Temperature and capping dependence of NIR emission from PbS nano–microcrystallites with different morphologies

We have prepared various morphological PbS nano–microcrystallites by three different techniques namely, facile hydrothermal technique, chemical bath deposition and surfactant-assisted solution growth. This is the first report on the photoluminescence emission bands around 0.60 eV and their evolution with temperature in dendrite/rod shaped PbS microstructures. The 0.60 eV band, which is common to all our samples, quenches at low temperatures up to 60–70 K. However, after surface capping with mercaptoethanol (C2H5OSH), a new band around 1.0 eV appears and evolves with temperature, indicating bimodal size distribution in these dendritic nanostructures. On the other hand, the samples grown by chemical bath deposition exhibited this bimodal size distribution even without surface capping. However, after surface is protected with mercaptoethanol, enhancement in 0.60 eV band intensity (4–5 times) with lowering temperature is a specific characteristic of these samples. Anomalous temperature dependence of photoluminescence intensity with corresponding changes in full width at half maxima is an interesting behaviour that indicates thermalization of the carriers in nano-particles of different sizes. We note that the surface capping is an important step in understanding the bimodal nature of hydrothermal grown nanostructure and microstructure. The present results indicate the possibility of white light emission from dendritic structures.