Preparation Of ZnS, ZnS:Mn Nanomaterials And Study On Their Performance

ZnS is a kind of important ?-? group compound semiconductor material,having good optical and electrical properties,and it has been widely used in optoelectronic devices,light-emitting diodes,sensors,detectors,solar cells and chemical engineering,etc.ZnS:Mn crystals show excellent optical properties by doping Mn in ZnS.Especially,the different nanostructures of ZnS often exhibit special photoelectric performances which are different from its bulk material due to quantum confinement effect.ZnS,ZnS:Mn films and their nanostructures were prepared on Si substrate using pulsed laser deposition technique and hydrothermal method respectively,and the influence of different growth conditions on the structure,morphology and optical properties were studied.Then,ZnS:Mn films and its nanoparticles were deposited on GaN substrates,and ZnS:Mn/GaN composite system can emit white light by reasonably adjust the growth parameters and post-annealing treatment conditions of the films.In addition,in order to improve the quality of white light emission,ZnO thin films or ZnO nanorods were inserted as the middle layer,then ZnS:Mn/ZnO/GaN composite system and its core-shell nanorods array which have good white light emission performance were obtained.The electroluminescent characteristics of ZnS:Mn/ZnO/Ga N core-shell nanorods array device were preliminary studied.Finally,ZAZ?ZnS/Au/ZnS?ZnS/Au/ZnO?transparent conductive tri-layer films were prepared on transparent quartz substrates,and their photoelectric properties were studied in detail.Specific contents are as follows:1.ZnS and ZnS:Mn films were grown on Si?100?substrates using PLD technology under different experimental conditions.By utilizing X-ray diffraction?XRD?,atomic force microscope?AFM?and photoluminescence?PL?technology,the structure,morphology and luminescence properties of ZnS and ZnS:Mn films were studied.The results show that,the prepared ZnS is polycrystalline film,and its PL peak located at 425 nm and 445 nm.When the substrate temperature increases from room temperature to 400 ?,the obtained ZnS:Mn is also polycrystalline film,however,when the substrate temperature increases up to 500 ? and 600 ?,the obtained ZnS:Mn is single crystal film,and there is only one strong diffraction peak near 28.5°,which is belong to cubic ?-ZnS?111?orientation.With the increase ofsubstrate temperature,the diffraction peak gradually becomes strong and sharp,which indicates that the film quality is gradually getting better.With the increase of annealing temperature,the crystallization quality of ZnS:Mn films is improved.At the same time,we also found that the substrate temperature and annealing temperature had a great influence on the photoluminescence properties of ZnS:Mn thin films.With the increase of temperature,the PL intensity of orange-red light around 590 nm which is ascribed to 4T1-6A1 emission of Mn2+ gradually increases,along with the blueshift of the peak.2.ZnS nanostructures were grown on Si?100?substrate using hydrothermal synthesis method under different experimental conditions.It is found that,the luminous performance of ZnS spherical nanoparticles is best which were obtained using Zn?NO3?2·6H2O as Zn source,thiourea?SC?NH2?2?as S source.Based on this,the influences of solution concentration,growth temperature and seed layer on the crystal structure and luminescence properties of ZnS spherical nanoparticles were studied.The results show that,under different preparation conditions,all the spectrum of the samples is a 400⁷00nm wide band,which is composed of green emission band centered near 520 nm and a shoulder peak around 570 nm.When the concentration of solution is 0.03 mol/L and the growth temperature is 140?,the luminous intensity of ZnS spherical nanoparticles is the largest.However,for the ZnS nanoparticles grown on ZnS seed layer,the emission peak position blue shifts to about 500 nm,and the PL intensity decreases.In addition,ZnS:Mn nanostructures were prepared using Mn?CH3COOH?2·4H2O as the doping source,and studied the effects of Mn doping concentration on its structure and luminescent properties.SEM results showed that the surface morphology is also spherical particles.Compared with pure