Preparation And Optics Properties Of Doped ZnS Nanopowders

ZnS nano-semiconductor is a direct band gap semiconductor.Its band gap?3.67eV?is much wider than that of bulk materials.Owing to the high transmittance in the infrared band,excellent photocatalytic performance,narrow fluorescence emission band,low toxicity,high wear resistance and shading coefficient,it has been widely used in biology,medicine,sensors,detectors and other fields.In this paper,firstly,ZnS nano-powders were synthesized by hydrothermal method.The effects of reaction temperature,holding time and raw material ratio on the structure,morphology and luminescent properties of ZnS nano-powders were investigated.Then,ZnS nano-powders doped with different surfactants,transition metals and rare earth ions were prepared.Their effects on the structure,morphology and luminescent properties of the samples were discussed,and the luminescent mechanism was investigated systematically.ZnS nano-powders synthesized at different reaction temperatures were prepared.The results show that the average particle size decreases but the dispersion increases with the increase of hydrothermal temperature,and the samples are nearly spherical.On the other hand,the wide emission band from 400 nm to 600 nm can be observed.With the increase of hydrothermal temperature,the emission peak shifts from 445nm to 460 nm,and the emission intensity increases 4.4 times.ZnS nano-powders synthesized at different holding time were prepared.The results show that the average particle size of the samples is in the range of 15-19 nm which increases slightly with the increase of holding time,and the samples are nearly spherical;with the extension of holding time,the emission peak is red-shifted from457 nm to 464 nm,and the emission intensity is slightly enhanced.ZnS nano-powders synthesized at different S/Zn ratios were prepared.The results show that with the increase of S/Zn molar ratio,the average particle size increases and the dispersion increases.When the molar ratio of S/Zn is less than or equal to 1,a wide emission band from 400 nm to 600 nm at 450 nm is observed.While the molar ratio of S/Zn continues to increase,the emission peak is red-shifted from 450 nm to 540 nm.ZnS nano-powders synthesized with different surfactants were prepared.The results show that with the addition of the surfactants,the shape of ZnS particles does not change,and it still retains the nearly spherical shape.Though it has a slight effect on the particle size and dispersion.With the addition of PEG-2000 and CTAB,the emission intensity is enhanced,but with the addition of SDS,the emission intensity is slightly reduced.ZnS nano-powders synthesized with different concentrations of CTAB were prepared.The results show that the addition of CTAB does not change the phase structure of ZnS nanoparticles but decreases the crystalline size slightly,and all samples are sphalerite.However,the addition of proper amount of CTAB in the preparation process greatly improves the emission intensity.The samples with a diameter of¹0-12 nm have a broad emission band centered at 457 nm with full width at half maximum?FWHM?of 113 nm.As prepared ZnS nanoparticles have potential application in nanoscale optoelectronic fields.Ni²⁺doped ZnS nano-powders were prepared.The results show that a small amount of Ni²⁺doping has little effect on the growth of ZnS nano-powders.However,Ni²⁺doping strongly affects the optical properties of ZnS nanopowders.The emission peak of ZnS nano-powder is blue shifted with the increase of Ni²⁺content.At the low temperature of 600 ^oC?compare with 1020 ^oC?,the sphalerite phase has been transformed into wurtzite phase.The annealing behavior changes the particle size of ZnS nano-powders from 20 nm to 1?m.After annealing,three new emission peaks appeare,which are located at 490 nm,547 nm and 580 nm respectively.Er³⁺and Yb³⁺co-doped ZnS nano-powders were prepared.The results show that the samples prepared by hydrothermal method do not show obvious characteristic luminescence peaks of Er³⁺,but the samples prepared by solid-state method via introducing NaF do.The crystal phase of ZnS does not change with the introduction of NaF.A broad emission band from 400 nm to 650 nm centered at⁵00 nm and a weak emission peak positioned at 525 nm can be observed under the excitation of 373 nm.Besides,a relatively weak emission band centered at about 567nm and a strong and sharp emission band at 663 nm can be observed under the excitation of 980 nm.The up-conversion emission intensity is 17 times that of the ZnS:Er³⁺,Yb³⁺sample.In addition,the influence of different metal ions doping on the luminescent properties was further studied.It is found that the emission intensity reaches a maximum when Na⁺is introduced,and the up-conversion emission intensity reaches a maximum when Li⁺is introduced,which is 25.6 times of the ZnS:Er³⁺,Yb³⁺nanocrystals.