Light emitter, method for producing light emitter, and biological substance labeling agent

Abstract

A light emitter is formed from nanoparticles including a compound semiconductor containing an Ag component, In component, and Se component. The peak wavelength of the emission intensity falls within the range of 700 to 1400 nm, and the half-value width ΔH for the peak wavelength is 100 nm or less. The light emitted is configured to emit strong light in the near-infrared region, and which is capable of detecting biological information, and is preferred for bioimaging.

Claims

1. A light emitter for labeling a biological substance, the light emitter comprising: nanoparticles composed of a compound semiconductor that contains an Ag compound, an In component, and a Se component, wherein the compound semiconductor is a light-emitting material that emits light at an emission intensity having a peak wavelength within a range between 700 nm and 1400 nm, and wherein a mixing ratio of the In component to the Ag component is between 2 and 3 in terms of molar ratio, such that the light-emitting material is constructed to emit light at the emission intensity having the peak wavelength that is 85 nm or less in half-value width.

2. The light emitter according to claim 1, wherein the peak wavelength is between 700 nm and 1000 nm.

3. The light emitter according to claim 1, wherein the compound semiconductor contains the In component in excess with respect to the stoichiometric composition of the compound semiconductor.

4. The light emitter according to claim 1, wherein the emitted light comprises an absorption wavelength with at least a portion between 700 nm and 1000 nm.

5. The light emitter according to claim 1, wherein the compound semiconductor has an average particle size between 0.1 nm and 20 nm.

6. A biological substance labeling agent comprising the light emitter according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a profile showing a main part of an emission spectrum of a light emitter according to an exemplary embodiment.

(2) FIG. 2 is a profile showing an example of an emission spectrum, an absorption spectrum, and a Stokes shift of a light emitter according to an exemplary embodiment.

(3) FIG. 3 is a profile diagram of an emission spectrum, an absorption spectrum, and a Stokes shift for sample number 3 according to Example 1.

(4) FIG. 4 is a profile showing emission spectra for each sample according to Example 1.

(5) FIG. 5 is a profile of enlarged falling skirt parts of absorption spectra for each sample according to Example 1.

(6) FIG. 6 is a profile showing emission spectra for sample number 3 and sample number 11 according to Example 2.

(7) FIG. 7 is a diagram showing X-ray diffraction spectra for sample number 3 and sample number 11, together with diffraction profiles of Se and tetragonal AgInSe.sub.2 as standard samples.

(8) FIG. 8 is a profile showing an emission spectrum for sample number 21 according to Example 3.

(9) FIG. 9 is a profile showing an emission spectrum for sample number 22 according to Example 3.

(10) FIG. 10 is a profile showing an emission spectrum for sample number 23 according to Example 3.

(11) FIG. 11 is a TEM image for sample number 21 mentioned above.

(12) FIG. 12 is a TEM image for sample number 22 mentioned above.

(13) FIG. 13 is a TEM image for sample number 23 mentioned above.

(14) FIG. 14 is a diagram showing an emission spectrum according to Example 4.

(15) FIG. 15 is a profile showing the relationship among an emission spectrum, an absorption spectrum, and a Stokes shift according to a comparative example.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(16) Exemplary embodiments of the present disclosure will be described in detail as follows.

(17) FIG. 1 is a profile schematically showing a main part of an emission spectrum of a light emitter according to an exemplary embodiment of the present disclosure, where the horizontal axis indicates a wavelength, whereas the vertical axis indicates emission intensity.

(18) The light emitter according to the present disclosure is formed from nanoparticles composed of a compound semiconductor containing an Ag component, an In component, and an Se component (hereinafter, referred to as an “Ag—In—Se based compound semiconductor” for purposes of this disclosure). Further, the peak wavelength of the emission intensity falls within the range of 700 to 1400 nm, and the half-value width ΔH for the peak wavelength should be 100 nm or less.

(19) Thus, a light emitter is provided that is suitable for a biomarker in bioimaging for confirming a medication effect and a cell state in regenerative medicine, cancer therapy, or the like, thereby making it possible to give fluorescence to a biological substance, and dynamically analyze an image with a high sensitivity and multiple colors.

(20) The reason as to why the peak wavelength of the light emission intensity, the light-emitting material, and the half-value width ΔH for the peak wavelength are adjusted to fall within the ranges described above will be described below.

