Patent ID: 12232847

DESCRIPTION OF EMBODIMENTS

A detailed description is given below of a wavelength converter, and a light emitting device, a medical system, an electronic apparatus, and an inspection method using the wavelength converter according to a present embodiment. Note that dimensional ratios in the drawings are exaggerated for convenience of explanation, and are sometimes different from actual ratios.

[Wavelength Converter]

As illustrated inFIG.1, a wavelength converter1according to the present embodiment includes a first phosphor2and a second phosphor3. The first phosphor2is a phosphor activated with Cr3+. The second phosphor3is a phosphor activated with at least one ion of Ce3+or Eu2+.

FIG.2is an example of an excitation spectrum and a fluorescence spectrum of the first phosphor2. For example, as illustrated inFIG.2, the first phosphor2strongly absorbs a light in a blue wavelength range of 400 nm or more to less than 500 nm, and a light in an orange to red wavelength range of 580 nm or more to less than 660 nm. The first phosphor2absorbs the blue light and the orange-red light, converts the wavelength thereof, and emits a near-infrared fluorescence of 680 nm or more to less than 800 nm.

FIG.3is an example of an excitation spectrum and a fluorescence spectrum of the second phosphor3. The fluorescence spectrum of the fluorescence emitted by the second phosphor3has a peak where the fluorescence intensity shows a maximum value in a wavelength range of 500 nm or more to less than 580 nm. Specifically, as illustrated inFIG.3, the fluorescence spectrum of the fluorescence emitted by the second phosphor3includes a green to yellow fluorescence component in a wavelength range of 500 nm or more to less than 580 nm as a main fluorescence component and has a broad fluorescence component including a blue fluorescence component and an orange to red fluorescence component.

As described above, the wavelength converter1includes the first phosphor2and the second phosphor3. Therefore, the blue and orange to red fluorescent components emitted by the second phosphor3are absorbed by the first phosphor2and are wavelength-converted into a near-infrared fluorescence.

As a result, the intensity of the blue and orange to red fluorescent components among the broad fluorescent components emitted by the second phosphor3decreases, and the intensity of the green to yellow fluorescent component emitted by the second phosphor3relatively increases. In particular, the intensity of the deep red fluorescent component among the broad fluorescent components emitted by the second phosphor3decreases. In contrast, since the first phosphor2emits a near-infrared fluorescence, the intensity of the near-infrared fluorescence component emitted by the wavelength converter1increases.

That is, in the light emitted by the wavelength converter1, the intensity of the green to yellow and near-infrared fluorescent components increases, and the intensity of the orange to red fluorescent component decreases. Therefore, the wavelength converter1emits a wavelength-converted light in which the green to yellow fluorescent component and the near-infrared fluorescent component are sufficiently separated. The wavelength converter1emits a wavelength-converted light in which the intensity of the deep red fluorescent component, which becomes noise in a near-infrared image sensor, is relatively small.

The green to yellow fluorescent component emitted by the wavelength converter1is usable as a light component advantageous for the visual inspection of a diseased part of a patient. The near-infrared fluorescent component emitted by the wavelength converter1is usable as a light component advantageous for excitation of a fluorescent drug administered in a living body. The wavelength converter1is thus suitable for the coexistence of normal observation using visible light and special observation using near-infrared light.

The wavelength converter1emits a fluorescence having a light component over the entire wavelength range of 500 nm or more to less than 580 nm. Emitting such a fluorescence enables the wavelength converter1to effectively emit a green to yellow fluorescent component that is advantageous for visual inspection of a diseased part of a patient. The fluorescence emitted by the wavelength converter1may have a light component over the entire wavelength range of 500 nm or more to less than 600 nm.

The wavelength converter1emits a light having a spectrum in which the ratio of the minimum light emission intensity to the maximum light emission intensity is 40% or less within a wavelength range of 550 nm or more to 700 nm or less. The ratio of the minimum light emission intensity to the maximum light emission intensity is preferably 30% or less, more preferably 20% or less, still more preferably 10% or less, particularly preferably 5% or less. This enables the wavelength converter1to emit a wavelength-converted light in which the green to yellow fluorescent component and the near-infrared fluorescent component are more separated. A wavelength having the maximum light emission intensity may be 550 nm or more and less than 580 nm. A wavelength having the minimum light emission intensity may be 580 nm or more and 700 nm or less, 600 nm or more and 700 nm or less.

The fluorescence emitted by the first phosphor2preferably has a light component over the entire wavelength range of 700 nm or more to 800 nm or less, more preferably has a light component over the entire wavelength range of 750 nm or more to 800 nm or less. This enables the wavelength converter1to emit a near-infrared excitation light capable of efficiently exciting a drug, even if a drug having a light absorption property of near-infrared rays that is likely to vary is used. Thus, a light emitting device10having a large number of near-infrared lights emitted by a fluorescent drug or heat rays emitted by a photosensitive drug is obtained.

Preferably, the fluorescence spectrum of the fluorescence emitted by the first phosphor2has a peak where the fluorescence intensity shows a maximum value in a wavelength range of 710 nm or more. This enables the wavelength converter1to emit a fluorescence including a large number of near-infrared light components with high living body permeability. The fluorescence spectrum of the fluorescence emitted by the first phosphor2may have a peak where the fluorescence intensity shows a maximum value in a wavelength range of 710 nm or more to 900 nm or less.

Preferably, the fluorescence emitted by the first phosphor2includes a fluorescence based on the electronic energy transition of Cr3+, and the fluorescence spectrum of the fluorescence emitted by the first phosphor2has a peak where the fluorescence intensity shows a maximum value in a wavelength range exceeding 720 nm. This enables the first phosphor2to emit a fluorescence in which a broad spectral component of a short afterglow property is more dominant than a linear spectral component of a long afterglow property. As a result, the wavelength converter1emits a light including a large number of near-infrared components. The linear spectrum component is a fluorescence component based on the electron energy transition (spin-forbidden transition) of2E→4A2(t23) of Cr3+and has a peak where the fluorescence intensity shows a maximum value in a wavelength range of 680 nm to 720 nm. The broad spectral component is a fluorescence component based on the electron energy transition (spin-allowed transition) of4T2(t22e)→4A2(t23) of Cr3+and has a peak where the fluorescence intensity shows a maximum value in a wavelength range exceeding 720 nm.

The fluorescence spectrum of the fluorescence emitted by the first phosphor2more preferably has a peak where the fluorescence intensity shows a maximum value in a wavelength range exceeding 730 nm, still more preferably has a peak where the fluorescence intensity shows a maximum value in a wavelength range exceeding 750 nm.

The 1/10 afterglow time of the fluorescence emitted by the first phosphor2is preferably less than 1 ms, more preferably less than 300 μs, still more preferably less than 100 μs. Thus, even when the light density of the excitation light for exciting the first phosphor2is high, the output of the fluorescence emitted by the first phosphor2hardly saturates. Thus, the wavelength converter1capable of emitting a high output near-infrared light is obtained. Note that the 1/10 afterglow time means time τ1/10taken from the time when the maximum light emission intensity is shown to the time when the intensity becomes 1/10 of the maximum light emission intensity.

