WO2021166819A1 - 有機レーザー素子および三重項再利用剤 - Google Patents

有機レーザー素子および三重項再利用剤 Download PDF

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WO2021166819A1
WO2021166819A1 PCT/JP2021/005404 JP2021005404W WO2021166819A1 WO 2021166819 A1 WO2021166819 A1 WO 2021166819A1 JP 2021005404 W JP2021005404 W JP 2021005404W WO 2021166819 A1 WO2021166819 A1 WO 2021166819A1
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triplet
organic laser
reusing
agent
organic
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PCT/JP2021/005404
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French (fr)
Japanese (ja)
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敏則 松島
誠矢 吉田
安達　千波矢
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国立大学法人九州大学
株式会社ＫＯＡＬＡ Ｔｅｃｈ
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/36—Structure or shape of the active region; Materials used for the active region comprising organic materials

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  • the present invention relates to an organic laser device and a triplet reusing agent used therein.
  • the organic laser dye is in a singlet excited state and a triplet excited state by supplying excitation energy.
  • the organic laser dye is excited into a singlet excited state and a triplet excited state by the recombination of the carriers.
  • photoexcitation after being excited to a singlet excited state, a part of the excited state becomes a triplet excited state due to intersystem crossing.
  • the energy of the singlet excited state is used for laser oscillation.
  • triplet excitons accumulate and hinder laser oscillation, which may increase the threshold value and deteriorate the performance of the organic laser device. Therefore, conventionally, triplet excitons have been removed by adding a triplet remover (see Non-Patent Documents 1 and 2).
  • Equation (1) S (Q)> S1 (D) Equation (2) T1 (D)> T (Q)
  • S1 (D) represents the energy level of the at least singlet excited state of the organic laser dye
  • S (Q) is the triplet-triplet of the triplet reusing agent.
  • the energy level of the singlet excited state generated by the term pair annihilation T1 (D) represents the energy level of the lowest triplet excited state of the organic laser dye
  • T (Q) represents the triplet reusing agent. Represents the energy level of the triplet excited state of.
  • An organic laser element containing an organic laser dye and a triplet-reusing agent that causes triplet-triplet pair annihilation.
  • the energy of the lowest triplet excited state of the organic laser dye is transferred to the triplet excited state of the triplet reusing agent, and the triplet-triplet pair annihilation of the triplet reusing agent forms a triplet exciter to form a triplet.
  • the organic laser device according to any one of [1] to [6], wherein the triplet reusing agent is a compound consisting of only an arylene group and an aryl group.
  • the triplet reusing agent is a compound having six or more benzene rings in the molecule.
  • the triplet reusing agent is a compound in which one or more benzene rings, one or more naphthalene rings, and one or more anthracene rings are bonded to each other.
  • the organic laser element according to one.
  • T1 (D) represents the energy level of the lowest triplet excited state of the organic laser dye
  • T (Q) represents the triplet reusing agent. Represents the energy level of the triplet excited state of.
  • the triplet reusing agent according to [14] which has lower crystallinity than 9,10-di (naphtha-2-yl) anthracene.
  • the triplet reusing agent according to [14] or [15] which can form an amorphous film together with the organic laser dye.
  • an organic laser device that realizes a low threshold value, improves exciton utilization efficiency, or achieves a low threshold value and at the same time improves exciton utilization efficiency. It is also possible to provide a triplet reusing agent capable of providing such an organic laser device.
  • the organic laser device of the present invention is a laser device containing an organic compound.
  • it is an organic laser element containing an organic laser dye composed of an organic compound and a triple term reusing agent composed of an organic compound.
  • it is an organic laser element containing an organic laser dye composed of an organic compound containing no metal atom and a triple term reusing agent composed of an organic compound containing no metal atom.
  • the organic laser device of the present invention is an organic composed of only a plurality of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms and silicon atoms.
  • An organic laser element containing a laser dye and a triple term reusing agent consisting of an organic compound composed of only a plurality of atoms selected from the group consisting of carbon atom, hydrogen atom, nitrogen atom, oxygen atom, sulfur atom and silicon atom. Is.
  • the organic laser dye used in the organic laser device of the present invention is composed of an organic compound composed of only a plurality of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms and sulfur atoms. It may also consist of an organic compound composed of only a plurality of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms and oxygen atoms, and may consist of carbon atoms, hydrogen atoms, nitrogen atoms and sulfur.
  • It may consist of an organic compound composed of only a plurality of atoms selected from the group consisting of atoms, and may consist only of a plurality of atoms selected from the group consisting of carbon atoms, hydrogen atoms and nitrogen atoms. It may be composed of an organic compound, or may be composed of only a plurality of atoms selected from the group consisting of a carbon atom, a hydrogen atom and an oxygen atom, and may be composed of a carbon atom and a hydrogen atom. And it may be composed of an organic compound composed of only a plurality of atoms selected from the group consisting of sulfur atoms.
  • the organic laser dye used in the organic laser device of the present invention may have a repeating unit.
