JP6344756B2 - Spherical polymer particle and optical element for whispering galery mode oscillation - Google Patents

Description

  The present invention relates to spherical polymer particles and an optical element using the same. More specifically, the present invention relates to microspherical particles formed using a light-emitting polymer and an optical element using the light emission characteristics.

  Colloidal crystals produced by integrating nano-sized and micro-sized fine particles are attracting attention from the viewpoint of three-dimensional photonic crystals exhibiting new optical functions. For example, conventionally, colloidal crystals in which a luminescent organic dye, an organometallic coordination compound, a polymer light emitting material, or semiconductor nanoparticles are introduced into the mesopores of monodispersed spherical mesoporous silica have been proposed (Patent Document 1). reference).

  In addition, research to develop whispering gallery mode (WGM) oscillation by adding dyes to polymer beads such as polystyrene, or by applying luminescent organic molecules or luminescent polymers. (For example, refer nonpatent literatures 1-3.). The spherical particles having such light emission characteristics are expected to be applied to various optical devices such as optical resonators, optical amplifiers, and sensors.

JP 2010-87489 A

Makoto Kuwata-Gonokami, 1 other, “Polymer whispering gallery mode lasers”, Optical Materials, 1998, Vol. 9, p. 12-17 M. Humar, 3 others, “Electrically tunable liquid crystal optical microresonators”, NATURE PHOTONICS, October 2009, Volume 3, p. 595-600 Van Duong Ta, 1 other, “Tuning Whispering Gallery Mode Lasing from Self-Assembled Polymer Droplets”, SCIENTIFIC REPORTS, 2013, 3: 1362

  However, conventional spherical particles that have been confirmed to have WGM oscillation require the use of a light-emitting material such as a dye, and there is a problem that the manufacturing process is complicated.

  Therefore, the main object of the present invention is to provide spherical polymer particles and an optical element that can exhibit whispering, galley, and mode oscillation without using a light emitting material such as a dye.

  In order to solve the above-described problems, the present inventor has conducted extensive experimental studies. As a result, if microspherical particles can be formed from a light-emitting polymer, spherical polymer particles that perform WGM oscillation with a single material can be obtained. As a result, the present invention has been found.

That is, the spherical polymer particles according to the present invention are spherical or substantially spherical particles made of a light-emitting polymer, and whispering galley mode oscillation is generated inside by irradiation with excitation light.
For example, a π-conjugated alternating copolymer can be used as the light emitting polymer.
The spherical polymer particles of the present invention have a particle diameter measured by, for example, an electron microscope of 2 μm or more.
The spherical polymer particles of the present invention can be formed by, for example, a vapor diffusion method.

  The optical element according to the present invention uses the aforementioned spherical polymer particles.

  According to the present invention, spherical polymer particles that exhibit whispering galley mode oscillation can be realized with a single material without using a light emitting material such as a pigment.

It is a figure which shows the emission spectrum of the spherical polymer particle (diameter 2.3 micrometers) which consists of (pi) conjugate alternating copolymer F8TMT2. It is a schematic diagram which shows the oscillation from a spherical polymer particle. It is a SEM photograph (drawing substitute photograph) which shows the spherical polymer particle which consists of (pi) conjugate alternating copolymer F8TMT2. It is a SEM photograph (drawing substitute photograph) which shows the spherical polymer particle which consists of (pi) conjugate alternating copolymer 2,7-CTMT2. It is a SEM photograph (drawing substitute photograph) which shows the spherical polymer particle which consists of (pi) conjugated alternating copolymer PTTMT2. It is a SEM photograph (drawing substitute photograph) which shows the spherical polymer particle which consists of (pi) conjugate alternating copolymer AZOANI. It is a figure which shows the emission spectrum of the spherical polymer particle which consists of (pi) conjugate alternating copolymer F8TMT2. It is a figure which shows the emission spectrum of the spherical polymer particle which consists of (pi) conjugate alternating copolymer 2,7-CTMT2. It is a figure which shows the emission spectrum of the spherical polymer particle which consists of (pi) conjugate alternating copolymer PTTMT2. It is a figure which shows the emission spectrum of the spherical polymer particle which consists of (pi) conjugate alternating copolymer AZOANI.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments described below.

[overall structure]
The spherical polymer particles according to the embodiment of the present invention are spherical or substantially spherical particles made of a light emitting polymer. And when the spherical polymer particle of this embodiment irradiates the light (excitation light) of a specific wavelength, WGM oscillation will arise inside.

[Luminescent polymer]
The light-emitting polymer that forms the spherical polymer particles of the present embodiment is not particularly limited as long as it emits light by excitation light, but is a π-conjugated polymer having both light-emitting and conductive properties. Is preferred. Among various π-conjugated polymers, a π-conjugated alternating copolymer having a steric hindrance introduced into the main chain easily forms spherical particles and is particularly suitable as a material for spherical polymer particles.

