High-Concentration Synthesis And Application Of Colloidal Quantum Dots

Commercial white-light-emitting diodes （WLEDs）, which are made by using a type of phosphor and a blue-emitting GaN-based chip, often have a low color rendering index （CRI）, greatly limiting its applications. Mn-doped semiconductor quantum dots （QDs） has broad application prospects in optoelectronic devices such as WLEDs owing to their large light absorption cross sections, large Stokes shifts, and almost complete lack of self-absorption, and their emission wavelength could be tuned with the Mn ion’s environment inside the QDs. In this thesis, high-concentrationsynthesis and applicationsof QDs in the WLEDs are studied in detail.¹0g of Mn-doped CdS/ZnS core/shell QDs could be yielded in 1.5 L of solvents by using a one-pot method with an improved growth doping technique, and the QDs’ fluorescence peak could be varied from 564 to 616 nm by changing the Mn2+ doping process and ZnS shell thickness. The ligand concentration, amount of element sulfur and the order of surfactant addition play an important role in the nucleation with high density.Based on the electro-optical energy transfer process, the pseudo-spectral-luminous efficiency function （ΦQD） of QDs is introduced, the equations of chromaticity coordinates, luminous efficiency and the QDs’mass for the WLEDs with CdSe, CuInS2 and CdS:Mn QDs are yielded, and the calculation results are coincident with the experimental ones.A reverse microemulsion method was used to encapsulate CdS:Mn/ZnS QDs with SiO₂ aerosols to improve their toxicity and photostability and extand their use range. QDs are well coated within silica obtained from TEM image. A comparison of the variation in the PL intensity and lifetime of CdS:Mn/ZnS and CdS:Mn/ZnS@SiO₂ QDs under strong UV light （Wavelength=365 run, radiant intensity=10 W/mm2） reveals that the photostability of the silica-coated QDs is obviously greater.To efficiently improve the photostability and lifetime of WLEDs, the WLEDs were packaged with SiO₂ aerosols instead of traditional encapsulation material yielding inorganic WLEDs. The red part in the EL spectrum of the WLED was compensated after Mn-doped QDs were added, and the CRI of the YAG:Ce3+-based WLED was improved significantly. The measured CRI is 88, which is larger than that of the YAG:Ce3+-based device （CRI-70） and suitable for indoor lighting.