Light-emitting device and manufacturing method thereof

A light-emitting device of the present invention includes: a light-emitting element; and a phosphor layer containing phosphors that absorb light from the light-emitting element and wavelength-convert the absorbed light to emit light. The phosphor layer has a structure in which the phosphors are disposed on an applied adhesive with a thickness equal to or less than an average particle size of the phosphors. A thickness of the phosphor layer is equal to or less than five times the average particle size of the phosphors, and an occupancy ratio of the phosphors in the phosphor layer is 50% or more. Further, the phosphors disposed on the adhesive has an adjusted particle size.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device emitting white light with reduced tone unevenness, which is used as, for example, an illumination light source, a light source of a backlight of a liquid crystal display, and relates to a manufacturing method thereof.

2. Description of the Related Art

In recent years, a light-emitting device has been developed which emits white light having a wide emission wavelength interval by combining a light-emitting element which emits ultraviolet light or blue light and phosphors which absorb the light from the light-emitting element and wavelength-converts the absorbed light to emit long-wavelength light. Since such a light-emitting device is used as, for example, an illumination light source, a light source of a backlight of a liquid crystal display, and the like, it is very important to reduce tone unevenness of light emitted from the light-emitting device to improve its color rendering property.

Japanese Patent Application Laid-open No. 2003-115614 discloses a light-emitting device art of forming a phosphor layer containing phosphors which are uniformly dispersed on a light-emitting element by spraying a coating solution containing the phosphors to the light-emitting element with a spray or a dispenser. This Japanese Patent Application Laid-open No. 2003-115614 realizes reduced tone unevenness since light emitted from the light-emitting element to the phosphor layer is uniformly wavelength-converted.

Japanese Patent Application Laid-open No. 2003-115614 discloses a light-emitting device art reducing tone unevenness by realizing uniform distribution of phosphors owing to a phosphor layer with a constant thickness which is formed by spraying the phosphors from above an adhesive layer absorbing irregularities of a light-emitting element and its appendix after forming the adhesive layer by applying an adhesive (epoxy resin with a thickness used as the adhesive) on the light-emitting element.

Japanese Patent Application Laid-open No. 2001-127346 discloses a light-emitting device art realizing a higher color rendering property by disposing, on a light-emitting element, a layer formed of transparent resin in which two kinds or more of phosphors performing different kinds of wavelength conversion are dispersed, and mixing light from the light-emitting element and lights wavelength-converted by the phosphors.

SUMMARY OF THE INVENTION

However, in the light-emitting device art described in the aforesaid Japanese Patent Application Laid-open No. 2003-115614, a thickness of the phosphor layer formed at a time when the coating solution containing the phosphors is applied on the light-emitting element is, for example, about 20 μm or more, which is larger than an average particle size of typical phosphors. Therefore, the phosphors settle in the coating solution before the coating solution cures, resulting in uneven distribution of the phosphors in the phosphor layer. Further, since the phosphors are dispersed in the coating solution for use, surface tension unique to liquid occurs in the coating solution applied on the light-emitting element, and due to an influence of the surface tension, thickness variation occurs in the phosphor layer, and this also causes uneven distribution of the phosphors. Due to such uneven distribution of the phosphors, an amount of wavelength conversion of light from the light-emitting element varies depending on light emission directions, resulting in uneven tone and a decreased color rendering property of light emitted by the light-emitting device.

In the light-emitting device art described in the aforesaid Japanese Patent Application Laid-open No. 2003-115614, before the adhesive cures, the phosphors are sprayed to the adhesive layer provided on the light-emitting element by using gas, and therefore, the adhesive deforms due to the pressure of the gas, resulting in thickness variation of the adhesive layer. Especially because the adhesive layer has a predetermined thickness or more so as to absorb the irregularities of the light-emitting element and its appendix, thickness variation of the adhesive layer easily occurs. Accordingly, shape variation of the phosphor layer formed on the adhesive layer also occurs and thus the distribution of the contained phosphors becomes uneven, resulting in uneven tone and a decreased color rendering property of the light emitted by the light-emitting device.

In the light-emitting device art described in the aforesaid Japanese Patent Application Laid-open No. 2001-127346, since the phosphors are dispersed in the resin layer for use, the phosphors settle in the resin layer to be unevenly distributed in the resin layer, resulting in uneven tone and a decreased color rendering property of the light emitted by the light-emitting device, as is the case in Japanese Patent Application Laid-open No. 2003-115614.

The present invention was made in view of the above-described problems, and its object is to provide a light-emitting device realizing reduced tone unevenness and an improved color rendering property, and to provide a manufacturing method thereof.

To solve the above problems, according to the present invention, there is provided a light-emitting device including: a light-emitting element; and a phosphor layer containing phosphors that absorb light from the light-emitting element and wavelength-convert the absorbed light to emit light, wherein a difference between a maximum thickness and a minimum thickness of the phosphor layer is equal to or less than two times an average particle size of the phosphors, and an occupancy ratio of the phosphors in the phosphor layer is 50% or more.

In the above light-emitting device, the phosphor layer is composed of a plurality of phosphor layers containing different phosphors, and the difference between the maximum thickness and the minimum thickness of the phosphor layer closest to the light-emitting element, among the plural phosphor layers, may be equal to or less than two times the average particle size of the phosphors contained in the phosphor layer closest to the light-emitting element.

In the above light-emitting device, a thickness of the phosphor layer may be equal to or less than five times the average particle size of the phosphors.

In the above light-emitting device, the phosphor layer may be composed of one or more stacked phosphor forming layers in which the phosphors are disposed on an adhesive whose thickness is equal to or less than the average particle size of the phosphors.

