CN114591724B - CdSe quantum dot luminescence property regulation and control method - Google Patents
CdSe quantum dot luminescence property regulation and control method Download PDFInfo
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Abstract
The invention belongs to the field of colloid quantum dot luminescent materials, and discloses a method for regulating and controlling the luminescent performance of CdSe quantum dots, which comprises the steps of dispersing CdSe quantum dots in a solvent, adding quaternized pyridine macromolecules and/or quaternized pyridine micromolecules into the solvent, and obtaining the CdSe quantum dots with passivated surfaces after reaction; the method can neutralize the surface dangling bond of the CdSe quantum dot, so that the proportion of radiation transition in fluorescence emission is increased, and meanwhile, the fluorescence quantum yield of the quantum dot is improved by forming a metal compound, so that the luminescence performance of the quantum dot is regulated and controlled. According to the invention, pyridine compounds are introduced into the surface of the CdSe quantum dot to realize surface passivation, and the photoluminescent color change of the CdSe quantum dot can be realized by adjusting the quaternization degree of a polymer or the concentration of a small molecule and the pH value of a system, so that the problems of complicated materials, low fluorescence quantum yield and the like of the CdSe quantum dot with blue light emission can be effectively solved.
Description
Technical Field
The invention belongs to the field of colloidal quantum dot luminescent materials, and in particular relates to a method for regulating and controlling the luminescent performance of CdSe quantum dots, which improves photoluminescence of CdSe quantum dots by passivating the surfaces of pyridine. The method can be used for adjusting the light-induced blue light of the CdSe quantum dots.
Background
Blue luminescent materials are of great interest in the photochemical field due to their potential applications in display, lighting, biomedical and optical communications. For example, blue light is the core component of solid state lighting and full color display blue light emission. Heretofore, a variety of blue light emitting materials have been developed which can be used as electronic circuit devices as well as quantum dot light emitting diodes (QLEDs). Recent developments in quantum dot based light emitting diodes have met the requirements of the display, and the need to increase its quantum efficiency (EQE) [ Gao, q.et al visible quantum dot light-emitting diodes with simultaneous high brightness and efficiency nature Photonics 2019,13 (3), 192-197 is inevitable.]. The Chunxing She task group reports that the maximum external quantum efficiency of blue light of a light-emitting diode based on a CdSe/ZnSe core/shell structure can reach 8.05%, and the corresponding brightness is 10,100cdm -2 . But the preparation of blue QLED still faces great difficulties: even though the peak EQE is increased by more than 10%, the corresponding brightness is still very low. Thus, despite the success in achieving tunable luminescent colors, developing blue luminescent materials with high fluorescence quantum yields remains a formidable challenge.
The colloidal quantum dot has unique optical characteristics such as tunable Photoluminescence (PL), high thermodynamic stability, high color purity and the like, and is widely applied to the fields of illumination, photocatalysis and the like. In 2005 Rosenthal et al reported for the first time an ultra-small (1.5 nm) CdSe Nanocrystal (NC) with broad fluorescence emission in the visible spectrum, but with a fluorescence Quantum Yield (QY) of only 2-3%. Later, they found that treatment of microminiature CdSe NCs with organic acids significantly improved their QY. Due to the large surface area to volume ratio of quantum dots, dual emission with edge emission and surface trap emission is typically produced. The spectral properties of this photoluminescence are common in CdSe quantum dots of small size [ s.j.rosenthal et al j.am.chem.soc.,2012,134,8006-8009 ]. In 2013, kambhamati's group describes that temperature and surface ligand exchange change the ratio of core radiation and surface radiation of ultra-small CdSe NCs, and high purity blue light emission of CdSe NCs can be achieved by temperature control. This also suggests that external conditions can change the luminescent color and intensity of the quantum dot, but that it requires stringent reaction conditions and precise time control in synthesis [ m.m. krausen et al acs Nano,2013,7 (7), 5922-9 ]. Andrey L.Rogach et al studied interactions, conformational and distance changes in hybrid nanosystems by Fluorescence Resonance Energy Transfer (FRET) spectroscopic techniques, summarizing directed energy transfer of different sized CdTe semiconductor nanocrystals layer-by-layer assembly multilayers and energy transfer from single rod-like CdSe/CdS quantum dots to single dye molecules, elucidating the laws of band gap luminescence regulation by size [ Rogach, A.L.et al energy transfer with semiconductor nanocrystals.J.Mater.chem.2009,19 (9), 1208-1221 ]. Furthermore, studies by s.r.corero et al show that luminescence of CdSe quantum dot monolayers can be strongly affected by interactions of water molecules adsorbed on the surface. The photoinduced change of surface state after water adsorption results in a quasi-reversible luminescence change in the quantum dots. Exciton emission exhibits an exponential blue shift of approximately 16nm (60 meV) [ Cordero, s.r. et al photo-activated Luminescence of Cdse Quantum Dot mol ayers. The Journal of Physical Chemistry B, 2000,104 (51), 12137-12142 ]. From the analysis of the results reported at present, the existing method for adjusting the blue light emission of CdSe quantum dots is complicated, and strict reaction conditions and time control are mostly unavoidable.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention aims to provide a method for regulating and controlling the luminescence performance of CdSe quantum dots, which is characterized in that pyridine compounds are introduced to the surfaces of the CdSe quantum dots to realize surface passivation, and the photoluminescence color of the CdSe quantum dots can be changed by regulating the quaternization degree of macromolecules or the concentration of small molecules and the pH value of a system. In addition, based on the method, the photoluminescence of CdSe QDs in different solvent systems (such as water, DMF and the like) can be regulated and controlled by a high molecular pyridine compound and a small molecular pyridine compound.
