Luminescent ZnS:Mn/thioglycerol and ZnS:Mn/ZnS core/shell nanocrystals: Synthesis and characterization

The synthesis and photoluminescent properties of Mn2+-doped ZnS nanocrystals coated with an organic shell of thioglycerol and an inorganic shell of ZnS are reported in this paper. The photoluminescence spectra of bare ZnS:Mn nanocrystals exhibited a dominant ultraviolet–violet emission peaked at the wavelength range of 395–450 nm and an weak orange emission peaked at the wavelength range of 580–600 nm. The ultraviolet–violet emission was attributed to the surface defect states. The orange emission was assigned to the 4T1–6A1 transition of Mn2+ ions. These two channels of radiative recombination compete with each other. The coating ZnS:Mn nanocrystals with the thioglycerol shells or the ZnS shells reduced the surface defects and led to the enhancement of the emission of Mn2+ ions. On the other hand, the overcoating ZnS:Mn nanocrystals by thioglycerol shell restricted the growth of the nanocrystals, while the overcoating ZnS:Mn nanocrystals by ZnS shells made the band edge of the ZnS:Mn/ZnS core/shell nanocrystals shift to the lower energy side (the red shift) compared with the bare ZnS:Mn nanocrystals as observed in both the absorption and the photoluminescence excitation spectra.

► The coating ZnS:Mn nanocrystals with a thioglycerol shell prevents their growth.
► The coating ZnS:Mn core with a ZnS shell made its band edge shift to the low energy.
► The coating ZnS:Mn core with the TG and ZnS shells enhanced the emission of Mn2+.
► The observed phenomena clearly exhibit the quantum confinement effect.