Preferably, the 1/10 afterglow time of the fluorescence emitted by the first phosphor2is longer than the 1/10 afterglow time of the fluorescence emitted by the second phosphor3. Preferably, the 1/10 afterglow time of the fluorescence emitted by the first phosphor2is specifically 10 μs or more. Note that the 1/10 afterglow time of the fluorescence emitted by the first phosphor2activated with Cr3+is longer than the 1/10 afterglow time of a short afterglow (less than 10 μs) fluorescence based on a parity-allowed transition of Ce3+, Eu2+, or the like. This is because the fluorescence emitted by the first phosphor2is a fluorescence based on the electron energy transition of the spin-allowed type of Cr3+, which has relatively long afterglow time.

Preferably, the 1/10 afterglow time difference, which is the difference between the 1/10 afterglow time of the fluorescence emitted by the first phosphor2and the 1/10 afterglow time of the fluorescence emitted by the second phosphor3, exceeds 50 μs. Thus, even if the intensity of the fluorescent component of the visible light emitted by the second phosphor3as the main component is greatly reduced, the fluorescent component of the near infrared light emitted by the first phosphor2as the main component maintains a relatively large intensity. It is thus possible to control the output ratio of the near-infrared fluorescent component and the visible fluorescent component by using the afterglow time difference. Preferably, the 1/10 afterglow time difference is less than 1 ms.

Preferably, in the fluorescence spectrum of the fluorescence emitted by the first phosphor2, the spectral width at an intensity of 80% of the maximum value of the fluorescence intensity is 20 nm or more and less than 80 nm. Thus, the main component of the fluorescence emitted by the first phosphor2becomes a broad spectrum component. Therefore, even when there is a variation in the wavelength dependence of the sensitivity of a fluorescent drug or photosensitive drug in a medical field using a fluorescence imaging method or photodynamic therapy (PDT method), the wavelength converter1emits high output near-infrared light that enables these drugs to function sufficiently.

Preferably, in the fluorescence spectrum of the fluorescence emitted by the first phosphor2, the ratio of the fluorescence intensity at a wavelength of 780 nm to the maximum fluorescence intensity exceeds 30%. The ratio of the fluorescence intensity at a wavelength of 780 nm to the maximum fluorescence intensity more preferably exceeds 60%, even more preferably exceeds 80%. This enables the first phosphor2to emit a fluorescence including a large number of fluorescent components of a near-infrared wavelength range (650 to 1000 nm) through which light easily penetrates the living body, which is called a “living body window”. Therefore, the above-described wavelength converter1increases the light intensity of the near infrared that penetrates the living body.

Preferably, the fluorescence spectrum of the fluorescence emitted by the first phosphor2does not leave a trail of a linear spectral component derived from the electronic energy transition of Cr3+. That is, preferably, the fluorescence emitted by the first phosphor2has only a broad spectral component (short afterglow property) having a peak where the fluorescence intensity shows a maximum value in a wavelength range exceeding 720 nm. Thus, the first phosphor2does not include a long afterglow fluorescent component due to the spin-forbidden transition of Cr3+but only includes a short afterglow fluorescent component due to the spin-allowed transition of Cr3+. Thus, even when the light density of the excitation light for exciting the first phosphor2is high, the output of the fluorescence emitted by the first phosphor2hardly saturates. Therefore, the light emitting device of a point light source capable of emitting a near-infrared light of higher output is obtained.

Preferably, the first phosphor2includes no activator other than Cr3+. This enables the light absorbed by the first phosphor2to be converted into only the fluorescence based on the electronic energy transition of Cr3+, which provides the wavelength converter1with easy design of output light for maximizing the output ratio of the near-infrared fluorescent component.

Preferably, the first phosphor2includes two or more kinds of Cr3+-activated phosphors. This enables the output light component in at least the near-infrared wavelength range to be controlled, which provides the wavelength converter1with easy adjustment of the spectral distribution in accordance with the application utilizing the near-infrared fluorescence component.

The first phosphor2is preferably an oxide-based phosphor, more preferably an oxide phosphor. The oxide-based phosphor means a phosphor including oxygen but not nitrogen or sulfur. The oxide-based phosphor may include at least one selected from the group consisting of an oxide, a complex oxide, and a compound including oxygen or halogen as an anion.

Since the oxide is stable in the atmosphere, even when the oxide phosphor generates heat due to high density photoexcitation by laser light, it is difficult for phosphor crystals to be altered by oxidation in the atmosphere, as occurs in nitride phosphors. Therefore, when all the phosphors in the wavelength converter1are oxide phosphors, the light emitting device that is highly reliable is obtained.

Preferably, the first phosphor2has a garnet crystal structure. Preferably, the first phosphor2is an oxide phosphor with a garnet crystal structure. Since a garnet phosphor is easily deformed in composition and provides a number of phosphor compounds, a crystal field around Cr3+is easily adjusted, and the color tone of fluorescence based on the electronic energy transition of Cr3+is easily controlled.

The phosphor with a garnet structure, especially the oxide, has a polyhedral particle shape close to a sphere and has excellent dispersibility of a phosphor particle group. Therefore, when the phosphor included in the wavelength converter1has a garnet structure, the wavelength converter1excellent in light transmittance is manufactured relatively easily, which enables higher output of the light emitting device. Further, since a phosphor with a garnet crystal structure has practical experience as a phosphor for LEDs, the light emitting device that is a highly reliable is obtained when the first phosphor2has the garnet crystal structure.

The first phosphor2may include at least one phosphor selected from the group consisting of: Lu2CaMg2(SiO4)3:Cr3+, Y3Ga2(AlO4)3:Cr3+, Y3Ga2(GaO4)3:Cr3+, Gd3Ga2(AlO4)3:Cr3+, Gd3Ga2(GaO4)3:Cr3+, (Y,La)3Ga2(GaO4)3:Cr3+, (Gd,La)3Ga2(GaO4)3:Cr3+, Ca2LuZr2(AlO4)3:Cr3+, Ca2GdZr2(AlO4)3:Cr3+, Lu3Sc2(GaO4)3:Cr3+, Y3Sc2(AlO4)3: Cr3+, Y3Sc2(GaO4)3:Cr3+, Gd3Sc2(GaO4)3:Cr3+, La3Sc2(GaO4)3:Cr3+, Ca3Sc2(SiO4)3:Cr3+, Ca3Sc2(GeO4)3:Cr3+, BeAl2O4:Cr3+, LiAl5O8:Cr3+, LiGa5O8:Cr3+, Mg2SiO4:Cr3+, Li+, La3Ga5GeO14:Cr3+, and La3Ga5.5Nb0.5O14:Cr3+.