(21) (1) Peak Wavelength of Emission Intensity and Light Emitting Material

(22) As described in the Background section above, biological constituent substances, such as hemoglobin, are highly absorbent in the visible light region of shorter than 700 nm, which is shorter in wavelength than the near-infrared region, whereas when the wavelength is longer than 1700 nm, moisture absorption is increased, and for this reason, no light can pass through a living body with high efficiency, and it is difficult to obtain desired biological information even if luminescence is produced in the living body.

(23) On the other hand, the light transmittance with respect to a living body is favorable in the near-infrared region of 700 to 1700 nm in wavelength, which is considered suitable for dynamic image analyses of living tissues through the use of bioimaging technology. In particular, in the near-infrared region, the range of 700 to 1400 nm in wavelength is referred to as a “biological window”, which has favorable light transmittance with respect to a living body, and an emission spectrum is obtained such that the emission intensity has a peak wavelength in the foregoing range, thereby making it possible to acquire desired biological information.

(24) Therefore, according to the present disclosure, the peak wavelength of the emission intensity is adjusted to fall within the range of 700 to 1400 nm, preferably 700 to 1000 nm.

(25) Then, an Ag—In—Se based semiconductor compound is used as a light-emitting material that has a peak wavelength in the wavelength range mentioned above.

(26) More specifically, an Ag—In—Se based semiconductor compound that has a chalcopyrite-type crystal structure is low in toxicity unlike a Cd-based material such as CdSe or CdTe, and the composition is adjusted to form a solid solution, thereby allowing the control of the emission wavelength. Moreover, as also described above, the Ag—In—S based semiconductor compound of using S instead of Se, for example, AgInS.sub.2 has bandgap energy of 1.87 eV (660 nm in terms of wavelength) in a bulk state, which is large bandgap energy, and produces luminescence in the visible light region, whereas the Ag—In—Se based semiconductor compound, for example, AgInSe.sub.2 has bandgap energy of 1.24 eV (1000 nm in terms of wavelength) in a bulk state, which is small bandgap energy, and produces luminescence in the near-infrared region. Therefore, it is believed that the Ag—In—Se based semiconductor compound is made into nanoparticles, and controlled in terms of particle size, thereby exerting a quantum size effect, and even with the same composition, emitting light at various wavelengths in the above-described near-infrared region.

(27) Therefore, according to the present embodiment, an Ag—In—Se based compound semiconductor is used as the light-emitting material.

(28) (2) Half-Value Width ΔH for Peak Wavelength

(29) In order to obtain desired biological information with the use of the bioimaging technique, it is necessary to increase the resolution with strong light emitted by the light emitter, and to that end, there is need for the profile near the peak wavelength of the emission spectrum needs to be steep and sharp. Then, the steepness/sharpness of the peak wavelength can be evaluated by the wavelength width at ½P of the peak wavelength P of the emission intensity, that is, the half-value width ΔH.

(30) The half-value width ΔH is related to the Stokes shift S, and hereinafter, the relationship between the Stokes shift S and the half-value width ΔH will be described.

(31) FIG. 2 is a profile showing the relationship among an absorption spectrum, an emission spectrum, and a Stokes shift S.

(32) As shown in section (a) of FIG. 2, a profile with the absorption spectrum and the emission spectrum, where the horizontal axis indicates a wavelength λ, the left vertical axis indicates an absorption coefficient α, and the right vertical axis indicates an emission intensity PL.

(33) As shown in section (b) of FIG. 2, a profile of a derivative dα/dλ for differentiating the absorption coefficient α once with the wavelength λ, where the horizontal axis indicates a wavelength λ, whereas the vertical axis indicates dα/dλ.

(34) As shown in section (c) of FIG. 2, a profile of a second order derivative d.sup.2α/dλ.sup.2 for differentiating the absorption coefficient α twice with the wavelength λ, where the horizontal axis indicates a wavelength λ, whereas the vertical axis indicates d.sup.2α/dλ.sup.2.

(35) When photon energy is imparted to the light emitter, the light absorber absorbs light, thereby exciting electrons in the valence band in the ground state to the conduction band, and forming holes in the valence band. Then, the excited electrons are attracted to the valence band side in the ground state where holes are present due to the Coulomb force, and the electrons and the holes are recombined to produce luminescence. In this case, when the photon energy is partially consumed for vibration energy and the like by electrons returning from the excited state to the valence band side, a deviation referred to as a Stokes shift S is produced between the absorption wavelength and the emission wavelength.

