Near-infrared light emitting device, spectroscopic device, and spectroscopy

Abstract

A near-infrared light emitting device (100) is configured to satisfy the relationship 0.853MVIS  MNIR < 1.147MVIS, MVIS is the ratio of Imax-VIS-150 to Imax-VIS-30, Imax-VIS-30 is the maximum fluorescence intensity value of the visible fluorescent component when the temperature of a wavelength converter (2) is 30°C, Imax-VIS-150 is the maximum fluorescence intensity value of the visible fluorescent component when the temperature of the wavelength converter (2) is 150°C, MNIR is the ratio of Imax-NIR-150 to Imax-NIR-30, Imax-NIR-30 is the maximum fluorescence intensity value of the near-infrared fluorescent component when the temperature of the wavelength converter (2) is 30°C, and Imax-NIR-150 is the maximum fluorescence intensity value of the near-infrared fluorescent component when the temperature of the wavelength converter (2) is 150°C.

Description

Near-infrared light emitting device, spectroscopic device, and spectroscopy

[0001] The present invention relates to a near-infrared light emitting device, and a spectroscopic device and a spectroscopy method using the same.

[0002] Conventionally, a near-infrared light-emitting device including a solid-state light-emitting element and a wavelength converter has been known as a light-emitting device. Such a near-infrared light-emitting device is disclosed in Patent Document 1, in which the wavelength converter includes a visible phosphor that emits fluorescence having a maximum fluorescence intensity within the wavelength range of visible light and a near-infrared phosphor that emits fluorescence having a maximum fluorescence intensity within the wavelength range of near-infrared light. Such a near-infrared light-emitting device has the advantage of being able to perform both normal observation using visible light and special observation using near-infrared light.

[0003] International Publication No. 2020 / 217671

[0004] However, the temperature quenching of conventional near-infrared phosphors is greater than that of visible phosphors. Therefore, as the temperature of the phosphor rises due to the lighting of the solid-state light-emitting device, the intensity of the near-infrared fluorescent component may decrease relative to the intensity of the visible fluorescent component. Therefore, it may take some time for the intensity of the output light of the near-infrared light-emitting device to stabilize.

[0005] The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a near-infrared light emitting device in which the shape of the spectral distribution changes little with an increase in temperature of the wavelength converter, and a spectroscopic device and a spectroscopic method using the same.

[0006] In order to solve the above problems, a near-infrared light emitting device according to an aspect of the present invention comprises a solid-state light emitting element, a wavelength converter including a visible phosphor that emits visible fluorescence having a maximum fluorescence intensity within the wavelength range of visible light, and a near-infrared phosphor that emits near-infrared fluorescence having a maximum fluorescence intensity within the wavelength range of near-infrared light. The near-infrared light emitting device emits output light including visible fluorescence and near-infrared fluorescence. The output light includes a visible fluorescent component having a spectral intensity within the wavelength range of visible light and a near-infrared fluorescent component having a spectral intensity within the wavelength range of near-infrared light. The near-infrared light emitting device has a wavelength conversion efficiency of 0.853M. ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳThe relationship is configured to satisfy the following. ＶＩＳ is I ｍａｘ－ＶＩＳ－３０ I against ｍａｘ－ＶＩＳ－１５０ The ratio is I ｍａｘ－ＶＩＳ－３０ is the maximum fluorescence intensity of the visible fluorescence component when the temperature of the wavelength converter is 30°C. ｍａｘ－ＶＩＳ－１５０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter is 150°C. ＮＩＲ is I ｍａｘ－ＮＩＲ－３０ I against ｍａｘ－ＮＩＲ－１５０ The ratio is I ｍａｘ－ＮＩＲ－３０ is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter is 30°C. ｍａｘ－ＮＩＲ－１５０ is the maximum fluorescence intensity of the near-infrared fluorescence component when the temperature of the wavelength converter is 150°C.

[0007] A spectroscopic device according to an aspect of the present invention includes a near-infrared light emitting device.

[0008] Spectroscopy according to aspects of the present invention utilizes near-infrared emitting devices.

[0009] FIG. 1 is a schematic diagram showing an example of the structure of a near-infrared light emitting device according to an embodiment. FIG. 2 is a schematic diagram showing an example of the structure of a spectroscopy device according to an embodiment. FIG. 3 is a schematic diagram showing an example of the structure of a spectroscopy device according to another embodiment. FIG. 4 shows the spectral distribution of output light emitted from the near-infrared light emitting device of this example. FIG. 5 is a graph showing the temperature quenching of visible phosphors and near-infrared phosphors used in evaluation. FIG. 6 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Example 2. FIG. 7 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Example 3. FIG. 8 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Example 4. FIG. 9 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Example 5. FIG. 10 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Example 6. FIG. 11 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Example 7. FIG. 12 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Comparative Example 1. FIG. 13 shows the fluorescence spectrum at each temperature of a mixed phosphor according to Comparative Example 2. FIG. 14 shows the fluorescence spectrum at each temperature of a LiGa ５ O ８ : Cr ３＋Near-infrared phosphor and LiGa according to Comparative Example 1 ５ O ８ : Cr ３＋ X-ray diffraction pattern of the deep red phosphor and LiGa registered in ICSD (Inorganic Crystal Structure Database) ５ O ８ FIG. 15 shows the X-ray diffraction pattern of LiGa ５ O ８ : Cr ３＋ Near-infrared phosphor and LiGa ５ O ８ : Cr ３＋ Fluorescence spectra of deep red phosphors. ５ O ８ : Cr ３＋ Near-infrared phosphor and LiGa ５ O ８ : Cr ３＋ 10 is a graph showing the relationship between the temperature of a deep red phosphor and the maximum intensity of fluorescence emitted by the phosphor.

[0010] The near-infrared light emitting device, spectroscopic device, and spectroscopic method according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0011] [Near-infrared light-emitting device] As described above, the temperature quenching of conventionally used near-infrared phosphors is larger than that of visible phosphors. The relatively large temperature quenching of near-infrared phosphors may be an essential issue resulting from the optical properties of near-infrared phosphors. The following provides an overview of the causes of this issue.

[0012] In the device mainly considered for practical use, the wavelength converter absorbs blue light. The absorbed blue light is then converted into visible phosphors (especially Ce) contained in the wavelength converter. ３＋ Activated phosphor or Eu ２＋ activated phosphors) and near-infrared phosphors (especially Cr ３＋ The absorbed blue light is converted into visible light and near-infrared light, which have wavelengths longer than that of the blue light absorbed by the activated phosphor.

[0013] Therefore, the fluorescence of near-infrared phosphors has a larger Stokes shift (energy difference between light absorption and fluorescence emission) than that of visible phosphors. This also means that the fluorescence of near-infrared phosphors is wavelength-converted light due to electron energy transition with a large Franck-Condon offset (shift in the equilibrium position between the ground state and the excited state). For example, Cr ３＋ It is thought that the equilibrium position of the excited state of the fluorescent ion in such near-infrared phosphors is close to the ground state, making thermal quenching more likely.

[0014] Therefore, in the present disclosure, the temperature quenching of the visible phosphor and the temperature quenching of the near-infrared phosphor are set within a predetermined range, and it has been found that this makes the spectral distribution of output light, which includes visible light from the visible phosphor and near-infrared fluorescence from the near-infrared phosphor, stable against the temperature of the wavelength converter.

[0015] A near-infrared light emitting device 100 according to this embodiment will be described below with reference to FIG. 1 . FIG. 1 is a schematic diagram showing an example of a near-infrared light emitting device 100 according to an embodiment. As shown in FIG. 1 , the near-infrared light emitting device 100 includes a solid-state light emitting element 1 and a wavelength converter 2. The wavelength converter 2 includes a visible phosphor and a near-infrared phosphor. The visible phosphor emits visible fluorescence 22 having a maximum fluorescence intensity within the wavelength range of visible light. The near-infrared phosphor emits near-infrared fluorescence 21 having a maximum fluorescence intensity within the wavelength range of near-infrared light. The near-infrared light emitting device 100 is configured to emit output light 20 including the visible fluorescence 22 and the near-infrared fluorescence 21. The output light 20 includes a visible fluorescent component having a spectral intensity within the wavelength range of visible light and a near-infrared fluorescent component having a spectral intensity within the wavelength range of near-infrared light.

[0016] The solid-state light-emitting element 1 is configured to emit primary light 10. The output light 20 may include the primary light 10. The primary light 10 is preferably blue light having a maximum fluorescence intensity within a blue wavelength range of 435 nm or more and less than 480 nm, particularly 440 nm or more and less than 470 nm. In this manner, a single type of solid-state light-emitting element 1 can excite both visible and near-infrared phosphors. This results in a near-infrared light-emitting device 100 that is advantageous in simplifying the lighting circuit. Furthermore, if the primary light 10 can excite both visible and near-infrared phosphors with relatively short-wavelength blue light, the technical options for visible phosphors can be expanded. In other words, the primary light 10 can be used in combination with any of the green, yellow, orange, and red phosphors described below.

[0017] The solid-state light-emitting element 1 is an element that converts electricity into light, and when powered and driven, converts the supplied electrical energy into light energy. The converted light energy is then emitted from the light extraction surface as primary light 10. Representative examples of the solid-state light-emitting element 1 include light-emitting diodes (LEDs) and laser diodes (LDs).

[0018] The wavelength converter 2 includes a visible phosphor and a near-infrared phosphor. The visible phosphor may be configured to be excited by the primary light 10 emitted by the solid-state light-emitting element 1. The near-infrared phosphor may be configured to be excited by the primary light 10 emitted by the solid-state light-emitting element 1.