In order to achieve the above-mentioned purpose, according to an aspect of the present invention, there is provided a method for controlling luminescence properties of CdSe quantum dots, which is characterized in that CdSe quantum dots to be controlled are used as raw materials, the CdSe quantum dots are dispersed in a solvent, and at the same time, quaternized pyridine polymers and/or quaternized pyridine small molecules are added as a controlling agent, and after reaction, cdSe quantum dots after surface passivation by the controlling agent are obtained; wherein the relative molecular mass of the small molecules is not higher than 500;
the method utilizes the regulating agent to neutralize the surface dangling bond of the CdSe quantum dot, so that the proportion of radiation transition in fluorescence emission is increased, and meanwhile, the fluorescent quantum yield of the quantum dot is improved by forming a metal compound on the surface of the regulating agent and the CdSe quantum dot, so that the luminescence performance of the quantum dot is regulated.
As a further preferred aspect of the present invention, when the regulator is a quaternized pyridine polymer, the change of the photoluminescence color of the quantum dots can be achieved by adjusting the quaternization degree of the polymer and/or the concentration of the polymer in the reaction liquid system;
preferably:
when the concentration of the polymer in the reaction liquid system is kept unchanged, the higher the quaternization degree of the polymer is, the blue the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained;
when the quaternization degree of the polymer is kept unchanged, the higher the concentration of the polymer in the reaction liquid system is, the blue the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained.
As a further preferred aspect of the present invention, when the modulator is a quaternized pyridine small molecule, the change in photoluminescence color of the quantum dot can be achieved by adjusting the concentration of the small molecule in the reaction liquid system;
and when the concentration of small molecules in the reaction liquid system is higher, the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained is blue.
As a further preferred aspect of the present invention, after the addition of the regulator, the change of the photoluminescence color of the quantum dots can be achieved by adjusting the pH value of the reaction liquid system;
the smaller the pH value of the reaction liquid system is, the blue the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained;
preferably, the pH value of the reaction system is adjusted to 5-12 after adding the regulator.
As a further preferred aspect of the present invention, the quaternized pyridine polymer is specifically a quaternized product of poly (4-vinylpyridine), and the structural formula is shown in formula I:
wherein R is 1 Is an aliphatic carbon chain of C1-C16, X - Is halogen ion or acid radical ion.
As a further preferred aspect of the present invention, the quaternized small pyridine molecule is specifically a quaternized product of 4-alkylpyridine having a structural formula shown in formula II:
wherein R is 2 Is C1-C6 alkyl, R 3 Is an aliphatic carbon chain of C1-C16, X - Is halogen ion or acid radical ion;
preferably, R 2 Methyl, ethyl, propyl, isopropyl, butyl or sec-butyl.
As a further preferred aspect of the invention, the particle size of the raw material CdSe quantum dot is 1nm-5nm, and the band edge emission of 450-500nm and the defect emission of 600-650nm can exist simultaneously;
and the raw material CdSe quantum dot is also treated by 3-mercaptopropionic acid.
As a further preferred aspect of the present invention, the CdSe quantum dots are dispersed in a solvent, and the concentration of the CdSe solution formed is 0.1mg/mL-0.4mg/mL.
As a further preferred aspect of the present invention, the solvent is at least one of water, N-Dimethylformamide (DMF), methanol, ethanol, acetonitrile, and tetrahydrofuran;
the reaction is standing and ageing for 8-12 hours.
According to another aspect of the present invention, there is provided a surface-passivated CdSe quantum dot obtained by the above method.
Compared with the prior art, the quantum dot surface passivation method based on the interaction between the pyridine quaternary ammonium salt and the CdSe quantum dot surface adjusts the luminescence color and the luminescence quantum yield of the quantum dot through the surface passivation of the pyridine quaternary ammonium salt polymer and the small molecule. For the pyridine quaternary ammonium salt polymer, the proportion of the band edge peak and the defect peak intensity of the CdSe quantum dot can be directly regulated and controlled by regulating the quaternary amination degree of pyridine in a polymer chain segment, and the luminous quantum yield of the CdSe quantum dot can be improved, and the band edge peak is mainly in a blue short wave region of 450-500nm, the defect peak is in a red long wave region of 600-650nm, so that the luminous color of the quantum dot can be further controlled by regulating the relative intensity of the two peaks. For pyridine quaternary ammonium salt small molecules, the color and the intensity of the quantum dots can be adjusted by adjusting the added concentration and controlling the pH of the system.
The previous research result CN113174252A of the inventor subject group discloses that white light regulation and control of CdSe quantum dots are realized by dispersing CdSe in a compound solution containing amino groups, and blue light color regulation and control of CdSe quantum dots are realized by introducing quaternized pyridine macromolecules and/or quaternized pyridine micromolecules. Because the CdSe quantum dots generally have the characteristic of double-peak emission, the band edge peak is in a blue emission region of short wave, and the defect peak is in a red emission region of long wave, the CdSe quantum dot aqueous solution emits orange-yellow light at room temperature. In the present invention, taking high molecular pyridine quaternary ammonium salt as an example, among the pyridine quaternary ammonium salts with different quaternization degrees, the non-quaternized pyridine moiety (py) has strong coordination ability, and can raise both the band edge peak and the emission peak, while the quaternized pyridine salt (py + ) The intensity of both peaks can be reduced to some extent. As will be seen from the examples below: in an aqueous solution system, water molecules only play a solvating role on CdSe, and a series of experiments are carried out by a controlled variable method, so that the method can prove that the maximum fluorescence quantum yield can be achieved by adding P4VP with the quaternization degree of 50% and the concentration of 0.2mmol/L (mM) into a quantum dot aqueous solution with the concentration of 0.2mg/mL, and maintaining the pH of the aqueous solution at about 7-8. In DMF systems, since there is some interaction between DMF molecules and CdSe quantum dots, which can make the defect peak lower, increasing the degree of quaternization only reduces the fluorescence intensity of the whole system.
