Organic microcavity laser with adjustable emergent angle and polarization and preparation method thereof

Abstract

The invention discloses an emitting angle and polarization adjustable organic microcavity laser and a preparation method thereof, and relates to the technical field of optical microcavities and organic photoelectricity. The organic microcavity laser structurally comprises an upper-layer silver film, an organic photoelectric material and a lower-layer silver film from top to bottom, wherein the organic photoelectric material is a DPAVBi crystal or a BDAVBi crystal. According to the invention, spin-orbit coupling is designed through the organic microcavity laser, and the excited excimer laser with controllable emergent angle and polarization is formed under the combined action of the condensation of the excited excimer laser and the splitting of the transverse electric field-transverse magnetic field.

Description

Technical Field

[0001] The invention relates to the field of optical microcavity and organic photoelectric technology, and in particular to an organic microcavity laser with adjustable emission angle and polarization and a preparation method thereof. Background Art

[0002] Exciton polaritons are bosonic quasiparticles obtained through the strong interaction (strong coupling) between excitons and photons in a microcavity. Their extremely light effective mass comes from the photon component, making polaritons candidates for bosonic condensation. Polariton lasers are different from traditional photon lasers in that they do not require population inversion and can form coherent light at a lower threshold. Previous research on polariton lasers and condensation has mainly focused on III-V inorganic semiconductors due to their mature epitaxial growth technology. However, most inorganic semiconductors (except ZnO and GaN) have small exciton binding energies, which limits their device operation to low temperature conditions.

[0003] Recently, organic and inorganic perovskite materials have also made important progress in strong exciton-photon coupling, but they are also limited by the complexity of microcavity preparation technology. Organic semiconductors have high exciton binding energy and large oscillator strength, which can achieve strong exciton-photon coupling at room temperature, and polariton condensation in the visible light spectrum can be observed using a wide range of organic semiconductors. Moreover, the coherent nature of organic polariton condensation has been demonstrated in organic polariton transistors and superfluid transport, which is an important step towards the development of functional organic polariton circuits. The observation of low-threshold polariton lasing in organic semiconductor microcavities, the ease of fabrication of microcavities, and the potential for charge and excitation injection make them attractive candidates for continuous optical pumping, electrically pumped functionalized photon polariton circuits and organic polariton lasers operating at room temperature.

[0004] The spin degree of freedom of electrons has been widely exploited in condensed matter physics and is central to many efficient data transmission, quantum information processing and storage of information. The underlying physics of their potential applications relies on the splitting of electron energy bands induced by the spin-orbit interaction (SOI), the fundamental feature of which is that a spin-polarized electron moving in an electrostatic field experiences an effective magnetic field. SOI for electrons in solid-state systems was first realized by Rashba and Dresselhaus in structural inversion asymmetric materials and bulk inversion asymmetric materials. Light has an intrinsic polarization degree of freedom, where the polarization of a photon resembles the spin property of an electron. In optics, SOI for light opens up significant new opportunities to manipulate the pseudo-spin of photons, which has inspired the study of the optical spin Hall effect (OSHE) and optical topological insulators. In these areas, the synthetic gauge fields created by SOI play a central role. It is well known that SOI for light in optical microcavities can be induced by transverse electric-transverse magnetic mode splitting, which can be modeled as an effective magnetic field and thus construct an artificial gauge field. In optical SOI research, organic crystalline materials have attracted great attention because their large optical anisotropy leads to significant transverse electric field-transverse magnetic field splitting.

[0005] According to literature reports, in recent years, optical microcavities have attracted more and more attention. The excellent confinement ability of microcavities greatly enhances the interaction between light and matter. Initially, people carried out research on strong coupling of excitons and photons in microcavities of inorganic semiconductor materials, and with the improvement of microcavity quality and the progress of equipment, polaritons lasers and Bose-Einstein condensation have gradually been realized. However, due to the small exciton binding energy and oscillator strength of Wannier-Mott excitons in inorganic materials, most experiments are limited to low temperature and liquid helium conditions, which limits practical applications. In the 1990s, people expanded the research on light and matter to organic semiconductor materials. The Frenkel excitons in organic semiconductors have large oscillator strength and high exciton binding energy, which makes the Rabi splitting energy of strong coupling of photons and excitons orders of magnitude higher than that of inorganic semiconductors. Therefore, stable polaritons at room temperature, as well as room temperature polaritons condensation, BEC and superfluidity can be realized. The observation of low-threshold polaritons, the ease of preparation, and the potential for electrical injection, including charge and excitation, make organic semiconductor microcrystals very attractive candidates for continuous-wave electrically pumped photonic polaritons circuits and organic polaritons lasers. Summary of the invention