[0019] The visible phosphor emits visible fluorescence 22 having a maximum fluorescence intensity within the wavelength range of visible light. The visible phosphor may be at least one phosphor selected from the group consisting of a green phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 490 nm or more and less than 570 nm, a yellow phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 570 nm or more and less than 585 nm, an orange phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 585 nm or more and less than 620 nm, and a red phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 620 nm or more and less than 780 nm. This allows the spectral distribution of the visible fluorescent component to be adjusted. Therefore, the visible fluorescent component of the output light 20 emitted from the near-infrared light-emitting device 100 can be adjusted according to the application.

[0020] The visible phosphor is Ce ３＋ Garnet phosphor activated with Eu ２＋ Alkaline earth metal nitrosilicate activated with Eu ２＋ Alternatively, the near-infrared light emitting device 100 may include at least one phosphor selected from the group consisting of alkaline earth metal nitride aluminosilicates activated with an alkali metal nitrate. These visible phosphors have a proven track record of practical use in LED lighting. Therefore, the near-infrared light emitting device 100 includes these visible phosphors that are not only easy to procure but also safe in terms of reliability and handling.

[0021] Ce ３＋ Examples of the garnet phosphor activated by the general formula RE ３ Al ２ (AlO ４ ) ３ : Ce ３＋ a phosphor represented by the formula: Ca ３ Sc ２ (SiO ４ ) ３ : Ce ３＋ , Y ３ Ga ２ (AlO ４ ) ３ : Ce ３＋ In the above general formula, RE represents a rare earth element, and is, for example, at least one rare earth element selected from the group consisting of Sc, Y, La, Tb, Gd, and Lu. ３ Al ２ (AlO ４ ) ３ : Ce ３＋ Specific examples of the phosphor represented by the formula include Lu ３ Al ２ (AlO ４ ) ３ : Ce ３＋ , Y ３ Al ２ (AlO ４ ) ３ : Ce ３＋ (YAG) and (Y,Gd) ３ Al ２ (AlO ４ ) ３ : Ce３＋ Examples include:

[0022] EU ２＋ Examples of activated alkaline earth metal nitrosilicates include Sr ２ Si ５ N ８ :Eu ２＋ , Ca ２ Si ５ N ８ :Eu ２＋ and solid solutions thereof.

[0023] EU ２＋ Examples of activated alkaline earth metal nitride aluminosilicates include those represented by the general formula MAlSiN ３ :Eu ２＋ In the above general formula, M represents magnesium or an alkaline earth metal, and is, for example, at least one metal element selected from the group consisting of Mg, Ca, Sr, and Ba. Specifically, Eu ２＋ Examples of activated alkaline earth metal nitride aluminosilicates include CaAlSiN ３ :Eu ２＋ (CASN), SrAlSiN ３ :Eu ２＋ , (Sr,Ca)AlSiN ３ :Eu ２＋ (SCASN) and solid solutions thereof.

[0024] Among these, it is preferable that the visible phosphor contains at least one phosphor selected from the group consisting of YAG, CASN, and SCASN.

[0025] The near-infrared phosphor emits near-infrared fluorescence 21 having a maximum fluorescence intensity within the near-infrared wavelength range. The near-infrared fluorescence 21 may have a spectral intensity across at least the entire wavelength range from 700 nm to 1000 nm. Such a spectral distribution is suitable for detecting the characteristic absorption bands of the stretching vibrations of N-H, C-H, and O-H by spectroscopy. In a preferred embodiment, the spectral intensity at a wavelength of 1000 nm in the spectral distribution is greater than the spectral intensity at a wavelength of 700 nm. In a preferred embodiment, the fluorescence emitted has a greater proportion of near-infrared light components at wavelengths longer than 750 nm, more preferably 780 nm, than the proportion of light components at wavelengths shorter than the wavelengths. Such a spectral distribution is particularly suitable for a near-infrared light-emitting device 100 for infrared spectroscopy.

[0026] The near-infrared fluorescent light 21 may have a maximum fluorescence intensity within a wavelength range of 800 nm or more and less than 900 nm. Such near-infrared fluorescent light 21 may be, for example, LiGa ５ O ８ : Cr ３＋ Near-infrared phosphors and similar near-infrared phosphors can be emitted by using near-infrared phosphors that exhibit fluorescent properties with extremely small temperature quenching. ３＋ Activated garnet phosphor and Eu ２＋ The near-infrared light emitting device 100 is advantageously configured when combined with a visible phosphor with small temperature quenching, such as an activated alkaline earth metal nitride aluminosilicate phosphor, to form the wavelength converter 2. The near-infrared fluorescence 21 preferably has a maximum fluorescence intensity within a wavelength range of 800 nm or more and 860 nm or less.

[0027] The half-width of the spectrum having the maximum fluorescence intensity of the near-infrared fluorescence 21 preferably exceeds 180 nm. Therefore, it is possible to obtain near-infrared light components having a spectral distribution over a wide wavelength range of 700 to 1000 nm using only one type of near-infrared phosphor, without using several types of near-infrared phosphors. This reduces the risk of changes in the shape of the spectral distribution of the near-infrared fluorescence 21 or the near-infrared fluorescent components due to differences in temperature quenching when using different types of near-infrared phosphors. The spectral half-width of the near-infrared fluorescence 21 may be 180 nm or more and 240 nm or less, or 200 nm or more and 220 nm or less.

[0028] The near-infrared phosphor is the compound LiGa ５ O ８ At least chromium ions that function as fluorescent ions may be added to the crystal of an inorganic compound having the same spinel-type crystal structure as the compound LiGa. ５ O ８ Whether or not a near-infrared phosphor has the same spinel-type crystal structure as the compound LiGa registered in ICSD can be determined by measuring the X-ray diffraction pattern by X-ray diffraction. ５ O ８ This means that the XRD pattern is substantially the same as that of (Registry No.: 33716).

[0029] The crystal may contain an alkali metal of Group 1 element, at least one of a Group 13 element and scandium, and oxygen. ｙ (D １－ｘ Cr ｘ ) ５ O ８ In the above formula, A may mainly contain an alkali metal, and D may mainly contain at least one of a Group 13 element and scandium. Note that D may mainly contain a Group 13 element.

[0030] Here, "A containing an alkali metal as a main component" means that A contains 75 mol% or more of an alkali metal. A may contain 90 mol% or more, 95 mol% or more, or even 100 mol% of an alkali metal. Furthermore, "D containing at least one of a Group 13 element and scandium as a main component" means that D contains 75 mol% or more of at least one of a Group 13 element and scandium. D may contain 90 mol% or more, 95 mol% or more, or even 100 mol% of at least one of a Group 13 element and scandium.

[0031] The alkali metal is preferably at least one element selected from the group consisting of Li, Na, K, Rb, and Cs, and more preferably at least one of Li and K. The Group 13 element is preferably at least one element selected from the group consisting of Al, Ga, and In, and more preferably Ga.

[0032] The crystal preferably has a low alkali metal content relative to the stoichiometric composition. １－ｘ Cr ｘ ) ５ O ８ In this way, the chemical properties of the near-infrared phosphor are such that the element A is deficient. ５ O ８ Therefore, LiGa is a material that uses a crystal similar to that of ５ O ８ : Cr ３＋ It is expected to exhibit unique fluorescent properties similar to those of near-infrared phosphors, and when applied to spectroscopy, it is expected to enable highly accurate non-destructive measurements.

[0033] The near-infrared phosphor has the general formula A ｙ (D １－ｘ Cr ｘ ) ５ O ８where A mainly contains an alkali metal, D mainly contains at least one of a Group 13 element and scandium, and y is preferably smaller than 1. When y is smaller than 1, a near-infrared phosphor with a low proportion of emission components of emission lines is obtained. y is more preferably 0.90 or less, even more preferably 0.85 or less, and particularly preferably 0.83 or less. y is preferably 0.70 or more. When y is 0.70 or more, the β-Ga ２ O ３ : Cr ３＋ The phosphors are less likely to be mixed together, and the desired unique fluorescent properties are more likely to be obtained. y is more preferably 0.75 or more, and even more preferably 0.77 or more.

[0034] The above crystal is LiGa ５ O ８ It is preferable that the crystal contains LiGa as the main component, and that a part of Ga is substituted with Cr. ５ O ８ "Containing mainly LiGa" means that the crystal is ５ O ８ It means that the compound contains 75 mol % or more of the compound, and preferably contains 90 mol % or more of the compound.

[0035] Here, the general formula LiGa ５ O ８ : Cr ３＋ A phosphor represented by the formula (hereinafter referred to as LiGa ５ O ８ : Cr ３＋ The LiGaP phosphor has been known as a deep red phosphor that emits a line-shaped deep red fluorescent component with a maximum fluorescence intensity around 715 to 720 nm. ５ O ８ : Cr ３＋ We have produced several prototype phosphors and evaluated their fluorescent properties, and found that they function as near-infrared phosphors when produced under specific blending and synthesis conditions. ５ O ８ : Cr ３＋ It has also been found that there are examples of phosphors that exhibit the following fluorescent properties, which are unusual for near-infrared phosphors.