  • repeating unit When it has a repeating unit, it has two or more repeating units in the molecule, three or more repeating units, four or more repeating units, or five or more repeating units. You may. Further, it may have three or less repeating units, or may have two or less repeating units.
  • the organic laser dye used in the organic laser device of the present invention may not have a repeating unit.
  • the organic laser dye used in the organic laser device of the present invention is preferably a compound having two or more benzene rings.
  • the number of benzene rings in the molecule may be 4 or more, 6 or more, or 8 or more. For example, it may be 50 or less, 20 or less, 15 or less, 10 or less, or 8 or less.
  • One or more of the benzene rings present in the molecule may be a benzene ring in which an aromatic ring is condensed.
  • one or more of the benzene rings existing in the molecule may be a benzene ring in which a heteroaromatic ring is condensed.
  • the organic laser dye used in the organic laser device of the present invention may contain a heteroaromatic ring.
  • the heteroaromatic ring referred to here may constitute the main chain of the molecule of the organic laser dye.
  • the main chain means a chain of atoms (groups) connecting the two end atoms when two end atoms are selected so as to have the longest molecular length.
  • a preferable heteroaromatic ring for example, a furan ring can be mentioned.
  • a thiophene ring can be mentioned.
  • Another aromatic ring may be condensed on the heteroaromatic ring.
  • the organic laser dye used in the organic laser device of the present invention may not contain a heteroaromatic ring.
  • the organic laser dye used in the organic laser element of the present invention is preferably a compound in which the entire main chain is conjugated.
  • the main chain may contain an alkenylene group.
  • the number of carbon atoms of the alkenylene group is preferably 2 to 10, more preferably 2 to 6, further preferably 2 to 4, and preferably 2.
  • the main chain may contain an atom having an unshared electron pair.
  • it may contain a nitrogen atom.
  • the nitrogen atom preferably connects the aromatic ring to the aromatic ring.
  • the main chain may not contain an atom having an unshared electron pair.
  • the main chain of the organic laser dye is preferably composed of only those selected from the group consisting of an aromatic ring, an alkenylene group and a nitrogen atom.
  • the aromatic ring referred to here is a concept including both a hydrocarbon aromatic ring in which the ring skeleton constituent atom is composed of only carbon atoms and a heteroaromatic ring containing a hetero atom as the ring skeleton constituent atom.
  • the backbone of the organic laser dye is composed of one or more selected from the group consisting of hydrocarbon aromatic rings, alkenylene groups and nitrogen atoms.
  • the backbone of the organic laser dye is composed of two or more selected from the group consisting of hydrocarbon aromatic rings, alkenylene groups and nitrogen atoms.
  • the backbone of the organic laser dye is composed of a hydrocarbon aromatic ring, an alkenylene group and a nitrogen atom.
  • the backbone of the organic laser dye comprises only one or more selected from the group consisting of hydrocarbon aromatic rings, alkenylene groups and nitrogen atoms, and heteroaromatic rings. In another preferred embodiment, the backbone of the organic laser dye comprises only two or more selected from the group consisting of hydrocarbon aromatic rings, alkenylene groups and nitrogen atoms, and heteroaromatic rings.
  • a hydrocarbon aromatic ring When a hydrocarbon aromatic ring is contained in the main chain, specific examples thereof include 1,4-phenylene group, 1,3-phenylene group, 1,2-phenylene group, 1,8-naphthylene group, 1, 7-naphthylene group, 1,6-naphthylene group, 1,5-naphthylene group, 2,6-naphthylene group, 2,7-naphthylene group, 1,5-anthracenylene group, 2,6-anthracenylene group can be mentioned.
  • a 1,4-phenylene group can be mentioned as a preferable specific example.
  • a heteroaromatic ring When a heteroaromatic ring is contained in the main chain, specific examples thereof include a furan-2,5-diyl group and a thiophene-2,5-diyl group.
  • an alkenylene group When an alkenylene group is contained in the main chain, an ethylene group can be mentioned as a specific example thereof.
  • the structural unit of aromatic ring-alkenylene group-aromatic ring is included in the main chain.
  • a hydrocarbon aromatic ring-alkenylene group-hydrocarbon aromatic ring structural unit is included in the main chain.
  • the structural unit of a heteroaromatic ring-alkenylene group-heteroaromatic ring is included in the main chain.
  • the hydrocarbon aromatic ring-hydrocarbon aromatic ring structural unit is included in the main chain.
  • a hydrocarbon aromatic ring-nitrogen atom-hydrocarbon aromatic ring structural unit is included in the main chain.
  • the aromatic ring, alkenylene group and nitrogen atom constituting the main chain of the organic laser dye may be substituted.
  • the substituent include an alkyl group, an alkoxy group, an aryl group, an aryloxy group, a heteroaryl group, a heteroaryloxy group, a dialkylamino group, a diarylamino group and a halogen atom.
  • it may be an alkyl group or an aryl group.
  • the alkyl group referred to in the present specification may be linear, branched or cyclic, and the number of carbon atoms is usually 1 to 30, for example, in the range of 1 to 20, or in the range of 1 to 10. It may be selected within the range of 1 to 6. Specific examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a t-butyl group, a pentyl group, a hexyl group, an isopropyl group and a cyclohexyl group.
