Method for enhancing luminous intensity of chiral quantum dots and optical device

Abstract

The invention discloses a method for enhancing luminous intensity of a chiral quantum dot and an optical device, the method is particularly used for improving the luminous intensity of the chiral quantum dot prepared by a ligand exchange method, and the method belongs to the field of interaction of the chiral quantum dot and laser. The method is characterized in that firstly, a chiral quantum dot solution is subjected to spin-coating through a spin-coating method to prepare a film, and then the chiral quantum dot film under the air condition is continuously irradiated through ultraviolet continuous laser, so that the surface defects of the quantum dot film are reduced, radiation composite channels are increased, and the luminous intensity is enhanced. The luminous intensity of the quantum dot film under the air condition is forty times higher than the initial luminous intensity. The higher the power density of the irradiation light is, the higher the speed of luminous intensity enhancement is. The method has the characteristics of simple optical device, low price, high enhancement efficiency and the like.

Description

Technical Field

[0001] The invention belongs to the field of chiral quantum dots and laser interaction, and relates to a method for enhancing the luminescence intensity of chiral quantum dots and an optical device thereof; in particular, it is used to enhance the luminescence intensity of chiral quantum dot films prepared by a ligand exchange method. Background Art

[0002] Chiral quantum dots are a new type of nanomaterial. Due to their unique physical properties, they have broad application prospects in the fields of bio-labeling, chiral separation, spin electronics and circularly polarized light sources. Ligand exchange is a commonly used method for preparing chiral quantum dots, which has the advantages of low cost and simplicity. However, the ligand exchange method will inevitably increase the surface defect states of quantum dots. Photogenerated carriers are easily captured by these surface defect states, thereby reducing the luminescence intensity of quantum dots and adversely affecting the potential applications of chiral quantum dots. Summary of the invention

[0003] The purpose of the present invention is to provide a method and an optical device for enhancing the luminescence intensity of chiral quantum dots. The method is to use ultraviolet continuous laser to irradiate the chiral quantum dot film. With the assistance of water molecules in the air, the surface defect states of the quantum dot film are reduced, the radiation recombination rate of photogenerated carriers is increased, and the luminescence intensity is enhanced.

[0004] The specific technical solution for achieving the purpose of the present invention is: A method for enhancing the luminescence intensity of chiral quantum dots, the method firstly prepares a chiral quantum dot aqueous solution into a film by static spin coating, waits for the film to be completely dried, and fixes the film on a target frame; then uses an ultraviolet continuous laser as an irradiation light source, the wavelength of the irradiation light source is less than the excitation wavelength of the quantum dots; the irradiation light passes through a concave lens and irradiates the entire surface of the quantum dot film; another continuous laser is used as an excitation light source, the wavelength of the excitation light is less than the excitation wavelength of the quantum dots; the excitation light passes through a neutral density filter and irradiates the surface of the quantum dot film, the fluorescence emitted by the chiral quantum dot film passes through a convex lens, a long-wave pass filter and a convex lens and enters a fiber spectrometer, and the fiber spectrometer records the luminescence spectrum of the chiral quantum dots; the power density of the irradiation light is fixed, the luminescence intensity at different irradiation times is measured, and an image of the luminescence intensity changing with the irradiation time is obtained; the power density of the irradiation light is changed, the luminescence intensity at different irradiation times is measured, and an image of the luminescence intensity changing with the irradiation time is obtained under several irradiation light power densities; wherein the long-wave pass filter is used to filter the irradiation light and the excitation light.

[0005] An optical device for implementing the above method comprises a first continuous laser, a concave lens, a second continuous laser, a neutral density filter, a first convex lens, a long-wave pass filter, a second convex lens and a fiber spectrometer; the first continuous laser and the concave lens are sequentially arranged on an irradiation light path, and the irradiation light irradiates a chiral quantum dot film at an incident angle of 5°; the second continuous laser and the neutral density filter are sequentially arranged on an excitation light path, and the incident light is perpendicular to the chiral quantum dot film; the first convex lens, the long-wave pass filter, the second convex lens and the fiber spectrometer are sequentially arranged on a detection light path.

[0006] Furthermore, the first continuous laser is an irradiation light source, and an ultraviolet laser is used. The luminescence enhancement effect of the chiral quantum dot film irradiated by a laser with an ultraviolet wavelength is obvious; the second continuous laser is an excitation light source, and the wavelength of the excitation light source should be smaller than the excitation wavelength of the quantum dots. The excitation light generates electron-hole pairs in the chiral quantum dots; the irradiation light is expanded by a concave lens and irradiated on the entire quantum dot film; the neutral density filter adjusts the power density of the excitation light; and a long-wave pass filter is placed behind the quantum dot film to block the excitation light and irradiation light signals.