[0036] (1) It has a maximum fluorescence intensity (fluorescence peak) in the wavelength range of 800 nm to 900 nm, for example, around 830 nm. (2) It has fluorescent components over a wide wavelength range of 700 to 1000 nm. (3) It has an extremely broad fluorescence spectrum, with the half-width of the spectrum with the maximum fluorescence intensity exceeding 180 nm. (4) It has very small temperature quenching (the maximum fluorescence intensity at a phosphor temperature of 150°C exceeds 90% of the maximum fluorescence intensity at 30°C). (5) The wavelength conversion efficiency (internal quantum efficiency) for converting absorbed visible light components to near-infrared light components exceeds 80%, even though it is a prototype in the early stages of development.

[0037] That is, LiGa ５ O ８ : Cr ３＋ It was found that the phosphor does not primarily function as a deep-red phosphor, but rather functions as a highly efficient phosphor that emits near-infrared light components with an ultra-wide fluorescence spectrum and has extremely small temperature quenching. Utilizing these fluorescence characteristics, which are unique among near-infrared phosphors, it can be utilized in a near-infrared light-emitting device 100 that shows only small changes in the shape of the spectral distribution with an increase in temperature of the wavelength converter 2 and is suitable for high-precision non-destructive testing by spectroscopy.

[0038] For the purpose of facilitating understanding of the present disclosure, Table 1 summarizes the fluorescence intensity maintenance rate, internal quantum efficiency, fluorescence peak wavelength, and FWHM of some reported near-infrared phosphors. ５ O ８ : Cr ３＋ Near-infrared phosphor and LiGa according to Comparative Example 1 ５ O ８ : Cr ３＋ The fluorescence properties of the deep red phosphors are also described.

[0039] The fluorescence intensity retention rate is a value inversely correlated with temperature quenching, and is defined as the maximum fluorescence intensity at a phosphor temperature of 150°C relative to the maximum fluorescence intensity at a phosphor temperature of 30°C. The internal quantum efficiency is the efficiency of photon conversion of absorbed visible light components into near-infrared light components. The fluorescence peak wavelength is the wavelength at which the fluorescence intensity is maximum. The FWHM is the half-width of the spectrum having the maximum fluorescence intensity.

[0040] For reference, Table 2 summarizes the fluorescent properties of representative visible phosphors known for use in LED lighting.

[0041]

[0042]

[0043] Generally, for many phosphors, the degree of temperature quenching correlates with the wavelength conversion efficiency level of the phosphor when the manufacturing conditions are optimized. Therefore, as can be seen from Tables 1 and 2, phosphors with higher fluorescence intensity retention tend to exhibit higher internal quantum efficiency.

[0044] In the table, some phosphors with low fluorescence intensity retention rates exhibit high internal quantum efficiency, but this is due to differences in the mode of temperature quenching characteristics. For example, a phosphor that exhibits temperature quenching characteristics that cause a rapid drop in fluorescence intensity above about 100°C will have high internal quantum efficiency at room temperature, such as 30°C, but low fluorescence intensity at 150°C. In other words, a phosphor with high internal quantum efficiency at room temperature does not necessarily have low temperature quenching (high maximum fluorescence intensity), but a phosphor with low temperature quenching can be expected to have a high level of internal quantum efficiency.

[0045] As can be seen from a comparison of Tables 1 and 2, many of the near-infrared phosphors in Table 1 have lower fluorescence intensity maintenance rates than the visible phosphors in Table 2, and most of the phosphors have large temperature quenching.

[0046] As far as the inventors' investigations and evaluations are concerned, the near-infrared phosphors that have a fluorescence intensity maintenance rate of more than 90% when the phosphor temperature is 150° C. are the Ca phosphors listed in Table 1. ３ Sc ２ Si ３ O １２ : Cr ３＋ and LiGa ５ O ８ : Cr ３＋Among these phosphors, when it comes to near-infrared phosphors that have a fluorescence peak in the wavelength region exceeding 800 nm or that emit fluorescence with a FWHM exceeding 180 nm, LiGa ５ O ８ : Cr ３＋ Therefore, the near-infrared phosphor according to the present disclosure is limited to LiGa. ５ O ８ : Cr ３＋ is considered a near-infrared phosphor that exhibits exceptional fluorescence properties.

[0047] In addition, LiGa, which has a maximum fluorescence intensity in the wavelength region exceeding 800 nm, particularly in the vicinity of 850 nm, ５ O ８ : Cr ３＋ The fluorescence of near-infrared phosphors has a form that is relatively close to the spectral distribution of halogen lamps. Therefore, the use of such near-infrared fluorescent components is suitable for replacing halogen lamps, which emit a lot of heat. In addition, it has been discovered in recent years that simply irradiating harvested fruits and vegetables with near-infrared light of a wavelength of around 850 nm for a very short time can prevent subsequent loss of freshness and decay, and can improve fruit quality by maintaining vitamin C, preventing softening, and maintaining luster. For this reason, LiGa ５ O ８ : Cr ３＋ The fluorescence of near-infrared fluorescent materials is also suitable for preserving the freshness of fruits and vegetables as described above.

[0048] On the other hand, LiGa according to one embodiment ５ O ８ : Cr ３＋ Near-infrared phosphors emit ultra-broadband near-infrared light components with a fluorescence spectrum half-width exceeding 180 nm. Therefore, with just one type of near-infrared phosphor, it is possible to obtain near-infrared light components with a spectral distribution over a wide wavelength range from 700 to 1000 nm. This reduces the need to use multiple types of near-infrared light components with different fluorescence peak wavelengths, making it suitable for simplifying the technology.

[0049] It should be noted that many near-infrared phosphors, especially those that emit long-wavelength near-infrared light components, exhibit relatively large temperature quenching.５ O ８ : Cr ３＋ There are many unknowns about why near-infrared phosphors exhibit the exceptional fluorescent properties described above. Future academic investigations into these causes are anticipated. One hypothesis, as mentioned at the beginning, is that the equilibrium position of the excited state of the fluorescent ion tends to be close to the ground state.

[0050] The near-infrared fluorescence 21 or the near-infrared fluorescence component may have a spike in the wavelength range of 710 nm to 730 nm. ５ O ８ : Cr ３＋ Generally, such a spike is observed in the fluorescence spectrum of a near-infrared phosphor. In other words, a near-infrared phosphor that emits fluorescence with such a spike may have extremely small temperature quenching. On the other hand, the near-infrared fluorescence 21 or the near-infrared fluorescent component may not have a spike in the wavelength range of 710 nm or more and 730 nm or less. Alternatively, even if the near-infrared fluorescence 21 or the near-infrared fluorescent component has a spike, it may have a maximum fluorescence intensity within the wavelength range of 800 nm or more and 860 nm or less. ＮＩＲ , the maximum spike intensity is I ＤＲ In this case, I ＤＲ Ga I ＮＩＲ It is preferable that the peak wavelength is less than twice the wavelength of the near-infrared light emitting device 100. Here, the spike refers to a sharp peak near 720 nm, as shown in FIG. 15, for example. When the spectral distribution is expressed as spectral data in 1 nm increments, the spike occurs when the spectral data changes by more than 7% / nm within the above wavelength range. The near-infrared phosphor as described above emits fluorescence with a large proportion of near-infrared light components on the wavelength side longer than 800 nm. Such a near-infrared phosphor is more suitable for the near-infrared light emitting device 100 for infrared spectroscopy. In addition, I ＤＲ is I ＮＩＲ It may be less than 1.25 times, less than 1.0 times, or less than 0.8 times.

[0051] The near-infrared phosphor is Cr ３＋ The visible phosphor is activated by Eu ２＋Alkaline earth metal nitrosilicate activated with Eu ２＋ The phosphor may be at least one of alkaline earth metal nitride aluminosilicate activated with Cr. ３＋ The activated phosphor tends to have an excitation peak (absorption peak) in the orange to red wavelength region of 600 nm or more and less than 650 nm. ２＋ Alkaline earth metal nitride silicates and alkaline earth metal nitride aluminosilicates activated with SiO 2 tend to have a fluorescence peak in the orange to red wavelength region of 600 nm or more and less than 650 nm. Therefore, this configuration is advantageous in maintaining a constant ratio of light components absorbed by the near-infrared phosphor when the fluorescence spectrum of the visible phosphor shifts to longer wavelengths with increasing temperature, resulting in a near-infrared light-emitting device 100 that is advantageous in suppressing fluctuations in the spectral distribution with increasing temperature.

[0052] The wavelength converter 2 may contain a resin fluorescent film, fluorescent ceramics, a composite, or the like. The composite may contain at least one of a resin fluorescent film and fluorescent ceramics. The wavelength converter 2 may contain 95% by mass or more, 99% by mass or more, or even 100% by mass, of an inorganic compound. A wavelength converter 2 with a high proportion of inorganic compounds has excellent thermal conductivity and can improve heat dissipation.

[0053] The resin fluorescent film may have particulate phosphor dispersed in the resin. The resin fluorescent film can be formed, for example, by curing a phosphor paste obtained by mixing a resin with a powdered phosphor. The resin may be a translucent resin, such as a silicone resin. The fluorescent ceramic may be a molded body obtained by molding a phosphor. The fluorescent ceramic can be formed, for example, by pressurizing and heating phosphor raw material or phosphor powder to cause reactive sintering.

[0054] The wavelength converter 2 may contain a fluorescent ceramic. The wavelength converter 2 may contain a fluorescent ceramic as a main component. The wavelength converter 2 containing a fluorescent ceramic as a main component means that the wavelength converter 2 contains 75% by weight or more of fluorescent ceramic. The wavelength converter 2 may contain 90% by weight or more of fluorescent ceramic.