On the other hand, taking small molecule pyridine quaternary ammonium salt as an example, since the small molecule contains pyridine quaternary ammonium salt structure, quenching of two peaks is caused when the small molecule is added into the system at the beginning, but the small molecule and the quantum dot form clusters again with the lapse of time, and further the peaks with edges and defects rise. Under the same time condition, compared with a high molecular system, the small molecules have smaller effect on the defect peaks of the CdSe quantum dots, and have larger promotion on the band edge peaks.
In particular, the invention can achieve the following beneficial effects:
(1) The invention discloses a method for regulating and controlling photoluminescence of CdSe quantum dots in different solvent systems. The key point of the invention is to utilize the synergistic effect between the inherent emission of the quantum dot and the emission generated by the pyridine compound forming the compound interacted on the surface of the quantum dot to improve the fluorescence quantum yield, and the pyridine compound neutralizes the surface dangling bond of the quantum dot, so that the proportion of radiation transition in the fluorescence emission is increased, and the fluorescence quantum yield of the CdSe quantum dot is improved through surface passivation.
(2) The invention can realize the relative intensity adjustment of two peaks of CdSe quantum dots by adjusting the quaternization degree, concentration, solution pH value and the like of the pyridine compound, and further can control the luminescence color of the quantum dots to change between orange and blue. The CdSe quantum dots used in the invention can be prepared in large quantity by a simple water bath method. The invention respectively utilizes the pyridine compounds of the high polymer and the small molecule to regulate and control the luminescence of the CdSe quantum dots, is applicable to various solution systems, and has simple and feasible implementation method and convenient operation.
(3) For the CdSe quantum dots with bimodal emission, the luminescence performance can be controlled in various ways, but there is no control method for reducing the defect peak intensity and improving the band edge peak intensity reported. Because the luminescence of the CdSe quantum dots is regulated, the intensity of two peaks is usually increased or decreased simultaneously. The method of the invention increases the intensity of two peaks one by one, changes the proportion of the two peaks, and further has the effect of regulating and controlling the luminescence color and the fluorescence quantum yield of the CdSe quantum dots.
In addition, the CdSe quantum dots used in the invention can be prepared in a large quantity by a simple water bath method, and the pyridine quaternary ammonium salt polymer and the small molecule can be prepared by quaternization reaction of polyvinyl pyridine and pyridine molecules with haloalkane, so that the method is very beneficial to practical application.
In summary, the invention can regulate and control the fluorescence emission of the CdSe quantum dots emitted in double peaks by simply regulating the quaternization degree, concentration, type and solution pH of the pyridine compound, realize the change from orange yellow to blue and improve the luminous intensity. The method is simple and easy to operate, and the CdSe quantum dot solution capable of emitting pure blue light can be simply and conveniently obtained in different solution systems. The invention realizes the regulation and control of the luminescence color and the improvement of the luminescence quantum yield of CdSe quantum dots by using high molecules and small molecules, is suitable for water and other organic solution systems, has simple and feasible implementation method, is convenient to operate, and has potential application in the aspects of solid-state illumination, metal ion detection and the like.
Drawings
FIG. 1 is a graph of ultraviolet absorption and fluorescence spectra of pure CdSe quantum dots in aqueous and DMF solutions; wherein a in fig. 1 corresponds to the ultraviolet absorption diagram, and b in fig. 1 corresponds to the fluorescence spectrum diagram.
FIG. 2 shows py and py in the fixed P4VP + The total concentration is 0.8mM, and the fluorescence spectrum diagram and the corresponding CIE coordinate diagram of the CdSe quantum dot aqueous solution with different quaternization degrees of P4VP surface passivation are provided; wherein a in fig. 2 corresponds to the fluorescence spectrum, and b in fig. 2 corresponds to the CIE coordinate diagram.
FIG. 3 is a graph of fluorescence spectra and corresponding CIE coordinates of aqueous solutions of surface-passivated CdSe quantum dots with different concentrations of P4VP with a degree of quaternization of 50%; wherein a in fig. 3 corresponds to a fluorescence spectrum, and b in fig. 3 corresponds to a CIE coordinate diagram.
FIG. 4 is a bar graph of peak area versus pH for aqueous solutions of P4VP surface-passivated CdSe quantum dots at different pH values and corresponding CIE coordinate diagrams; where a in fig. 4 corresponds to the peak area-pH histogram and b in fig. 4 corresponds to the CIE coordinate diagram.
FIG. 5 shows py and py in the fixed P4VP + A fluorescence spectrum chart and a corresponding CIE coordinate chart of CdSe quantum dot DMF solutions with different quaternization degrees of P4VP surface passivation with the total concentration of 0.8 mM; wherein a in fig. 5 corresponds to a fluorescence spectrum, and b in fig. 5 corresponds to a CIE coordinate diagram.
FIG. 6 is a fluorescence spectrum and corresponding CIE coordinate diagram of P4VP with a quaternization degree of 23.7%, and CdSe quantum dot DMF solutions with different concentrations of P4VP surface passivation; wherein a in fig. 6 corresponds to a fluorescence spectrum, and b in fig. 6 corresponds to a CIE coordinate diagram.
FIG. 7 is a graph of fluorescence spectra and corresponding CIE coordinates of aqueous solutions of quaternized 4-EP surface-passivated CdSe quantum dots of varying concentrations; wherein a in fig. 7 corresponds to a fluorescence spectrum, and b in fig. 7 corresponds to a CIE coordinate diagram.
