Light emitting device, cell for light emitting device, and method for manufacturing light emitting device

Provided are a long-life light emitting device less likely to degrade luminescence properties over time, a method for manufacturing the same, and a cell for a light emitting device used for the same. A light emitting device 1 includes a cell 10 and a luminescent material encapsulated in the cell 10. The cell 10 includes a pair of glass sheets 12 and 13 and a glass-made fused part 14a. The pair of glass sheets 12 and 13 are disposed to face each other with a space therebetween. The fused part 14a is disposed between respective peripheral portions of the pair of glass sheets 12 and 13. The fused part 14a is fused to each of the pair of glass sheets 12 and 13.

TECHNICAL FIELD

This invention relates to a light emitting device, a cell for a light emitting device used for the same, and a method for manufacturing a light emitting device. Particularly, this invention relates to a light emitting device in which luminescent material particles are encapsulated in an internal space of a cell, a cell for a light emitting device used for the same, and a method for manufacturing a light emitting device in which luminescent material particles are encapsulated in an internal space of a cell.

BACKGROUND ART

In recent years, a light emitting device using a luminescent material made of quantum dots has been proposed in, for example, Patent Literature 1 below. Specifically, Patent Literature 1 proposes a light emitting device (light sheet) in which a film or layer containing quantum dots is disposed on at least a portion of a surface of a waveguide. The light emitting device described in this Patent Literature 1 is a device for emitting, upon irradiation with excitation light, light having a different wavelength from the excitation light.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in the light emitting device described in Patent Literature 1, the luminescence properties thereof cannot be sufficiently prevented from degrading owing to contact between the luminescent material and oxygen and, thus, a problem of ease of time degradation in luminescence properties occurs.

The present invention has been made in view of the above point and an object thereof is to provide a long-life light emitting device less likely to degrade luminescence properties over time, a cell for a light emitting device used for the same, and a method for manufacturing the light emitting device.

Solution to Problem

A light emitting device according to the present invention includes a cell and a luminescent material encapsulated in the cell. The cell includes a pair of glass sheets and a glass-made fused part. The pair of glass sheets are disposed to face each other with a space therebetween. The fused part is disposed between respective peripheral portions of the pair of glass sheets. The fused part is fused to each of the pair of glass sheets.

The luminescent material is preferably formed of an inorganic phosphor. The inorganic phosphor is preferably made of quantum dots.

The light emitting device according to the present invention may further include a glass ribbon disposed between the pair of glass sheets, and the fused part may be formed of at least a portion of the glass ribbon.

Note that the term “glass ribbon” in the present invention means a strip-shaped glass member having a thickness of 1 mm or less. The glass ribbon may be linear or may have a bent or curved shape. The glass ribbon may be in the shape of a picture frame.

The glass ribbon preferably includes a portion unfused to the glass sheets.

The fused part may be formed by melting a bonding agent containing glass powder by heating.

The fused part may include a first portion formed of at least a portion of the glass ribbon disposed between the pair of glass sheets and a second portion formed by melting a bonding agent containing glass powder by heating. In this case, it is preferred that the number of the first portions included in the fused part be at least two, one of the at least two first portions be disposed at one ends of the glass sheets in one direction extending along surfaces of the glass sheets, and the other be disposed at the other ends of the glass sheets in the one direction.

The cell preferably has a through hole formed to communicate with a space in the cell. In this case, a glass-made sealing member is preferably provided which is disposed to close the through hole and fused to the cell.

The sealing member is preferably formed of a glass ribbon.

A cell for a light emitting device according to the present invention pertains to a cell used for a light emitting device including the cell and a luminescent material encapsulated in the cell. The cell for a light emitting device according to the present invention includes a pair of glass sheets and a glass-made fused part. The pair of glass sheets are disposed to face each other with a space therebetween. The fused part is disposed between respective peripheral portions of the pair of glass sheets. The fused part is fused to each of the pair of glass sheets.

A method for manufacturing a light emitting device according to the present invention pertains a method for manufacturing a light emitting device including a cell and a luminescent material encapsulated in the cell. In the method for manufacturing a light emitting device according to the present invention, respective peripheral portions of a pair of glass sheets disposed to face each other with a space therebetween are fused by using glass, thus producing the cell having an encapsulation hole. The luminescent material is encapsulated through the encapsulation hole into the cell.