[0055] The fluorescent ceramic may contain a near-infrared phosphor as a main component. The term "a fluorescent ceramic containing a near-infrared phosphor as a main component" means that the fluorescent ceramic contains 75% or more by weight of the near-infrared phosphor. The fluorescent ceramic may contain 90% or more by weight, or even 100% by weight, of the near-infrared phosphor. The fluorescent ceramic may also contain at least the phosphor with the greatest temperature quenching among the phosphors used. This not only provides excellent thermal conductivity but also increases the optical absorption rate of the excitation light. This is advantageous for heat dissipation design and high output, particularly for increasing the output of near-infrared light components and fluorescent components emitted by phosphors with large temperature quenching.

[0056] The output light 20 includes a visible fluorescent component and a near-infrared fluorescent component. The visible fluorescent component has a spectral intensity within the wavelength range of visible light. The near-infrared fluorescent component has a spectral intensity within the wavelength range of near-infrared light.

[0057] The output light 20 may have a spectral intensity over the entire wavelength range of at least 700 nm to 1000 nm, and the near-infrared light emitting device 100 emitting such output light 20 is suitable for detecting or analyzing the characteristic absorption bands of the N-H, C-H, and O-H stretching vibrations by spectroscopy.

[0058] It is preferable that the output light 20 does not have the above-mentioned spikes. Specifically, it is preferable that the spectral distribution within the wavelength range of 700 nm to 1000 nm change smoothly with wavelength. This makes it possible to suppress measurement errors and analysis errors at specific wavelengths and obtain highly reliable evaluation data, resulting in a near-infrared light-emitting device 100 that is advantageous for near-infrared spectroscopy. More specifically, when the spectral distribution is expressed as spectral data in 1-nm increments, it is preferable that the spectral data do not change by more than 7% / nm, particularly 5% / nm, within the wavelength range of 700 nm to 1000 nm.

[0059] The output light 20 may have a spectral peak within a wavelength range of at least 800 nm to 900 nm, particularly 800 nm to 860 nm. Such output light 20 has a spectral peak in the near-infrared wavelength region similar to that of a halogen bulb. This allows for relatively easy use of components and accompanying software from conventional spectroscopic devices that use halogen bulbs. Therefore, spectroscopic devices can be industrially produced without major design changes. Furthermore, it has recently been discovered that simply irradiating harvested fruits and vegetables with near-infrared light at a wavelength of approximately 850 nm for a very short period of time can prevent subsequent loss of freshness and spoilage, and can improve fruit quality by maintaining vitamin C, inhibiting softening, and maintaining luster. Therefore, the near-infrared light-emitting device 100 according to this embodiment is advantageous for preserving the freshness of such fruits and vegetables.

[0060] The half-width of the spectrum having the maximum fluorescence intensity in the wavelength range of 800 nm or more and less than 900 nm may exceed 180 nm. This allows for the generation of near-infrared light components with a spectral distribution over a wide wavelength range. Therefore, the near-infrared light emitting device 100 is suitable for near-infrared spectroscopy.

[0061] The near-infrared light emitting device 100 has a wavelength of 0.853 M ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳ The relationship is configured to satisfy the following: ＶＩＳ is I ｍａｘ－ＶＩＳ－３０ I against ｍａｘ－ＶＩＳ－１５０ The ratio (I ｍａｘ－ＶＩＳ－１５０ / I ｍａｘ－ＶＩＳ－３０ ) M ＶＩＳ represents the visible light intensity maintenance rate. ｍａｘ－ＶＩＳ－３０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter 2 is 30°C. ｍａｘ－ＶＩＳ－１５０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter 2 is 150°C. ＮＩＲ is I ｍａｘ－ＮＩＲ－３０ I against ｍａｘ－ＮＩＲ－１５０ The ratio (I ｍａｘ－ＮＩＲ－１５０ / I ｍａｘ－ＮＩＲ－３０ ) M ＮＩＲ represents the near-infrared intensity maintenance rate. ｍａｘ－ＮＩＲ－３０is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter 2 is 30°C. ｍａｘ－ＮＩＲ－１５０ is the maximum value of the fluorescence intensity of the near-infrared fluorescence component when the temperature of the wavelength converter 2 is 150°C.

[0062] That is, a near-infrared phosphor having a small temperature quenching difference with respect to the visible phosphor is used in combination with the visible phosphor. As a result, even if time passes after the near-infrared light emitting device 100 is turned on and the temperature of the wavelength converter 2 rises, the change in the intensity ratio between the visible fluorescent component and the near-infrared fluorescent component is small, so the spectral distribution of the output light 20 is stable. The near-infrared light emitting device 100 is preferably 0.90M ＶＩＳ ≦M ＮＩＲ <1.10M ＶＩＳ、 More preferably 0.95M ＶＩＳ ≦M ＮＩＲ <1.05M ＶＩＳ The relationship may be satisfied.

[0063] M ＮＩＲ is preferably more than 90%. In other words, even when the temperature of the wavelength converter 2 increases, the decrease in the fluorescence intensity of the near-infrared fluorescent component is small. Such a wavelength converter 2 can be obtained by using a near-infrared phosphor that has small temperature quenching and a fluorescence intensity maintenance rate of more than 90% when the phosphor temperature is 150°C.

[0064] M ＶＩＳ is preferably more than 90%. In other words, even when the temperature of the wavelength converter 2 increases, the decrease in the fluorescence intensity of the visible fluorescent component is small. Such a wavelength converter 2 can be obtained, for example, by using a phosphor shown in Table 2 above that has small temperature quenching and a fluorescence intensity maintenance rate of more than 90%, such as a phosphor for LED lighting.

[0065] M ＮＩＲ and M ＶＩＳIt is more preferable that both of the above values ​​exceed 90%. In this case, even if the temperature of the wavelength converter 2 increases, the intensity of the output light 20 hardly decreases. Therefore, it is possible to expect even higher output power of the output light 20. Such a near-infrared light emitting device 100 is even more suitable for spectroscopy. Specifically, such a near-infrared light emitting device 100 can evaluate the quality of objects such as fruits and vegetables non-destructively and with high accuracy. Furthermore, such a near-infrared light emitting device 100 can be used to maintain the freshness of fruits and vegetables by irradiating them with near-infrared rays, and can also be used to evaluate the quality of substances with uneven body color.

[0066] The near-infrared light emitting device 100 according to this embodiment can be widely used for non-destructive testing using spectroscopy, particularly for evaluating the quality of fruits and vegetables, etc. The near-infrared light emitting device 100 can be used, for example, as a small, high-performance near-infrared light source.

[0067] As described above, the near-infrared light emitting device 100 according to this embodiment includes a solid-state light emitting element 1 and a wavelength converter 2. The wavelength converter 2 includes a visible phosphor that emits visible fluorescence 22 having a maximum fluorescence intensity within the wavelength range of visible light, and a near-infrared phosphor that emits near-infrared fluorescence 21 having a maximum fluorescence intensity within the wavelength range of near-infrared light. The near-infrared light emitting device 100 emits output light 20 that includes visible fluorescence and near-infrared fluorescence 21. The output light 20 includes a visible fluorescent component that has a spectral intensity within the wavelength range of visible light, and a near-infrared fluorescent component that has a spectral intensity within the wavelength range of near-infrared light. The near-infrared light emitting device 100 has a luminance of 0.853M. ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳ The relationship is configured to satisfy the following. ＶＩＳ is I ｍａｘ－ＶＩＳ－３０ I against ｍａｘ－ＶＩＳ－１５０ The ratio is I ｍａｘ－ＶＩＳ－３０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter 2 is 30°C. ｍａｘ－ＶＩＳ－１５０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter 2 is 150°C. ＮＩＲ is I ｍａｘ－ＮＩＲ－３０ I against ｍａｘ－ＮＩＲ－１５０ The ratio is I ｍａｘ－ＮＩＲ－３０is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter 2 is 30°C. ｍａｘ－ＮＩＲ－１５０ is the maximum fluorescence intensity of the near-infrared fluorescence component when the temperature of the wavelength converter 2 is 150°C.

[0068] In a conventional near-infrared light-emitting device, even if an attempt is made to evaluate the quality of fruits and vegetables non-destructively using, for example, a visible phosphor and a near-infrared phosphor, there is a risk that the intensity of the near-infrared fluorescent component will decrease relative to the intensity of the visible fluorescent component as the temperature of the phosphor rises due to lighting of the solid-state light-emitting element 1. Therefore, with the conventional near-infrared light-emitting device, there is a problem in that highly accurate evaluation of quality cannot be expected within a short time after lighting.

[0069] On the other hand, the near-infrared light emitting device 100 according to this embodiment has a luminance of 0.853M ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳ Therefore, even if the temperature of the wavelength converter 2 rises after time has passed since the near-infrared light emitting device 100 was turned on, the amount of change in the intensity ratio between the visible fluorescent component and the near-infrared fluorescent component is small. Therefore, the near-infrared light emitting device 100 experiences only a small change in the shape of the spectral distribution accompanying a rise in the temperature of the wavelength converter 2.

[0070] [Spectroscopic Device and Spectroscopy] Next, the spectroscopic device 200 and the spectroscopy method according to this embodiment will be described with reference to Figs. 2 and 3. The spectroscopic device 200 is, for example, a near-infrared spectroscopic device. The spectroscopy method is, for example, near-infrared spectroscopy. Fig. 2 is a schematic diagram showing an example of a transmission-type spectroscopic device 200. Fig. 3 is a schematic diagram showing an example of a reflection-type spectroscopic device 200. As shown in Figs. 2 and 3, the spectroscopic device 200 includes a near-infrared light-emitting device 100. That is, the spectroscopic device 200 relates to a spectroscopy method that uses the near-infrared light-emitting device 100.

