https://libjncir.jncasr.ac.in/xmlui/handle/10572/1539 2026-04-04T05:31:56Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2503 The curious case of CdTe/CdS: photoabsorption versus photoemission Saha, Avijit; Chattopadhyay, Soma; Shibata, Tomohiro; Viswanatha, Ranjani The potential of nanomaterials arises from the fine tuning of material properties by changing their composition, size and shape. Here, we show that by varying the local Cd and Te/S environment using CdTe/CdS as the host, a highly promising photovoltaicmaterial can be easily converted to an efficient photo-emitting material. Thus we demonstrate for the first time that the internal structure can be used to tune the properties of the nanomaterial leading to competing and contrasting applications. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2501 Cu Doping in Ligand Free CdS Nanocrystals: Conductivity and Electronic Structure Study Grandhi, G. Krishnamurthy; Swathi, K.; Narayan, K. S.; Viswanatha, Ranjani Ligand-free Cu-doped CdS nanocrystals (NCs) have been synthesized to elucidate their surface electronic structure. The Cu-doped ligand-free NCs unlike their undoped counterparts are shown to be luminescent. We used this Cu-related emission as a probe to study the nature of the surface trap states that results in negligible luminescence in the undoped NCs. The concentration of the sulfide ligands is shown to play a crucial role in the surface passivation of the NCs. Electrical conductivity of these NCs was also studied, and they were shown to exhibit significant conductivity of similar to 10(-4) S cm(-1). Further we have shown that the electrical conductivity is closely correlated to the surface charge and hence the trap states of the individual NCs have far-reaching consequences in the device optimization. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2502 Large-area luminescent solar concentrators based on 'Stokes-shift-engineered' nanocrystals in a mass-polymerized PMMA matrix Meinardi, Francesco; Colombo, Annalisa; Velizhanin, Kirill A.; Simonutti, Roberto; Lorenzon, Monica; Beverina, Luca; Viswanatha, Ranjani; Klimov, Victor I.; Brovelli, Sergio Luminescent solar concentrators are cost-effective complements to semiconductor photovoltaics that can boost the output of solar cells and allow for the integration of photovoltaic-active architectural elements into buildings (for example, photovoltaic windows). Colloidal quantum dots are attractive for use in luminescent solar concentrators, but their small Stokes shift results in reabsorption losses that hinder the realization of large-area devices. Here, we use 'Stokes-shiftengineered' CdSe/CdS quantum dots with giant shells (giant quantum dots) to realize luminescent solar concentrators without reabsorption losses for device dimensions up to tens of centimetres. Monte-Carlo simulations show a 100-fold increase in efficiency using giant quantum dots compared with core-only nanocrystals. We demonstrate the feasibility of this approach by using high-optical-quality quantum dot-polymethylmethacrylate nanocomposites fabricated using a modified industrial method that preserves the light-emitting properties of giant quantum dots upon incorporation into the polymer. Study of these luminescent solar concentrators yields optical efficiencies > 10% and an effective concentration factor of 4.4. These results demonstrate the significant promise of Stokes-shift-engineered quantum dots for large-area luminescent solar concentrators. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2222 Ligand assisted digestion and formation of monodisperse FeCoS2 nanocrystals Shetty, Amitha; Saha, Avijit; Makkar, Mahima; Viswanatha, Ranjani Digestive ripening of bimetallic magnetic nanocrystals from uniform microsheets to spherical nanocrystals was observed in FeCoS2 nanocrystals leading to the formation of monodisperse nanocrystals. Earlier examples of digestive ripening are associated with the transformation of polydisperse particles to monodisperse particles deriving energetic stabilization from the monodispersity. However, it is interesting to note that in the current case, not only did we observe a transformation from uniform sheets to spherical particles but we also observed it in the absence of thiol, the most commonly used digestive ripening agent. We have then studied the effect of ligands such as oleic acid and oleylamine responsible for this ripening process. Long chain acids were found to be majorly responsible for digestive ripening while the amines assist in the formation of microsheets. A plausible mechanism has then been proposed. Restricted Access 2016-01-01T00:00:00Z