(36) On the other hand, if the crystal structures of the nanoparticles have defects, the defects forms various energy levels, that is, defect levels between bands. Therefore, when electrons excited by light absorption transit from the conduction band to the valence band, the electrons are believed to transition through a relaxation process by the defect levels mentioned above. More specifically, the excited electrons are accompanied by energy loss, and recombined with holes at the above-mentioned defect levels to produce luminescence (defect luminescence). Further, the defects can take various levels between the bands as described above, the energy consumed by the transition from the conduction band to the valence band will thus also vary, and for this reason, the defect luminescence will have an emission spectrum with a large half-value width αH, which reflects the energy loss. Therefore, in order to obtain a light emission with a small half-value width αH and a steep and sharp peak wavelength, it is necessary to suppress defect luminescence, and to that end, it is necessary to reduce the energy loss due to defects, photon vibrations, and the like. Further, since this energy loss produces a Stokes shift S that indicates a deviation between the absorption wavelength and the emission wavelength, the reduction in Stokes shift S can narrow the half-value width αH, thereby allowing the emission characteristics to be improved.

(37) Therefore, according to the present embodiment, through the reduction in Stokes shift S, the half-value width αH for the peak wavelength is adjusted to 100 nm or less as described above, thereby a high-resolution light emitter suitable for a biomarker with energy loss suppressed.

(38) This Stokes shift S is, as shown in FIG. 2, quantitatively evaluated by the difference between the minimum value M of the second order derivative d.sup.2α/dλ.sup.2 which is the change rate of the tangent of the absorption coefficient α and the peak wavelength P of the emission wavelength.

(39) In order to make the half-value width αH 100 nm or less, experimentally, the Stokes shift S is desirably 180 nm or less, preferably 70 nm or less, although it is difficult to evaluate the Stokes shift S theoretically.

(40) In addition, when the emission wavelength is 700 to 1400 nm which corresponds to the biological window, the emission wavelength is brought close to the absorption wavelength, with a small Stokes shift S, as long as a falling skirt part A of the absorption wavelength falls within the wavelength range of 700 to 1000 nm in the absorption spectrum. Therefore, both the light absorption process and the light emission process are enabled in the wavelength range of 700 to 1400 nm, and excited luminescence can be thus achieved effectively through the use of the biological window.

(41) As long as the Stokes shift S is extremely small as just above, the band-edge luminescence with high energy efficiency with energy loss suppressed is obtained, thereby making it possible to achieve both an efficient emission and a steep and sharp peak wavelength.

(42) It is to be noted that when the half-value width αH for the peak wavelength exceeds 100 nm, the peak wavelength is excessively broadened, and the peak wavelength draws a shallow curve without steepness and with the lack of sharpness, thus leading to a decrease in resolution, and making it difficult to obtain a lot of biological information in the range of 700 to 1400 nm. In addition, there is unfavorably a possibility that the wavelength range of the emission intensity may be partially less than 700 nm, or may greater than 1400 nm.

(43) In addition, the composition ratios of the respective components of the Ag—In—Se based compound semiconductor are not to be considered particularly limited as long as the peak wavelength of the emission intensity is 700 to 1400 nm, and as long as the half-value width αH for the peak wavelength is 100 nm or less, but it is preferable to contain the In component in excess of the stoichiometric composition.

(44) While the stoichiometric compositions of the Ag component and the In component meet 1:1, containing the In component for production in excess of the stoichiometric composition is believed to make it possible to suppress the non-radiative deactivation process of emitting no light when excited electrons return to the ground state, thereby allowing for obtaining an emission peak with intensity further improved. However, when containing the In component for production in excess of the stoichiometric composition, there is possibility that impurities such as different phases may be produced, and for this reason, there is also a possibility that a decrease in purity may be caused, thereby rather decreasing the intensity of the emission peak. In consideration of the foregoing, in the case of containing the In component for production in excess of the stoichiometric composition, the combination ratio of the In component to the Ag component is preferably from 1.5 to 3 in terms of molar ratio.

(45) In addition, the average particle size of the Ag—In—Se based compound semiconductor is not to be considered particularly limited as long as a quantum size effect is exhibited in the wavelength region of 700 to 1400 nm, and for example, nanoparticles in the range of 0.1 to 20 nm can be used.

(46) It is to be noted that as long as the exemplary embodiments of the present disclosure are adapted to satisfy the three requirements: (i) it is formed from nanoparticles composed of a compound semiconductor containing an Ag component, an In component, and an Se component; (ii) the peak wavelength of emission intensity falls within the range of 700 nm to 1400 nm; and (iii) the half-value width αH for the peak wavelength is 100 nm or less, the production method is not to be considered particularly limited.

(47) Next, an embodiment of a method for producing the light emitter will be described in detail.

