Researches On Synthesis And Photoluminescent Properties Of Nano-structure Zinc Silicate By Solvothermal Method

Mn doped Zn₂SiO₄phosphors were synthesized by sovothermal method. The phasestructures, morphologies, light adsorption, and photoluminescent properties of the productswere characterized by X-ray diffraction （XRD）, Scanning Electron Microscopy （SEM）,Transmission Electron Microscopy （TEM）, Adsorption spectroscopy （UV-ViS）, andFluorescence spectrophotometer （PL）. Effects of reaction time, heat treatment temperatureand atmosphere, pH value, silicon source and reaction medium on the products ofmorphology, crystal structure and luminescence properties had been studied.This thesis includes three parts:In the first part of the thesis, a brief overview of luminescence mechanism andclassification of the luminescence materials were introduced. The preparation methods,properties, applications and research status of the nanostructured luminescent materialswere reviewed mainly.In the second part of this thesis, rice-like Zn₂SiO₄:Mn phosphors nano-particles withuniform size, regular morphology, good dispersivity, and strong green emssion weresynthesized by sovothermal method. The results showed that the intermediateZn₄Si₂O₇（OH）₂H₂O generated firstly during the synthesis of Zn₂SiO₄, and graduallytransformed into Zn₂SiO₄. Also, luminescent intensity of the products enhanced withprolonging the reaction time. When heat treated at the different temperature and ambience,the luminescent intensity enhanced with heat treating temperature from200to400℃in air.When the products were heat at500℃or even higher temperature in air, no luminescenceband can be detected due to the oxidation of Mn²⁺ions in the Zn₂SiO₄host. It was foundthat the luminescent intensity of products enhanced with temperature increasing from600to700℃in hydrogen ambience.In the third part, rod-like Zn₂SiO₄:Mn phosphors were synthesized by sovothermalmethod. Effect of pH value on the morphology and luminescent properties of the productssynthysized using amorphous SiO2has been studied. The results showed that when the pHvalues were7and9, single phase of Zn₂SiO₄with the shape of nanowire was obtained.However, the products were mostly Zn₄Si₂O₇（OH）₂H₂O intermediate phase when pH valuewas11. The morphologies of the products were affected by the concentration of OH-ions.When pH value was at9, the product gave the highest luminescent intensity. The products synthesized using crystalline SiO2and amorphous SiO2as Si source inwater solution were studied comparatively. When using crystalline SiO2, the products werelong rod-like with the diameter of about800nm and length of5⁸μm averagely. Theelectron diffraction pattern showed that the product was single crystal structure. However,the products were polycrystalline by using the amorphous SiO2as silicon source. Theparticles were short rod-like with about500nm in length and100nm in diameter. Theluminescent intensity of the products using amorphous SiO2is higher than that of the otherone.The products synthesized in differet solution systems were studied. It was found thatthe rod-like Zn₂SiO₄can be synthesized using crystalline SiO2only in the water-ethanol andwater-glycol solution, and only Zn₄Si₂O₇（OH）₂H₂O phase can be obtianed inwater-glycerol solution. The luminescent intensity of the product synthesized in water washigher than that of the others.