| The increasing desire of energy conservation and environmental protection was ascribed to the environment pollution and increasing energy crisis in the past twenty years.Solid state lighting technology based on light emitting diodes(LEDs)is becoming popular rapidly due to its low energy consumption,high stability and long life-time.White light is often generated through the combination of InGaN blue-emitting chip with YAG yellow-emitting phosphor,which shows low color rendering index due to the lack of green and red band.The white light generated from this combination cannot meet the increasing demand,which can be solved with adding the green and red-emitting phosphor.Many scholars focused on exploring novel phosphors and optimizing phosphor properties.The increasing attention to oxo/nitrido silicate phosphors is ascribed to its high quantum efficiency,high chemical stability,good thermal quenching and thermal degradation.The emitting band of oxo/nitrido silicates phosphor could cover the whole visible light region because of the diversity of host lattice,which is composed of[SiN4],[SiO4],[SiON3],etc.We synthesised a series of oxo/nitrido silicate phosphors and significantly increased their stability through hydrophobic surface modification.Specifically,this thesis could be divided into six chapters.Chapter 1 reviewed the development of lighting technology,luminescence,rare-earth doped luminescent materials,the energy transfer and transport between rare earth ions.The phosphors for white LEDs,mainly the(oxy)nitride phosphors and synthetic method,were reviewed.Chapter 2 studied the synthetic method of La-Si-O-N series and photoluminescence of rare-earth doped La2Si6O3N8.The energy transfer between Ce3+and Tb3+ was mainly studied.According to Blasse and Dexter,the energy transfer from Ce3+ to Tb3+ was governed by a dipole-dipole interaction mechanism,and the energy transfer efficiency was more than 70%in the La2-x-ySi6O3N8:Ce3+&Tb3+(x=0.2,y=0.5)sample.And then,Ce3+-doped L4Si2O7N2(L=La,Y,Lu,),Ce3+-doped La5Si3O12N and Ce3+-doped LaSi02N blue-green emitting phosphor were synthesized via direct silicon nitridation at 1500?under NH3 atmosphere successfully.Chapter 3 studied the synthesis and photoluminescence of Sr2Si5N8:Eu2+,Ca2Si5N8:Eu2+ and CaSrSi5N8:Eu2+ solid solution using metallic oxide and metallic carbide.The effect of the Sr/Si ratio,calcination temperature,atmosphere,the Eu2+concentration,raw materials and cation doping on photoluminescence,phase and microstructure,were described specifically.Chapter 4 reported the improvement of stability of Sr2Si5N8:Eu2+ and Ba2SiO4:Eu2+ phosphors via surface hydrophobic modification.The decrease of stability and luminescence in Sr2Si5N8:Eu2+ and Ba2Si04:Eu2+ phosphors were ascribed to the oxidation of lattice and luminescence center.The mechanism that the hydrophibic layer formed on the phosphor particle via hydrolysis and polymerization of PDMS and TEOS has been illuminated.It was reported that nanoporous silicon oxynitridocarbide fibers possesssuper hydrophobicity due to the presence of-CH3 groups at the surface.While an amorphous M-Si-O-N layer forms on the as-prepared phosphor particles.A hydrophobic modified surface layer could effectively improve the oxidation and hydrolysis resistance and the thermal stability of the produced phosphors under severe conditions of high-pressure water steam.Chapter 5 reported the highly stable Ba2SiO4:Eu2+ phosphors with a robust hydrophobic inorganic surface layer of silicon nitroxycarbide.The mechanism that the inorganic nano hydrophibic layer formed on the phosphor particle via ammnolysis and pyrolysis of chlorosilane has been illuminated.A hydrophobic modified surface layer with a thickness of 20-40 nm could effectively improve the oxidation and hydrolysis resistance and the thermal stability of the produced phosphors under severe conditions of high-pressurewater steam.Chapter 6 is the conclusion and outlook of this dissertation.The shortcomings and some suggestions for further study have been given. |
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