Investigations on photoluminescence enhancement of poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots

In our work, we focused on the photoluminescence (PL) enhancement of poly(vinyl alcohol) (PVA)-encapsulated Mn2+-doped zinc sulfide quantum dots (ZnS:Mn2+ QDs) synthesized at 80 °C in basic aqueous solutions. The structural, morphological and optical properties were investigated using characterization techniques such as X-ray powder diffraction (XRD), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption and photoluminescence (PL) spectroscopy. According to the results of UV-vis absorption spectra, the optical bandgap of the quantum dots was higher than that of the bulk ZnS due to the quantum confinement effect. The studied result showed that the Mn2+ 4T1 → 6A1 emission intensity at the wavelength of 600 nm significantly increased with the increase of Mn2+ doping content and reached its maximum value at the Mn2+ concentration of 4.5%. In addition, the effect of PVA/Zn2+ molar ratio on the PL enhancement of PVA-encapsulated Mn2+-doped ZnS quantum dots also was systematically investigated and explained in this paper. The studied results indicated the energy transfer process from the ZnS host lattice and PVA capping molecules to Mn2+ centers is more efficient at the optimal PVA/Zn2+ molar ratio of 3 × 10−4. Furthermore, a mechanism for the formation of the PVA-encapsulated Mn2+-doped ZnS quantum has also been suggested in this study.