(48) First, an Ag compound containing an Ag component and an In compound containing an In component are prepared, and the Ag compound and the In compound are each weighed such that the combination ratio between the Ag component and the In component after synthesis preferably makes the In component in excess of the stoichiometric composition. The In component is combined in excess of the stoichiometric composition, thereby causing the absorption wavelength to shift to the longer wavelength side, thus making it to bring the absorption wavelength close to the emission wavelength, and allowing band-edge luminescence.

(49) However, when the composition ratio of the In component to the Ag component is excessively increased, impurities such as different phases are estimated to be produced, and thus, the Ag compound and the In compound are preferably weighed such that the element ratio (In/Ag) is 1.5 to 3 in terms of molar ratio.

(50) It is to be noted that the types the compounds used for the Ag compound and the In compound are not to be considered particularly limited, but metal complexes that are relatively inexpensive, chemically stable, and easily available, for example, Ag(OCOCH.sub.3) (silver acetate) and In(OCOCH.sub.3).sub.3 (indium acetate) can be preferably used which have, as a ligand, a carboxylate ion such as an acetate ion.

(51) Next, these weighed materials are dissolved in a high boiling point solvent to prepare an Ag—In precursor solution. The high boiling point solvent is not to be considered particularly limited as long as the solvent is high in boiling point and chemically stable at high temperature, and a mixed solution can be used which includes, for example, at least one selected from 1-dodecanethiol, octadecene, oleylamine, and n-octyl ether.

(52) In addition, a Se powder is prepared, and this Se powder is dissolved in a solvent to prepare a Se precursor solution. The solvent is not to be considered particularly limited, and for example, a mixed solution of an alkylthiol such as 1-dodecanethiol and hexanethiol and an alkylamine such as oleylamine, and a phosphine such as tributylphosphine and trioctylphosphine can be used.

(53) Then, the Ag—In precursor solution is put in a container, degassed under reduced pressure, and then purged with nitrogen. Thereafter, a heat treatment is carried out to raise the temperature of the reaction field from room temperature to a predetermined temperature (for example, 150° C.)

(54) Next, the Se precursor solution is injected into the Ag—In precursor solution heated to the predetermined temperature, then heated to a predetermined reaction temperature, and kept at the reaction temperature for a predetermined period of reaction time, thereby providing a reaction product.

(55) In this regard, the reaction temperature is preferably higher than the predetermined temperature, for example, 200° C. or higher, thereby making it possible to promote grain growth moderately to such an extent that the nanoparticles are not coarsened. As a result, the nanoparticles have crystallinity improved with defect generation suppressed, and also have a reduced variation in average particle size, thereby reducing the Stokes shift S, and thus making it possible to obtain a peak wavelength with a small in half-value width ΔH.

(56) In addition, the reaction time is not to be considered particularly limited, and can be set to be, for example, 30 to 120 minutes. Further, grain growth can be controlled by varying the reaction time, and the average grain size can be thus adjusted. Yet further, the adjustment of the average grain size varies the emission wavelength due to the quantum size effect, and the peak wavelength of the emission intensity can be thus controlled.

(57) Next, this reaction product is left to cool until reaching room temperature, and then centrifuged to separate into a supernatant liquid and a precipitate, and the supernatant liquid is collected, and the precipitate is discarded. Then, a poor solvent such as methanol, ethanol, acetone, or acetonitrile is added to the supernatant liquid to form a precipitate, and the precipitate is separated and collected by centrifugation again. Subsequently, the operation of: the addition of the poor solvent.fwdarw.centrifugation treatment.fwdarw.the collection of the precipitate is repeated more than once to prepare a high-purity precipitate containing no impurities such as different phases. Then, this precipitate is dissolved through the addition of a nonpolar solvent such as chloroform, toluene, or hexane, thereby making it possible to prepare a dispersion solution of Ag—In—Se based compound semiconductor nanoparticles dispersed therein.

(58) As described above, a method for producing a compound semiconductor according to an exemplary embodiment of the present disclosure includes preparing an Ag—In precursor solution by dissolving an Ag compound and an In compound in a high boiling point solvent, dissolving the Se powder in a solvent to prepare a Se precursor; injecting the Se precursor solution into the Ag—In precursor solution while heating the Ag—In precursor solution to a predetermined temperature to prepare a mixed solution; and heating the reaction temperature at a reaction temperature higher than the predetermined temperature for a predetermined reaction time, so that the crystallinity of the nanoparticles is improved and defect formation of the nanoparticles is suppressed. More specifically, the improved crystallinity reduces the variation in average grain size, and allows for the reduction of the energy loss derived from the defect level, thereby making it possible to obtain, with high efficiency, a light emitter capable of band-edge luminescence with a small half-value width αH and a small Stokes shift.

