Tran Minh Thi

The effect of polyvinylpyrrolidone on the optical properties of the Ni-doped ZnS nanocrystalline thin films synthesized by chemical method

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 520nm luminescence peak position of samples remains unchanged, but their peak intensity changes with PVP concentration. The PVP polymer is emissive with peak maximum at 394nm with the exciting wavelength of 325 nm. The photoluminescence exciting (PLE) spectrum of PVP recorded at 394nm 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 350nm 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.

STUDY OF MICROSTRUCTURE AND OPTICAL PROPERTIES OF PVA-CAPPED ZnS: Cu NANOCRYSTALLINE THIN FILMS

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.

Thin films containing Mn-doped ZnS nanocrystals synthesised by chemical method and study of some of their optical properties

In this article, we present the optical properties of thin films containing Mn-doped ZnS nanocrystals synthesised by the chemical method. The ZnS nanoparticles within the polymer matrix (polyvinyl alcohol) were investigated by SEM and TEM images and analysed by X-ray diffraction. The effect of polymer concentration on the direct band gap of Mn-doped ZnS thin films was calculated from the data for absorption measurements. The values of the band gap are in the range of 3.73–3.90 eV. In addition, we discuss the photoluminescence of these films.

Absorption and Radiation Transitions in Configuration of Mn-Doped ZnS Nanoparticles Synthesized by a Hydrothermal Method

The Mn-doped ZnS nanoparticles with Mn content of 0–15 mol% were synthesized by a hydrothermal method from the solutions Zn(CH3COO)2 0.1 M, Mn(CH3COO)2 0.01 M, and Na2S2O3 0.1 M at 220°C for 15 h. These nanoparticles presented the cubic structure with average particle size about 16 nm. The yellow-orange photoluminescence (PL) band at 586 nm was attributed to the radiation transition of the electrons in 3d5 unfilled shell of Mn2

INFLUENCE OF THE CAPPED POLYMER ON THE OPTICAL OF ZnS:Cu NANOCRYSTALLINE THIN FILMS

The ZnS:Cu nanopowders were synthesized by the wet chemical method with Cu con- centrations of 0.1, 0.15, 0.2, 0.3 and 0.4%. The microstructure of samples was investigated by the X-ray diffraction (XRD) measurement. The results show that the prepared samples belong to the Wurtzite structure with the average particle size of about 3-7 nm. The highest luminescence intensity of ZnS:Cu nanopowders corresponds to sample with Cu concentration of 0.2%. To in- vestigate the effect of polyvinylacohol (PVA) on the structure of ZnS:Cu, we have prepared the polyvinylacohol (PVA)-capped ZnS:Cu thin films with a Cu concentration of 0.2% by dip-coating method. The PVA did not affect the microstructure of ZnS nanomaterials. The optical properties of samples were studied by measuring the absorption and the photoluminescence spectra in the wavelength range from 300 nm to 900 nm at room temperature. The value of direct band gap is about 3.8 eV. The dependence of the photoluminescence (PL) spectra of samples on the exciting power density, their time-resolved-luminescence spectra were also investigated.

The effect of ultraviolet irradiation on the optical properties of ZnS: Mn synthesized by hydrothermal method and using thioglycolic acid

ZnS:Mn nanoparticles (C_Mn = 15 mol%) were synthesized from thioglycolic acid HSCH₂COOH (TGA) and initial chemicals Zn(CH₃COO)₂.2H₂O, Mn(CH₃COO)₂.4H₂O by the hydrothermal method at 220 °C for 5h and 20 h. The XRD patterns show that nanoparticles possess a hexagonal wurtzite crystalline structure with size about of 10-20 nm. Due to TGA creating a S^2- source, the hydroxyl groups of a-hydroxyl acetic acid (glycolic acid) molecules with electron pairs can be coordinated with vacancy 3d (t_2g) orbitale of Zn²⁺, Mn²⁺ ions and to form surface passive shells of ZnS and ZnS:Mn. The effect of ultraviolet (UV) irradiation on the photoluminescence (PL) spectra of coated ZnS, ZnS:Mn nanoparticles also was investigated by UV wavelength of 337 nm. The results show that the yellow-orange band intensity increases with increasing UV irradiation time, but their PL peak position unchanged. These results can be explained by the energy transition process, polymerization, photochemical process and gradual diffusion of Mn²⁺ into a ZnS crystal network due to the activity of this UV irradiation.

The Optical Property of Mn- Doped ZnS Nanoparticles Synthesized by a Co-precipitation Method

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/cm to 0.21 W/cm. However, while the intensity increases with the increasing of Mn content its position is almost unchanged. This band is attributed to the radiative transition of electron in 3dunfulfilled shell of Mn ions [T1( G)→A1( S). 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 Mn 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 A1( S) to excited states T2( D), A1( G) E(G), T2( G) of Mnions in ZnS crystal, respectively.

Influence of Mn 2+ Concentration and UV Irradiation Time on the Luminescence Properties of Mn-doped ZnS Nanocrystals

ZnS:Mn were prepared by wet chemical method with Mn doping concentration from 0 at% to 12 at%. The structure and particle size of the obtained powders were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and shown that all samples are single phase with sphalerite crystal structure and average particle size of about 5 - 7 nm. The dependence of Mn2+ ions doped concentration, and UV irradiation time on the luminescent intensity of ZnS:Mn nanocrystals was discussed.