Synthesis and photoluminescence enhancement of PVA capped Mn2+ doped ZnS nanoparticles and observation of tunable dual emission: A new approach

This paper reports the enhanced photoluminescence (PL) property of polyvinyl alcohol (PVA) capped Mn2+ doped ZnS nanocrystals prepared by chemical precipitation method. The surface-modified Mn2+ doped ZnS nanocrystals resulted in the multi-color property. The morphology and crystallite size were characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques. The crystallite size was estimated to be 5 nm from HRTEM and calculated as 2-4 nm from peak broadening of the X-ray diffraction (XRD) pattern with cubic zincblende structure. Increase in the band gap with decrease in the crystallite size was observed from the UV-visible absorption spectrum, which confirms the quantum confinement effect. The room temperature photoluminescence (PL) emission measurements revealed the presence of blue (427 nm) and near IR reddish-orange (752 nm) emission bands in addition to the typical yellow-orange (585 nm) bands in all the Mn2+ doped samples, which were attributed due to transition within the 3ds configuration of Mn2+ ions incorporation in ZnS host under UV excitation at 320 nm. As far as we know, the reddish-orange bands at 752 nm near IR region along with the blue and yellow-orange colored PL are reported for the first time. In this way, the PL color from these ZnS nanocrystals can be tuned from UV to near infrared region (IR). The synthesized ZnS:Mn NPs can be further functionalized for using them as biolabels.