(59) Further, the biological substance labelling agent is provided with the present light emitter, thereby making it possible to, since the light emitter emits light so as to have a steep and sharp peak wavelength in the near infrared region, dynamically analyze a biological image with a desirable high sensitivity and multiple colors. As such, a biological substance labeling agent is provided that is suitable for biomarkers in bioimaging.

(60) It is to be noted that the present invention is not to be considered limited to the embodiment mentioned above. The above-mentioned embodiment is an exemplary embodiment of the present invention, which can be obviously changed unless the spirit is changed.

(61) In addition, the light emitter according to the exemplary embodiment can be used as a biological substance labeling agent as described above, and also utilized for a light source for exciting a label in a living organism. For example, when a sealed part of a blue light emitting diode or an ultraviolet light emitting diode is filled with the nanoparticles according to the present disclosure, the nanoparticles are excited by the blue light emitting diode or the ultraviolet light emitting diode to emit light in the near-infrared region of 700 to 1400 nm, which can be used as light for exciting a label in a living body in the foregoing wavelength range.

(62) Next, examples of the present invention will be specifically described.

EXAMPLE 1

(63) [Preparation of Sample]

(64) Prepared were: Ag(OCOCH.sub.3) with a purity of 99% (manufactured by Nacalai Tesque, Inc.) and In(OCOCH.sub.3).sub.3 with a purity of 99.99% (trade name “Alfa Aesar”, manufactured by Johnson Matthey Catalyst); a selenium powder with a purity of 99.99% (manufactured by Kojundo Chemical Laboratory Co., Ltd.); 1-octadecene with a purity of 90% (manufactured by Sigma-Aldrich); and 1-dodecanethiol (manufactured by Tokyo Chemical Industry Co., Ltd.), and an oleylamine with a purity of 80 to 90% (manufactured by Across Organics Inc.) as a solvent.

(65) Then, the Ag(OCOCH.sub.3) and the In(OCOCH.sub.3).sub.3 were weighed for 0.2 mmol of in total so that the Ag/In ratio after synthesis was 1/1 to 1/8.

(66) Next, this weighed material was put into a three-necked flask with an internal volume of 50 mL together with a stirrer chip, and then, 8 mL of the octadecene and 1 mL of the 1-dodecanethiol were added thereto as a high boiling point solvent, and stirred to prepare an Ag—In precursor solution.

(67) In addition, 0.2 mmol of the Se powder was dissolved in 1 mL of 1-dodecanethiol and 1 mL of oleylamine as a solvent to prepare a Se precursor solution.

(68) Next, the interior of the three-necked flask with the Ag—In precursor solution accumulated therein was degassed under reduced pressure, and then purged with nitrogen, and thereafter, the three-necked flask was heated with a heater to raise the temperature the temperature from room temperature. Then, with the temperature of the reaction field at 150° C., the Se precursor solution was injected into the three-necked flask, the temperature of the reaction field was raised up to 200° C., and at this temperature, a heat treatment was carried out for 30 minutes, thereby providing a reaction product.

(69) Next, this reaction product was air-cooled to room temperature, and then centrifuged at 5000 rpm for 5 minutes to separate into a supernatant liquid and a precipitate, and the supernatant liquid was collected, and the precipitate was discarded.

(70) Next, methanol (poor solvent) that was about 3 times as large as the volume of the supernatant liquid was added to precipitate crystal particles. Thereafter, the crystal particles were collected by centrifugation again, 3 mL of methanol was added to the collected precipitate, and the crystal particles were collected again by centrifugation. Thereafter, the operation of: the addition of methanol.fwdarw.centrifugation.fwdarw.the collection of crystal particles was repeated more than once, and the obtained high-purity crystal particles were dispersed in chloroform as a nonpolar solvent, thereby preparing samples of sample numbers 1 to 6.

(71) [Evaluation of Sample]

(72) The absorption spectrum, the emission spectrum, the half-value width for the peak wavelength, the Stokes shift S, and the absolute emission quantum yield (hereinafter referred to simply as a “quantum yield”) were determined for each of the sample numbers 1 to 6.

(73) Specifically, the emission spectrum and the quantum yield were measured at room temperature of 25° C. with the use of an absolute emission quantum yield measurement device (C9920-02, manufactured by Hamamatsu Photonics K.K.), and the full width at half maximum for the peak wavelength was determined from the emission spectrum.