In the above light-emitting device, the occupancy ratio in the phosphor forming layer farthest from the light-emitting element, among the one or more phosphor forming layers, may be 50% or less.

In the above light-emitting device, the phosphors may have an adjusted particle size.

In the above light-emitting device, the phosphor layer may be stacked in one layer or more on a light-emitting surface of the light-emitting element.

According to another aspect of the present invention, there is provided a light-emitting device emitting light, a difference between maximum color temperature and minimum color temperature of the light in a half power angle being 250 K or less and an average color rendering index of the light being 90 or more.

According to another aspect of the present invention, there is provided a manufacturing method of a light-emitting device including: a light-emitting element; and a phosphor layer containing phosphors that absorb light from the light-emitting element and wavelength-convert the absorbed light to emit light, the method including: forming the phosphor layer directly or via an intermediate layer on a light-emitting surface of the light-emitting element so as to cover the light-emitting surface of the light-emitting element, a difference between a maximum thickness and a minimum thickness of the phosphor layer being equal to or less than two times an average particle size of the phosphors and an occupancy ratio of the phosphors contained in the phosphor layer being 50% or more.

In the above manufacturing method of the light-emitting device, the phosphor layer may be formed to have a thickness that is equal to or less than five times the average particle size of the phosphors.

In the above manufacturing method of the light-emitting device, in forming the phosphor layer, a step of forming a phosphor forming layer may be performed until desired color temperature is obtained from the phosphor layer, the step of forming the phosphor forming layer being a step in which an adhesive with a thickness equal to or less than the average particle size of the phosphors is applied on a surface for stacking, and the phosphors are disposed on the applied adhesive to form the phosphor forming layer.

In the above manufacturing method of the light-emitting device, in forming the phosphor layer, the color temperature of the phosphors in the phosphor layer may be adjusted by setting an occupancy ratio of the phosphors in the phosphor forming layer formed last to 50% or less.

In the above manufacturing method of the light-emitting device, in applying the adhesive, viscosity of the adhesive may be lowered.

In the above manufacturing method of the light-emitting device, in disposing the phosphors, a particle size of the phosphors to be disposed may be adjusted.

According to the present invention, since the sedimentation of the phosphors in the phosphor forming layer can be prevented, the phosphors can be uniformly distributed in the phosphor layer. This makes it possible to provide a light-emitting device emitting light with reduced tone unevenness and an improved color rendering property, and to provide a manufacturing method thereof.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In the specification and the drawings, the same reference numerals and symbols are used to designate substantially the same constituent elements, and redundant description thereof will be omitted.

FIG. 1is a view showing the whole structure of a light-emitting element1according to a first embodiment of the present invention.FIG. 2is an enlarged view showing, in an enlarged manner, a light-emitting element5included in the light-emitting device1shown inFIG. 1.FIG. 3is an enlarged view showing, in an enlarged manner, a phosphor layer10and a phosphor layer11formed on the light-emitting element5shown inFIG. 2.

As shown inFIG. 1, the light-emitting device1according to the embodiment of the present invention has a structure in which, for example, a LED emitting blue light is mounted as the light-emitting element5on a substrate2in a flat plate shape. A sidewall3formed in a ring shape so as to surround the periphery of the light-emitting element5is provided on the substrate2. External electrodes6supplied with power from an external power source (not shown) are provided on the substrate2. The external electrodes6are connected to the light-emitting element5via lead wires7.

As shown inFIG. 1andFIG. 2, two kinds of phosphor layers10,11each having a thickness of, for example, not less than a 20 μm nor more than 50 μm are provided in sequence on the light-emitting element5so as to cover an upper surface and side surfaces, which are light-emitting surfaces, of the light-emitting element5. The term “light-emitting surfaces” means light exit surfaces, of the light-emitting element5, which serve as light sources radiating light to an area around the light-emitting device1, and in the case of the light-emitting element5shown inFIG. 1, since the light-emitting element is disposed on the substrate2, the upper surface and the side surfaces except a bottom surface are the light-emitting surfaces. The expression “cover the light-emitting surfaces” of the light-emitting element5by using the phosphor layer10and so on is used in the following two meanings: “the phosphor layer10etc. are disposed directly on the light-emitting surfaces of the light-emitting element5to cover the light-emitting surfaces” and “the phosphor layer10etc. are disposed above the light-emitting surfaces of the light-emitting element5via an intermediate layer, a space, or the like without being in direct contact with the light-emitting surfaces to cover the light-emitting surfaces.

A sealing member12such as, for example, transparent resin is filled from above the phosphor layers10,11into a recessed portion formed by the sidewall3formed in the ring shape and the substrate2to confine the light-emitting element5. As shown inFIG. 3, the phosphor layer10is composed of three phosphor forming layers10ato10cwhich are stacked in this order from the bottom on the light-emitting element5. The phosphor layer11is composed of three phosphor forming layers11ato11cwhich are stacked in this order from the bottom on the phosphor layer10(that is, the phosphor forming layer10c). Here, a difference between the maximum thickness and the minimum thickness of the phosphor layer10is set equal to or less than two times an average particle size of phosphors20contained in the phosphor layer10. Likewise, a difference between the maximum thickness and the minimum thickness of the phosphor layer11is set equal to or less than two times an average particle size of phosphors25contained in the phosphor layer11. In this specification, the average particle sizes of the phosphors20,25are measured in the following manner. The phosphor layer of the light-emitting device1is cut, its cross section is photographed by a scanning electron microscope (SEM), the longest diameter value of each particle of the phosphors20,25is measured based on an obtained SEM photograph, and an average diameter value of the particles whose longest diameter values are 1 μm or more is calculated.