[0071] As shown in FIG. 2 , the transmission-type spectroscopic device 200 includes a near-infrared light emitting device 100 and a spectroscope 6. An inspection object 5 is disposed between the near-infrared light emitting device 100 and the spectroscope 6. The near-infrared light emitting device 100 is configured to emit output light 20. The inspection object 5 is disposed so as to be irradiated with the output light 20. The spectroscope 6 is disposed so as to receive transmitted light 11, particularly near-infrared transmitted light, that has passed through the interior of the inspection object 5, of the output light 20 irradiated onto the inspection object 5. The spectroscope 6 detects and disperses the transmitted light 11. The spectroscope 6 may be, for example, a near-infrared spectroscope. The spectroscope 200 may be an inspection device. The inspection device may analyze data spectrally analyzed by the spectroscope 6. The inspection device may include an analysis unit (not shown), which may be used to grasp or determine whether the inspection item, such as the internal condition or quality of the inspection object 5, is acceptable or unacceptable. The analysis unit may include a central processing unit (CPU), a read-only memory (ROM), and a random access memory (RAM). The CPU may read the program and reference data stored in the ROM and process information related to the analysis of the test items according to the program.

[0072] 3, the reflective spectroscopic device 200 also includes a near-infrared light emitting device 100 and a spectroscope 6. However, in the reflective spectroscopic device 200, the spectroscope 6 is arranged to receive reflected light 12, particularly near-infrared reflected light, reflected by the inspection object 5 out of the output light 20 irradiated onto the inspection object 5. Other than the above, the reflective spectroscopic device 200 is the same as the transmission spectroscopic device 200, and therefore a description thereof will be omitted.

[0073] The reflection-type spectroscopic device 200 may include a reflective member (not shown), such as a metal plate, in particular a near-infrared reflective member. If the near-infrared fluorescent component of the output light 20 that has passed through the inspection object 5 is reflected by the reflective member and passes through the interior of the inspection object 5 again, it is possible to easily obtain near-infrared spectroscopic data specific to the inspection object 5, even if the inspection object 5 is a liquid or the like.

[0074] It is sufficient that the transmitted light 11 and the reflected light 12 contain at least a near-infrared fluorescent component. The visible fluorescent component can be transmitted or reflected depending on the form of the inspection object 5. When the visible light component is reflected, the visible light component may be separated into spectra, or may be used for visual inspection of the inspection object 5.

[0075] The inspection target object 5 may be food. Note that "food" is a general term for items consumed by humans, such as ingredients for lunch boxes, grains, fruits and vegetables, meat, fish, processed foods, and beverages.

[0076] The spectroscopic device 200 can also be used as a foreign matter inspection device that inspects whether or not the inspection target 5 contains foreign matter. For example, the spectroscopic device 200 can be used to detect the presence and condition of foreign matter mixed into food. The spectroscopic device 200 can also be used as an inspection device other than a foreign matter inspection device, such as a quality control device that evaluates the quality of fruits and vegetables. Such a spectroscopic device 200 is suitable for quality control of fruits and vegetables, because it can evaluate or measure the sugar content, acidity, internal damage, etc. of fruits and vegetables by examining the amount of transmission of near-infrared light irradiated onto the fruits and vegetables.

[0077] In this way, the spectroscopic device 200 utilizes at least the near-infrared light component contained in the output light 20. The spectroscopic device 200 may detect, for example, a characteristic absorption band of at least one stretching vibration selected from the group consisting of N-H, C-H, and O-H. In other words, the spectroscopic device 200 may be configured to obtain near-infrared spectroscopic data such as these characteristic absorption bands. Because the characteristic absorption band is detected as analytical data, the spectroscopic device 200 can be used in a wide range of applications, and is highly versatile, which is preferable.

[0078] As described above, the spectroscopic device 200 includes the near-infrared light emitting device 100. The spectroscopy method utilizes the near-infrared light emitting device 100. As described above, the near-infrared light emitting device 100 causes only a small change in the shape of the spectral distribution associated with an increase in temperature of the wavelength converter 2. Therefore, the spectroscopic device 200 and the spectroscopy method also cause only a small change in the shape of the spectral distribution associated with an increase in temperature of the wavelength converter 2. The spectroscopic device 200 and the spectroscopy method of this embodiment can be widely used for foreign matter inspection, quality inspection, and the like.

[0079] In the above embodiment, unless otherwise specified, the spectra of the spectral distributions of the output light 20, the near-infrared fluorescence 21, and the visible fluorescence 22 may be spectra when the wavelength of the primary light 10 (excitation light) is 450 nm. Furthermore, unless otherwise specified, the above spectra may be spectra at 30°C. Specifically, the above spectra may be spectra when the temperature of the phosphor or wavelength converter is 30°C.

[0080] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples. Evaluations were carried out at 30° C. unless otherwise specified.

[0081] (Example 1) A near-infrared light emitting device (wavelength conversion type light emitting element) including a solid-state light emitting element and a wavelength converter was fabricated using the following components 1) to 4). 1) Solid-state light emitting element: High-power blue LED (measured peak wavelength: 460 nm) (product number: SMBB450H-1100, Ushio Opto Semiconductor Co., Ltd.) 2) Wavelength converter 2-1) CaAlSiN ３ :Eu ２＋ (CASN) Red phosphor (fluorescence peak wavelength: 651 nm) (Mitsubishi Chemical Corporation) 2-2) LiGa ５ O ８ : Cr ３＋ (LGO) near-infrared phosphor (fluorescence peak wavelength: 833 nm) (prepared by the method described below) 2-3) Two-component thermosetting silicone resin (LED encapsulant, product name: KER-2600A / B, Shin-Etsu Chemical Co., Ltd.)

[0082] (Preparation of Wavelength Converter) A wavelength converter was prepared by laminating a first wavelength converter (one CASN red phosphor sheet) and a second wavelength converter (two LGO near-infrared phosphor sheets) prepared as follows.

[0083] (Preparation of First Wavelength Converter) 0.68 g of CASN red phosphor and silicone resin (1 g of KER-2600A and 1 g of KER-2600B) were mixed using a stirring and degassing device, followed by degassing. The stirring and degassing device used was a Thinky Mixer (registered trademark) model ARE-310 manufactured by Shinki Corporation. The rotation speed of the stirring and degassing device was set to approximately 2000 rpm, and the process was carried out for 3 minutes. In this way, a phosphor paste containing CASN red phosphor and silicone resin was prepared. The obtained phosphor paste was dropped into a frame approximately 140 μm high using a dispenser (model: ML-5000XII, manufactured by Musashi Engineering Co., Ltd.). The phosphor paste was then heated in the atmosphere at 150°C for 2 hours to harden. In this way, a resin phosphor film (CASN red phosphor sheet: length 10 mm×width 10 mm) having a thickness of about 130 μm was formed, and a first wavelength converter was obtained.

[0084] (Preparation of second wavelength converter) First, LiGa was prepared by the following procedure. ５ O ８ : Cr ３＋ A near-infrared phosphor was synthesized. The following compound powders were prepared as raw materials: 1) Lithium carbonate (Li ２ CO ３ 2) Gallium oxide (Ga ２ O ３ 3) Chromium oxide (Cr): Purity 4N, manufactured by Asia Physical Materials Co., Ltd. ２ O ３ ): Purity 3N, manufactured by Kojundo Kagaku Kenkyusho Co., Ltd.

[0085] Li(Ga ０．９７ Cr ０．０３ ) ５ O ８ The raw materials were weighed and mixed to obtain a compound having the composition shown in Table 1, i.e., the desired ratio of metal elements. The mixed raw materials were dry-mixed using a mortar and pestle to obtain a mixed raw material. The mixed raw material was transferred to an alumina crucible with a lid and fired in air at 1500°C for 4 hours using a box-type electric furnace. The fired product obtained by firing was lightly crushed to obtain LiGa ５ O ８ : Cr ３＋The properties of the LGO near-infrared phosphor will be described later.

[0086] Next, 0.40 g of the LGO near-infrared phosphor and silicone resin (1 g of KER-2600A and 1 g of KER-2600B) were mixed using a stirring and degassing device, similar to the first wavelength converter, and further degassed. In this way, a phosphor paste containing the LGO near-infrared phosphor and silicone resin was prepared. The obtained phosphor paste was dropped into a frame with a height of approximately 320 μm using the above-mentioned dispenser. The phosphor paste was then heated in air at 150°C for 2 hours to be cured. In this way, a resin phosphor film (LGO near-infrared phosphor sheet: length 10 mm × width 10 mm) with a thickness of approximately 300 μm was formed, and a second wavelength converter was obtained.

[0087] (Fabrication of near-infrared light-emitting device) A phosphor sheet was placed on the main light extraction surface of the blue LED so that the blue LED and the second wavelength converter of the stacked wavelength converter faced each other, and a near-infrared light-emitting device as shown in Figure 1 was fabricated.