(74) In addition, the absorption spectrum was measured at room temperature of 25° C. with the use of a spectrophotometer (U4100 manufactured by Hitachi High-Technologies Corporation).

(75) In addition, the Stokes shift S was calculated on the basis of the peak wavelength of the emission intensity PL of the sample and the absorption coefficient α.

(76) FIG. 3 is a diagram showing the relationship among the emission spectrum, the absorption spectrum, and the Stokes shift for sample number 3.

(77) As shown in section (a) of FIG. 3, the emission spectrum and the absorption spectrum for sample number 3, where the horizontal axis indicates a wavelength λ (nm), the left vertical axis indicates an absorption coefficient α (a.u.), and the right vertical axis indicates an emission intensity PL (a.u.).

(78) As shown in section (b) of FIG. 3, a profile diagram of a derivative for differentiating the absorption coefficient α for sample number 3 once with the wavelength λ, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates a derivative dα/dλ.

(79) As shown in section (c) of FIG. 3, a profile diagram of a second order derivative for differentiating the absorption coefficient α for sample number 3 twice with the wavelength λ, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates a second order derivative d.sup.2α/dλ.sup.2.

(80) Then, the difference between the peak wavelength of the emission intensity and the wavelength for the minimum of the second order derivative d.sup.2α/dλ.sup.2 was calculated, and regarded as the Stokes shift S. More specifically, the Stokes shift S can be calculated on the basis of the peak wavelength of the emission intensity PL of the sample and the absorption coefficient α.

(81) Although not shown in the figure, Stokes shift S was also calculated in the same manner for sample numbers 2, 4, and 5.

(82) FIG. 4 shows the emission spectra for sample numbers 1 to 6, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates an emission intensity PL (a.u.).

(83) In addition, Table 1 shows the Ag/In ratio, the half-value width, the Stokes shift, and the quantum yield for sample numbers 1 to 6.

(84) TABLE-US-00001 TABLE 1 Half-Value Stokes Quantum Sample Ag/In Width shift Yield No. Ratio (nm) (nm) (%) 1 1/1 <100 — 1.1 2 1/1.5 <100 72 5.1 3 1/2 85 65 12 4 1/3 82 175 7.7 5* 1/4 167 170 4.1 6 1/8 <100 — 1.5 *outside the scope of the present disclosure.

(85) As clearly shown in FIG. 4, it is determined that sample numbers 1 to 6 all emit light in the near-infrared region of 700 to 1000 nm, which is referred to as a “biological window” for purposes of this disclosure.

(86) However, Sample No. 5 has failed to achieve a steep peak waveform, since the half-value width was as wide as 167 nm. This is believed to be, even with In in excessive of the stoichiometric composition, impurities such as different phase were mixed in the sample.

(87) On the other hand, it has been determined that sample numbers 1 to 4 and 6 achieve peak wavelengths of 100 nm or less in half-value width in the wavelength region of 700 to 1000 nm.

(88) It is to be noted that sample numbers 1 and 6 are as low in quantum yield as 1.1 to 1.5%, and thus inferior in emission intensity, but 100 nm or less in half-value width in the wavelength region of 700 to 1000 nm, and thus, the matters specified in the present disclosure are satisfied, while the emission intensity is low.

(89) From the foregoing, it has been determined that the appropriate control of the Ag/In ratio achieves a light emitter which has favorable emission characteristics with a half-value width of 100 nm or less in the wavelength region of 700 to 1000 nm, referred to as a “biological window” for purposes of this disclosure.

(90) In addition, it has been determined that sample numbers 2 to 4 of 100 nm or less in half-value width, are also 65 nm to 175 nm in Stokes shift, which is 180 nm or less, thereby making it possible to achieve light emitters with reduced energy loss derived from the defect levels.

(91) FIG. 5 is a diagram showing the falling skirt part of the absorption spectrum, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates an absorption coefficient α (a.u.).

(92) As is clear from FIG. 5, as the Ag/In ratio is lower, that is, as the sample is richer in In, the absorption wavelength is shifted to the shorter wavelength side, and thus, it has been determined that the Ag/In ratio is adjusted, thereby making it possible to adjust the absorption edge wavelength.

(93) In addition, as is clear from FIG. 5, the falling skirt part of the absorption spectrum is shorter than the wavelength (=1000 nm) of the bulk AgInSe.sub.2, and thus, it has been determined that ultrafine atomization shortens the absorption wavelength to increase the bandgap energy, thereby producing a quantum size effect due to the variation in the average grain size.