  • the aryl group may be a monocyclic ring or a fused ring, and the number of carbon atoms is usually 6 to 30, for example, 6 to 18 or 6 to 10.
  • a phenyl group and a naphthyl group include a phenyl group and a naphthyl group.
  • the heteroaryl group may also be a monocyclic ring or a fused ring, and the number of ring skeleton constituent atoms is usually 5 to 30, for example, in the range of 5 to 18, in the range of 5 to 10, in the range of 5 to 7, and in the range of 5 to 6. You may select within the range.
  • Specific examples thereof include pyridyl group, pyridadyl group, pyrimidyl group, triazil group, triazolyl group, benzotriazolyl group and carbazolyl group.
  • heteroaryl groups may be a group bonded via a hetero atom or a group bonded via a carbon atom constituting a heteroaryl ring. Some or all of the hydrogen atoms present in the groups described in this paragraph may be substituted with substituents.
  • the alkyl moiety of the alkoxy group and the dialkylamino group the description of the alkyl group above can be referred to.
  • the aryl portion of the aryloxy group and the diallylamino group the description of the aryl group can be referred to above.
  • the heteroaryl portion of the heteroaryloxy group the description of the heteroaryl group above can be referred to.
  • the two alkyl groups of the dialkylamino group may be the same or different from each other, but are preferably the same.
  • the two aryl groups of the diarylamino group may be the same or different from each other, but are preferably the same.
  • the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
  • a fluorine atom can be adopted.
  • the molecular weight of the organic laser dye is preferably 600 or more, and can be selected from, for example, a region of 3000 or less, a region of 2000 or less, and a region of 1000 or less.
  • the emission wavelength of the organic laser dye is preferably in the visible region.
  • the emission colors are purple (400 to 435 nm), blue (435 to 480 nm), patina and blue green (480 to 500 nm), green (500 to 580 nm), yellow (580 to 610 nm), and red (610 to 750 nm).
  • Each color of patina (750 to 800 nm) can also be selected.
  • the emission wavelength of the organic laser dye may be in the near infrared region (800 nm or more, for example, 800 to 1400 nm) or the ultraviolet region (100 to 400 nm, for example, 315 to 400 nm).
  • the triplet reusing agent used in the organic laser element of the present invention has a function of removing triplet excitators of the organic laser dye so that the energy of the triplet excited state of the organic laser dye can be used for laser oscillation.
  • the triple term reusing agent used in the organic laser device of the present invention may consist of an organic compound composed of only a plurality of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms and oxygen atoms.
  • the organic laser device of the present invention may consist of an organic compound composed of only a plurality of atoms selected from the group consisting of carbon atom, hydrogen atom, nitrogen atom and sulfur atom, and may consist of a group consisting of carbon atom, hydrogen atom and nitrogen atom. It may be composed of an organic compound composed of only a plurality of selected atoms, or may be composed of an organic compound composed of only carbon atoms and hydrogen atoms.
  • the triplet reusing agent used in the organic laser device of the present invention preferably has no repeating unit.
  • the triplet reusing agent used in the organic laser device of the present invention is preferably a compound having two or more benzene rings.
  • the number of benzene rings in the molecule may be 4 or more, 6 or more, or 8 or more. For example, it may be 50 or less, 20 or less, 15 or less, 10 or less, or 8 or less. It is preferable that one or more of the benzene rings present in the molecule are benzene rings in which aromatic rings are condensed. In a preferred embodiment, one or more of the benzene rings present in the molecule is a benzene ring in which two or more aromatic rings are condensed. In a preferred embodiment, the molecule has two or more condensed aromatic rings.
  • the molecule has three or more condensed aromatic rings. In a preferred embodiment, it comprises a structure in which two fused aromatic rings are linked to each other. In a preferred embodiment, it comprises a structure in which two fused aromatic rings are linked to each other via a substituted or unsubstituted phenylene group. In a preferred embodiment, the structure comprises two fused aromatic rings linked to each other and has three or more condensed aromatic rings in the molecule. In a preferred embodiment, it comprises a structure in which two fused aromatic rings are linked to each other via a substituted or unsubstituted phenylene group, and has three or more condensed aromatic rings in the molecule.
  • the triplet reusing agent consists only of an arylene group and an aryl group. In a preferred embodiment, the triplet reusing agent consists only of two or more arylene groups and two or more aryl groups. In a preferred embodiment, the arylene and aryl groups in the molecule are unsubstituted arylene and unsubstituted aryl groups. In a preferred embodiment, the molecule comprises one or more unsubstituted 1,4-phenylene groups.
  • those in which the arylene group and the aryl group in the molecule are substituted can also be used, and for the substituent in that case, the description of the substituent in the organic laser dye can be referred to.
  • the molecule contains only one unsubstituted 1,4-phenylene group.
  • the molecule contains an anthracene ring.
  • the molecule contains a naphthalene ring.