[0007] Principle of the present invention: When quantum dots are irradiated with light, if the wavelength of the light is less than the excitation wavelength of the quantum dots, the quantum dots absorb photons, causing the electrons in the valence band to jump to the conduction band to form electron-hole pairs. There are two different recombination channels for photoexcited electron-hole pairs, namely radiative recombination and non-radiative recombination. For the radiative recombination process, the electrons in the conduction band return directly to the valence band, and the excess energy is released in the form of emitted photons, resulting in the photoluminescence phenomenon of quantum dots. For the non-radiative recombination process, the electrons in the conduction band first jump to the defect energy level, and then return to the valence band from the defect energy level. No photons are emitted in this process, and the excess energy is dissipated in the form of heat through the lattice vibration of the quantum dots. Defects on the surface of quantum dots will create defect energy levels in the band gap, thereby reducing the luminescence intensity of the quantum dots. The ligand exchange method for preparing chiral quantum dots will form a large number of defects on the surface of quantum dots, resulting in a significant reduction in the photoluminescence intensity of chiral quantum dots compared to original quantum dots. When the chiral quantum dot film is exposed to humid air, with the assistance of water molecules, light irradiation will passivate the surface defects of the chiral quantum dots, eliminate surface defect states, and reduce the non-radiative recombination channels of quantum dot electron-hole pairs, thereby enhancing the luminescence intensity of the quantum dots.

[0008] The present invention has the following advantages: low cost, simple operation, and large enhancement of the luminous intensity of quantum dots. In an air environment, the luminous intensity of the quantum dots can be enhanced to forty times the initial intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the structure of the optical device of the present invention; Figure 2 The diagram is a result of enhancing the luminescence intensity of chiral L-cys-CdSe and L-cys-CdS quantum dot films under different irradiation power densities using the method of the present invention. DETAILED DESCRIPTION

[0010] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0011] The enhancement method of the present invention is as follows: a beam of continuous laser is irradiated onto the surface of a chiral quantum dot film at an incident angle of 5° through a concave lens, another beam of continuous laser is vertically incident onto the surface of a chiral quantum dot film through a neutral density filter, the fluorescence emitted by the chiral quantum dots is first collected by a convex lens, then blocked by a long-wave filter from the irradiation laser and the excitation laser, and then focused by a convex lens on the fluorescence signal, and the signal finally enters a fiber optic spectrometer for measurement.

[0012] See also Figure 1 The device for implementing the above detection method includes: a first continuous laser 1, a concave lens 2, a second continuous laser 3, a neutral density filter 4, a first convex lens 5, a long-wave pass filter 6, a second convex lens 7, and an optical fiber spectrometer 8. The first continuous laser 1 and the concave lens 2 are sequentially arranged on the irradiation light path to irradiate the entire chiral quantum dot film at an incident angle of 5°; the second continuous laser 3 and the neutral density filter 4 are sequentially arranged on the excitation light path to vertically irradiate the chiral quantum dot film; the first convex lens 5, the long-wave pass filter 6, the second convex lens 7, and the optical fiber spectrometer 8 are sequentially arranged on the detection light path.

[0013] The first continuous laser 1 is an irradiation light source, and an ultraviolet laser is used. The luminescence enhancement effect of the chiral quantum dots irradiated by the laser with an ultraviolet wavelength is obvious; the second continuous laser 3 is an excitation light source, and its excitation wavelength is shorter than the excitation wavelength of the quantum dots. The excitation light generates electron-hole pairs in the chiral quantum dots; the irradiation light is expanded by the concave lens 2 and irradiated on the entire quantum dot film; the neutral density filter 4 adjusts the power density of the excitation light; and a long-wave pass filter 6 is placed behind the quantum dot film to block the excitation light and the irradiation light. Example

[0014] Taking chiral L-cys-CdSe quantum dot film and chiral L-cys-CdS quantum dot film as examples, under continuous laser irradiation with a wavelength of 360nm and continuous laser excitation at 360nm, the enhancement relationship between the luminescence intensity of the chiral quantum dots and the irradiation time was obtained. Figure 1A specific optical device for enhancing the luminescence intensity of chiral quantum dots. The first continuous laser 1 irradiates the entire chiral L-cys-CdSe quantum dot film or the chiral L-cys-CdS quantum dot film through a concave lens 2, the second continuous laser 3 vertically incidents the chiral quantum dot film through a neutral density filter 4, the first convex lens 5 collects the luminescence, the 400nm long-wave filter 6 filters out the two laser beams, the second convex lens 7 converges the luminescence signal again, and the luminescence signal finally enters the fiber optic spectrometer 8 for detection, and the integration time of the fiber optic spectrometer is 100ms.