[0006] The purpose of the present invention is to provide an organic microcavity laser with adjustable emission angle and polarization and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art and develop a new material for photonic integrated chip, quantum information and optoelectronic applications.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] The present invention provides an organic microcavity laser with adjustable emission angle and polarization. The structure of the organic microcavity laser comprises, from top to bottom:

[0009] An upper silver film, an organic optoelectronic material and a lower silver film;

[0010] The organic photoelectric material is DPAVBi crystal or BDAVBi crystal.

[0011] In the present invention, DPAVBi is 4,4'-bis[4-(di-p-tolylamino)phenylvinyl]biphenyl, and BDAVBi is 4,4\'-bis[4-(diphenylamino)phenylvinyl]biphenyl.

[0012] Furthermore, the thickness of the upper silver film is 35-40 nm, and the thickness of the lower silver film is 100-105 nm.

[0013] Furthermore, the DPAVBi crystal is prepared by the following steps: adding DPAVBi into tetrahydrofuran to prepare a DPAVBi / THF solution, adding the DPAVBi / THF solution into n-hexane, and growing at 25° C. to obtain the DPAVBi crystal.

[0014] Furthermore, the BDAVBi crystal is prepared by the following steps: adding BDAVBi into chlorobenzene to prepare a BDAVBi / chloroform solution, and then adding the BDAVBi / chloroform solution into anhydrous ethanol to grow the BDAVBi crystal at 25°C.

[0015] The present invention also provides a method for preparing the above-mentioned organic microcavity laser with adjustable emission angle and polarization, comprising the following steps:

[0016] The upper silver film and the lower silver film are respectively evaporated on the upper and lower surfaces of the organic photoelectric material to obtain the organic microcavity laser with adjustable emission angle and polarization.

[0017] The BDAVBi and DPAVBi used in the present invention are optoelectronic materials with excellent performance and are expected to be applied in the fields of OLED, information transmission, laser, etc.

[0018] The organic materials used in the present invention have strong exciton binding energy, can produce condensation at room temperature, and have strong anisotropy to produce photon spin-orbit coupling, and have the characteristics of simple growth and adjustable size.

[0019] The present invention studies the optical spin-orbit coupling of organic semiconductors in microcavities. The birefringence of organic crystals can cause the transverse electric field and transverse magnetic field modes to split at the position of wave vector k=0, which makes the transverse electric field mode and transverse magnetic field mode of different odd and even numbers approach each other, so that anti-crossing occurs at a certain wave vector, and an open Dirac cone point appears. Since no external conditions, such as the introduction of a magnetic field, are used in the entire research process, the overall structure retains the time reversal symmetry. It is precisely because of the existence of time reversal symmetry that the Berry curvature extracted from the Dirac cone is two signals of opposite positive and negative, and the energy band is a non-trivial geometric structure locally: that is, two localized topological valley states appear. Since the topological charges of the two valleys are opposite, the total topological charge of the photon energy band is zero, but the local area is topologically non-trivial. The formation of this topological valley is completely dependent on the optical polarization effect, and the exploration that does not rely on any optical periodic structure and external field effect is very meaningful in subsequent topological optical research, and provides a new method for further realizing the spin and valley Hall effect and spin-orbit coupling manipulation on photonic chips.

[0020] The invention provides a laser with adjustable emission angle and polarization, and is designed to generate an exciton laser with controllable emission angle and polarization.

[0021] More specifically, the present invention preferably uses DPAVBi and BDAVBi as starting materials, prepares H-aggregated two-dimensional micron-belt DPAVBi and BDAVBi organic single crystals as active layers by a reprecipitation method, and constructs a microcavity structure by using a silver film with a simple preparation process as a high reflector.

