Effect of pyridine capping on morphological and optical properties of ZnS:Mn²⁺ core–shell quantum dots

In this work, pyridine-coated ZnS:Mn²⁺ core–shell quantum dots are synthesized through a simple soft chemical route, namely the chemical precipitation method and the effect of pyridine capping has been studied on the morphological and optical parameters of the quantum dots. Morphological properties are investigated through X-ray diffraction (XRD) and transmission electron microscopy. XRD measurements showed that both the ZnS:Mn⁺ quantum dots and the ZnS quantum dots possessed a zinc blende structure and the crystal structure is not changed with the capping and Mn²⁺ doping. Bandgap measurements are made through UV–visible spectroscopy. FTIR spectra gave the direct evidence that pyridine shells have been successfully coated on the ZnS:Mn⁺ quantum dots. Room-temperature photoluminescence spectrum of the undoped sample, exhibited only a blue-light emission peaked at 422.6 nm under UV excitation. However, from the Mn²⁺ doped samples, a yellow-orange emission from the Mn²⁺ (⁴T₁ − ⁶A₁) transition has been observed along with the blue emission. For 1 % capping concentration efficient emission of yellow-orange light with the emission peak at 590 nm is observed along with the suppressed defect related blue emission. As pyridine is an excellent capping agent for functionalization of quantum dots by ligand exchange process so the synthesized highly fluorescent core–shell quantum dots are very important for biological applications.