ZnS,the average particle size decreases after Mn is doped.As the doping concentration increases,the diffraction peak shifts to the small angle.As Mn doping concentration increases from0.5% to 2%,the PL intensity of 4T1-6A1 emission from Mn around 580 nm increases.However,when more than 2%,the luminous intensity decreases.3.ZnS:Mn films were prepared on GaN substrates using PLD technique and the effects of substrate temperature and annealing temperature on luminescence properties of ZnS:Mn/GaN composite systems were studied.The results found that,the PL spectrum of ZnS:Mn/GaN includes orange red light peaked around 600 nm and blue light centered at 440 nm.ZnS:Mn/GaN composite systems can emit white light by appropriatly adjusting the proportion of blue light and red light emission intensity.However,in order to obtain high quality white light emission,the green light should be emitted out from the composites,according to the three primary colors?red,green and blue?superposition principle.Therefore,utilizing the favorable condition that ZnO can emit deep level emission around 550 nm,ZnO thin films or ZnO nanorods were inserted between GaN substrate and ZnS:Mn films,then ZnS:Mn/ZnO/GaN composite system and its core-shell nanorods array device were obtained.The PL spectra of ZnS:Mn/ZnO/GaN cover from ultraviolet to red light?350⁷00nm?in the entire area of the visible light region.The color coordinates are?0.3103,0.3063?and?0.3347,0.318?respectively,very close to the standard white light area?0.33,0.33?.This indicates that the prepared ZnS:Mn/ZnO/GaN core-shell nanorods array device can emit intensive white light.In addition,ZnS:Mn nanoparticles were prepared on GaN substrates using hydrothermal systheis method,and its structure and PL properties were studied in detail.The studies show that,the PL spectrum of ZnS:Mn/GaN nanoparticles consists of three emission bands,that is,the blue light at440 nm emitting from GaN,the green light near 500 nm which is attributed to the recombination of electrons from the energy level of S vacancies?neutral donor?with the holes from the energy level of Zn vacancies?neutral acceptor?with the band gap,and orange light at 580 nm which origins from 4T1-6A1 transition of Mn ions.Through the analysis,the CIE coordinates of its luminous is?0.3319,0.3196?,close to white light emission.In addition,the electroluminescent?EL?characteristics of ZnS:Mn/ZnO/Ga N core-shell nanorods array device were preliminary studied.It is found that,under the forward voltage,the EL spectrum is composed of blue-violet emission around 415 nm and orange light at 610 nm.With the increase of excitation voltage,the luminous intensity gradually increased.The color coordinates of EL spectra are very close to the white area.Through the fitting multi-peak processing,the EL spectrum is composed of 400,430,570 and 630 nm.The specific luminescence mechanism of the heterojunction devices and its availability needs further research.4.ZnS/Au/ZnS transparent conductive tri-layer films were prepared on transparent quartz substrates using PLD technique.The influences of Au thickness,ZnS thickness,substrate temperature and annealing temperature on photoelectric performance of ZnS/Au/ZnS tri-layer films were studied in detail.The results show that,the carrier concentration and sheet resistance of the tri-layer films are mainly depends on the thickness of Au layer.When the thickness of Au layer and ZnS layer are 10 nm and 60 nm respectively,the tri-layer film has the highest quality factor of 3.34×10-3 ?^-1,and the average transmittance is 81% in the visible light area,sheet resistance is 36.4 ?/sq,carrier concentration is 1.91×1021cm-3.By studying the effects of substrate temperature and annealing temperature on the photoelectric performances of ZnS/Au/ZnS tri-layer composite films,it is found that,the tri-layer films prepared at room temperature has the best photoelectric performances.When it is annealed at proper temperatures,its photoelectric properties can be improved.When the annealing temperature is 200?,the quality factor of tri-layer films is 5.48×10-3?^-1,and the average transmittance is 82.7%,sheet resistance is 27.3?/sq.In addition,the photoelectric characteristics of ZnS/Au/ZnO composite films were preliminary studied.