The phosphor forming layer10ais formed such that the phosphors20whose average particle size is, for example, 7 μm are fixed to an adhesive21applied to, for example, a 5 μm thickness smaller than the average particle size of the phosphors20. An occupancy ratio of the phosphors20in the phosphor forming layer10ais set to 60% or more. Here, the term “occupancy ratio” will be explained. The term “occupancy ratio” used in this specification means a ratio of an area occupied by phosphors included in a cross section of a cut phosphor layer or phosphor forming layer of the light-emitting device1relative to the total area of the cross section. In measuring an occupancy ratio of phosphors in a phosphor layer or a phosphor forming layer, the occupancy ratio is calculated based on a photograph of the cut light-emitting device1, as in measuring the average particle size of phosphors described above. The higher a ratio of a volume of the phosphors to the total volume of the phosphor layer (that is, a filling factor) is, the higher the calculated occupancy ratio of the phosphor layer is.

The phosphor forming layers10b,10chave the same structure as that of the phosphor forming layer10a. Since the filling factors of the phosphors20contained in the phosphor forming layers10ato10care high, that is, since the occupancy ratios of the phosphors in the cross sections of the phosphor forming layers10ato10care all set to 60% or more, the occupancy ratio of the phosphors20in the phosphor layer10is 60% or more. Similarly to the phosphor forming layer10a, the phosphor forming layer11ais formed such that the phosphors25, of a different type from the phosphors20, whose average particle size is, for example, 10 μm are fixed to an adhesive26applied to, for example, a 5 μm thickness smaller than the average particle size of the phosphors25. The phosphor forming layers11b,11care formed in the same manner as the phosphor forming layer11a. Since the occupancy ratios of the phosphors25in the phosphor forming layers11ato11care all set to 60% or more, the occupancy ratio of the phosphors25in the phosphor layer11is 60% or more.

In this embodiment, as the phosphors20, used are phosphors which absorb blue light emitted by the light-emitting element5and wavelength-convert the absorbed light to emit red light. As the phosphors25, used are phosphors which absorb blue light emitted by the light-emitting element5and wavelength-convert the absorbed light to emit green light. When two kinds or more of the phosphors20,25are thus disposed, the phosphors20,25are disposed so as to prevent light that the phosphors20contained in the phosphor layer10on a side closer to the light-emitting element5(that is, on an inner side) emit after wavelength-converting the absorbed light from being further wavelength-converted by the phosphors25of another kind contained in the phosphor layer11on a side farther from the light-emitting element5(that is, on an outer side). Consequently, tone adjustment can be easily made and the light-emitting element can have high emission efficiency.

Concretely, in this embodiment, for example, a wavelength of red light emitted by the phosphors20disposed in the phosphor layer10closer to the light-emitting element5does not fall in a wavelength range (energy range) that the phosphors25disposed in the phosphor layer11farther from the light-emitting element5absorb in order to emit green light, and therefore, the red light from the phosphors20on a lower layer has no risk of being absorbed and wavelength-converted by the phosphors25on an upper layer. In this manner, by disposing the phosphors20emitting light with a longer wavelength on a side closer to the light-emitting element5(that is, on an inner side) and disposing the phosphors25absorbing light with a shorter wavelength on a side farther from the light-emitting element5(that is, on an outer side), it is possible to prevent a decrease in emission power ascribable to repeated wavelength conversion by two kinds or more of the phosphors20,25.

Next, a manufacturing method according to an embodiment of the present invention for manufacturing the light-emitting device1as structured above will be described by usingFIG. 4.FIG. 4is a flowchart showing the whole procedure of the manufacturing method according to the embodiment of the present invention.

As shown inFIG. 4, at the start of the manufacture of the light-emitting device1(Step0), the light-emitting element5is first disposed on the substrate2by using, for example, solder or conductive paste (Step1). Next, the lead wires7are connected to the light-emitting element5and the external electrodes6by using, for example, an ultrasonic bonding method or a pressure bonding method (Step2). Thereafter, layers including the phosphor layers10,11are formed in a predetermined sequence on the light-emitting element5so as to cover the light-emitting surfaces of the light-emitting element5(Step3). In this embodiment, as shown inFIG. 1andFIG. 2, the two different phosphor layers10,11are sequentially formed in stack on the light-emitting element5. After the formation of the phosphor layers10,11is finished, the sealing member12such as, for example, transparent resin is filled from above the phosphor layer11into the recessed portion formed by the sidewall3formed in the ring shape and the substrate2to confine the light-emitting element5together with the phosphor layers10,11(Step4). Through Step0to Step4described above, the manufacture of the light-emitting device1is completed (Step5).

The following will describe in detail the procedure for forming the phosphor layers10,11in forming the various layers at Step3. In this embodiment, the phosphor layers10,11are formed in sequence on the light-emitting surfaces of the light-emitting element5.FIG. 5is a flowchart showing the procedure for forming the phosphor layers10,11at Step3. In the following description, the phosphor layer10formed directly on the light-emitting element5will be taken as an example.

As shown inFIG. 5, when the formation of the phosphor layer10is started (Step10), the adhesive21such as, for example, silicon or epoxy is applied on the light-emitting element5, which is a surface for stacking, by, for example, a dispense method or a spray method (Step11).FIG. 6andFIG. 7are explanatory views showing the procedure for applying the adhesive21on the light-emitting element5by the dispense method at Step10.