As described above, the fluorescence emitted by the first phosphor2has a specific fluorescence component based on the electronic energy transition of Cr3+. This enables the wavelength converter1to efficiently excite a fluorescent drug, such as ICG, or a photosensitive drug (which is also a fluorescent drug), such as phthalocyanine.

The second phosphor3is a phosphor activated with at least one ion of Ce3+or Eu2+. Preferably, the second phosphor3is a phosphor activated with Ce3+. The phosphor activated with Ce3+has a phtophysical property of emitting fluorescence having a spectral shape with a long tail at a long wavelength side. Thus, the light emitted by the second phosphor3has a large proportion of an orange to red fluorescent component, which is advantageous for the excitation of the first phosphor2, and thus is advantageous for enhancing the intensity of the near-infrared fluorescent component emitted by the first phosphor2.

The second phosphor3may be at least one of an oxide-based phosphor, such as an oxide or a halogen oxide, or a nitride-based phosphor, such as a nitride or an oxynitride.

Preferably, the second phosphor3is a Ce3+-activated phosphor having a matrix of a compound with at least one, as a main component, selected from the compound group consisting of a garnet type crystal structure, a calcium ferrite type crystal structure, and a lanthanum silicon nitride (La3Si6N11) type crystal structure. Preferably, the second phosphor3is a Ce3+-activated phosphor having a matrix of at least one selected from the compound group consisting of a garnet type crystal structure, a calcium ferrite type crystal structure, and a lanthanum silicon nitride (La3Si6N11) type crystal structure. Using the above-described second phosphor3provides output light with a large number of light components from green to yellow.

Preferably, the second phosphor3is specifically a Ce3+-activated phosphor having a matrix of a compound with at least one, as a main component, selected from the group consisting of M3RE2(SiO4)3, RE3Al2(AlO4)3, MRE2O4, and RE3Si6N11. Preferably, the second phosphor3is a Ce3+-activated phosphor having a matrix of at least one selected from the group consisting of M3RE2(SiO4)3, RE3Al2(AlO4)3, MRE2O4, and RE3Si6N11. Preferably, the second phosphor3is a Ce3+-activated phosphor having a matrix of a solid solution having the above-described compound as an end component. Note that M is an alkaline earth metal, and RE is a rare earth element.

The above-described second phosphor3well absorbs light in a wavelength range of 430 nm or more to 480 nm or less and converts it to green to yellow light with a peak where the fluorescence intensity shows a maximum value in a wavelength range of 540 nm or more to less than 580 nm with high efficiency. Therefore, a visible light component is easily obtained by using such a phosphor as the second phosphor3with the light source5that emits cold color light in a wavelength range of 430 nm or more to 480 nm or less as the primary light6.

Preferably, the wavelength converter1includes an inorganic material. Here, the inorganic material means materials other than organic materials and includes ceramics and metals as a concept. When the wavelength converter1includes an inorganic material, the wavelength converter1has the heat conductivity higher than that of the wavelength converter including an organic material, such as a sealing resin, thereby facilitating the heat radiation design. Thus, the temperature rise of the wavelength converter1is effectively prevented even when the phosphor is photoexcited with high density by the primary light6emitted from the light source5. As a result, the temperature quenching of the phosphor in the wavelength converter1is prevented, and thus higher output of light emission is possible. Accordingly, the heat dissipation of the phosphor is improved, and thus the decrease in output of the phosphor due to temperature quenching is prevented, and high output near-infrared light is emitted.

Preferably, all of the wavelength converter1is made of an inorganic material. As a result, the heat dissipation of the first phosphor2and the second phosphor3is improved, and thus the decrease in output of the phosphor due to temperature quenching is prevented, and the light emitting device that emits a high output near-infrared light is obtained.

At least one of the first phosphor2or the second phosphor3may be a ceramic. This increases the thermal conductivity of the wavelength converter1, which provides the light emitting device10with less heat generation and high output. Here, the ceramic means a sintered body in which particles are bonded to each other.

As illustrated inFIG.1, preferably, the wavelength converter1further includes a sealing material4that disperses the first phosphor2and the second phosphor3, in addition to the first phosphor2and the second phosphor3. Preferably, the wavelength converter1has the first phosphor2and the second phosphor3dispersed in the sealing material4. By dispersing the first phosphor2and the second phosphor3in the sealing material4, the light emitted to the wavelength converter1is efficiently absorbed and wavelength-converted into a near-infrared light. Further, the wavelength converter1is easily formed into a sheet shape or a film shape.

Preferably, the sealing material4is at least one of an organic material or an inorganic material, particularly at least one of a transparent (light transmitting) organic material or a transparent (light transmitting) inorganic material. Examples of the sealing material of the organic material include a transparent organic material, such as a silicone resin. Examples of the sealing material of the inorganic material include a transparent inorganic material, such as a low melting point glass.

As described above, the wavelength converter1preferably includes an inorganic material, and thus the sealing material4preferably includes an inorganic material. Preferably, zinc oxide (ZnO) is used as the inorganic material. This further enhances the heat dissipation of the phosphor, which prevents the output of the phosphor from decreasing due to temperature quenching and provides the wavelength converter1that emits high output near-infrared light.

FIG.1illustrates an example in which the first phosphor2and the second phosphor3are uniformly mixed and dispersed in a single layer of the sealing material4. However, the wavelength converter1is not limited to such a configuration. As illustrated inFIG.4, for example, the wavelength converter1may have a first sealing material4A and a second sealing material4B. The first phosphor2may be dispersed in the first sealing material4A, and the second phosphor3may be dispersed in the second sealing material4B. As illustrated inFIG.4, the first sealing material4A and the second sealing material4B each may form a layer, and layers may be stacked to overlap each other. The first sealing material4A and the second sealing material4B may be formed of the same material or different materials.

As illustrated inFIGS.5and6, the wavelength converter1may not use the sealing material4. More specifically, as illustrated inFIG.5, the wavelength converter1does not have the sealing material4, and the first phosphor2and the second phosphor3may be uniformly mixed and dispersed. As illustrated inFIG.6, the wavelength converter1does not have the sealing material4, the first phosphor2and the second phosphor3may each form an aggregated layer, and layers may be stacked to overlap each other. In this case, the phosphor may be fixed to each other by using an organic or inorganic binder. The phosphor is fixable to each other by using the heating reaction of the phosphor. As the binder, a commonly used resin-based adhesive, ceramic fine particles, low melting point glass, or the like is usable. The wavelength converter1without using the sealing material4is made thin and thus is suitably used for the light emitting device.

[Light Emitting Device]

Next, the light emitting device10according to the present embodiment is described with reference toFIGS.7and8.