[0088] The light-emitting characteristics of the obtained near-infrared light-emitting device were evaluated. When a current of 10 mA (2.6 V) was applied to the blue LED chip, blue light was emitted from the blue LED chip as primary light. A portion of this blue light was then converted into a near-infrared fluorescent component by the second wavelength converter. Furthermore, a portion of the primary light that passed through the second wavelength converter was converted into red light as a visible fluorescent component by the first wavelength converter. A mixed light containing the blue light as primary light, the near-infrared fluorescent component, and the visible fluorescent component was then emitted from the near-infrared light-emitting device as output light. For reference, the output light appeared to be purple light, and its color tone could not be considered white light. Note that purple light is considered to be light resulting from an additive mixture of the blue light component of the primary light and the red light components of the near-infrared fluorescent component and the visible fluorescent component.

[0089] The spectral distribution of the output light emitted from the near-infrared light emitting device of this example is shown in Fig. 4. As can be seen from Fig. 4, the spectral distribution of the output light is mainly composed of a light component 10A derived from the primary light, a light component 20A derived from the near-infrared phosphor of the second wavelength converter, and a light component 20B derived from the visible phosphor of the first wavelength converter.

[0090] As can be seen from Figure 4, using only one type of near-infrared phosphor, it was possible to obtain output light with a maximum fluorescence intensity around 830 nm. Furthermore, using only one type of near-infrared phosphor, it was possible to obtain output light with not only a spectral intensity over a wide wavelength range of 700 nm to less than 1000 nm, but also a relatively strong spectral intensity over a wavelength range of 700 nm to less than 950 nm. Furthermore, by using this in combination with a CASN red phosphor as a visible phosphor, it was possible to obtain a near-infrared light-emitting device that emits output light with a uniform spectral intensity over a wavelength range of 570 nm to less than 1000 nm and a small rate of change in intensity with respect to wavelength.

[0091] As shown in Tables 1 and 2, the temperature quenching of the LGO near-infrared phosphor and the CASN red phosphor is small, and the near-infrared intensity maintenance rate (M ＮＩＲ ) is 92%, exceeding 90%, and the visible light intensity maintenance rate (M ＶＩＳ ) is 98%. Therefore, the near-infrared light emitting device ＶＩＳ and M ＮＩＲ But 0.853M ＶＩＳ (≒0.836)≦M ＮＩＲ (≒0.920)<1.147M ＶＩＳ (=1.124).

[0092] Therefore, even if the temperature of the wavelength converter increases when the near-infrared light emitting device is turned on, the change in the shape of the spectrum of the wavelength-converted light by the phosphor, which is located on the longer wavelength side than about 490 nm, is small. In this way, a near-infrared light emitting device suitable for spectroscopy and capable of highly accurate quality evaluation within a short time after turning on, for example, in non-destructive measurement of fruits and vegetables, has been constructed.

[0093] The spectral shape of the output light of a near-infrared light-emitting device that uses a phosphor film containing a visible phosphor and a near-infrared phosphor can be evaluated using a mixed phosphor of these phosphors, without constructing a near-infrared light-emitting device, as long as it is only the wavelength-converted light component produced by the phosphor. Furthermore, the spectral change of the wavelength-converted light component accompanying the temperature rise of the phosphor film can be determined by investigating the temperature dependence of the fluorescence of the mixed phosphor. Therefore, we performed a simple evaluation of the temperature dependence of the fluorescence spectrum of several mixed phosphors that are mixtures of visible phosphors and near-infrared phosphors.

[0094] (Examples 2 to 7 and Comparative Examples 1 and 2) The visible phosphors and near-infrared phosphors used in the evaluation are summarized in Table 3. For reference, the temperature quenching of these phosphors is shown in FIG.

[0095]

[0096] Next, mixed phosphors according to Examples 2 to 7 and Comparative Examples 1 and 2 were prepared using the compositions shown in Table 4.

[0097]

[0098] To demonstrate the temperature dependency of the mixed phosphor, the fluorescence spectrum was evaluated when the temperature of the mixed phosphor was changed from 30° C. to 270° C. in increments of 40° C. The wavelength of the excitation light that excited the mixed phosphor was 450 nm.

[0099] Fig. 6 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Example 2. Fig. 7 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Example 3. Fig. 8 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Example 4. Fig. 9 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Example 5. Fig. 10 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Example 6. Fig. 11 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Example 7. Fig. 12 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Comparative Example 1. Fig. 13 shows the fluorescence spectrum at each temperature of the mixed phosphor according to Comparative Example 2.

[0100] All of this data is spectral data normalized by the maximum fluorescence intensity of the visible phosphor in order to visualize the change in the shape of the spectral distribution. In the figure, the spectral data around 450 nm is the leakage component of the excitation light.

[0101] The following trends are observed from Figures 6 to 13. (1) In the mixed phosphors of Comparative Examples 1 and 2, which are mixtures of a visible phosphor with small temperature quenching and a near-infrared phosphor with large temperature quenching, a decrease in the intensity of the near-infrared light component is observed as the temperature rises. (2) In the mixed phosphors of Examples 2 to 7, which are mixtures of a visible phosphor with small temperature quenching and a near-infrared phosphor with small temperature quenching, the intensities of the visible light component and the near-infrared light component are almost unchanged as the temperature rises, or a slight increase in the intensity of the near-infrared light component is observed. (3) In the mixed phosphors of Examples 2 to 7, which are mixtures of a visible phosphor with small temperature quenching and a near-infrared phosphor with small temperature quenching, a decrease in the intensity of the near-infrared light component is observed as the temperature rises. ３＋ In the case of the garnet phosphor activated with Eu (Examples 4, 5 and 7), ２＋ In comparison with nitride-based phosphors activated with M (Examples 2, 3, and 6), the latter showed a smaller change in spectrum with increasing temperature. This situation is summarized in Table 5. In Table 5, "150°C / 30°C" indicates the change in the M ＮＩＲ / M ＶＩＳ is equivalent to

[0102]

[0103] In other words, in order to suppress the fluctuation of the spectral distribution of the output light due to the temperature rise, the near-infrared light emitting device needs to be 0.853M ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳ It has been found that it is effective to configure the fluorescent lamp so as to satisfy the relationship: (1) A combination of a visible phosphor and a near-infrared phosphor, each of which has a small temperature extinction difference. (2) Eu ２＋ and a red phosphor activated with Cr ３＋ In combination with a near-infrared phosphor activated with

[0104] In addition, Eu is used to suppress fluctuations in the spectral distribution of the output light due to temperature rise. ２＋ and a red phosphor activated with Cr ３＋The reason why the combination of the phosphor with the near-infrared phosphor activated with Cr was effective is thought to be due to the following effects. ３＋ The activated near-infrared phosphor tends to have an excitation peak (absorption peak) in the orange to red wavelength region of 600 nm or more and less than 650 nm, and Eu ２＋ The activated red phosphor tends to have a fluorescence peak in the orange to red wavelength range of 600 nm or more and less than 650 nm. Therefore, even if the fluorescence spectrum of the visible phosphor shifts slightly to longer wavelengths with increasing temperature, the excitation peak of the near-infrared phosphor also shifts slightly to longer wavelengths. Therefore, the proportion of light components absorbed by the near-infrared phosphor does not change significantly with increasing temperature of the phosphor.

[0105] To suppress the decrease in the intensity of the output light due to the rise in temperature, it is preferable to use a phosphor with a small absolute value of temperature quenching. Furthermore, if there is a choice between a combination of phosphors whose intensity of the near-infrared light component decreases with the rise in temperature and a combination of phosphors whose intensity of the near-infrared light component increases, it is preferable to use the latter combination.

[0106] Next, LiGa ５ O ８ : Cr ３＋ A deep red phosphor was synthesized using the LiGa ５ O ８ : Cr ３＋ It was evaluated for comparison with near-infrared phosphors.

[0107] (LiGa ５ O ８ : Cr ３＋ Synthesis of deep red phosphor) The same procedure as in Example 1 was repeated except that the firing temperature was 1200°C. ５ O ８ : Cr ３＋ The phosphor was prepared in the same manner as the near-infrared phosphor.

[0108] (LiGa ５ O ８ : Cr ３＋Evaluation of phosphor) First, the X-ray diffraction pattern was measured by X-ray diffraction using a desktop X-ray diffractometer MiniFlex 600 (Rigaku Corporation). The crystalline phase of the compound constituting the phosphor was identified by comparing it with the diffraction pattern of the compound crystals whose data had been registered.

[0109] FIG. 14 shows LiGa ５ O ８ : Cr ３＋ Near-infrared phosphors and LiGa ５ O ８ : Cr ３＋ X-ray diffraction pattern of the deep red phosphor and LiGa registered in ICSD (Inorganic Crystal Structure Database) ５ O ８ As can be seen from FIG. ５ O ８ : Cr ３＋ The XRD pattern of the near-infrared phosphor is LiGa ５ O ８ : Cr ３＋ The XRD pattern was the same as that of the deep red phosphor. ５ O ８ : Cr ３＋ The near-infrared phosphor is the compound LiGa ５ O ８ It was found that the crystal has the same atomic arrangement as

[0110] Next, the fluorescence spectrum, temperature quenching, and internal quantum efficiency of the phosphor were evaluated using a Quantaurus-QY Plus (extended absolute PL quantum yield measurement device with heating mechanism) C13534-02 (manufactured by Hamamatsu Photonics K.K.) when excited at an excitation wavelength of 450 nm.