At the time of the application of the adhesive21, the upper surface and the side surfaces as the light-emitting surfaces of the light-emitting element5on which the adhesive21is to be applied are heated by a heater30disposed under the light-emitting element5and the substrate2, as shown inFIG. 6. The adhesive21discharged from a needle-shaped discharge port31is heated on thus heated light-emitting surfaces to decrease in viscosity, and is distributed on the light-emitting surfaces of the light-emitting element5to have a uniform thickness owing to a reduced influence of surface tension, as shown inFIG. 7. Consequently, thickness variation of the adhesive21is prevented because the adhesive21does not rise on the light-emitting surfaces of the light-emitting element5due to surface tension. As a result, the thickness of the adhesive21applied on the surface for stacking becomes equal to or less than the average particle size of the phosphors20sprayed to the adhesive21at Step12which will be described later.

While the adhesive21applied on the light-emitting surfaces of the light-emitting element5at Step11is kept viscous, the phosphors20are sprayed to the applied adhesive21(Step12) to be disposed on the whole light-emitting surfaces of the light-emitting element5.FIG. 8shows the procedure for spraying the phosphors20to the applied adhesive21in a case where compressed gas is used, as an example.

As shown inFIG. 8, a nozzle35spraying the phosphors20is disposed at an upper position facing the light-emitting surfaces of the light-emitting element5. A cartridge36supplying the phosphors20to be sprayed is connected to the nozzle35via a pipe37. A storage part40storing the compressed gas such as, for example, air, nitrogen, or argon is further connected to the nozzle35via a pipe41. A pressure adjusting device42and an opening/closing valve43which adjust a flow rate and the like of the compressed gas sent from the storage part40are attached to the pipe41. With this structure, the phosphors20supplied from the cartridge36are ejected from the nozzle35with the assist of the compressed gas whose ejection amount has been adjusted by the pressure adjusting device42and the opening/closing valve43, and the phosphors20are sprayed to the adhesive21applied on the light-emitting surfaces of the light-emitting element5.

In this embodiment, a sieve (not shown) is provided in the nozzle35, so that only the phosphors20whose particle size is equal to or less than a predetermined value can be ejected from the nozzle35. In this manner, the particle size of the phosphors20sprayed to the applied adhesive21from the nozzle35is adjusted.

The adhesive21on which the phosphors20are disposed is heated, for example, at 200° C. for one minute and is temporarily cured (Step13). Through Steps11to13described above, the phosphor forming layer10ais formed on the light-emitting surfaces of the light-emitting element5.

In order to determine whether or not desired light emission is obtained from the phosphor forming layer10aformed on the light-emitting surfaces of the light-emitting element5, color temperature of the light-emitting device1is measured (Step14).FIG. 9is an explanatory view showing a tone unevenness measuring device70, as an example of a method of measuring the color temperature of the light-emitting device1. As shown inFIG. 9, a detector46detecting light is disposed at a position facing the light-emitting device1. In this embodiment, the distance between the light-emitting device1and the detector46is set to 1.5 m. The detector46is connected to a spectroscope48via an optical fiber47. The external electrodes6of the light-emitting device1as an object to be measured are connected to positive and negative electrodes of a power source50via wiring lines49and are supplied with power, and the measurement is conducted while the light-emitting device1is emitting light.

The measurement of the color temperature is conducted while the light-emitting device1as an object to be measured is rotated rightward and leftward in the same vertical plane (paper surface ofFIG. 9) from the position shown inFIG. 9. As shown inFIG. 9, the position of the light-emitting device1when light radiated therefrom in a direction perpendicular to an upper surface of the substrate can be measured is defined as angle 90°. The position of the light-emitting device1rotated rightward by 90 degrees is 0°. The position of the light-emitting device1rotated leftward by 90 degrees is 180°. Generally, luminance of a light-emitting device is low when the light-emitting device is at the 0° position, and the luminance increases as the position of the light-emitting device gets closer to 90° from 0°, and decreases again as the position gets closer to 180° from 90°.

Light detected by the detector46is sent to the spectroscope48via the optical fiber47. The spectroscope48spectrum-analyzes the light detected by the detector46, and luminance and correlated color temperature of the light-emitting device1are measured based on the analysis results.

If the measurement results obtained at Step14show that the desired light emission is obtained from the light-emitting device1on which the phosphor forming layer10ais formed (Yes at Step15), the formation of the phosphor layer10is completed (Step16). On the other hand, if the desired light emission is not obtained (No at Step15), the process returns to Step11, and Steps11to13are repeated to stack the new phosphor forming layer10b.FIG. 10toFIG. 12are explanatory views showing the procedure for stacking the new phosphor forming layer10b. Concretely, the adhesive21is applied on the phosphor forming layer10aas a surface for stacking, which is shown inFIG. 10, formed on the light-emitting surfaces of the light-emitting element5, as shown inFIG. 11. Then, as shown inFIG. 12, the phosphors20are sprayed to and disposed on the adhesive21applied on the phosphor forming layer10a, and thereafter, the adhesive21is temporarily cured, whereby the new phosphor forming layer10bis formed.

In order to determine whether or not the desired light emission is realized in the light-emitting device1by the phosphor forming layers10a,10bwhich are stacked as a result of the repetition of Steps11to13, color temperature of the light-emitting device1is measured (Step14). If the measurement results show that the desired light emission is obtained (Yes at Step15), the formation of the phosphor layer10is completed (Step16). On the other hand, if the desired light emission is not obtained (No at Step15), the process returns to Step11, and Steps11to13are repeated. In the above-described manner, Steps11to15are repeated as the formation step of forming the phosphor forming layer, thereby stacking the phosphor forming layers10a,10b, . . . until the desired light emission is realized in the light-emitting device1, and the formation of the phosphor layer10is completed (Step16). In this embodiment, the phosphor layer10in which the three phosphor forming layers10ato10care stacked is formed as shown inFIG. 3, so that the desired light emission is realized by the phosphor layer10. By thus stacking the phosphor forming layers10ato10c, it is possible to form the phosphor layer10with a very small thickness and to set the difference between the maximum thickness and the minimum thickness of the phosphor layer10equal to or less than two times the average particle size of the phosphors20. An average thickness of the phosphor layer10formed by stacking the phosphor forming layers (10a,10b, . . . ) is preferably set equal to or less than five times the average particle size of the phosphors20contained therein.