  • the molecule comprises an anthracene ring and a naphthalene ring.
  • the molecule comprises an anthracene ring and two or more naphthalene rings. In a preferred embodiment, it comprises a structure in which a naphthalene ring and an anthracene ring are bonded via a phenylene group.
  • the triplet reusing agent has a structure in which only hydrocarbon aromatic rings are linked to each other.
  • the triplet reusing agent has a structure in which two or more selected from the group consisting of a benzene ring, a naphthalene ring and an anthracene ring are linked to each other.
  • the triplet reusing agent has a structure in which one or more benzene rings, one or more naphthalene rings, and one or more anthracene rings are bonded to each other.
  • the triplet reusing agent has a structure in which one or more benzene rings, two or more naphthalene rings, and one or more anthracene rings are bonded to each other.
  • the triplet reusable agent comprises a 9,10-anthracenylene group.
  • the triplet reusing agent comprises a 1-naphthyl group.
  • the triplet reusing agent comprises a 2-naphthyl group.
  • the triplet reusing agent comprises both a 1-naphthyl group and a 2-naphthyl group.
  • the triplet reusing agent comprises a 1,4-phenylene group.
  • the triplet reusing agent comprises a 1,4-phenylene group, a naphthyl group and a 9,10-anthracenylene group.
  • the triplet reusing agent used in the organic laser device of the present invention preferably does not contain a heteroaromatic ring.
  • the triplet reusing agent used in the organic laser device of the present invention may contain a heteroaromatic ring.
  • the molecular weight of the triplet reusing agent used in the organic laser device of the present invention is preferably 400 or more, for example, a region of 500 or more, a region of 2000 or less, a region of 1000 or less, a region of 800 or less, and a region of 600 or less. It is also possible to select from.
  • the triplet reusing agent has low crystallinity and is preferably amorphous. For example, it is preferably less crystalline than 9,10-di (naphtha-2-yl) anthracene (ADN).
  • the organic laser element of the present invention preferably has an amorphous film containing an organic laser dye and a triplet reusing agent.
  • Equation (1) S (Q)> S1 (D) Equation (2) T1 (D)> T (Q)
  • S1 (D) represents the energy level of the at least singlet excited state of the organic laser dye
  • S (Q) is the triplet-triplet of the triplet reusing agent.
  • the energy level of the singlet excited state generated by pair annihilation is represented
  • T1 (D) represents the energy level of the lowest triplet excited state of the organic laser dye
  • T (Q) represents the energy level of the triplet excited state. Represents the energy level of the triplet excited state.
  • S1 (Q) -S1 (D) is preferably 0.1 eV, and may be selected from, for example, a range of 0.2 eV or more, a range of 0.3 eV or more, a range of 0.5 eV or more, and 2 You may select from a range of 0.0 eV or less, a range of 1.5 eV or less, and a range of 1.0 eV or less.
  • T1 (D) -T1 (Q) is preferably 0.1 eV, and may be selected from, for example, a range of 0.2 eV or more, a range of 0.3 eV or more, a range of 0.5 eV or more, and 2 You may select from a range of 0.0 eV or less, a range of 1.5 eV or less, and a range of 1.0 eV or less.
  • S1 (D) -T1 (D) is in the range of more than 0.1 eV, the range of more than 0.2 eV, the range of more than 0.3 eV, the range of more than 0.5 eV, the range of more than 0.8 eV, and the range of more than 1.2 eV.
  • the range may be selected from a range of 2.5 eV or less, a range of 2.0 eV or less, and a range of 1.5 eV or less.
  • S (Q) typically represents the energy level of the lowest singlet excited state generated by triplet-triplet annihilation of the triplet reusing agent.
  • T (Q) typically represents the energy level of the lowest triplet excited state of triplet reuse.
  • the organic laser dye is in a singlet excited state and a triplet excited state by supplying excitation energy.
  • the organic laser dye is excited into a singlet excited state and a triplet excited state by the recombination of the carriers.
  • the energy in the singlet excited state is used for laser oscillation, and the energy in the triplet excited state is not used for laser oscillation. Accumulation of long-lived triplet excitons interferes with laser oscillation, so it is desirable to remove triplet excitons. Therefore, conventionally, triplet excitons have been removed by adding a triplet remover.
  • the energy of the triplet excited state is not used for laser oscillation. Therefore, in the present invention, it is decided to remove triplet excitons and convert the energy of the triplet excited state into the energy of the singlet excited state for use in laser oscillation by the presence of a triplet reusing agent. ..
  • the energy of the triplet excited state of the organic laser dye generated by the supply of excitation energy and the energy of the triplet excited state transitioned by the intersystem crossing from the singlet excited state of the organic laser dye are used.
  • the triplet reusing agent is moved to the triplet excited state.
  • the triplet excitons of the triplet reusing agent collide with each other to cause energy transfer, and triplet-triplet upconversion (TTU) produces singlet excitons.
  • TTU triplet-triplet upconversion
  • the organic laser element of the present invention has a composition containing an organic laser dye and a triplet reusing agent.