The cell is preferably produced by placing a glass ribbon between the respective peripheral portions of the pair of glass sheets disposed to face each other with the space therebetween and fusing the glass ribbon to each of the pair of glass sheets.

A portion of the glass ribbon is preferably fused to each of the pair of glass sheets.

The cell may be produced by placing a glass ribbon and a bonding agent containing glass powder between the respective peripheral portions of the pair of glass sheets and fusing each of the glass ribbon and the bonding agent to each of the pair of glass sheets. In this case, it is preferred that at least two glass ribbons be placed between the respective peripheral portions of the pair of glass sheets, one of the at least two glass ribbons be placed at one ends of the pair of glass sheets in one direction extending along surfaces of the glass sheets, and the other be placed at the other ends of the pair of glass sheets in the one direction.

The method for manufacturing a light emitting device according to the present invention preferably further includes the step of placing a glass ribbon to cover the encapsulation hole in the cell containing the luminescent material encapsulated therein and then fusing the glass ribbon to the cell to close the encapsulation hole.

Advantageous Effects of Invention

The present invention can provide a long-life light emitting device less likely to degrade luminescence properties over time, a method for manufacturing the same, and a cell for a light emitting device used for the same.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a description will be given of an exemplary preferred embodiment for working of the present invention. However, the following embodiment is simply illustrative. The present invention is not at all limited to embodiments below.

First Embodiment

FIG. 1is a schematic perspective view of alight emitting device according to a first embodiment.FIG. 2is a schematic plan view of the light emitting device according to the first embodiment.FIG. 3is a schematic cross-sectional view taken along the line III-III inFIG. 2. First with reference toFIGS. 1 to 3, the structure of a light emitting device1according to this embodiment is described.

The light emitting device1is a device for emitting, upon incidence of excitation light, light having a different wavelength from the excitation light. The light emitting device1may be a device for emitting mixed light of excitation light and light produced by irradiation with the excitation light.

The light emitting device1includes a cell10. The cell10has an internal space10a. A luminescent material is encapsulated in the internal space10a. Specifically, encapsulated in the internal space10ais a light emitting part11in which a luminescent material is dispersed in a dispersion medium.

No particular limitation is placed on the type of the luminescent material. Examples of the luminescent material include phosphors, such as, for example, inorganic phosphors and organic phosphors. Of these, the preferred are inorganic phosphors.

Specific examples of the inorganic phosphor which produces a blue visible light (fluorescence having a wavelength of 440 to 480 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm include Sr5(PO4)3Cl:Eu2+and (Sr, Ba) MgAl10O17:Eu2+. Specific examples of the inorganic phosphor which produces a green fluorescence (fluorescence having a wavelength of 500 nm to 540 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm include SrAl2O4:Eu2+and SrGa2S4:Eu2+. Specific examples of the inorganic phosphor which produces a green visible light (fluorescence having a wavelength of 500 nm to 540 nm) upon irradiation with a blue excitation light having a wavelength of 440 to 480 nm include SrAl2O4:Eu2+and SrGa2S4:Eu2+. A specific example of the inorganic phosphor which produces a yellow visible light (fluorescence having a wavelength of 540 nm to 595 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm is ZnS:Eu2+. A specific example of the inorganic phosphor which produces a yellow visible light (fluorescence having a wavelength of 540 nm to 595 nm) upon irradiation with a blue excitation light having a wavelength of 440 to 480 nm is Y3(Al,Gd)5O12:Ce2−. Specific examples of the inorganic phosphor which produces a red visible light (fluorescence having a wavelength of 600 nm to 700 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm include Gd3Ga4O12:Cr3−and CaGa2S4:Mn2+. Specific examples of the inorganic phosphor which produces a red visible light (fluorescence having a wavelength of 600 nm to 700 nm) upon irradiation with a blue excitation light having a wavelength of 440 to 480 nm include Mg2TiO4:Mn4+and K2SiF6:Mn4+. The inorganic phosphors that can be used are those having a particle size of about 5 μm to about 50 μm.