[0015] Figure 2 It is the specific experimental result. The vertical axis is the normalized intensity of the luminescence signal of the chiral quantum dot film, and the horizontal axis is the irradiation time of the irradiated light. Figure 2 The chiral L-cys-CdSe and L-cys-CdS quantum dot films were respectively 2 、182mW / cm 2 、910mW / cm 2 The graph of the change of luminescence intensity with irradiation time under irradiation of . It can be seen that whether it is chiral L-cys-CdSe quantum dot film or chiral L-cys-CdS quantum dot film, the luminescence intensity of quantum dots is significantly enhanced with the extension of irradiation time. L-cys-CdSe quantum dot film at a power density of 36.4mW / cm 2 、182mW / cm 2 、910mW / cm 2 Under the irradiation of , the luminous intensity reaches the maximum value after 220 minutes, 120 minutes and 15 minutes respectively. The irradiation power density is 910mW / cm 2 When the luminescence intensity of the chiral CdSe quantum dots reaches the maximum, it begins to decrease. This is because the continuous high-power density light irradiation causes photo-oxidation reaction on the surface of the quantum dots, re-forming new defects, which in turn causes the luminescence intensity of the quantum dots to decrease. This shows that the irradiation power density and irradiation time of the quantum dot film need to be precisely controlled. The irradiation time should not be too long, and the irradiation power density should not be too large. The chiral L-cys-CdS quantum dot film has a high luminescence intensity when the laser power density is 36.4mW / cm 2 、182mW / cm 2 、910mW / cm 2 Under irradiation of , it takes 46 minutes, 24 minutes and 8 minutes respectively to reach the maximum luminous intensity, and after reaching the maximum, the luminous intensity begins to decrease.

[0016] At this point, the luminescence intensity of the chiral quantum dot film can be significantly enhanced by irradiating it with ultraviolet continuous laser.

Claims

1. A method for enhancing the luminescence intensity of chiral quantum dots, characterized in that: The method first prepares a chiral quantum dot aqueous solution into a thin film by static spin coating, waits for the film to be completely dried, and fixes the film on a target frame; then uses an ultraviolet continuous laser as an irradiation light source, and the wavelength of the irradiation light source is smaller than the excitation wavelength of the quantum dots; the irradiation light passes through a concave lens and irradiates the entire surface of the quantum dot film; Another continuous laser is used as an excitation light source, and the wavelength of the excitation light is smaller than the excitation wavelength of the quantum dots; the excitation light passes through a neutral density filter and then irradiates the surface of the quantum dot film, and the fluorescence emitted by the chiral quantum dot film passes through a convex lens, a long-wave pass filter and a convex lens into a fiber spectrometer, and the fiber spectrometer records the luminescence spectrum of the chiral quantum dots; the power density of the irradiated light is fixed, the luminous intensity at different irradiation times is measured, and an image of the luminous intensity changing with the irradiation time is obtained; the power density of the irradiated light is changed, the luminous intensity at different irradiation times is measured, and an image of the luminous intensity changing with the irradiation time is obtained under several irradiation light power densities; wherein the long-wave pass filter is used to filter the irradiated light and the excitation light.

2. An optical device for implementing the method of claim 1, characterized in that: The device comprises a first continuous laser (1), a concave lens (2), a second continuous laser (3), a neutral density filter (4), a first convex lens (5), a long-wave filter (6), a second convex lens (7) and a fiber spectrometer (8); the first continuous laser (1) and the concave lens (2) are arranged in sequence on an irradiation light path, and the irradiation light irradiates the chiral quantum dot film at an incident angle of 5°; the second continuous laser (3) and the neutral density filter (4) are arranged in sequence on an excitation light path, and the incident light is perpendicular to the chiral quantum dot film; the first convex lens (5), the long-wave filter (6), the second convex lens (7) and the fiber spectrometer (8) are arranged in sequence on a detection light path.

3. The optical device according to claim 2, characterized in that The first continuous laser (1) is an irradiation light source, and an ultraviolet laser is used. The luminescence enhancement effect of the chiral quantum dot film irradiated by the ultraviolet wavelength laser is obvious; the second continuous laser (3) is an excitation light source, and the wavelength of the excitation light source is smaller than the excitation wavelength of the quantum dots, and the excitation light generates electron-hole pairs in the chiral quantum dots; the irradiation light is expanded by a concave lens (2) and irradiated on the entire quantum dot film; the neutral density filter (4) adjusts the power density of the excitation light; and a long-wave pass filter (6) is placed behind the quantum dot film to block the excitation light and irradiation light signals.

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