Preparation And Optical Properties Of ZnS Low - Dimensional Materials

Ⅱ-Ⅵ semiconductors have attracted much attention due to their unique properties and applications. Zinc sulfide semiconductor material has been studied for a variety of applications, including light-emitting diodes, electroluminescence, flat panel displays, optical sensors, phosphors etc. As a compound semiconductor, ZnS film is a direct wide band gap with band gap energy (Eg=3.7eV). Owing to the large band gap of ZnS, it can easily host different transition metal ions as luminescent centers. Some experimental results showed that transition metal Mn2+ions doped nanostructures exhibit prominent yellow emission, which can be used as efficient phosphors. Mn-doped ZnS crystals have good luminescent properties and are currently of great interest owing to their pronounced electrical, magnetic and new possibilities of application in white LEDS and optoelectronics. For these materials people have brought some promising results, including ZnS:Mnnanoparticles and nanowries, nanoribbons. ZnS:Mn thin films have been prepared on GaN substrates by pulsed laser deposition, and their structures and optical properties have been investigated. On the other hand, ZnS was successfully used as a photocatalyst for the degradation of various pollutants under UV light irradiation, and ZnS spheres displayed effective photocatalytic activity under UV irradiation. As a photocatalyst, ZnS has been examined for degradation of water pollutants, reduction of toxic heavy metals and water-splitting for H2evolution. Generally, as is known, the photoactivity of semiconductor materials can be intensively influenced by their structure and particle size, in which particle size is a particularly important factor. The smaller size and rough surface of the nanocrystals could result in their high-surface area, which could provide more ideal adsorption sites for reactant molecules, but recent studies showed that particle size was not the main factor in determining the photocatalytic activity of the ZnS nanoparticles.Therefore, it is a good choice to prepare a novel ZnS structure, which has better photocatalytic degradation of dye.This The discussions are presented as follows:Firstly, the ZnS:Mn ceramics with different doping content were successfully synthesized by the solid-state reaction method under1050℃.The morphologies of the obtained ZnS:Mn ceramics were thoroughly studied using scanning electron microscopy, which show that the ball-milling have an effect on the density of ZnS:Mn ceramics.The Structures of ZnS:Mn ceramicswere thoroughly studied using x-ray diffraction. From the room temperature photoluminescence (PL) measurements of these ZnS:Mn ceramics only one emission band located at～580nm was observed. The yellow emission band (580nm) exhibited a red shift (from577to587nm) with the doping concentration from1%to5%while the luminous intensity became weak and the crystal quality poorer.Secondly, ZnS:Mn thin films have been prepared on GaN substrates by pulsed laser deposition, and their structures and optical properties have been investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), photoluminescence (PL) measurement, electron paramagnetic resonance. It shows that thin films have a cubic structure oriented mainly along (111) plane, and the crystal qualities were optimized via deposition conditions. Room temperature PL measurements with a325nm excitation show that there are three emission bands located at434nm,465nm and～600nm, respectively. The intensity ratio of the blue emission to the orange is determined by the deposition conditions. The broad orange emission (600nm) consisted of two emission bands centered at590and615nm, shows a red shift from5to70K, then a blue one up to300K. The tunable blue and orange dual color emissions can be used as a warm white lighting emitting device.Thirdly, ZnS microflakes and films were deposited on Au-coated and uncoated quartz substrates by thermal evaporation method. Structures and morphologies were thoroughly studied using x-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. Raman spectra measurements indicated that more than5times larger enhanced Raman scattering for the microflakes than the ZnS film were observed, the enhanced Raman scattering is mainly associated with the surface defects. The photocatalytic degradation test showed that the ZnS microflakes exhibit better degradation of rhodamine B (RhB) with the degradation rate constant of3.5×10-3min-1, which is more than3times larger than that of ZnS films of1.0×10-3min-1, the better photodegradation efficiencies can be attributed to the larger specific surface area.