We present a facile one-pot synthesis and simple surface modification strategies to prepare ternary CuInS2/ZnS quantum dots (CIS/ZnS QDs) functionalized with alkyl-, carboxyl- and hydroxyl-terminated ligands. Photoluminescence quantum yields (PLQY) up to 60% can be achieved for CIS/ZnS QDs synthesized on a gram scale. Aqueous mercaptopropionic acid (MPA) capped QDs are used as a base for further surface modification. On the one hand ligand-solvent interactions have been found to play a major role in the luminescence quenching mechanism of aqueous CIS/ZnS QDs. On the other hand, solvent extraction, immobilization in a polymer matrix or phase transfer greatly enhances the photoluminescence. Quantum yields in solution and in solid matrices differ greatly in the case of aqueous QDs both in polymers and in sol-gel silica. Surface engineered QDs are assessed for their usefulness in LED down-conversion experiments. We demonstrate that down-converter layer properties are not only dependent on the QD type and PLQY, but also on the matrix and the type of ligand shell. Despite significant (up to a factor of two) differences in PLQY between the hydrophobic and hydrophilic dots, their LED conversion efficiencies are comparable and up to 49% and 46% for hydrophobic and for hydrophilic QDs, respectively. Additionally, sol-gel nanocomposites incorporating CuInS2/ZnS QDs with OH-terminated ligands that can withstand 200 h high power blue LED irradiation are presented for the first time
Quantum dots that efficiently emit white light directly or feature a "candle-like" orange photoluminescence with a high Stokes shift are presented. The key to obtaining these unique emission properties is through controlled annealing of the core Cu-In-Ga-S quantum dots in the presence of zinc ions, thus forming Zn-Cu-In-Ga-S solid solutions with different distributions of the substitution and dopant elements. The as-obtained nanocrystals feature excellent quantum yields of up to 82% with limited or even eliminated reabsorption and a color rendering index of bare particles of up to 88, enabling the production of high-quality white LEDs using a single color converter layer. Furthermore, the color properties can be tuned by changing the experimental conditions as well as by varying the excitation wavelength. The multicomponent luminescence mechanism is discussed in detail based on similar literature reports. White LEDs with unparalleled color quality and competitive luminous efficacies are presented herein.
Herein we present the preparation of ultrastable CuInS 2 /ZnS-silica composites able to withstand high density irradiation for more than 100 h without degradation using a blue LED operated at 20 mA forward current. The high photostability is obtained by employing a novel polymer-infused silica/QD composite. The versatility of the (3-mercaptopropyl)trimethoxy-silane/tetraethyl orthosilicate matrix used in this study is demonstrated by incorporating QDs with positively (amine) and negatively (carboxyl) charged ligands yielding transparent and highly luminescent gels with up to 20% solid loading. Quantum yields in solution (40-50%) are retained or even slightly improved in the silica matrix further proving efficient encapsulation without damaging the nanocrystal surface. White LED fabricated from green and orange ternary QDs exhibit a luminous efficacy of 30 lm W À1 and a color rendering index of 87 as compared to a blackbody radiator with 3850 K color temperature.
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