As illustrated inFIG.7, the light emitting device10according to the present embodiment includes the above-described wavelength converter1and the light source5emitting a light that is wavelength-converted by the wavelength converter1. That is, the light emitting device10is the light emitting device10including at least a combination of the light source5emitting the primary light6, the first phosphor2, and the second phosphor3. The wavelength converter1receives the primary light6emitted by the light source5and emits a fluorescence having a wavelength longer than that of the primary light6. The light emitting device10inFIG.7receives the primary light6at the front1A of the wavelength converter1and emits fluorescence from the back1B of the wavelength converter1.

The emitted fluorescence includes a first wavelength-converted light7and a second wavelength-converted light8. The second wavelength-converted light8is a fluorescence emitted by wavelength conversion of a part of the primary light6absorbed by the second phosphor3. The first wavelength-converted light7is a fluorescence emitted by wavelength conversion of a part of the primary light6and/or the second wavelength-converted light8absorbed by the first phosphor2. The first wavelength-converted light7having a specific fluorescence component based on the electronic energy transition of Cr3+enables the light emitting device10to emit a fluorescence based on the electronic energy transition of Cr3+.

As described above, the wavelength converter1emits a wavelength-converted light in which the green to yellow fluorescent component and the near-infrared fluorescent component are sufficiently separated. Therefore, the above-described light emitting device10emits output light in which the green to yellow fluorescent components and the near-infrared fluorescent components are sufficiently separated. The green to yellow fluorescent component is usable as a light component that is advantageous for visual inspection of a diseased area of a patient. In contrast, the near-infrared fluorescent component is usable as a light component advantageous for excitation of a drug administered in a living body. For this reason, the light emitting device10is advantageous in diagnosing because it achieves the coexistence of normal observation using visible light and special observation using near-infrared light.

As described above, the light source5emits a light that is wavelength-converted by the wavelength converter1, and the light emitted by the light source5is preferably a laser light. The laser light is a high-output point light source with strong directivity, and thus it not only reduces the size of the optical system and the diameter of the light guiding part but also improves the coupling efficiency of the laser light to an optical fiber. Accordingly, the light emitting device10that facilitates high output is obtained. Preferably, the laser light is emitted by a semiconductor light emitting device from the viewpoint of miniaturization of the light emitting device10.

Preferably, the spectrum of the light emitted by the light source5has a peak where the intensity shows a maximum value in a range of 400 nm or more to less than 500 nm. Also preferably, the spectrum of the light emitted by the light source5has a peak where the intensity shows a maximum value in a wavelength range of 420 nm or more to less than 480 nm, and the light emitted by the light source5is blue light. The spectrum of the light emitted by the light source5has a peak where the intensity shows a maximum value more preferably in a wavelength range of 430 nm or more to less than 480 nm, even more preferably in a wavelength range of 440 nm or more to less than 470 nm. In this way, not only the first phosphor2activated with Cr3+is excited with high efficiency, but also a high-efficiency phosphor having a high performance for LED lighting is usable as the second phosphor3activated with at least one of Ce3+or Eu2+. Thus, the light emitting device10with high output is obtained.

The light source5may include a red laser device. The light source5may include a blue laser device. The red laser device has a small energy difference from the near-infrared light component and a small energy loss associated with wavelength conversion, which is preferable in achieving high efficiency of the light emitting device10. In contrast, a laser device with high efficiency and high output is easily available for the blue laser device, and thus the blue laser device is preferable in achieving high output of the light emitting device10. Preferably, the light source5includes a blue laser device as an excitation source and emits blue laser light. Thus, the first phosphor2and the second phosphor3are excited with high efficiency and high output, which enables the light emitting device10to emit high-output near-infrared light.

Preferably, the light source5includes a solid-state light emitting device, and the above-described blue light is emitted by the solid-state light emitting device. In this way, a small-sized light emitting device with high reliability is used as a light emitting source of the above-described blue light, which provides a small-sized light emitting device10with high reliability.

The solid-state light emitting device is a light emitting device that emits the primary light6. Any solid-state light emitting device is usable as long as it emits the primary light6with a high energy density. The solid-state light emitting device is preferably at least one of a laser device or a light-emitting diode (LED), more preferably a laser device. The light source5may be, for example, a surface emitting laser diode.

The rated light output of the solid-state light emitting device is preferably 1 W or more, more preferably 3 W or more. This enables the light source5to emit the primary light6with high output, and thus the light emitting device10that facilitates high output is obtained.

The upper limit of the rated light output is not limited, and the rated light output is increased by the light source5having a plurality of solid-state light emitting devices. However, for practical purposes, the rated light output is preferably less than 10 kW, more preferably less than 3 kW.

The light density of the primary light6is preferably more than 0.5 W/mm2, more preferably more than 3 W/mm2, still more preferably more than 10 W/mm2. The light density may exceed 30 W/mm2. In this way, the first phosphor2and the second phosphor3are photoexcited at high density, which enables the wavelength converter1to emit a fluorescent component of high output.

Preferably, the primary light6is a continuous pulsed light. In this way, immediately after the pulsed light is turned off, the first wavelength-converted light7having a near-infrared fluorescent component emits phosphorescence longer than the second wavelength-converted light8that becomes visible light. Utilizing the phosphorescence component as the excitation light of the above-described drug provides the light emitting device10that is easily designed so that only the near-infrared fluorescent component emitted by the drug enters the image sensor, and the second wavelength-converted light8hardly enters the image sensor. Accordingly, the light emitting device10advantageous for the improvement of the S/N ratio of the near-infrared fluorescent component emitted by the drug is obtained.

Preferably, the correlated color temperature of the mixed light of the primary light6and the second wavelength converter light8is 2500 K or more and less than 7000 K. The correlated color temperature is more preferably 2700 K or more and less than 5500 K, more preferably 2800 K or more and less than 3200 K or 4500 K or more and less than 5500 K. The output light with a correlated color temperature within the above-described range is a white output light, and a diseased part visible through an image display device or an optical device appears similar to the diseased part observed under natural light. Therefore, the light emitting device10is obtained that easily makes use of the medical experience of doctors, which is preferable for medical use.

Next, the operation of the light emitting device10according to the present embodiment is described. In the light emitting device10illustrated inFIG.7, first, the primary light6emitted by the light source5is emitted to a front1A of the wavelength converter1. Most of the emitted primary light6enters the wavelength converter1from the front1A of the wavelength converter1and passes through the wavelength converter1, and a part of the emitted primary light6is reflected on the surface of the wavelength converter1. The second phosphor3absorbs a part of the primary light6and converts it into the second wavelength-converted light8, and the first phosphor2absorbs a part of the primary light6and/or a part of the second wavelength-converted light8and converts it into the first wavelength-converted light7. Thus, the light emitting device10emits a light including the primary light6, the first wavelength-converted light7, and the second wavelength-converted light8from a back1B of the wavelength converter1, as output light.