[0111] FIG. 15 shows the LiGa ５ O ８ : Cr ３＋ Near-infrared phosphor and LiGa ５ O ８ : Cr ３＋ Fluorescence spectra of deep red phosphors. ５ O ８ : Cr ３＋The fluorescence spectrum of the near-infrared phosphor had a maximum fluorescence intensity around 833 nm. ５ O ８ : Cr ３＋ The fluorescence spectrum of the near-infrared phosphor had fluorescent components over a wide wavelength range of 700 to 1100 nm. ５ O ８ : Cr ３＋ As shown in Table 1, the fluorescence spectrum of the near-infrared phosphor had a FWHM of 214 nm, exceeding 200 nm, and was therefore broad. ５ O ８ : Cr ３＋ The fluorescence spectrum of the deep red phosphor had a line-shaped maximum fluorescence intensity around 715 to 720 nm, and the FWHM was 4 nm. ５ O ８ : Cr ３＋ The fluorescence spectrum of the near-infrared phosphor is ５ O ８ : Cr ３＋ The fluorescence spectrum was significantly different from that of the deep red phosphor.

[0112] FIG. 16 shows LiGa ５ O ８ : Cr ３＋ Near-infrared phosphor and LiGa ５ O ８ : Cr ３＋ 1 is a graph showing the relationship between the temperature of a deep red phosphor and the maximum fluorescence intensity (temperature quenching characteristic) emitted by the phosphor. ５ O ８ : Cr ３＋ The fluorescence intensity retention rate of the near-infrared phosphor was 92%, exceeding 90%, and the temperature quenching was very small. ５ O ８ : Cr ３＋ The fluorescence intensity maintenance rate of the deep red phosphor was 61%.

[0113] The internal quantum efficiency is shown in Table 1. ５ O ８ : Cr ３＋ Near-infrared phosphors account for 85% of the total, while LiGa ５ O８ : Cr ３＋ The deep red phosphor was 54%. ５ O ８ : Cr ３＋ The internal quantum efficiency of the near-infrared phosphor was found to exceed 80%, even though it was a prototype in the early stages of development.

[0114] Finally, LiGa ５ O ８ : Cr ３＋ Near-infrared phosphor and LiGa ５ O ８ : Cr ３＋ To improve the accuracy of compositional information related to differences from deep-red phosphors, the main component compositions of these phosphors were analyzed. The composition ratios of Li, Ga, and Cr, which are the main components of the phosphors, were quantitatively evaluated by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using an iCAP7400 Duo (manufactured by Thermo Fisher Scientific).

[0115] As a result, the composition of the deep red phosphor was Li ０．９４ (Ga ０．７５ Cr ０．０３ ) ５ O ８ーα whereas the composition of the near-infrared phosphor is Li ０．８１ (Ga ０．７５ Cr ０．０３ ) ５ O ８ーα It was. ５ O ８ : Cr ３＋ The near-infrared phosphor is a stoichiometric Li(Ga １－ｘ Cr ｘ ) ５ O ８ These results demonstrate that when the amount of Li is small relative to the stoichiometric composition, the resulting phosphor functions as a near-infrared phosphor.

[0116] For reference, LiGa ５ O ８ : Cr ３＋ The following is a hypothesis on why near-infrared phosphors exhibit the unique fluorescent properties described above.

[0117] LiGa ５ O ８ : Cr ３＋ The near-infrared phosphor is a composition that can be considered to be clearly Li-deficient with respect to the stoichiometric composition. ５ O ８ : Cr ３＋ It has substantially the same crystal structure as the deep red phosphor. ５ O ８ : Cr ３＋ In the near-infrared phosphor crystal, Ga ３＋ Part of Ga ＋ It is possible that the valence changes to maintain the crystal structure.

[0118] That is, originally LiGa(III) ３ (GaO ４ ) ２ The crystal to be formed is X(LiGa(I)Ga(III) ２ (GaO ４ ) ２ ) (wherein X is a value satisfying 0<X<1), and LiGa ５ O ８ The hypothesis is that the crystal structure of Ga is maintained. ＋ Ga whose valence changes to ３＋ Cr substituting the lattice site of ３＋ (First Cr ３＋ ) is Ga ＋ This effect can change the spectral shape and can be observed as broad light.

[0119] In addition, Ga ＋ Ga with no valence change ３＋ Cr which had substituted the lattice site of ３＋ (Second Cr ３＋ The maximum fluorescence intensity (wavelength: about 718 nm) of the first Cr ３＋ The wavelength of the first Cr is shorter than the maximum fluorescence intensity (wavelength: about 830 nm) of the first Cr. ３＋ is the second Cr ３＋ On the other hand, it is possible that Cr absorbs the emission line components. ３＋It is known that X(LiGa(I)Ga(III)) does not normally take a tetrahedral coordination. ２ (GaO ４ ) ２ In the crystal of Cr ３＋ is (GaO ４ It is presumed that they exist at the lattice sites of Ga(I) and Ga(III) other than the Ga lattice sites of Ga(I).

[0120] Here, the ratio of Ga(I):Ga(III) is 1:2. Therefore, the first Cr atoms substituting these Ga lattice sites ３＋ The relative number of moles of the second Cr ３＋ Therefore, the second Cr ３＋ (brightness line emission) from the first Cr ３＋ It cannot be denied that there is a possibility that efficient energy transfer occurs to the second Cr ３＋ Almost no emission line due to the first Cr ３＋ The broad emission component due to α- and β-glucan may become the dominant fluorescence spectral shape.

[0121] Also, the first Cr ３＋ However, if we consider that the electrons exist in a state of charge distortion, it is undeniable that the ground and excited states may have deep potential wells. If we assume that such electronic states exist, these electronic states cannot easily change their positions unless they receive high energy. Therefore, non-radiative transitions from the excited state to the ground state are unlikely, and the electrons may exhibit high fluorescence efficiency at high temperatures, similar to that at room temperature.

[0122] It should be noted that the fact that many near-infrared phosphors exhibit relatively large temperature quenching is an essential issue for near-infrared phosphors, and this may be due to their optical properties.

[0123] The fluorescence of near-infrared phosphors is, for example, fluorescence obtained by absorbing blue light and converting it into near-infrared light. Therefore, compared to the fluorescence of visible phosphors, the wavelength-converted light has a larger Stokes shift (which indicates the energy difference between light absorption and fluorescent emission). This also means that the wavelength-converted light is due to electron energy transition with a larger Franck-Condon offset (the shift in the equilibrium position between the ground state and the excited state). For this reason, the fluorescent ions (e.g., Cr) of near-infrared phosphors are ３＋ ) is likely to have an equilibrium position close to the ground state. Fluorescence transitions in this manner may be prone to thermal quenching.

[0124] Homemade LiGa ５ O ８ : Cr ３＋ The near-infrared phosphor is Cr ３＋ But LiGa ５ O ８ Because it is placed in such a special environment within the crystal, it may become a phosphor that combines an exceptional fluorescence spectrum and temperature quenching properties.

[0125] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0126] (Technology 1) A near-infrared light emitting device comprising a solid-state light emitting element, a visible phosphor that emits visible fluorescence having a maximum fluorescence intensity within the wavelength range of visible light, and a wavelength converter that includes a near-infrared phosphor that emits near-infrared fluorescence having a maximum fluorescence intensity within the wavelength range of near-infrared light, wherein the near-infrared light emitting device emits output light that includes the visible fluorescence and the near-infrared fluorescence, and the output light includes a visible fluorescent component having a spectral intensity within the wavelength range of visible light and a near-infrared fluorescent component having a spectral intensity within the wavelength range of near-infrared light, and the near-infrared light emitting device has a wavelength conversion efficiency of 0.853M. ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳ The relationship of M is satisfied. ＶＩＳ is I ｍａｘ－ＶＩＳ－３０ I against ｍａｘ－ＶＩＳ－１５０ The ratio of I ｍａｘ－ＶＩＳ－３０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter is 30°C, and Iｍａｘ－ＶＩＳ－１５０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter is 150°C, and M ＮＩＲ is I ｍａｘ－ＮＩＲ－３０ I against ｍａｘ－ＮＩＲ－１５０ is the ratio of I ｍａｘ－ＮＩＲ－３０ is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter is 30°C, and I ｍａｘ－ＮＩＲ－１５０ is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter is 150°C.

[0127] With this configuration, even if the temperature of the wavelength converter increases over time after the near-infrared light emitting device is turned on, the change in the intensity ratio between the visible fluorescent component and the near-infrared fluorescent component is small, and therefore, the near-infrared light emitting device experiences only a small change in the shape of its spectral distribution due to an increase in the temperature of the wavelength converter.

[0128] (Technology 2) The near-infrared light emitting device according to Technology 1, wherein the half-width of the spectrum having the maximum fluorescence intensity of the near-infrared fluorescence exceeds 180 nm. This configuration makes it possible to obtain near-infrared light components having a spectral distribution over a wide wavelength range of 700 to 1000 nm using only one type of near-infrared phosphor, without using several types of near-infrared phosphors. This reduces the risk of changes in the shape of the spectral distribution of the near-infrared fluorescence or near-infrared fluorescent components due to differences in temperature quenching when using different types of near-infrared phosphors.

[0129] (Technology 3) The near-infrared phosphor is a compound LiGa ５ O ８ The near-infrared light emitting device according to the first or second aspect of the present invention, wherein at least chromium ions functioning as fluorescent ions are added to a crystal of an inorganic compound having the same spinel-type crystal structure as that of LiGa. ５ O ８ It has been found that LiGa exhibits a unique fluorescence spectrum shape and temperature quenching as a near-infrared phosphor because it uses a crystal similar to ５ O ８ : Cr ３＋Therefore, it is advantageous to combine it with visible phosphors with small thermal quenching, and when applied to spectroscopy, it is expected to enable highly accurate non-destructive measurements.