In this embodiment, the occupancy ratios of the phosphors20in the phosphor forming layers (10a,10b, . . . ) are all set to 60% or more, so that the occupancy ratio of the phosphors20in the phosphor layer10composed of the phosphor forming layers (10a,10b, . . . ) is set to 60% or more. At the time of the adjustment of the color temperature of the light-emitting device1, by adjusting the occupancy ratio of the phosphors20in the phosphor forming layer that is the farthest from the light-emitting element5and formed last to 50% or less, it is possible to finely adjust the color temperature. For example, if the phosphor layer10is composed of four phosphor forming layers10ato10d(10dis not shown), by setting the occupancy ratios of the phosphors20in the three phosphor forming layers10ato10cstacked closer to the light-emitting element5to 60% or more and setting the occupancy ratio of the phosphors20in the phosphor forming layer10dwhich is formed last on these three layers (10ato10c) to 5%, it is possible to change the color temperature in a 100 K unit. At this time, the occupancy ratio of the phosphors20in the phosphor layer10is about 50%.

The above example describes the phosphor layer10which is formed in stack directly on the light-emitting surfaces of the light-emitting element5, but the same procedure is followed for forming the phosphor layer11in stack on the phosphor layer10which is a surface for stacking, after the phosphor layer10is formed. Further, in this embodiment, the adhesive26used when the phosphor layer11is formed is the same as the adhesive21used when the phosphor layer10is formed, but may be different from the adhesive21.

In a conventional method, if phosphors contained in resin has a high filling factor, that is, if the phosphors are mixed in the resin so as to enable the formation of a phosphor layer in which an occupancy ratio of the phosphors is 50% or more, the resin having the phosphors mixed therein becomes in a sticky sand form and cling to a needle, which makes it difficult to discharge the resin from a dispenser. In this case, a lump of a large amount of phosphors is applied, and thus the phosphor layer cannot be thinned and has a thickness of several hundreds μm. Though the phosphors can be transferred like a stamp, a difference between the maximum thickness and the minimum thickness of the phosphor layer becomes great.

On the other hand, according to the embodiment described above, a phosphor layer with a high filling factor of phosphors, that is, with a 50% occupancy ratio or more of the phosphors can be formed, and the phosphor layer with a very small thickness can be formed. Concretely, it is possible to set the color temperature to an aimed value even when the thickness of the phosphor layer is set equal to less than five times the average particle size. Consequently, a difference between the maximum thickness and the minimum thickness of the phosphor layer (thickness variation) can be reduced to a small value. Further, more uniform distribution of the phosphors20in the phosphor layer10can be realized. In particular, it is more effective if the difference between the maximum thickness and the minimum thickness in the phosphor layer10is reduced to a value equal to or less than two times the average particle size of the phosphors20. Owing to the reduced thickness variation of the phosphor layer and the uniform distribution of the phosphors, lights radiated in respective emission directions from the light-emitting element5to the phosphor layer10can be uniformly wavelength-converted. Consequently, it is possible to provide the light-emitting device1emitting light with reduced tone unevenness and an improved color rendering property, and to provide the manufacturing method thereof.

Since the phosphor layer10has the structure in which the phosphor forming layers10ato10care stacked in one layer or more, it is possible to adjust the distribution of the phosphors20in the phosphor layer10in a unit of a phosphor forming layer whose thickness is equal to the average particle size of the phosphors20, which enables more uniform distribution of the phosphors20in the phosphor layer10. In particular, since each of the phosphor forming layers10ato10chas the structure in which the phosphors20are disposed on the adhesive21whose thickness is equal to or less than the average particle size of the phosphors20, the phosphors20does not settle in the thickness direction of each of the phosphor forming layers10ato10c, realizing more uniform distribution of the phosphors20in the phosphor layer10in the thickness direction than has been conventionally realized and thus making it possible to increase a filling factor of the phosphors20.

Further, since the adhesive21, when applied on a surface for stacking, is heated to decrease in viscosity and is distributed uniformly on the surface for stacking, the thickness of the phosphor forming layers10ato10ccan be more uniform and the phosphors20can be distributed more uniformly in the phosphor layer10.

Further, since the adhesive21is diluted by a solvent to decrease in viscosity and is uniformly distributed on the surface for stacking, it is possible to make the thickness of the phosphor forming layers10ato10cmore uniform, enabling more uniform distribution of the phosphors20in the phosphor layer10.

Further, in the process of forming the phosphor layer10, color temperature of the light-emitting device1is measured every time each of the phosphor forming layers10ato10cforming the phosphor layer10is formed, and accordingly, the color temperature of the phosphor layer10of the light-emitting device1can be adjusted to a desired value. In particular, by adjusting an amount of the phosphors contained in one phosphor forming layer, it is possible to finely adjust the color temperature, enabling the adjustment of the color temperature in a 100 K unit. This enables the manufacture of the light-emitting device1whose phosphor layer10can realize light emission which is closer to desired light emission than in a conventional light-emitting device.

