Enhancement of photoluminescence of ZnS : Mn nanocrystals by hybridizing with polymerized acrylic acid

Mn2+-doped ZnS (ZnS:Mn) nanocrystals are hybridized with polymerized acrylic acid. By using either acrylic acid (AA) monomer or poly(acrylic acid) (PAA) polymer as a starting material, differences in optical and chemical properties of hybrid nanocrystals are compared. The enhancement of photoluminescence at 580 nm due to the d–d transition of Mn2+ is larger for ZnS : Mn nanocrystals modified by AA and aged at 80°C for tage hours for polymerization (the sample ZSAA5-tage, 0≤tage≤24), as compared with that modified by PAA (the sample ZSPAA). The CO groups and ZnS are excited simultaneously by a light of 350 nm to stimulate energy transfer to Mn2+ ions jointly. In the samples ZSAA5-tage, oxygen atoms of carboxyl groups form SOC(O) bonds and the valence number of sulfur increases from −2 to+6, as confirmed by infrared absorption and X-ray photoelectron spectra. As a result, electrons of sulfur atoms are pushed toward carboxyl groups to enhance the emissions from both CO groups and Mn2+ ions. In contrast, the sample ZSPAA exhibits predominant interaction of CO groups with metallic ions to form COMe bonds (Me=Zn2+ and Mn2+). This decrease in the amount of CO groups reduces energy transfer to Mn2+ ions.