EXAMPLE 2

(94) A sample according to sample number 11 was prepared by the same method and procedure as for sample number 3 according to Example 1 except that the reaction time was adjusted to 120 minutes.

(95) Next, for the sample of sample number 11, an emission spectrum and a quantum yield were determined by the same method and procedure as in Example 1, and the peak wavelength and the half-value width were determined from the emission spectrum.

(96) FIG. 6 is a diagram showing the emission spectrum of sample number 11 together with the emission spectrum of sample number 3, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates an emission intensity PL (a.u.).

(97) Sample number 11 was 85 nm in half-value width, and 12% in quantum yield as is the case with sample number 3, but as shown in FIG. 6, the peak wavelength was substantially parallel shifted to the longer wavelength side with respect to sample number 3, and the peak wavelength was about 850 nm. This is believed to be due to the fact that the reaction time was 120 minutes for heating for a longer period of time as compared with sample number 3 for which the reaction time was 30 minutes, thus promoting grain growth, increasing the average grain size, and making a shift to the longer wavelength side.

(98) It has been determined that the adjustment of the reaction time according to the present example as just described can control the average grain size, thereby allowing for the control of the peak wavelength of the emission intensity.

(99) Next, an X-ray diffraction spectrum was measured with the use of an X-ray diffractometer (RINT-K1, manufactured by Rigaku Corporation).

(100) FIG. 7 shows the X-ray diffraction spectra for sample number 3 and sample number 11 together with diffraction patterns of Se and tetragonal AgInSe.sub.2, wherein the horizontal axis indicates a diffraction angle 2θ (°) and the vertical axis indicates an X-ray intensity (a.u.).

(101) Both sample number 3 and sample number 11 substantially coincided with the diffraction pattern of tetragonal AgInSe.sub.2, and it has been confirmed that the Ag—In—Se based compound has semiconductor nanoparticles obtained.

(102) However, a peak wavelength derived from Se was detected in the case of sample number 3 for which the reaction time was 30 minutes.

(103) On the other hand, a peak wavelength derived from Se was not detected in the case of sample number 11 for which the reaction time was 120 minutes. This is believed to be due to the fact that crystallinity is improved by making the reaction time longer, thereby providing a high-purity Ag—In—Se based compound semiconductor.

EXAMPLE 3

(104) Samples of sample numbers 21 to 23 were prepared by the same method and procedure as for sample number 3 according to Example 1, except that oleylamine was used as a high boiling point solvent instead of octadecene, the reaction time was adjusted to 120 minutes, and the reaction time was adjusted to 150° C., 200° C., and 250° C.

(105) For each sample of numbers 21 to 23, emission spectra were measured by the same method and procedure as in Example 1, and the peak wavelength and the half-value width were determined from the emission spectra.

(106) FIGS. 8 to 10 illustrate the respective emission spectra of sample numbers 21 to 23, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates an emission intensity PL (a.u.).

(107) In addition, for each sample of sample numbers 21 to 23, STEM images were taken at 600,000-fold magnification with the use of a scanning transmission electron microscope (HD-2300A, manufactured by Hitachi High-Technologies Corporation).

(108) FIGS. 11 to 13 illustrate the respective STEM images of sample numbers 21 to 23.

(109) From the areas for field of view, observed in the STEM images as shown in FIGS. 11 to 13, 100 crystal grains were randomly extracted, and the maximum aspect diameter (Krummbein diameter) was measured for each crystal grain. Then, for each crystal grain, the average value for the measured values was regarded as an average grain diameter Dav, and the standard deviation σ was determined.

(110) Table 2 shows the average grain diameters Dav, standard deviations σ, emission spectra, and STEM image numbers of sample numbers 21 to 23.

(111) TABLE-US-00002 TABLE 2 Reaction Half- Average Grain Standard Peak Sample Temperature Value Width Diameter Dav Deviations σ Wavelength Emission TEM No. (° C.) (nm) (nm) (nm) (nm) Spectrum IMAGE 21* 150 >100 4.7 0.8 880 FIG. 8 FIG. 11 22 200 82 6.1 1.2 820 FIG. 9 FIG. 12 23 250 72 8.0 2.5 890 FIG. 10 FIG. 13 *outside the scope of the present disclosure.

(112) Sample number 21 was 880 nm in peak wavelength, but greater than 100 nm in half-value width. This is believed to be because the reaction temperature was as low as 150° C., thus leading to low crystallinity, generating many defects in the crystal grains, causing an energy loss derived from the defect levels, as a result, making the peak wavelength of the emission intensity gentle, and thus failing to obtain any steep peak wavelength.