  Specific examples of the π-conjugated alternating copolymer include 2,7-CTMT2 having a structure represented by the following chemical formula 1, F8TMT2 having a structure represented by the following chemical formula 2, PTTMT2 having a structure represented by the following chemical formula 3, and a structure having the structure represented by the following chemical formula 4. AZOANI, 3,6-CTMT2 having a structure represented by the following chemical formula 5, F8EDOT having a structure represented by the following chemical formula 6, DOPTMT2 having a structure represented by the following chemical formula 7, and the like. Among these π-conjugated alternating copolymers, 2,7-CTMT2 (Chemical Formula 1), F8TMT2 (Chemical Formula 2), PTTMT2 (Chemical Formula 3), and AZOANI (Chemical Formula 4) are nearly spherical and have a uniform internal structure. In addition, spherical polymer particles having excellent shape stability can be obtained, which is particularly preferable.

[Particle size]
The size of the spherical polymer particles of the present embodiment can be appropriately selected according to the emission wavelength, the physical properties of the polymer material, and the like. However, when the particle diameter (diameter) is smaller than 2 μm, WGM oscillation is hardly exhibited. There is a trend. Therefore, the size of the spherical polymer particles is preferably 2 μm or more in diameter. The particle diameter here is a value calculated from an image taken by microscopic observation.

[Production method]
The spherical polymer particles of the present embodiment can be formed by, for example, a vapor diffusion method. The vapor diffusion method is a method of crystallizing a polymer dissolved in a good solvent by placing it in a poor solvent vapor. At that time, trichloromethane (CHCl ₃ ), dichloromethane (CH ₂ Cl ₂ ), chlorobenzene (PhCl), tetrahydrofuran (THF), toluene, and the like can be used as the poor solvent, and methanol, acetone, hexane, and the like can be used as the good solvent. Can be used.

  The solvent used in the vapor diffusion method is not limited to those described above, and can be appropriately selected according to the type of polymer and used in combination. Further, the method for producing spherical polymer particles of the present embodiment is not limited to the vapor diffusion method, and various methods capable of producing spherical or substantially spherical microparticles can be applied. However, the vapor diffusion method is preferable from the viewpoint of easy production of spherical polymer particles.

[Operation]
FIG. 1 is a diagram showing an emission spectrum of spherical polymer particles made of F8TMT2, and FIG. 2 is a schematic diagram showing oscillation from spherical polymer particles. When the spherical polymer particles of the present embodiment are irradiated with, for example, laser light, a waveform in which a plurality of spike-like peaks as shown in FIG. 1 overlaps the emission spectrum is observed. This is a phenomenon that is not observed when measured in a bulk state without being spherical.

  This unique waveform is due to WGM oscillation. As shown in FIG. 2, the light generated inside the spherical polymer particles by laser excitation is totally reflected in the vicinity of the interface due to the difference in refractive index from the outside (air). This occurs because it is confined within the spherical polymer particles. And when the integral multiple of the wavelength of the light confined in the spherical polymer particles coincides with the optical path length, the emission intensity increases and appears as a peak. In particular, when the side surface portion of the spherical polymer particle is photoexcited, the light can swirl inside the spherical particle without passing through the contact surface with the substrate, thereby reducing the decrease in light emission efficiency due to light leakage and enhancing light emission. be able to.

  Here, the index n of each peak shown in FIG. 1 is a value calculated from the following formula 1 when the diameter of the spherical polymer particles is d, the refractive index of the spherical polymer particles is η, and the peak wavelength λ.

  The number and position of spikes appearing in the emission spectrum are modulated depending on the diameter d and refractive index η of the spherical polymer particles. Therefore, by changing these values, it is possible to design spherical polymer particles having arbitrary light emission characteristics.

  For example, when the diameter d of the spherical polymer particles is increased, the optical path length is also increased, so that more spikes are observed in the emission spectrum. In addition, the Q value is larger when the diameter d is larger than the spherical polymer particles having a smaller diameter d. This is presumably because the radius of curvature of the spherical polymer particles increases as the diameter d increases, so that total reflection of light is more likely to occur.

[Optical element]
The spherical polymer particles of the present embodiment can be applied to various optical elements such as an optical resonator, an optical amplifier, a light emitting colloid photonic crystal, an optical sensor, a laser oscillation element, and an electroluminescence element.

  Since the spherical polymer particles of the present embodiment have both a function as a light emitter and a function as an optical resonator, there is no need to combine a plurality of materials as in the case of conventional spherical particles, and WGM oscillation can be achieved with a single material. Can be realized. As a result, spherical polymer particles and optical elements can be produced with a simple process.