[0022] The present invention verifies the correctness of organic single crystal growth by means of SEM, XRD, absorption and photoluminescence spectra, angle-resolved spectra, and the correctness of organic single crystal microcavity design. The angle-resolved reflection spectrum and photoluminescence spectrum of the DPAVBi micron strip microcavity at room temperature (298K) were measured by homemade micro-area Fourier imaging, and the polarization-dependent angle-resolved reflection spectrum and photoluminescence spectrum of the above-mentioned microcavity were further measured by sequentially adding a λ / 4 glass plate and a linear polarizer to the detection light path. Through the test, it can be seen that the laser emitted by the exciton condensation at the position of wave vector k=0 is linearly polarized light, and the laser emitted by the exciton condensation at the position of wave vector k≠0, that is, the transverse electric field-transverse magnetic field splitting occurs, is circularly polarized light, and the research finds that the emission angle and polarization of the exciton laser are strongly related to the angle of the incident pump light, that is, the angle of the incident pump light is adjusted to achieve an exciton laser with controllable emission angle and polarization.

[0023] The organic single crystal microcavity of the present invention has photon spin-orbit coupling and can produce photon spin Hall effect. The organic single crystal microcavity has the observation of low threshold polariton condensation and is easy to manufacture, making it possible to operate organic semiconductor microcavities at room temperature with continuous wave pumping and electric pumping functional photon polariton circuits and organic polariton lasers. The organic single crystal microcavity can control spin-orbit coupling in the organic single crystal microcavity by using purely optical means, which provides a unique method for advanced quantum control strategies of on-chip integrated photonics and optical communications.

[0024] At present, there is no report on the in-situ continuous adjustment of the emission angle and polarization of the exciton laser. The present invention constructs a microcavity structure of organic crystals DPAVBi and BDAVBi, and uses a femtosecond laser with a wavelength of 400nm to excite it to emit exciton lasers of different angles and polarizations. At the same time, with the adjustment of the angle of the femtosecond laser with a wavelength of 400nm, the polarization and emission angle of the exciton laser also change accordingly, reflecting the regulation of luminescence. First, the observation of low-threshold polaritons and the ease of preparation make organic semiconductor microcrystals a very favorable candidate for continuous-wave electrically pumped photon polariton circuits and organic polariton lasers. Secondly, it has strong anisotropy, which allows the control of spin-orbit coupling in organic single crystal microcavities by using purely optical means, which provides a unique method for advanced quantum control strategies of on-chip integrated photonics and optical communications.

[0025] The organic microcavity laser of the present invention can obtain an exciton laser with adjustable emission angle and polarization, which is generated by the condensation of exciton polaritons formed by the strong interaction between excitons and photons in the microcavity. Since the organic single crystal microcavity has the characteristic of anisotropy, there is spin-orbit coupling in the transverse magnetic field-transverse electric field mode in the microcavity, making the polarization of the exciton laser adjustable. Since it is a type with high exciton binding energy and large oscillator strength, it can realize the strong interaction between excitons and photons at room temperature. The observation of low threshold polaritons condensation and easy manufacture make it possible to operate the organic semiconductor microcavity at room temperature with continuous wave pumping and electric pumping functional photon polaritons circuits and organic polaritons lasers.

[0026] The present invention designs and prepares an organic single crystal microcavity from which an exciton laser with adjustable emission angle and polarization is generated. The laser has the characteristics of low threshold, can be excited at room temperature, does not require an external field, does not require an optical periodic structure, and has in-situ adjustable angle and polarization. Due to the spin-orbit coupling of photons, the spin Hall effect of photons can be generated.

[0027] The present invention can control spin-orbit coupling in an organic single crystal microcavity by using purely optical means, which provides a unique method for advanced quantum control strategies of on-chip integrated photonics and optical communications.

[0028] The present invention discloses the following technical effects:

[0029] The present invention provides an organic microcavity laser with adjustable emission angle and polarization. By adjusting the exciton-photon interaction and designing the spin-orbit coupling, an exciton laser with controllable emission angle and polarization is obtained under the combined action of exciton laser condensation and transverse electric field-transverse magnetic field splitting. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 Schematic diagram of the structure of the DPAVBi organic single crystal microcavity laser in Example 1 of the present invention.

[0032] Figure 2 In the figure, a is a fluorescence micrograph of DPAVBi microribbons, and b is a herringbone stacking arrangement structure along the b-axis of the DPAVBi crystal.

[0033] Figure 3 In the figure, a is the luminescence polarization of a single DPAVBi microribbon, and b is the horizontally polarized absorption spectrum (blue line), vertically polarized absorption spectrum (green line) and photoluminescence spectrum (black line) of a single DPAVBi microribbon.