(113) On the other hand, sample numbers 22 and 23 were, since the reaction temperature was as high as 200 to 250° C., also high in crystallinity, and with grain growth promoted, 6.1 to 8.0 nm in average grain diameter Dav, and also 1.2 to 2.5 nm in standard deviation σ. It has been determined that favorable emission characteristics are obtained, also with the half-value width from 72 to 82 nm in the wavelength range of 820 to 890 nm, and a steep curve drawn by the emission intensity.

(114) For comparison, sample number 22 was 52 nm in Stokes shift, whereas sample number 21 was as large as 200 nm in Stokes shift.

EXAMPLE 4

(115) A sample of sample number 31 was prepared by the same method and procedure as for sample number 3, except that n-octyl ether with a purity of 95% (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as a high boiling point solvent, instead of 1-octadecene, and that the reaction time was adjusted to 120 minutes.

(116) Next, for each sample of sample number 31, an emission spectrum, an absorption spectrum, and a quantum yield were determined by the same method and procedure as in Example 1, and the peak wavelength, the half-value width, and the absorption coefficient were determined from the emission spectrum and the absorption spectrum, and furthermore, the Stokes shift S was obtained from the peak wavelength and the absorption coefficient.

(117) FIG. 14 shows the emission spectrum of sample number 31, where the vertical axis indicates an emission intensity PL (a.u.), whereas the horizontal axis indicates a wavelength λ (nm).

(118) As is clear from FIG. 14, the peak wavelength of the emission intensity was about 830 nm, and the half-value width was 65 nm. In addition, with the quantum yield of 14% and the Stokes shift of 54 nm, it has been determined that a light emitter which has substantially the same favorable emission characteristics as sample number 3 is obtained even when the type of the high boiling point solvent is changed.

COMPARATIVE EXAMPLE

(119) AgInS.sub.2 was prepared with the use of S instead of Se in AgInSe.sub.2, and the emission spectrum and the absorption spectrum were each measured, and the Stokes shift was obtained, evaluating the emission characteristics.

(120) More specifically, 0.1 mmol of Ag(OCOCH.sub.3), 0.1 mmol of In(OCOCH.sub.3).sub.3, and 0.2 mmol of CH.sub.4N.sub.2S (thiourea) were each weighed, and the weighed material was poured together with a stirrer chip into a test tube of 16 mm in inner diameter and of 180 mm in total length. Then, a mixed solvent of 2.95 mL of oleylamine and 0.05 mL of 1-dodecanethiol was poured into the test tube, the test tube was then closed with a double cap, the inside of the test tube was degassed under reduced pressure and purged with nitrogen, and thereafter, the test tube was placed on a hot stirrer heated to 250° C., and heated for 10 minutes. Thereafter, as in Example 1, air-cooling, centrifugation, and the like were carried out for cleaning and purification, and the obtained ultrafine particles of AgInS.sub.2 were then dispersed in chloroform to prepare a sample composed of an AgInS.sub.2 nanoparticle dispersion solution according to a comparative example.

(121) Then, the emission spectrum, the absorption spectrum, the quantum yield, the half-value width, and the Stokes shift were determined by the same method and procedure as in Example 1.

(122) FIG. 15 is a profile showing the measurement results.

(123) More specifically, as shown in section (a) of FIG. 15, the emission spectrum and the absorption spectrum for the sample according to the comparative example, where the horizontal axis indicates a wavelength λ (nm), the left vertical axis indicates an absorption coefficient α (a.u.), and the right vertical axis indicates an emission intensity PL (a.u.).

(124) As shown in section (b) of FIG. 15, a profile of a derivative dα/dλ for the sample according to the comparative example, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates a derivative dα/dλ.

(125) As shown in section (c) of FIG. 15, a profile of a second order derivative d.sup.2α/dλ.sup.2 for the sample according to the comparative example, where the horizontal axis indicates a wavelength λ (nm), whereas the vertical axis indicates a second order derivative d.sup.2α/dλ.sup.2.

(126) While the quantum yield of the sample according to the comparative example was as high as 52%, the half-value width of the sample was about 200 nm, with an emission peak in a wide wavelength range, as is clear from FIG. 15, thus failing to obtain a steep emission peak. In addition, the Stokes shift S is also as large as 351 nm, and luminescence derived from the defect levels is believed to be produced.

(127) Thus, in view of the foregoing disclosure, a light emitter is provided that is configured to emit strong light with a small half-value width αH in the near-infrared region of 700 to 1400 nm. As such, a biological substance labeling agent is disclosed that is suitable for a biomarker in bioimaging.