Further, since the particle size of the phosphors20contained in the phosphor layer10is adjusted to, for example, a predetermined value or less, it can be prevented that a portion to which large particles adhere is left as thickness unevenness, and each of the phosphor forming layers10ato10cforming the phosphor layer10can have more uniform thickness. Because the phosphor layer has the structure in which the phosphor forming layers are stacked, thickness variation of the phosphor layer causing a difference in color temperature of the light-emitting device1can be reduced to a value equal to or less than two times the average particle size of the contained phosphors, resulting in further reduced tone unevenness and improved color rendering property.

As another example of the first embodiment of the present invention, electrostatic attraction may be used when the phosphors20are disposed on the light-emitting surfaces of the light-emitting element5on which the adhesive21is applied, as shown inFIG. 13. InFIG. 13, both electrodes of a power source55capable of applying high voltage are connected to the substrate2and the cartridge36which supplies the phosphors20to the nozzle35. A voltage pattern applied between the substrate2and the cartridge36is controlled by a voltage control device56connected to the power source55. With this structure, the phosphors20in the cartridge36can be negatively charged to be electrostatically attracted to the adhesive21on the positively charged substrate2side via the nozzle35.

As a second embodiment of the present invention, the number of phosphor layers disposed so as to cover light-emitting surfaces of a light-emitting element5may be three or more, as shown inFIG. 14. In the case shown inFIG. 14, three kinds of phosphor layers10,11,60are provided on the light-emitting element5. The phosphor layer60is formed in the same manner as the phosphor layers10,11. The phosphor layer60contains phosphors101emitting, for example, blue light. In the second embodiment, a LED emitting ultraviolet light is used as the light-emitting element5. The second embodiment of the present invention have the same effects as those of the first embodiment of the present invention shown inFIG. 2.

As a third embodiment of the present invention, phosphor layers disposed to cover light-emitting surfaces of a light-emitting element5may be disposed above the light-emitting surfaces of the light-emitting element5, not directly but via an intermediate layer formed of a sealing member12such as, for example, transparent resin, as shown inFIG. 15. In the case shown inFIG. 15, two kinds of phosphor layers10,11are provided on the sealing member12as the intermediate layer. The third embodiment of the present invention has the same effects as those of the first embodiment of the present invention shown inFIG. 2.

As a fourth embodiment of the present invention, a light-emitting device1, though having substantially the same structure as that of the light-emitting device1shown inFIG. 15, may have a light-emitting element5emitting ultraviolet light and have three phosphor layers10,11,60formed above the light-emitting element5via an intermediate layer12, as shown inFIG. 16. The phosphor layer60of the light-emitting device1shown inFIG. 16is structured in the same manner as the phosphor layers10,11, and contains phosphors101different from the phosphors20,25contained in the respective phosphor layers10,11. The fourth embodiment of the present invention has the same effects as those of the first embodiment of the present invention shown inFIG. 2.

As a fifth embodiment of the present invention, a phosphor layer10disposed directly on light-emitting surfaces of a light-emitting element5may be used together with a conventionally known thick phosphor layer dispersed in resin, as shown inFIG. 17. In the case shown inFIG. 17, phosphors25are mixed in resin12around the phosphor layer10to form a conventionally known thick phosphor layer61. At this time, if the resin12contains, as the phosphors25, fine particles with a 10 μm particle size or less or contains an extremely small amount of the phosphors25, an influence of the sedimentation of the phosphors25is very small, and consequently, the fifth embodiment of the present invention has the same effects as those of the first embodiment of the present invention shown inFIG. 2.

Hitherto, the preferred embodiments of the present invention have been described with reference to the appended drawings, but the present invention is not limited to such examples. It is apparent that those skilled in the art could reach various modified examples or corrected examples within the technical idea described in the claims, and it should be naturally understood that these examples also belong to the technical scope of the present invention.

The above embodiments describe the cases where the LED emitting blue light or ultraviolet light is used as the light-emitting element5, but the light-emitting element5may be an LED emitting other light, or a light-emitting element other than the LED may be used as the light-emitting element5.

The above embodiments describe the cases where the number of the phosphor forming layers forming the phosphor layer10is two or three, but the number of the phosphor forming layers forming the phosphor layer10may be any.

The above embodiments describe the cases where the phosphors20of one kind are contained in the phosphor layer10, but the phosphor layer10may contain phosphors of two kinds or more.

The above embodiments describe the cases where the intermediate layer formed on the light-emitting surfaces of the light-emitting element5is the sealing member12such as transparent resin, but the intermediate layer may be formed of a material other than the transparent resin.

The above embodiments describe the cases where the heater30is used to heat the applied adhesive21to lower its viscosity, but a heating device other than the heater30may be used for heating the adhesive21to lower the viscosity. Further, the viscosity may be lowered by a solvent diluting the adhesive21. Further, the dilution of the adhesive21by the solvent and the heating may both be adopted.

The above embodiments describe the cases where the sieve (not shown) provided in the nozzle35is used to adjust the particle size of the phosphors20disposed on the applied adhesive21, but a method other than the sieve may be used. A method, other than the sieve, for adjusting the particle size of the sprayed phosphors20may be, for example, that the phosphors20, after pulverized, washed, separated, and dried by a ball mill, are put in a shuttle and the inside diameter of a nozzle attached to a tip of the shuttle is adjusted.

EXAMPLES

The present invention will be described by using examples and comparative examples.

Examples 1 to 4 described below are the results of measuring tone unevenness of the light-emitting device1according to the embodiment of the present invention, and comparative examples 1, 2 are the results of measuring tone unevenness of conventionally known light-emitting devices100respectively. With the use of the tone unevenness measuring device70shown inFIG. 9, the tone unevenness was measured based on the results of spectrum analysis of light emitted from each of the light-emitting devices as objects to be measured and detected by the detector46.