FIG. 8 is a fluorescence spectrum and corresponding CIE coordinate diagram of different concentrations of quaternized 4-EP surface-passivated CdSe quantum dot DMF solutions; wherein a in fig. 8 corresponds to a fluorescence spectrum, and b in fig. 8 corresponds to a CIE coordinate diagram.
FIG. 9 is a graph of fluorescence spectra of pure aqueous CdSe quantum dots (0.2 mg/mL), aqueous CdSe quantum dots quaternized to 50% P4VP and quaternized 4-EP surface-passivated.
FIG. 10 is a graph of fluorescence spectra of a DMF solution of pure CdSe quantum dots (0.2 mg/mL concentration) and a DMF solution of P4VP surface-passivated CdSe quantum dots quaternized to 23.7%.
Further, for each of the legends appearing in the figures, wherein the percentages represent the degree of quaternization of the polymer and the decimal fraction represents the concentration of the polymer or small molecule (unit: mM, i.e., mmol/L) in the solution system being tested, unless otherwise specified.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
In general, the invention carries out surface passivation on CdSe quantum dots by adding high molecular pyridine quaternary ammonium salt and corresponding small molecules, on one hand, the synergistic effect between the inherent emission of the quantum dots and the emission generated by the formation of a compound by molecules interacted on the surfaces of the quantum dots is utilized, and the fluorescence quantum yield is improved; on the other hand, the pyridine structure in the molecule neutralizes the surface dangling bond of the quantum dot, so that the proportion of radiation transition in fluorescence emission is increased, and the fluorescence quantum yield of the CdSe quantum dot is improved.
For the macromolecule, the coordination condition of pyridine on the surface of the CdSe quantum dot is indirectly controlled by adjusting the quaternization degree of the macromolecule, so that the proportion of the CdSe quantum dot with side peak and defect peak intensity can be directly adjusted, the CdSe quantum dot has double-emission characteristic, and the luminous color of the quantum dot can be further controlled by adjusting the relative intensities of the two peaks. For small molecules, the color and the intensity of the quantum dots can be adjusted by adjusting the added concentration and controlling the pH of the system.
Taking quaternized P4VP and quaternized 4-EP as examples, the method can realize the light-emitting regulation and control of CdSe quantum dots by using the quaternized P4VP and the quaternized 4-EP, is applicable to various solution systems, and has the advantages of simple and feasible implementation method and convenient operation.
And the CdSe quantum dots used in the invention can be prepared in a large quantity by a simple water bath method.
In some embodiments, under the condition that the concentration of the aqueous solution of the CdSe quantum dots is 0.2mg/mL, the quaternization degree of the P4VP is regulated to be 0-100%, the photoluminescence of the aqueous solution of the CdSe quantum dots with passivated polymer surfaces can be changed along with the change of the quaternization degree of the polymer, and the relative intensity of the band edge peak and the defect peak of the CdSe quantum dots can be regulated along with the quaternization degree.
In some embodiments, under the condition that the quaternization degree of the P4VP of the surface passivation CdSe quantum dot aqueous solution is 50%, the concentration of the P4VP is regulated to be 0.2mg/mL-0.8mg/mL, so that photoluminescence of the polymer surface passivation CdSe quantum dot aqueous solution can be changed along with the change of the concentration of the P4VP, and the relative intensity of a band edge peak and a defect peak of the CdSe quantum dot can be regulated along with the concentration of the P4 VP.
In some embodiments, the pH of the aqueous solution of the CdSe quantum dots with the surfaces passivated by the quaternized polymers is adjusted by an acid-base solution, photoluminescence of the aqueous solution can be changed along with the change of the pH, and the relative intensity of the band edge peak and the defect peak of the CdSe quantum dots can be adjusted along with the pH of the solution.
Preferably, the acid-base solution is hydrochloric acid or sodium hydroxide.
In some embodiments, under the condition that the concentration of the CdSe quantum dot DMF solution is 0.2mg/mL, the quaternization degree of P4VP is regulated to be 0-100%, the photoluminescence of the CdSe quantum dot DMF solution with the passivated polymer surface can be changed along with the change of the quaternization degree of the polymer, and the relative intensity of the band edge peak and the defect peak of the CdSe quantum dot can be regulated along with the quaternization degree. In addition, when the CdSe quantum dot DMF solution is prepared, the volume ratio of the CdSe quantum dot aqueous solution to the DMF solvent is 1:9, so that DMF exists in a large amount in the mixed system, and water only plays a basic solvation role. The DMF solutions mentioned hereinafter are all formulated in a similar manner.
In some embodiments, under the condition that the quaternization degree of the P4VP of the surface passivation CdSe quantum dot DMF solution is 23.7%, the concentration of the P4VP is regulated to be 0.2mg/mL-0.8mg/mL, so that the photoluminescence of the polymer surface passivation CdSe quantum dot DMF solution can be changed along with the change of the concentration of the P4VP, and the relative intensity of the band edge peak and the defect peak of the CdSe quantum dot can be regulated along with the concentration of the P4 VP.
In some embodiments, when the concentration of the aqueous solution of CdSe quantum dots is 0.2mg/mL, the concentration of the quaternized 4-EP is regulated to be 0.2mg/mL-0.8mg/mL, so that photoluminescence of the aqueous solution of CdSe quantum dots with passivated small molecular surfaces can be changed along with the change of the concentration of the quaternized 4-EP, and the relative intensity of the band edge peak and the defect peak of the CdSe quantum dots can be regulated along with the concentration of the quaternized 4-EP.