The light emitting device10is not limited to the configuration inFIG.7and is not limited to the configuration of receiving the primary light6from the front1A of the wavelength converter1and emitting the first wavelength-converted light7and the second wavelength-converted light8from the back1B of the wavelength converter1as illustrated inFIG.7. As illustrated inFIG.8, the light emitting device10may receive the primary light6from the front1A of the wavelength converter1and emit the first wavelength-converted light7and the second wavelength-converted light8from the front1A of the wavelength converter1. Specifically, in the light emitting device10illustrated inFIG.8, first, the primary light6emitted by the light source5is emitted to the front1A of the wavelength converter1. Most of the emitted primary light6enters the wavelength converter1from the front1A of the wavelength converter1, and a part of the emitted primary light6is reflected on the surface of the wavelength converter1. The second phosphor3absorbs a part of the primary light6and converts it into the second wavelength-converted light8, and the first phosphor2absorbs a part of the primary light6and/or a part of the second wavelength-converted light8and converts it into the first wavelength-converted light7. In this way, the light emitting device10emits a light including the primary light6, the first wavelength-converted light7, and the second wavelength-converted light8from the front1A of the wavelength converter1, as output light.

Thus, the light emitting device10according to the present embodiment emits the first wavelength-converted light7including a large number of long-afterglow near-infrared fluorescent components based on the electron energy transition of Cr3+. The near-infrared fluorescent component is usable as a light component advantageous for excitation of the fluorescent drug administered in a living body. The light emitting device10according to the present embodiment emits the second wavelength-converted light8including a large number of short-afterglow green to yellow fluorescent components based on the electronic energy transition of Ce3+or Eu2+. The green to yellow fluorescent component is usable as a light component that is advantageous for visual inspection of a diseased part of a patient.

Accordingly, the light emitting device10may be used for medical purposes. That is, the light emitting device10may be a medical light emitting device. In other words, the light emitting device10may be a medical illumination device. In this way, the light emitting device10emits output light in which the green to yellow fluorescent component and the near-infrared fluorescent component are sufficiently separated and thus achieves the coexistence of the normal observation and the special observation as described above, which is advantageous in diagnosing disease state.

The light emitting device10may be used for optical coherence tomography (OCT) or the like. However, preferably, the light emitting device10is used for either a fluorescence imaging method or photodynamic therapy. The light emitting device10used in these methods is a light emitting device for a medical system using a drug, such as a fluorescent drug or a photosensitive drug. These methods are a promising medical technology with a wide range of applications and are highly practical. The light emitting device10illuminates the inside of the living body with a broad near-infrared high-output light through the “living body window” and makes the fluorescent drug or photosensitive drug taken into the living body fully functional, which is expected to have a large therapeutic effect.

The fluorescence imaging method is a method of observing a lesion by administering a fluorescent drug that selectively binds to the lesion, such as a tumor, to a subject, exciting the fluorescent drug with a specific light, and detecting and imaging fluorescence emitted from the fluorescent drug with an image sensor. The fluorescence imaging method makes it possible to observe lesions that are difficult to observe using only general illumination. As the fluorescent drug, a drug that absorbs excitation light in the near-infrared range, and emits fluorescence in the near-infrared range and at a wavelength longer than the excitation light is usable. Examples of the fluorescent drug used include at least one selected from the group consisting of indocyanine green (ICG), a phthalocyanine-based compound, a talaporfin sodium-based compound, and a dipicolylcyanine (DIPCY)-based compound.

The photodynamic therapy is a treatment method of administering a photosensitive drug that selectively binds to a target biological tissue to a subject and irradiating the photosensitive drug with near-infrared light. When the photosensitive drug is irradiated with the near-infrared light, the photosensitive drug generates active oxygen, which is usable to treat lesions, such as tumors or infections. Examples of the photosensitive drug used include at least one selected from the group consisting of a phthalocyanine-based compound, a talaporfin sodium-based compound, and a porfimer sodium-based compound.

The light emitting device10according to the present embodiment may be used as a light source for a sensing system or an illumination system for a sensing system. With the light emitting device10, an orthodox light receiving element having light receiving sensitivity in the near-infrared wavelength range may be used to configure a high-sensitivity sensing system. This provides a light emitting device that facilitates miniaturization of the sensing system and broadening of the sensing range.

[Healthcare System]

Next, a medical system including the above-described light emitting device10is described. Specifically, as an example of the medical system, an endoscope11provided with the light emitting device10and an endoscope system100using the endoscope11are described with reference toFIGS.9to11.

(Endoscope)

As illustrated inFIG.9, the endoscope11according to the present embodiment includes the above-described light emitting device10. The endoscope11includes a scope110, a light source connector111, a mount adapter112, a relay lens113, a camera head114, and an operation switch115.

The scope110is an elongated light guide member capable of guiding light from end to end and is inserted into the body when in use. The scope110includes an imaging window110zat its tip. For the imaging window110z, an optical material, such as optical glass or optical plastic, is used. The scope110includes an optical fiber for guiding light introduced from the light source connector111to the tip, and an optical fiber for transmitting an optical image that enters through the imaging window110z.

The light source connector111introduces illumination light emitted to a diseased part and the like in the body from the light emitting device10. In the present embodiment, the illumination light includes visible light and near-infrared light. The light introduced into the light source connector111is guided to the tip of the scope110through the optical fiber to be emitted to a diseased part and the like in the body from the imaging window110z. As illustrated inFIG.9, the light source connector111is provided with a transmission cable111zfor guiding illumination light from the light emitting device10to the scope110. The transmission cable111zmay include an optical fiber.

The mount adapter112is a member for mounting the scope110on the camera head114. Various scopes110are detachably mountable on the mount adapter112.

The relay lens113converges the optical image transmitted through the scope110on the imaging surface of the image sensor. The relay lens113may be moved in accordance with the operation amount of the operation switch115to perform focus adjustment and magnification adjustment.

The camera head114includes a color separation prism inside. The color separation prism separates the light converged by the relay lens113into four colors of R light (red light), G light (green light), B light (blue light), and IR light (near-infrared light). The color separation prism includes, for example, a light transmitting member, such as glass.

The camera head114further includes an image sensor114A as a detector inside. The image sensor114A is not limited, but at least one of CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) is usable. The image sensor114A may include multiple types of image sensors.

The image sensor114A may include, for example, an IR light image sensor114IR and a visible light image sensor114V as inFIG.10. The visible light image sensor114V may include an R light image sensor114R, a G light image sensor114G, and a B light image sensor114B. The IR light image sensor114IR is a dedicated sensor for receiving an IR component (near-infrared component) light. The R light image sensor114R is a dedicated sensor for receiving R component (red component) light. The G light image sensor114G is a dedicated sensor for receiving G component (green component) light. The B light image sensor114B is a dedicated sensor for receiving B component (blue component) light. The IR light image sensor114IR, the R light image sensor114R, the G light image sensor114G, and the B light image sensor114B convert optical images formed on respective imaging surfaces into electric signals.

The camera head114may have a color filter inside instead of the color separation prism. The color filter is provided on the imaging surface of the image sensor114A. For example, four color filters are provided, and the four color filters receive the light converged by the relay lens113and selectively transmit R light (red light), G light (green light), B light (blue light), and IR light (near-infrared light), respectively.