[0034] Figure 4 Schematic diagram of the structure of the BDAVBi organic single crystal microcavity laser in Example 2 of the present invention.

[0035] Figure 5 In the figure, a is a fluorescence micrograph of BDAVBi microribbons, and b is a herringbone stacking arrangement structure along the b-axis of the BDAVBi crystal.

[0036] Figure 6 In the figure, a is the luminescence polarization of a single BDAVBi microribbon, and b is the horizontally polarized absorption spectrum (red line), vertically polarized absorption spectrum (blue line) and photoluminescence spectrum (black line) of a single BDAVBi microribbon.

[0037] Figure 7 In the figure, a, b, and c are the angle-resolved spectra of the polariton laser excited by the DPAVBi organic single crystal microcavity laser in Example 1 when the pump laser wave vector k=-5, 0, and 5, respectively. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0043] Example 1

[0044] Preparation of DPAVBi organic single crystal microcavity laser:

[0045] (1) 0.01 g of DPAVBi was placed in 1 mL of tetrahydrofuran solution and heated and ultrasonicated for 30 min until the solid was completely dissolved to prepare a 10 mg / ml DPAVBi / THF stock solution;

[0046] (2) taking 0.2 mL of the DPAVBi solution prepared in step (1) and adding it into 2 mL of n-hexane, and growing DPAVBi crystals at 25° C.;

[0047] (3) The DPAVBi crystal grown in step (2) is taken out, and silver films with thicknesses of 35 nm and 100 nm are evaporated on the upper and lower surfaces of the DPAVBi crystal, respectively, to obtain a DPAVBi organic single crystal microcavity laser.

[0048] Figure 1 FIG. 1 is a schematic diagram of the structure of the DPAVBi organic single crystal microcavity laser in Example 1 of the present invention. Figure 1 It can be seen that the DPAVBi organic single crystal microcavity laser consists of three parts. More specifically: the bottom layer is a 100nm silver film (reflectivity is about 99.99%), the middle layer is a DPAVBi crystal, and the upper layer is a 35nm silver film (reflectivity is about 50%).

[0049] The DPAVBi organic single crystal microcavity laser is excited by a femtosecond laser with a wavelength of 400 nm. The photoluminescence is linearly polarized light when the wave vector k=0, and circularly polarized light when the wave vector k≠0.

[0050] Figure 2 In the figure, a is a fluorescence micrograph of a DPAVBi microbelt, and b is a herringbone stacking arrangement structure along the b-axis of the DPAVBi crystal. The transition dipole moment direction (μ) of DPAVBi is along the long axis of the molecule, tilted 36° relative to the molecular stacking direction. Therefore, the dipole moment component (μ∥) along the length direction of the microbelt is much larger than the dipole moment component (μ⊥) along the width direction.

[0051] Figure 3 In the figure, a is the luminescence polarization of a single DPAVBi microbelt. The 0° direction is parallel to the long axis of the crystal. It can be seen from the figure that the microbelt luminescence is highly polarized along the long axis of the crystal, and the polarization degree (ρ=(I0-I90) / (I0+I90); I0 and I90 represent the luminescence intensity of the crystal in the 0° and 90° polarization directions, respectively) is greater than 0.9. b is the horizontal polarization absorption spectrum (blue), vertical polarization absorption spectrum (green) and photoluminescence spectrum (black) of a single DPAVBi microbelt.

[0052] Polarized absorption and photoluminescence spectra of a single DPAVBi microbelt show that when the polarization direction of the halogen light source is parallel to the long axis of the DPAVBi microbelt (∥ polarization), an absorption peak with a maximum value at 450nm can be observed. However, when the polarization direction of the light source is perpendicular to the long axis of the microbelt (⊥ polarization), a weaker absorption spectrum can be observed. These obvious polarization-dependent absorption spectral features are consistent with the highly ordered uniaxial arrangement (μ∥>μ⊥) in the DPAVBi single crystal microbelt.

[0053] Example 2

[0054] Preparation of BDAVBi organic single crystal microcavity laser:

[0055] (1) 0.002 g of BDAVBi was placed in 1 mL of chlorobenzene solution and heated and ultrasonicated at 40 °C for 30 min until the solid was completely dissolved to obtain a BDAVBi solution;

[0056] (2) taking 0.2 mL of the BDAVBi solution prepared in step (1) and adding it into 2 mL of anhydrous ethanol, and growing BDAVBi crystals at 25° C.;

[0057] (3) The BDAVBi crystal grown in step (2) is taken out, and silver films with thicknesses of 35 nm and 100 nm are evaporated on the upper and lower surfaces of the BDAVBi crystal, respectively, to obtain a BDAVBi organic single crystal microcavity laser.