  • a composition is preferably in the form of a film (film or layer).
  • the organic laser dye in an amount of 0.1% by weight or more based on the total weight of the organic laser dye and the triplet reusing agent.
  • the organic laser dye may be used, for example, in a region of 0.5% by weight or more, a region of 1% by weight or more, a region of 2% by weight or more, a region of 3% by weight or more, and a region of less than 50% by weight.
  • the composition may contain components other than the organic laser dye and the triplet reusing agent.
  • the content of such a component may be, for example, in the range of 0.01 to 10% by weight of the entire composition, or in the range of 0.01 to 1% by weight.
  • an organic EL undergoes singlet excitons and triplet through injection of holes and electrons from electrodes, transport of holes and electrons, and recombination of holes and electrons. It forms two types of excitons. At this time, singlet excitons and triplet excitons are generated at a ratio of 1: 3 according to the spin-statistics rule [8] .
  • the EQE ( ⁇ ext ) of an organic EL is an important guideline for evaluating device performance, and is defined as the ratio of the number of photons taken out to the total amount of injected electrons. EQE can be calculated by the following formula.
  • ⁇ r is a hole and electron injection balance factor, which is determined by the ratio of the hole density and the electron density injected into the device, and can be approached to 100% by using an appropriate device structure.
  • .. ⁇ is the exciton generation efficiency, and it is known that singlet excitons and triplet excitons are generated at a ratio of 1: 3 in current excitation according to the spin statistical law [8] .
  • ⁇ PL is the emission quantum yield of the luminescent molecule itself, and can be approached to 100% by selecting the organic material to be used.
  • ⁇ out is the light extraction efficiency, which indicates how much the light emitted inside the element is extracted to the outside of the element, and is only 20-30% in general organic EL.
  • the first generation organic EL is a fluorescent organic EL based on radiation deactivation from singlet excitons. Since triplet excitons are thermally deactivated by non-radiative deactivation, only singlet excitons, which are 25% of the generated excitons, can contribute to light emission. The upper limit remains at 5%.
  • the second generation organic EL is an organic EL using phosphorescence from the triplet excited state. In 1998, Baldo et al. Discovered a mechanism for utilizing triplet excitons for light emission by efficient singlet-triplet mixing through strong spin-orbit interaction using organometallic compounds containing heavy atoms. [9] ..
  • TADF thermally activated delayed fluorescence
  • RISC reverse intersystem crossing
  • OSL distributed feedback
  • Lasers are an indispensable technology used in a wide range of fields of our lives. This is because the laser has the unique properties shown below. First, the laser is monochromatic and has a very high energy density. This property is used in CD / DVD players, barcode readers, laser machines, pointers, medical devices, optical communications, etc. Furthermore, since lasers have high directivity, they are also used for distance measurement and entertainment light sources. Usually, gas (N 2 or Ar), metal (CdHe or Cu), inorganic substance (YAG, Ti: sapphire) and inorganic semiconductor substance (GaN or InGaAsP) are used.
  • FIG. 2 shows the basic photoexcitation process and light emission process.
  • a molecule in the ground state is excited to the excited state by absorbing a photon h ⁇ having an energy equal to ⁇ E, which corresponds to the energy difference between the ground state and the excited state.
  • ⁇ E an energy equal to the energy difference between the ground state and the excited state.
  • the excited molecule is induced by h ⁇ to emit h ⁇ , or spontaneously emits h ⁇ and returns to the ground state. From the above, it is necessary to form a population inversion for ASE oscillation.
  • Population inversion is a state in which the existence probability of a molecule in an excited state is higher than that of a molecule in the ground state.
  • stimulated emission is more likely to occur than light absorption, so stimulated emission occurs in a chain with photons h ⁇ .
  • the photons generated by stimulated emission have high directivity, and the emitted light is amplified to form an ASE with a sharpened spectrum.
  • ASE is a phenomenon that occurs in a gain medium that does not involve a resonator. In order to obtain laser oscillation, as shown in FIG. 3, it is necessary to incorporate a gain medium in which stimulated emission occurs efficiently into the optical resonator.
  • the optical resonator plays a role of amplifying a specific wavelength.
  • the excitation forms a population inversion in the gain medium, stimulated emission occurs continuously, resulting in ASE.
  • the photons generated by stimulated emission have exactly the same phase, frequency, and directivity as the incident photons, but since the photon that is the starting point in the gain medium is not single, it is considered that multiple ASE groups are generated. be able to.
  • the optical resonator amplifies only light having a specific wavelength and directivity, and emits other light without being amplified. Therefore, only a specific ASE group that matches the optical resonator design is amplified, and the amplified light causes stimulated emission.
  • the excitation means for forming a population inversion in the gain medium is called a photoexcitation type when it is light from the outside and a current excitation type when it is a current.
  • a photoexcitation type organic laser is composed of an organic thin film as a gain medium and a resonator, but a current excitation type organic laser incorporates a resonator in a light emitting element such as an organic EL in order to inject a charge into the gain medium.
  • FIG. 4 shows the relationship between the current density and the exciton density.
