Design And Synthesis Of Dual Emissive Quantum Dots With Tuable Emission Covering The Whole Visible Region

Quantum dots(QDs) were among the most attractive phosphor materials to be exploited for solution-processed optoelectronic applications because of their unique properties. Hence, the development of single phase and low-cost luminescent QD phosphors with broad band emission was most desirable for use as color converters in white-light-emitting-diodes(WLEDs). According to the band gap structure parameters we have obtained in the references, we designed a single component colloidal semiconductor nanocrystal phosphor with broadband emission spectra. This may open a door for on existing technical applications of semiconductor nanocrystals, ranging from LEDs, biomedical labeling, to molecular barcoding. In this thesis, the original works were organized as follows:In the second chapter, according to the band gap structure parameters, we designed a single component colloidal semiconductor nanocrystal phosphor Cu:Cd S/Zn S/Cd S dual emissive quantum dots consisting of a doping-core and a quantum-well separated by a layer of Zn S, which have been well-characterized using a combination of optical and structural techniques. By control of the thickness of Zn S barriers, as-prepared doping-core/quantum-well QDs presented dual emission bands, one of which being attributed to d-cores, namely, a zero-dimension(0D) quantum system, so we called it Doping-PL(photoluminenscence), and the other resulting from q-wells, namely, the two-dimension(2D) quantum systems, herein we named it as Well-PL. The dual emissive peaks are flexibly tunable by simple control of the core size and the well thickness, the emission range of Cd S well layer is 400 nm to 480 nm, and doped emission range is 550 nm to 680 nm, respectively.In the third chapter, we successfully prepared a single component colloidal nanocrystal phosphor consisting of Cu:Cd S/Zn S/Cd Se/Zn S dual-emissive quantum dots by changing the well materials, which has been well characterized using a combination of optical and structural techniques. As-prepared QDs showed dual emissive bands, one of which was attributed to the Cu:Cd S core and the other resulted from the Cd Se quantum well structure. The dual emissive peaks were flexibly tunable ranging from the visible to the near infrared(NIR) region by simple control of the core size and shell thickness, respectively. The emission peaks of the as-prepared samples can be tuned over a range of 550-700 nm for Doping-PL and 480-610 nm for Well-PL. Surface termination with Zn S greatly improved the quantum efficiency(QY) of samples, and resulted in better photochemical and thermal stabilities. A WLED lamp was fabricated using a commercial blue LED chip combined with the optimal phosphors as color converters. As-fabricated WLED showed improved color rendering properties with a CRI of 86, CIE chromaticity coordinates of(0.355, 0.349) and color temperature of 4452 K. These results indicated that these as-prepared single phase phosphors were promising versatile light-emitting materials for various applications ranging from solid-state lighting to bioimaging because of their flexibly tunable dual emission position in the visible to NIR region.