In some embodiments, under the condition that the concentration of the CdSe quantum dot DMF solution is 0.2mg/mL, the concentration of the quaternized 4-EP is regulated to be 0.2mg/mL-0.8mg/mL, so that photoluminescence of the CdSe quantum dot DMF solution with the passivated small molecular surface can be changed along with the change of the concentration of the quaternized 4-EP, and the relative intensity of the band edge peak and the defect peak of the CdSe quantum dot can be regulated along with the concentration of the quaternized 4-EP.
The following are specific examples:
it should be noted that in the first place,
(i) The raw material CdSe quantum dot (namely, pure CdSe quantum dot) adopted in the embodiment of the invention has the following synthesis steps:
sodium selenosulfate (Na) 2 SeSO 3 ) Preparation of the solution: 189mg of anhydrous Na was added to 100mL of water 2 SO 3 Then 40mg selenium powder is added. Reflux is carried out at 130 ℃ until the selenium powder is completely reacted, and Na is obtained after cooling to room temperature 2 SeSO 3 A solution.
Synthesis of CdSe quantum dots: na to be prepared in advance 2 SeSO 3 The solution (10 mL) was injected into an argon saturated CdCl 2 In solution, the resulting mixture was refluxed under the condition of 3-mercaptopropionic acid (26 μl) at pH 11 as a stabilizer, and the growth of quantum dots during the reflux was monitored using uv-vis spectrum. After the reaction is completed, the reaction solution is concentrated, isopropanol is used for precipitation, centrifugation, washing and drying are carried out to obtain CdSe QDs,
the ultraviolet absorption diagram and fluorescence spectrum diagram corresponding to the obtained CdSe quantum dot (namely, the pure CdSe quantum dot) are shown in figure 1.
Moreover, since the preparation process uses 3-mercaptopropionic acid, the surface of the CdSe quantum dot obtained correspondingly is also modified with 3-mercaptopropionic acid (namely, cdSe QDs with 3-mercaptopropionic acid as ligand); modification of 3-mercaptopropionic acid will facilitate the stable presence of CdSe in a solvent (e.g., water).
An aqueous solution of CdSe quantum dots having a concentration of 0.2mg/mL was prepared using CdSe QDs, and the CIE coordinates thereof were (0.278,0.262) (the CIE coordinates are also shown in b in fig. 2, b in fig. 3, and b in fig. 7, and are also denoted as "CdSe water" in the drawings).
A CdSe quantum dot DMF solution having a concentration of 0.2mg/mL was prepared using CdSe QDs and had a CIE coordinate of (0.178,0.275) (the CIE coordinate is also shown in FIG. 5 b, FIG. 8 b, and is denoted as "CdSe DMF").
(ii) The high molecular pyridine quaternary ammonium salt adopted in the embodiment of the invention takes the bromobutane quaternary amination product for synthesizing the P4VP as an example,
the structure is as follows:
the synthesis steps comprise:
500mg of P4VP (poly (4-vinylpyridine)) having a molecular weight of 50000 was dissolved in 3mL of ethanol and added without addingThe same volume of n-bromobutane was heated at 70℃and the degree of quaternization of the P4VP was controlled by adjusting the equivalence ratio of the n-bromobutane added and the time of heating. Washing with diethyl ether after the reaction, centrifuging, steaming for three times, drying, collecting the obtained white yellow powder into small glass bottle, and using nuclear magnetic resonance 1 The degree of quaternization was calculated on the H spectrum. The three products with different quaternization degrees were named PB23.7%, PB50% and PB70%.
50mg of the corresponding solid powder is taken in a small centrifuge tube, 5mL of pure water is added, and the solution is prepared into 10mg/mL of quaternized P4VP water solution by ultrasonic dissolution.
And respectively taking 50mg of PB23.7%, 50% of PB and 70% of PB into the small centrifuge tubes, adding 5mL of DMF solvent, and ultrasonically dissolving to prepare 10mg/mL of different quaternized P4VP DMF solutions.
(iii) The small molecular pyridine quaternary ammonium salt adopted in the embodiment of the invention takes the bromobutane quaternary amination product of synthetic 4-EP as an example,
the structure is as follows:
the synthesis steps comprise:
500mg of 4-EP (4-ethylpyridine) having a molecular weight of 107.15 was dissolved in 3mL of ethanol, and 2.55mL (5-fold equivalent) of n-bromobutane was added and mixed, followed by heating at 70℃for 12 hours. After the reaction, the mixture was washed with diethyl ether, centrifuged three times, and dried by rotary evaporation, and the obtained tan solid was collected in a vial.
50mg of the corresponding solid powder was placed in a small centrifuge tube, 5mL of pure water was added, and the solution was sonicated to prepare 10mg/mL of an aqueous quaternized 4-EP solution.
Then 50mg of the prepared quaternized 4-EP powder was taken in a small centrifuge tube, 5mL of DMF was added, and the solution was prepared into 10mg/mL of quaternized 4-EP DMF solution by ultrasonic dissolution.
In the following examples, examples 1-5: photoluminescent regulation and control method for CdSe quantum dots in water and DMF system by quaternized P4VP
Examples 6 to 7: photoluminescent regulation and control method for CdSe quantum dots in water and DMF system by quaternized 4-EP
Example 1
And (3) fixing the volume of 50mg of CdSe quantum dots in a 10mL volumetric flask by using pure water to prepare a CdSe aqueous solution with the concentration of 5mg/mL, and fixing the volume of 2mL of the CdSe aqueous solution with the concentration of 0.2mg/mL from the CdSe aqueous solution to the 50mL volumetric flask. Neglecting the volume effect of each solvent, respectively taking 0.2mg/mL of CdSe aqueous solution and 10mg/mL of quaternized P4VP aqueous solution, respectively adding the aqueous solution into 3 small centrifuge tubes to prepare 3mL solutions with the quantum dot concentration of 0.2mg/mL and the quaternization degree of 23.7%, 50% and 70%, wherein the volume of the added pyridine polymer aqueous solution is small enough (less than 100 mu L), and neglecting the volume change caused by adding the aqueous solution of the quantum dots. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ The volumes of each solution added to the reaction are shown in Table 1.