Alternatively, the inorganic phosphor may be quantum dots. The quantum dot emits, upon incidence of excitation light, light having a different wavelength from the excitation light. The wavelength of light emitted from the quantum dot depends upon the particle size of the quantum dot. In other words, the wavelength of light obtained can be controlled by changing the particle size of the quantum dot. Therefore, the particle size of the quantum dot is selected to be a particle size meeting a desired wavelength of light. The quantum dot is generally less likely to be degraded by the contact with oxygen.

Examples of the quantum dot that can be used include those having a particle size of about 2 nm to about 10 nm. Specific examples of the quantum dot which produces a blue visible light (fluorescence having a wavelength of 440 to 480 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm include CdSe nanocrystals having a particle size of about 2.0 nm to about 3.0 nm. Specific examples of the quantum dot which produces a green visible light (fluorescence having a wavelength of 500 nm to 540 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm or a blue light having a wavelength of 440 to 480 nm include CdSe nanocrystals having a particle size of about 3.0 nm to about 3.3 nm. Specific examples of the quantum dot which produces a yellow visible light (fluorescence having a wavelength of 540 nm to 595 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm or a blue light having a wavelength of 440 to 480 nm include CdSe nanocrystals having a particle size of about 3.3 nm to about 4.5 nm. Specific examples of the quantum dot which produces a red visible light (fluorescence having a wavelength of 600 nm to 700 nm) upon irradiation with an ultraviolet to near-ultraviolet excitation light having a wavelength of 300 to 440 nm or a blue light having a wavelength of 440 to 480 nm include CdSe nanocrystals having a particle size of about 4.5 nm to about 10 nm.

A single type or a plurality of types of luminescent materials may be encapsulated in the internal space10adepending upon the wavelength range of the excitation light and which color luminescence to be produced. For example, if a white light having superior color rendition is to be produced by irradiation with an ultraviolet to near-ultraviolet excitation light, respective luminescent materials capable of producing blue, green, and red visible lights by irradiation with the ultraviolet to near-ultraviolet excitation light can be used in combination. Alternatively, if a white light having superior color rendition is to be produced by irradiation with a blue excitation light, respective luminescent materials capable of producing green and red visible lights by irradiation with the blue excitation light can be used in combination.

No particular limitation is placed on the type of the dispersion medium so long as it can suitably disperse the luminescent material. The dispersion medium may be in liquid form or may be made of resin, glass or other materials.

The cell10includes a pair of glass sheets12and13. The pair of glass sheets12and13are disposed to face each other with a space therebetween. The glass sheet12and the glass sheet13are parallel to each other. It is not always necessary that both the glass sheets12and13transmit both of luminescence and excitation light from the luminescent material. However, at least one of the glass sheets12and13needs to transmit luminescence from the luminescent material and at least one of them needs to transmit excitation light of the luminescent material. For example, the glass sheet12may transmit excitation light, whereas the glass sheet13may transmit luminescence.

The glass sheets12and13are preferably those having superior weatherability and less likely to react with the luminescent material and the dispersion medium. The glass sheets12and13can be made of, for example, silicate glass. The glass sheets12and13may be crystallized glass sheets.

No particular limitation is placed on the thickness of the glass sheets12and13but the thickness can be, for example, about 0.5 to about 2.0 mm.

A glass ribbon14is disposed between respective peripheral portions of the glass sheets12and13. Specifically, the glass ribbon14is provided in the shape of a picture frame except for one point on the peripheral portions of the glass sheets12and13.

In this embodiment, at least a portion of the glass ribbon14is fused to each of the glass sheets12and13. This portion of the glass ribbon14fused to the glass sheets12and13constitutes a fused part14a. In other words, in this embodiment, the fused part14ais formed of a portion of the glass ribbon14.

The fused part14ais formed in the shape of a picture frame and the fused part14aand the glass sheets12and13define the internal space10a. The rest of the glass ribbon14other than the fused part14ais not fused to the glass sheets12and13and has the function of a spacer. Thus, the glass ribbon14determines the thickness of the internal space10a.

The materials for the glass ribbon14that can be used are glasses, including silicate glasses, borosilicate glasses, soda-lime glasses, alkali-free glasses, and crystallized glasses. Furthermore, it may be made of a glass of different type from that of the glass sheets12and13but is preferably made of a glass of the same type as that of the glass sheets12and13. Thus, the glass sheets12and13can be equal in coefficient of thermal expansion to the glass ribbon14. Therefore, the deformation of the cell10upon application of heat can be reduced.

