RU2417483C1 - Exciton-plasmon nano radiator - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: proposed nano radiator comprises 4-6 nm-dia nucleus of noble metal surrounded by two concentric envelopments. Envelopment nearest to nucleus represents an optically neutral organic layer with thickness of about 1 nm. Second 1-3 nm-thick envelopment is made up of J-aggregates of cyanine dyes. During electron excitation of metal nucleus plasmons, the latter actively interact with J-aggregate envelopment to excite cyanine dyes (Frenkel's excitons) and radiate light in visible range. Metal nucleus electrons may be excited by both photons and electrons. ^ EFFECT: high quantum output of luminescence and controlled spectrum of radiation in visible range. ^ 3 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of optics, in particular to electroluminescent nanostructures, and can be used to create effective light-emitting devices. The relevance of creating fundamentally new photon nano-emitters is determined by the need for efficient and cheap light sources for lighting, as well as for creating a new generation of alphanumeric displays.

There are a number of approaches to solving this problem, but the most promising is the use of OLED technologies to create low-energy organic light-emitting diodes. For OLED technology, in turn, the most important is the use of hybrid materials as an active medium, which eliminate the main disadvantage of OLED technology - the fragility of light-emitting devices. Hybrid materials are an organic matrix with embedded quantum dots (nano-objects). Currently, semiconductor bicomponent nanocrystals are used as quantum dots [G. Jonathan et al, Fabrication and Properties of Organic Light-Emitting "Nanodiode" Arrays, Nanoletters, 2 (2002) 333].

The closest technical solutions of the proposed device are:

1. by optical properties: two-component nanocrystals of the CdSe / ZnS, CdTe / CdSe type and similar so-called core-shell nanoparticles (core-shell in the English language literature). [Jialong Zhao et al, Efficient CdSe / CdS Quantum Dot Light-Emitting Diodes Using a Thermally Polymerized Hole Transport Layer Nanoletters, 6 (2006) 463]. Attempts to use these nano-objects in organic light-emitting diodes do significantly increase the service life of the latter, but they have serious technological problems - it is necessary to create a monolayer of two-component nanoparticles between organic p- and n-type semiconductors [Tetsuo Tsutsui, A light-emitting sandwich filling. Nature 420 (2002) 752].

2. on electronic properties: two-component nano-objects of the Ag / J-aggregate type [Jian Zhang, Joseph R. Lakowicz, Enhanced Luminescence of Phenyl-phenanthridine Dye on Aggregated Small Silver Nanoparticles, J. Phys. Chem. B, 109 (2005) 8701], the production technology of which is fundamentally developed and in which it is possible to obtain significant plasma resonance. The absence of an intermediate layer between the metal core and the J-aggregate shell makes it impossible to obtain luminescence of such nano-objects.

For J-aggregates located on the surface of a metal nanoparticle, additional features appear associated with plasma effects in the metal core, as well as with the interaction of the nucleus plasmon with the exciton of the organic shell. The adsorption properties of two-component organometallic core-shell nanoparticles attract attention [V.S. Lebedev, A. G. Vitukhnovsky et al. Absorption Properties of the Composite Silver / Dye Nanoparticles in Colloidal Solutions Col. and surf. A, 326 (2008) 204] as potential active nanostructures, however, the luminescence of the J-aggregate is completely quenched by the electrons of the metal core.

The problem solved by the invention is to expand the class of alternative light sources for an energy-saving economy by creating an exciton-plasmon nano-emitter with a high quantum yield of luminescence and an adjustable emission spectrum in the visible wavelength range (400-650 m). Evaluation of the introduction of LED light sources only at housing and public utilities objects Russia will be able to free up about 2500 MWh of electric power and save about 100 billion rubles for 2010-2021.

It is proposed to use, as nanoobjects embedded in an organic matrix, three-component nanoparticles with a metal core and two spherical shells. Due to plasmon-exciton interaction (the metal core is the outer shell), the emissivity of the dye in the form of a J-aggregate on the outer shell is significantly enhanced.

