source. In that case, the light emitting unit may be provided on the first or second main wall in the cell.

In the light emitting device according to the present invention, the light source preferably emits divergent light to the light emitting portion.

In the light emitting device according to the present invention, preferably, the light emitting section has a larger area than the light source in plan view.

In the light emitting device according to the present invention, the light emitting section preferably emits mixed light of the light emission of the quantum dots and the light emitted from the light source and transmitted through the light emitting section.

According to the present invention, it is possible to provide a light emitting device using quantum dots and having a small color unevenness.

FIG. 1 is a schematic cross-sectional view of the light emitting device according to the first embodiment. FIG. 2 is a schematic cross-sectional view of the light emitting device according to the second embodiment. FIG. 3 is a schematic cross-sectional view of a light emitting device according to a third embodiment. FIG. 4 is a schematic cross-sectional view of a light emitting device according to a fourth embodiment. FIG. 5 is a schematic cross-sectional view of a light emitting device according to a fifth embodiment.

Hereinafter, an example of a preferable embodiment in which the present invention is implemented will be described. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

In each drawing referred to in the embodiment and the like, members having substantially the same function are referred to by the same reference numerals. The drawings referred to in the embodiments and the like are schematically described. A ratio of dimensions of an object drawn in a drawing may be different from a ratio of dimensions of an actual object. The dimensional ratio of the object may be different between the drawings. The specific dimensional ratio of the object should be determined in consideration of the following description.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of a light emitting device 1 according to the first embodiment.

The light emitting device 1 is a device that emits light having a wavelength different from that of the excitation light when the excitation light is incident. The light emitting device 1 may emit mixed light of excitation light and light generated by irradiation of excitation light.

The light emitting device 1 has a device body 10. The device main body 10 includes a first member 11 and a second member 12. The second member 12 is provided on the first member 11. The second member 12 is provided with a through hole 12 a that opens to the first member 11. A recess 13 is formed by the through hole 12a. The through hole 12a tapers toward the first member 11 side. For this reason, the side wall 13 a of the recess 13 is inclined with respect to the main surface of the first member 11.

The device body 10 may be made of any material. The device body 10 may be made of, for example, ceramics such as low-temperature co-fired ceramics, metal, resin, glass, or the like. The material constituting the first member 11 and the material constituting the second member 12 may be the same or different.

The light source 20 is disposed on the bottom wall 13b of the recess 13 of the device body 10. The light source 20 can be composed of, for example, an LED (Light Emitting Diode) element, an LD (Laser Diode) element, or the like. In the present embodiment, an example in which the light source 20 is configured by LEDs will be described.

A light emitting unit 30 is arranged in the recess 13. The light emitting unit 30 and the light source 20 are accommodated in the recess 13. The light emitting unit 30 is arranged so that light from the light source 20 enters. Specifically, in the light emitting device 1, the light emitting unit 30 is provided on the surface of the cover member 40 on the concave portion 13 side. The light emitting unit 30 is disposed above the light source 20 so as to cover the light source 20.

The light source 20 emits divergent light to the light emitting unit 30. The light source 20 emits light having an excitation wavelength of quantum dots included in the light emitting unit 30 to the light emitting unit 30. Note that the light emitted from the light source 20 is not necessarily limited to the light having the excitation wavelength of the quantum dots. The light emitted from the light source 20 may include, for example, light of other wavelengths in addition to the light of the excitation wavelength of the quantum dots.

In plan view, the light source 20 is arranged at the center of the light emitting unit 30. The light source 20 is arranged so as to overlap the center line C extending in the thickness direction of the light emitting unit 30. The light emitting unit 30 has a larger area than the light source 20. The area of the light emitting unit 30 is preferably 2 to 400 times the area of the light source 20, and more preferably 20 to 75 times. If the area of the light emitting unit 30 is too small, a portion that passes through and exits the light emitting unit 30 and a portion that exits without passing through the light emitting unit 30 are likely to exist in a plan view, and uneven color tone increases. On the other hand, if the area of the light emitting unit 30 is too large, the light emitted from the light source 20 is difficult to be applied to the peripheral part of the light emitting unit 30, and the color tone unevenness increases.

The light emitting unit 30 includes quantum dots. The light emitting unit 30 may include one type of quantum dot or may include a plurality of types of quantum dots.

The quantum dot emits light having a wavelength different from that of the excitation light when the quantum dot excitation light is incident. The wavelength of the light emitted from the quantum dot depends on the particle diameter of the quantum dot. That is, the wavelength of the light obtained by changing the particle diameter of the quantum dots can be adjusted. For this reason, the particle diameter of a quantum dot is made into the particle diameter according to the wavelength of the light to obtain. The particle size of the quantum dots is usually about 2 nm to 10 nm.