Preferably, the color filter for selectively transmitting IR light includes a barrier film for cutting the reflection component of near-infrared light (IR light) included in the illumination light. This enables only the fluorescence composed of IR light emitted from a fluorescent drug, such as ICG, to form an image on the imaging surface of the image sensor114IR for IR light. Therefore, the diseased part luminous with the fluorescent drug is easily observed clearly.

As illustrated inFIG.9, a signal cable114zis connected to the camera head114to transmit an electric signal from the image sensor114A to a CCU12described later.

In the endoscope11having such a configuration, light from a subject is guided to the relay lens113through the scope110and is further transmitted through the color separation prism in the camera head114to form images on the four image sensors.

(Endoscope System)

As illustrated inFIG.11, the endoscope system100includes the endoscope11for imaging the inside of a subject, a CCU (Camera Control Unit)12, and a display device13, such as a display.

The CCU12includes at least an RGB signal processing unit, an IR signal processing unit, and an output unit. The CCU12executes a program stored in the internal or external memory of the CCU12to realize the respective functions of the RGB signal processing unit, the IR signal processing unit, and the output unit.

The RGB signal processing unit converts the R component, G component, and B component electrical signals from the visible light image sensor114V into video signals that are displayable on the display device13and outputs the video signals to the output unit. The IR signal processing unit converts the IR component electrical signal from the IR light image sensor114IR into a video signal and outputs the video signal to the output unit.

The output unit outputs at least one of the video signals of respective RGB color components or the video signal of the IR component to the display device13. For example, the output unit outputs video signals on the basis of either a simultaneous output mode or a superimposed output mode.

In the simultaneous output mode, the output unit simultaneously outputs the RGB image and the IR image on separate screens. The simultaneous output mode enables the diseased part to be observed by comparing the RGB image and the IR image on the separate screens. In the superimposed output mode, the output unit outputs a composite image in which the RGB image and the IR image are superimposed. The superimposed output mode enables the diseased part luminous with the ICG to be clearly observed, for example in the RGB image.

The display device13displays an image of an object, such as a diseased part, on a screen on the basis of video signals from the CCU12. In the simultaneous output mode, the display device13divides the screen into multiple screens and displays the RGB image and the IR image side by side on each screen. In the superimposed output mode, the display device13displays a composite image in which an RGB image and an IR image are superimposed on each other on a single screen.

Next, functions of the endoscope11and the endoscope system100according to the present embodiment are described. When a subject is observed using the endoscope system100, first, indocyanine green (ICG) as a fluorescent substance is administered to the subject. As a result, ICG accumulates at a site of lymph, tumor, or the like (diseased part).

Next, visible light and near-infrared light are introduced from the light emitting device10to the light source connector111through the transmission cable111z. The light introduced into the light source connector111is guided to the tip side of the scope110and projected from the imaging window110zto be emitted to the diseased part and the periphery of the diseased part. The light reflected from the diseased part and the like and the fluorescence emitted from the ICG are guided to the rear end side of the scope110through the imaging window110zand the optical fiber, converged by the relay lens113to enter into the color separation prism inside the camera head114.

In the color separation prism, among the incident light, the light of the IR component separated by the IR separation prism is imaged as an optical image of an infrared component by the IR light image sensor114IR. The light of the R component separated by the red separation prism is imaged as an optical image of the red component by the R light image sensor114R. The light of the G component separated by the green separation prism is imaged as an optical image of the green component by the G light image sensor114G. The light of the B component separated by the blue separation prism is imaged as an optical image of the blue component by the B light image sensor114B.

The electrical signal of the IR component converted by the IR light image sensor114IR is converted into a video signal by the IR signal processing unit in the CCU12. The electric signals of the R component, G component, and B component converted by the visible light image sensor114V are converted into respective video signals by the RGB signal processing unit in the CCU12. The image signal of the IR component, and the image signals of the R component, G component, and B component in synchronization with each other are output to the display device13.

When the simultaneous output mode is set in the CCU12, the RGB image and the IR image are simultaneously displayed on two screens on the display device13. When the superimposed output mode is set in the CCU12, a composite image in which the RGB image and the IR image are superimposed is displayed on the display device13.

As described above, the endoscope11according to the present embodiment includes the light emitting device10. Therefore, by efficiently exciting the fluorescent drug to emit light using the endoscope11, the diseased part is clearly observed.

Preferably, the endoscope11according to the present embodiment further includes a detector for detecting fluorescence emitted from a fluorescent drug that has absorbed the first wavelength-converted light7. Specifically, preferably, the endoscope11includes the image sensor114A as described above. By providing the endoscope11with the detector for detecting fluorescence emitted from a fluorescent drug in addition to the light emitting device10, the diseased part is specified only by the endoscope11. This makes it possible to perform medical examination and treatment with less burden on the patient, since there is no need to open the abdomen wide to identify the diseased part as in the conventional method. This also enables the doctor using the endoscope11to accurately identify the diseased part, which improves the efficiency of treatment.

Preferably, the medical system is used for either the fluorescence imaging method or photodynamic therapy. The medical system used in these methods is a promising medical technology with a wide range of applications and is highly practical. The medical system illuminates the inside of the living body with a broad near-infrared high-output light through the “living body window” and makes the fluorescent drug or photosensitive drug taken into the living body fully functional, which is expected to have a large therapeutic effect. Further, such a medical system uses the light emitting device10having a relatively simple configuration, which is advantageous in reducing the size and the cost.

The medical system may further include a first image sensor and a second image sensor in addition to the light emitting device10. The first image sensor may detect a reflected light of a visible light component emitted by the light emitting device10. The second image sensor may detect a near-infrared fluorescence component emitted by the drug. The drug is excited by a light emitted by the light emitting device10. The first image sensor is, for example, the visible light image sensor114V as described above. The second image sensor is, for example, the IR light image sensor114IR as described above. The drug is, for example, the fluorescent drug described above.

In this way, it becomes easy to divide the visual image of a diseased part of a living body and the state observation of a near-infrared fluorescent component emitted by the drug (fluorescent protein) administered into the living body into the first image sensor and the second image sensor, respectively. Such a medical system achieves the coexistence of normal observation and special observation, which is advantageous in diagnosing disease state.

[Electronic Apparatus]

Next, an electronic apparatus according to the present embodiment is described. The electronic apparatus according to the present embodiment includes a light emitting device10. As described above, the light emitting device10is expected to have a large therapeutic effect, and it is easy to miniaturize the sensing system. Since the electronic apparatus according to the present embodiment uses the light emitting device10, when it is used for a medical device or a sensing device, a large therapeutic effect, miniaturization of the sensing system, and the like are expected.

