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Title: Ternary XInS2 nanocrystals for optoelectronics
Author: Yeom, Inji
ISNI:       0000 0004 6497 6897
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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The primary focus of this thesis is to develop new synthesis routes for core-shell copper indium di-sulphide (CuInS2)–zinc sulphide (ZnS), and core-only silver indium di-sulphide (AgInS2) nanocrystals with enhanced photoluminescence quantum yield (PLQY) and study their application in luminescent concentrators. CuInS2-ZnS nanocrystal photoluminescence (PL) properties were investigated using different synthesis conditions. Through a combination of PL, absorption (Abs), and transmission electron microscopy (TEM), the importance of relative stoichiometry between the two cations (copper and indium) are understood. To further study this effect, different injection temperatures and precursor ratios were employed. It was determined that with increasing indium (In) content, the PL blue shifted while increased PLQY was noted. Optimal synthesis conditions for monodispersed nanocrystals was found to be at an injection temperature of 30°C with a 1:4 Cu:In ratio, which achieved a PLQY of 40%. By using various halide precursor combinations of fluoride, chloride, bromide, and iodide, 16 combinations were evaluated in the control of the reactivity of the two cation precursors. Overall, this study demonstrated that the reactivity of Cu and In can be regulated to a certain extent. Additionally, the halide precursor counter ions potentially provided surface passivation, which enhanced PLQY by up to 60%. The synthesis method established was repeated with replacement of the easily oxidised Cu with more stable Ag to form AgInS2 nanocrystals. It was shown that by-products of Ag and Ag2S nanocrystals were observed, which reduced the overall PLQY. With in-situ PL, synthesis dynamics were examined. Ag2S nanocrystals were formed from the Ag nanocrystals formed prior to sulfur injection. Through changes in reduction temperature and halide precursor combinations, the by-product quantity was reduced and a high PLQY of 89% was achieved. Using AgInS2, the first ternary nanocrystal luminescent concentrator for visible light communication (VLC) was fabricated. Modifying the polymer and nanocrystal concentrations resulted in changes in transmittance and reflectance properties. It was determined that the best combination used was ethyl cellulose 8wt% with 9mg/ml AgInS2 (AIS) nanocrystals. With the addition of a mirror and a low refractive polymer layer, the gain, when compared to a single photodiode (PD), was seven times higher.
Supervisor: Assender, Hazel ; Watt, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available