According to the process, the fluorescence quantum yield of the CdSe quantum dot aqueous solution passivated by the surface of the macromolecular quaternary ammonium salt shows a tendency of increasing and then decreasing with the increase of the quaternization degree of the P4VP, the fluorescence color of the CdSe quantum dot aqueous solution changes from light yellow to blue, the CIE coordinate of the solution with PB50 percent is 0.23,029, and the brightness and the purity of the blue light are high. As shown in FIG. 2, with the adjustment of the quaternization degree of the pyridine polymer, two fluorescence peaks of the CdSe quantum dot aqueous solution passivated by the surface of the polymer quaternary ammonium salt can be changed, thereby realizing the photoluminescence adjustment and control of the quaternization degree in the aqueous solution on the CdSe quantum dot.
TABLE 1
Example 2
Ignoring the volume effect of each solvent, respectively taking 0.2mg/mL CdSe aqueous solution and 10mg/mL PB50% aqueous solution, respectively adding into 3 small centrifuge tubes to prepare 3mL solutions with quantum dot concentration of 0.2mg/mL and PB50% concentration of 0.1mM, 0.2mM and 0.4mM, respectively, and dissolving the added pyridine polymer in waterThe liquid volume was small enough (less than 100 μl) to ignore the volume change caused when added to the aqueous quantum dot solution. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ The volumes of each solution added to the reaction are shown in Table 2.
TABLE 2
The aqueous solution of CdSe quantum dots passivated by the surface of the macromolecular quaternary ammonium salt prepared by the process has the tendency that the fluorescence quantum yield of the aqueous solution of CdSe quantum dots is increased and then reduced with the increase of the volume of PB50 percent, the fluorescence color of the aqueous solution is changed from light yellow to blue, the CIE coordinate of the solution with the concentration of P4VP of 0.2mM is 0.22,0.28, and the brightness and the purity of the blue light are higher. The fluorescence spectrum of each solution is shown in figure 3, along with the adjustment of the concentration of the added pyridine polymer, two fluorescence peaks of the CdSe quantum dot aqueous solution passivated by the surface of the polymer quaternary ammonium salt can be changed along with the adjustment, and the photoluminescence adjustment and control of the concentration of the polymer in the aqueous solution on the CdSe quantum dot is realized.
Example 3
5 groups of P4VP water solution with the quaternization degree of 50% and the concentration of 0.2mmol/L and P4VP surface-passivated CdSe quantum dot water solution with the quantum dot concentration of 0.2mg/mL are prepared. The pH of the 5-group solutions was adjusted to 4.75, 6.34, 7.69, 9.78, 10.19, respectively. Wherein 7.69 is the pH of the stock solution. As shown in FIG. 4, the luminescence intensity of the CdSe quantum dots is strongest at the original pH, the peak intensity of the CdSe quantum dots is reduced by about 480nm as the pH value is reduced, and the band edge peak is greatly quenched at about 5 pH, so that only weak luminescence exists. As the pH increases, the CIE emission sites move toward the blue region and the CIE coordinates are shown in table 3.
TABLE 3 Table 3
Example 4
50mg of CdSe quantum dots were purified waterPreparing CdSe aqueous solution with concentration of 5mg/mL in a volumetric flask with volume of 10mL, taking 2mL quantum dot aqueous solution from the aqueous solution into a volumetric flask with volume of 50mL, adding 3mL pure water, and preparing DMF solution with concentration of 0.2mg/mL CdSe by using DMF to volume of 50 mL. Neglecting the volume effect of each solvent, respectively taking 0.2mg/mL of CdSe quantum dot DMF solution and 10mg/mL of quaternized P4VP DMF solution, respectively adding the solution into 3 small centrifuge tubes to prepare 3mL solutions with the quantum dot concentration of 0.2mg/mL and the quaternized P4VP degrees of 23.7%, 50% and 70%, wherein the added pyridine macromolecule DMF solution is small enough (less than 100 mu L), and neglecting the volume change caused by adding the solution into the quantum dot DMF solution. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ The volumes of each solution added to the reaction are shown in Table 4.
The fluorescence quantum yield of the CdSe quantum dot DMF solution passivated by the surface of the macromolecular quaternary ammonium salt prepared by the process is reduced along with the increase of the quaternization degree of the P4VP, the fluorescence color of the solution is changed from light yellow to blue-green, the CIE coordinate of the solution at PB23.7% is 0.13,0.35, and the brightness and the purity of the blue light emitted by the solution are high. As shown in FIG. 5, with the adjustment of the quaternization degree of the pyridine polymer, two fluorescence peaks of the CdSe quantum dot DMF solution passivated by the surface of the polymer quaternary ammonium salt can be changed, thereby realizing the photoluminescence adjustment and control of the quaternization degree in the DMF system on the CdSe quantum dot.
TABLE 4 Table 4
Example 5
Ignoring the volume effect of each solvent, respectively taking 0.2mg/mL of CdSe quantum dot DMF solution and 10mg/mL of PB23.7% DMF solution, respectively adding into 3 small centrifuge tubes to prepare a solution with the quantum dot concentration of 0.2mg/mL and the PB23.7% concentration of 0.2mM,0.4mM and 0.6m respectivelyM in 3mL solution, the added pyridine polymer DMF solution was small enough (less than 100. Mu.L), ignoring the volume change caused by the addition to the quantum dot DMF solution. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ The volumes of each solution added to the reaction are shown in Table 5.