The electronic apparatus includes, for example, the light emitting device10, and a light receiving element. The light receiving element is, for example, a sensor, such as an infrared sensor for detecting light in a near-infrared wavelength range. The electronic apparatus may be any of an information recognition device, a sorting device, a detection device, or an inspection device. As described above, these devices also facilitate miniaturization of the sensing system and broadening of the sensing range.

The information recognition device is, for example, a driver support system that recognizes the surrounding situation by detecting reflected components of emitted infrared rays.

The sorting device is, for example, a device that sorts an irradiated object into predetermined categories by using the difference in infrared light components between the irradiation light and reflected light reflected by the irradiated object.

The detection device is, for example, a device that detects a liquid. Examples of liquids include water, and flammable liquids that are prohibited from being transported in aircraft. Specifically, the detection device may be a device for detecting moisture adhering to glass, and moisture absorbed by an object, such as sponge or fine powder. The detection device may visualize the detected liquid. Specifically, the detection device may visualize the distribution information of the detected liquid.

The inspection device may be any of a medical inspection device, an agricultural and livestock inspection device, a fishery inspection device, or an industrial inspection device. These devices are useful for inspecting an inspection object in each industry.

The medical inspection device is, for example, an examination device that examines the health condition of a human or non-human animal. Non-human animals are, for example, domestic animals. The medical inspection device is, for example, a device used for a biological examination, such as a fundus examination or a blood oxygen saturation examination, and a device used for examination of an organ, such as a blood vessel or an organ. The medical inspection device may be a device for examining the inside of a living body or a device for examining the outside of a living body.

The agricultural and livestock inspection device is, for example, a device for inspecting agricultural and livestock products including agricultural products and livestock products. Agricultural products may be used as foods, for example, fruits and vegetables, or cereals, or as fuels, such as oils. Livestock products include, for example, meat and dairy products. The agricultural and livestock inspection device may be a device for non-destructively inspecting the inside or outside of the agricultural and livestock products. Examples of the agricultural and livestock inspection device includes a device for inspecting the sugar content of vegetables and fruits, a device for inspecting the acidity of vegetables and fruits, a device for inspecting the freshness of vegetables and fruits by the visualization of leaf veins, a device for inspecting the quality of vegetables and fruits by the visualization of wounds and internal defects, a device for inspecting the quality of meat, and a device for inspecting the quality of processed foods processed with milk, meat, or the like as raw materials.

The fishery inspection device is, for example, a device for inspecting the flesh quality of fish, such as tuna, or a device for inspecting the presence or absence of the contents in shells of shellfish.

The industrial inspection device is, for example, a foreign matter inspection device, a content inspection device, a condition inspection device, or a structure inspection device.

Examples of the foreign matter inspection device include a device for inspecting foreign matter in a liquid contained in a container, such as a beverage or a liquid medicine, a device for inspecting foreign matter in a packaging material, a device for inspecting foreign matter in a printed image, a device for inspecting foreign matter in a semiconductor or an electronic component, a device for inspecting foreign matter, such as residual bone in food, dust, or machine oil, a device for inspecting foreign matter in processed food in a container, and a device for inspecting foreign matter in medical devices, such as adhesive plasters, medical and pharmaceutical products, or quasi-drugs.

Examples of the content inspection device include a device for inspecting the content of a liquid contained in a container, such as a beverage or a liquid medicine, a device for inspecting the content of a processed food contained in a container, and a device for inspecting the content of asbestos in building materials.

Examples of the state inspection device include a device for inspecting packaging state of a packaging material, and a device for inspecting printing state of a packaging material.

Examples of the structure inspection device include an internal non-destructive inspection device and an external non-destructive inspection device for a composite member or a composite component, such as a resin product. A specific example of the resin product is, for example, a metal brush with a part of metal wire embedded in the resin, and the inspection device inspects the bonding state of the resin and the metal.

The electronic apparatus may use color night vision technology. Color night vision technology uses a correlation of reflection intensity between visible light and infrared rays to colorize an image by assigning infrared rays to RGB signals for each wavelength. According to the color night vision technology, a color image is obtained only by infrared rays, and it is particularly suitable for a security device.

As described above, the electronic apparatus includes the light emitting device10. When the light emitting device10includes a power source, a light source5, and a wavelength converter1, it is not necessary to accommodate all of them in one housing. Therefore, the electronic apparatus according to the present embodiment provides a highly accurate and compact inspection method, or the like, with excellent operability.

[Inspection Method]

Next, an inspection method according to the present embodiment is described. As described above, the electronic apparatus including the light emitting device10is also usable as an inspection device. That is, the light emitting device10is usabel in the inspection method according to the present embodiment. This provides a highly accurate and compact inspection method with excellent operability.

EXAMPLES

The present embodiment is described below in more detail with reference to examples, but the present embodiment is not limited to these examples.

[Preparation of Phosphor]

Example 1

A phosphor activated with Cr3+and a phosphor activated with Ce3+used in example 1 were synthesized using a preparation method utilizing a solid phase reaction. The Cr3+-activated phosphor used in example 1 is an oxide phosphor represented by a formula: Y3(Ga0.97Cr0.03)2Ga3O12. In synthesizing the phosphor activated with Cr3+used in example 1, the following compound powders were used as main raw materials.

Yttrium oxide (Y2O3): purity 3N, Shin-Etsu Chemical Co., Ltd.

Gallium oxide (Ga2O3): purity 4N, Wako Pure Chemical Corporation

Chromium oxide (Cr2O3): Purity 3N, Kojundo Chemical Laboratory Co., Ltd.

First, the above-described raw materials were weighed to obtain a compound of a stoichiometric composition Y3(Ga0.97Cr0.03)2Ga3O12. The weighed raw materials were then put into a beaker containing pure water and stirred with a magnetic stirrer for 1 hour. Thus, a slurry-like mixed raw material of the pure water and raw materials was obtained. Then, the slurry-like mixed raw material was dried entirely using a dryer. The mixed raw material after drying was pulverized using a mortar and a pestle to obtain a calcined raw material.

The above-described calcined raw material was transferred to a small alumina crucible and calcined in air at 1350° C. to 1450° C. for 1 hour in a box-type electric furnace to obtain the phosphor activated with Cr3+. The temperature rise and fall rate was set at 400° C./h. The body color of the obtained phosphor was deep green.

The Ce3+-activated phosphor used in example 1 was a commercially available oxide phosphor expressed by a formula: (Y0.75Gd0.22Ce0.03)3Al2Al3O12.

The obtained phosphor activated with Cr3+and the phosphor activated with Ce3+were mixed so that the weight ratio was 1:1 to obtain a mixed powder of example 1. A mortar and pestle were used for mixing, and the mixing time was 3 minutes.

Example 2

A phosphor activated with Cr3+and a phosphor activated with Ce3+used in example 2 were synthesized using a preparation method utilizing a solid phase reaction. The Cr3+-activated phosphor used in example 2 is an oxide phosphor represented by a formula: (Gd0.75La0.25)3(Ga0.97Cr0.03)2Ga3O12. In synthesizing the phosphor activated with Cr3+used in example 2, the following compound powders were used as main raw materials.