  • the exciton density should be as shown by the solid line in the figure.
  • the luminous efficiency decreases due to exciton deactivation and decrease in charge recombination efficiency [33] . This decrease in luminous efficiency at high current densities is called efficiency roll-off.
  • S 1 and T 1 are the excitators of the lowest singlet excited state energy level (S 1 level) and triplet excited state energy level (T 1 level), respectively, and p is polaron and S.
  • n and T n indicate the singlet and triplet excited states of the higher-order excited state.
  • SSA, STA, and SPA are caused by the formation of new absorption bands by singlet excitons, triplet excitons, and polarons generated by driving.
  • the excited state absorption spectra of S 1 and T 1 or the absorption spectrum of polaron overlap with the laser oscillation wavelength, the energy of the luminescent S 1 excitons is converted to T 1 excitons by Felster-type energy transfer.
  • NS the excited state absorption spectra of S 1 and T 1 or the absorption spectrum of polaron overlap with the laser oscillation wavelength
  • the singlet energy (S) of the triplet removing agent 1 ) should be higher than S 1 of the laser molecule and the triplet energy (T 1 ) of the triplet remover should be lower than T 1 of the laser molecule.
  • TTU Triple-triplet upconversion
  • TTU organic EL roll-off is suppressed in molecules with a large TTU rate constant due to the synergistic effect of increased exciton utilization efficiency due to the generation of singlet excitons and suppression of STA due to the consumption of triplet excitons. This is also a point to note [49] .
  • NaNaP-A which is a TTU host. Since NaNaP-A has a sufficiently high singlet energy (S 1 ) and a sufficiently low triplet energy (T 1 ), it can be expected to be effective as a triplet remover. Furthermore, this molecule is known to exhibit TTU, and we knew if the removed triplet excitons could be used for luminescence through the TTU process.
  • Substrate cleaning method In this study, a quartz substrate (Rayon Industry) or a glass substrate (Matsunami Glass Industry) was used and washed as follows before forming an organic thin film. (1) The substrate was set in a beaker, and ultrasonic cleaning was performed twice for 10 minutes using acetone. (2) After ultrasonic cleaning for 15 minutes using a neutral detergent (Deer Clean) diluted 10-fold with ultrapure water, it was left overnight in a neutral detergent. (3) Ultrapure water was used to perform ultrasonic cleaning for 5 minutes three times. (4) Ultrasonic cleaning was performed for 10 minutes using isopropanol.
  • a neutral detergent Deer Clean
  • UV ozone treatment was performed for 15 minutes using a UV ozone cleaner (Filgen).
  • the excitation wavelength is set to 400 nm for BDAVBi monolayers, 330 nm for CBP monolayers, BDAVBi: CBP co-deposited films, and 380 nm for NaNaP-A monolayers and BDAVBi: NaNaP-A co-deposited films.
  • the emission spectrum was measured. [Measurement of emission quantum yield] The emission quantum yield was measured using an absolute PL quantum yield measuring device (Quantaurus-QY, Hamamatsu Photonics). The base measurement was performed with a reference sample (quartz substrate), and then the sample was measured. The emission quantum yield was calculated from the excitation light absorbed by the sample and the emission spectrum.
  • the excitation wavelength was set to 400 nm for the BDAVBi monolayer, 330 nm for the CBP monolayer and BDAVBi: CBP co-deposited film, and 380 nm for the NaNaP-A monolayer and BDAVBi: NaNaP-A co-deposited film. ..
  • the measurement was performed in an argon atmosphere.
  • ASE oscillation characteristics [ASE measurement system] A sharp sample end face was prepared by dividing the sample prepared for ASE characteristic evaluation along a notch introduced into the substrate in advance. A measurement system as shown in FIG. 8 was used to evaluate the ASE characteristics. At this time, the ASE characteristics were measured in a nitrogen atmosphere in order to prevent deterioration due to water and oxygen in the atmosphere. A nitrogen gas laser (KEN-2020, USHO., Pulse width ⁇ 800 ps, frequency 20 Hz) with a wavelength of 337 nm was used as the excitation light source.
  • KEN-2020, USHO., Pulse width ⁇ 800 ps, frequency 20 Hz was used as the excitation light source.
  • the excitation light to irradiate the sample was focused on an area of 0.2 ⁇ 0.5 cm 2 using a slit and a cylindrical lens, and the sample was irradiated in a striped shape. Emissions from the sample end faces at various excitation light intensities were measured by a multi-channel photodiode (PMA-12, Hamamatsu Photonics). The excitation light intensity at the sample position was measured using a laser energy meter (microjoule meter, LTB). The excitation light irradiation area was measured using a beam profiler (WinCamD-LCM, DataRay).
  • the end face emission spectrum was measured by varying the excitation light intensity between 0.01 and 100% using a Neutral Density (ND) filter (Asahi spectroscopy). The emission peak intensity and full width at half maximum (FWHM) were plotted against the excitation light intensity. Sharpening (ASE) of the emission spectrum was observed when the excitation light intensity above the ASE oscillation threshold was used. The ASE oscillation threshold was determined from the change point of the slope of the peak intensity. [Calculation of excitation light intensity] The excitation light intensity was calculated using the following formula.
