We report the optical properties of polyvinyl-pyrrolidone (PVP) and the influence of PVP concentration on the photoluminescence spectra of the PVP (PL) coated ZnS : Ni nanocrystalline thin films synthesized by the wet chemical method and spin-coating. PL spectra of samples were clearly showed that the 520 nm luminescence peak position of samples remains unchanged, but their peak intensity changes with PVP concentration. The PVP polymer is emissive with peak maximum at 394 nm with the exciting wavelength of 325 nm. The photoluminescence exciting (PLE) spectrum of PVP recorded at 394 nm emission shows peak maximum at 332 nm. This excitation band is attributed to the electronic transitions in PVP molecular orbitals. The absorption edges of the PVP-coated ZnS : Ni0.3% samples that were shifted towards shorter wavelength with increasing of PVP concentration can be explained by the absorption of PVP in range of 350 nm to 400 nm. While the PVP coating does not affect the microstructure of ZnS : Ni nanomaterial, the analyzed results of the PL, PLE, and time-resolved PL spectra and luminescence decay curves of the PVP and PVP-coated ZnS : Ni samples allow to explain the energy transition process from surface PVP molecules to the Ni2+centers that occurs via hot ZnS.

A study has been carried out on the Cu doping and PVA capping induced optical property changes in ZnS : Cu nanocrystalline powders and thin film. For this study, ZnS : Cu nanopowders with Cu concentrations of 0.1%, 0.15%, 0.2%, 0.3% and 0.4% are synthesized by the wet chemical method. The polyvinyl alcohol (PVA)-capped ZnS thin film with 0.2% Cu concentration and various PVA concentrations are prepared by the spin-coating method. The microstructures of the samples are investigated by the X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM). The results show that the prepared samples belong to the wurtzite structure with the average particle size of about 3–7 nm. The optical properties of samples are studied by measuring absorption and photoluminescence (PL) spectra in the wavelength range from 300 nm to 900 nm at 300 K. It is shown that the luminescent intensity of ZnS : Cu nanopowders reaches the highest intensity for optimal Cu concentration of 0.2% with the corresponding values of its direct band gap estimated to be about 3.90 eV. While the PVA coating does not affect the microstructure of ZnS nanometerials, the PL spectra of the samples are found to be affected by the PVA concentration as well as the exciting power density. The influence of the polymer coating on the optical properties can be explained by the quantum confinement effect of ZnS nanoparticles in the PVA matrix.

By a co-precipitation method, we have synthesized Mn-doped ZnS  nanoparticles with the Mn contents of 2-12 mol%from solutions Zn(CH3COO)2 0.1M, Mn(CH3COO)2 0.1M and Na2S 0.1M. XRD patterns, TEM images show these nanoparticles possess cubic crystalline structure with average size about of 3-4 nm. Photoluminescence spectra of samples present a broad yellow-orange band of 603 nm, its intensity increases with the increasing of Mn content from 2 mol%  to 8 mol % when the excitation power density increases from 0.06 W/cm2 to 0.21 W/cm2. However, while the intensity increases with the increasing of Mn content its position is almost unchanged. This band is attributed to the radiativetransition of electron in 3d5unfulfilled shell of Mn2+ ions [4T1(4G)→ 6A1(6S). The absorption spectra show main bands at 308-328 nm with strong intensity related to absorption near band edge of ZnS crystal. These bands related to Mn2+ absorption also appeared with weaker intensity. The photoluminescence excitation spectra monitored at the yellow-orange band  exhibited a band at 354 nm with strong intensity and  bands at 432, 466, 497 nm with weaker intensity.The band of 354 nm is attributed to the absorption near band edge. Simultaneously, the  bands of 432, 466, 497 nm are attributed to the absorption transitions of electrons from ground state 6A1(6S) to excited states 4T2(4D), 4A1(4G) - 4E(4G), 4T2(4G) of Mn2+ions in ZnS crystal, respectively.

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