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RGB light emitting ZnSe based nanocrystals: ZnSe (blue), ZnSe:Cu (green) and ZnSe:Mn (red) were synthesized by capping the surface of the nanocrystals with oleic acid. The obtained nanocrystal powders were characterized by using XRD, HR-TEM, ICP-AES, FT-IR, and FT-Raman spectroscopies. The optical properties were also measured by UV/Vis and photoluminescence (PL) spectroscopies. The PL spectra showed broad emission peaks at 471 nm (ZnSe), 530 nm (ZnSe:Cu) and 665 nm (ZnSe:Mn), with relative PL efficiencies in the range of 0.7% to 5.1% compared to a reference organic dye standard. The measured average particle sizes from the HR-TEM images for those three nanocrystals were 4.5 nm on average, which were also supported well by the Debye-Scherrer calculations. The elemental compositions of the ZnSe based nanocrystals were determined by ICP-AES analyses. Finally, the drawn CIE diagram showed the color coordinates of (0.15, 0.16) for ZnSe, (0.22, 0.57) for ZnSe:Cu, and (0.62, 0.35) for ZnSe:Mn respectively, which were fairly well matched to that of the RGB color standards.

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Colloidal l‐cysteine (Cys)‐capped ZnS:Mn nanocrystals were synthesized and exposed to various pH conditions to modify their surface for further applications as photo‐chemical sensors. The observed zeta‐potential values indicated that the ZnS:Mn–Cys nanocrystals formed positive charged nanocrystal surface at pH 3 condition. Therefore, they were considered to be applied as an anion sensor. As a result, the fluorescence of the ZnS:Mn–Cys‐pH 3 nanocrystals was exclusively quenched by the addition of nitrite (NO2−) ions. In addition, the ZnS:Mn–Cys nanocrystals, which were exposed to pH 7 and pH 13, formed negatively charged surfaces, which were presumed to be applied as cation photosensors. Consequently, the fluorescence of the ZnS:Mn–Cys‐pH 7 nanocrystals were amplified by the addition of Zn2+ ions, whereas the most added metal ions caused quenching of the emission lights of the ZnS:Mn–Cys‐pH 7 nanocrystals. Moreover, the fluorescence of the ZnS:Mn–Cys‐pH 13 nanocrystals was quenched only when Cu2+ ions were added.

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