  In particular, since spherical polymer particles formed of π-conjugated polymers have not only light emission characteristics but also conductive characteristics, it is possible to emit light by charge injection, and thus a new light emitting device can be realized. .

  Hereinafter, the effects of the present invention will be described in detail by way of examples of the present invention. In this example, spherical polymer particles were prepared using the π-conjugated alternating high polymers represented by the above chemical formulas 1 to 4, and the light emission characteristics thereof were examined.

  Specifically, F8TMT2 (Chemical Formula 2), 2,7-CTMT2 (Chemical Formula 1), PTTMT2 (Chemical Formula 3), and AZOANI (Chemical Formula 4) are each combined at a specific solvent combination by a vapor diffusion method at room temperature. The polymer particles were allowed to settle for 3 days.

  The obtained polymer particles were observed with a scanning electron microscope (SEM) and a cross-sectional transmission electron microscope (XSTEM) to confirm the internal structure and the like. 3 to 6 are photomicrographs of spherical polymer particles formed using each π-conjugated alternating copolymer. As shown in FIGS. 3 to 6, it was confirmed that all the polymer particles formed in this example were spherical particles having a uniform internal structure.

  Next, a solution containing spherical polymer particles is dropped on a silicon substrate, and each spherical polymer particle is dispersed by being rotated for 1 minute at a speed of 1000 rpm by a spin coater, and each spherical polymer particle is present alone. I did it. Thereafter, the solvent was evaporated in the air, and the emission characteristics were used as a measurement sample.

  The light emission characteristics of each particle were evaluated by microscopic photoluminescence (μ-PL) measurement by irradiating the end of the spherical polymer particle with a laser beam having an excitation wavelength of 407 nm and evaluating the result. Here, the reason for irradiating the end of the spherical polymer particle with laser light is that if the central part of the spherical polymer particle is excited, the optical path of the excitation light leaks from the contact point with the silicon substrate. .

  The measurement of μ-PL was performed by selecting one of spherical polymer particles having a diameter d of 1 μm to 10 μm using a light microscope and irradiating a laser beam at room temperature and low temperature (10K). Based on the result of this μ-PL measurement, the difference in WGM oscillation depending on the measurement temperature and size was compared.

  FIGS. 7-10 is a figure which shows the emission spectrum of the spherical polymer particle formed using each (pi) conjugate alternating copolymer. As shown in FIGS. 7 to 10, WGM oscillation was confirmed in any spherical polymer particle. In particular, a clear spike was confirmed in spherical polymer particles having a diameter d of 2 μm or more. And the number of spikes increased as the diameter d of the spherical polymer particles increased.

Furthermore, in order to obtain a sharper WGM oscillation, a high refractive index material (C ₆₀ , Au, Cu, Ti, Al) was deposited around the spherical polymer particles by a vacuum deposition method. In that case, the thickness of the vapor deposition layer was 5 nm and 20 nm. Then, μ-PL measurement was performed on spherical polymer particles coated with a material having a high refractive index and spherical polymer particles not coated, and the difference in light emission characteristics was compared.

  As a result, the spherical polymer particles coated with a high refractive index material have an increased Q value compared to those not coated, and this tendency is particularly noticeable when a metal material having a higher refractive index is deposited. Met. This is considered to be because the efficiency of total reflection of light inside the spherical polymer particles is increased and the light confinement efficiency is improved because the relative refractive index between the inside and the outside (air) of the spherical polymer particles is increased.

  From the above results, according to the present invention, it was confirmed that spherical polymer particles capable of developing WGM oscillation can be realized without using a light emitting material such as a dye together.

1 Spherical polymer particle 2 Light

Claims (6)

Spherical or substantially spherical particles made of a light-emitting polymer,
The particle size measured by an electron microscope is 2 μm or more, and
Spherical polymer particles for generating whispering galley mode oscillation, in which whispering galley mode oscillation occurs internally by excitation light irradiation. 2. The spherical polymer particle for expressing whispering galley mode oscillation according to claim 1, wherein the light emitting polymer is a π-conjugated alternating copolymer. The spherical polymer particles for expressing whispering gallery mode oscillation according to claim 1 or 2 , wherein the spherical polymer particles are formed by a vapor diffusion method. C ₆₀ The whispering galley mode oscillation according to any one of claims 1 to 3, wherein at least one high refractive index material selected from the group consisting of Au, Cu, Ti, and Al is deposited by a vacuum deposition method. Spherical polymer particles for expression. The optical element using the spherical polymer particle for whispering gallery mode oscillation expression of any one of Claims 1-4. A method of generating whispering galley mode oscillation inside spherical polymer particles by irradiating excitation light,
The method in which the particles are spherical or substantially spherical particles made of a light-emitting polymer and have a particle diameter measured by an electron microscope of 2 μm or more.