  • I ex is the excitation light intensity actually absorbed by the sample
  • I is the excitation light intensity per pulse before absorption
  • x is the light absorption rate of the sample at 337 nm
  • S is the excitation light area.
  • the absorbances of the BDAVBi: CBP co-deposited film and the BDAVBi: NaNaP-A co-deposited film were 0.899 and 0.197, respectively, and the absorption rates were 87.4% and 36.5%, respectively.
  • Table 1 shows the measurement results of the emission quantum yield (PLQY) of each organic thin film.
  • the BDAVBi monolayer film showed a low PLQY of 27.4% due to the effect of concentration quenching, but it was found that the concentration quenching was suppressed by doping with CBP and NaNaP-A, and the PLQY improved to about 80%.
  • FIG. 10 shows 3 wt% BDAVBi: CBP co-deposited film (150 nm) and 3 wt% BDAVBi: NaNaP-A co-deposited film (150 nm) formed on a glass substrate.
  • the excitation intensity dependence of the end face emission spectrum (ASE spectrum) from is shown. It was observed that the end face emission spectrum sharpened as the excitation intensity increased.
  • FIG. 11 shows the emission intensity and the excitation intensity dependence of the half width at each peak wavelength. In FIG. 11, when the intensity of the excitation light exceeds a certain level, a rapid increase in the emission intensity and a decrease in the half width are observed.
  • the ASE oscillation threshold is calculated to be 1.34 ⁇ J / cm 2 for the 3 wt% BDAVBi: CBP co -deposited film and 1.01 ⁇ J / cm 2 for the 3 wt% BDAVBi: NaNaP-A co-deposited film.
  • a reduction in threshold was observed. Since the PLQY of each co-deposited film is 79.5% and 79.1%, one of the causes of the decrease in the ASE oscillation threshold is the emission of the laser dye BDAVBi by NaNaP-A introduced as a triplet remover. It is probable that the deactivating triplet excitons have been removed.
  • Transient PL characteristic measurement method 3-2-1 Sample preparation In order to clarify the reason why the ASE threshold was reduced, a 3 wt% BDAVBi: CBP co-deposited film and a 3 wt% BDAVBi: NaNaP-A co-deposited film were prepared and emitted during photoexcitation. The time change of intensity (transient PL) was measured. The same method as in 2-2-1 was used for the substrate cleaning method and the organic thin film film forming method. In order to prevent photodegradation of the organic thin film due to irradiation with excitation light during measurement, the organic thin film was sealed by the following method. [Sealing method] (1) The prepared sample was transported from the organic vapor deposition chamber to the nitrogen glove box.
  • UV curable resin Naagase Chemtex
  • the UV curable resin was cured by irradiating with UV for 10 minutes using a UV curing device. At this time, in order to prevent photodegradation of the organic thin film due to UV irradiation, a silicon plate was used to protect the organic film.
  • Transient PL characteristics Transient PL measurement system
  • Photomultiplier tube R928, Hamamatsu Photonics
  • oscilloscope Wave Surfer 3034, Teledyne LeCroy
  • high-speed bipolar power supply HSA 4101, NF circuit design block
  • multifunction generator WF1974, NF circuit design block
  • the sample is irradiated with pulsed light with a wavelength of 355 nm, and the light emitted during excitation light irradiation is photoelectron doubled. Detected in.
  • the pulse width of the irradiated pulsed light was 40 ⁇ s, the frequency was 10 Hz, and the time change of light emission was measured with an oscilloscope as a voltage output.
  • the excitation light was focused by a lens and irradiated in an area of 4.33 ⁇ 10 -6 cm 2.
  • the excitation light intensity at the sample position was measured using a thermal sensor (3A-PF-12, Ophir Optics).
  • the reagent powders to be used were placed in an alumina crucible and set in a tungsten basket heater in an organic vacuum deposition machine.
  • the cathodes LiF and Al were set on the V-boat and BN-boat in the metal vacuum deposition machine, respectively.
  • the washed ITO substrate was fixed to the substrate holder, further fixed on the holder with the organic vapor deposition mask, and set in the organic vacuum vapor deposition machine.
  • HTL hole transport layer
  • ⁇ -NPD hole transport layer
  • EML light emitting layer
  • TPBi electron transport layer
  • the element that has completed the organic thin film deposition is transported from the organic vapor deposition chamber to the metal vapor deposition chamber while maintaining the vacuum, fixed on a holder with a metal vapor deposition mask, and set in the metal vacuum deposition machine. bottom.
  • a metal thin film of the cathode was deposited by resistance heating by passing an electric current through each of the V-boat and BN-boat.
  • the metal thin film was formed in the following order and conditions. 1.
  • LiF was vacuum-deposited so that the deposition rate was 0.01 nm / s and the film thickness was 0.8 nm.
  • Al was vacuum-deposited so that the vapor deposition rate was 0.3-4 nm / s and the film thickness was 100 nm.