“A half power angle (2θ(½))” indicating a directional characteristic of light emitted by the light-emitting device as an object to be measured was calculated as follows based on the analysis results of luminance obtained by the spectroscope48.
2θ(½)=|θ1−θ2|
If the largest luminance value is defined as 100% and an angle at this time is defined as a reference angle, θ1is an angle at which luminance becomes 50% when the light-emitting device is rotated toward the 0° position side from the reference angle and θ2is an angle at which luminance becomes 50% when the light-emitting device is rotated toward the 180° position side from the reference angle.

“Color temperature difference (ΔCCT)” indicating the degree of tone unevenness of the light-emitting device as an object to be measured was calculated as a difference between the maximum value and the minimum value of color temperature CCT (Correlated Color Temperature) which was measured within the aforesaid half power angle (2θ(½)), based on the spectrum analysis results obtained by the spectroscope48. Its unit is K (Kelvin).

As for a color rendering property of light emitted by the light-emitting device as an object to be measured, “an average color rendering index (Ra)” indicating the degree of faithful reproduction of standard light specified by JIS was calculated based on the spectrum analysis results obtained by the spectroscope48.

FIG. 18shows measurement results of a luminance ratio and correlated color temperature of the light-emitting device1shown inFIG. 2in which the two different phosphor layers10,11are stacked directly on the light-emitting element5emitting blue light, the measurement being conducted while the position of the light-emitting device1was varied in a range from 0° to 180°. In the example 1, the phosphors20contained in the phosphor layer10emit red light, and the phosphors25contained in the phosphor layer11emit green light. A particle size of the phosphors20was adjusted to 10 μm or less, and a particle size of the phosphors25was adjusted to 13 μm or less.

When a cross section of the above sample was observed, occupancy ratios of the phosphors20and the phosphors25in the phosphor layer10and the phosphor layer11were both 60% or more, and thicknesses of the phosphor layer10and the phosphor layer11were equal to or less than five times average particle sizes of the phosphors20and the phosphors25contained in the respective layers. Further, thickness variation (difference between the maximum thickness and the minimum thickness) of each of the phosphor layer10and the phosphor layer11was equal to or less than an average particle size of each of the phosphors20and the phosphors25contained in the respective layers. The average particle sizes of the phosphors20,25contained in the phosphor layers10,11were 7 μm and 10 μm respectively.

InFIG. 19, the measurement results inFIG. 18are shown, being plotted on coordinates with angle (°) of the light-emitting device1taken on the horizontal axis and correlated color temperature (K) taken on the vertical axis. As shown inFIG. 18andFIG. 19, the half power angle (2θ(½)) was 126°, and the color temperature difference ΔCCT was 155 K. The average color rendering index Ra when the light-emitting device was at a 90° position was 92.

FIG. 20shows measurement results of a luminance ratio and correlated color temperature of the light-emitting device1shown inFIG. 14in which the three different phosphor layers10,11,60are stacked directly on the light-emitting element5emitting ultraviolet light, the measurement being conducted while the position of the light-emitting device1was varied in a range from 0° to 180°. In the example 2, the phosphors20contained in the phosphor layer10emit red light, the phosphors25contained in the phosphor layer11emit green light, and the phosphors101contained in the phosphor layer60emit blue light. A particle size of the phosphors20was adjusted to 10 μm or less, a particle size of the phosphors25was adjusted to 13 μm or less, and a particle size of the phosphors101was adjusted to 20 μm or less.

When a cross section of the above sample was observed, occupancy ratios of the phosphors20, the phosphors25, and the phosphors101in the phosphor layer10, the phosphor layer11, and the phosphor layer60were all 60% or more, and thicknesses of the phosphor layer10, the phosphor layer11, and the phosphor layer60were equal to or less than five times average particle sizes of the phosphors20, the phosphors25, and the phosphors101contained in the respective layers. Further, thickness variation (difference between the maximum thickness and the minimum thickness) of each of the phosphor layer10, the phosphor layer11, and the phosphor layer60was equal to or less than the average particle size of each of the phosphors20, the phosphors25, and the phosphors101contained in the respective layers. The average particle sizes of the phosphors20,25,101contained in the phosphor layers10,11,60were 7 μm, 10 μm, and 18 μm respectively.

InFIG. 21, the measurement results inFIG. 20are shown, being plotted on coordinates with angle (°) of the light-emitting device1taken on the horizontal axis and correlated color temperature (K) taken on the vertical axis. As shown inFIG. 20andFIG. 21, the half power angle (2θ(½)) was 115°, and the color temperature difference ΔCCT was 33 K. The average color rendering index Ra when the light-emitting device was at a 90° position was 94.

FIG. 22shows measurement results of a luminance ratio and correlated color temperature of the light-emitting device1shown inFIG. 15in which the two different phosphor layers10,11are stacked above the light-emitting element5emitting blue light, via the intermediate layer12provided on the light-emitting element5, the measurement being conducted while the position of the light-emitting device1was varied in a range from 0° to 180°. In the example 3, the phosphors20contained in the phosphor layer10emit red light, and the phosphors25contained in the phosphor layer11emit green light. A particle size of the phosphors20was adjusted to 10 μm or less, and a particle size of the phosphors25was adjusted to 13 μm or less. Average particle sizes of the phosphors20,25contained in the phosphor layers10,11were 7 μm and 10 μm respectively.

When a cross section of the above sample was observed, occupancy ratios of the phosphors20and the phosphors25in the phosphor layer10and the phosphor layer11were both 60% or more, and thicknesses of the phosphor layer10and the phosphor layer11were equal to or less than five times average particle sizes of the phosphors20and the phosphors25contained in the respective layers. Further, thickness variation (difference between the maximum thickness and the minimum thickness) of each of the phosphor layer10and the phosphor layer11was equal to or less than the average particle size of each of the phosphors20and the phosphors25contained in the respective layers.