Molecular ensembles with a specific package of cyanine dye molecules, called J-aggregates, can easily be created in aqueous solutions by increasing the concentration, adding some inorganic and organic cations, rare-earth ions. Plasmon resonance is a collective oscillation of conduction electrons on the surface of nanoparticles under the influence of an electromagnetic field. The frequency of plasmon resonance depends on the size and shape of the particles. This is due to the internal size effect, which is due to the influence of the surface of the nanoparticle, a change in the atomic structure, an increase in the localization of electrons, a change in the coordination number, which is expressed in the dependence of the dielectric constant on size and shape [A.C. Templeton et al. Solvent Refractive Index and Core Charge Influences on the Surface Plasmon Adsorbance of Alkanethiolate Monolayer-Protected Gold Clusters, J. Phys. Chem. B., 104 (2000) 564].

It is proposed to use the synthesis of three-component composite nanoparticles developed for the first time by the authors of the application, consisting of a metal core (Au, Ag) with a diameter of 6 nm, coated with two concentric shells of organic matter: a TMA (N, N, N-trimethyl (11-mercaptoundecyl) ammonium chloride monolayer), on top of which was the shell of 3,3'-di (γ-sulfopropyl) -4 ', 5' - [1 "" - methylindolo (3 ", 2")] - thiothiazolocyanine in the J-aggregate state.

In the present invention, the idea of an organometallic nanoparticle is realized in which the J-aggregate of the dye is 1.2 nm apart from the core, approximately equal to the length of the TMA molecule. With this design of the nanoparticles, it becomes possible to significantly attenuate the luminescence quenching of the J-aggregate, while maintaining the interaction of the nucleus plasmons and shell excitons.

The standard synthesis of metal nanoparticles is carried out by colloid chemistry using surfactants [Daniel M.C. and Astruc D. Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties and Applications toward Biology, Catalysis and Nanotechnolog, Chem. Rev. 104 (2004) 293]. Similar synthesis methods for creating a metal core / dye shell nanoparticle are not suitable, since the goal is to synthesize two-component nanoparticles in which a monomethine cyanine dye is in the J-aggregate state on the surface of the metal core. For similar reasons, synthetic methods in polymer matrices are not suitable. The authors of the application chose a technique for the synthesis of nanoparticles by the reduction of noble metal atoms from a salt solution.

In [G.D. Hale et al. Enhancing the active lifetime of luminescent semiconducting polymers via doping with metal nanoshells, 78 (2001) 1502] and [J. Park, et al. Polymer / Gold Nanoparticle Nanocomposite Light-Emitting Diodes: Enhancement of Electroluminescence Stability and Quantum Efficiency of Blue-Light-Emitfing Polymers, Chem. Mater. 16 (4) (2004) 688] gold nanoparticles were used to increase the radiation efficiency of organic light emitting diodes. In one case, this was achieved by introducing nanoparticles directly into the active layer, and in the other, the effect of metal nanoparticles was simply reduced to improving the injection of charge carriers from the electrodes. In the work of [H. Mertens, A. Polman. Plasmon-enchanced erbium luminescence, Appl. Phys. Lett, 89 (2006) 2111071] shows the effect of plasmons in metal nanoparticles on the luminescence of the Er complex in the IR spectrum.

The problem is solved as follows.

An exciton-plasmon nano-emitter containing a noble metal core (diameter 4-8 nm) surrounded by two concentric shells is proposed. The shell closest to the metal core is an optically neutral organic layer about 1 nm thick. The second shell of variable thickness (1-3 nm) is created from J-aggregates of cyanine dyes. During electronic excitation of plasmons of the metal core, an effective interaction occurs with the J-aggregate shell, leading to excited states of the cyanine dye (Frenkel excitons), followed by light emission in the visible range (400-650 nm). The excitation of a metal core is possible with the help of both photons and electrons.

The proposed new optoelectronic device uses the unique property of noble metals (Au, Ag, Pt) - the effective generation of plasma oscillations (plasmons).