[0130] (Technology 4) The near-infrared light-emitting device according to any one of Technologies 1 to 3, wherein the near-infrared fluorescence has a spike in the wavelength range of 710 nm or more and 730 nm or less. A near-infrared phosphor that emits fluorescence with such a spike may have extremely small temperature quenching. Therefore, it may be possible to provide a near-infrared light-emitting device with extremely small temperature quenching.

[0131] (Technology 5) The near-infrared light-emitting device according to any one of Technologies 1 to 4, wherein the visible phosphor is at least one phosphor selected from the group consisting of a green phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 490 nm or more and less than 570 nm, a yellow phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 570 nm or more and less than 585 nm, an orange phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 585 nm or more and less than 620 nm, and a red phosphor emitting light having a maximum fluorescence intensity within a wavelength range of 620 nm or more and less than 780 nm. This configuration allows the spectral distribution of the visible fluorescent component to be adjusted. Therefore, the visible fluorescent component of the output light emitted from the near-infrared light-emitting device can be adjusted according to the application.

[0132] (Technology 6) The visible phosphor is Ce ３＋ Garnet phosphor activated with Eu ２＋ Alkaline earth metal nitrosilicate activated with Eu ２＋ The near-infrared light-emitting device according to any one of the first to fifth aspects of the present invention is characterized in that the visible phosphor is at least one phosphor selected from the group consisting of alkaline earth metal nitride aluminosilicates activated with an alkali metal. Such visible phosphors have a proven track record for use in LED lighting. These visible phosphors are not only easy to procure but also safe in terms of reliability and ease of handling.

[0133] (Technology 7) The near-infrared phosphor is Cr ３＋ The visible phosphor is activated by Eu ２＋ Alkaline earth metal nitrosilicate activated with Eu ２＋The near-infrared light emitting device according to any one of the first to sixth aspects of the present invention is characterized in that the phosphor is at least one of an alkaline earth metal nitride aluminosilicate activated with an alkali metal nitride. Such a near-infrared light emitting device is advantageous in that it can maintain a constant ratio of light components absorbed by the near-infrared phosphor when the fluorescence spectrum of the visible phosphor shifts to longer wavelengths with increasing temperature, and is therefore advantageous in suppressing fluctuations in the spectral distribution with increasing temperature.

[0134] (Technology 8) The near-infrared light emitting device according to any one of Technologies 1 to 7, wherein the wavelength converter contains fluorescent ceramics. This configuration not only provides the wavelength converter with excellent thermal conductivity, but also increases the optical absorption rate of the excitation light. This is advantageous for heat dissipation design and high output.

[0135] (Technology 9) The near-infrared light emitting device according to any one of Technologies 1 to 8, wherein the visible phosphor and the near-infrared phosphor are excited by primary light emitted by the solid-state light emitting element. This configuration allows the visible phosphor and the near-infrared phosphor to be excited by only one type of solid-state light emitting element. This is advantageous in simplifying the lighting circuit.

[0136] (Technology 10) The near-infrared light emitting device according to any one of Technologies 1 to 9, wherein the output light has a spectral intensity over at least the entire wavelength range of 700 nm to 1000 nm. Such output light contains light components in the characteristic absorption bands of the N-H, C-H, and O-H stretching vibrations. Therefore, such a near-infrared light emitting device is suitable for detecting the characteristic absorption bands of the N-H, C-H, and O-H stretching vibrations by spectroscopy.

[0137] (Technology 11) The near-infrared light emitting device according to any one of Technologies 1 to 10, wherein the output light has a spectral peak at least within a wavelength range of 800 nm to 900 nm. The spectral peak of such output light in the near-infrared wavelength region is similar to that of a halogen bulb. This makes it relatively easy to use the components and accompanying software of conventional spectroscopic devices that use halogen bulbs. Therefore, spectroscopic devices can be industrially produced without major design changes.

[0138] (Technology 12) A spectroscopic device including the near-infrared light emitting device according to any one of technologies 1 to 11. Such a spectroscopic device utilizes a near-infrared light emitting device that exhibits little change in the shape of its spectral distribution due to a rise in temperature of the wavelength converter. Therefore, the spectroscopic device enables high-precision spectroscopy.

[0139] (Technology 13) A spectroscopy method using the near-infrared light emitting device according to any one of Technologies 1 to 11. Such a spectroscopy method uses a near-infrared light emitting device in which the shape of the spectral distribution changes little with an increase in temperature of the wavelength converter, thereby enabling high-precision spectroscopy.

[0140] The entire contents of Japanese Patent Application No. 2023-010886 (filing date: January 27, 2023) are incorporated herein by reference.

[0141] The contents of this embodiment have been described above using examples, but this embodiment is not limited to these examples, and it will be obvious to those skilled in the art that various modifications and improvements are possible within the scope of the gist of this embodiment.

[0142] According to the present disclosure, it is possible to provide a near-infrared light emitting device in which the shape of the spectral distribution changes little with an increase in temperature of the wavelength converter, as well as a spectroscopic device and a spectroscopy method using the same.

[0143] REFERENCE SIGNS LIST 1 solid-state light-emitting element 2 wavelength converter 10 primary light 20 output light 21 near-infrared fluorescence 22 visible fluorescence 100 near-infrared light-emitting device 200 spectroscopic device

Claims

1. a solid-state light-emitting element; a wavelength converter including a visible phosphor that emits visible fluorescence having a maximum fluorescence intensity within the wavelength range of visible light and a near-infrared phosphor that emits near-infrared fluorescence having a maximum fluorescence intensity within the wavelength range of near-infrared light; A near-infrared light emitting device comprising: the near-infrared light emitting device emits output light including the visible fluorescent light and the near-infrared fluorescent light; the output light includes a visible fluorescent component having a spectral intensity within a wavelength range of visible light and a near-infrared fluorescent component having a spectral intensity within a wavelength range of near-infrared light, The near-infrared light emitting device has a temperature of 0.853M ＶＩＳ ≦M ＮＩＲ <1.147M ＶＩＳ The relationship is configured to satisfy Said M ＶＩＳ is I ｍａｘ－ＶＩＳ－３０ I against ｍａｘ－ＶＩＳ－１５０ is the percentage of I ｍａｘ－ＶＩＳ－３０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter is 30°C, I ｍａｘ－ＶＩＳ－１５０ is the maximum fluorescence intensity of the visible fluorescent component when the temperature of the wavelength converter is 150°C, Said M ＮＩＲ is I ｍａｘ－ＮＩＲ－３０ I against ｍａｘ－ＮＩＲ－１５０ is the percentage of I ｍａｘ－ＮＩＲ－３０ is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter is 30°C, I ｍａｘ－ＮＩＲ－１５０ is the maximum fluorescence intensity of the near-infrared fluorescent component when the temperature of the wavelength converter is 150°C.

2. 2. The near-infrared light emitting device according to claim 1, wherein the near-infrared fluorescence has a half-width of a spectrum having the maximum fluorescence intensity exceeding 180 nm.

3. The near-infrared phosphor is the compound LiGa ５ O ８ 3. The near-infrared light emitting device according to claim 1, wherein at least chromium ions functioning as fluorescent ions are added to a crystal of an inorganic compound having the same spinel type crystal structure as that of the compound of claim 1.

4. 4. The near-infrared light emitting device according to claim 1, wherein the near-infrared fluorescence has a spike in a wavelength range of 710 nm or more and 730 nm or less.

5. 5. The near-infrared light emitting device according to claim 1, wherein the visible phosphor is at least one phosphor selected from the group consisting of a green phosphor that emits light having a maximum fluorescence intensity within a wavelength range of 490 nm or more and less than 570 nm, a yellow phosphor that emits light having a maximum fluorescence intensity within a wavelength range of 570 nm or more and less than 585 nm, an orange phosphor that emits light having a maximum fluorescence intensity within a wavelength range of 585 nm or more and less than 620 nm, and a red phosphor that emits light having a maximum fluorescence intensity within a wavelength range of 620 nm or more and less than 780 nm.

6. The visible phosphor is Ce ３＋ Garnet phosphor activated with Eu ２＋ Alkaline earth metal nitrosilicate activated with Eu ２＋ 6. The near-infrared light emitting device according to claim 1, wherein the phosphor is at least one selected from the group consisting of alkaline earth metal nitride aluminosilicates activated with an alkali metal.

7. The near-infrared phosphor is Cr ３＋ is a phosphor activated by The visible phosphor is Eu ２＋ Alkaline earth metal nitrosilicate activated with Eu ２＋ 7. The near-infrared light emitting device according to claim 1, wherein the phosphor is at least one of alkaline earth metal nitride aluminosilicate activated with an alkali metal nitrate.

8. 8. The near-infrared light emitting device according to claim 1, wherein the wavelength converter comprises a fluorescent ceramic.

9. 9. The near-infrared light emitting device according to claim 1, wherein the visible phosphor and the near-infrared phosphor are excited by primary light emitted by the solid-state light emitting element.

10. 10. The near-infrared light emitting device according to claim 1, wherein the output light has a spectral intensity over the entire wavelength range of at least 700 nm to 1000 nm.

11. 11. The near-infrared light emitting device according to claim 1, wherein the output light has a spectral peak at least within a wavelength range of 800 nm to 900 nm.

12. A spectroscopic device comprising the near-infrared light emitting device according to any one of claims 1 to 11.

13. A spectroscopy method using the near-infrared emitting device according to any one of claims 1 to 11.