The cell10has a through hole10bformed to communicate with the internal space10a. Specifically, the through hole10bis formed in the fused part14a. This through hole10bis used for encapsulating the quantum dots into the internal space10a. The through hole10bis closed by a glass-made sealing member15fused to the cell10. In this embodiment, the sealing member15is formed of a glass ribbon.

As described previously, in this embodiment, the internal space10acontaining a luminescent material encapsulated therein is defined by the glass sheets12and13and the glass-made fused part14a. For this reason, the internal space10ais surrounded by the glass members having high weatherability and low gas permeability. Therefore, degradation due to contact between the luminescent material encapsulated in the internal space10aand oxygen is less likely to occur. Hence, in the case of using, as the luminescent material, particularly quantum dots less likely to cause degradation due to contact with oxygen, the luminescence properties of the light emitting device1of this embodiment become less likely to degrade over time and, therefore, the light emitting device1has a long life. In addition, in this embodiment, the sealing member15is also made of glass. Therefore, the contact between the luminescent material and oxygen can be more effectively prevented. Hence, the light emitting device can achieve a longer life.

Furthermore, since the cell10is made of glass and has high thermal resistance, the cell10is less likely to be deformed or degraded by heat from, for example, a light source, such as an LED, for emitting excitation light to the light emitting device1.

Moreover, since the fused part14ais formed of the glass ribbon14, the thickness of the internal space10acan be accurately controlled to a desired thickness. Therefore, thickness variations of the internal space10acan be reduced to reduce in-plane variations in luminescence properties. Particularly in this embodiment, the glass ribbon14is partly not fused to the glass sheets12and13. Therefore, thickness variations of the internal space10acan be more effectively reduced to more effectively reduce in-plane variations in luminescence properties.

Next, a description is given of an example of a manufacturing method of the light emitting device1according to this embodiment. However, the following manufacturing method is simply illustrative and the manufacturing method of the light emitting device according to the present invention is not at all limited to the following manufacturing method.

First, a glass sheet13is prepared. Next, as shown inFIG. 4, a glass ribbon14is placed on a peripheral portion of the glass sheet13. Specifically, this embodiment describes an example in which four linear glass ribbons14are placed but, alternatively, two L-shaped glass ribbons may be placed or a single glass ribbon in the shape of a picture frame may be placed. As shown inFIG. 8, the glass sheet13may be square. In this case, the four glass ribbons14can be the same length. Thus, glass ribbons14of a single type only have to be prepared, which simplifies the manufacturing process of the cell10. Note that in the example shown inFIG. 8the length of each side of the glass sheet13is approximately equal to the sum of the length and width of the glass ribbon14.

Next, the glass sheet13is laid on a glass sheet12with the glass ribbon(s)14between them. Thereafter, the glass ribbon14and at least one of the glass sheets12and13are heated by irradiating a portion to be formed into a fused part14awith a laser, such as for example a CO2laser, causing a portion of the glass ribbon14to be fused to the glass sheets12and13. Thus, a cell10is produced. In short, in this embodiment, a glass ribbon14is placed between respective peripheral portions of a pair of glass sheets12and13disposed to face each other with a space therebetween and only a portion of the glass ribbon14is fused to each of the glass sheets12and13to produce a cell10.

Next, a luminescent material is encapsulated through the through hole10binto the internal space10a. Although no particular limitation is placed on the method for encapsulating the luminescent material, an example is a method of supplying, with the internal space10aput in a pressure-reduced atmosphere, a liquid containing a luminescent material dispersed therein to the internal space10a.

Finally, a sealing member15formed of a glass ribbon is placed to cover the through hole (encapsulation hole)10band irradiated with a laser to fuse the sealing member15to the cell10, resulting in closure of the through hole10b. Through the above steps, a light emitting device1can be manufactured.

By following the above manufacturing method of this embodiment, a light emitting device having a long life can be suitably manufactured.

Furthermore, since the fused part14ais formed using a glass ribbon14with a small thickness, local heat application can be easily implemented, such as with a laser, so that a cell10made of glass can be easily manufactured. In addition, with the use of a glass ribbon14, the residual strain of the cell10can be small.

