Epitaxial growth of colloidal hydrophilic lattice matched HgTe/CdTe core/shell nanocrystals for UV luminescence

The present work reports a bottom up approach to synthesize water dispersed and highly luminescent hydrophilic l-cysteine ethyl ester hydrochloride (LEEH) capped and lattice matched HgTe/CdTe core/shell nanoparticles (NPs). The LEEH concentration was varied to optimize the luminescent properties of the core/shell NPs by controlling the particle size and its size distribution. FTIR measurements confirm the LEEH capping to the core/shell nanostructures. Transmission electron microscopy (TEM) measurements identify the HgTe, core size as 2.0 nm and that of the shell, epitaxially grown over the core has the thickness as 0.8 nm which corresponds to 2.1 monolayers of CdTe for an optimum LEEH concentration of 4.8 mM. The absorption studies showed excitonic absorption at 293 nm for the optimized core/shell NPs. More than three fold increase of fluorescence (FL) yield in case of the core/shell structure compared to the core has been observed in this study. X-ray diffraction and micro-Raman studies do not show an alloying effect. The crystalline sizes estimated both from X-ray diffraction and HRTEM are found to be comparable.