InFIG. 23, the measurement results inFIG. 22are shown, being plotted on coordinates with angle (°) of the light-emitting device1taken on the horizontal axis and correlated color temperature (K) taken on the vertical axis. As shown inFIG. 22andFIG. 23, the half power angle (2θ(½)) was 118°, and the color temperature difference ΔCCT was 249 K. The average color rendering index Ra when the light-emitting device was at a 90° position was 92.

FIG. 24shows measurement results of a luminance ratio and correlated color temperature of the light-emitting device1shown inFIG. 16which, though having substantially the same structure as that of the light-emitting device1shown inFIG. 15, has the light-emitting element5emitting ultraviolet light and has the three phosphor layers10,11,60formed above the light-emitting element5via the intermediate layer12, the measurement being conducted while the position of the light-emitting device1was varied in a range from 0° to 180°. In the example 4, the phosphors20contained in the phosphor layer10emit red light, the phosphors25contained in the phosphor layer11emit green light, and the phosphors101contained in the phosphor layer60emit blue light. A particle size of the phosphors20was adjusted to 10 μm or less, a particle size of the phosphors25was adjusted to 13 μm or less, and a particle size of the phosphors101was adjusted to 20 μm or less.

When a cross section of the above sample was observed, occupancy ratios of the phosphors20, the phosphors25, and the phosphors101in the phosphor layer10, the phosphor layer11, and the phosphor layer60were all 60% or more, and thicknesses of the phosphor layer10, the phosphor layer11, and the phosphor layer60were equal to or less than five times average particle sizes of the phosphors20, the phosphors25, and the phosphors101contained in the respective layers. Further, thickness variation (difference between the maximum thickness and the minimum thickness) of each of the phosphor layer10, the phosphor layer11, and phosphor layer60was equal to or less than two times the average particle size of each of the phosphors20, the phosphors25, and the phosphors101contained in the respective layers. The average particle sizes of the phosphors20,25,101contained in the phosphor layers10,11,60were 7 μm, 10 μm, and 18 μm respectively.

InFIG. 25, the measurement results inFIG. 24are shown, being plotted on coordinates with angle (°) of the light-emitting device1taken on the horizontal axis and correlated color temperature (K) taken on the vertical axis. As shown inFIG. 24andFIG. 25, the half power angle (2θ(½)) was 115°, and the color temperature difference ΔCCT was 86 K. The average color rendering index Ra when the light-emitting device was at a 90° position was 92.

FIG. 26shows measurement results of a luminance ratio and correlated color temperature of a conventionally known light-emitting device100shown inFIG. 27, the measurement being conducted while the position of the light-emitting device100was varied in a range from 0° to 180°. InFIG. 28, the measurement results inFIG. 26are shown, being plotted on coordinates with angle (°) of the light-emitting device100taken on the horizontal axis and correlated color temperature (K) taken on the vertical axis. The conventionally known light-emitting device100shown inFIG. 27is structured such that resin in which the phosphors20emitting red light and the phosphors25emitting green light are mixed is thickly disposed around the light-emitting element5disposed on the substrate2. As the light-emitting element5, the light-emitting element5emitting blue light was used.

The total occupancy ratio of the phosphors20and the phosphors25in the resin was less than 50%, specifically 5%, and thickness variation (difference between the maximum thickness and the minimum thickness) of the phosphor layer exceeded two times an average particle size of the phosphors20,25.

As shown inFIG. 26andFIG. 28, the half power angle (2θ(½)) was 122°, and the color temperature difference ΔCCT was 580 K. The average color rendering index Ra when the light-emitting device was at a 90° position was 94.

FIG. 29shows measurement results of a luminance ratio and correlated color temperature of another conventionally known light-emitting device100shown inFIG. 30, the measurement being conducted while the position of the light-emitting device100was varied in a range from 0° to 180°. InFIG. 31, the measurement results inFIG. 29are shown, being plotted on coordinates with angle (°) of the light-emitting device100taken on the horizontal axis and correlated color temperature (K) taken on the vertical axis. The other conventionally known light-emitting device100shown inFIG. 30is structured such that resin in which the phosphors20emitting red light, the phosphors25emitting green light, and the phosphors101emitting blue light are mixed is thickly disposed around the light-emitting element5disposed on the substrate2. As the light-emitting element5, the light-emitting element5emitting ultraviolet light was used.

The total occupancy ratio of the phosphors20,25,101in the resin was less than 50%, specifically 5%, and thickness variation (difference between the maximum thickness and the minimum thickness) of the phosphor layer exceeded two times an average particle size of the phosphors20,25,101.

As shown inFIG. 29andFIG. 31, the half power angle (2θ(½)) was 133°, and the color temperature difference ΔCCT was 494 K. The average color rendering index Ra when the light-emitting device was at a 90° position was 91.

As described above, in the examples 1 to 4 for the light-emitting device1of the present invention, the values of the color temperature difference ΔCCT indicating the degree of tone unevenness are 33 K to 249 K and it is seen that, compared with the values 580 K and 494 K of ΔCCT in the comparative examples 1, 2 for the conventionally known light-emitting device100, tone unevenness of light emitted by the light-emitting device of the present invention is greatly reduced. Further, the values of the average color rending property Ra in the examples 1 to 4 for the light-emitting device1of the present invention are 92 to 94, and thus it is seen that white light emitted by the light-emitting device1of the present invention has a high color rendering property and can be the reproduction of light closer to the standard light.