Gadolinium oxide (Gd2O3): purity 3N, Wako Pure Chemical Corporation

Lanthanum oxide (La2O3): purity 3N, Wako Pure Chemical Corporation

Gallium oxide (Ga2O3): purity 4N, Wako Pure Chemical Corporation

Chromium oxide (Cr2O3): Purity 3N, Kojundo Chemical Laboratory Co., Ltd.

First, the above-described raw materials were weighed to obtain a compound of a stoichiometric composition (Gd0.75La0.25)3(Ga0.97Cr0.03)2Ga3O12. The weighed raw materials were then put into a beaker containing pure water and stirred with a magnetic stirrer for 1 hour. Thus, a slurry-like mixed raw material of the pure water and raw materials was obtained. Then, the slurry-like mixed raw material was dried entirely using a dryer. The mixed raw material after drying was pulverized using a mortar and a pestle to obtain a calcined raw material.

The above-described calcined raw material was transferred to a small alumina crucible and calcined in air at 1400° C. to 1500° C. for 1 hour in a box-type electric furnace to obtain the phosphor activated with Cr3+. The temperature rise and fall rate was set at 400° C./h. The body color of the obtained phosphor was light green.

The Ce3+-activated phosphor used in example 2 was a commercially available LuAG phosphor (Lu3Al2Al3O12:Ce3+). In consideration of the fluorescence peak wavelength and the like, the chemical composition of the LuAG phosphor is estimated to be (Lu0.995Ce0.005)3Al2Al3O12.

The obtained phosphor activated with Cr3+and the phosphor activated with Ce3+were mixed so that the weight ratio was 1:1 to obtain a mixed powder of example 2. A mortar and pestle were used for mixing, and the mixing time was 3 minutes.

[Evaluation]

(Crystal Structure Analysis)

The crystal structures of the Cr3+-activated phosphor and the Ce3+-activated phosphor used in example 1 were evaluated using an X-ray diffraction apparatus (X'Pert PRO; manufactured by Spectris Co., Ltd., PANalytical).

As a result of evaluation, it was found that the Cr3+-activated phosphor and the Ce3+-activated phosphor used in example 1 were mainly made from compounds with a garnet crystal structure, although the details are omitted. That is, both the Cr3+-activated phosphor and the Ce3+-activated phosphor used in example 1 were found to be garnet phosphors.

Next, the crystal structures of the Cr3+-activated phosphor and the Ce3+-activated phosphor used in example 2 were evaluated using an X-ray diffraction apparatus (X'Pert PRO; manufactured by Spectris Co., Ltd., PANalytical).

As a result of evaluation, it was found that the Cr3+-activated phosphor and the Ce3+-activated phosphor used in example 2 were mainly made from compounds with a garnet crystal structure, although the details are omitted. That is, both the Cr3+-activated phosphor and the Ce3+-activated phosphor used in example 2 were found to be garnet phosphors.

(Spectroscopic Property)

Next, the mixed powders of example 1 and example 2 were each laid in a stainless steel cylindrical folder having a diameter of 10 mm and a depth of 1 mm to form a wavelength converter, and the fluorescence spectral characteristics were evaluated. A quantum efficiency measurement system (QE-1100, manufactured by Otsuka Electronics Co., Ltd.) provided with an instantaneous multi-photometric system (MCPD-9800, manufactured by Otsuka Electronics Co., Ltd.) was used for the evaluation. The excitation wavelength was set to 450 nm.

FIG.12illustrates the fluorescence spectrum of example 1. The fluorescence spectrum is normalized so that the maximum light emission intensity is 1. The fluorescence spectrum of example 1 was formed from a broad spectrum determined to be attributed to the 5d1→4f1transition of Ce3+and a broad spectrum determined to be attributed to the d-d transition of Cr3+. The peak wavelengths of respective spectra were 558 nm and 710 nm.

As is seen fromFIG.12, the fluorescence spectrum of example 1 has a less amount of a deep red light component, which becomes noise in the near-infrared light image sensor, than the conventional fluorescence spectrum. This is considered to be because the Cr3+-activated phosphor strongly absorbed the light component in the deep red range among the fluorescent components of the Ce3+-activated phosphor. It is not known that such an effect actually works, and it is demonstrated only by experimental verification.

In the fluorescence spectrum of example 1, the ratio of the minimum light emission intensity to the maximum light emission intensity was 39% in the wavelength range of 550 nm or more to 700 nm or less. This indicates that the wavelength converter of example 1 receives blue light and emits a fluorescence in which the ratio of the minimum light emission intensity to the maximum light emission intensity is 40% or less in the wavelength range of 550 nm or more to 700 nm or less.

FIG.13illustrates the fluorescence spectrum of example 2. The fluorescence spectrum is normalized so that the maximum light emission intensity is 1. The fluorescence spectrum of example 2 was formed from a broad spectrum determined to be attributed to the 5d1→4f1transition of Ce3+and a broad spectrum determined to be attributed to the d-d transition of Cr3+. The peak wavelengths of respective spectra were 517 nm and 750 nm.

As is seen fromFIG.13, the fluorescence spectrum of example 2 has a less amount of a deep red light component, which becomes noise in the near-infrared light image sensor, than the conventional fluorescence spectrum. This is considered to be because the Cr3+-activated phosphor strongly absorbed the light component in the deep red range among the fluorescent components of the Ce3+-activated phosphor. It is not known that such an effect actually works, and it is demonstrated only by experimental verification.

In the fluorescence spectrum of example 2, the ratio of the minimum light emission intensity to the maximum light emission intensity was 4% in the wavelength range of 550 nm or more to 700 nm or less. This indicates that the wavelength converter of example 2 receives blue light and emits a fluorescence in which the ratio of the minimum light emission intensity to the maximum light emission intensity is 40% or less in the wavelength range of 550 nm or more to 700 nm or less.

The entire contents of Japanese Patent Application No. 2019-082925 (filed Apr. 24, 2019) are incorporated herein by reference.

Although the contents of the present embodiment have been described in accordance with the examples above, it is obvious to those skilled in the art that the present embodiment is not limited to these descriptions, and that various modifications and improvements are possible.

INDUSTRIAL APPLICABILITY

In accordance with the present disclosure, there is provided a wavelength converter capable of emitting a fluorescence spectrum in which a visible light fluorescent component and a near-infrared fluorescent component are sufficiently separated and the light emission intensity of a deep red light is relatively low, and a light emitting device, a medical system, an electronic apparatus and an inspection method using the wavelength converter.

REFERENCE SIGNS LIST

1Wavelength converter2First phosphor3Second phosphor5Light source10Light emitting device11Endoscope (medical system)101Endoscope system (medical system)114V Visible light image sensor (first image sensor)114IR IR light image sensor (second image sensor)