The synthesis of Me / TMA / J aggregate nanoparticles developed by the authors of the application is carried out in 3 stages: first, Me / OLA nanoparticles are synthesized (metal coated with a layer of oleylamine), then the shell is replaced by an oleylamine with a TMA layer [A. Kalsin, et al. Electrostatic Self-Assembly of Binary Nanoparticle Crystals with a Diamond-Like Lattice // Science, 312 (2006) 420]. The resulting Me / TMA nanoparticles are coated with a dye layer that forms J-aggregates on the surface. For the synthesis of Me / OLA nanoparticles, a mixture of 3 ml of oleylamine and 15 ml of toluene is heated to boiling (~ 140 ° C). Then, 50 mg of gold tetrachloride tetrahydrate (HAuCl4 · 4H2O) (in the case of the gold core) and 1.2 grams of oleylamine dissolved in 1.0 ml of toluene are poured into this boiling solution. After a few minutes, the color of the solution changes to dark red, which means the formation of gold nanoparticles. The colloidal solution is heated for 2 hours, after which the solution is cooled to room temperature. The ligand is replaced as follows: 25 ml of methanol is added to 9 ml of the prepared colloidal Au / TMS solution, which is accompanied by precipitation. After centrifugation at 4000 rpm for 25 minutes, the solvent with an excess of oleylamine is discharged, and the precipitate is dissolved in 15 ml of toluene, to which 1 ml of a solution of TMA in methanol (~ 30 mM) is added. The resulting liquid is again centrifuged at a speed of 4000 rpm for 15 minutes, after which decantation is again applied. The resulting precipitate was washed with ethyl acetate (15 ml) 3 times and dried. The resulting dry powder containing nanoparticles is dissolved in 4 ml of bidistilled water.

For the synthesis of three-component nanoparticles, Au / TMA / dye, the Au / TMA hydrosol is diluted so that the optical density at 400 nm becomes 0.625 cm ^-1 . 1 ml of a 5 * 10 ^-5 M dye solution is added to 4 ml of diluted Au / TMA hydrosol

In the inventive device (see drawing), the nano-emitter is a core (1) of a noble metal (diameter - 4-8 nm), surrounded by two spherical shells. The closest shell (2) to the metal core is an optically neutral organic layer about 1 nm thick. The second shell (3) of variable thickness (1-3 nm) was created from J-aggregates of cyanine dyes.

The table shows examples of cyanine dyes forming J-aggregates on the surface of metal nanoparticles, and the structural formula of the material for the separation layer.

The structural formula of the dye TC-sodium salt of 3,3'-di (γ-sulfopropyl) -5,5'-dichlorothiacyanine The structural formula of the dye “6824” is the triethylammonium salt of 3,3'-di (γ-sulfopropyl) -4 ', 5'-1' '- methylindolo (3' ', 2``)] - thiatiazolocyanine The structural formula of the "separator" TMA

It is possible to use a plasmon-exciton nano-emitter when excited by photons and electrons. When a light emitting diode is introduced into the organic matrix, a nano-emitter with an appropriate selection of electrode materials can emit light in the visible range (400-650 nm) with a variable diameter of the metal core and shell thicknesses.

Claims (3)

1. An exciton-plasmon nanoparticle based on nanoparticles in the form of a noble metal core with a concentric shell, characterized in that the nanoparticles are made three-layer with a noble metal core surrounded by two concentric shells, the closest shell to the core being an optically neutral organic layer and plays the role of the spatial separator, and the outer shell of the J-aggregate of a cyanine dye with a large value of the dynamic dipole moment has a high luminescence yield nation. 2. The exciton-plasmon nano-emitter according to claim 1, characterized in that a core with a diameter of 4-8 nm and a thickness of the outer shell of 1-3 nm is selected as a core of a noble metal to control the emission spectrum in the range of 400-650 nm. 3. The exciton-plasmon nano-emitter according to claim 1, characterized in that it is configured to excite plasmons in the nucleus of a noble metal using both photons and electrons of the corresponding energies determined by the size of the nucleus and the type of noble metal.