TABLE 5
The fluorescence quantum yield of the CdSe quantum dot DMF solution passivated by the surface of the quaternary amination P4VP prepared by the process is increased along with the increase of PB23.7%, the fluorescence color of the CdSe quantum dot DMF solution is changed from light yellow to blue-green, the CIE coordinate of the solution with the concentration of P4VP being 0.6mM is 0.14,0.31, and the brightness and the purity of the blue light emitted by the CdSe quantum dot DMF solution are high. The fluorescence spectrum of each solution is shown in figure 6, along with the adjustment of the concentration of the added pyridine polymer, two fluorescence peaks of the CdSe quantum dot DMF solution passivated by the surface of the quaternized polymer can be changed along with the adjustment, and the photoluminescence adjustment and control of the concentration of the polymer to the CdSe quantum dot in the DMF system are realized.
Example 6
Neglecting the volume effect of each solvent, respectively taking 0.2mg/mL CdSe quantum dot aqueous solution and 10mg/mL quaternized 4-EP aqueous solution, respectively adding the aqueous solution and the quaternized 4-EP aqueous solution into 3 small centrifuge tubes to prepare 3mL solutions with the quantum dot concentration of 0.2mg/mL and the quaternized 4-EP concentration of 0.1mM, 0.2mM and 0.4mM, wherein the volume of the added pyridine small molecule aqueous solution is small enough (less than 100 mu L), and neglecting the volume change caused when the aqueous solution is added into the quantum dot aqueous solution. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ The volumes of each solution added to the interaction are shown in Table 6.
TABLE 6
The aqueous solution of CdSe quantum dots surface-passivated by quaternization of 4-EP prepared according to the above procedure increases with increasing concentration of the aqueous solution of 4-EP, and the fluorescence quantum yield increases and decreases, wherein the CIE coordinate of the solution at 0.2mM of P4VP is (0.25,0.24). As shown in FIG. 7, the fluorescence spectrum of each solution can be changed along with the adjustment of the concentration of the added pyridine small molecules, so that the brightness of the CdSe quantum dot aqueous solution passivated by the surface of the small molecule quaternary ammonium salt can be adjusted and controlled by the small molecule concentration in the aqueous solution.
Example 7
Neglecting the volume effect of each solvent, respectively taking 0.2mg/mL of CdSe quantum dot DMF solution and 10mg/mL of quaternized 4-EP DMF solution, respectively adding the solution into 3 small centrifuge tubes to prepare 3mL solutions with the quantum dot concentration of 0.2mg/mL and the quaternized 4-EP concentration of 0.1mM, 0.2mM and 0.4mM, wherein the added pyridine small molecule DMF solution has a volume small enough (less than 100 mu L), and neglecting the volume change caused when the solution is added into the quantum dot DMF solution. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ The volumes of each solution added to the reaction are shown in Table 7.
TABLE 7
The solution of CdSe quantum dots DMF surface-passivated by quaternization of 4-EP prepared according to the above procedure has a fluorescence quantum yield which increases and decreases with increasing concentration of 4-EP DMF solution, wherein the solution with 0.2mM P4VP concentration has CIE coordinates (0.13,0.29). As shown in FIG. 8, the fluorescence spectrum of each solution can be changed along with the adjustment of the concentration of the added pyridine small molecules, and the brightness of the CdSe quantum dot DMF solution passivated by the surface of the small molecule quaternary ammonium salt can be adjusted.
Example 8
50mg of CdSe quantum dot is fixed in a 10mL volumetric flask by pure water to prepare a CdSe aqueous solution with the concentration of 5mg/mL, and then the CdSe aqueous solution is taken out1mL of quantum dot aqueous solution is fixed in a 50mL volumetric flask to prepare a CdSe aqueous solution with the concentration of 0.1mg/mL, 4mL of quantum dot aqueous solution is taken from 5mg/mL of CdSe aqueous solution to be fixed in the 50mL volumetric flask to prepare a CdSe aqueous solution with the concentration of 0.4mg/mL. Neglecting the volume effect of each solvent, respectively taking CdSe aqueous solutions with the concentrations of 0.1, 0.2 and 0.4mg/mL, adding PB50% with the concentrations of 0.2mmol/L into 3 small centrifuge tubes to prepare 3mL solutions with the quantum dot concentrations of 0.1, 0.2 and 0.4mg/mL respectively, wherein the volume of the added pyridine polymer aqueous solution is small enough (less than 100 mu L), and neglecting the volume change caused by adding the pyridine polymer aqueous solution into the quantum dot aqueous solution. Standing for 12h to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ Interaction.
In the CdSe quantum dot aqueous solution passivated by the surface of the quaternary amination P4VP prepared by the process, the concentration of the quantum dot is too low in a sample of 0.1mg/mL, the color change is small after the polymer solution is added, and the CdSe quantum dot aqueous solution is still not obviously improved after being placed for more than 12 hours; in a sample of 0.4mg/mL, the concentration of the quantum dots is high, so that the solution is in a relatively obvious yellow color, the solution is placed for 12 hours after the polymer solution is added, the color of the solution becomes pale yellow, and the fluorescence intensity of the solution is lower than that of the original CdSe quantum dots. It is presumed that this is because the concentration is too high, which results in the aggravation of the self-quenching effect of CdSe quantum dots, and that the quenching effect of py+ after the binding with the polymer results in the decrease of the intensity of the band edge peak thereof, so that the concentration of the quantum dots should be ensured to be 0.1-0.4mg/mL.