[0058] Figure 4 FIG. 1 is a schematic diagram of the structure of the BDAVBi organic single crystal microcavity laser in Example 2 of the present invention. Figure 4 It can be seen that the BDAVBi organic single crystal microcavity laser consists of three parts. More specifically: the bottom layer is a 100nm silver film (reflectivity is about 99.99%), the middle layer is a BDAVBi crystal, and the upper layer is a 35nm silver film (reflectivity is about 50%).

[0059] The BDAVBi organic single crystal microcavity laser is excited by a femtosecond laser with a wavelength of 400nm. The photoluminescence is linearly polarized light when the wave vector k=0, and circularly polarized light when the wave vector k≠0.

[0060] Figure 5 In the figure, a is a fluorescence micrograph of a BDAVBi microbelt, and b is a herringbone stacking arrangement structure along the b-axis of the BDAVBi crystal. The transition dipole moment direction (μ) of BDAVBi is along the long axis of the molecule. Therefore, the dipole moment component along the length direction of the microbelt (μ∥) is much larger than the dipole moment component along the width direction (μ⊥).

[0061] Figure 6 In the figure, a is the luminescence polarization of a single BDAVBi microbelt. The 0° direction is parallel to the long axis of the crystal. It can be seen from the figure that the luminescence of the microbelt is highly polarized along the long axis of the crystal. The polarized absorption spectrum and photoluminescence spectrum of a single BDAVBi microbelt. When the polarization direction of the halogen light source is parallel to the long axis of the BDAVBi microbelt (∥ polarization), an absorption peak with a maximum value at 450nm can be observed. However, when the polarization direction of the light source is perpendicular to the long axis of the microbelt (⊥ polarization), a weaker absorption spectrum can be observed. These obvious polarization-dependent absorption spectrum features are consistent with the highly ordered uniaxial arrangement (μ∥>μ⊥) in the BDAVBi single crystal microbelt. b is the horizontally polarized absorption spectrum (red line), vertically polarized absorption spectrum (blue line) and photoluminescence spectrum (black line) of a single BDAVBi microbelt.

[0062] Figure 7 This shows the effective spin switch of polariton condensation, and can realize the emission of polariton lasers with different angles and polarizations at the original position. Wherein, a, b, and c are the angle-resolved spectra of the polariton laser excited by the DPAVBi organic single crystal microcavity laser in Example 1 when the pump laser wave vector k=-5, 0, and 5, respectively. This shows that the polariton laser can be adjusted by adjusting the pump laser.

[0063] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. An organic microcavity laser with adjustable emission angle and polarization, characterized in that: The structure from top to bottom includes: An upper silver film, an organic optoelectronic material and a lower silver film; The organic photoelectric material is DPAVBi crystal or BDAVBi crystal.

2. The organic microcavity laser with adjustable emission angle and polarization according to claim 1, characterized in that: The thickness of the upper silver film is 35-40 nm, and the thickness of the lower silver film is 100-105 nm.

3. The organic microcavity laser with adjustable emission angle and polarization according to claim 1, characterized in that: The DPAVBi crystal is prepared by the following steps: adding DPAVBi into tetrahydrofuran to prepare a DPAVBi / THF solution, adding the DPAVBi / THF solution into n-hexane, and growing at 25° C. to obtain the DPAVBi crystal.

4. The organic microcavity laser with adjustable emission angle and polarization according to claim 1, characterized in that: The BDAVBi crystal is prepared by the following steps: adding BDAVBi into chlorobenzene to prepare a BDAVBi / chloroform solution, then adding the BDAVBi / chloroform solution into anhydrous ethanol, and growing the BDAVBi crystal at 25°C.

5. The method for preparing an organic microcavity laser with adjustable emission angle and polarization according to any one of claims 1 to 4, characterized in that: The following steps are involved: The upper silver film and the lower silver film are respectively deposited on the upper and lower surfaces of the organic photoelectric material to obtain the organic microcavity laser with adjustable emission angle and polarization.

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