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The Preparation Of Carbon Quantum Dots Based Luminescent Films With Their Photoluminescent And Electroluminescent Properties

Posted on:2018-04-02Degree:MasterType:Thesis
Country:ChinaCandidate:F ZhangFull Text:PDF
GTID:2348330536466244Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
Carbon quantum dots(CQDs)are one type of quasi-zero dimensional carbon nanoparticle with size less than 10 nm and fluorescence property,which mainly consist of C,H,O and many functional groups on the surface.CQDs possess the excellent features of flexible modification,tunable fluorescence wavelength range,friendly enviroment and low preparation cost.CQDs gradually show broad prospects in wide fields,such as bioimaging,optics sensor,photocatalysis,chemical sensor and optoelectronics.In this dissertation,the preparation of CQDs was carried out for their applications in light emitting devices.CQDs mainly exhibit the photoluminescence(PL)and the electroluminescence(EL),which apply to the light-emitting diode(LED)as phosphor material and the electroluminescent quantum dots-based LED(QLED)as emitting layer material in optoelectronic field,respectively.CQDs based LED and QLED still have some drawbacks.On one hand,the CQDs as phosphor in LED exhibit some deficiencies including low quantum yield(QY),low red-green-blue(RGB)spectral composition and poor dispersibility in adhesive agents.On the other hand,the approach of CQDs as emitting layer in QLED is a new attempt,which exists low QY,poor charge-transporting ability of CQDs and complicated preparation process of device.As a result,this dissertation aims at the preparation of CQDs with high QY,RGB spectral composition and direct film-forming ability used in LED and CQDs with high QY good charge-transporting ability applied in QLED,separately.The main contents and results are as follows:First,photoluminescent organosilane-functionalized CQDs,2.5-3.5 nm in diameter,were synthesized through a facile hydrothermal method using citric acid(CA)monohydrate as carbon source and N-(3-(trimethoxysilyl)propyl)ethylenediamine(KH-792)as additive.The CQDs exhibit excitation-independent behavior with QY of 57.3% and RGB spectral composition of 60.1%.Meanwhile,the CQDs exhibit direct film-forming ability through simple heat treatment.The white LED was fabricated by combining the CQDs phosphor film with UV-LED chip,which exhibits cool white light with CIE coordinate of(0.31,0.36),correlated color temperature of 6282 K and color rending index of 84.In addition,the white LED exhibits good optical stability under various working voltages and different working time intervals.In brief,the reaction system,containing carbon sources of organic acid with-COOH and-OH and introduction of nitrogen atom,could contribute to the formation of CQDs with high QY and RGB spectral composition.The directly film-forming CQD solution can be obtained with the participation of additive that serves as the adhesive agent,which is applied to LED.Second,the CQDs,with QY of 29.3% and excitation-dependent behavior,were prepared through one-step hydrothermal method using phthalic acid as carbon source and ethylenediamine as additive.The CQDs are well dispersed with most particles in the range of 4-7 nm in diameter.The CQDs have a crystalline structure with lattice spacing of 0.22 nm.The as-obtained CQDs were employed as the emitting layer material to prepare the QLED combining the PEDOT:PSS as hole transporting layer and TPBI as electron transporting layer.The influence of different thickness of emitting layer,which is controlled by spin-coating dosage of CQDs,spin-coating rate and time,on the device performance is investigated.It turned out that the QLED exhibits blue light with a brightness of 4.9 cd/m2 and turn-on voltage of 5.5 V on the terms that the spin-coating dosage of 360 ?L,spin-coating rate of 1000 rpm and time of 30 s.Therefore,the CQDs with crystallinity can be prepared by employing the carbon sources with aromatic ring structure.The performance of QLED based on the CQDs is affected by the properties of CQDs,as well as the device structure and thickness of emitting layer.
Keywords/Search Tags:carbon quantum dots, photoluminescence, electroluminescence, light-emitting diode
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