For example, as a specific example of a quantum dot that emits blue visible light (fluorescence with a wavelength of 440 nm to 480 nm) when irradiated with excitation light of ultraviolet to near ultraviolet with a wavelength of 300 nm to 440 nm, the particle diameter is about 2.0 nm to 3.0 nm. And CdSe / ZnS microcrystals. Specific examples of quantum dots that emit green visible light (fluorescence having a wavelength of 500 nm to 540 nm) when irradiated with ultraviolet to near ultraviolet excitation light having a wavelength of 300 nm to 440 nm or blue excitation light having a wavelength of 440 nm to 480 nm include particle diameters. CdSe / ZnS microcrystals having a thickness of about 3.0 nm to 3.3 nm. Specific examples of quantum dots that emit yellow visible light (fluorescence having a wavelength of 540 nm to 595 nm) when irradiated with ultraviolet to near ultraviolet excitation light having a wavelength of 300 nm to 440 nm or blue excitation light having a wavelength of 440 nm to 480 nm include particle diameters. And CdSe / ZnS microcrystals having a thickness of about 3.3 nm to 4.5 nm. Specific examples of quantum dots that emit red visible light (fluorescence with a wavelength of 600 nm to 700 nm) when irradiated with ultraviolet to near ultraviolet excitation light with a wavelength of 300 nm to 440 nm or blue excitation light with a wavelength of 440 nm to 480 nm include particle diameters. CdSe / ZnS microcrystals having a thickness of about 4.5 nm to 10 nm.

In the present embodiment, the light emitting unit 30 is solid. Specifically, the light emitting unit 30 includes a resin in which quantum dots are dispersed. The quantum dots are preferably dispersed substantially uniformly in the dispersion medium. By dispersing the quantum dots substantially uniformly in the dispersion medium, in-plane variation in the amount of light from the light emitting unit 30 can be suppressed. Specific examples of the resin preferably used include a silicone resin, an epoxy resin, and an acrylic resin.

In addition, in order to further suppress in-plane variation in the amount of light from the light emitting unit 30, the light emitting unit 30 may further include, for example, a light dispersing agent in addition to the resin and the quantum dots.

In addition, the light emission part 30 may be comprised by the laminated body of the multiple layers of light emitting layer. In that case, the plurality of light emitting layers may include a plurality of light emitting layers including quantum dots that emit light having different wavelengths. For example, a stacked body of a plurality of light-emitting layers including a first light-emitting layer including quantum dots that emit light having a first wavelength and a second light-emitting layer including quantum dots that emit light having a second wavelength You may comprise the light emission part 30 by.

The recess 13 is closed by the cover member 40. The cover member 40 and the device body 10 are joined. A sealing space 50 is defined by the cover member 40 and the device body 10. The light source 20 and the light emitting unit 30 are sealed in the sealed space 50.

By the way, from the viewpoint of reducing in-plane variation in the amount of light from the light emitting part, it may be preferable to provide the light emitting part with a uniform thickness. However, when the light emitting part having a uniform thickness is provided, the optical path length in the light emitting part of the light incident on the light emitting part is different between the part located immediately above the light source and the other part of the light emitting part. . For example, the incident angle of light to the light emitting unit is perpendicular to the portion of the light emitting unit located immediately above the light source. That is, in the portion located immediately above the light source, the incident angle of light to the light emitting portion is 0 °. Therefore, the optical path length is shortened in the portion located immediately above the light source. The incident angle of light to the light emitting unit increases as the distance from the light source increases in plan view. Therefore, the optical path length increases as the distance from the light source increases in plan view. For this reason, when the light emitting part has a uniform thickness, the optical path length in the light emitting part of the incident light to the light emitting part becomes longer as the distance from the light source in plan view. Therefore, in a plan view, in the portion near the light source in the light emitting unit, the amount of excitation light absorbed by the quantum dots is reduced by the amount of the optical path length, and the amount of light emitted from the quantum dots is also reduced. On the other hand, in the part away from the light source in the light emitting unit, the amount of excitation light absorbed by the quantum dots increases as the optical path length increases, and the amount of light emitted from the quantum dots also increases. For this reason, in a light emitting device that emits mixed light of light from a light source and light emitted from a quantum dot, the color tone of light emitted from the light emitting unit varies depending on the position of the light emitting unit. Specifically, the color tone of light emitted from the light emitting device is different between a portion near the light source and a portion away from the light source in the plan view.

In the light emitting device 1, the thickness of the light emitting unit 30 gradually decreases toward the outside at least at the peripheral portion of the light emitting unit 30. For this reason, the optical path length in the peripheral part of the light emission part 30 is short. Therefore, the difference between the optical path length in the central portion of the light emitting unit 30 and the optical path length in the peripheral portion of the light emitting unit 30 is small. Therefore, the difference between the color tone of the light emitted from the central portion of the light emitting unit 30 and the color tone of the light emitted from the peripheral portion of the light emitting unit 30 is small. Therefore, the color unevenness is small in the light emitting device 1.

From the viewpoint of further reducing the color tone unevenness of the light emitting device 1, it is preferable that the optical path length of the light emitted from the light source in the light emitting unit 30 is substantially constant in any part of the light emitting unit 30. Therefore, for example, as in the present embodiment, it may be preferable that the thickness of the light emitting unit 30 monotonously decreases from the center in a plan view toward the outside.

Hereinafter, another example of the preferred embodiment of the present invention will be described. In the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(Second Embodiment)
FIG. 2 is a schematic cross-sectional view of a light emitting device 1a according to the second embodiment.