Example 9
And (3) fixing the volume of 50mg of CdSe quantum dots in a 10mL volumetric flask by using pure water to prepare a CdSe aqueous solution with the concentration of 5mg/mL, and fixing the volume of 2mL of the CdSe aqueous solution with the concentration of 0.2mg/mL from the CdSe aqueous solution to the 50mL volumetric flask. And (3) neglecting the volume effect of each solvent, respectively taking 0.2mg/mL of CdSe aqueous solution and 10mg/mL of quaternized P4VP aqueous solution, respectively adding the aqueous solution and the solution into 3 small centrifuge tubes to prepare 3mL solutions with the quantum dot concentration of 0.2mg/mL and the quaternization degree of 50%, wherein the volume of the added pyridine macromolecule aqueous solution is small enough (less than 100 mu L), and neglecting the volume change caused by adding the aqueous solution into the quantum dots. Standing for 6h, 12h and 18h respectively to ensure that the pyridine compound fully combines with Cd on the surface of the quantum dot 2+ Interaction.
The CdSe quantum dot aqueous solution with the surface passivated by the quaternary amination P4VP prepared by the process has the fluorescent intensity of a sample placed for 6 hours which is obviously lower than that of a sample placed for 12 hours, and the fluorescent intensity of a sample placed for 18 hours is basically unchanged from that of a sample placed for 12 hours. There is a kinetic and thermodynamic interconversion during the interaction of the quantum dots and the macromolecules, which may lead to a fluctuation in fluorescence intensity in a certain range at the beginning of passivation, and as time increases, passivation is substantially complete, and fluorescence intensity is stabilized to a fixed value. Therefore, the stable passivation of the quantum dots is better after standing for 8-12 hours.
The above examples are only examples of water and DMF solvents, and the invention is also applicable to other solvent systems (such as methanol, ethanol, etc.), and correspondingly, the quaternization degree and concentration of the polymer, the concentration of the small molecule, the pH of the system, and the regulating effect on the photoluminescence color of CdSe quantum dots have similar trend.
In addition, the molecular weight of the small molecules in the invention meets the conventional requirements, and the relative molecular weight is not higher than 500.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (9)
1. The application of the regulator in regulating and controlling the defect peak intensity and the band edge peak intensity of the CdSe quantum dot is characterized in that the CdSe quantum dot to be regulated and controlled is taken as a raw material, the CdSe quantum dot is dispersed in a solvent, and meanwhile, quaternized pyridine polymers and/or quaternized pyridine small molecules are added into the solvent to serve as the regulator, and the CdSe quantum dot after surface passivation of the regulator can be obtained after reaction; wherein the relative molecular mass of the small molecules is not higher than 500;
the particle size of the raw material CdSe quantum dot is 1nm-5nm, and the band edge emission of 450-500nm and the defect emission of 600-650nm can exist at the same time; in addition, the raw material CdSe quantum dot is also treated by 3-mercaptopropionic acid;
the application utilizes the regulating agent to neutralize the surface dangling bond of the CdSe quantum dot, so that the proportion of radiation transition in fluorescence emission is increased, and meanwhile, the fluorescent quantum yield of the quantum dot is improved by forming a metal compound on the surface of the regulating agent and the CdSe quantum dot, so that the luminous performance of the quantum dot is regulated, and the defect peak intensity and the band edge peak intensity of the CdSe quantum dot are regulated;
the quaternized pyridine polymer is specifically a quaternized product of poly (4-vinylpyridine), and the structural formula of the quaternized product is shown as formula I:
wherein R is 1 Is an aliphatic carbon chain of C1-C16, X - Is halogen ion or acid radical ion;
the quaternized pyridine micromolecules are specifically quaternized products of 4-alkylpyridine, and the structural formula of the quaternized product is shown as formula II:
wherein R is 2 Is C1-C6 alkyl, R 3 Is an aliphatic carbon chain of C1-C16, X - Is halogen ion or acid radical ion.
2. The use according to claim 1, wherein when the modulator is a quaternized pyridine polymer, the change in photoluminescent color of the quantum dots can be achieved by adjusting the degree of quaternization of the polymer and/or the concentration of the polymer in the reaction liquid system.
3. The use according to claim 2, wherein,
when the concentration of the polymer in the reaction liquid system is kept unchanged, the higher the quaternization degree of the polymer is, the blue the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained;
when the quaternization degree of the polymer is kept unchanged, the higher the concentration of the polymer in the reaction liquid system is, the blue the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained.
4. The use according to claim 1, wherein when the modulator is a quaternized pyridine-based small molecule, the change in photoluminescence color of the quantum dot can be achieved by adjusting the concentration of the small molecule in the reaction liquid system;
and when the concentration of small molecules in the reaction liquid system is higher, the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained is blue.
5. The use according to claim 1, wherein after addition of the modulator, a change in the photoluminescent colour of the quantum dots is achieved by adjusting the pH of the reaction liquid system;
the smaller the pH value of the reaction liquid system is, the blue the photoluminescence color of the CdSe quantum dot after the surface passivation is correspondingly obtained.
6. The method according to claim 5, wherein the pH of the reaction system is adjusted to 5-12 after the addition of the regulator.
7. The use according to claim 1, wherein R 2 Methyl, ethyl, propyl, isopropyl, butyl or sec-butyl.
8. The use according to claim 1, wherein the CdSe quantum dots are dispersed in a solvent to form a CdSe solution having a concentration of 0.1mg/mL to 0.4mg/mL.
9. The use according to claim 1, wherein the solvent is at least one of water, N-Dimethylformamide (DMF), methanol, ethanol, acetonitrile, tetrahydrofuran;
the reaction is standing and ageing for 8-12 hours.
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