Moreover, since only a portion of the glass ribbon1is fused to the glass sheets12and13, the distance between the glass sheets12and13is held by the glass ribbon14. Therefore, there is no need to provide, in the fusing step, another member for holding the distance between the glass sheets12and13, so that the distance between the glass sheets12and13can be easily held constant.

Since, likewise, the sealing member1is formed using a glass ribbon, the sealing member15can also be easily formed. Furthermore, since the sealing member15can be formed by local heat application with a laser, the thermal degradation of the luminescent material in the internal space10acan be reduced in the step of forming the sealing member15. Therefore, a light emitting device1having a high luminous efficiency can be manufactured.

Hereinafter, a description will be given of another exemplary preferred embodiment for working of the present invention. In the following description, elements having substantially the same functions as those in the first embodiment are referred to by the common references and further explanation thereof will be omitted.

Second Embodiment

FIG. 5is a schematic perspective view of alight emitting device according to a second embodiment.FIG. 6is a schematic plan view of the light emitting device according to the second embodiment.

The first embodiment above has described an example in which the fused part14ais formed of the glass ribbon14placed between the glass sheets12and13. In contrast, in this embodiment, the fused part14ais formed by melting a bonding agent containing glass powder by heating.

In manufacturing the light emitting device of this embodiment, instead of placing a glass ribbon14on a glass sheet13, a bonding agent16is placed on it as shown inFIG. 7. In the case of a bonding agent16in paste form, the bonding agent16is placed by application. Thereafter, a glass sheet12is laid on the glass sheet13and the bonding agent16is heated, such as using a laser, to soften it, resulting in the formation of a fused part14a.

Examples of the glass powder contained in the bonding agent16include, for example, glass powders of tin phosphate glasses and glass powders of bismuth-based glasses. The glass powder may contain a light-absorbing material. The bonding agent16may contain ceramic powder. Examples of the ceramic powder contained in the bonding agent16include, for example, ceramic powders of alumina, titania and zirconia. The bonding agent16may contain, instead of or in addition to glass powder or ceramic powder, for example, carbon.

In the case where a bonding agent16containing glass powder is used to place it on a peripheral portion of the glass sheet13and form a fused part14a, the provision of a through hole10bin the inner surface of the glass sheet12enables the luminescent material to be supplied to the internal space10aof the cell10.

Third Embodiment

FIG. 9is a schematic plan view of alight emitting device according to a third embodiment.

The first embodiment above has described an example in which the fused part14ais formed of the glass ribbon14placed between the glass sheets12and13. The second embodiment above has described an example in which the fused part14ais formed by melting a bonding agent16containing glass powder by heating.

Unlike the above embodiments, in this embodiment, the fused part14aincludes: two first portions14a1and14a2each formed of at least a portion of a glass ribbon14; and two second portions14a3and14a4each formed by melting a bonding agent16containing glass powder by heating.

The first portion14a1is disposed at an x1-side end of the glass sheet12in one direction x extending along the surface of the glass sheet12. On the other hand, the first portion14a2is disposed at an x2-side end of the glass sheet12in the direction x. Therefore, the thickness of the internal space10acan be accurately controlled to a desired thickness. Hence, a light emitting device having a desired luminescence intensity can be obtained. Furthermore, thickness variations of the internal space10acan be reduced to reduce in-plane variations in luminescence intensity. From the viewpoint of reducing variations, the first portion14a1and the first portion14a2should preferably be opposed to each other.

The light emitting device of this embodiment can be manufactured, for example, in the following manner. First, as shown inFIG. 10, glass ribbons14and a bonding agent16are placed on a glass sheet13. Thereafter, a glass sheet12is laid on the glass sheet13with the glass ribbons14and the bonding agent16between them. Next, at least portions of the glass ribbons14and the bonding agent16are heated, such as using a laser, to soften them, causing each of the glass ribbons14and the bonding agent16to be fused to the glass sheets12and13. Thus, a fused part14ais formed.

The third embodiment has described an example in which the fused part14aincludes the two first portions14a1and14a2and the two second portions14a3and14a4. However, the present invention is not limited to this configuration. The fused part may include a single first portion and a single second portion or may include three or more first portions and/or three or more second portions.

Furthermore, in the case where the fused part includes the two first portions, the first portions do not always have to be opposed to each other.

REFERENCE SIGNS LIST