Structural, optical and ion sensing properties of 2-mercaptoethanol capped Mn-doped ZnS nanocrystals
Kuldeep Deka, Manos P.C. Kalita
Superlattices and Microstructures
Zn1-xMnxS (x = 0.005, 0.01, 0.015, 0.02) nanocrystals were synthesized by a chemical route at room temperature. 2-mercaptoethanol was used as capping agent for the nanocrystals. The crystallite sizes (band gaps) have been found to be about 3.5 nm (3.8 eV) for all the Mn-doped ZnS nanocrystals. The photoluminescence spectra exhibit a broad emission centred at 410 nm which has been attributed to the presence of various defects in ZnS nanocrystals and a highly intense yellow emission at 578 nm due to the 4T1 – 6A1 transition of the Mn2+ dopant. The intensity of the yellow emission has been found to be maximum for the 1.5% Mn-doped ZnS nanocrystals. The possibility of the nanocrystals for ion sensing viz. Fe2+, Co2+, Ni2+and Mn2+ through photoluminescence quenching of the yellow emission of the 1.5% Mn-doped ZnS nanocrystals has been investigated. The intensity of the yellow emission has been found to be highly sensitive to the presence of the ions. The limit of detection for the Fe2+, Co2+, Ni2+ and Mn2+ has been found to be 5 μM, 10 μM, 0.5 nM and 1 nM, respectively. For particular high concentration ranges which are different for the different ions, the well-known Stern-Volmer linear relationship between F0/F (F0 and F are the photoluminescence intensities without and with ions) and ion concentration has been found to be obeyed. In case of Ni2+ and Mn2+, in the very low concentration ranges, plots between F0/F and logarithm (concentration) have been found to be linear. The 2-mercaptoethanol capped Mn-doped ZnS nanocrystals thus have the potential for development of phosphorescence sensor for detection of extremely low concentration of ions, particularly Ni2+ and Mn2+.
Fluorescence, Photoluminescence, Chemical stability, Phosphorescence, Sensors, Nanostructures, Materials