  • the element was sealed by the following method.
  • (1) The sample after forming the metal thin film was conveyed from the metal deposition chamber to the glove box via the organic vapor deposition chamber in a nitrogen atmosphere.
  • (3) The UV curable resin was cured by irradiating with UV for 10 minutes using a UV curing device. At this time, in order to prevent photodegradation of the organic thin film due to UV irradiation, a silicon plate was used to protect the organic film.
  • EL characteristics The EL characteristics of the produced organic EL were evaluated using an external quantum efficiency measuring device (C9920-12, Hamamatsu Photonics).
  • the organic EL produced in the integrating sphere is set, a voltage is applied by a source meter, the EL is measured by a multi-channel photodiode (PMA-12, Hamamatsu Photonics) connected to the integrating sphere, and the current density (J)- The voltage (V) characteristics and the external quantum efficiency (EQE) -current density (J) characteristics were evaluated.
  • Transient EL characteristics Transient EL measurement system
  • Photomultiplier tube R928, Hamamatsu Photonics
  • oscilloscope MSO6104A, Agilent Technologies
  • high-speed bipolar power supply HSA 4101, NF circuit design block
  • multifunction generator WF1974, NF circuit design block
  • the pulse voltage oscillated from the multifunction generator was amplified via a high-speed bipolar power supply and applied to the device with a forward bias.
  • the EL intensity during application of an electric field was detected by a photomultiplier tube and measured using an oscilloscope as a voltage output.
  • the pulse width of the applied pulse voltage was 20 ⁇ s and the frequency was 1 Hz, and the current density actually flowing through the element was calculated from the voltage applied to the 100 ⁇ resistor installed in parallel with the element.
  • FIG. 15 shows the measurement results of the JV characteristics and EQE-J characteristics of each element. Comparing the two elements, there was no significant difference in the rising voltage of the current density.
  • the maximum value of the external emission quantum yield was 3.4% (0.1 mA / cm 2 ) in the BDAVBi: CBP system and 3.1% (17.4 mA / cm 2 ) in the BDAVBi: NaNaP-A system.
  • the roll-off of the external quantum efficiency was confirmed in both devices, but it was confirmed that the device using NaNaP-A greatly suppressed the decrease in the external emission quantum yield in the high current density region.
  • the roll-off of external quantum efficiency in organic EL is due to the deactivation of singlet excitons by triplet excitons, polarons, heat, electric fields, and the like.
  • the ASE characteristics of the 3 wt% BDAVBi: NaNaP-A co-deposited film and the 3 wt% BDAVBi: CBP co-deposited film were evaluated. ASE oscillation was confirmed from both co-deposited films, and the ASE threshold was calculated from the dependence of the ASE intensity on the excitation light intensity.
  • the BDAVBi: NaNaP-A co-deposited film showed a lower ASE threshold than the BDAVBi: CBP co-deposited film.
  • One possible cause is the removal of triplet excitons by NaNaP-A.
  • transient PL characteristics of 3 wt% BDAVBi: NaNaP-A co-deposited film and 3 wt% BDAVBi: CBP co-deposited film were measured.
  • the BDAVBi: NaNaP-A co-deposited film suppressed the deactivation of light emission as compared with the BDAVBi: CBP co-deposited film, and it was confirmed that the triplet excitons were removed by the introduction of NaNaP-A. Revealed. Furthermore, an organic EL using each co-deposited film as a light emitting layer was prototyped, and its initial characteristics and transient EL were evaluated. In the device using NaNaP-A as the host of the laser material, we succeeded in suppressing the deactivation caused by the triplet and suppressing the roll-off observed in the organic EL. Furthermore, emission amplification due to TTU was confirmed from the transient EL characteristics.
  • the triplet remover also serves as a TTU host as examined in this study, the triplet remover is present in the light emitting layer at a high concentration, and the excitons in the triplet remover are generated by TTU. It is expected that TTU, which can be consumed, will improve the luminous efficiency. Moreover, since this method can be achieved by combining molecules having appropriate energy levels, it can be said that it is also useful from the viewpoint of material search.
  • SPA exciton deactivation process
  • SHA SHA
  • EHQ exciton deactivation process
  • SPA a method of separating polarons from each other so as not to interact with singlet excitons can be mentioned as a countermeasure.
  • K. Hayashi et al. Succeeded in suppressing SPQ by creating a fine structure in the device using electron beam lithography [50].
  • FIG. 17 [51] shows the mechanism of SPA suppression.
  • SHA is a phenomenon in which excitons are dissociated by heat. Joule heat generated by device driving leads not only to exciton deactivation but also to device destruction, which is one of the important issues in device driving at a high current density.
  • the main countermeasures reported so far include pulse-driving the device, reducing the active region of the device, and using a substrate with good thermal conductivity [51-57] .
  • EFQ EFQ
  • organic semiconductor materials form Frenkel excitons, and because the exciton binding energy is relatively high [59] , excitons do not dissociate unless an extremely high electric field is applied. , It is considered that the influence is small in the exciton annihilation process.

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