In the light emitting device 1 according to the first embodiment, the example in which the thickness of the light emitting unit 30 is preferably monotonously decreasing from the center in plan view to the outside has been described. However, the present invention is not limited to this configuration. For example, as shown in FIG. 2, in the light emitting device 1 a, the thickness of the portion excluding the peripheral portion of the light emitting unit 30 is substantially constant. The thickness of the light emitting portion 30 is gradually reduced toward the outside at the peripheral edge.

In addition, in a part of the light emitting portion, there may be a portion where the thickness increases toward the outside.

(Third embodiment)
FIG. 3 is a schematic cross-sectional view of a light emitting device 1b according to the third embodiment.

1st and 2nd embodiment demonstrated the example in which the light emission part 30 was formed in the surface inside the recessed part 13 of the cover member 40. As shown in FIG. However, the present invention is not limited to this configuration. As shown in FIG. 3, in the light emitting device 1 b, the light emitting unit 30 is provided in the recess 13 so as to block the light source 20. Even in this case, uneven color tone can be reduced by configuring the light emitting unit 30 so that the thickness of the light emitting unit 30 gradually decreases toward the outside at least at the peripheral portion of the light emitting unit 30.

(Fourth embodiment)
FIG. 4 is a schematic cross-sectional view of a light emitting device 1c according to the third embodiment.

As shown in FIG. 4, the light emitting device 1 c includes a cell 60. The cell 60 has a first main wall portion 61, a second main wall portion 62, and a side wall portion 63. The first main wall portion 61 and the second main wall portion 62 are opposed to each other at an interval. The side wall portion 63 is provided between the first main wall portion 61 and the second main wall portion 62. The side wall portion 63 is joined to each of the first and second main wall portions 61 and 62. The side wall portion 63 and the first and second main wall portions 61 and 62 may be joined using, for example, anodic bonding, welding, or an inorganic bonding material.

The first and second main wall portions 61 and 62 can be made of glass, ceramics, or the like, for example. The side wall 63 can be made of, for example, glass, ceramics, metal, a glass material covered with a metal coating layer, a ceramic material, or the like.

The light emitting unit 30 is provided on the inner wall of each of the first and second main wall portions 61 and 62. Specifically, in the present embodiment, it is provided on the inner wall of the first main wall portion 61 located on the opposite side to the light source 20. But the light emission part may be provided on the inner wall of the 2nd main wall part by the side of a light source.

The heat from the light source 20 is not easily transmitted to the light emitting unit 30 by arranging the light emitting unit 30 in the cell 60 separated from the light source 20 as in the present embodiment. Therefore, thermal degradation of the light emitting unit 30 can be suppressed.

(Fifth embodiment)
FIG. 5 is a schematic cross-sectional view of a light emitting device according to a fifth embodiment.

1st and 2nd embodiment demonstrated the example in which the sealing space 50 located between the light source 20 and the light emission part 30 was comprised by the space. However, the present invention is not limited to this configuration.

As illustrated in FIG. 5, in the light emitting device 1 d according to the fifth embodiment, the sealing space 50 is filled with a resin 70. In this case, the refractive index difference between the resin 70 and the light emitting unit 30 and the refractive index difference between the resin 70 and the light source 20 can be reduced. Therefore, the light emission efficiency can be improved.

Resin 70 can be made of, for example, a silicone resin, an epoxy resin, an acrylic resin, or the like.

Resin 70 may contain a light dispersing agent. In this case, the uniformity of light from the light source 20 to the light emitting unit 30 can be further enhanced.

1, 1a, 1b, 1c, 1d Light emitting device 10 Device main body 11 First member 12 Second member 12a Through hole 13 Recess 13a Side wall 13b Bottom wall 20 Light source 30 Light emitting unit 40 Cover member 50 Sealing space 60 Cell 61 First 1 main wall 62 second main wall 70 resin 63 side wall C center line

Claims (6)

A light emitting unit including quantum dots;
A light source that is disposed at a central portion in a plan view of the light emitting unit, and emits light having an excitation wavelength of the quantum dots to the light emitting unit;
With
The light-emitting device in which the thickness of the light-emitting part gradually decreases toward the outside at least at the peripheral part of the light-emitting part. A device body having a recess for accommodating the light source and the light emitting unit;
A cover member that covers the recess and seals the light source and the light emitting unit together with the device body;
With
The light emitting device according to claim 1, wherein the light emitting unit is provided on a surface of the cover member on the concave side. A first main wall,
A second main wall portion facing the first main wall portion at an interval;
A side wall portion connecting the first main wall portion and the second main wall portion;
And further comprising a cell disposed apart from the light source,
The light emitting device according to claim 1, wherein the light emitting unit is provided on the first or second main wall in the cell. The light emitting device according to any one of claims 1 to 3, wherein the light source emits divergent light to the light emitting unit. The light-emitting device according to any one of claims 1 to 4, wherein the light-emitting portion has a larger area than the light source in plan view. The light emitting device according to any one of claims 1 to 5, wherein the light emitting unit emits mixed light of light emission of the quantum dots and light emitted from the light source and transmitted through the light emitting unit.

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