ABSTRACT
Recently, quantum dots (QDs) have been successfully developed as efficient color converters for light-emitting diodes (LEDs) display due to excellent optical properties of QDs. Herein, we demonstrate a new approach to form metal oxide layers (or metal oxide coating) on the exterior surface of gradient alloy QDs (the most advanced chemical architecture QDs developed thus far wherein the lattice parameter from the core to shell is changing in a gradient fashion) in order to improve the photochemical stability and photoluminescence efficiency. The resulting CdO-treated QDs are incorporated into polymer matrix films to fabricate a backlight unit as a part of display panel wherein CdO-treated gradient alloy QDs are utilized as color converters upon the blue-LED excitation. The fabricated 9.7 in. iPad 2 tablet liquid crystal display panel exhibited an excellent uniformity in terms of CIE chromaticity, luminance, and bright variation and superb durability test results (maintenance of ca. 110% brightness compared to initial value even after 3 weeks of operation).
ABSTRACT
Highly efficient blue-emitting CdSe-derived core/shell gradient alloy quantum dots (CSGA QDs) with photoluminescence quantum yield (PL QY) of ca. 90% have been synthesized through a facile "one-pot" approach. CdSe nuclei are initially formed as core and gradient alloy shells such as CdSexS1-x/ZnSeyS1-y simultaneously encapsulate the preformed CdSe core in an energy-gradient fashion eventually followed by coating with ZnS shells due to the faster precursor reaction kinetics of Cd and Se compared to analog of Zn and S. During the formation of core/shell structure, red-shifting of absorption/emission peaks followed by blue-shifting of analogues were observed due to the intradiffusion of sulfur anion to CdSe luminescent center. In this gradient architecture, interfacial lattice strain can be effectively alleviated, and thus high PL QY (ca. 90%) and enhanced photochemical stability can be achieved. The synthesized blue-emitting gradient alloy QDs with superior optical properties tunable in the range of 450-490 nm can be used for highly efficient blue-emitters and potentially applicable for the fabrication of white-light LEDs.
ABSTRACT
Several zinc alkyldithiocarbamates [Zn(S(2)CNR(2))(2)] were synthesized, and their thermal decomposition in the presence of alkylamines was studied in order to understand the formation of metal sulfide nanoparticles. The major intermediates and side products were isolated under various conditions and characterized by NMR spectroscopy and LC-MS. The analysis results showed that nucleophilic attack of the metal-coordinated amine on the most electron-deficient thiocarbonyl carbon of the alkyldithiocarbamate ligands at high temperature initiated the decomposition to generate thiourea, hydrogen sulfide, and solid metal sulfide nanoparticles. From the proposed decomposition mechanism, the role of amines in thermolysis was studied, and methods for synthesizing various metal sulfide nanoparticles were generalized. Formation of the desired products was confirmed by carrying out model experiments.
